**6. Applications of power spectral analysis of HRV in laboratory animals**

HRV has provided increasing interest as a noninvasive index of autonomic nervous activity (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996). Because we thought that the power spectral analysis of HRV from the ECG recorded by a telemetry system may be more reliable for assessing autonomic nervous activity than that recorded by a tethering system. Therefore, we have recorded ECGs for this analysis by the telemetry system from many laboratory animals including mouse, rats, guinea pigs, rabbits, and miniature pigs to investigate autonomic nervous function in these animals. First, we have established the characteristics of HRV in the normal animals. Second, we applied to some pathophysiological studies. In this section, I would like to show the results of these studies.

#### **6.1 Characteristics of HRV in the normal animals**

An off-line analysis was performed on an ECG processor analyzing system (SRV-2W, Softron) and a microcomputer using ECG data stored on a hard disk recorded by a telemetry system from many laboratory animals. The computer program first detected R waves and calculated the R-R interval tachogram as the raw HRV in sequence order. From this tachogram, data sets of 512 points were resampled at defined time as each animal species. Time of resampling differed according to their heart rate. The length of this tachogram has been selected as the best compromise between the need for a large time series, in order to achieve greater accuracy during computation, and the desire for short time periods. We then applied each set of data to the Hamming window and the fast Fourier transform to obtain the power spectrum of the fluctuation. The power spectrum has unit of msec2/Hz. The integral over LF areas was calculated as the LF power and HF areas as the

**6. Applications of power spectral analysis of HRV in laboratory animals** 

HRV has provided increasing interest as a noninvasive index of autonomic nervous activity (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996). Because we thought that the power spectral analysis of HRV from the ECG recorded by a telemetry system may be more reliable for assessing autonomic nervous activity than that recorded by a tethering system. Therefore, we have recorded ECGs for this analysis by the telemetry system from many laboratory animals including mouse, rats, guinea pigs, rabbits, and miniature pigs to investigate autonomic nervous function in these animals. First, we have established the characteristics of HRV in the normal animals. Second, we applied to some pathophysiological studies. In this section,

An off-line analysis was performed on an ECG processor analyzing system (SRV-2W, Softron) and a microcomputer using ECG data stored on a hard disk recorded by a telemetry system from many laboratory animals. The computer program first detected R waves and calculated the R-R interval tachogram as the raw HRV in sequence order. From this tachogram, data sets of 512 points were resampled at defined time as each animal species. Time of resampling differed according to their heart rate. The length of this tachogram has been selected as the best compromise between the need for a large time series, in order to achieve greater accuracy during computation, and the desire for short time periods. We then applied each set of data to the Hamming window and the fast Fourier transform to obtain the power spectrum of the fluctuation. The power spectrum has unit of msec2/Hz. The integral over LF areas was calculated as the LF power and HF areas as the

Fig. 9. Power spectrum obtained from human

I would like to show the results of these studies.

**6.1 Characteristics of HRV in the normal animals** 

HF power. These powers have units of msec2. The ratio of LF power and HF power (LF/HF) was also calculated and this is unitless.

All animals shared a characteristic pattern in their power spectrum analysis. Representative power spectra of HRV in each animal species are shown in Fig. 10.

Fig. 10. Representative power spectra obtained from many animal species

There were two major spectral components of LF and HF spectra for HRV. Since the HF power is represented by the component corresponding to respiration, the range of HF was set so that the respiration rate would be included in it. As for the LF, the upper limit was set at the same frequency as the lower limit of HF. The lower limit of LF was set according to the resampling time of the R-R interval time series. In the method of fast Fourier transform, the components at very low frequencies include noise from the data analyzed and makes that part unreliable. The frequency range which includes this noise is in relation to the resampling time. With this in mind, we have set the lower limit of LF according to the limit we observed to be a reliable one. On the basis of these data, two frequency bands of interest were decided in each animal species as shown in Table 1.

The values of HRV in each animal species obtained from our experiments are also summarized in Table 2.

Recent Advances in Telemetry Monitoring and Analysis for Laboratory Animals 155

both strains, the LF power in the SHR was significantly larger than that in the WKY after 6 weeks of age. The level of the LF/HF ratio in the SHR was almost twice that in the WKY after 3 weeks of age. Furthermore, at 6 weeks of age, systolic blood pressure became significantly higher in the SHR than in the age-matched WKY, and this significant difference between them persisted throughout the experimental period. These results suggest that the predominant sympathetic activity from prehypertensive stages may play an important role in the development of irreversible hypertension in the SHR (Kuwahara,

Fig. 11. Changes in body weight, heart rate (HR), systolic blood pressure (SBP), LF power,

Asthma has been characterized by intermittent reversible airway obstruction, airway inflammation, and airway hyperresponsiveness. Asthma is also thought to be associated with abnormal autonomic nervous function, because there is markedly increased bronchial sensitivity to cholinergic and non-adrenergic non-cholinergic constrictors, and decreased sensitivity to β2-adrenergic and non-adrenergic non-cholinergic dilators (Barnes, 1992). Bronchial-hypersensitive (BHS) and bronchial-hyposensitive (BHR) strain guinea pigs are spontaneous model animals of airway hyper- and hyposensitivity (Mikami, et al., 1991). We considered that these animal models might provide new insight into the regulatory roles of autonomic nervous function in asthma. As shown the results

HF power, and LF/HF ratio in SHR and WKY during the developmental stages.

et al., 1996).


Table 1. Frequency band determined to each animal species.


Table 2. The values of HRV obtained from each animal species.

#### **6.2 Pathophysiological studies**

In the previous section, I have shown the characteristics of power spectrum of HRV in various animal species. The HF component corresponding to the frequency of respiration and the LF component which seemed reflect the arterial blood pressure oscillations were observed in each animal species. From these results, we have suggested that these components could be used for assessment of cardiac autonomic outflow as utilized in human beings. Then, we have applied this method to pathophysiological studies in animals.

#### **6.2.1 Animal models for diseases**

Spontaneously hypertensive rats (SHR) have been extensively studied as a model of essential hypertension. Young SHR show an arterial blood pressure not different from that of their normotensive progenitors, the Wistar-Kyoto rats (WKY). The irreversible hypertension in the SHR occurs only at the more advanced age of 3 months. Therefore, we studied power spectral analysis of HRV throughout the developmental stages in the SHR and WKY, hypothesizing that an altered neural outflow may trigger hypertension in the SHR. As shown the results in Fig. 11, the HF power increased with age without significant difference between the two strains. Although the LF power tended to increase with age in

**Species LF (Hz) HF (Hz)**  Mouse 0.1-1.0 1.0-5.0 Vole 0.1-1.0 1.0-5.0 Rat 0.04-1.0 1.0-3.0 Guinea pig 0.07-0.7 0.7-3.0 Rabbit 0.01-0.4 0.4-1.0 Dog 0.04-0.15 0.15-1.0 Goat 0.04-0.2 0.2-1.0 Miniature pig 0.01-0.07 0.07-1.0 Thoroughbred horse 0.01-0.07 0.07-0.6

**HF** 

Mouse 576 1.9 0.5 4.9 Ishii et al. (1996) Vole 458 32 45 0.8 Ishii et al. (1996) Rat 337 14.1 2.1 6.5 Kuwahara et al. (1994)

Guinea pig 244 6.0 1.7 4.0 Akita et al. (2002) Miniature pig 92 1987 2924 1.0 Kuwahara et al. (1999) Thoroughbred horse 33 1536 173 6.8 Kuwahara et al. (1996)

In the previous section, I have shown the characteristics of power spectrum of HRV in various animal species. The HF component corresponding to the frequency of respiration and the LF component which seemed reflect the arterial blood pressure oscillations were observed in each animal species. From these results, we have suggested that these components could be used for assessment of cardiac autonomic outflow as utilized in human beings. Then, we have applied this method to pathophysiological studies in

Spontaneously hypertensive rats (SHR) have been extensively studied as a model of essential hypertension. Young SHR show an arterial blood pressure not different from that of their normotensive progenitors, the Wistar-Kyoto rats (WKY). The irreversible hypertension in the SHR occurs only at the more advanced age of 3 months. Therefore, we studied power spectral analysis of HRV throughout the developmental stages in the SHR and WKY, hypothesizing that an altered neural outflow may trigger hypertension in the SHR. As shown the results in Fig. 11, the HF power increased with age without significant difference between the two strains. Although the LF power tended to increase with age in

**(msec2) LF/HF References** 

Table 1. Frequency band determined to each animal species.

Table 2. The values of HRV obtained from each animal species.

**LF (msec2)** 

**(bpm)** 

**Species HR** 

**6.2 Pathophysiological studies** 

**6.2.1 Animal models for diseases** 

animals.

both strains, the LF power in the SHR was significantly larger than that in the WKY after 6 weeks of age. The level of the LF/HF ratio in the SHR was almost twice that in the WKY after 3 weeks of age. Furthermore, at 6 weeks of age, systolic blood pressure became significantly higher in the SHR than in the age-matched WKY, and this significant difference between them persisted throughout the experimental period. These results suggest that the predominant sympathetic activity from prehypertensive stages may play an important role in the development of irreversible hypertension in the SHR (Kuwahara, et al., 1996).

Fig. 11. Changes in body weight, heart rate (HR), systolic blood pressure (SBP), LF power, HF power, and LF/HF ratio in SHR and WKY during the developmental stages.

Asthma has been characterized by intermittent reversible airway obstruction, airway inflammation, and airway hyperresponsiveness. Asthma is also thought to be associated with abnormal autonomic nervous function, because there is markedly increased bronchial sensitivity to cholinergic and non-adrenergic non-cholinergic constrictors, and decreased sensitivity to β2-adrenergic and non-adrenergic non-cholinergic dilators (Barnes, 1992). Bronchial-hypersensitive (BHS) and bronchial-hyposensitive (BHR) strain guinea pigs are spontaneous model animals of airway hyper- and hyposensitivity (Mikami, et al., 1991). We considered that these animal models might provide new insight into the regulatory roles of autonomic nervous function in asthma. As shown the results

Recent Advances in Telemetry Monitoring and Analysis for Laboratory Animals 157

Fig. 13. Heart rate, coefficient variance (CO), LF power, HF power, LF/HF ratio, and locomotor activity (LA) of hourly averaged values (left) and averaged 24 hour, dark and

Various epidemiological reports indicate that consumption of foods rich in polyphenols is associated with lower incidence of cardiovascular diseases (Hertog, et al., 1993; Manach, et al., 2005). Cacao beans are consumed widely as cocoa or chocolate and are known to be rich in polyphenolic substances containing primarily procyanidins that are the oligomers of flavonoids (Porter, et al., 1991). Because the autonomic nervous system is an important regulatory mechanism for the cardiovascular function, we sought to determine the effect of cacao liquor polyphenol on the cardiovascular and autonomic nervous functions in an animal model of familial hypercholesterolaemia. Kurosawa and Kusanagihypercholesterolaemic rabbits exhibit hypercholesterolaemia from birth due to lack of lowdensity lipoprotein (LDL) receptors and spontaneously develop atherosclerosis (Kurosawa, et al., 1995). We hypothesize that cacao liquor polyphenols increase the depressed HRV and restore the cardiovascular function in the process of development of atherosclerosis in this animal model. After 6 months of dietary administration of cacao liquor polyphenols, heart rate (HR) and systolic blood pressure (SBP) were lowered (Table 3). The HF power in the control group was significantly decreased with aging, but that in the cacao liquor polyphenol group was not significantly different with aging. These results suggest that cacao liquor polyphenols may play an important role to protect cardiovascular and

light period (right) in Zucker-fatty and Zucker-lean rats.

autonomic nervous functions (Akita, et al., 2008).

**6.2.2 Effects of drug and food** 

in Fig. 12, the autonomic nervous activity in BHS showed a daily pattern, although BHR did not show such rhythmicity. The HF power in BHS was higher than that in BHR throughout the day. The LF/HF ratio in BHS was lower than that in BHR throughout the day. These results suggest that parasympathetic nervous activity may be predominant in BHS (Akita, et al., 2004).

Fig. 12. Changes in hourly averaged values of heart rate, body temperature, locomotor activity, LF power, HF power, and LF/HF ratio in BHS and BHR.

The Zucker-fatty rat showing hyperphagia due to mutation of the leptin receptor gene is a well-established model of insulin resistance (Chau, et al., 1996; Phillips, et al., 1996). Plasma glucose and blood pressure in Zucker-fatty rats are relatively similar to those in Zucker-lean rats (Jermendy, et al., 1996; Pamidimukkala & Jandhyal, 1996). These characteristics show that the Zucker-fatty rat may be suitable for research on effects of insulin resistance on autonomic nervous function. Therefore, we conducted to clarify autonomic nervous function in these animal models. As shown the results in Fig. 13, heart rate in Zucker-fatty rats was lower than that in Zucker-lean rats, but there were no significant differences in the HF and LF power, and LF/HF ratio between Zucker-fatty and Zucker-lean rats. These results suggest that the autonomic nervous function of insulin-resistant Zucker-fatty rats remain normal from the aspect of power spectral analysis of HRV (Towa, et al., 2004).

Fig. 13. Heart rate, coefficient variance (CO), LF power, HF power, LF/HF ratio, and locomotor activity (LA) of hourly averaged values (left) and averaged 24 hour, dark and light period (right) in Zucker-fatty and Zucker-lean rats.

#### **6.2.2 Effects of drug and food**

156 Modern Telemetry

in Fig. 12, the autonomic nervous activity in BHS showed a daily pattern, although BHR did not show such rhythmicity. The HF power in BHS was higher than that in BHR throughout the day. The LF/HF ratio in BHS was lower than that in BHR throughout the day. These results suggest that parasympathetic nervous activity may be predominant in

Fig. 12. Changes in hourly averaged values of heart rate, body temperature, locomotor

The Zucker-fatty rat showing hyperphagia due to mutation of the leptin receptor gene is a well-established model of insulin resistance (Chau, et al., 1996; Phillips, et al., 1996). Plasma glucose and blood pressure in Zucker-fatty rats are relatively similar to those in Zucker-lean rats (Jermendy, et al., 1996; Pamidimukkala & Jandhyal, 1996). These characteristics show that the Zucker-fatty rat may be suitable for research on effects of insulin resistance on autonomic nervous function. Therefore, we conducted to clarify autonomic nervous function in these animal models. As shown the results in Fig. 13, heart rate in Zucker-fatty rats was lower than that in Zucker-lean rats, but there were no significant differences in the HF and LF power, and LF/HF ratio between Zucker-fatty and Zucker-lean rats. These results suggest that the autonomic nervous function of insulin-resistant Zucker-fatty rats remain normal from the aspect of power spectral

activity, LF power, HF power, and LF/HF ratio in BHS and BHR.

analysis of HRV (Towa, et al., 2004).

BHS (Akita, et al., 2004).

Various epidemiological reports indicate that consumption of foods rich in polyphenols is associated with lower incidence of cardiovascular diseases (Hertog, et al., 1993; Manach, et al., 2005). Cacao beans are consumed widely as cocoa or chocolate and are known to be rich in polyphenolic substances containing primarily procyanidins that are the oligomers of flavonoids (Porter, et al., 1991). Because the autonomic nervous system is an important regulatory mechanism for the cardiovascular function, we sought to determine the effect of cacao liquor polyphenol on the cardiovascular and autonomic nervous functions in an animal model of familial hypercholesterolaemia. Kurosawa and Kusanagihypercholesterolaemic rabbits exhibit hypercholesterolaemia from birth due to lack of lowdensity lipoprotein (LDL) receptors and spontaneously develop atherosclerosis (Kurosawa, et al., 1995). We hypothesize that cacao liquor polyphenols increase the depressed HRV and restore the cardiovascular function in the process of development of atherosclerosis in this animal model. After 6 months of dietary administration of cacao liquor polyphenols, heart rate (HR) and systolic blood pressure (SBP) were lowered (Table 3). The HF power in the control group was significantly decreased with aging, but that in the cacao liquor polyphenol group was not significantly different with aging. These results suggest that cacao liquor polyphenols may play an important role to protect cardiovascular and autonomic nervous functions (Akita, et al., 2008).

Recent Advances in Telemetry Monitoring and Analysis for Laboratory Animals 159

Individual animal responses to acute and chronic stress are interesting in both experimental and industrial animals from the point of view of animal well-being. Breeding circumstances such as mixing are known to be accompanied by increased agonistic behaviour and may result in social stress (Muller, & Ladewig, 1989). Therefore, we investigated heart rate and autonomic nervous function in miniature swine to clarify the effects of pair housing of animals. As shown the results in Fig. 15, when two miniature swine were housed together, heart rate and the LF/HF were significantly increased throughout the day. Although these changed gradually recovered to basal levels, these parameters had not completely returned to basal levels even after 2 weeks. Heart rate and autonomic nervous activity returned to basal levels about 2 weeks after re-housing. These results suggest that it takes miniature swine at least 2 weeks to adapt to different circumstances. Furthermore, the power spectral analysis of HRV can be used as a useful method in a study for answering controversial

Fig. 15. Light and dark phase values of heart rate(left), LF power, HF power, and LF/HF ratio (right). Before mixing (Before), ont eh day of mixing (Mixing), 2 weeks after mixing (Mix 2wks), on the day of separation (Separate), 2 weeks after separation (Sep 2 wks).

Psychological stress is a risk factor increasing cardiovascular morbidity and mortality (Rosengren, et al., 1991; Ruberman, et al., 1984). The effects of psychological stress on electrical activity of the heart are largely mediated by the autonomic nervous system (Sgoifo, et al., 1997). We evoked anxiety-like or fear-like states in rats by means of classical conditioning and examined changes in autonomic nervous activity using a power spectral analysis of HRV. Anxiety-like states resulted in a significant increase in heart rate, LF power, and LF/HF ratio. Fear-like states resulted in a significant increase in heart rate and a significant decrease in HF power with no significant change in both LF power and LF/HF ratio. These results suggest that autonomic balance becomes predominant in sympathetic

**6.2.3 Stress and psychological effects** 

issues related to stress response (Kuwahara, et al., 2004).


Table 3. Effects of cacao liquor on cardiovascular and autonomic nervous functions.

Taurine is one of the most abundant free amino acids in animal tissues (Jacobsen, & Smith, 1968) and possesses many important physiological roles. Because antihypertensive action of taurine by suppression of sympathetic overactivity was reported (Sato, et al., 1987), we evaluated effects of taurine on cold-induced hypertension which is a prototypical model of environmentally induced hypertension. After the 7 days control period, both taurine (1%) administrated and control groups of rats were exposed a cold temperature. There were no differences in heart rate, blood pressure, but parasympathetic nervous function was somewhat predominant in taurine group before cold exposure. Heart rate and blood pressure in both groups increased greatly by cold exposure. Heart rate in taurine group was much higher than that in control group (Fig. 14). The LF and HF powers were decreased by cold exposure in both groups. Although no differences were observed in the LF power, decrease of the HF power in taurine group was greater than that in control group. The HF power was reduced, but the LF power of blood pressure variability (BP-LF; index of sympathetic nervous activity) was increased by onset of cold exposure. BP-LF and HF power were gradually increased in chronic stage of cold exposure. Almost the same responses in these parameters were observed between control and taurine groups except time course changes in onset or offset to cold exposure. These results suggest that taurine may provide some reservoir for cardiovascular and autonomic nervous functions to cold stress in rats (Kuwahara, et al., 2009).

Fig. 14. Effects of taurine on heart rate, systolic blood pressure (left) and autonomic nervous function (middle and right) to cold exposure in rats.

#### **6.2.3 Stress and psychological effects**

158 Modern Telemetry

Table 3. Effects of cacao liquor on cardiovascular and autonomic nervous functions.

stress in rats (Kuwahara, et al., 2009).

function (middle and right) to cold exposure in rats.

Taurine is one of the most abundant free amino acids in animal tissues (Jacobsen, & Smith, 1968) and possesses many important physiological roles. Because antihypertensive action of taurine by suppression of sympathetic overactivity was reported (Sato, et al., 1987), we evaluated effects of taurine on cold-induced hypertension which is a prototypical model of environmentally induced hypertension. After the 7 days control period, both taurine (1%) administrated and control groups of rats were exposed a cold temperature. There were no differences in heart rate, blood pressure, but parasympathetic nervous function was somewhat predominant in taurine group before cold exposure. Heart rate and blood pressure in both groups increased greatly by cold exposure. Heart rate in taurine group was much higher than that in control group (Fig. 14). The LF and HF powers were decreased by cold exposure in both groups. Although no differences were observed in the LF power, decrease of the HF power in taurine group was greater than that in control group. The HF power was reduced, but the LF power of blood pressure variability (BP-LF; index of sympathetic nervous activity) was increased by onset of cold exposure. BP-LF and HF power were gradually increased in chronic stage of cold exposure. Almost the same responses in these parameters were observed between control and taurine groups except time course changes in onset or offset to cold exposure. These results suggest that taurine may provide some reservoir for cardiovascular and autonomic nervous functions to cold

Fig. 14. Effects of taurine on heart rate, systolic blood pressure (left) and autonomic nervous

**Group HR (bpm) SBP (mmHg) LF(msec2) HF(msec2) LF/HF**  5 months control 196.9 93.9 80.6 12.0 7.6 5 months cacao 197.7 85.7 88.2 9.8 14.0 10 months control 226.4 96.1 41.5 4.0 10.9 10 months cacao 185.2 75.9 51.0 5.0 9.9

Individual animal responses to acute and chronic stress are interesting in both experimental and industrial animals from the point of view of animal well-being. Breeding circumstances such as mixing are known to be accompanied by increased agonistic behaviour and may result in social stress (Muller, & Ladewig, 1989). Therefore, we investigated heart rate and autonomic nervous function in miniature swine to clarify the effects of pair housing of animals. As shown the results in Fig. 15, when two miniature swine were housed together, heart rate and the LF/HF were significantly increased throughout the day. Although these changed gradually recovered to basal levels, these parameters had not completely returned to basal levels even after 2 weeks. Heart rate and autonomic nervous activity returned to basal levels about 2 weeks after re-housing. These results suggest that it takes miniature swine at least 2 weeks to adapt to different circumstances. Furthermore, the power spectral analysis of HRV can be used as a useful method in a study for answering controversial issues related to stress response (Kuwahara, et al., 2004).

Fig. 15. Light and dark phase values of heart rate(left), LF power, HF power, and LF/HF ratio (right). Before mixing (Before), ont eh day of mixing (Mixing), 2 weeks after mixing (Mix 2wks), on the day of separation (Separate), 2 weeks after separation (Sep 2 wks).

Psychological stress is a risk factor increasing cardiovascular morbidity and mortality (Rosengren, et al., 1991; Ruberman, et al., 1984). The effects of psychological stress on electrical activity of the heart are largely mediated by the autonomic nervous system (Sgoifo, et al., 1997). We evoked anxiety-like or fear-like states in rats by means of classical conditioning and examined changes in autonomic nervous activity using a power spectral analysis of HRV. Anxiety-like states resulted in a significant increase in heart rate, LF power, and LF/HF ratio. Fear-like states resulted in a significant increase in heart rate and a significant decrease in HF power with no significant change in both LF power and LF/HF ratio. These results suggest that autonomic balance becomes predominant in sympathetic

Recent Advances in Telemetry Monitoring and Analysis for Laboratory Animals 161

A neural efferent vagus nerve-mediated mechanism, termed 'cholinergic anti-inflammatory pathway' (CAP), that can suppress the overproduction of pro-inflammatory cytokines such as TNF-α and IL-1β has been described (Borovikova, et al., 2000; Rosas-Ballina, & Tracey, 2009). CAP inhibits unrestrained inflammatory response and improves survival in variety of experimental lethal models. However, limited research has been done yet to examine the mechanisms of activating CAP on bio-behavioral changes. We hypothesize that stimulation of CAP may attenuate the endotoxin-induced septic changes in bio-behavioral function by not only reducing the production of the early proinflammatory cytokines but also maintaining autonomic nervous function as a neuroimmune interaction. Therefore, we evaluated bio-behavioral activity changes in biotelemetry rats to clarify pathophysiological mechanisms of CAP. Autonomic nervous activity was also analyzed by power spectral analysis of HRV. There were no remarkable changes on nicotine treatment in heart rate and autonocimc nervous activity before LPS administration (Fig. 17). Nicotine significantly

Fig. 17. Effect of nicotine (0.4 mg/kg, i.p.) on LPS (1.0mg/kg, i.p) -induced changes in heart rate, HF and LF power and LF/HF ratio. Arrow indicates LPS injiction point. Control group

(open symbols) and nicotine-treated group (filled symbols).

nervous activity in both anxiety-like and fear-like states. These changes in rats correspond to changes which are relevant to cardiovascular diseases under many kinds of psychological stress (Inagaki, et al., 2004).

#### **6.2.4 Hypoxia and inflammation**

Hypoxia induces a range of behavioural, cardiopulmonary, hormonal and neural responses. Although a small number of studies have investigated to hypoxia exposure in conscious rats, most have used anesthetized animals for short term hypoxia. Therefore, the time courses of changes in cardiovascular and autonomic nervous functions during acclimatization to hypoxia were studied in conscious rats. As shown the results in Fig. 16, the heart rate, HF power of HRV (HR-HF) and LF power of blood pressure variability (BP-LF) were significantly increased after 1 h of hypoxia. Both heart rate and the BP-LF decreased after this initial increase. On the first day of hypoxia, heart rate and BP-LF were significantly lower than those of the control rats. Subsequently, these values altered so that they were similar to the control after 14 days of hypoxia. These results suggest that a sequence of dynamic interactions between sympathetic and parasympathetic nervous activities might have important roles in the regulation cardiovascular function during acclimatization to hypoxia (Kawaguchi, et al., 2005).

Fig. 16. Representative traces of cardiovascular and autonomic nervous function s during a 21-day period of hypoxia (left) and autonomic nervous function during acclimatization to hypoxia (right). Control data (Cont) were obtained in normoxic conditions from 2 days before hypoxic exposure. Open, solid and gray columns indicate the light, dark and overall periods, respectively.

nervous activity in both anxiety-like and fear-like states. These changes in rats correspond to changes which are relevant to cardiovascular diseases under many kinds of psychological

Hypoxia induces a range of behavioural, cardiopulmonary, hormonal and neural responses. Although a small number of studies have investigated to hypoxia exposure in conscious rats, most have used anesthetized animals for short term hypoxia. Therefore, the time courses of changes in cardiovascular and autonomic nervous functions during acclimatization to hypoxia were studied in conscious rats. As shown the results in Fig. 16, the heart rate, HF power of HRV (HR-HF) and LF power of blood pressure variability (BP-LF) were significantly increased after 1 h of hypoxia. Both heart rate and the BP-LF decreased after this initial increase. On the first day of hypoxia, heart rate and BP-LF were significantly lower than those of the control rats. Subsequently, these values altered so that they were similar to the control after 14 days of hypoxia. These results suggest that a sequence of dynamic interactions between sympathetic and parasympathetic nervous activities might have important roles in the regulation cardiovascular function during

Fig. 16. Representative traces of cardiovascular and autonomic nervous function s during a 21-day period of hypoxia (left) and autonomic nervous function during acclimatization to hypoxia (right). Control data (Cont) were obtained in normoxic conditions from 2 days before hypoxic exposure. Open, solid and gray columns indicate the light, dark and overall

stress (Inagaki, et al., 2004).

periods, respectively.

**6.2.4 Hypoxia and inflammation** 

acclimatization to hypoxia (Kawaguchi, et al., 2005).

A neural efferent vagus nerve-mediated mechanism, termed 'cholinergic anti-inflammatory pathway' (CAP), that can suppress the overproduction of pro-inflammatory cytokines such as TNF-α and IL-1β has been described (Borovikova, et al., 2000; Rosas-Ballina, & Tracey, 2009). CAP inhibits unrestrained inflammatory response and improves survival in variety of experimental lethal models. However, limited research has been done yet to examine the mechanisms of activating CAP on bio-behavioral changes. We hypothesize that stimulation of CAP may attenuate the endotoxin-induced septic changes in bio-behavioral function by not only reducing the production of the early proinflammatory cytokines but also maintaining autonomic nervous function as a neuroimmune interaction. Therefore, we evaluated bio-behavioral activity changes in biotelemetry rats to clarify pathophysiological mechanisms of CAP. Autonomic nervous activity was also analyzed by power spectral analysis of HRV. There were no remarkable changes on nicotine treatment in heart rate and autonocimc nervous activity before LPS administration (Fig. 17). Nicotine significantly

Fig. 17. Effect of nicotine (0.4 mg/kg, i.p.) on LPS (1.0mg/kg, i.p) -induced changes in heart rate, HF and LF power and LF/HF ratio. Arrow indicates LPS injiction point. Control group (open symbols) and nicotine-treated group (filled symbols).

Recent Advances in Telemetry Monitoring and Analysis for Laboratory Animals 163

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improved survival in LPS-induced endotoxemia. Survival rates of the control and nicotine groups were 67% and 100%, respectively. Heart rate showed increases a few hours after LPS administration in the both control and nicotine groups. Although the elevated heart rate persisted for almost 2 days after LPS injection in the control group, heart rate returned to the baseline value and the diurnal variation was not affected in the nicotine group. The control group showed significant decrease in the HF and LF powers after LPS administration. Lower values of the HF power were continued more than one day. But in the nicotine group, autonomic nervous activity was not affected by LPS injection and index of these values were kept at the base line. Nicotine significantly attenuated LPS-induced changes in heart rate and autonomic nervous activity. These changes were accompanied by significant inhibition of TNF-α and IL-1β gene expression and protein synthesis. However the LPSinduced physiological responses persisted much longer than cytokine production. The plausible explanation is that autonomic nervous activity was lowered by LPS injection for a longer time. These results suggest that the efficacy of nicotine treatment in protecting autonomic nervous system seems likely to have a very important role especially after the acute phase of systemic inflammatory responses (Kojima, et al., 2011).
