Section 3 Gap Junction

**71**

neurons.

**Chapter 4**

**Abstract**

Ganglia

*Vishwajit Ravindra Deshmukh*

many neurological disorders.

performs at an incredibly greater capacity.

**1. Introduction**

ganglia.

Gap Junctions in the Dorsal Root

Dorsal root ganglion (DRG) or spinal ganglia are present in relation to the dorsal ramus of the spinal nerves. The neurons in the dorsal root ganglion are pseudounipolar in type. The single process from the soma or body will divide into the central and peripheral processes. Dorsal root ganglion neurons constitute the first-order neurons for the pain pathways and can be categorized as small, medium and large varieties. Peripheral process collects the impulses from the peripheral receptors and the central process reaches out to the central nervous system. The neurons in the DRG were surrounded by the satellite glial cells (SGC). These cells ensheath the neurons from all the sides. Besides covering the neurons, they share features very much similar to the astrocytes such as expression of glutamine synthetase. Many quantitative studies have identified the different proportion of satellite glial cells for individual neurons. These cells have been identified to get activated when confronted by the noxious stimuli, injury or inflammation. Clinically, these cells were implied to be related to the

**Keywords:** neurons, satellite glial cells, communicating junctions, pain, connexin-43,

The human nervous system is an extremely efficient, compact, fast and reliable computing system, yet it weighs substantially less than most of the computers and

The nervous system is subdivided, morphologically into two components, the central nervous system (CNS) consisting of the brain and spinal cord and the peripheral nervous system (PNS) comprising of cranial and spinal nerves and

Discrete collections of nerve cell bodies in the CNS are known as nuclei while in PNS, these are called ganglia. The nerve cell bodies are of varying sizes and shapes. Ganglia are present in the dorsal root of spinal nerves, the sensory root of the trigeminal nerve (Vth), Facial (VIIth), Glossopharyngeal (IXth), Vagus (Xth) nerves and in the autonomic nervous system [1]. Some of them have independent nomenclature like the "Gasserian ganglion" for the Vth nerve. Thus ganglia can be divided into two types somatic and autonomic (**Figure 1**). The nerve cell bodies in each of these differ in their size and shape. Somatic ganglia contain small to large pseudounipolar neurons while the autonomic ganglia contain small multipolar

glial fibrillary acidic protein, peripherin, Nissl stain, immunohistochemistry

**Chapter 4**

## Gap Junctions in the Dorsal Root Ganglia

*Vishwajit Ravindra Deshmukh*

#### **Abstract**

Dorsal root ganglion (DRG) or spinal ganglia are present in relation to the dorsal ramus of the spinal nerves. The neurons in the dorsal root ganglion are pseudounipolar in type. The single process from the soma or body will divide into the central and peripheral processes. Dorsal root ganglion neurons constitute the first-order neurons for the pain pathways and can be categorized as small, medium and large varieties. Peripheral process collects the impulses from the peripheral receptors and the central process reaches out to the central nervous system. The neurons in the DRG were surrounded by the satellite glial cells (SGC). These cells ensheath the neurons from all the sides. Besides covering the neurons, they share features very much similar to the astrocytes such as expression of glutamine synthetase. Many quantitative studies have identified the different proportion of satellite glial cells for individual neurons. These cells have been identified to get activated when confronted by the noxious stimuli, injury or inflammation. Clinically, these cells were implied to be related to the many neurological disorders.

**Keywords:** neurons, satellite glial cells, communicating junctions, pain, connexin-43, glial fibrillary acidic protein, peripherin, Nissl stain, immunohistochemistry

#### **1. Introduction**

The human nervous system is an extremely efficient, compact, fast and reliable computing system, yet it weighs substantially less than most of the computers and performs at an incredibly greater capacity.

The nervous system is subdivided, morphologically into two components, the central nervous system (CNS) consisting of the brain and spinal cord and the peripheral nervous system (PNS) comprising of cranial and spinal nerves and ganglia.

Discrete collections of nerve cell bodies in the CNS are known as nuclei while in PNS, these are called ganglia. The nerve cell bodies are of varying sizes and shapes. Ganglia are present in the dorsal root of spinal nerves, the sensory root of the trigeminal nerve (Vth), Facial (VIIth), Glossopharyngeal (IXth), Vagus (Xth) nerves and in the autonomic nervous system [1]. Some of them have independent nomenclature like the "Gasserian ganglion" for the Vth nerve. Thus ganglia can be divided into two types somatic and autonomic (**Figure 1**). The nerve cell bodies in each of these differ in their size and shape. Somatic ganglia contain small to large pseudounipolar neurons while the autonomic ganglia contain small multipolar neurons.

**Figure 1.** *Differences in sensory and autonomic ganglia (courtesy: Cranial Nerves and Functional Anatomy, 1st ed. p. 12).*

**Figure 2.** *Types of neurons in nervous system.*

Depending on the number of processes, a neuron can be classified into various categories. Unipolar neurons (no dendrites only an axon) are rare in vertebrates, bipolar neurons (possesses an axon and a dendrite) present in olfactory mucosa and the retina and multipolar neurons (single axon and two or more dendrites) present in the central nervous system except the mesencephalic nucleus of the Vth cranial nerve. An additional type of neuron, the pseudounipolar neuron is present in sensory ganglia and the ganglia of Vth, VIIth, IXth and Xth cranial nerves. It divides into a central and peripheral process (**Figure 2**).

The neurons in sensory ganglia are at first bipolar, but the two neurites soon unite to form a single process during development. Structurally and electrophysiologically, both these processes show characteristic features of the axon [2]. Small satellite glial cells tightly wrap the cell bodies of the pseudounipolar neurons in the ganglion. The satellite cells that surround the pseudounipolar neuron are continuous with the Schwann cell sheath that surrounds the axon [3]. A distinctive feature of satellite glial cells by which they are distinguished from astrocytes is that they completely surround the individual sensory neuron. The neuron and its surrounding satellite glial cells form a distinct morphological and probably a functional unit [4]. The somatic ganglia of all the mammalian and avian species demonstrate this arrangement [5]. Satellite glial cells have been implicated in neuronal nutrition, homeostasis, and the process of apoptosis. It is known that astrocytes in the central nervous system perform 'spatial buffering' (regulation of K+ ) and it is presumed

**73**

**Figure 3.**

*B, Extraforaminal type: DRG located distal to line B [9].*

*Gap Junctions in the Dorsal Root Ganglia DOI: http://dx.doi.org/10.5772/intechopen.82128*

lowering of pain.

that SGCs also perform the same function [5]. Removing K+

**2. Morphology of Dorsal root ganglia (DRG)**

environment would reduce neuronal excitation and therefore contribute to the

Dorsal root ganglia (sensory ganglia) contain the cell bodies of primary afferent neurons that transmit the sensory information from the periphery into the central nervous system (CNS) [6]. Sensory ganglia were located near the entrance of dorsal root into the spinal cord, and are not a part of CNS. Sensory (somatic) ganglia lie outside the blood-brain barrier and are densely vascularized by fenestrated capillaries, making the neurons and SGCs easily accessible to compounds in the circulation, including chemotherapeutic drugs [7]. Chemotherapeutic drugs show greater accumulation in sensory ganglia than in peripheral nerves [8]. Dorsal root ganglia are more sensitive to heat than other nervous tissues [9]. It is known that pulsed radiofrequency can selectively block sensory nerves while minimizing the destruction of motor nerves. Sluijter et al. reported that the placement of a cannula 1–2 cm peripheral to the dorsal root ganglia could result in maximum effect when pulsed radiofrequency was applied on dorsal root ganglia of the spinal cord [10]. Kikuchi et al. [9] classified anatomical positions and variations of dorsal root ganglia into intraspinal (IS), intraforaminal (IF), and extraforaminal (EF) (**Figure 3**).

*Positions of dorsal root ganglia (DRG) were determined by two schematic lines and classified into three types. Line A: aligning the medial borders of L4 and L5 pedicles, Line B: aligning the centers of L4 and L5 pedicles, Intraspinal type (IS): DRG located proximal to line A, Intraforaminal type: DRG located between line A and* 

from the perineuronal

*Neurons - Dendrites and Axons*

**Figure 1.**

**Figure 2.**

*Types of neurons in nervous system.*

Depending on the number of processes, a neuron can be classified into various categories. Unipolar neurons (no dendrites only an axon) are rare in vertebrates, bipolar neurons (possesses an axon and a dendrite) present in olfactory mucosa and the retina and multipolar neurons (single axon and two or more dendrites) present in the central nervous system except the mesencephalic nucleus of the Vth cranial nerve. An additional type of neuron, the pseudounipolar neuron is present in sensory ganglia and the ganglia of Vth, VIIth, IXth and Xth cranial nerves. It divides

*Differences in sensory and autonomic ganglia (courtesy: Cranial Nerves and Functional Anatomy, 1st ed. p. 12).*

The neurons in sensory ganglia are at first bipolar, but the two neurites soon unite to form a single process during development. Structurally and electrophysiologically, both these processes show characteristic features of the axon [2]. Small satellite glial cells tightly wrap the cell bodies of the pseudounipolar neurons in the ganglion. The satellite cells that surround the pseudounipolar neuron are continuous with the Schwann cell sheath that surrounds the axon [3]. A distinctive feature of satellite glial cells by which they are distinguished from astrocytes is that they completely surround the individual sensory neuron. The neuron and its surrounding satellite glial cells form a distinct morphological and probably a functional unit [4]. The somatic ganglia of all the mammalian and avian species demonstrate this arrangement [5]. Satellite glial cells have been implicated in neuronal nutrition, homeostasis, and the process of apoptosis. It is known that astrocytes in the central

) and it is presumed

into a central and peripheral process (**Figure 2**).

nervous system perform 'spatial buffering' (regulation of K+

**72**

that SGCs also perform the same function [5]. Removing K+ from the perineuronal environment would reduce neuronal excitation and therefore contribute to the lowering of pain.

### **2. Morphology of Dorsal root ganglia (DRG)**

Dorsal root ganglia (sensory ganglia) contain the cell bodies of primary afferent neurons that transmit the sensory information from the periphery into the central nervous system (CNS) [6]. Sensory ganglia were located near the entrance of dorsal root into the spinal cord, and are not a part of CNS. Sensory (somatic) ganglia lie outside the blood-brain barrier and are densely vascularized by fenestrated capillaries, making the neurons and SGCs easily accessible to compounds in the circulation, including chemotherapeutic drugs [7]. Chemotherapeutic drugs show greater accumulation in sensory ganglia than in peripheral nerves [8]. Dorsal root ganglia are more sensitive to heat than other nervous tissues [9]. It is known that pulsed radiofrequency can selectively block sensory nerves while minimizing the destruction of motor nerves. Sluijter et al. reported that the placement of a cannula 1–2 cm peripheral to the dorsal root ganglia could result in maximum effect when pulsed radiofrequency was applied on dorsal root ganglia of the spinal cord [10]. Kikuchi et al. [9] classified anatomical positions and variations of dorsal root ganglia into intraspinal (IS), intraforaminal (IF), and extraforaminal (EF) (**Figure 3**).

#### **Figure 3.**

*Positions of dorsal root ganglia (DRG) were determined by two schematic lines and classified into three types. Line A: aligning the medial borders of L4 and L5 pedicles, Line B: aligning the centers of L4 and L5 pedicles, Intraspinal type (IS): DRG located proximal to line A, Intraforaminal type: DRG located between line A and B, Extraforaminal type: DRG located distal to line B [9].*

#### **3. Morphology and histology of sensory (somatic) ganglia**

The segmental nature of the spinal cord is demonstrated by the presence of 31 pairs of spinal nerves, but there is little indication of segmentation in its internal structure. Each dorsal root is broken up into a series of rootlets that are attached to the spinal cord along the corresponding segment. The ventral root arises similarly as a series of rootlets. These rootlets join to form the ventral and dorsal roots. The dorsal and ventral roots traverse the subarachnoid space and pierce the arachnoid and dura mater. At this point, the dura mater becomes continuous with the epineurium. After passing through the epidural space, the roots reach the intervertebral foramina, where the dorsal root ganglia are located on the dorsal root.

Certain authors have put forward their views regarding the classification of the neurons in the dorsal root ganglia based upon their staining properties into two histological types called "large light" and "small dark", visible under the light microscope. This has been confirmed by recent electron microscopic analysis that indicates [11] the existence of two basic types of DRG neurons usually termed as type A and type B rather than large light and small dark [12]. The neurons in the dorsal root ganglion can also be divided into three types (small, medium and large neurons) based upon the size of their cell bodies. This classification seems to be more appropriate because the size of the neuronal cell bodies determine their function. The large neurons are mainly concerned with the transmission of proprioception and discriminative touch while the medium-sized neurons transmit nerve impulses associated with sensations like light touch, pressure, pain and temperature. However, the small-sized neurons exclusively transmit action potentials related to pain and temperature.

Glial cells are involved in various pathological processes affecting the central nervous system [13]. There is strong evidence that CNS glial cells are involved (microglia and astrocytes) in the induction and maintenance of neuropathic pain [14]. Following injury of a peripheral nerve, satellite glial cells (SGCs) in the dorsal root ganglia undergo changes in cell number, structure and function, similar to those in the CNS

#### **Figure 4.**

*Schematic diagram describing the structural and functional relations between SGCs and neurons in sensory ganglia, and the consequences of peripheral injury.*

**75**

*Gap Junctions in the Dorsal Root Ganglia DOI: http://dx.doi.org/10.5772/intechopen.82128*

**small, medium and large**

[15]. Peripheral nerve transection increases gap junctions and intercellular coupling of SGCs. SGCs also upregulated the production of proinflammatory cytokines such as

Thus it is well established that glial cells play a critical role in the genesis and persistence of pain [17]. This is particularly true for the sensory ganglia. Though there are far fewer satellite glial cells than astrocytes or Schwann cells, yet because of their unique location in sensory ganglia, SGCs can strongly influence the afferent sensation. They also respond to the nerve injury by upregulating glial fibrillary acidic protein (GFAP) [18]. One of the ways glial cells in the sensory ganglia transmit signals is through intercellular calcium waves (ICWs) via gap junctions and adenosine-5′-triphosphate (ATP) acting on purinergic type 2 (P2) receptors [19]. This signaling

has been shown to be bi-directional between SGCs and neurons (**Figure 4**).

dorsal root ganglia neurons into small, medium and large categories.

contributes to the regulation of the soma size and metabolic activity [27].

those giving rise to C, Aδ and Aβ fibers, respectively [21].

One of the studies involving chronic constriction injury model of Bennet and Xie [23] that retains the connection with the original receptive field so that hyperalgesia and allodynia can be demonstrated, classify the neurons in DRG into small (23–30 μm), medium (31–40 μm) and large (41–53 μm), based on the optical measurement of the average diameter [23]. These grouping roughly correspond to

More recently sensory neurons in dorsal root ganglia were classified depending upon the immunohistochemical staining such as Nav1.8 expression in sensory neurons isolated from dorsal root ganglia into small (27–31 μm), medium (31–40 μm) and large (40–50 μm) [24]. There are two factors, namely DNA content and transcriptional activity, that are determinants of cell size [25]. Differences in neuronal body size seem to be primarily determined by the transcriptional activity. A positive correlation between the cell body and total RNA synthesis has been demonstrated in frog neurons, indicating that large neurons need higher transcriptional activities to maintain their large size [26]. The neurons transcription rate is, in turn, positively related to the magnitude of interactions between neurons and their targets, which

**4. Classification of pseudounipolar neurons of dorsal root ganglia into** 

Older literature suggests that neurons in dorsal root ganglia can be divided into two histological types called "large light (LL)" and "small dark (SD)" on the basis of staining properties under the light microscope [20]. This population overlaps, but still, they show the several physiological, biochemical and functional differences. Small dark neurons transmit the sensation particularly carried by C fibers (nonmyelinated, slow conducting) [21]. Whereas Large light transmits the sensation carried via a fiber (myelinated and fast conducting). Many of the small dark neurons contain substance P or calcitonin gene-related peptide, and they are concerned with thermo- and mechanoreception, and many of them are nociceptive. The terminals of Large light neurons are low threshold mechanoreceptors [22]. Neurons in the sensory ganglia have no dendrites and also do not receive synapses but are still endowed with receptors for numerous neurotransmitters. More recently depending upon the electron microscopic appearance neurons in the dorsal root ganglia were divided into Type A and Type B for large light and small dark neurons respectively. Various other electrophysiological classification depending upon conduction velocity, modality and adaptation rate serves to distinguished large number of functional types of sensory neurons, but it is not clear how these are related to the two basic histological types. There are contradictions among the researchers regarding the classification of

tumor necrosis factor-α after lumbar facet joint injury [16].

#### *Gap Junctions in the Dorsal Root Ganglia DOI: http://dx.doi.org/10.5772/intechopen.82128*

*Neurons - Dendrites and Axons*

related to pain and temperature.

**3. Morphology and histology of sensory (somatic) ganglia**

foramina, where the dorsal root ganglia are located on the dorsal root.

The segmental nature of the spinal cord is demonstrated by the presence of 31 pairs of spinal nerves, but there is little indication of segmentation in its internal structure. Each dorsal root is broken up into a series of rootlets that are attached to the spinal cord along the corresponding segment. The ventral root arises similarly as a series of rootlets. These rootlets join to form the ventral and dorsal roots. The dorsal and ventral roots traverse the subarachnoid space and pierce the arachnoid and dura mater. At this point, the dura mater becomes continuous with the epineurium. After passing through the epidural space, the roots reach the intervertebral

Certain authors have put forward their views regarding the classification of the neurons in the dorsal root ganglia based upon their staining properties into two histological types called "large light" and "small dark", visible under the light microscope. This has been confirmed by recent electron microscopic analysis that indicates [11] the existence of two basic types of DRG neurons usually termed as type A and type B rather than large light and small dark [12]. The neurons in the dorsal root ganglion can also be divided into three types (small, medium and large neurons) based upon the size of their cell bodies. This classification seems to be more appropriate because the size of the neuronal cell bodies determine their function. The large neurons are mainly concerned with the transmission of proprioception and discriminative touch while the medium-sized neurons transmit nerve impulses associated with sensations like light touch, pressure, pain and temperature. However, the small-sized neurons exclusively transmit action potentials

Glial cells are involved in various pathological processes affecting the central nervous system [13]. There is strong evidence that CNS glial cells are involved (microglia and astrocytes) in the induction and maintenance of neuropathic pain [14]. Following injury of a peripheral nerve, satellite glial cells (SGCs) in the dorsal root ganglia undergo changes in cell number, structure and function, similar to those in the CNS

*Schematic diagram describing the structural and functional relations between SGCs and neurons in sensory* 

**74**

**Figure 4.**

*ganglia, and the consequences of peripheral injury.*

[15]. Peripheral nerve transection increases gap junctions and intercellular coupling of SGCs. SGCs also upregulated the production of proinflammatory cytokines such as tumor necrosis factor-α after lumbar facet joint injury [16].

Thus it is well established that glial cells play a critical role in the genesis and persistence of pain [17]. This is particularly true for the sensory ganglia. Though there are far fewer satellite glial cells than astrocytes or Schwann cells, yet because of their unique location in sensory ganglia, SGCs can strongly influence the afferent sensation. They also respond to the nerve injury by upregulating glial fibrillary acidic protein (GFAP) [18]. One of the ways glial cells in the sensory ganglia transmit signals is through intercellular calcium waves (ICWs) via gap junctions and adenosine-5′-triphosphate (ATP) acting on purinergic type 2 (P2) receptors [19]. This signaling has been shown to be bi-directional between SGCs and neurons (**Figure 4**).

#### **4. Classification of pseudounipolar neurons of dorsal root ganglia into small, medium and large**

Older literature suggests that neurons in dorsal root ganglia can be divided into two histological types called "large light (LL)" and "small dark (SD)" on the basis of staining properties under the light microscope [20]. This population overlaps, but still, they show the several physiological, biochemical and functional differences. Small dark neurons transmit the sensation particularly carried by C fibers (nonmyelinated, slow conducting) [21]. Whereas Large light transmits the sensation carried via a fiber (myelinated and fast conducting). Many of the small dark neurons contain substance P or calcitonin gene-related peptide, and they are concerned with thermo- and mechanoreception, and many of them are nociceptive. The terminals of Large light neurons are low threshold mechanoreceptors [22]. Neurons in the sensory ganglia have no dendrites and also do not receive synapses but are still endowed with receptors for numerous neurotransmitters. More recently depending upon the electron microscopic appearance neurons in the dorsal root ganglia were divided into Type A and Type B for large light and small dark neurons respectively. Various other electrophysiological classification depending upon conduction velocity, modality and adaptation rate serves to distinguished large number of functional types of sensory neurons, but it is not clear how these are related to the two basic histological types.

There are contradictions among the researchers regarding the classification of dorsal root ganglia neurons into small, medium and large categories.

One of the studies involving chronic constriction injury model of Bennet and Xie [23] that retains the connection with the original receptive field so that hyperalgesia and allodynia can be demonstrated, classify the neurons in DRG into small (23–30 μm), medium (31–40 μm) and large (41–53 μm), based on the optical measurement of the average diameter [23]. These grouping roughly correspond to those giving rise to C, Aδ and Aβ fibers, respectively [21].

More recently sensory neurons in dorsal root ganglia were classified depending upon the immunohistochemical staining such as Nav1.8 expression in sensory neurons isolated from dorsal root ganglia into small (27–31 μm), medium (31–40 μm) and large (40–50 μm) [24]. There are two factors, namely DNA content and transcriptional activity, that are determinants of cell size [25]. Differences in neuronal body size seem to be primarily determined by the transcriptional activity. A positive correlation between the cell body and total RNA synthesis has been demonstrated in frog neurons, indicating that large neurons need higher transcriptional activities to maintain their large size [26]. The neurons transcription rate is, in turn, positively related to the magnitude of interactions between neurons and their targets, which contributes to the regulation of the soma size and metabolic activity [27].

Sensory neurons of the dorsal root ganglia express multiple voltage-gated sodium channels that substantially differ in gating kinetics and pharmacology. Small diameter (less than 25 μm) neurons isolated from the rat DRG express a combination of fast tetrodotoxin-sensitive (TTX-S) and slow TTX-resistant (TTX-R) sodium channels while large diameter neurons (more than 30 μm) predominantly expresses TTX-S Na current [28].

Viral study including adeno-associated viral vectors (AAV) are increasingly used to deliver therapeutic genes to the central nervous system where they promote transgene expression in postmitotic neurons for long periods with little or no toxicity. In adult rat dorsal root ganglia authors investigated the cellular tropism of AAV8 containing green fluorescent protein gene (GFP) after intra-lumbar DRG injection. And after injection, 2% of small DRG neurons (less than 30 μm) were GFP (+) as compared to 32% large (more than 60 μm) DRG neurons [29].

Electron microscopic features of dorsal root a ganglion divides the neurons depending upon their size and the distribution of their organelles (**Figure 5**). They were further subdivided into six subtypes according to the arrangement and three-dimensional organization of the Nissl bodies and Golgi apparatus in the perikarya. Type A1 cells were large, clear neurons in which Nissl bodies, separated from each other by pale narrow strands of cytoplasm containing small stacks of Golgi saccules and rod-like mitochondria, were evenly distributed throughout the perikaryon. In type A2, the Nissl bodies assumed a similar distribution but were separated by much wider strands of cytoplasm. Type A3, the smallest of the type A category, displayed densely packed Nissl bodies and long stacks of Golgi saccules which formed a perinuclear ring in the midportion of the perikaryon. Type B cells were smaller and showed a concentric zonation of their organelles. In type B1, large Nissl bodies located in an outer cytoplasmic zone were made of long piles of parallel cisternae interrupted by curved Golgi stacks. Type B2 was characterized by a ring-like Golgi apparatus separating the perikaryon in a cortical zone composed mainly of Nissl substance and a juxtanuclear zone containing mitochondria and smooth endoplasmic reticulum. Type C cells were the smallest of the ganglion cells

#### **Figure 5.**

*Nissl's staining showing the variety of neurons in the dorsal root ganglion. Black arrow represents the large neurons, red arrow represents the surrounding capsule and the asterisk showed the location of centrally placed collection of nerve fibers [33].*

**77**

mission of pain (**Figure 6**).

*Gap Junctions in the Dorsal Root Ganglia DOI: http://dx.doi.org/10.5772/intechopen.82128*

apparatus [30].

observed [31].

light neurons [32].

and contained small, poorly demarcated Nissl bodies and a juxtanuclear Golgi

A, which are released by the C-type primary afferent terminals of the small DRG neurons, plays important role in spinal nociception. By means of non-radioactive in situ hybridization and whole-cell recording, authors showed that the small rat DRG neurons also express the NK-1 tachykinin receptor. In situ hybridization demonstrated that the positive neurons in rat DRG sections were mainly small with a diameter of less than 25 μm. And the remaining positive neurons were cells with a medium diameter between 26 and 40 μm. No positive large neurons (more than 40 μm) were

Neurotransmitter study involving tachykinin like substance P (SP) and neurokinin

Depending upon the molecular weight of neurofilaments and their expression in various categories of neurons in dorsal root ganglia, three different neurofilament subunits have been identified, i.e. light (NF-L), middle (NF-M) and high (NF-H). Previous data showed that all the dorsal root ganglia neurons express NF-M and NF-H while only NF-L defines a distinct group of neurons and significantly large-

**5. Peripherin: marker to differentiate the neurons in the DRG**

Peripherin, a protein formerly called Y, was first identified by two-dimensional gel electrophoresis in the insoluble fraction of cellular extracts from mouse neuroblastoma cell lines [34]. Its presence has been previously established in the rodent peripheral nervous system mostly by biochemical studies; moreover, biochemical characterization following nerve transection also supports its localization in neurons within the peripheral nervous system [35]. This observation leads to coining of the term "Peripherin" to designate this particular protein entity. Peripherin is a 57-kDa-type III neuronal intermediate filament protein, which is capable of either self-assembling or co-assembling with all of the individual neurofilament subunits [36]. In particular, the small cells of the dorsal root ganglia neurons selectively contain peripherin [35] and thus becoming a useful marker to define the small ganglion cell subpopulation. The exact function of the peripherin is still unknown though it has been suggested to be a determinant of the shape and architecture of the peripheral nerve axons and also provides structural integrity to the cells [37]. Peripherin immunolabeling has seen to be an important marker especially for the study of peripheral nerve development and regeneration since this intermediate filament protein is highly over-expressed during axon elongation [38]. Previously this neurofilament were thought to be inert but in fact these are highly dynamic structures with many diverse function such as relaying the signals from the plasma membrane to the nucleus [39], maintaining the position and function of cellular organelles, and also regulating the protein synthesis [40]. This neurofilament is clinically relevant because of their association with the pathogenesis of some major neuronal disorders. Mainly, accumulation of neurofilament protein and peripherin in proximal axons are associated with amyotrophic lateral sclerosis [41] and also seen in other diseases such as Alzheimer's disease [42]. Peripherin was used to identify the small to medium-sized neurons in the rat dorsal root ganglia in the present study as because these are associated with the transmission of pain from the periphery to the central nervous system. This would give an idea as to the actual number of neurons within the dorsal root ganglia involved in the trans*Neurons - Dendrites and Axons*

expresses TTX-S Na current [28].

Sensory neurons of the dorsal root ganglia express multiple voltage-gated sodium channels that substantially differ in gating kinetics and pharmacology. Small diameter (less than 25 μm) neurons isolated from the rat DRG express a combination of fast tetrodotoxin-sensitive (TTX-S) and slow TTX-resistant (TTX-R) sodium channels while large diameter neurons (more than 30 μm) predominantly

Viral study including adeno-associated viral vectors (AAV) are increasingly

used to deliver therapeutic genes to the central nervous system where they promote transgene expression in postmitotic neurons for long periods with little or no toxicity. In adult rat dorsal root ganglia authors investigated the cellular tropism of AAV8 containing green fluorescent protein gene (GFP) after intra-lumbar DRG injection. And after injection, 2% of small DRG neurons (less than 30 μm) were GFP (+) as compared to 32% large (more than 60 μm) DRG neurons [29]. Electron microscopic features of dorsal root a ganglion divides the neurons depending upon their size and the distribution of their organelles (**Figure 5**). They were further subdivided into six subtypes according to the arrangement and three-dimensional organization of the Nissl bodies and Golgi apparatus in the perikarya. Type A1 cells were large, clear neurons in which Nissl bodies, separated from each other by pale narrow strands of cytoplasm containing small stacks of Golgi saccules and rod-like mitochondria, were evenly distributed throughout the perikaryon. In type A2, the Nissl bodies assumed a similar distribution but were separated by much wider strands of cytoplasm. Type A3, the smallest of the type A category, displayed densely packed Nissl bodies and long stacks of Golgi saccules which formed a perinuclear ring in the midportion of the perikaryon. Type B cells were smaller and showed a concentric zonation of their organelles. In type B1, large Nissl bodies located in an outer cytoplasmic zone were made of long piles of parallel cisternae interrupted by curved Golgi stacks. Type B2 was characterized by a ring-like Golgi apparatus separating the perikaryon in a cortical zone composed mainly of Nissl substance and a juxtanuclear zone containing mitochondria and smooth endoplasmic reticulum. Type C cells were the smallest of the ganglion cells

*Nissl's staining showing the variety of neurons in the dorsal root ganglion. Black arrow represents the large neurons, red arrow represents the surrounding capsule and the asterisk showed the location of centrally placed* 

**76**

**Figure 5.**

*collection of nerve fibers [33].*

and contained small, poorly demarcated Nissl bodies and a juxtanuclear Golgi apparatus [30].

Neurotransmitter study involving tachykinin like substance P (SP) and neurokinin A, which are released by the C-type primary afferent terminals of the small DRG neurons, plays important role in spinal nociception. By means of non-radioactive in situ hybridization and whole-cell recording, authors showed that the small rat DRG neurons also express the NK-1 tachykinin receptor. In situ hybridization demonstrated that the positive neurons in rat DRG sections were mainly small with a diameter of less than 25 μm. And the remaining positive neurons were cells with a medium diameter between 26 and 40 μm. No positive large neurons (more than 40 μm) were observed [31].

Depending upon the molecular weight of neurofilaments and their expression in various categories of neurons in dorsal root ganglia, three different neurofilament subunits have been identified, i.e. light (NF-L), middle (NF-M) and high (NF-H). Previous data showed that all the dorsal root ganglia neurons express NF-M and NF-H while only NF-L defines a distinct group of neurons and significantly largelight neurons [32].

#### **5. Peripherin: marker to differentiate the neurons in the DRG**

Peripherin, a protein formerly called Y, was first identified by two-dimensional gel electrophoresis in the insoluble fraction of cellular extracts from mouse neuroblastoma cell lines [34]. Its presence has been previously established in the rodent peripheral nervous system mostly by biochemical studies; moreover, biochemical characterization following nerve transection also supports its localization in neurons within the peripheral nervous system [35]. This observation leads to coining of the term "Peripherin" to designate this particular protein entity. Peripherin is a 57-kDa-type III neuronal intermediate filament protein, which is capable of either self-assembling or co-assembling with all of the individual neurofilament subunits [36]. In particular, the small cells of the dorsal root ganglia neurons selectively contain peripherin [35] and thus becoming a useful marker to define the small ganglion cell subpopulation. The exact function of the peripherin is still unknown though it has been suggested to be a determinant of the shape and architecture of the peripheral nerve axons and also provides structural integrity to the cells [37]. Peripherin immunolabeling has seen to be an important marker especially for the study of peripheral nerve development and regeneration since this intermediate filament protein is highly over-expressed during axon elongation [38]. Previously this neurofilament were thought to be inert but in fact these are highly dynamic structures with many diverse function such as relaying the signals from the plasma membrane to the nucleus [39], maintaining the position and function of cellular organelles, and also regulating the protein synthesis [40]. This neurofilament is clinically relevant because of their association with the pathogenesis of some major neuronal disorders. Mainly, accumulation of neurofilament protein and peripherin in proximal axons are associated with amyotrophic lateral sclerosis [41] and also seen in other diseases such as Alzheimer's disease [42]. Peripherin was used to identify the small to medium-sized neurons in the rat dorsal root ganglia in the present study as because these are associated with the transmission of pain from the periphery to the central nervous system. This would give an idea as to the actual number of neurons within the dorsal root ganglia involved in the transmission of pain (**Figure 6**).

#### **Figure 6.**

*Immunohistochemical stained section with peripherin antibody of dorsal root ganglion representing the specific staining in small to medium sized neurons (white arrows). Larger neurons (black arrows) [33].*

#### **6. Satellite glial cells**

Sensory neurons in the dorsal root ganglia are ensheathed by specialized glial cells termed 'satellite glial cells' (SGCs). Recently, there has been considerable interest in these cells as they are profoundly altered by peripheral injuries used to study pain behavior and appear to contribute to chronic pain [43]. Satellite glial cells are the peripheral glial cells, but share many properties with astrocytes in the central nervous system (CNS), including the expression of glutamine synthetase and transporters of amino acids neurotransmitters. However, satellite glial cells differ in some respects from astrocytes, particularly by the tight sheath they make around the neuronal cell bodies [44]. In the dorsal root ganglion, Schwann cells and the satellite cells are activated in response to ischemia, traumatic injury and inflammation [45]. Application of various cytokines to the exposed Dorsal root ganglia resulted in an increase in the discharge rate as well as increased mechanosensitivity of DRG and peripheral receptive fields [46]. Satellite glial cells are the consistent component of the DRG in all the species, yet their contribution to the basic neuronal function remains unknown, although these satellite cells were implicated in neuronal nutrition, homeostasis and the process of apoptosis [5].

Recent studies have demonstrated that a specific glial cell population, the satellite glial cells, has the ability to regulate ion concentration [47] and possess mechanisms for the release of cytokines [48], ATP [19] and other chemical messengers like calcium. Satellite glial cells influence neuronal excitability via the gap junctions [49]. The satellite glial cells undergo major changes as a result of injury to peripheral nerves and appear to contribute to chronic pain [4]. Quantitative studies on several species showed that a number of satellite glial cells per neuron increases in proportion to the neuron's volume, consistent with the idea that these satellite glial cells support the neurons metabolically [50].

During pathological conditions, such as nerve injury or inflammation, SGCs demonstrate an altered phenotype similar to that seen in activated astrocytes, which includes increased expression of the glial fibrillary acidic protein (GFAP) and synthesis of cytokines [51]. SGCs are therefore said to undergo activation due

**79**

*Gap Junctions in the Dorsal Root Ganglia DOI: http://dx.doi.org/10.5772/intechopen.82128*

several inflammatory pain and axotomy models [52].

**7. Satellite glial cells as a structural unit**

Schwann cells and oligodendrocytes [53].

to the neurons during lead poisoning.

**8. Satellite glial cells maintain ionic concentration**

The satellite glial cells neighboring the pseudounipolar neurons have a highly negative resting membrane potential and noticeable potassium permeability. The primary means of limiting extracellular levels of potassium in the sensory ganglia occurs through the process commonly called spatial buffering or syphoning which

to injury. Increased coupling by gap junctions between SGCs has been observed in

Satellite glial cells (SGCs) in sensory ganglia wraps completely around the neuron. Several investigators claimed that SGCs bear processes and are therefore structurally similar to astrocytes but recent researches are that SGCs are laminar and have no true processes. In general, each sensory neuron has its own SGCs sheath, which usually consists of several SGCs, and thus the neuron and its surrounding satellite glial cells form a distinct morphological and probably functional unit. The region containing connective tissue separates these units. In some cases (5.6% in rat DRG) neurons from a small group containing two to three cells that are enclosed in common connective tissue space [44]. The neurons in the clusters are in most cases separated from each other by SGC sheath. The SGCs envelope usually consists of flat processes that lie close to the neuronal plasma membrane. The distance between the glial cell and neuronal plasma membrane is about 20 nm [44]. The neurons send numerous fine processes (microvilli), some of which fit into the invaginations of SGCs thus increasing the neuronal surface area and may allow an extensive exchange of chemicals between two cell types. A study on cultured SGCs of embryonic and neonatal rats showed that SGCs could transform into astrocytes,

Quantitative studies on several species showed that the number of SGCs per neuron increases in proportion to the neuron volume [50] consistent with the idea that SGCs support the neurons metabolically. It was also found that the mean volume of the nerve cell body corresponding to an SGC was lower for small neurons than for large neurons, which implies that the metabolic needs of small neurons are better satisfied than those of large ones. Therefore, smaller neurons have a higher resistance to insults, which seems to be the case for mercury poisoning. However, there is experimental evidence that smaller neurons are more likely to die following axonal damage [54]. As sensory ganglia are not protected from substances circulating in the blood, SGCs may be important in the context of exposure to toxic substances. In several studies, SGCs were examined after poisoning with heavy metals and it was found that these cells take up organic mercury compounds [55], and lead [56]. Mercury poisoning also caused SGCs proliferation [57]. Nineteen days after the administration of organic mercury to rats, SGCs in DRG were heavily labeled for mercury, and their ability to take up GABA was greatly diminished. Interestingly, small neurons were considerably less labeled for mercury than large neurons, which could be attributed to a more effective protection by SGCs. Prolonged (3–18 months) administration of lead acetate to rats resulted in prominent changes in SGCs in DRG, which included proliferation and hypertrophy of these cells. Although a certain degree of neuronal damage was observed, it can be proposed that the changes in SGCs provide a better protection

*Neurons - Dendrites and Axons*

**6. Satellite glial cells**

**Figure 6.**

Sensory neurons in the dorsal root ganglia are ensheathed by specialized glial cells termed 'satellite glial cells' (SGCs). Recently, there has been considerable interest in these cells as they are profoundly altered by peripheral injuries used to study pain behavior and appear to contribute to chronic pain [43]. Satellite glial cells are the peripheral glial cells, but share many properties with astrocytes in the central nervous system (CNS), including the expression of glutamine synthetase and transporters of amino acids neurotransmitters. However, satellite glial cells differ in some respects from astrocytes, particularly by the tight sheath they make around the neuronal cell bodies [44]. In the dorsal root ganglion, Schwann cells and the satellite cells are activated in response to ischemia, traumatic injury and inflammation [45]. Application of various cytokines to the exposed Dorsal root ganglia resulted in an increase in the discharge rate as well as increased mechanosensitivity of DRG and peripheral receptive fields [46]. Satellite glial cells are the consistent component of the DRG in all the species, yet their contribution to the basic neuronal function remains unknown, although these satellite cells were implicated in neuronal nutrition, homeostasis and the process of

*Immunohistochemical stained section with peripherin antibody of dorsal root ganglion representing the specific* 

*staining in small to medium sized neurons (white arrows). Larger neurons (black arrows) [33].*

Recent studies have demonstrated that a specific glial cell population, the satellite glial cells, has the ability to regulate ion concentration [47] and possess mechanisms for the release of cytokines [48], ATP [19] and other chemical messengers like calcium. Satellite glial cells influence neuronal excitability via the gap junctions [49]. The satellite glial cells undergo major changes as a result of injury to peripheral nerves and appear to contribute to chronic pain [4]. Quantitative studies on several species showed that a number of satellite glial cells per neuron increases in proportion to the neuron's volume, consistent with the idea that these satellite glial cells support the

During pathological conditions, such as nerve injury or inflammation, SGCs demonstrate an altered phenotype similar to that seen in activated astrocytes, which includes increased expression of the glial fibrillary acidic protein (GFAP) and synthesis of cytokines [51]. SGCs are therefore said to undergo activation due

**78**

apoptosis [5].

neurons metabolically [50].

to injury. Increased coupling by gap junctions between SGCs has been observed in several inflammatory pain and axotomy models [52].

#### **7. Satellite glial cells as a structural unit**

Satellite glial cells (SGCs) in sensory ganglia wraps completely around the neuron. Several investigators claimed that SGCs bear processes and are therefore structurally similar to astrocytes but recent researches are that SGCs are laminar and have no true processes. In general, each sensory neuron has its own SGCs sheath, which usually consists of several SGCs, and thus the neuron and its surrounding satellite glial cells form a distinct morphological and probably functional unit. The region containing connective tissue separates these units. In some cases (5.6% in rat DRG) neurons from a small group containing two to three cells that are enclosed in common connective tissue space [44]. The neurons in the clusters are in most cases separated from each other by SGC sheath. The SGCs envelope usually consists of flat processes that lie close to the neuronal plasma membrane. The distance between the glial cell and neuronal plasma membrane is about 20 nm [44]. The neurons send numerous fine processes (microvilli), some of which fit into the invaginations of SGCs thus increasing the neuronal surface area and may allow an extensive exchange of chemicals between two cell types. A study on cultured SGCs of embryonic and neonatal rats showed that SGCs could transform into astrocytes, Schwann cells and oligodendrocytes [53].

Quantitative studies on several species showed that the number of SGCs per neuron increases in proportion to the neuron volume [50] consistent with the idea that SGCs support the neurons metabolically. It was also found that the mean volume of the nerve cell body corresponding to an SGC was lower for small neurons than for large neurons, which implies that the metabolic needs of small neurons are better satisfied than those of large ones. Therefore, smaller neurons have a higher resistance to insults, which seems to be the case for mercury poisoning. However, there is experimental evidence that smaller neurons are more likely to die following axonal damage [54]. As sensory ganglia are not protected from substances circulating in the blood, SGCs may be important in the context of exposure to toxic substances. In several studies, SGCs were examined after poisoning with heavy metals and it was found that these cells take up organic mercury compounds [55], and lead [56]. Mercury poisoning also caused SGCs proliferation [57]. Nineteen days after the administration of organic mercury to rats, SGCs in DRG were heavily labeled for mercury, and their ability to take up GABA was greatly diminished. Interestingly, small neurons were considerably less labeled for mercury than large neurons, which could be attributed to a more effective protection by SGCs. Prolonged (3–18 months) administration of lead acetate to rats resulted in prominent changes in SGCs in DRG, which included proliferation and hypertrophy of these cells. Although a certain degree of neuronal damage was observed, it can be proposed that the changes in SGCs provide a better protection to the neurons during lead poisoning.

#### **8. Satellite glial cells maintain ionic concentration**

The satellite glial cells neighboring the pseudounipolar neurons have a highly negative resting membrane potential and noticeable potassium permeability. The primary means of limiting extracellular levels of potassium in the sensory ganglia occurs through the process commonly called spatial buffering or syphoning which is mediated by satellite glial cells. The maintenance of a low extracellular potassium concentration is crucial for controlling the neuronal resting membrane potential and neuronal excitability. In sensory ganglia increased neuronal excitability has been associated with the occurrence of altered sensation, including the development of the neuropathic pain [58]. In the CNS buffering of extracellular potassium ions is carried by astrocytes, which consist of uptake by inwardly rectifying potassium (Kir) channels and dissipation through other channels and gap junctions [59]. It is established that the Kir current and Kir4.1 expression occur in the satellite glial cells [60]. Voltage-gated potassium channels are one of the important physiological regulators of the membrane potentials in excitable cells including sensory ganglion neurons.

#### **9. Neuron-glial interactions**

Central nervous system glial cells are increasingly known to be important regulator of synaptic activity and the key functional unit of nervous system [61]. Even though many of the same voltage-sensitive ion channels and neurotransmitter receptors of neurons are found in glia; glial cells lack the membrane properties obligatory to fire action potentials. Nevertheless, these ion channels and electrogenic membrane transporters permit glia to sense indirectly the level of neuronal activity by monitoring activity-dependent changes in the chemical surroundings shared by these two cell types. Complex imaging methods, which allow observation of changes in intracellular and extracellular signaling molecules in real time, show that glia, communicate with one another and with neurons primarily through chemical signals rather than electrical signals. Many of these signaling systems overlap with the neurotransmitter signaling systems of neurons, but some are specialized for glial-glial and neuron-glial communication. Neuron-glia cell interaction through gap junctions and extracellular paracrine/autocrine processes are believed to be important in the development of peripheral sensitization within the trigeminal ganglia [62]. Peripheral sensitization, which is characterized by increased neuronal excitability and a lowered threshold for activation, may possibly trigger a migraine attack. Moreover, activation and sensitization of the trigeminovascular afferent fibers appear crucial for initiation of migraine pain and for subsequent central centralization, in which increased excitability of second-order neurons leads to pain and allodynia. Increased gap junction communication between neurons and satellite glial cells was observed in the trigeminal ganglion in response to chemical activation of sensory trigeminal nerves [62].

Increased neuronal-glial signaling by way of gap junctions is common in neuroinflammatory CNS disorders, such as cerebral ischemia and Alzheimer's disease and may have underlying pathological significance [63]. Tonabersat (SB-220453), a compound that binds selectively and with high affinity to a unique stereoselective site i.e. the gap junctions and inhibits it in rats and human brains [64]. After an injury, the numbers of gap junctions that connect satellite glial cells increases [43] in a probable adjust to the greater release of potassium ions with intense neuronal activity. Injury to a peripheral nerve does not directly impact satellite glial cells integrity. However, changes in injured neurons can influence the ability of the surrounding SGCs to regulate K+ via neuromodulators such as adenosine triphosphate (ATP) and nitric oxide (NO) [65].

Satellite glial cells have unique proteins that include the inwardly rectifying K+ channel Kir4.1 [43], the connexin-43 (Cx43) subunit of gap junctions the purinergic receptor P2Y4 [66] and soluble guanylate cyclase. There is also evidence of the presence of small-conductance Ca2+−activated K+ channel SK3 that is present only in satellite glial cells. All the above proteins are involved, either directly or indirectly,

**81**

*Gap Junctions in the Dorsal Root Ganglia DOI: http://dx.doi.org/10.5772/intechopen.82128*

in potassium ion (K<sup>+</sup>

**Figure 7.**

tions are restored [66, 67].

**satellite glial cells**

) buffering and, thus, can influence the level of neuronal

excitability, which, in turn, has been associated with neuropathic pain conditions (**Figure 7**). They also used in vivo RNA interference to reduce the expression of Cx43 (present only in SGCs) in the rat trigeminal ganglion and showed that this resulted in the development of spontaneous pain behavior. The pain behavior is present only when Cx43 is reduced and returns to normal when Cx43 concentra-

*Satellite glial cells involved in maintenance of potassium homeostasis [66].*

**10. Glial fibrillary acidic protein (GFAP): locator molecule for the** 

sion of GFAP in the satellite glial cells following acute pain (**Figure 8**).

GFAP is a marker of activated satellite glial cells and astrocytes [48]. These ropes like filaments are called intermediate filaments because their diameter of 8–10 nm is

Glial fibrillary acidic protein is principle intermediate filament in mature astrocytes of the central nervous system and satellite glial cells of sensory ganglia [4]. GFAP is strongly unregulated in response to CNS damage [68]. It is thought to be important in astrocyte neuronal interactions, astrocyte mobility and shape and for maintenance of homeostasis and vascular permeability at the blood-tissue interface [69]. GFAP is essential for normal white matter architecture and blood-brain barrier integrity and its absence leads to late-onset CNS dysmyelination [70]. Increased GFAP expression occurs in activated glial cells. Activated astrocytes are characterized by hypertrophy, the release of pro-inflammatory cytokines (IL-1, IL-6 and TNF-a), the release of nitric oxide and prostaglandins, and up-regulation of the intermediate filaments GFAP and vimentin [17]. Likewise, satellite glial cells (SGCs) display increased expression of GFAP after neuronal injury or inflammation and undergo a number of changes similar to those seen in astrocytes, such as synthesis of cytokines [71]. GFAP expression increases in the satellite glial cells of trigeminal ganglia after tooth pulp injury [72]. The present study also investigated the expres*Neurons - Dendrites and Axons*

**9. Neuron-glial interactions**

neurons.

is mediated by satellite glial cells. The maintenance of a low extracellular potassium concentration is crucial for controlling the neuronal resting membrane potential and neuronal excitability. In sensory ganglia increased neuronal excitability has been associated with the occurrence of altered sensation, including the development of the neuropathic pain [58]. In the CNS buffering of extracellular potassium ions is carried by astrocytes, which consist of uptake by inwardly rectifying potassium (Kir) channels and dissipation through other channels and gap junctions [59]. It is established that the Kir current and Kir4.1 expression occur in the satellite glial cells [60]. Voltage-gated potassium channels are one of the important physiological regulators of the membrane potentials in excitable cells including sensory ganglion

Central nervous system glial cells are increasingly known to be important regulator of synaptic activity and the key functional unit of nervous system [61]. Even though many of the same voltage-sensitive ion channels and neurotransmitter receptors of neurons are found in glia; glial cells lack the membrane properties obligatory to fire action potentials. Nevertheless, these ion channels and electrogenic membrane transporters permit glia to sense indirectly the level of neuronal activity by monitoring activity-dependent changes in the chemical surroundings shared by these two cell types. Complex imaging methods, which allow observation of changes in intracellular and extracellular signaling molecules in real time, show that glia, communicate with one another and with neurons primarily through chemical signals rather than electrical signals. Many of these signaling systems overlap with the neurotransmitter signaling systems of neurons, but some are specialized for glial-glial and neuron-glial communication. Neuron-glia cell interaction through gap junctions and extracellular paracrine/autocrine processes are believed to be important in the development of peripheral sensitization within the trigeminal ganglia [62]. Peripheral sensitization, which is characterized by increased neuronal excitability and a lowered threshold for activation, may possibly trigger a migraine attack. Moreover, activation and sensitization of the trigeminovascular afferent fibers appear crucial for initiation of migraine pain and for subsequent central centralization, in which increased excitability of second-order neurons leads to pain and allodynia. Increased gap junction communication between neurons and satellite glial cells was observed in the trigeminal ganglion in response to chemical activation of sensory trigeminal nerves [62]. Increased neuronal-glial signaling by way of gap junctions is common in neuroinflammatory CNS disorders, such as cerebral ischemia and Alzheimer's disease and may have underlying pathological significance [63]. Tonabersat (SB-220453), a compound that binds selectively and with high affinity to a unique stereoselective site i.e. the gap junctions and inhibits it in rats and human brains [64]. After an injury, the numbers of gap junctions that connect satellite glial cells increases [43] in a probable adjust to the greater release of potassium ions with intense neuronal activity. Injury to a peripheral nerve does not directly impact satellite glial cells integrity. However, changes in injured neurons can influence the ability of the sur-

via neuromodulators such as adenosine triphosphate

channel SK3 that is present only in

Satellite glial cells have unique proteins that include the inwardly rectifying K+ channel Kir4.1 [43], the connexin-43 (Cx43) subunit of gap junctions the purinergic receptor P2Y4 [66] and soluble guanylate cyclase. There is also evidence of the pres-

satellite glial cells. All the above proteins are involved, either directly or indirectly,

**80**

rounding SGCs to regulate K+

(ATP) and nitric oxide (NO) [65].

ence of small-conductance Ca2+−activated K+

**Figure 7.** *Satellite glial cells involved in maintenance of potassium homeostasis [66].*

in potassium ion (K<sup>+</sup> ) buffering and, thus, can influence the level of neuronal excitability, which, in turn, has been associated with neuropathic pain conditions (**Figure 7**). They also used in vivo RNA interference to reduce the expression of Cx43 (present only in SGCs) in the rat trigeminal ganglion and showed that this resulted in the development of spontaneous pain behavior. The pain behavior is present only when Cx43 is reduced and returns to normal when Cx43 concentrations are restored [66, 67].

#### **10. Glial fibrillary acidic protein (GFAP): locator molecule for the satellite glial cells**

Glial fibrillary acidic protein is principle intermediate filament in mature astrocytes of the central nervous system and satellite glial cells of sensory ganglia [4]. GFAP is strongly unregulated in response to CNS damage [68]. It is thought to be important in astrocyte neuronal interactions, astrocyte mobility and shape and for maintenance of homeostasis and vascular permeability at the blood-tissue interface [69]. GFAP is essential for normal white matter architecture and blood-brain barrier integrity and its absence leads to late-onset CNS dysmyelination [70]. Increased GFAP expression occurs in activated glial cells. Activated astrocytes are characterized by hypertrophy, the release of pro-inflammatory cytokines (IL-1, IL-6 and TNF-a), the release of nitric oxide and prostaglandins, and up-regulation of the intermediate filaments GFAP and vimentin [17]. Likewise, satellite glial cells (SGCs) display increased expression of GFAP after neuronal injury or inflammation and undergo a number of changes similar to those seen in astrocytes, such as synthesis of cytokines [71]. GFAP expression increases in the satellite glial cells of trigeminal ganglia after tooth pulp injury [72]. The present study also investigated the expression of GFAP in the satellite glial cells following acute pain (**Figure 8**).

GFAP is a marker of activated satellite glial cells and astrocytes [48]. These ropes like filaments are called intermediate filaments because their diameter of 8–10 nm is

#### **Figure 8.**

*Immunohistochemical staining for the section of DRG using GFAP antibody. Black arrows representing the location of satellite glial cells. Red arrow showing the communication between two neurons [33].*

between those of actin filaments and microtubules. Nearly all-intermediate filaments consist of subunits with a molecular weight of about 50 kDa. Some evidence suggests that many of the stable structural proteins in intermediate filaments evolved from highly conserved enzymes, with only minor genetic modification. Intermediate filaments are formed from nonpolar and highly variable intermediate filament subunits. Unlike those of microfilaments and microtubules, the protein subunits of intermediate filaments show considerable diversity and tissue specificity. In addition, they do not possess enzymatic activity and form nonpolar filaments. Intermediate filaments also do not typically disappear and reform in the continuous manner characteristic of most microtubules and actin filaments. For these reasons, intermediate filaments are believed to play a primarily structural role within the cell and to compose the cytoplasmic link of a tissue-wide continuum of cytoplasmic, nuclear, and extracellular filaments. A highly variable central rod-shaped domain with strictly conserved globular domains at either end characterizes intermediate filament proteins. Although the various classes of intermediate filaments differ in the amino acid sequence of the rod-shaped domain and show some variation in molecular weight, they all share a homologous region that is important in filament self-assembly. Intermediate filaments are assembled from a pair of helical monomers that twist around each other to form coiled-coil dimers. Then, two coiled-coil dimers twist around each other in antiparallel fashion (parallel but pointing in opposite directions) to generate a staggered tetramer of two coiled-coil dimers, thus forming the nonpolarized unit of the intermediate filaments. Each tetramer, acting as an individual unit, is aligned along the axis of the filament. The ends of the tetramers are bound together to form the free ends of the filament. This assembly process provides a stable, staggered, helical array in which filaments are packed together and additionally stabilized by lateral binding interactions between adjacent tetramers [2].

Total six classes of intermediate filament are present in body, e.g., Class II and I include keratin and cytokeratin and class III include vimentin, glial acidic fibrillary protein (GFAP) and peripherin.

GFAP is the principal intermediate filament in mature astrocytes. GFAP is a soluble protein isolated from the multiple sclerosis plaques and presumably arising from the glial filaments [73]. The GFAP gene is located on the long (q) arm of chromosome 17 at position 21. Mutation in the GFAP results in Alexander disease

**83**

*Gap Junctions in the Dorsal Root Ganglia DOI: http://dx.doi.org/10.5772/intechopen.82128*

**11. Gap junctions in the nervous system**

characterized by rare leukoencephalopathy affecting predominantly the brainstem and cervical cord with insidious onset of clinical features and unified by the presence in astrocytes of Rosenthal fibers (protein aggregates mainly contain glial fibrillary acidic protein (GFAP) and small stress proteins) in the astrocytes especially in the subpial and subependymal in location. It is strongly upregulated in response to the CNS damage [68]. It is thought to be important in astrocyte-neuronal communication and is believed to modulate astrocyte motility and shape. Satellite glial cells (SGCs) responsible for the maintenance of homeostasis and vascular permeability at the blood-tissue interface [69]. In the peripheral nervous system, neurons located in sensory ganglia are tightly surrounded by SGCs, following injury these cells undergo modification in structure and function [15]. According to Feng et al., after ligation of the L5 spinal nerve, mechanical allodynia developed in the ipsilateral hind paw and expression of GFAP in the ipsilateral DRG increased significantly as early as 4 hours after surgery, and gradually increases up to peak level at day 7 and then stayed at high level till day 56 [74]. Significant change seen among the sizes of neurons means small to medium size neurons shows maximum GFAP immunoreactivity at 12 hours and on day 7, a number of larger neurons was surrounded by GFAP stained satellite cells.

Gap junctions, tight junctions, adherens junctions, desmosomes, hemidesmosomes, focal adhesions, chemical synapses, and immunological synapses are complex multiunit plasma membrane structures that assemble in a localized spatial and temporal organization to maintain structural tissue organization and to provide the cell signaling functions. At least nine connexins (Cx26, Cx32, Cx33, Cx36, Cx37, Cx40, Cx43, Cx45, Cx46) are expressed to various degrees in the nervous system. Functional studies in diverse cell types and in various exogenous expression systems have revealed that gap junction channels formed by different connexins are regulated differently, both at the single channel level (gating controls such as voltage sensitivity and variations in unitary conductance) and at the level of synthesis (expression, altered for example by hormones, extracellular matrix). Some gap junction channels are more sensitive to various gating stimuli than others, some display some degree of ionic selectivity, and some will pair promiscuously with other connexins (heterologous channels) while others are quite selective in their interaction (homologous channels). Such differences are important from the standpoint of the physiological roles of gap junctions in different cell types, as well as in the establishment of communication compartments within the nervous system [75]. Connexins are differentially expressed in the brain during ontogeny. Most recently, tissue culture preparations from embryonic neural tissue have allowed manipulation of individual cells and evaluation of changes in junctional distribution and expression during maturation. Such studies have clarified the relationships between sequential changes in phenotypes of neural cells, with the extent of coupling mediated by Cx43 (which is abundant in neural precursor populations) and the appearance of other gap junction proteins. Expression pattern of Cx32, Cx43 and Cx30 during the development in rat brain indicates the Connexin-43 appears first at embryonic days 12-18 [76] and that Cx32 protein and mRNA appear during first or second postnatal week and increases during development. Immunohistochemical analysis of postnatal rat brain has shown that Cx43 first appears along radial glial cells and is most intense along cerebellar Bergmann glial cells [77]. Glia represents the major cell population in the CNS coupled by gap junctions. Indeed, compared to neurons, the level of connexin expression is high in these cells and persists until the adult stage [75]. For the two main types

#### *Gap Junctions in the Dorsal Root Ganglia DOI: http://dx.doi.org/10.5772/intechopen.82128*

*Neurons - Dendrites and Axons*

**Figure 8.**

between those of actin filaments and microtubules. Nearly all-intermediate filaments consist of subunits with a molecular weight of about 50 kDa. Some evidence suggests that many of the stable structural proteins in intermediate filaments evolved from highly conserved enzymes, with only minor genetic modification. Intermediate filaments are formed from nonpolar and highly variable intermediate filament subunits. Unlike those of microfilaments and microtubules, the protein subunits of intermediate filaments show considerable diversity and tissue specificity. In addition, they do not possess enzymatic activity and form nonpolar filaments. Intermediate filaments also do not typically disappear and reform in the continuous manner characteristic of most microtubules and actin filaments. For these reasons, intermediate filaments are believed to play a primarily structural role within the cell and to compose the cytoplasmic link of a tissue-wide continuum of cytoplasmic, nuclear, and extracellular filaments. A highly variable central rod-shaped domain with strictly conserved globular domains at either end characterizes intermediate filament proteins. Although the various classes of intermediate filaments differ in the amino acid sequence of the rod-shaped domain and show some variation in molecular weight, they all share a homologous region that is important in filament self-assembly. Intermediate filaments are assembled from a pair of helical monomers that twist around each other to form coiled-coil dimers. Then, two coiled-coil dimers twist around each other in antiparallel fashion (parallel but pointing in opposite directions) to generate a staggered tetramer of two coiled-coil dimers, thus forming the nonpolarized unit of the intermediate filaments. Each tetramer, acting as an individual unit, is aligned along the axis of the filament. The ends of the tetramers are bound together to form the free ends of the filament. This assembly process provides a stable, staggered, helical array in which filaments are packed together and additionally stabilized by lateral binding interactions between adjacent tetramers [2]. Total six classes of intermediate filament are present in body, e.g., Class II and I include keratin and cytokeratin and class III include vimentin, glial acidic fibrillary

*Immunohistochemical staining for the section of DRG using GFAP antibody. Black arrows representing the location of satellite glial cells. Red arrow showing the communication between two neurons [33].*

GFAP is the principal intermediate filament in mature astrocytes. GFAP is a soluble protein isolated from the multiple sclerosis plaques and presumably arising from the glial filaments [73]. The GFAP gene is located on the long (q) arm of chromosome 17 at position 21. Mutation in the GFAP results in Alexander disease

**82**

protein (GFAP) and peripherin.

characterized by rare leukoencephalopathy affecting predominantly the brainstem and cervical cord with insidious onset of clinical features and unified by the presence in astrocytes of Rosenthal fibers (protein aggregates mainly contain glial fibrillary acidic protein (GFAP) and small stress proteins) in the astrocytes especially in the subpial and subependymal in location. It is strongly upregulated in response to the CNS damage [68]. It is thought to be important in astrocyte-neuronal communication and is believed to modulate astrocyte motility and shape. Satellite glial cells (SGCs) responsible for the maintenance of homeostasis and vascular permeability at the blood-tissue interface [69]. In the peripheral nervous system, neurons located in sensory ganglia are tightly surrounded by SGCs, following injury these cells undergo modification in structure and function [15]. According to Feng et al., after ligation of the L5 spinal nerve, mechanical allodynia developed in the ipsilateral hind paw and expression of GFAP in the ipsilateral DRG increased significantly as early as 4 hours after surgery, and gradually increases up to peak level at day 7 and then stayed at high level till day 56 [74]. Significant change seen among the sizes of neurons means small to medium size neurons shows maximum GFAP immunoreactivity at 12 hours and on day 7, a number of larger neurons was surrounded by GFAP stained satellite cells.

#### **11. Gap junctions in the nervous system**

Gap junctions, tight junctions, adherens junctions, desmosomes, hemidesmosomes, focal adhesions, chemical synapses, and immunological synapses are complex multiunit plasma membrane structures that assemble in a localized spatial and temporal organization to maintain structural tissue organization and to provide the cell signaling functions. At least nine connexins (Cx26, Cx32, Cx33, Cx36, Cx37, Cx40, Cx43, Cx45, Cx46) are expressed to various degrees in the nervous system. Functional studies in diverse cell types and in various exogenous expression systems have revealed that gap junction channels formed by different connexins are regulated differently, both at the single channel level (gating controls such as voltage sensitivity and variations in unitary conductance) and at the level of synthesis (expression, altered for example by hormones, extracellular matrix). Some gap junction channels are more sensitive to various gating stimuli than others, some display some degree of ionic selectivity, and some will pair promiscuously with other connexins (heterologous channels) while others are quite selective in their interaction (homologous channels). Such differences are important from the standpoint of the physiological roles of gap junctions in different cell types, as well as in the establishment of communication compartments within the nervous system [75]. Connexins are differentially expressed in the brain during ontogeny. Most recently, tissue culture preparations from embryonic neural tissue have allowed manipulation of individual cells and evaluation of changes in junctional distribution and expression during maturation. Such studies have clarified the relationships between sequential changes in phenotypes of neural cells, with the extent of coupling mediated by Cx43 (which is abundant in neural precursor populations) and the appearance of other gap junction proteins. Expression pattern of Cx32, Cx43 and Cx30 during the development in rat brain indicates the Connexin-43 appears first at embryonic days 12-18 [76] and that Cx32 protein and mRNA appear during first or second postnatal week and increases during development. Immunohistochemical analysis of postnatal rat brain has shown that Cx43 first appears along radial glial cells and is most intense along cerebellar Bergmann glial cells [77]. Glia represents the major cell population in the CNS coupled by gap junctions. Indeed, compared to neurons, the level of connexin expression is high in these cells and persists until the adult stage [75]. For the two main types of macroglial cells, the astrocytes and the oligodendrocytes, several connexins have been detected [78]. Gap junctional communication is not limited to either astrocyteto-astrocyte or oligodendrocyte-to-oligodendrocyte, but it also occurs in between both cell types. In the adult brains, the predominant connexin is Cx43, which is abundant in astrocytes and is also expressed in leptomeninges, endothelial cells and ependyma. The second type of microglia, the oligodendrocytes (and their peripheral counterparts, the Schwann cells), appear to express a different gap junction protein, Cx32, although to a lower extent in situ than the level of Cx43 expression exhibited by astrocytes. Astrocytes express Cx43 and are well coupled in vivo and under culture conditions. However, the strength of coupling and degree of Cx43 expression between astrocytes varies depending on brain regions being higher in the hypothalamus than in the striatum. Although glial gap junctions do not generate action potentials in normal conditions and are devoid of synaptic contacts, connexin channels provide a route that allows changes in membrane potential to be transmitted from one cell to its neighbors. Recently, the participation of astrocytic gap junction in neuroprotection has been investigated by comparing neuronal vulnerability in the presence of either communicating or non-communicating astrocytes [75].

### **12. Gap junctions and connexins**

Gap junctions and their consistent connexin proteins have represented a new challenge in all tissues where they occur but no structure is more complex or more interconnected than the mammalian central and peripheral nervous systems (CNS and PNS). The term "Gap junctions" arose from the work of Revel and Karnovsky, who described the fine structure of the interconnections between mouse cardiomyocytes and between hepatocytes. Later development of specific antibodies to gap junction proteins and eventually the cloning of these connexin molecules have now led to the availability of a variety of techniques by which the distribution and expression patterns of specific types of gap junctions have been defined in a varied number of tissues, including the brain. Gap junctions are the clusters of intercellular channels that are composed of 12 subunits, 6 of which form a connexion or hemichannel contributed by each of the coupled cells [79]. Gap junctions are permeant to molecules up to 1 kDa and are found in virtually all cell types in mammals; few exceptions include circulating erythrocytes, spermatozoids and adult innervated skeletal muscle cells [80]. Gap junctional communication is essential for many physiological events, including cell synchronization, differentiation, cell growth, and metabolic coordination of avascular organ including epidermis and lens [81]. Connexin family members share a similar structural topology. Each connexin has four transmembrane domains that constitute the wall/pore of the channels. These domains are linked by two extracellular loops that play roles in the cell-cell recognition and docking processes. There are three unchanged cysteine residues in each loop, which solely form intraconnexin disulfide bonds [82]. The transmembrane domains and extracellular loops are highly conserved among the family members. Furthermore, connexin proteins have cytoplasmic N- and C-terminal and a cytoplasm loop linking the second and third transmembrane domains. Although the N-terminus is conserved, the cytoplasmic loop and C-terminus show great variation in terms of sequence and length. The cytoplasmic tail and loop are susceptible to various post-translational modifications (e.g., phosphorylation), which are believed to have regulatory roles [83]. Connexons (hemichannels) are then carried to the cell surface via vesicles transported through microtubules, which fuse to the plasma membrane. These hemichannels can either form nonjunctional channels in unopposed areas of the cell membrane or diffuse freely to regions of cell-to-cell contact to find a partner connexon from a neighboring cell to complete

**85**

**Figure 9.**

*Gap Junctions in the Dorsal Root Ganglia DOI: http://dx.doi.org/10.5772/intechopen.82128*

the formation of intercellular channels. Intercellular channels then cluster into gap junction plaques, a highly dynamic event involving removal of old channels from the center of the plaque, while adding new gap junction subunits to the periphery [84]. The intercellular channels from the middle of the plaque are internalized into vesicular structures called "annular junctions" [85], which either fuse with the lysosome for degradation by lysosomal enzymes or are targeted to the proteasomal pathway [86]. The continuous synthesis and degradation of connexins through these mechanisms may provide for the quick adaptation of tissues to changing environmental conditions. Unopposed hemichannels can also be functional under certain conditions, including mechanical and ischemic stress. Under these circumstances, open hemichannels are thought to facilitate the release of a variety of factors such as ATP, glutamate, and NAD+ into the extracellular space, generating different physiological responses [87]. Up to date, there were 20 proposed members of the connexin family of proteins that form gap junctional intercellular communication channels in mammalian tissues, and over half are reported to be present in the nervous system. Identification of the several connexin proteins at gap junctions between each neuronal and glial cell type is necessary for the sensible design of investigations into the functions of gap junctions between glial cells and into the functional contributions of electrical and "mixed" (chemical plus electrical) synapses to communication between

*Immunohistochemical staining using connexin-43 antibody. Black arrows represent the location of gap junctions* 

Gap junction's role has been well evaluated concerning cell-to-cell interaction. There are two effects derived from gap junction's function that may determine life and death of the connected cells [89]. The bystander effect promotes the death of normal cells adjacent to an apoptotic cell by diffusing toxic metabolites through gap junctions. In the same way there is the Good Samaritan effect that allows

neurons in the mammalian nervous system (**Figure 9**).

**13. Pathophysiology of connexins**

*between the satellite glial cells and the neuronal bodies [33].*

#### **Figure 9.**

*Neurons - Dendrites and Axons*

**12. Gap junctions and connexins**

of macroglial cells, the astrocytes and the oligodendrocytes, several connexins have been detected [78]. Gap junctional communication is not limited to either astrocyteto-astrocyte or oligodendrocyte-to-oligodendrocyte, but it also occurs in between both cell types. In the adult brains, the predominant connexin is Cx43, which is abundant in astrocytes and is also expressed in leptomeninges, endothelial cells and ependyma. The second type of microglia, the oligodendrocytes (and their peripheral counterparts, the Schwann cells), appear to express a different gap junction protein, Cx32, although to a lower extent in situ than the level of Cx43 expression exhibited by astrocytes. Astrocytes express Cx43 and are well coupled in vivo and under culture conditions. However, the strength of coupling and degree of Cx43 expression between astrocytes varies depending on brain regions being higher in the hypothalamus than in the striatum. Although glial gap junctions do not generate action potentials in normal conditions and are devoid of synaptic contacts, connexin channels provide a route that allows changes in membrane potential to be transmitted from one cell to its neighbors. Recently, the participation of astrocytic gap junction in neuroprotection has been investigated by comparing neuronal vulnerability in the

presence of either communicating or non-communicating astrocytes [75].

Gap junctions and their consistent connexin proteins have represented a new challenge in all tissues where they occur but no structure is more complex or more interconnected than the mammalian central and peripheral nervous systems (CNS and PNS). The term "Gap junctions" arose from the work of Revel and Karnovsky, who described the fine structure of the interconnections between mouse cardiomyocytes and between hepatocytes. Later development of specific antibodies to gap junction proteins and eventually the cloning of these connexin molecules have now led to the availability of a variety of techniques by which the distribution and expression patterns of specific types of gap junctions have been defined in a varied number of tissues, including the brain. Gap junctions are the clusters of intercellular channels that are composed of 12 subunits, 6 of which form a connexion or hemichannel contributed by each of the coupled cells [79]. Gap junctions are permeant to molecules up to 1 kDa and are found in virtually all cell types in mammals; few exceptions include circulating erythrocytes, spermatozoids and adult innervated skeletal muscle cells [80]. Gap junctional communication is essential for many physiological events, including cell synchronization, differentiation, cell growth, and metabolic coordination of avascular organ including epidermis and lens [81]. Connexin family members share a similar structural topology. Each connexin has four transmembrane domains that constitute the wall/pore of the channels. These domains are linked by two extracellular loops that play roles in the cell-cell recognition and docking processes. There are three unchanged cysteine residues in each loop, which solely form intraconnexin disulfide bonds [82]. The transmembrane domains and extracellular loops are highly conserved among the family members. Furthermore, connexin proteins have cytoplasmic N- and C-terminal and a cytoplasm loop linking the second and third transmembrane domains. Although the N-terminus is conserved, the cytoplasmic loop and C-terminus show great variation in terms of sequence and length. The cytoplasmic tail and loop are susceptible to various post-translational modifications (e.g., phosphorylation), which are believed to have regulatory roles [83]. Connexons (hemichannels) are then carried to the cell surface via vesicles transported through microtubules, which fuse to the plasma membrane. These hemichannels can either form nonjunctional channels in unopposed areas of the cell membrane or diffuse freely to regions of cell-to-cell contact to find a partner connexon from a neighboring cell to complete

**84**

*Immunohistochemical staining using connexin-43 antibody. Black arrows represent the location of gap junctions between the satellite glial cells and the neuronal bodies [33].*

the formation of intercellular channels. Intercellular channels then cluster into gap junction plaques, a highly dynamic event involving removal of old channels from the center of the plaque, while adding new gap junction subunits to the periphery [84]. The intercellular channels from the middle of the plaque are internalized into vesicular structures called "annular junctions" [85], which either fuse with the lysosome for degradation by lysosomal enzymes or are targeted to the proteasomal pathway [86]. The continuous synthesis and degradation of connexins through these mechanisms may provide for the quick adaptation of tissues to changing environmental conditions. Unopposed hemichannels can also be functional under certain conditions, including mechanical and ischemic stress. Under these circumstances, open hemichannels are thought to facilitate the release of a variety of factors such as ATP, glutamate, and NAD+ into the extracellular space, generating different physiological responses [87].

Up to date, there were 20 proposed members of the connexin family of proteins that form gap junctional intercellular communication channels in mammalian tissues, and over half are reported to be present in the nervous system. Identification of the several connexin proteins at gap junctions between each neuronal and glial cell type is necessary for the sensible design of investigations into the functions of gap junctions between glial cells and into the functional contributions of electrical and "mixed" (chemical plus electrical) synapses to communication between neurons in the mammalian nervous system (**Figure 9**).

#### **13. Pathophysiology of connexins**

Gap junction's role has been well evaluated concerning cell-to-cell interaction. There are two effects derived from gap junction's function that may determine life and death of the connected cells [89]. The bystander effect promotes the death of normal cells adjacent to an apoptotic cell by diffusing toxic metabolites through gap junctions. In the same way there is the Good Samaritan effect that allows

a condemned cell to live by draining the toxic metabolites to adjacent cells and maintaining cells integrity and thus tissue homeostasis. In this way gap junctions perform a dual function either saving or killing interconnected cells [88]. Some pathological conditions are directly related to gap junctions or to their altered function. Some human diseases are caused by mutated connexins [89]. Mutations on Cx32 induce a peripheral neuropathy named Charcot-Marie-Tooth disease. The many conductivity changes observed in this disease may be caused by altered protein traffic to the junctions, altered channel permeability and, sometimes, altered conformation of heterotypic channels [78]. Mutations of Cx36 may lead to the most common hereditary non-syndromic deafness. Cx43 structure may be altered in some forms of human epilepsy where Cx43 mRNA expression may or may not be altered. High Cx43 levels have been detected in β-4 positive amyloid plaques of Alzheimer's disease [77], indicating either astrocytes invasion of the plaques or increased Cx43 expression by astrocytes, as observed in PC12 cells (cells from a rat pheochromocytoma) with increased expression of carboxy-terminal portions of amyloid precursor protein [90]. However a higher Cx43 expression in that area may reflect the existence of many activated macrophages/microglia. The decrease of Cx43 within an inflammatory focus suggests that factors as IL-1 β are involved in astrocytic connectivity decrease as observed in autoimmune experimental encephalitis.

#### **Author details**

Vishwajit Ravindra Deshmukh Department of Anatomy, All India Institute of Medical Sciences, Nagpur, Maharashtra, India

\*Address all correspondence to: drvishwajitdeshmukh@gmail.com

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**87**

2008;**4**:10

*Gap Junctions in the Dorsal Root Ganglia DOI: http://dx.doi.org/10.5772/intechopen.82128*

[1] Standring S. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 40th edition. London, UK: Churchill

administration. Neurotoxicology.

[9] Kikuchi S, Sato K, Konno S, Hasue M. Anatomic and radiographic study of dorsal root ganglia. Spine (Phila Pa

[10] Sluijter ME. Radiofrequency, Part I: The Lumbosacral Region. Meggen: Flivopress SA; 2001. pp. 119-138

[11] Lawson SN, Caddy KWT, Biscoe TJ. Development of rat dorsal root ganglia neurons. Cell and Tissue Research. 1974;**153**:399-414

[12] Duce IR, Keen P. An ultrastructural classification of the neuronal cells bodies of the rat dorsal root ganglia using the zinc-iodide-osmium

impregnation. Cell and Tissue Research.

[13] Allen NJ, Barres BA. Gliamore than just brain glue. Nature.

[14] Cao H, Zhang YQ. Spinal glial activation contributes to

and Biobehavioral Reviews.

pathological pain states. Neuroscience

[15] Cherkas PS, Huang TY, Pannicke T, Tal M, Reichenbach A, Hanani M. The effects of axotomy on neurons and satellite glial cells in mouse trigeminal ganglion. Pain. 2004;**110**:290-298

[16] Miyagi M, Ohtori S, Ishikawa T, Aoki Y, Ozawa T, Doya H, et al. Up-regulation of TNFalpha in DRG satellite cells following lumbar facet joint injury in rats. European Spine

[17] Watkins LR, Milligan ED, Maier SF.

Glial activation: A driving force for pathological pain. Trends in Neurosciences. 2001;**24**:450-455

Journal. 2006;**15**:953-958

2000;**21**:389-393

1976). 1994;**19**:6-11

1997;**185**:263-277

2009;**457**:675-677

2008;**32**:972-983

[2] Ross M, Pawlina W. Histology: A Text and Atlas of Histology. 6th edition. Baltimore, MD: Lippincott Williams and

Wilkins; 2006. pp. 62 and 354

[3] Kiernan JA. Barr's The Human Nervous System. Philadelphia: Wolters

[4] Hanani M. Satellite glial cells in sensory ganglia: From form to function. Brain Research. Brain Research Reviews.

[5] Pannese E. Observation on the morphology, submicroscopic structure and biological properties of satellite cells in sensory ganglia of mammals. Zeitschrift für Zellforschung

und Mikroskopische Anatomie.

[6] Aldskogius H, Elfvin LG, Forsman CA. Primary sensory afferents in the inferior mesenteric ganglion and related nerves of the guinea pig. An experimental study with anterogradely transported wheat germ agglutininhorseradish peroxidase conjugate. Journal of the Autonomic Nervous

Livingstone; 2008. p. 55

Kluwer; 2009. p. 44

2005;**48**:457-476

1960;**52**:567-597

System. 1986;**15**:179-190

nervous system of the rat after repeated intravenous

[7] Jimenez-Andrade J, Herrera M, Ghilardi J, Vardanyan M, Melemedjian O, Mantyh P. Vascularization of the dorsal root ganglia and peripheral nerve of the mouse: Implications for chemical-induced peripheral sensory neuropathies. Molecular Pain.

[8] Cavaletti G, Cavalletti E, Oggioni N, Sottani C, Minoia C, D'Incalci M, et al. Distribution of paclitaxel within the

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*Gap Junctions in the Dorsal Root Ganglia DOI: http://dx.doi.org/10.5772/intechopen.82128*

#### **References**

*Neurons - Dendrites and Axons*

**86**

**Author details**

encephalitis.

Maharashtra, India

Vishwajit Ravindra Deshmukh

provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Department of Anatomy, All India Institute of Medical Sciences, Nagpur,

a condemned cell to live by draining the toxic metabolites to adjacent cells and maintaining cells integrity and thus tissue homeostasis. In this way gap junctions perform a dual function either saving or killing interconnected cells [88]. Some pathological conditions are directly related to gap junctions or to their altered function. Some human diseases are caused by mutated connexins [89]. Mutations on Cx32 induce a peripheral neuropathy named Charcot-Marie-Tooth disease. The many conductivity changes observed in this disease may be caused by altered protein traffic to the junctions, altered channel permeability and, sometimes, altered conformation of heterotypic channels [78]. Mutations of Cx36 may lead to the most common hereditary non-syndromic deafness. Cx43 structure may be altered in some forms of human epilepsy where Cx43 mRNA expression may or may not be altered. High Cx43 levels have been detected in β-4 positive amyloid plaques of Alzheimer's disease [77], indicating either astrocytes invasion of the plaques or increased Cx43 expression by astrocytes, as observed in PC12 cells (cells from a rat pheochromocytoma) with increased expression of carboxy-terminal portions of amyloid precursor protein [90]. However a higher Cx43 expression in that area may reflect the existence of many activated macrophages/microglia. The decrease of Cx43 within an inflammatory focus suggests that factors as IL-1 β are involved in astrocytic connectivity decrease as observed in autoimmune experimental

\*Address all correspondence to: drvishwajitdeshmukh@gmail.com

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*Neurons - Dendrites and Axons*

[19] Suadicani SO, Cherkas PS, Zuckerman J, Smith DN, Spray DC, Hanani M. Bidirectional calcium signaling between satellite glial cells and neurons in cultured mouse trigeminal ganglia. Neuron Glia Biology. 2010;**6**:43-51

[20] Hatai S. Number and size of spinal ganglion cells and dorsal root fibres in the white rat at different ages. The Journal of Comparative Neurology.

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[24] Ramchandra R, Mc Grew S, Baxter J,

[25] Cavalier-Smith T. Nuclear volume control by nucleoskeletal DNA, selection for cell volume and cell growth rate, and the solution of the DNA C-value paradox. Journal of Cell

[26] Sato S, Burgess SB, McIlwain DL. Transcription and motoneuron

Elmslie KS. Nav1.8 channels are expressed in large, as well as small, diameter sensory afferent neurons.

Channels. 2013;**7**(1):34-37

Science. 1978;**34**:247-278

2009;**42**:143-149

1902;**12**:107-124

Press; 1999. pp. 27-59

[18] Gungigake KK, Goto T, Nakao K, Kobayashi S, Yamaguchi K. Activation of satellite glial cells in rat trigeminal ganglia after upper molar extraction. Acta Histochemica et Cytochemica.

size. Journal of Neurochemistry.

[27] Goldschmidt RB, Steward O. Retrograde regulation of neuronal size in the enthorhinal cortex: Consequences of the destruction of dentate gyrus granule cells with colchicine. Restorative

Neurology and Neuroscience.

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[55] Kumamoto T, Fukuhara N, Miyatake T, Araki K, Takahashi Y, Araki S. Experimental neuropathy induced by methyl mercury com-pounds: Autoradiographic study of GABA uptake by dorsal root ganglia. European Neurology. 1986;**25**:269-277

[56] Schlaepfer WW. Experimental lead neuropathy: A disease of the supporting cells in the peripheral nervous system. Journal of Neuropathology and Experimental Neurology. 1969;**28**:401-418

[57] Schionning JD, Danscher G. Autometallographic mercury correlates with degnera tive changes in dorsal root ganglia of rats intoxicated with organic mercury. APMIS. 1999;**107**:303-310

[58] Amir R, Devor M. Electrical excitability of the soma of sensory neurons is required for spike invasion of the soma, but not for throughconduction. Biophysical Journal. 2003;**84**(4):2181-2191

[59] Konishi T. Developmental and activity-dependent changes in K+ currents in satellite glial cells in mouse superior cervical ganglion. Brain Research. 1996;**708**:7-15

[60] Hibino H, Horio Y, Fujita A, Inanobe A, Doi K, Gotow T, et al. Expression of an inwardly rectifying K+ channel, Kir4.1, in satellite cells of rat cochlear ganglia. The American Journal of Physiology. 1999;**277**:C638-C644

[61] Fields RD, Stevens-Graham B. New insights into neuronglia communication. Science. 2002;**298**(5593):556-562

[62] Thalakoti S, Patil VV, Damodaram S, Vause CV, Langford LE, Freeman SE, et al. Neuron-glia signaling in trigeminal ganglion: Implications for migraine pathology. Headache. 2007;**47**:1008-1023

[63] Kielian T, Esen N. Effects of neuroinflammation on gliaglia gap junctional intercellular communication: A perspective. Neurochemistry International. 2004;**45**:429-436

[64] Upton N, Thompson M. Benzo[b] pyranols and related novel antiepileptic agents. Progress in Medicinal Chemistry. 2000;**37**:177-200

[65] Benfenati V, Caprini M, Nobile M, Rapisarda C, Ferroni S. Guanosine promotes the up-regulation of inward rectifier potassium current mediated by Kir4.1 in cultured rat cortical astrocytes. Journal of Neurochemistry. 2006 Jul;**98**(2):430-445

[66] Vit JP, Jasmin L, Bhargava A, Ohara PT. Satellite glial cells in the trigeminal ganglion as a determinant of orofacial neuropathic pain. Neuron Glia Biology. 2006;**2**(4):247-257

[67] Weick M, Cherkas P, S, Härtig W, Pannicke T, Uckermann O, Bringmann A,

**91**

*Gap Junctions in the Dorsal Root Ganglia DOI: http://dx.doi.org/10.5772/intechopen.82128*

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2003;**120**:969-977

Glia. 2006;**53**:677-687

2007;**127**:555-563

1995;**131**:11-22

1972;**43**:429-435

2011;**1427**:65-77

2000;**32**:308-315

Neuron. 1996;**17**:607-615

[71] Jasmin L, Vit JP, Bhargava A, Ohara PT. Can satellite glial cells be therapeutic targets for pain control? Neuron Glia Biology. 2010;**6**:63-71

[72] Stephenson JL, Byers MR. GFAP immunoreactivity in trigeminal ganglion satellite cells after tooth injury in rats. Experimental Neurology.

[73] Bignami A, Eng LF, Dahl D, Uyeda CT. Localization of the glial acidic fibrillary protein in astrocyte by immunofluoroscence. Brain Research.

[74] Liu F-Y, Sun Y-N, Wang F-t, Li Q, Li S, Zhao Z-F. Activation of satellite glial cells in lumbar dorsal root ganglia contributes to neuropathic pain after spinal nerve ligation. Brain Research.

[75] Andrade-Rozental AF, Rozental R, Hopperstad MG, Wu JK, Vrionis FD, Spray DC. Gap junctions: The "kiss of death" and the "kiss of life". Brain Research. Brain Research Reviews.

et al. P2 receptors in satellite glial cells in trigeminal ganglia of mice. Neuroscience. [76] Belliveau DJ, Naus CCJ. Cellular localization of gap junctions mRNAs in developing rat brain. Developmental

[77] Yamamoto T, Vukelic J, Hertzberg EL, Nagy JI. Differential anatomical and cellular patterns of connexin 43 expression during postnatal development

of rat brain. Developmental Brain

[78] Dermietzel R, Spray DC. From neuro-glue ('Nervenkitt') to glia: A

[79] Spray DC, Scemes E, Rozental R. Introduction to cell-cell communication.

[80] Sohl G, Maxeiner S, Willecke K. Expression and functions of neuronal gap junctions. Nature Reviews. Neuroscience. 2005;**6**:191-200

[81] Vinken M, Vanhaecke T, Papeleu P,

H. Connexin gene mutations in human genetic diseases. Mutation Research.

Connexins, gap junctional intercellular communication and kinases. Biology of

[84] Gaietta G, Deerinck TJ, Adams SR, Bouwer J, Tour O, Laird DW, et al. Multicolor and electron microscopic imaging of connexin trafficking. Science. 2002;**296**:503-507

[85] Jordan K, Chodock R, Hand AR, Laird DW. The origin of annular

junctions: A mechanism of gap junction internalization. Journal of Cell Science.

Snykers S, Henkens T, Rogiers V. Connexins and their channels in cell growth and cell death. Cellular Signalling. 2006;**18**:592-600

[82] Krutovskikh V, Yamasaki

[83] Cruciani V, Mikalsen SO.

the Cell. 2002;**94**:433-443

2000;**462**:197-207

2001;**114**:763-773

In: Zigmond B, Landis S, editors. Fundamental neuroscience. New York, NY: Academic Press; 1998. pp. 317-343

Research. 1992;**66**:165-180

prologue. Glia. 1998;**24**:1-7

Neuroscience. 1995;**17**:81-96

[69] Danielyan L, Tolstonog G, Traub P, et al. Colocalization of glial fibrillary acidicprotein, metallothionein, and MHC II in human, rat, NOD/ SCID, and nude mouse skin keratinocytes and fibroblasts. The Journal of Investigative Dermatology.

[70] Liedtke W, Edelmann W, Bieri PL, et al. GFAP is necessary for the integrity of CNS white matter architecture and long term maintainance of myelination.

*Gap Junctions in the Dorsal Root Ganglia DOI: http://dx.doi.org/10.5772/intechopen.82128*

*Neurons - Dendrites and Axons*

Letters. 1989;**98**:8-12

2002;**114**:279-283

pp. 71-105

[51] Woodham P, Anderson PN, Nadim W, Turmaine M. Satellite cells surrounding axotomised rat dorsal root ganglion cells increase expression of a GFAP-like protein. Neuroscience

[59] Konishi T. Developmental and activity-dependent changes in K+ currents in satellite glial cells in mouse superior cervical ganglion. Brain

[60] Hibino H, Horio Y, Fujita A, Inanobe A, Doi K, Gotow T, et al. Expression of an inwardly rectifying

 channel, Kir4.1, in satellite cells of rat cochlear ganglia. The American Journal of Physiology.

[61] Fields RD, Stevens-Graham B.

[62] Thalakoti S, Patil VV, Damodaram S, Vause CV, Langford LE, Freeman SE, et al. Neuron-glia signaling in trigeminal ganglion: Implications for migraine pathology. Headache.

Research. 1996;**708**:7-15

1999;**277**:C638-C644

2007;**47**:1008-1023

2004;**45**:429-436

Jul;**98**(2):430-445

[63] Kielian T, Esen N. Effects of neuroinflammation on gliaglia gap junctional intercellular communication: A perspective. Neurochemistry International.

agents. Progress in Medicinal Chemistry. 2000;**37**:177-200

[64] Upton N, Thompson M. Benzo[b] pyranols and related novel antiepileptic

[65] Benfenati V, Caprini M, Nobile M, Rapisarda C, Ferroni S. Guanosine promotes the up-regulation of inward rectifier potassium current mediated by Kir4.1 in cultured rat cortical astrocytes. Journal of Neurochemistry. 2006

[66] Vit JP, Jasmin L, Bhargava A, Ohara PT. Satellite glial cells in the trigeminal ganglion as a determinant of orofacial neuropathic pain. Neuron Glia

[67] Weick M, Cherkas P, S, Härtig W, Pannicke T, Uckermann O, Bringmann A,

Biology. 2006;**2**(4):247-257

New insights into neuronglia communication. Science. 2002;**298**(5593):556-562

K+

[52] Hanani M, Haung TY, Cherkas PS,

Ledda M, Pannese E. Glial cell plasticity in sensory ganglia induced by nrve damage. Neuroscience.

[53] Svennigsen AF, Colman DR, Pedraza L. Satellite cells of dorsal root ganglia are multipotential glial precursors.

Neuron Glia Biology. 2004;**1**:85-93

[54] Lieberman AR. Some factors affecting retrograde neuronal responses to axonal lesions. In: Bellairs R, Gray EG, editors. Essays on the Nervous System. Oxford: Clarendon; 1974.

[55] Kumamoto T, Fukuhara N,

Neurology. 1986;**25**:269-277

cells in the peripheral nervous system. Journal of Neuropathology and Experimental Neurology.

[57] Schionning JD, Danscher G.

[58] Amir R, Devor M. Electrical excitability of the soma of sensory neurons is required for spike invasion of the soma, but not for throughconduction. Biophysical Journal.

Autometallographic mercury correlates with degnera tive changes in dorsal root ganglia of rats intoxicated with organic mercury. APMIS.

1969;**28**:401-418

1999;**107**:303-310

2003;**84**(4):2181-2191

Miyatake T, Araki K, Takahashi Y, Araki S. Experimental neuropathy induced by methyl mercury com-pounds: Autoradiographic study of GABA uptake by dorsal root ganglia. European

[56] Schlaepfer WW. Experimental lead neuropathy: A disease of the supporting

**90**

et al. P2 receptors in satellite glial cells in trigeminal ganglia of mice. Neuroscience. 2003;**120**:969-977

[68] Lee Y, Su M, Messing A, et al. Astrocyte heterogeneity revealed by expression of a GFAP-Lac Z transgene. Glia. 2006;**53**:677-687

[69] Danielyan L, Tolstonog G, Traub P, et al. Colocalization of glial fibrillary acidicprotein, metallothionein, and MHC II in human, rat, NOD/ SCID, and nude mouse skin keratinocytes and fibroblasts. The Journal of Investigative Dermatology. 2007;**127**:555-563

[70] Liedtke W, Edelmann W, Bieri PL, et al. GFAP is necessary for the integrity of CNS white matter architecture and long term maintainance of myelination. Neuron. 1996;**17**:607-615

[71] Jasmin L, Vit JP, Bhargava A, Ohara PT. Can satellite glial cells be therapeutic targets for pain control? Neuron Glia Biology. 2010;**6**:63-71

[72] Stephenson JL, Byers MR. GFAP immunoreactivity in trigeminal ganglion satellite cells after tooth injury in rats. Experimental Neurology. 1995;**131**:11-22

[73] Bignami A, Eng LF, Dahl D, Uyeda CT. Localization of the glial acidic fibrillary protein in astrocyte by immunofluoroscence. Brain Research. 1972;**43**:429-435

[74] Liu F-Y, Sun Y-N, Wang F-t, Li Q, Li S, Zhao Z-F. Activation of satellite glial cells in lumbar dorsal root ganglia contributes to neuropathic pain after spinal nerve ligation. Brain Research. 2011;**1427**:65-77

[75] Andrade-Rozental AF, Rozental R, Hopperstad MG, Wu JK, Vrionis FD, Spray DC. Gap junctions: The "kiss of death" and the "kiss of life". Brain Research. Brain Research Reviews. 2000;**32**:308-315

[76] Belliveau DJ, Naus CCJ. Cellular localization of gap junctions mRNAs in developing rat brain. Developmental Neuroscience. 1995;**17**:81-96

[77] Yamamoto T, Vukelic J, Hertzberg EL, Nagy JI. Differential anatomical and cellular patterns of connexin 43 expression during postnatal development of rat brain. Developmental Brain Research. 1992;**66**:165-180

[78] Dermietzel R, Spray DC. From neuro-glue ('Nervenkitt') to glia: A prologue. Glia. 1998;**24**:1-7

[79] Spray DC, Scemes E, Rozental R. Introduction to cell-cell communication. In: Zigmond B, Landis S, editors. Fundamental neuroscience. New York, NY: Academic Press; 1998. pp. 317-343

[80] Sohl G, Maxeiner S, Willecke K. Expression and functions of neuronal gap junctions. Nature Reviews. Neuroscience. 2005;**6**:191-200

[81] Vinken M, Vanhaecke T, Papeleu P, Snykers S, Henkens T, Rogiers V. Connexins and their channels in cell growth and cell death. Cellular Signalling. 2006;**18**:592-600

[82] Krutovskikh V, Yamasaki H. Connexin gene mutations in human genetic diseases. Mutation Research. 2000;**462**:197-207

[83] Cruciani V, Mikalsen SO. Connexins, gap junctional intercellular communication and kinases. Biology of the Cell. 2002;**94**:433-443

[84] Gaietta G, Deerinck TJ, Adams SR, Bouwer J, Tour O, Laird DW, et al. Multicolor and electron microscopic imaging of connexin trafficking. Science. 2002;**296**:503-507

[85] Jordan K, Chodock R, Hand AR, Laird DW. The origin of annular junctions: A mechanism of gap junction internalization. Journal of Cell Science. 2001;**114**:763-773

#### *Neurons - Dendrites and Axons*

[86] Qin H, Shao Q, Igdoura SA, Alaoui-Jamali MA, Laird DW. Lysosomal and proteasomal degradation play distinct roles in the life cycle of Cx43 in gap junctional intercellular communicationdeficient and -competent breast tumor cells. The Journal of Biological Chemistry. 2003;**278**:30005-30014

[87] Evans WH, De VE, Leybaert L. The gap junction cellular internet: Connexin hemichannels enter the signalling limelight. The Biochemical Journal. 2006;**397**:1-14

[88] Farahani R, Pina-Benabou MH, Kyrozis A, Siddiq A, Barradas PC, Chiu FC, et al. Alterations in metabolism and gap junction expression may determine the role of astrocytes as "good samaritans" or executioners. Glia. 2005;**50**:351-361

[89] Rosenthal R, Giaume C, Spray DC. Gap junctions in the nervous system. Brain Research Reviews. 2000;**32**:11-15

[90] Lynn BD, Marotta CA, Nagy JI. Propagation of intercellular calcium waves in Pc12 cells overexpressing a carboxy-terminal fragment of amyloid precursor protein. Neuroscience Letters. 1995;**199**:21-24

**93**

Section 4

Nerve Interface

Section 4 Nerve Interface

*Neurons - Dendrites and Axons*

[86] Qin H, Shao Q, Igdoura SA, Alaoui-Jamali MA, Laird DW. Lysosomal and proteasomal degradation play distinct roles in the life cycle of Cx43 in gap junctional intercellular communication-

[87] Evans WH, De VE, Leybaert L. The gap junction cellular internet: Connexin hemichannels enter the signalling limelight. The Biochemical Journal.

[88] Farahani R, Pina-Benabou MH, Kyrozis A, Siddiq A, Barradas PC, Chiu FC, et al. Alterations in

metabolism and gap junction expression may determine the role of astrocytes as "good samaritans" or executioners. Glia.

[89] Rosenthal R, Giaume C, Spray DC. Gap junctions in the nervous system. Brain Research Reviews. 2000;**32**:11-15

[90] Lynn BD, Marotta CA, Nagy JI. Propagation of intercellular calcium waves in Pc12 cells overexpressing a carboxy-terminal fragment of amyloid precursor protein. Neuroscience Letters.

deficient and -competent breast tumor cells. The Journal of Biological Chemistry. 2003;**278**:30005-30014

2006;**397**:1-14

2005;**50**:351-361

1995;**199**:21-24

**92**

**95**

**Chapter 5**

**Abstract**

**1. Introduction**

Interface Nerve Tissue-Silicon

Nanowire for Regeneration of

*Klimovskaya Alla, Chaikovsky Yuri, Liptuga Anatoliy,* 

*Lichodievskiy Volodymyr and Serozhkin Yuriy*

Electronic Device

Injured Nerve and Creation of Bio-

This overview presents the results of scientific and practical research into the development of the interface "neuron-electronic device" based on silicon nanowire. The work has been carried out for several years by a team of scientists specializing in various fields of science and technology: neuroscience, surface science, nanoelectronics, crystal growth, physics and chemistry of nanotechnology, and nanocomputing. The technology of formation of the interface "nerve fiber-silicon nanowire" was developed. The experiments were performed *in vivo* on Wistar rats. The developed technology was used in the manufacture of implants for the regeneration of the injured sciatic nerve. The results of the studies showed the effectiveness of using such implants not only for the regeneration of nerves with severe injuries but also for the creation of a *bioelectronic* interface for *neurocomputers* that can be used *in vivo* for a long time.

**Keywords:** interface, silicon nanowires, Wistar rats, sciatic nerve, experiment *in vivo*, laser heterodyne interferometric technique, application of SiNW-FET,

In the last decade, along with the solution of medical problems on the restoration of the human nervous system by traditional methods, a new direction of neuroscience arose related to the development of hybrid intellect that has to combine the best intellectual resources of human brain and the best achievements of nanoand quantum computing. By the computation speed, modern computers considerably exceed human capabilities, but they have two significant drawbacks. Providing their work with the intellectual capabilities of man using modern nanoelectronics requires considerable power consumption. This leads to an increase in the physical dimensions of the computer in order to provide a thermal regime acceptable for modern nanoelectronics. On the other hand, the human brain, accomplishing a huge amount of work on physical and intellectual interaction and to ensure the correlated work of the organism as a whole, is characterized by *extremely low energy costs* in comparison with quantum computers. Therefore, an idea arisen on creating

physical model of the interface nervous tissue-silicon nanowires

#### **Chapter 5**

## Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation of Bio-Electronic Device

*Klimovskaya Alla, Chaikovsky Yuri, Liptuga Anatoliy, Lichodievskiy Volodymyr and Serozhkin Yuriy*

### **Abstract**

This overview presents the results of scientific and practical research into the development of the interface "neuron-electronic device" based on silicon nanowire. The work has been carried out for several years by a team of scientists specializing in various fields of science and technology: neuroscience, surface science, nanoelectronics, crystal growth, physics and chemistry of nanotechnology, and nanocomputing. The technology of formation of the interface "nerve fiber-silicon nanowire" was developed. The experiments were performed *in vivo* on Wistar rats. The developed technology was used in the manufacture of implants for the regeneration of the injured sciatic nerve. The results of the studies showed the effectiveness of using such implants not only for the regeneration of nerves with severe injuries but also for the creation of a *bioelectronic* interface for *neurocomputers* that can be used *in vivo* for a long time.

**Keywords:** interface, silicon nanowires, Wistar rats, sciatic nerve, experiment *in vivo*, laser heterodyne interferometric technique, application of SiNW-FET, physical model of the interface nervous tissue-silicon nanowires

#### **1. Introduction**

In the last decade, along with the solution of medical problems on the restoration of the human nervous system by traditional methods, a new direction of neuroscience arose related to the development of hybrid intellect that has to combine the best intellectual resources of human brain and the best achievements of nanoand quantum computing. By the computation speed, modern computers considerably exceed human capabilities, but they have two significant drawbacks. Providing their work with the intellectual capabilities of man using modern nanoelectronics requires considerable power consumption. This leads to an increase in the physical dimensions of the computer in order to provide a thermal regime acceptable for modern nanoelectronics. On the other hand, the human brain, accomplishing a huge amount of work on physical and intellectual interaction and to ensure the correlated work of the organism as a whole, is characterized by *extremely low energy costs* in comparison with quantum computers. Therefore, an idea arisen on creating

a hybrid intellect that physically combines the neural networks of the brain with modern, including quantum, computing devices. The development of such devices required detailed studies of the structure of neural networks of the brain and subsequent modeling of such networks on silicon nanostructures using living neurons or by implanting silicon nanostructures into a neural network of a living organism. The end product of this device will be a hybrid brain that is capable, unlike traditional computers, including quantum ones, to apply both logical and associative methods of solving problems with low energy consumption. The main task of the hybrid brain is to provide a constant two-way communication between the central and peripheral nervous system, which will allow, in extreme case, to constantly monitor the organism as a whole and, if necessary, already in the first stages of the disease, to correct the work of those organs that have deviations from the norm, using, first of all, the internal resources of the body.

By 2015, the strategy for creating hybrid brain has already been developed [1], and a call has been issued [2, 3] to the international community to concentrate scientific and financial resources on the solution of the problem that will make a revolution not only in the field of medicine but also in all spheres of human existence.

Detailed studies of neural networks were started about 10 years ago with the work on the study of the morphology of neural network [4]. Then, a large number of animal studies were made of the relationship between the structure of neural networks and the behavioral characteristics of animals. A detailed review of these studies was published recently [5]. In parallel with studies of the central nervous system and its connection with the peripheral nervous system, work was begun on the creation of a bioelectronic complex on silicon nanostructures with the artificial cultivation of neural networks in a biological environment [6–8]. The results obtained in experiments *in vitro* allowed the transition to animal experiments and then to begin clinical experiments for the treatment of diseases that could not be treated with application of traditional medicine. *Massachusetts General Hospital and Draper Labs* develop a tiny, implanted chip to place it between a patient's skull and scalp. A series of electrodes placed at varying depths in different regions of the brain would record neurological data. In the framework of the program *ElectRx, a closed-loop system* is developed to monitor and to regulate organ functions using the internal resources of the body. *Silent speech information generated directly from the activity of neurons* is involved in speech production via an intracortical microelectrode brain-computer interface [9]. It was shown that *Macaca nemestrina* monkeys can *directly control stimulation of muscles using the activity of neurons in the motor cortex*. Monkeys learned to use artificial connections from cortical cells to muscles to generate bidirectional wrist torques and controlled multiple neuron-muscle pairs simultaneously [10].

Despite encouraging results in the development and testing of bioelectronic complexes capable of recording neural impulses produced by a neuron and transferring them to subsequent processing into a nanocomputer, there are still many unresolved problems, the first of which is the development of a central link of the hybrid intelligence the "neuron-electronic device" interface [11–15]. To date, the greatest difficulty in creating such an interface is the problem of maintaining its working capacity in a living organism for a time comparable to the human lifespan. The most suitable material for creating such an interface is crystalline silicon. First, silicon is a biocompatible material, and, second, it is the main material of nano- and microelectronic technology, which makes it easy to integrate it into electronic circuits for subsequent signal processing. Taking into account the size of neurons (of the order of tens of micrometers), the silicon wires are the most suitable for creating an interface with a neuron. So, in the past decade, the "silicon crystal-nervous tissue" interface has been attracting huge interest. Various designs of electronic circuits of field-effect transistors [16] (SiNW-FET) have been developed. The main attention

**97**

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation...*

in the development of these devices was given to obtaining a high sensitivity of the device for reliable registration of nerve impulses. For this purpose, the SiNW-FET design was developed, in which a dielectric layer between the neuron and the SiNW was created of the ultimate small thickness. The best results on the sensitivity of the SiNW-FET were obtained using the chemical compound poly-L-Lysine as a dielectric between neuron and FET. However, after long-term tests of this design, it was found that the lifetime of such an interface is estimated in a several days or a

So, a major hurdle in brain-machine interfaces (BMIs) is the lack of an implantable neural interface system that *remains viable for a substantial fraction of the user's lifetime and* the lack of a *high-density, chronic interface to enable recording and stimulation from thousands of sites* in a clinically relevant manner with little or no tissue response remains as one of the grand challenges of the twenty-first century.

The success of the research of our group in experiments on laboratory animals has shown the prospects for application of silicon nanowires in creation of bio-consistent and bioactive implants. The key problem of these works was the study of the biophysical state of the interface "neuron-silicon nanowire" and the development of methods for the purposeful management of its properties. At present, on the basis of this interface, we have developed and patented technology for the manufacture of implants [17], which provides auto-electronic stimulation of the regenerative processes of damaged nerve tissue. The most important feature of the developed technology that significantly distinguishes it from existing ones is to provide conditions for the continuous effective migration of biological cells to the implant site. This feature indicates the promise of its use for the development of neuro-electronic interfaces for neurocomputers, suitable for use over a long period of time, compa-

In 2-d part of the overview, we present the research on formation of the interface "silicon wire-nerve tissue." Experiments were carried out *in vivo* by simulation of a sciatic nerve injury and following recovery of the injury using silicon nanowires. In 3-d part, we present experimental techniques used to test how nerve fibers restore functional ability after implantation a conduit with silicon nanowires. In addition to the techniques traditionally used for this purpose, we apply a test to evaluate bidirectional communication between the brain and corresponding peripheral nerve by registration *in real-time in vivo* a nerve displacement initiated due to action potential propagation. We apply additionally SiNW-FET to measure charge state of the interface, when it forms. Furthermore, this experiment gives rise to direct definition of sign and surface charge densities both on silicon wire and nerve fiber in living organism. In 4-d part we present experimental results on evolution of the restore functionality of the damaged nerve after implantation conduit with silicon nanowires. We analyze prospects to use the interface nervous tissue—silicon nanowire in the global problem brain-computer interface—particularly on possible application quantum HEM device [18] based on silicon nanowires as a nerve pulse binary adder [19, 20].

**2. Formation of the interface silicon wire-nerve tissue**

The research on formation of the interface "silicon wire-nerve tissue" was carried out *in vivo* on Wistar rats by simulation of a sciatic nerve injury and further replacement fault of the nerve trunk by implant with a set of silicon nanowires.

One of the procedures published in details elsewhere [21, 22] includes several stages: growing of silicon wires, handling the implants, surgical procedure, and various test experiments in vivo for evaluation of motor function recovery by "the method of walking track" [23] and by recording a bilateral interaction between neuronal nets of a brain

*DOI: http://dx.doi.org/10.5772/intechopen.80739*

maximum of a few weeks.

rable to the years of human life.

#### *Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation... DOI: http://dx.doi.org/10.5772/intechopen.80739*

in the development of these devices was given to obtaining a high sensitivity of the device for reliable registration of nerve impulses. For this purpose, the SiNW-FET design was developed, in which a dielectric layer between the neuron and the SiNW was created of the ultimate small thickness. The best results on the sensitivity of the SiNW-FET were obtained using the chemical compound poly-L-Lysine as a dielectric between neuron and FET. However, after long-term tests of this design, it was found that the lifetime of such an interface is estimated in a several days or a maximum of a few weeks.

So, a major hurdle in brain-machine interfaces (BMIs) is the lack of an implantable neural interface system that *remains viable for a substantial fraction of the user's lifetime and* the lack of a *high-density, chronic interface to enable recording and stimulation from thousands of sites* in a clinically relevant manner with little or no tissue response remains as one of the grand challenges of the twenty-first century.

The success of the research of our group in experiments on laboratory animals has shown the prospects for application of silicon nanowires in creation of bio-consistent and bioactive implants. The key problem of these works was the study of the biophysical state of the interface "neuron-silicon nanowire" and the development of methods for the purposeful management of its properties. At present, on the basis of this interface, we have developed and patented technology for the manufacture of implants [17], which provides auto-electronic stimulation of the regenerative processes of damaged nerve tissue. The most important feature of the developed technology that significantly distinguishes it from existing ones is to provide conditions for the continuous effective migration of biological cells to the implant site. This feature indicates the promise of its use for the development of neuro-electronic interfaces for neurocomputers, suitable for use over a long period of time, comparable to the years of human life.

In 2-d part of the overview, we present the research on formation of the interface "silicon wire-nerve tissue." Experiments were carried out *in vivo* by simulation of a sciatic nerve injury and following recovery of the injury using silicon nanowires.

In 3-d part, we present experimental techniques used to test how nerve fibers restore functional ability after implantation a conduit with silicon nanowires. In addition to the techniques traditionally used for this purpose, we apply a test to evaluate bidirectional communication between the brain and corresponding peripheral nerve by registration *in real-time in vivo* a nerve displacement initiated due to action potential propagation. We apply additionally SiNW-FET to measure charge state of the interface, when it forms. Furthermore, this experiment gives rise to direct definition of sign and surface charge densities both on silicon wire and nerve fiber in living organism.

In 4-d part we present experimental results on evolution of the restore functionality of the damaged nerve after implantation conduit with silicon nanowires. We analyze prospects to use the interface nervous tissue—silicon nanowire in the global problem brain-computer interface—particularly on possible application quantum HEM device [18] based on silicon nanowires as a nerve pulse binary adder [19, 20].

#### **2. Formation of the interface silicon wire-nerve tissue**

The research on formation of the interface "silicon wire-nerve tissue" was carried out *in vivo* on Wistar rats by simulation of a sciatic nerve injury and further replacement fault of the nerve trunk by implant with a set of silicon nanowires.

One of the procedures published in details elsewhere [21, 22] includes several stages: growing of silicon wires, handling the implants, surgical procedure, and various test experiments in vivo for evaluation of motor function recovery by "the method of walking track" [23] and by recording a bilateral interaction between neuronal nets of a brain

*Neurons - Dendrites and Axons*

using, first of all, the internal resources of the body.

a hybrid intellect that physically combines the neural networks of the brain with modern, including quantum, computing devices. The development of such devices required detailed studies of the structure of neural networks of the brain and subsequent modeling of such networks on silicon nanostructures using living neurons or by implanting silicon nanostructures into a neural network of a living organism. The end product of this device will be a hybrid brain that is capable, unlike traditional computers, including quantum ones, to apply both logical and associative methods of solving problems with low energy consumption. The main task of the hybrid brain is to provide a constant two-way communication between the central and peripheral nervous system, which will allow, in extreme case, to constantly monitor the organism as a whole and, if necessary, already in the first stages of the disease, to correct the work of those organs that have deviations from the norm,

By 2015, the strategy for creating hybrid brain has already been developed [1], and a call has been issued [2, 3] to the international community to concentrate scientific and financial resources on the solution of the problem that will make a revolution not only in the field of medicine but also in all spheres of human existence. Detailed studies of neural networks were started about 10 years ago with the work on the study of the morphology of neural network [4]. Then, a large number of animal studies were made of the relationship between the structure of neural networks and the behavioral characteristics of animals. A detailed review of these studies was published recently [5]. In parallel with studies of the central nervous system and its connection with the peripheral nervous system, work was begun on the creation of a bioelectronic complex on silicon nanostructures with the artificial cultivation of neural networks in a biological environment [6–8]. The results obtained in experiments *in vitro* allowed the transition to animal experiments and then to begin clinical experiments for the treatment of diseases that could not be treated with application of traditional medicine. *Massachusetts General Hospital and Draper Labs* develop a tiny, implanted chip to place it between a patient's skull and scalp. A series of electrodes placed at varying depths in different regions of the brain would record neurological data. In the framework of the program *ElectRx, a closed-loop system* is developed to monitor and to regulate organ functions using the internal resources of the body. *Silent speech information generated directly from the activity of neurons* is involved in speech production via an intracortical microelectrode brain-computer interface [9]. It was shown that *Macaca nemestrina* monkeys can *directly control stimulation of muscles using the activity of neurons in the motor cortex*. Monkeys learned to use artificial connections from cortical cells to muscles to generate bidirectional wrist torques and controlled multiple neuron-muscle pairs simultaneously [10]. Despite encouraging results in the development and testing of bioelectronic complexes capable of recording neural impulses produced by a neuron and transferring them to subsequent processing into a nanocomputer, there are still many unresolved problems, the first of which is the development of a central link of the hybrid intelligence the "neuron-electronic device" interface [11–15]. To date, the greatest difficulty in creating such an interface is the problem of maintaining its working capacity in a living organism for a time comparable to the human lifespan. The most suitable material for creating such an interface is crystalline silicon. First, silicon is a biocompatible material, and, second, it is the main material of nano- and microelectronic technology, which makes it easy to integrate it into electronic circuits for subsequent signal processing. Taking into account the size of neurons (of the order of tens of micrometers), the silicon wires are the most suitable for creating an interface with a neuron. So, in the past decade, the "silicon crystal-nervous tissue" interface has been attracting huge interest. Various designs of electronic circuits of field-effect transistors [16] (SiNW-FET) have been developed. The main attention

**96**

and actuators of peripheral nerve by real-time registration nerve displacements due to action potential propagation [24–27] and test experiments in vitro to examine morphological features of the interface by optical and electron transmission microscopy.

#### **2.1 Growth of silicon wires**

Silicon wires (see **Figure 1**) were grown by the technology developed by Sandulova et al. [28]. This technology is based on a method of gas-phase reaction in a sealed tube at a temperature gradient. In order to provide the chemical reactions and to stimulate rapid growth of the wires, we used bromine and gold.

For growing wires with a prespecified type and value of conductivity, we added doping impurities into hot part of the tube. Due to differences in the reaction-binding energies of gold and the doping impurities with bromine, the temperature gradient provides a different amount of precipitation of these materials along the tube. That is why grown silicon wires are distributed along the tube by size (diameter, length) and by the level of doping [29, 30]. The thinner the diameter of a wire is, the smaller is the concentration of dopants. The diameter of the grown wires ranges from 10 nm to several tens of microns. Their length varies in a range from tens of microns up to a few centimeters. Furthermore, the shape of wires depends on their diameter, too.

The wires, which diameter was of nanometers, were cylindrical, while the wires with much greater diameters were hexahedral.

#### **2.2 Handling the implants**

Wires for preparation of implants are shown in **Figure 1**. Making of implant started from dividing the wires by diameters. The prepared set of nanowires was treated for purification of a surface in different etchants. Thereupon, the wires were oxidized by storage under ambient atmosphere at room temperature. The thickness of silicon oxide does not exceed one to two nanometers. Just before surgical operation, an antispiking gel ("Mesogel," Linteks Ltd., Russian Federation) was introduced into the aorta extracted from another rat. In order to avoid a rejection of

**Figure 1.** *Wires for preparation of implants. Scale bar is 80 μm on the left and 250 μm on the right side of the figure.*

**99**

hind limbs.

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation...*

the transplant, the aorta has been prefrozen in liquid nitrogen. Then, the set of the

Experiment was carried out on rats, weighing 180–250 g, that were housed in standard conditions with free access to food and water and natural light-dark cycle. The rats were randomly divided into several groups. Under thiopentone general anesthesia (40–60 mg/kg intraperitoneally), right sciatic nerve of animals were exposed in middle third, separated from surrounding tissues for approximately 10 mm in length, and isolated from underlying muscles. For the animals of one group, after dissection of sciatic nerve, we inserted the implant (**Figure 2**). Animals of the other groups were used for trauma simulating of the nerve and as sham-

Animal care, housing, and all experiments were performed in accordance with the National Institutes of Health guide for the care and use of laboratory animals (NIH Publications No. 8023, revised 1978). The research was approved by Bioethical Committee for human subjects or animal research at Bogomolets

Along with traditional methods of evaluation of a nerve recovery, we first used laser heterodyne interferometric techniques that give rise to record *in vivo* in real time an evolution of bilateral interaction of a brain and peripheral nerve [31] that

In the course up to 5 months, rats were tested on a degree of nerve regeneration. For evaluation of motor function recovery, we used "the method of walking tracks" [23]. The degree of motor function recovery was determined by the shape and size of prints of hind paws of animals when they pass through a narrow corridor. For quantitative assessment of sciatic function index (SFI), we used print length, toe spread, and intermediate toe spread on the prints of both post-operated and healthy

**3 Methods for evaluation of nerve recovery after implantation**

**3.1 Experiment** *in vivo* **for evaluation of motor function recovery**

National Medical University, December 30, 2015.

reflect a quality of the nerve recovery.

wires was placed into the gel and oriented along an axis of the aorta.

*DOI: http://dx.doi.org/10.5772/intechopen.80739*

**2.3 Surgical procedure**

**Figure 2.** *Surgical procedure.*

operated ones.

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation... DOI: http://dx.doi.org/10.5772/intechopen.80739*

**Figure 2.** *Surgical procedure.*

*Neurons - Dendrites and Axons*

**2.1 Growth of silicon wires**

and actuators of peripheral nerve by real-time registration nerve displacements due to action potential propagation [24–27] and test experiments in vitro to examine morphological features of the interface by optical and electron transmission microscopy.

Silicon wires (see **Figure 1**) were grown by the technology developed by Sandulova et al. [28]. This technology is based on a method of gas-phase reaction in a sealed tube at a temperature gradient. In order to provide the chemical reactions

For growing wires with a prespecified type and value of conductivity, we added doping impurities into hot part of the tube. Due to differences in the reaction-binding energies of gold and the doping impurities with bromine, the temperature gradient provides a different amount of precipitation of these materials along the tube. That is why grown silicon wires are distributed along the tube by size (diameter, length) and by the level of doping [29, 30]. The thinner the diameter of a wire is, the smaller is the concentration of dopants. The diameter of the grown wires ranges from 10 nm to several tens of microns. Their length varies in a range from tens of microns up to a few centimeters. Furthermore, the

The wires, which diameter was of nanometers, were cylindrical, while the wires

Wires for preparation of implants are shown in **Figure 1**. Making of implant started from dividing the wires by diameters. The prepared set of nanowires was treated for purification of a surface in different etchants. Thereupon, the wires were oxidized by storage under ambient atmosphere at room temperature. The thickness of silicon oxide does not exceed one to two nanometers. Just before surgical operation, an antispiking gel ("Mesogel," Linteks Ltd., Russian Federation) was introduced into the aorta extracted from another rat. In order to avoid a rejection of

*Wires for preparation of implants. Scale bar is 80 μm on the left and 250 μm on the right side of the figure.*

and to stimulate rapid growth of the wires, we used bromine and gold.

shape of wires depends on their diameter, too.

with much greater diameters were hexahedral.

**2.2 Handling the implants**

**98**

**Figure 1.**

the transplant, the aorta has been prefrozen in liquid nitrogen. Then, the set of the wires was placed into the gel and oriented along an axis of the aorta.

#### **2.3 Surgical procedure**

Experiment was carried out on rats, weighing 180–250 g, that were housed in standard conditions with free access to food and water and natural light-dark cycle. The rats were randomly divided into several groups. Under thiopentone general anesthesia (40–60 mg/kg intraperitoneally), right sciatic nerve of animals were exposed in middle third, separated from surrounding tissues for approximately 10 mm in length, and isolated from underlying muscles. For the animals of one group, after dissection of sciatic nerve, we inserted the implant (**Figure 2**). Animals of the other groups were used for trauma simulating of the nerve and as shamoperated ones.

Animal care, housing, and all experiments were performed in accordance with the National Institutes of Health guide for the care and use of laboratory animals (NIH Publications No. 8023, revised 1978). The research was approved by Bioethical Committee for human subjects or animal research at Bogomolets National Medical University, December 30, 2015.

#### **3 Methods for evaluation of nerve recovery after implantation**

Along with traditional methods of evaluation of a nerve recovery, we first used laser heterodyne interferometric techniques that give rise to record *in vivo* in real time an evolution of bilateral interaction of a brain and peripheral nerve [31] that reflect a quality of the nerve recovery.

#### **3.1 Experiment** *in vivo* **for evaluation of motor function recovery**

In the course up to 5 months, rats were tested on a degree of nerve regeneration. For evaluation of motor function recovery, we used "the method of walking tracks" [23]. The degree of motor function recovery was determined by the shape and size of prints of hind paws of animals when they pass through a narrow corridor. For quantitative assessment of sciatic function index (SFI), we used print length, toe spread, and intermediate toe spread on the prints of both post-operated and healthy hind limbs.

#### **3.2 Experiment** *in vivo* **for evaluation of a bilateral interaction of a brain and peripheral nerve**

To evaluate a recovery of bilateral interactions between neuronal net of a brain and actuators of peripheral nerve, we designed a setup on detection of nanometer displacement of nerve fibers [24–27] using laser heterodyne interferometric techniques with next specifications:


The installation includes a laser heterodyne displacement meter, a computer for controlling the meter, and a computer for processing and displaying measurement results. The principle of operation of the displacement meter is based on detecting changes in the phase of scattered radiation from the object under study, relative to the phase of radiation of the laser heterodyne. The information signal is a phasemodulated variable component of the photodetector current, which is formed as a result of interference of laser radiation and scattered radiation from the object under study, in the current case from the nerve of rat.

**101**

**Figure 4.**

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation...*

Around 6 weeks after the implantation, animals of the first group were taken out of the experiment by decapitation with the use of an overdose of thiopental anesthesia. Nerves with the implant were extracted, and slices were produced using a cryotome (MK-25, "Tekhnolog" Russia). Thereupon, the slices were stored during the day in 10% neutral formalin, next rinsed in distilled water, and fixed on a microscope slide. For the purposes of microscope investigation of the nerve fibers, samples were stained with silver nitrate [32]. Prepared slices of the interface "nerve fiber-silicon wire" were examined by light microscopes Carl Zeiss NU-2E and Olympus BX 51 equipped with a digital camera and transmission electron micro-

For light microscopy, material was prefixed by intracardiac perfusion with 10% formalin in 0.1 M phosphate buffer, postfixed in 10% formalin, dehydrated, and embedded in paraffin. Sections were cut and strained with hematoxylin-eosin, by the van Gieson method, impregnated with nitric silver. For TEM, material was prefixed by intracardiac perfusion with 1% glutaraldehyde in 0.1 M phosphate buffer, postfixed in 1% glutaraldehyde, 1% osmium oxide, dehydrated, and embedded in epone-araldite. Semi-thin and ultrathin sections were cut, contrasted by lead citrate and acetate.

**3.4 Experiment on ascertain energy state of the interface nerve tissue-silicon** 

To elucidate the energy state of both constituents of the interface, we carry out experiment with application of SiNW-FET biosensor based on SOI structure with two gates [33–35] as the sensor element to evaluate charge states of the surface of silicon nanowire and the nerve fiber during the interface formation. A schematic

In this transistor, the substrate is used as a control gate (back-gate, BG), modulating their conductivity. An analyte, which adheres to the free surface of the transistor, plays the role of the second gate (virtual local gate). If the charge at the surface of the nanotransistor changes due to adsorption of the analyte, so will change the conductivity of the nanotransistor and will shift its current-voltage Ids(Vbg) characteristic along voltage axis. A sign and value of the shifting allow

determining both the sign and the density of the adsorbed charge.

*Schematic presentation a dual-gated SiNW-FET biosensor based on SOI structure.*

*DOI: http://dx.doi.org/10.5772/intechopen.80739*

scope TЕМ-125К (SELMI, Ukraine).

**nanowire**

**3.3 Examination of morphology of the interface**

representation of this transistor is shown in **Figure 4**.

**Figure 3.** *Optical setup for detecting neuronal activity.*

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation... DOI: http://dx.doi.org/10.5772/intechopen.80739*

#### **3.3 Examination of morphology of the interface**

*Neurons - Dendrites and Axons*

**peripheral nerve**

0.1 nm

niques with next specifications:

• Laser wavelength 0.63 μm

• Power of the probing radiation 1 mW

• Bandwidth of the receiver 1–30 KHz

ronal activity is presented in **Figure 3**.

under study, in the current case from the nerve of rat.

**3.2 Experiment** *in vivo* **for evaluation of a bilateral interaction of a brain and** 

To evaluate a recovery of bilateral interactions between neuronal net of a brain and actuators of peripheral nerve, we designed a setup on detection of nanometer displacement of nerve fibers [24–27] using laser heterodyne interferometric tech-

• Noise level at frequency 1 KHz with bandwidth 3 KHz on distance 1 m about

• Optical setup for detecting the surface displacement that is accompanying neu-

The installation includes a laser heterodyne displacement meter, a computer for controlling the meter, and a computer for processing and displaying measurement results. The principle of operation of the displacement meter is based on detecting changes in the phase of scattered radiation from the object under study, relative to the phase of radiation of the laser heterodyne. The information signal is a phasemodulated variable component of the photodetector current, which is formed as a result of interference of laser radiation and scattered radiation from the object

**100**

**Figure 3.**

*Optical setup for detecting neuronal activity.*

Around 6 weeks after the implantation, animals of the first group were taken out of the experiment by decapitation with the use of an overdose of thiopental anesthesia. Nerves with the implant were extracted, and slices were produced using a cryotome (MK-25, "Tekhnolog" Russia). Thereupon, the slices were stored during the day in 10% neutral formalin, next rinsed in distilled water, and fixed on a microscope slide. For the purposes of microscope investigation of the nerve fibers, samples were stained with silver nitrate [32]. Prepared slices of the interface "nerve fiber-silicon wire" were examined by light microscopes Carl Zeiss NU-2E and Olympus BX 51 equipped with a digital camera and transmission electron microscope TЕМ-125К (SELMI, Ukraine).

For light microscopy, material was prefixed by intracardiac perfusion with 10% formalin in 0.1 M phosphate buffer, postfixed in 10% formalin, dehydrated, and embedded in paraffin. Sections were cut and strained with hematoxylin-eosin, by the van Gieson method, impregnated with nitric silver. For TEM, material was prefixed by intracardiac perfusion with 1% glutaraldehyde in 0.1 M phosphate buffer, postfixed in 1% glutaraldehyde, 1% osmium oxide, dehydrated, and embedded in epone-araldite. Semi-thin and ultrathin sections were cut, contrasted by lead citrate and acetate.

#### **3.4 Experiment on ascertain energy state of the interface nerve tissue-silicon nanowire**

To elucidate the energy state of both constituents of the interface, we carry out experiment with application of SiNW-FET biosensor based on SOI structure with two gates [33–35] as the sensor element to evaluate charge states of the surface of silicon nanowire and the nerve fiber during the interface formation. A schematic representation of this transistor is shown in **Figure 4**.

In this transistor, the substrate is used as a control gate (back-gate, BG), modulating their conductivity. An analyte, which adheres to the free surface of the transistor, plays the role of the second gate (virtual local gate). If the charge at the surface of the nanotransistor changes due to adsorption of the analyte, so will change the conductivity of the nanotransistor and will shift its current-voltage Ids(Vbg) characteristic along voltage axis. A sign and value of the shifting allow determining both the sign and the density of the adsorbed charge.

#### **Figure 4.** *Schematic presentation a dual-gated SiNW-FET biosensor based on SOI structure.*

To elucidate how the charge state of the nanotransistor surface changes during the interface formation, we carried out experiment *in vitro* and studied the current-voltage characteristics Ids(Vbg) in three cases: (1) initial state of the surface of the nanotransistor (without any analyte, i.e., a free surface covered with native oxide only), (2) the surface of the nanotransistor in contact with the physiological environment, and (3) the surface of the nanotransistor after adherence of a neuron when it is immersed into the physiological environment. The measured currentvoltage characteristics for these three cases give rise to calculate the surface density of the initial charge on silicon nanowire (biosensor), after adherence of components of the physiological environment and after adherence of a neuron as well.

#### **4. Results and discussion**

#### **4.1 Evaluation of motor function**

Results on recovery motor function of the limb by "the method of walking tracks" [23] are presented in **Figure 5**. It is seen that the sciatic function index (SFI) related to motor function of the limb, being normal before simulation of a sciatic nerve injury, instantly after implantation sharply decreases to abnormal state. However, in postoperative period about several months, functionality of the limb, even if slowly, improves.

#### **4.2 Evaluation of bidirectional communication between the brain and peripheral nerve**

To evaluate regeneration of sciatic nerve *in vivo*, we used additionally the laser heterodyne interferometric technique that allows in real-time record of efferent and afferent nerve impulses that provide bidirectional communication between neuronal net of a brain and actuators of peripheral nerve, notably a limb.

Propagation of nerve electrical impulses along the axon is known, to be accompanying several other phenomena such as displacements of the axon, propagation of elastic and thermal waves, and magnetic oscillations as well [36, 37].

**103**

**Figure 6.**

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation...*

impulses propagation persists enough high, especially on the proximal part.

The second step is to carry out surgical operation on implantation of the aorta filled by the silicon nanowires. Then, we measure nerve displacements immediately after implantation (**Figure 7**) in three places of the post-operated nerve: proximal

It is seen that immediately after implantation (**Figure 7**), the intensity of the nerve impulses generation on the proximal segment of the nerve slightly decreased,

*Record in real-time in vivo displacements of the healthy nerve (the top line) and after dissection of the nerve* 

*(the center line, the proximal part; the bottom line, the distal part of the nerve).*

In this work we study in real-time *in vivo* displacements of the nerve induced by nerve electrical impulses propagation. First of all, it should be noted that we measure the sum of the displacements of a bundle of the axons that forms the sciatic nerve. That is why the recorded displacements present the sum of independent cycles of a large number (about 1000 [38]) of the axon excitations. Consequently, we cannot observe a single excitation of regularly shaped spikelike to the observed *in vitro* on squid giant axon [39]. Furthermore, a magnitude of the spikes observed in the current experiment considerably exceeds the observed on a single axon. The first step of our measurement was recording *in vivo* in real time the displacements of healthy nerve that is shown in **Figure 6** (top line). The next step is dissection of the healthy nerve and a measurement of activity in both dissected proximal and distal parts of the nerve presented in **Figure 6** (center and bottom lines). From a comparison of the intensities of the nerve impulse generation of a healthy nerve, **Figure 6** (top line), and the proximal and distal parts of the dissected nerve (central and bottom line accordingly), it is seen that intensity of nerve

*DOI: http://dx.doi.org/10.5772/intechopen.80739*

part, implant and distal part.

**Figure 5.** *Evolution of the motor function recovery in postoperative period.*

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation... DOI: http://dx.doi.org/10.5772/intechopen.80739*

In this work we study in real-time *in vivo* displacements of the nerve induced by nerve electrical impulses propagation. First of all, it should be noted that we measure the sum of the displacements of a bundle of the axons that forms the sciatic nerve. That is why the recorded displacements present the sum of independent cycles of a large number (about 1000 [38]) of the axon excitations. Consequently, we cannot observe a single excitation of regularly shaped spikelike to the observed *in vitro* on squid giant axon [39]. Furthermore, a magnitude of the spikes observed in the current experiment considerably exceeds the observed on a single axon.

The first step of our measurement was recording *in vivo* in real time the displacements of healthy nerve that is shown in **Figure 6** (top line). The next step is dissection of the healthy nerve and a measurement of activity in both dissected proximal and distal parts of the nerve presented in **Figure 6** (center and bottom lines). From a comparison of the intensities of the nerve impulse generation of a healthy nerve, **Figure 6** (top line), and the proximal and distal parts of the dissected nerve (central and bottom line accordingly), it is seen that intensity of nerve impulses propagation persists enough high, especially on the proximal part.

The second step is to carry out surgical operation on implantation of the aorta filled by the silicon nanowires. Then, we measure nerve displacements immediately after implantation (**Figure 7**) in three places of the post-operated nerve: proximal part, implant and distal part.

It is seen that immediately after implantation (**Figure 7**), the intensity of the nerve impulses generation on the proximal segment of the nerve slightly decreased,

#### **Figure 6.**

*Record in real-time in vivo displacements of the healthy nerve (the top line) and after dissection of the nerve (the center line, the proximal part; the bottom line, the distal part of the nerve).*

*Neurons - Dendrites and Axons*

**4. Results and discussion**

even if slowly, improves.

**nerve**

**4.1 Evaluation of motor function**

To elucidate how the charge state of the nanotransistor surface changes during the interface formation, we carried out experiment *in vitro* and studied the current-voltage characteristics Ids(Vbg) in three cases: (1) initial state of the surface of the nanotransistor (without any analyte, i.e., a free surface covered with native oxide only), (2) the surface of the nanotransistor in contact with the physiological environment, and (3) the surface of the nanotransistor after adherence of a neuron when it is immersed into the physiological environment. The measured currentvoltage characteristics for these three cases give rise to calculate the surface density of the initial charge on silicon nanowire (biosensor), after adherence of components of the physiological environment and after adherence of a neuron as well.

Results on recovery motor function of the limb by "the method of walking tracks" [23] are presented in **Figure 5**. It is seen that the sciatic function index (SFI) related to motor function of the limb, being normal before simulation of a sciatic nerve injury, instantly after implantation sharply decreases to abnormal state. However, in postoperative period about several months, functionality of the limb,

**4.2 Evaluation of bidirectional communication between the brain and peripheral** 

To evaluate regeneration of sciatic nerve *in vivo*, we used additionally the laser heterodyne interferometric technique that allows in real-time record of efferent and afferent nerve impulses that provide bidirectional communication between neuro-

Propagation of nerve electrical impulses along the axon is known, to be accompanying several other phenomena such as displacements of the axon, propagation

nal net of a brain and actuators of peripheral nerve, notably a limb.

of elastic and thermal waves, and magnetic oscillations as well [36, 37].

**102**

**Figure 5.**

*Evolution of the motor function recovery in postoperative period.*

#### **Figure 7.**

*Record in real-time in vivo displacements of the nerve immediately after implantation in three places of the post-operated nerve: the proximal part (the top line), the implant (the central line) and the distal part (the bottom line).*

which could be expected, because this part of the nerve no longer receives signals generated in the paw. Generation of impulses produced in the paw (distal portion of the nerve) decreased more significantly. Nerve impulses in the area of the implant immediately after surgery are practically absent (**Figure 7**).

However, after 3 months the passage of nerve impulses through the regenerated nerve is already restored (**Figure 8**). Intensity propagations of nerve impulses through implant and distal parts are similar.

We conducted up to 20 experiments to study the passage of nerve impulses through the regenerating nerve. Summarizing results of all the test experiments, we can conclude that quality of restoration of the limb functionality depends on duration of postoperative period, number of silicon wires filling a gap, and physical properties of the wires.

#### **4.3. Morphology of the interfaces nerve fiber-silicon nanowires**

To understand the mechanism of neural tissue regeneration, a series of experiments were carried out to elucidate the morphological features of the interface "neuron-silicon nanowire." This research was published elsewhere [21, 22, 40],

**105**

**Figure 8.**

*bottom line) of the nerve.*

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation...*

while the main results and discussion are given below. The interfaces prepared *in vivo* were examined in various post-operation periods ranging from 3 weeks up to 12 months. The growing nerve fibers formed within the short period were unmyelinated, while the others had myelin sheath whose thickness depended on the length of the postoperative period. Micrographs of the interfaces "nerve fibersilicon wire" studied in light microscope are presented in **Figures 9** and **10a**. Before analyzing the micrographs, it is worthy to point out a specification of the preparation of slices that induced high difference in mechanical strength of nerve fiber and silicon wire. We attempted to prepare all the slices oriented primarily along the large axis of the wires. High deviation from this direction resulted in breaking off and falling out a piece of the crystal and in a persistence of a mark of

*Record in real-time in vivo displacements of the nerve after 3 months post-implantation in three places of the post-operated nerve: the proximal part (the top line), the implant (the central line), and the distal part (the* 

This may be seen in the micrographs of **Figure 9**(**a**, **b**). Slight deviation from this direction resulted in persistence of beveled cut of biomaterial placed on the crystal surface. In case, if the persistent layer of biomaterial is sufficiently thin, then one can see crystals, which accrete from every side by arrays of regenerating nerve fibers. In another case, interface "nerve fiber-silicon wire" is clearly seen along all lengths of the wire (see **Figure 9c**). High sensitivity of the nerve fibers to silicon wires is clearly seen from **Figure 9d**, which presents how the array of growing nerve fibers changes a direction of their growth, when it meets the silicon wire, adsorbs on a surface of the wire, and carries on further growth across the surface.

the crystal-removed part as a residual of the biomaterial.

*DOI: http://dx.doi.org/10.5772/intechopen.80739*

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation... DOI: http://dx.doi.org/10.5772/intechopen.80739*

#### **Figure 8.**

*Neurons - Dendrites and Axons*

which could be expected, because this part of the nerve no longer receives signals generated in the paw. Generation of impulses produced in the paw (distal portion of the nerve) decreased more significantly. Nerve impulses in the area of the implant

*Record in real-time in vivo displacements of the nerve immediately after implantation in three places of the post-operated nerve: the proximal part (the top line), the implant (the central line) and the distal part (the* 

However, after 3 months the passage of nerve impulses through the regenerated nerve is already restored (**Figure 8**). Intensity propagations of nerve impulses

We conducted up to 20 experiments to study the passage of nerve impulses through the regenerating nerve. Summarizing results of all the test experiments, we can conclude that quality of restoration of the limb functionality depends on duration of postoperative period, number of silicon wires filling a gap, and physical

To understand the mechanism of neural tissue regeneration, a series of experiments were carried out to elucidate the morphological features of the interface "neuron-silicon nanowire." This research was published elsewhere [21, 22, 40],

immediately after surgery are practically absent (**Figure 7**).

**4.3. Morphology of the interfaces nerve fiber-silicon nanowires**

through implant and distal parts are similar.

properties of the wires.

**104**

**Figure 7.**

*bottom line).*

*Record in real-time in vivo displacements of the nerve after 3 months post-implantation in three places of the post-operated nerve: the proximal part (the top line), the implant (the central line), and the distal part (the bottom line) of the nerve.*

while the main results and discussion are given below. The interfaces prepared *in vivo* were examined in various post-operation periods ranging from 3 weeks up to 12 months. The growing nerve fibers formed within the short period were unmyelinated, while the others had myelin sheath whose thickness depended on the length of the postoperative period. Micrographs of the interfaces "nerve fibersilicon wire" studied in light microscope are presented in **Figures 9** and **10a**.

Before analyzing the micrographs, it is worthy to point out a specification of the preparation of slices that induced high difference in mechanical strength of nerve fiber and silicon wire. We attempted to prepare all the slices oriented primarily along the large axis of the wires. High deviation from this direction resulted in breaking off and falling out a piece of the crystal and in a persistence of a mark of the crystal-removed part as a residual of the biomaterial.

This may be seen in the micrographs of **Figure 9**(**a**, **b**). Slight deviation from this direction resulted in persistence of beveled cut of biomaterial placed on the crystal surface. In case, if the persistent layer of biomaterial is sufficiently thin, then one can see crystals, which accrete from every side by arrays of regenerating nerve fibers. In another case, interface "nerve fiber-silicon wire" is clearly seen along all lengths of the wire (see **Figure 9c**). High sensitivity of the nerve fibers to silicon wires is clearly seen from **Figure 9d**, which presents how the array of growing nerve fibers changes a direction of their growth, when it meets the silicon wire, adsorbs on a surface of the wire, and carries on further growth across the surface.

#### **Figure 9.**

*Micrographs of the affected nerve with the implanted silicon wires. Scale bar is: (a) 150 μm, (b) 50 μm, (c) 60 μm, and (d) 80 μm.*

#### **Figure 10.**

*Micrographs of the interfaces: (a) made with light microscope, the slice is impregnated with nitric silver; plane of the slice coincides with the long axis of the silicon wire; here 1 is the silicon wire, and 2 is a bundle of the newly formed nerve fibers; (b) made with transmission electron microscope, the slice treated with 1% water solution of osmic acid; plane of the slice was perpendicular to the long axis of the silicon wire; here 1 is the silicon wire, 2 is myelin sheath, 3 is axoplasm, and 4 is new layers of the myelin sheath formed of Schwann cells. Scale bar: (a) 40 μm and (b) 50 nm.*

In all these cases, though their variety, we can conclude on high sensitivity of the growing nerve to the surface of silicon crystals. Typical micrographs of the "silicon wire-nerve fiber" interfaces made with the light and transmission electron microscopes are shown in **Figure 10**.

**107**

**Figure 11.**

*membrane, and 5 is the axoplasm.*

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation...*

Examination of the interface with different magnifications allowed seeing general picture of the growing nerve fibers in the vicinity of the silicon wire and a set of various cells supporting growth of the nerve. In **Figure 10** a micrograph of the interface made with light microscope demonstrates how a bundle of the newly grown young nerve fibers tightly adhere to the silicon wire. The micrograph of the interface made with transmission electron microscope (**Figure 10b**) shows how the newly formed layers of cell membrane of regenerating nerve fiber adhere to silicon crystal. The distance between membrane and silicon wire is less than a few nanometers. Having analyzed a great number of micrographs, we can conclude that young regenerating nerve fibers adhere to the surface of silicon

To understand the affinity of the nerve fiber to the surface of the silicon nanowires found experimentally, we have to consider the composition and the energy state

of both constituents of the interface, i.e., the nerve fiber and the silicon wire. The energy state of the near-surface region of the silicon wire at room atmosphere is shown in **Figure 11a**. In our experiment, we used silicon wires doped by boron that means that position of the Fermi level in the bulk of the crystal Ef is

A specific lattice restructuring of a few external atomic layers proper to the silicon surface is known [41] to initiate two energy bands located immediately at the surface. Density of the states in each of these bands is very high and approaches

face is placed near the middle of the energy gap Ei, and its position slightly depends on doping [42, 43] and growth of a thin native oxide as well. However, in p-type of silicon, which is used in our experiment, a positive charge at the surficial bands

*(a) The near-surface region of silicon wire, where 1 is the energy structure of the near-surface region of the silicon wire and 2 is a native oxide layer on the nanowire surface. (b) A structure of the membrane of nerve fiber (axon) in the living organism, where 3 is the extracellular physiological environment, 4 is the axon membrane composed of phospholipids molecules, and 5 is the axoplasm. (c) A morphology of the "silicon wirenervous tissue" interface generated in the living organism, where 6 is the silicon wire, 2–3 are the interface of a negatively charged native oxide and positively charged outer surface of the nerve fiber membrane, 4 is the axon* 

); therefore, the Fermi level at the sur-

*DOI: http://dx.doi.org/10.5772/intechopen.80739*

placed nearby the top of the valence band Ev.

density of atoms at the surface (~1014 cm−<sup>2</sup>

exceeds the negative one.

crystals.

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation... DOI: http://dx.doi.org/10.5772/intechopen.80739*

Examination of the interface with different magnifications allowed seeing general picture of the growing nerve fibers in the vicinity of the silicon wire and a set of various cells supporting growth of the nerve. In **Figure 10** a micrograph of the interface made with light microscope demonstrates how a bundle of the newly grown young nerve fibers tightly adhere to the silicon wire. The micrograph of the interface made with transmission electron microscope (**Figure 10b**) shows how the newly formed layers of cell membrane of regenerating nerve fiber adhere to silicon crystal. The distance between membrane and silicon wire is less than a few nanometers. Having analyzed a great number of micrographs, we can conclude that young regenerating nerve fibers adhere to the surface of silicon crystals.

To understand the affinity of the nerve fiber to the surface of the silicon nanowires found experimentally, we have to consider the composition and the energy state of both constituents of the interface, i.e., the nerve fiber and the silicon wire.

The energy state of the near-surface region of the silicon wire at room atmosphere is shown in **Figure 11a**. In our experiment, we used silicon wires doped by boron that means that position of the Fermi level in the bulk of the crystal Ef is placed nearby the top of the valence band Ev.

A specific lattice restructuring of a few external atomic layers proper to the silicon surface is known [41] to initiate two energy bands located immediately at the surface. Density of the states in each of these bands is very high and approaches density of atoms at the surface (~1014 cm−<sup>2</sup> ); therefore, the Fermi level at the surface is placed near the middle of the energy gap Ei, and its position slightly depends on doping [42, 43] and growth of a thin native oxide as well. However, in p-type of silicon, which is used in our experiment, a positive charge at the surficial bands exceeds the negative one.

#### **Figure 11.**

*Neurons - Dendrites and Axons*

**Figure 9.**

*(c) 60 μm, and (d) 80 μm.*

**106**

**Figure 10.**

scopes are shown in **Figure 10**.

*cells. Scale bar: (a) 40 μm and (b) 50 nm.*

In all these cases, though their variety, we can conclude on high sensitivity of the growing nerve to the surface of silicon crystals. Typical micrographs of the "silicon wire-nerve fiber" interfaces made with the light and transmission electron micro-

*Micrographs of the interfaces: (a) made with light microscope, the slice is impregnated with nitric silver; plane of the slice coincides with the long axis of the silicon wire; here 1 is the silicon wire, and 2 is a bundle of the newly formed nerve fibers; (b) made with transmission electron microscope, the slice treated with 1% water solution of osmic acid; plane of the slice was perpendicular to the long axis of the silicon wire; here 1 is the silicon wire, 2 is myelin sheath, 3 is axoplasm, and 4 is new layers of the myelin sheath formed of Schwann* 

*Micrographs of the affected nerve with the implanted silicon wires. Scale bar is: (a) 150 μm, (b) 50 μm,* 

*(a) The near-surface region of silicon wire, where 1 is the energy structure of the near-surface region of the silicon wire and 2 is a native oxide layer on the nanowire surface. (b) A structure of the membrane of nerve fiber (axon) in the living organism, where 3 is the extracellular physiological environment, 4 is the axon membrane composed of phospholipids molecules, and 5 is the axoplasm. (c) A morphology of the "silicon wirenervous tissue" interface generated in the living organism, where 6 is the silicon wire, 2–3 are the interface of a negatively charged native oxide and positively charged outer surface of the nerve fiber membrane, 4 is the axon membrane, and 5 is the axoplasm.*

Thus, the silicon wire being at vacuum or covered by the thin native oxide is entirely neutral, though the external surface of the silicon wire is charged positively.

The structure of the nerve fiber membrane inside a living organism is shown in **Figure 11b**. In our case preparation of the interface from the sciatic nerve of rats, the axon membrane is composed of phospholipid molecules that are known [44] to consist of polar heads and nonpolar tails and form the membrane in a shape of bilayer. It is worthwhile to emphasize that the outer side of the polar heads is charged positively. Surface density of this charge, according to the Richardson structure model, equals about 2 × 1013 cm−<sup>2</sup> . So, a large positive charge of about 2 × 1013 cm−<sup>2</sup> is permanently located at the outer side of the membrane.

Summarizing the above consideration, we can draw the following conclusion. If the near-surface region of the silicon nanowire conserves its charge state inside the living organism, then the silicon wire and the nerve fiber are similarly charged and have to repulse each other. Nevertheless, we do observe a strong adherence of the nerve fiber to the silicon nanowire that allows supposing that the physiological environment (interstitial fluid, cell cytoplasm, etc.) contributes to the formation of the interface. Analyzing how the environment may influence the charge state of silicon nanowire, we paid attention to the main properties of the physiological environment. About 80% of the environment consists of water and its pH > 7. On the other hand, thin native oxide layer, that covers the wires, is known [45] to consist primarily of intermediate oxidation states of Si atoms, in particular, Si1+(Si2O), Si2+(SiO), and Si3+(Si2O3). Thus, we can suppose that sub-oxidized Si atoms chemically react with OH<sup>−</sup> radicals of the environment, charge the surface of the nanowire negatively, and, thereby, provide Coulomb attraction between silicon wire and nerve fiber. To validate this assumption, we used a model experiment on contact of the nerve cells with silicon nanowire in the electrolyte with pH > 7, close to the physiological environment.

#### **4.4 Evaluation of the charge state of the interface nerve tissue-silicon nanowire**

In this experiment SiNW-FET based on SOI structure with two gates [32–34] has been used as the sensor element to evaluate charge states of the silicon nanowire during the interface formation.

An optical image of the nerve cell after its adherence on SiNW-FET is shown in **Figure 12**. In this transistor, the substrate is used as a control gate (back-gate, BG), modulating their conductivity. An analyte which adheres to the free surface of the transistor plays the role of the second gate (virtual local gate). If the charge at the surface of the nanotransistor changes due to adsorption of the analyte, so

**109**

**Figure 13.**

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation...*

determining both the sign and the density of the adsorbed charge.

voltage characteristics for these three cases are shown in **Figure 13**.

nanotransistor is negative and its density equals ~1∙1014 cm−<sup>2</sup>

of nanotransistor. The density of this charge is equal to ~2 · 1013 cm−<sup>2</sup>

will change the conductivity of the nanotransistor and will shift its current-voltage Ids(Vbg) characteristic along voltage axis. A sign and value of the shifting allow

To elucidate how the charge state of the nanotransistor surface changes in contact with the physiological environment and after adherence of a neuron, we studied current-voltage characteristics Ids(Vbg) in three cases: (1) initial state of the surface of the nanotransistor (without any analyte, i.e., a free surface covered with native oxide only), (2) the surface of the nanotransistor in contact with the physiological environment, and (3) the surface of the nanotransistor after adherence of a neuron when it is immersed into the physiological environment. The current-

It is seen that, when we immerse the nanotransistor into the physiological environment, the current-voltage characteristics shift to the greater voltage Vbg that corresponds, by conditions of our experiment, to a negative charging of the surface of the nanotransistor. Then, we immerse a neuron into the physiological environment and observe its adherence to the surface of the nanotransistor (**Figure 12**). The adherence of the neuron is accompanied by shifting of the

current-voltage characteristic in the opposite direction, in particular, to the smaller voltage Vbg that means an accumulation of a positive charge at the surface of the nanotransistor. Knowledge of the shifting of the current-voltage characteristics and geometric parameters of the nanotransistor allows calculating the surficial charge at the surface of the nanotransistor induced by the adherence of the analyte. We calculated the surface density of this charge after adherence of components of the physiological environment and after adherence of a neuron as well. We found that the charge accumulated in physiological environment on the surface of the silicon

the adsorption of a neuron initiates accumulation of a positive charge on the surface

So, the experiment *in vitro* proved the above-made assumption about chemical reaction of native oxide with OH<sup>−</sup> radicals and, hereby, negatively charging a

*Current-voltage characteristics Ids(Vbg) for three cases of the surface of biosensor. (1) The surface covered by native oxide (without any analyte), (2) the surface in contact with the physiological environment, and (3) the* 

*surface in contact with adsorbed neuron that was immersed into the physiological environment.*

. On the other hand,

.

*DOI: http://dx.doi.org/10.5772/intechopen.80739*

**Figure 12.** *Micrograph of a neuron adhering to the surface of biosensor.*

#### *Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation... DOI: http://dx.doi.org/10.5772/intechopen.80739*

will change the conductivity of the nanotransistor and will shift its current-voltage Ids(Vbg) characteristic along voltage axis. A sign and value of the shifting allow determining both the sign and the density of the adsorbed charge.

To elucidate how the charge state of the nanotransistor surface changes in contact with the physiological environment and after adherence of a neuron, we studied current-voltage characteristics Ids(Vbg) in three cases: (1) initial state of the surface of the nanotransistor (without any analyte, i.e., a free surface covered with native oxide only), (2) the surface of the nanotransistor in contact with the physiological environment, and (3) the surface of the nanotransistor after adherence of a neuron when it is immersed into the physiological environment. The currentvoltage characteristics for these three cases are shown in **Figure 13**.

It is seen that, when we immerse the nanotransistor into the physiological environment, the current-voltage characteristics shift to the greater voltage Vbg that corresponds, by conditions of our experiment, to a negative charging of the surface of the nanotransistor. Then, we immerse a neuron into the physiological environment and observe its adherence to the surface of the nanotransistor (**Figure 12**). The adherence of the neuron is accompanied by shifting of the current-voltage characteristic in the opposite direction, in particular, to the smaller voltage Vbg that means an accumulation of a positive charge at the surface of the nanotransistor. Knowledge of the shifting of the current-voltage characteristics and geometric parameters of the nanotransistor allows calculating the surficial charge at the surface of the nanotransistor induced by the adherence of the analyte. We calculated the surface density of this charge after adherence of components of the physiological environment and after adherence of a neuron as well. We found that the charge accumulated in physiological environment on the surface of the silicon nanotransistor is negative and its density equals ~1∙1014 cm−<sup>2</sup> . On the other hand, the adsorption of a neuron initiates accumulation of a positive charge on the surface of nanotransistor. The density of this charge is equal to ~2 · 1013 cm−<sup>2</sup> .

So, the experiment *in vitro* proved the above-made assumption about chemical reaction of native oxide with OH<sup>−</sup> radicals and, hereby, negatively charging a

#### **Figure 13.**

*Neurons - Dendrites and Axons*

2 × 1013 cm−<sup>2</sup>

structure model, equals about 2 × 1013 cm−<sup>2</sup>

to the physiological environment.

during the interface formation.

*Micrograph of a neuron adhering to the surface of biosensor.*

Thus, the silicon wire being at vacuum or covered by the thin native oxide is entirely neutral, though the external surface of the silicon wire is charged positively. The structure of the nerve fiber membrane inside a living organism is shown in **Figure 11b**. In our case preparation of the interface from the sciatic nerve of rats, the axon membrane is composed of phospholipid molecules that are known [44] to consist of polar heads and nonpolar tails and form the membrane in a shape of bilayer. It is worthwhile to emphasize that the outer side of the polar heads is charged positively. Surface density of this charge, according to the Richardson

 is permanently located at the outer side of the membrane. Summarizing the above consideration, we can draw the following conclusion. If the near-surface region of the silicon nanowire conserves its charge state inside the living organism, then the silicon wire and the nerve fiber are similarly charged and have to repulse each other. Nevertheless, we do observe a strong adherence of the nerve fiber to the silicon nanowire that allows supposing that the physiological environment (interstitial fluid, cell cytoplasm, etc.) contributes to the formation of the interface. Analyzing how the environment may influence the charge state of silicon nanowire, we paid attention to the main properties of the physiological environment. About 80% of the environment consists of water and its pH > 7. On the other hand, thin native oxide layer, that covers the wires, is known [45] to consist primarily of intermediate oxidation states of Si atoms, in particular, Si1+(Si2O), Si2+(SiO), and Si3+(Si2O3). Thus, we can suppose that sub-oxidized Si atoms chemically react with OH<sup>−</sup> radicals of the environment, charge the surface of the nanowire negatively, and, thereby, provide Coulomb attraction between silicon wire and nerve fiber. To validate this assumption, we used a model experiment on contact of the nerve cells with silicon nanowire in the electrolyte with pH > 7, close

**4.4 Evaluation of the charge state of the interface nerve tissue-silicon nanowire**

In this experiment SiNW-FET based on SOI structure with two gates [32–34] has been used as the sensor element to evaluate charge states of the silicon nanowire

An optical image of the nerve cell after its adherence on SiNW-FET is shown in **Figure 12**. In this transistor, the substrate is used as a control gate (back-gate, BG), modulating their conductivity. An analyte which adheres to the free surface of the transistor plays the role of the second gate (virtual local gate). If the charge at the surface of the nanotransistor changes due to adsorption of the analyte, so

. So, a large positive charge of about

**108**

**Figure 12.**

*Current-voltage characteristics Ids(Vbg) for three cases of the surface of biosensor. (1) The surface covered by native oxide (without any analyte), (2) the surface in contact with the physiological environment, and (3) the surface in contact with adsorbed neuron that was immersed into the physiological environment.*

surface of the native oxide of silicon wire. Furthermore, the density of the positive charge accumulated at the silicon nanotransistor after adsorption of the neuron coincides with the known value of the surface density of polar head of phospholipid molecules by the Richardson structure model [44]. So, from the *in vitro* experiment, we can draw a conclusion on the Coulomb origin of the interface formation and present morphology of the "silicon wire-nervous tissue" interface as it is shown in **Figure 11c**.

It is also evident that a propagation of the nerve impulse through the nerve fiber has to occur in a quite different way than the case when the nerve impulse passes through a free nerve fiber. A charge state of the formed interface during propagation of nerve impulse schematically is shown in **Figure 14**.

At a normal (resting) state of the nerve fiber, besides a permanent positive charge at the outer side of the membrane, there is an additional positive charge located inside the extracellular medium and the negative charge located inside the axoplasm. These charges produce potential difference across the axon membrane, the so called resting potential (Vrest ~ 70 mV) that acts throughout the entire length of the nerve fiber in a normal (resting) state of the nerve. However, when a nerve impulse passes along the nerve fiber, it reverses the potential difference across the axon membrane, the so called, "action potential" (Vaction ~ 40 mV). So, propagation

#### **Figure 14.**

*Charge state of the nervous fiber in physiological environment (a) and charge state of the interface (b) during a nerve impulse propagation (c). Here 1 is the axoplasm; 2 is the axon membrane; 3, 4, and 5 are the ion channels; 6 is the extracellular physiological environment; 7 is the native oxide with negative charge on its surface; and 8 is the silicon wire.*

**111**

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation...*

of the nerve impulse along the nerve fiber has to be accompanied by a flexural wave in the nerve due to recharge of the external side of the membrane and subsequent changing of the Coulomb attraction of the nerve fiber to the silicon wire by the Coulomb repulsion. Additionally, propagation of the nerve impulse has to generate an electronic surficial wave in a space charge region of the silicon wire. The latter may be used for extracellular recording of neuronal signal. Details of this process have to depend strongly on properties of silicon wires and call for further research.

Here we presented the study of the "silicon wire-nerve tissue" interface formed both *in vivo* and *in vitro* experiments. We have shown experimentally that there is a very good adhesion, of a nerve tissue to silicon wire, covered by thin native oxide, in the living organism. We analyzed the morphology of the interface from a physical point of view taking into account the energy structure of silicon surface, morphology of the surface layer of nerve fiber, and the composition of nutrient medium as well. Result of the analysis is indicated on Coulomb interaction between the constituents of the interface. To verify this conclusion, we carried out experiment using doubly gated SOI-SiNW-FET that is given rise to measure the surface densities of the charge both on the surface of silicon wire and on the surface of nerve fiber. This experiment has shown that strong adhesion of silicon wire and nerve fiber is given rise to Coulomb mutual attraction of the oppositely charged surfaces of the nerve fiber and silicon wire. We analyzed Coulomb interactions at the interface during propagation of a nerve impulse and concluded that nerve impulse has to initiate a flexural wave in the nerve fiber and to generate an electronic surficial wave in a space charge region of silicon wire. Moreover, the flexural wave has to provide *metabolism in the nerve fiber and, hereby vital capacity of the interface*. On the other hand, the electronic wave in the space-charge region of silicon nanowire allows using it for extracellular recording of neuronal signal. So, it is evident that the proposed method of the interface "nervous tissue-silicon nanowire" preparation is promising for application in the global project brain-computer interface, particularly on possible application quantum HEM device based on silicon nanowires as a

*DOI: http://dx.doi.org/10.5772/intechopen.80739*

**5. Conclusion**

nerve pulse binary adder.

**Conflict of interest**

We have no conflicts of interest to disclose.

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation... DOI: http://dx.doi.org/10.5772/intechopen.80739*

of the nerve impulse along the nerve fiber has to be accompanied by a flexural wave in the nerve due to recharge of the external side of the membrane and subsequent changing of the Coulomb attraction of the nerve fiber to the silicon wire by the Coulomb repulsion. Additionally, propagation of the nerve impulse has to generate an electronic surficial wave in a space charge region of the silicon wire. The latter may be used for extracellular recording of neuronal signal. Details of this process have to depend strongly on properties of silicon wires and call for further research.

#### **5. Conclusion**

*Neurons - Dendrites and Axons*

in **Figure 11c**.

surface of the native oxide of silicon wire. Furthermore, the density of the positive charge accumulated at the silicon nanotransistor after adsorption of the neuron coincides with the known value of the surface density of polar head of phospholipid molecules by the Richardson structure model [44]. So, from the *in vitro* experiment, we can draw a conclusion on the Coulomb origin of the interface formation and present morphology of the "silicon wire-nervous tissue" interface as it is shown

It is also evident that a propagation of the nerve impulse through the nerve fiber has to occur in a quite different way than the case when the nerve impulse passes through a free nerve fiber. A charge state of the formed interface during propaga-

At a normal (resting) state of the nerve fiber, besides a permanent positive charge at the outer side of the membrane, there is an additional positive charge located inside the extracellular medium and the negative charge located inside the axoplasm. These charges produce potential difference across the axon membrane, the so called resting potential (Vrest ~ 70 mV) that acts throughout the entire length of the nerve fiber in a normal (resting) state of the nerve. However, when a nerve impulse passes along the nerve fiber, it reverses the potential difference across the axon membrane, the so called, "action potential" (Vaction ~ 40 mV). So, propagation

*Charge state of the nervous fiber in physiological environment (a) and charge state of the interface (b) during a nerve impulse propagation (c). Here 1 is the axoplasm; 2 is the axon membrane; 3, 4, and 5 are the ion channels; 6 is the extracellular physiological environment; 7 is the native oxide with negative charge on its* 

tion of nerve impulse schematically is shown in **Figure 14**.

**110**

**Figure 14.**

*surface; and 8 is the silicon wire.*

Here we presented the study of the "silicon wire-nerve tissue" interface formed both *in vivo* and *in vitro* experiments. We have shown experimentally that there is a very good adhesion, of a nerve tissue to silicon wire, covered by thin native oxide, in the living organism. We analyzed the morphology of the interface from a physical point of view taking into account the energy structure of silicon surface, morphology of the surface layer of nerve fiber, and the composition of nutrient medium as well. Result of the analysis is indicated on Coulomb interaction between the constituents of the interface. To verify this conclusion, we carried out experiment using doubly gated SOI-SiNW-FET that is given rise to measure the surface densities of the charge both on the surface of silicon wire and on the surface of nerve fiber. This experiment has shown that strong adhesion of silicon wire and nerve fiber is given rise to Coulomb mutual attraction of the oppositely charged surfaces of the nerve fiber and silicon wire. We analyzed Coulomb interactions at the interface during propagation of a nerve impulse and concluded that nerve impulse has to initiate a flexural wave in the nerve fiber and to generate an electronic surficial wave in a space charge region of silicon wire. Moreover, the flexural wave has to provide *metabolism in the nerve fiber and, hereby vital capacity of the interface*. On the other hand, the electronic wave in the space-charge region of silicon nanowire allows using it for extracellular recording of neuronal signal. So, it is evident that the proposed method of the interface "nervous tissue-silicon nanowire" preparation is promising for application in the global project brain-computer interface, particularly on possible application quantum HEM device based on silicon nanowires as a nerve pulse binary adder.

#### **Conflict of interest**

We have no conflicts of interest to disclose.

*Neurons Dendrites and Axons*

### **Author details**

Klimovskaya Alla1 \*, Chaikovsky Yuri<sup>2</sup> , Liptuga Anatoliy1 , Lichodievskiy Volodymyr2 and Serozhkin Yuriy1

1 V.E. Lashkaryov Institute of Semiconductor Physics, Kyiv, Ukraine

2 O.O. Bogomolets National Medical University, Kyiv, Ukraine

\*Address all correspondence to: kaignn@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation...*

speech communication. Speech Communication. 2010;**52**(4):367-379. DOI: 10.1016/j.specom.2010.01.001

[10] Moritz CT, Perlmutter SI, Fetz EE. Direct control of paralyzed muscles by cortical neurons. Nature. 2008;**456**(7222):639-642. DOI: 10.1038/

[11] Coffer JL, editor. Semiconducting Silicon Nanowires for Biomedical Applications. Cambridge: Woodhead Publishing Series in Biomaterials; 2014. 296 p. ISBN: 9780857097712 (online)

[12] Wark HA, Sharma R, Mathews KS, Fernandez E, Yoo J, Christensen B, et al. A new high-density (25 electrodes/

) penetrating microelectrode array for recording and stimulating sub-millimeter neuroanatomical structures. Journal of Neural

Engineering. 2013;**10**(4):045003. DOI: 10.1088/1741-2560/10/4/045003

[13] Kruskal PB, Jiang Z, Gao T, Lieber CM. Beyond the patch clamp: Nanotechnologies for intracellular recording. Neuron. 2015;**86**(1):21-24. DOI: 10.1016/j.neuron.2015.01.004

[14] Winslow BD, Christensen MB, Yang WK, Solzbacher F, Tresco PA. A comparison of the tissue response to chronically implanted Parylene-C-coated and uncoated planar silicon microelectrode arrays in rat cortex. Biomaterials. 2010;**31**(35):9163-9172. DOI: 10.1016/j.

[15] Kim Y, Romero-Ortega MI. Material

biomaterials.2010.05.050

mrs.2012.99

considerations for peripheral nerve interfacing. MRS Bulletin. 2012;**37**(6):573-580. DOI: 10.1557/

[16] Noy A. Bionanoelectronics. Advanced Materials. 2011;**23**(7):807- 820. DOI: 10.1002/adma.201003751

nature07418

mm<sup>2</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.80739*

[1] Chang Edward F. Towards largescale, human-based, mesoscopic neurotechnologies. Neuron. 2015;**86**(1):68-78. DOI: 10.1016/j.

[2] Brose K. Global neuroscience.

[3] Fairhall A, Svoboda K, Nobre AC, Gradinaru V, Nusser Z, Ghosh A, et al. Global collaboration, learning from other fields. Neuron. 2016;**92**:561-563. DOI: 10.1016/j.neuron.2016.10.040

[4] Luo L, Callaway EM, Svoboda K. Genetic dissection of neural circuits. Neuron. 2008;**57**:634-660. DOI: 10.1016/j.neuron.2008.01.002

[5] Luo L, Callaway EM, Svoboda K. Genetic dissection of neural circuits: A decade of progress. Neuron. 2018;**98**(2):256-281. DOI: 10.1016/j.

[6] Lee K-Y, Shim S, Kim I-S, Oh H, Kim S, Ahn J-P, et al. Coupling of semiconductor nanowires with

neurons and their interfacial structure. Nanoscale Research Letters. 2010;**5**:410- 415. DOI: 10.1007/s11671-009-9498-0

[7] Kwiat M, Elnathan R, Pevzner A, Peretz A, Barak B, Peretz H, et al. Highly ordered large-scale neuronal networks of individual cells – Toward single cell to 3D nanowire intracellular interfaces. ACS Applied Materials & Interfaces. 2012;**4**(7):3542-3549. DOI:

[8] Lee K-Y, Kim I, Kim S-E, Jeong D-W, Kim J-J, Rhim H, et al. Vertical nanowire probes for intracellular signaling of living cells. Nanoscale Research Letters. 2014;**9**(1):56-63. DOI:

[9] Brumberg JS, Nieto-Castanon A,

neuron.2018.03.040

10.1021/am300602e

10.1186/1556-276X-9-56

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*Neurons Dendrites and Axons*

**112**

**Author details**

Klimovskaya Alla1

Lichodievskiy Volodymyr2

provided the original work is properly cited.

\*, Chaikovsky Yuri<sup>2</sup>

\*Address all correspondence to: kaignn@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

and Serozhkin Yuriy1

1 V.E. Lashkaryov Institute of Semiconductor Physics, Kyiv, Ukraine

2 O.O. Bogomolets National Medical University, Kyiv, Ukraine

, Liptuga Anatoliy1

,

[1] Chang Edward F. Towards largescale, human-based, mesoscopic neurotechnologies. Neuron. 2015;**86**(1):68-78. DOI: 10.1016/j. neuron.2015.03.037

[2] Brose K. Global neuroscience. Neuron. 2016;**92**:557-658

[3] Fairhall A, Svoboda K, Nobre AC, Gradinaru V, Nusser Z, Ghosh A, et al. Global collaboration, learning from other fields. Neuron. 2016;**92**:561-563. DOI: 10.1016/j.neuron.2016.10.040

[4] Luo L, Callaway EM, Svoboda K. Genetic dissection of neural circuits. Neuron. 2008;**57**:634-660. DOI: 10.1016/j.neuron.2008.01.002

[5] Luo L, Callaway EM, Svoboda K. Genetic dissection of neural circuits: A decade of progress. Neuron. 2018;**98**(2):256-281. DOI: 10.1016/j. neuron.2018.03.040

[6] Lee K-Y, Shim S, Kim I-S, Oh H, Kim S, Ahn J-P, et al. Coupling of semiconductor nanowires with neurons and their interfacial structure. Nanoscale Research Letters. 2010;**5**:410- 415. DOI: 10.1007/s11671-009-9498-0

[7] Kwiat M, Elnathan R, Pevzner A, Peretz A, Barak B, Peretz H, et al. Highly ordered large-scale neuronal networks of individual cells – Toward single cell to 3D nanowire intracellular interfaces. ACS Applied Materials & Interfaces. 2012;**4**(7):3542-3549. DOI: 10.1021/am300602e

[8] Lee K-Y, Kim I, Kim S-E, Jeong D-W, Kim J-J, Rhim H, et al. Vertical nanowire probes for intracellular signaling of living cells. Nanoscale Research Letters. 2014;**9**(1):56-63. DOI: 10.1186/1556-276X-9-56

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[11] Coffer JL, editor. Semiconducting Silicon Nanowires for Biomedical Applications. Cambridge: Woodhead Publishing Series in Biomaterials; 2014. 296 p. ISBN: 9780857097712 (online)

[12] Wark HA, Sharma R, Mathews KS, Fernandez E, Yoo J, Christensen B, et al. A new high-density (25 electrodes/ mm<sup>2</sup> ) penetrating microelectrode array for recording and stimulating sub-millimeter neuroanatomical structures. Journal of Neural Engineering. 2013;**10**(4):045003. DOI: 10.1088/1741-2560/10/4/045003

[13] Kruskal PB, Jiang Z, Gao T, Lieber CM. Beyond the patch clamp: Nanotechnologies for intracellular recording. Neuron. 2015;**86**(1):21-24. DOI: 10.1016/j.neuron.2015.01.004

[14] Winslow BD, Christensen MB, Yang WK, Solzbacher F, Tresco PA. A comparison of the tissue response to chronically implanted Parylene-C-coated and uncoated planar silicon microelectrode arrays in rat cortex. Biomaterials. 2010;**31**(35):9163-9172. DOI: 10.1016/j. biomaterials.2010.05.050

[15] Kim Y, Romero-Ortega MI. Material considerations for peripheral nerve interfacing. MRS Bulletin. 2012;**37**(6):573-580. DOI: 10.1557/ mrs.2012.99

[16] Noy A. Bionanoelectronics. Advanced Materials. 2011;**23**(7):807- 820. DOI: 10.1002/adma.201003751

[17] Chaikovsky Yu B, Klimovskaya AI, Vysotskaya NA, Korsak AV, Likhodiievskyi VV. Method of Electrostimulation of Regeneration of Nerve Tissues using Silicon Nanowires. Patent UA No. 104557. Bull. No. 3; 2016

[18] Klimovskaya AI, Raichev OE, Dadykin AA, Litvin Yu M, Lytvyn PM, Prokopenko IV, et al. Quantized field-electron emission at 300K in selfassembled arrays of silicon nanowires. Physica E: Low-dimensional Systems and Nanostructures. 2007;**37**:212-217. DOI: 10.1016/j.physe.2006.09.007

[19] Palagin OV, Boyun VP, Klimovskaya AI, Belik VK. Method of Binary Addition/subtraction. Patent UA No. 107130. Bull. No. 18; 2014

[20] Palagin OV, Boyun VP, Klimovskaya AI, Belik VK. Binary Adder. Patent UA No. 107131. Bull. No. 18; 2014

[21] Lichodievskiy V, Vysotskaya N, Ryabchikov O, Korsak A, Chaikovsky Y, Klimovskaya A, et al. Application of oxidized silicon nanowires for nerve fibers regeneration. Advanced Materials Research. 2014;**854**(7):157- 163. DOI: 10.4028/www.scientific.net/ AMR.854.157

[22] Klimovskaya A, Vysotskaya N, Chaikovsky Y, Korsak A, Lichodievskiy V, Ostrovskii I. Morphology of the interface "silicon wire – nerve fiber". Journal of Nanoparticle Research. 2016;**39**:214-220. DOI: 10.4028/www. scientific.net/JNanoR.39.214

[23] Sarikcioglu L, Demire BM, Utuk A. Walking track analysis: An assessment method for functional recovery after sciatic nerve injury in the rat. Folia Morphologica. 2009;**68**(1): 1-7. DOI: 10.4028/www.scientific.net/ AMR.854.157

[24] Yu S, Kollyukh O, Ye V. Detection of dust grains vibrations with a laser

heterodyne receiver of scattered light. Journal of Quantitative Spectroscopy and Radiative Transfer. 2008;**109**(8):1517-1526. DOI: 10.1016/j. jqsrt.2008.01.008

[25] Venger EF, Liptuga АІ, Serozhkin Yu G. Biaxial Laser Heterodyne Displacement Meter. Patent UA No. 105679. Bull. No. 11; 2014

[26] Liptuga A, Klimovskya A, Serozhkin Y, Likhodievskyi V, Chaikovsky Yu. Detection of nerve displacement using laser heterodyne interferometer [thesis]. Scientific and Technical Conference Laser Technologies. Lasers and Their Application (LTLA-2017); Truskavets, Ukraine; June 7-9, 2017

[27] Serozhkin Yu G, Klimovskaya AI, Chaikovsky Yu B, Lipteuga AI, Likhodiievskyi VV. Research by a Laser Heterodyne Nanodisplacements of Biological Tissues at Nerve Impulses Propagation [thesis]. The 8-st Sensor Electronics and Мicrosystem Technologies; Odessa, Ukraine; 28 May–1 June, 2018

[28] Sandulova V, Bogoyavlenskaya PS, Dronyuk MI. Patent USSR No. 160829. Bull. No. 5; 1964

[29] Klimovskaya AI, Ostrovskii IP, Ostrovskaya AS. Influence of growth conditions on morphology, composition, and electrical properties of n-Si wires. Physica Status Solidi A. 1996;**153**(2):465-472. DOI: 10.1002/ pssa.2211530221

[30] Klimovskaya AI, Prokopenko IV, Svechnikov SV, Cherneta TG, Oberemok A, Ostrovskii IP, et al. The structure, composition, and chemical state of the surface of wire-like silicon nanocrystal grown by self-organization technology. Journal of Physics: Condensed Matter. 2002;**14**(8):1735-1743. DOI: 10.1088/0953-8984/14/8/304

**115**

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation...*

[38] Popel' SL, Mytckan BM. Structural and morfometrics analysis of nerve fibers of sciatic nerve of rats of a different age in a norme and at

hypokinesia. Journal of the Grodno State Medical University. 2016;**14**(1):60-66

[39] Tasaki I, Iwasa K. Rapid mechanical changes in crab nerve and squid axon during action potentials. Journal of Physiology. 1981;**77**(9):1055-1059, Paris

[40] Klimovskaya AI, Chaikovsky Yu B, Naumova OV, Vysotskaya NA, Korsak AV, Likhodiievsky VV, et al. Coulomb interactions at the silicon wire-nervous tissue interface. World of Medicine and

Biology. 2016;**1**(55):136-141

[41] Davison SG, Levine JD, editors. Surface States. New York & London: Academic Press; 1970. pp. 94-102

[42] Gobeli CW, Allen FG. Direct and indirect excitation processes in photoelectric emission from silicon. Physics Review. 1962;**127**:141-150

[43] Allen FG, Gobeli CW. Work function, photoelectric threshold, and surface states of atomically clean silicon.

Physics Review. 1962;**127**:150-159

[45] Logofatu C, Negrila CC, Ghita RV, Ungureanu F, Cotirlan C, Ghica C, et al. Study of SiO2/Si interface by surface techniques. In: Basu S, editor. Crystalline Silicon–Properties and Uses. Rijeka, Croatia: InTechOpen; 2011.

Wien; 1972. pp. 6-12

pp. 23-42

[44] Branton D, Deamer DW. Membrane Structure. New York: Springer-Verlag

*DOI: http://dx.doi.org/10.5772/intechopen.80739*

[31] Serozhkin Yu G, Klimovskaya AI, Chaikovsky Yu B, Liptuga AI, Likhodiievskyi VV. Investigation of damaged nerve fibers regeneration with a laser heterodyne nanodisplacements [thesis]. The 8-st Sensor Electronics and Мicrosystem Technologies: Odessa,

Ukraine; 28 May–1 June, 2018

[32] Aescht E, Büchl-Zimmermann S, Burmester A, Dänhardt-Pfeiffer S, Desel C, Hamers C, Jach G, Kässens M, Makovitzky J, Mulisch M, et al. Färbungen. In: Mulisch M, Welsch U, editors. Romeis Mikroskopische Technik. Heidelberg: Springer Spektrum; 2010. p. 181-297. DOI: 10.1007/978-3-8274-2254-5

[33] Naumova V, Fomin BI, Nasimov DA, Dudchenko NV, Devyatova SF, Zhanaev ED, et al. Semiconductor Science and Technology. 2010;**25**:055004. DOI: 10.1088/0268-1242/25/5/055004

[34] Ivanov Yu D, Pleshakova TO, Kozlov AF, Malsagova KA, Krohin NV, Shumyantseva VV, et al. Lab on a Chip. 2012;**12**:5104-5511. DOI: 10.1039/

[35] Popov VP, Naumova OV, Ivanov Yu D. SOI nanowire transistors for femtomole electronic detectors of single particles and molecules in bioliquids and gases. In: Nazarov A, Colinge J-P, Balestra F, Raskin J-P, Gamiz F, Lysenko

VS, editors. Semiconductor-On-Insulator Materials for Nanoelectronic Application. Berlin Heidelberg:

10.1007/978-3-642-15868-1

DOI: 10.1038/ncomms7697

overview of biophysical forces

Springer-Verlag; 2011. pp. 343-354. DOI:

[36] El Hady A, Machta BB. Mechanical surface waves accompany action potential propagation. Nature Communications. 2015;**6**(6697):1-7.

[37] Mueller JK, Tyler WJ. A quantitative

impinging on neural function. Physical Biology. 2014;**11**(5):051001. DOI: 10.1088/1478-3975/11/5/051001

C2LC40555E

*Interface Nerve Tissue-Silicon Nanowire for Regeneration of Injured Nerve and Creation... DOI: http://dx.doi.org/10.5772/intechopen.80739*

[31] Serozhkin Yu G, Klimovskaya AI, Chaikovsky Yu B, Liptuga AI, Likhodiievskyi VV. Investigation of damaged nerve fibers regeneration with a laser heterodyne nanodisplacements [thesis]. The 8-st Sensor Electronics and Мicrosystem Technologies: Odessa, Ukraine; 28 May–1 June, 2018

*Neurons Dendrites and Axons*

[17] Chaikovsky Yu B, Klimovskaya AI, Vysotskaya NA, Korsak AV, Likhodiievskyi VV. Method of

heterodyne receiver of scattered light. Journal of Quantitative

jqsrt.2008.01.008

105679. Bull. No. 11; 2014

Ukraine; June 7-9, 2017

May–1 June, 2018

Bull. No. 5; 1964

pssa.2211530221

[27] Serozhkin Yu G, Klimovskaya AI, Chaikovsky Yu B, Lipteuga AI, Likhodiievskyi VV. Research by a Laser Heterodyne Nanodisplacements of Biological Tissues at Nerve Impulses Propagation [thesis]. The 8-st Sensor Electronics and Мicrosystem Technologies; Odessa, Ukraine; 28

[28] Sandulova V, Bogoyavlenskaya PS, Dronyuk MI. Patent USSR No. 160829.

[29] Klimovskaya AI, Ostrovskii IP, Ostrovskaya AS. Influence of growth conditions on morphology, composition, and electrical properties of n-Si wires. Physica Status Solidi A. 1996;**153**(2):465-472. DOI: 10.1002/

[30] Klimovskaya AI, Prokopenko IV, Svechnikov SV, Cherneta TG, Oberemok A, Ostrovskii IP, et al. The structure, composition, and chemical state of the surface of wire-like silicon nanocrystal grown by self-organization technology.

Journal of Physics: Condensed Matter. 2002;**14**(8):1735-1743. DOI: 10.1088/0953-8984/14/8/304

[26] Liptuga A, Klimovskya A, Serozhkin Y, Likhodievskyi V, Chaikovsky Yu. Detection of nerve displacement using laser heterodyne interferometer [thesis]. Scientific and Technical Conference Laser Technologies. Lasers and Their Application (LTLA-2017); Truskavets,

Spectroscopy and Radiative Transfer. 2008;**109**(8):1517-1526. DOI: 10.1016/j.

[25] Venger EF, Liptuga АІ, Serozhkin Yu G. Biaxial Laser Heterodyne Displacement Meter. Patent UA No.

Electrostimulation of Regeneration of Nerve Tissues using Silicon Nanowires. Patent UA No. 104557. Bull. No. 3; 2016

[18] Klimovskaya AI, Raichev OE, Dadykin AA, Litvin Yu M, Lytvyn PM, Prokopenko IV, et al. Quantized field-electron emission at 300K in selfassembled arrays of silicon nanowires. Physica E: Low-dimensional Systems and Nanostructures. 2007;**37**:212-217. DOI: 10.1016/j.physe.2006.09.007

[19] Palagin OV, Boyun VP, Klimovskaya

[20] Palagin OV, Boyun VP, Klimovskaya AI, Belik VK. Binary Adder. Patent UA

AI, Belik VK. Method of Binary Addition/subtraction. Patent UA No.

107130. Bull. No. 18; 2014

No. 107131. Bull. No. 18; 2014

AMR.854.157

[21] Lichodievskiy V, Vysotskaya N, Ryabchikov O, Korsak A, Chaikovsky Y, Klimovskaya A, et al. Application of oxidized silicon nanowires for nerve fibers regeneration. Advanced Materials Research. 2014;**854**(7):157- 163. DOI: 10.4028/www.scientific.net/

[22] Klimovskaya A, Vysotskaya N, Chaikovsky Y, Korsak A, Lichodievskiy V, Ostrovskii I. Morphology of the interface "silicon wire – nerve fiber". Journal of Nanoparticle Research. 2016;**39**:214-220. DOI: 10.4028/www.

scientific.net/JNanoR.39.214

[23] Sarikcioglu L, Demire BM, Utuk A. Walking track analysis: An assessment method for functional recovery after sciatic nerve injury in the rat. Folia Morphologica. 2009;**68**(1): 1-7. DOI: 10.4028/www.scientific.net/

[24] Yu S, Kollyukh O, Ye V. Detection of dust grains vibrations with a laser

**114**

AMR.854.157

[32] Aescht E, Büchl-Zimmermann S, Burmester A, Dänhardt-Pfeiffer S, Desel C, Hamers C, Jach G, Kässens M, Makovitzky J, Mulisch M, et al. Färbungen. In: Mulisch M, Welsch U, editors. Romeis Mikroskopische Technik. Heidelberg: Springer Spektrum; 2010. p. 181-297. DOI: 10.1007/978-3-8274-2254-5

[33] Naumova V, Fomin BI, Nasimov DA, Dudchenko NV, Devyatova SF, Zhanaev ED, et al. Semiconductor Science and Technology. 2010;**25**:055004. DOI: 10.1088/0268-1242/25/5/055004

[34] Ivanov Yu D, Pleshakova TO, Kozlov AF, Malsagova KA, Krohin NV, Shumyantseva VV, et al. Lab on a Chip. 2012;**12**:5104-5511. DOI: 10.1039/ C2LC40555E

[35] Popov VP, Naumova OV, Ivanov Yu D. SOI nanowire transistors for femtomole electronic detectors of single particles and molecules in bioliquids and gases. In: Nazarov A, Colinge J-P, Balestra F, Raskin J-P, Gamiz F, Lysenko VS, editors. Semiconductor-On-Insulator Materials for Nanoelectronic Application. Berlin Heidelberg: Springer-Verlag; 2011. pp. 343-354. DOI: 10.1007/978-3-642-15868-1

[36] El Hady A, Machta BB. Mechanical surface waves accompany action potential propagation. Nature Communications. 2015;**6**(6697):1-7. DOI: 10.1038/ncomms7697

[37] Mueller JK, Tyler WJ. A quantitative overview of biophysical forces impinging on neural function. Physical Biology. 2014;**11**(5):051001. DOI: 10.1088/1478-3975/11/5/051001

[38] Popel' SL, Mytckan BM. Structural and morfometrics analysis of nerve fibers of sciatic nerve of rats of a different age in a norme and at hypokinesia. Journal of the Grodno State Medical University. 2016;**14**(1):60-66

[39] Tasaki I, Iwasa K. Rapid mechanical changes in crab nerve and squid axon during action potentials. Journal of Physiology. 1981;**77**(9):1055-1059, Paris

[40] Klimovskaya AI, Chaikovsky Yu B, Naumova OV, Vysotskaya NA, Korsak AV, Likhodiievsky VV, et al. Coulomb interactions at the silicon wire-nervous tissue interface. World of Medicine and Biology. 2016;**1**(55):136-141

[41] Davison SG, Levine JD, editors. Surface States. New York & London: Academic Press; 1970. pp. 94-102

[42] Gobeli CW, Allen FG. Direct and indirect excitation processes in photoelectric emission from silicon. Physics Review. 1962;**127**:141-150

[43] Allen FG, Gobeli CW. Work function, photoelectric threshold, and surface states of atomically clean silicon. Physics Review. 1962;**127**:150-159

[44] Branton D, Deamer DW. Membrane Structure. New York: Springer-Verlag Wien; 1972. pp. 6-12

[45] Logofatu C, Negrila CC, Ghita RV, Ungureanu F, Cotirlan C, Ghica C, et al. Study of SiO2/Si interface by surface techniques. In: Basu S, editor. Crystalline Silicon–Properties and Uses. Rijeka, Croatia: InTechOpen; 2011. pp. 23-42

*Edited by Gonzalo Emiliano Aranda Abreu and María Elena Hernández Aguilar*

The brain is the most complex structure that exists in the universe, consisting of neurons whose function is to receive information through dendrites and transmit information through the axon. In neurosciences one of the main problems that exists are neurodegenerative diseases for which until now there has been no cure. This book is mainly focused on updating the information on the signaling process carried out in the development of axons. Topics such as axon guidance and its interaction with the extracellular matrix are discussed. Other important topics are semaphorins and their relationship with neurodegenerative diseases, and the neurobiology of the gap junction in the dorsal root ganglion. Finally, the topic of bioelectrical interfaces destined to regenerate damaged nerves is covered. The information in this book will be very important both for researchers who work with these issues and doctoral students who are involved in neuroscience.

Published in London, UK © 2019 IntechOpen © ktsimage / iStock

Neurons - Dendrites and Axons

Neurons

Dendrites and Axons

*Edited by Gonzalo Emiliano Aranda Abreu* 

*and María Elena Hernández Aguilar*