**1.2. Vasopressin**

Vasopressin (arginine vasopressin, AVP) is the first identified neuropeptide. AVP is a nonapeptide that is synthesized in magnocellular and parvocellular neurons, located in the paraventricular and supraoptic nuclei of the hypothalamus (Swaab et al., 1975). Most of vasopressin is released from the axonal terminals of magnocellular neurons directly iinto the bloodstream of the posterior pituitary.

The Effects of Some Neuropeptides on Motor Activity of Smooth Muscle Organs in Abdominal and Pelvic Cavities 113

rat pineal (Barassin et al., 2000). The suprachyasmatic nuclei, that are the main biological clock, contain vasopressinergic neurons. They demonstrate noticeable daily variation activity. In animals these vasopressin secreting neurons have very important role in the control of day/night rhythms. The reduced secretion of vasopressin in suprachyasmatic nuclei could contribute to the violation of sleep-wake rhythms during ageing and to

Vasopressin takes part in the regulation of maletypical social behaviors, vocal communication, aggression, and paternal care (Goodson & Bass, 2001). There are established projections of vasopressinergic neurons from the cells of the bed nucleus of the stria terminalis to the lateral septum with higher levels of density in nonaggressive animals. These lacalizations demonstrate the significance of vasopressinergic brain network in

AVP is a potent regulator of complex social maternal behaviors. The maternal cares that are vasopressin dependent were found to be independent of dam's trait anxiety. The authors suggest that manipulation of AVP system could contribute to the treatment of mothers

Vasopressin, secreted in olfactory bulb is involved in the processing of stimuli that are important for social behaviors. In this anatomic region Tobin and coauthors (2010) have identified population of vasopressin neurons, most of which do not project outside the olfactory bulb. They discuss the importance of vasopressin secreting neurons in filtering out

Vasopressin and corticoliberin, secreted from parvocellular portion of paraventricular nucleus in stress condition synergistically activate ACTH-adrenal axis. Aguilera supposed that in chronic stress there is preferential activation of vasopressin rather than corticoliberin and as a consequence a feedback mechanism is disintegrated (Aguilera, 1994). In contrast Zelena et al. (2006) demonstrate that AVP does not play critical role in stimulation of hypothalamic-

Ghrelin is a multifunctional peptide hormone (28 amino acids) secreted from the cells of the diffuse neuro-endocrine system. Ghrelin-secreting cells are found from the stomach to the colon (in the oxyntic glands of the fundus and less in the small and large intestine) (Broglio et al., 2002; Lee et al., 2002; Inui et al., 2004). Ghrelin has been detected in the central nervous system, e.g. in arcuate nucleus and hypothalamus (Lu et al., 2002), in pancreas (Date et al. 2002), in some cells of the immune system (lymphocytes and monocytes) (Mager et al., 2008) and also in human ovaries and testes (García et al., 2007). There is a hypothesis that ghrelin

might have not only endocrine but also autocrine and paracrine mechanism of action.

The presence of ghrelin receptor subtype GHS-R1a is detected in hypothalamus (n.arcuatus) and the pituitary gland, in multiple organs with nonendocrine and endocrine function (heart, lung, liver, kidney, pancreas, stomach, small and large intestines, adipose tissue,

development of depression (Kalsbeek et al., 2010).

development of aggression (Compaan, 1993).

**1.3. Ghrelin** 

suffering from postpartum depression (Bosch & Neumann, 2008).

of the olfactory signals and in social recognition (Tobin et al., 2010).

pituitary axis during chronic stress, but its role in acute stress is more important.

The effects of AVP are mediated mainly via V1and V2 receptors.

V1 receptors are located on the vascular smooth muscle membranes. They are also found in myometrium and urinary bladder smooth muscle cell membranes. V1-receptor activation mediates vasoconstriction by receptor-coupled activation of phospholipase C and release of Ca2+ from intracellular stores via the phosphoinositide cascade (Thibonnier, 1992, Briley et al., 1994).

V2 renal receptors are present in the renal collecting duct system and endothelial cells. Kidney V2 receptors interact (by the G protein complex) with adenylyl cyclase to increase intracellular cyclic adenosine monophosphate (cAMP) and cause retention of water (Orloff & Handler, 1967).

V3 pituitary receptors (formerly known as V1b or AVPr1B), have central neural system effects, such as increasing adrenocorticotropic hormone production, activating different G proteins, and act via increasing intracellular cAMP (Thibonnier et al, 1997, Holmes et al, 2001, Kam et al, 2007).

The classical effects of vasopressin are mainly related to maintenance of water-electrolyte homeostasis and blood pressure. During the last years the data about the effects of this neuropeptide on brain function and behavioral reactions increase. The brain effects of vasopressin can be divided into two main types: those related to its peripheral effects such as hormone and focused on the maintenance of water balance. Others are associated with higher brain functions as learning, memory, emotion and they are independent of its hormonal effects (Frank & Landgraf, 2008). Vasopressinergic axons propelled from hypothalamus to many brain regions as hipocampus, septum, amygdala and brainstem, secrete AVP that acts as neurotransmitter. This extrahypothalamic vasopressin network is an anatomical basis of involvement of limbic-midbrain structure in processes of learning and memory. AVP facilitates consolidation and retrieval of memory (Kovacs et al., 1979)

Vasopressin participates in formation of circadian rhythms and regulation of biological clock. The suprachiasmatic nucleus (SCN) is responsible for generation of circadian rhythmicity in mammalian brain and is an obvious source for a vasopressin innervation of GABAergic neurons located in this area (Hermes et al., 2000). A significant diurnal variation in vasopressin release in the SCN was detected, with the highest levels occurring during midday and a trough around midnight (Kalsbeek et al., 1995). It was demonstrated that melatonin synthesis was stimulated after local injection in pineal gland of vasopressin. Also the night melatonin plasma concentration was increased after prolonged period of water deprivation. These results show that vasopressin can modulate melatonin synthesis in the rat pineal (Barassin et al., 2000). The suprachyasmatic nuclei, that are the main biological clock, contain vasopressinergic neurons. They demonstrate noticeable daily variation activity. In animals these vasopressin secreting neurons have very important role in the control of day/night rhythms. The reduced secretion of vasopressin in suprachyasmatic nuclei could contribute to the violation of sleep-wake rhythms during ageing and to development of depression (Kalsbeek et al., 2010).

Vasopressin takes part in the regulation of maletypical social behaviors, vocal communication, aggression, and paternal care (Goodson & Bass, 2001). There are established projections of vasopressinergic neurons from the cells of the bed nucleus of the stria terminalis to the lateral septum with higher levels of density in nonaggressive animals. These lacalizations demonstrate the significance of vasopressinergic brain network in development of aggression (Compaan, 1993).

AVP is a potent regulator of complex social maternal behaviors. The maternal cares that are vasopressin dependent were found to be independent of dam's trait anxiety. The authors suggest that manipulation of AVP system could contribute to the treatment of mothers suffering from postpartum depression (Bosch & Neumann, 2008).

Vasopressin, secreted in olfactory bulb is involved in the processing of stimuli that are important for social behaviors. In this anatomic region Tobin and coauthors (2010) have identified population of vasopressin neurons, most of which do not project outside the olfactory bulb. They discuss the importance of vasopressin secreting neurons in filtering out of the olfactory signals and in social recognition (Tobin et al., 2010).

Vasopressin and corticoliberin, secreted from parvocellular portion of paraventricular nucleus in stress condition synergistically activate ACTH-adrenal axis. Aguilera supposed that in chronic stress there is preferential activation of vasopressin rather than corticoliberin and as a consequence a feedback mechanism is disintegrated (Aguilera, 1994). In contrast Zelena et al. (2006) demonstrate that AVP does not play critical role in stimulation of hypothalamicpituitary axis during chronic stress, but its role in acute stress is more important.
