Kiyoaki Katahira

Junctional adhesion molecule-1 is upregulated in spontaneously hypertensive rats: evidence for a prohypertensive role within the brain stem.

Junctional adhesion molecule-1 (JAM-1) forms part of the tight junction between adjacent endothelial cells. Using microarray technology, we showed previously that JAM-1 was differentially expressed in the brain stem of spontaneously hypertensive rats compared with normotensive Wistar–Kyoto (WKY) rats. In this study, we quantified the expression of JAM-1 in the brain stem of spontaneously hypertensive rats and WKY rats and established whether any differential expression was confined to this region of the brain or was ubiquitous throughout the central nervous system and, indeed, the whole body. Because the nucleus tractus solitarii plays a pivotal role in arterial pressure regulation, we assessed whether JAM-1 in this region affects the chronic regulation of arterial pressure. Real time RT-PCR revealed that JAM-1 mRNA was upregulated in multiple regions of the brain and all of the peripheral vascular beds studied. In the nucleus tractus solitarii, the level of JAM-1 mRNA was significantly higher in both young (3-week–old, prehypertensive) and adult male spontaneously hypertensive rats (15 to 18 weeks old) than that of age-matched WKY rats (fold differences; prehypertensives: 1.01±0.06 versus 1.59±0.13; n=10; P<0.01; adult: 1.08±0.14 versus 2.86±0.57; n=10; P<0.01). After adenoviral-mediated expression of JAM-1 in the nucleus tractus solitarii of adult WKY rats (15 weeks old; n=6), systolic pressure was increased from 120±4 to 132±4 mm Hg (P<0.01). Our data suggest that JAM-1 expression in the spontaneously hypertensive rat is upregulated throughout the body compared with the WKY rat and that this is not secondary to the hypertension. When JAM-1 is expressed in the nucleus tractus solitarii, it raises arterial pressure, suggesting a novel prohypertensive role for this protein within the brain stem.

Automation of analysis of cardiovascular autonomic function from chronic measurements of arterial pressure in conscious rats

At present, there is no single software package that provides a comprehensive power spectral analysis of pulse interval (PI) and arterial blood pressure (BP), spontaneous cardiac baroreceptor reflex gain (sBRG) and respiratory rate. Furthermore, scientific validation of the software that is currently commercially available and employed has not been published. We introduce ‘Hey‐Presto’ software, which fully evaluates cardiovascular autonomic function from the BP signal obtained from rats. The program performs power spectral analysis of HR and BP variability, respiratory rate and, based on a time‐series method, spontaneous cardiac baroreceptor (sBRG). We have validated Hey‐Presto with conventional pharmacological agents to block cardiac vagal and cardiac sympathetic transmission in conscious rats fitted with a radio‐telemetery BP transducer. Following administration of atropine (1 mg kg−1, i.v.), high‐frequency (HF) power of the PI decreased (P < 0.01) and was associated with the expected increase in HR. Subsequent cardiac sympathetic blockade (atenolol, 1 mg kg−1, i.v.) reduced the low frequency (LF) to HF ratio (LF:HF) of the PI (P < 0.01), which was consistent with the observed reduction in HR. We also found that alterations in sBRG after blockade of cardiac autonomic transmission were highly comparable to values computed manually using vasoactive drugs administered intravenously. The software also detected circadian rhythms in sBRG, HF component of the PI, LF:HF of the PI and LF component of the BP as well as BP and HR during continuous 24 h recording. By demonstrating its application to humans, we found appropriate changes in the power of PI and the LF power of the BP during postural changes. These results demonstrate that Hey‐Presto allows a fully automated, reliable, fast and comprehensive evaluation of cardiovascular autonomic function based on chronic measurements of BP in rats. Moreover, we have confirmed its versatility by demonstrating its application to man.

Dynamic exercise attenuates spontaneous baroreceptor reflex sensitivity in conscious rats

In humans, it has been reported that dynamic exercise attenuates spontaneous baroreceptor reflex sensitivity (sBRS), which is an index of the gain of the baroreceptor‐cardiac reflex. We demonstrated previously that endogenously produced NO from endothelial nitric oxide synthase (eNOS) within the nucleus tractus solitarii (NTS), the central terminal site of baroreceptor afferents, depressed sBRS. In this study, we investigated whether eNOS activity within the NTS plays any role in down‐modulating the sBRS during dynamic exercise. In conscious Wistar rats arterial pressure and heart rate (HR) were monitored continuously and chronically using radiotelemetry before and during wheel cage running at 6 m min−1 for 10 min. sBRS was determined by a time‐series method. During dynamic exercise systolic blood pressure (SBP) and HR were significantly increased (SBP: 138 ± 2 vs. 125 ± 2 mmHg, P < 0.001; HR: 447 ± 6 vs. 362 ± 8 beats min−1, P < 0.001) while sBRS was significantly decreased (0.53 ± 0.03 vs. 1.08 ± 0.08 ms mmHg−1, P < 0.001). In sino‐aortic denervated rats the change in SBP in response to dynamic exercise was significantly larger than that in baroreceptor‐intact rats (denervated: 21.6 ± 2.5 mmHg; intact: 12.0 ± 2.8 mmHg, P < 0.05). In contrast, denervation made no difference to the change in HR. Although disabling eNOS activity in the NTS by adenoviral‐directed expression of a dominant negative mutant form of eNOS increased resting sBRS (1.48 ± 0.20 vs. 1.09 ± 0.15 ms mmHg−1, P < 0.05), the absolute level reached during dynamic exercise was identical to control. These results demonstrate that during dynamic exercise (i) the sBRS decreases around the operating point of the baroreceptor‐cardiac reflex function curve in normotensive rats, (ii) the baroreceptor reflex operates to limit the rise in arterial pressure, and (iii) the attenuation of sBRS is not mediated by changes in eNOS activity within the NTS.

Spaceflight alters the fiber composition of the aortic nerve in the developing rat.

Hydrostatic pressure gradients due to the gravitational force in blood vessels disappear under conditions of microgravity during spaceflight, and the ability of the baroreceptor reflex to control arterial pressure and blood distribution may be altered. We hypothesized, on the basis of the results obtained in our previous experiments using the head-down tilt method in rats and rabbits, that the range of increase in arterial pressure caused by animal behavior narrows under conditions of microgravity, affecting the development of high-threshold unmyelinated fibers in the rat aortic nerve which sends signals from baroreceptors located in the aortic wall to the reflex center. We verified this hypothesis using 9-day-old rat neonates housed with their dams for 16 days on the space shuttle Columbia in outer space (STS-90, Neurolab Mission). Age-matched neonatal rats with the dams remained on the ground as controls. After breeding was carried out in the three experimental groups (FLT, spaceflight; AGC, asynchronous ground control; VIV, vivarium ground control), specimens of the 25-day-old rats were excised and five left aortic nerves in each group were examined by electron microscopy. The number of aortic unmyelinated fibers was significantly less in the FLT group than in each ground control (mean+/-S.D.; 139+/-37 in the FLT, 207+/-36 in the AGC, 283+/-121 in the VIV; P<0.05), which may be related to the weakness of the baroreceptor reflex under conditions of microgravity in space. This result may contribute to understanding of the several cardiovascular issues which occur under microgravity and after reexposure to gravity in human.

Analysis of antibody response by temperature-sensitive measles vaccine strain in the cotton rat model.

Measles virus (MeV) vaccine strain, AIK-C, is temperature sensitive (ts), which is thought to be associated with attenuation of virus pathogenicity. In this study, replication and antibody response were examined in cotton rats using viruses carrying different forms of the P gene, which is responsible for the ts phenotype of strain AIK-C and its parental Edmonston strain. When cotton rats were inoculated intranasally, ts viruses neither replicated in lungs, nor reproducibly generated an antibody response. When inoculated intramusculary (i.m.), however, ts strains raised an antibody titer in all animals. This response was not observed when ultraviolet-inactivated virus was used. ts virus, inoculated i.m., was recovered from cotton rat drainage lymph nodes. These results suggest that ts virus, inoculated i.m., could replicate in the cotton rat, presumably at the superficial lymph node, and induce an antibody response. Therefore, cotton rats can serve as a small-animal model for investigating immune responses to safer ts vaccine, as well as recombinant vaccine using AIK-C as a vector for protection against other infectious agents.

Developmental changes in functional characteristics of aortic baroreceptor afferents in rats

To investigate postnatal developmental changes in functional characteristics of the afferent pathway of the aortic baroreceptor reflex, the responses of aortic nerve activity (ANA) to blood pressure (BP) changes elicited by phenylephrine and sodium nitroprusside administration were tested in 3‐, 8‐ and 20‐week‐old male rats under chloralose (60 mg kg−1i.p.) and urethane (600 mg kg−1i.p.) anaesthesia. The function curve of ANA in response to BP changes showed a sigmoid shape that shifted to the right from 3 to 8 weeks of age. The maximal activity and maximal gain of the aortic nerve, which were calculated by a logistic function analysis, were significantly higher in 20‐week‐old rats (maximal activity, 532 ± 47% of baseline; maximal gain, 7.9 ± 0.8% of baseline mmHg−1; n= 9) than in 3‐week‐old rats (maximal ANA, 268 ± 25% of baseline, P < 0.001; maximal gain, 4.9 ± 0.5% of baseline mmHg−1, P < 0.01, n= 9) and 8‐week‐old rats (maximal ANA, 309 ± 18% of baseline, P < 0.001; maximal gain, 4.9 ± 0.3% of baseline mmHg−1, P < 0.01, n= 11). These results suggest that the operating point of aortic baroreceptor afferents is reset to the higher pressure level during development from 3 to 8 weeks of age and, thereafter, the afferent gain increases from 8 to 20 weeks of age. This functional change may be an important factor to prevent an excess increase of BP, which would result in pathophysiological problems.

Cardiovascular regulation during upright standing behavior in conscious rats.

Although rats often show an upright standing behavior the cardiovascular response during the behavior has not yet been fully clarified. In this study we quantified the activity of upright standing behavior in rats using infrared beam detectors and measured cardiovascular variables during the behavior. Rats demonstrated a high level of upright standing activity as they showed the upright posture more than 500 times per day at 10 weeks of age. The average upright standing duration time was less than 10s. Arterial pressure slightly decreased while heart rate increased in response to the behavior and these responses were not affected by sino-aortic denervation. Our results indicate that other mechanisms such as the vestibulo-cardiovascular reflex may completely compensate the lack of the baroreceptor reflex to maintain cardiovascular homeostasis in response to acute positional changes in rats. Moreover rats demonstrate complex integrative mechanisms maintaining cardiovascular homeostasis against the upright standing behavior which frequently occurs in rats.

Different sensitivity to the suppressive effects of isoflurane anesthesia on cardiorespiratory function in SHR/Izm, WKY/Izm, and Crl:CD (SD) rats

Isoflurane is a widely used anesthetic, but its effects with increase in inspired concentration on cardiovascular function have not yet been clarified in rodents. Additionally, there are only a few studies comparing isoflurane-induced cardiorespiratory effects between rat strains. Thus, we investigated the differences in cardiorespiratory responsiveness to increasing concentration of inspired isoflurane in SHR/Izm, WKY/Izm and Crl:CD (SD) rats, by increasing the setting values of vaporizer’s dial indicator. The rats were anesthetized with 1.5% isoflurane, and electrocardiograms, blood pressure, and respiratory rate were recorded simultaneously. Thereafter, the inspired concentration was increased stepwise to 2%, 3%, 4%, and 5%, and cardiorespiratory parameters were obtained at each concentration. Under anesthesia at more than 4%, although prolongation of the RR and PR intervals was observed in all strains, shortening of the QTC interval was found only in SHR/Izm rats. From frequency domain analysis of heart rate variability, an increase in LF/HF ratio and a decrease of HF components were observed in SHR/Izm and WKY/Izm rats, respectively, with 5% isoflurane anesthesia. Blood pressure and heart rate were remarkably reduced in SHR/Izm rats at higher concentrations, whereas the reduction was smallest in WKY/Izm rats among the three strains examined. Respiratory rate was inspired concentration-dependently decreased in all strains. These results suggested that SHR/Izm rats are more sensitive to suppressive effects of isoflurane anesthesia on cardiovascular function among these rat strains.

Spaceflight Affects Postnatal Development of the Aortic Wall in Rats

We investigated effect of microgravity environment during spaceflight on postnatal development of the rheological properties of the aorta in rats. The neonate rats were randomly divided at 7 days of age into the spaceflight, asynchronous ground control, and vivarium control groups (8 pups for one dam). The spaceflight group rats at 9 days of age were exposed to microgravity environment for 16 days. A longitudinal wall strip of the proximal descending thoracic aorta was subjected to stress-strain and stress-relaxation tests. Wall tensile force was significantly smaller in the spaceflight group than in the two control groups, whereas there were no significant differences in wall stress or incremental elastic modulus at each strain among the three groups. Wall thickness and number of smooth muscle fibers were significantly smaller in the spaceflight group than in the two control groups, but there were no significant differences in amounts of either the elastin or collagen fibers among the three groups. The decreased thickness was mainly caused by the decreased number of smooth muscle cells. Plastic deformation was observed only in the spaceflight group in the stress-strain test. A microgravity environment during spaceflight could affect postnatal development of the morphological and rheological properties of the aorta.

Chronic inhibition of standing behaviour alters baroreceptor reflex function in rats

Aim:  To investigate whether daily orthostatic stress during development is an important factor affecting arterial baroreceptor reflex function, we examined the effect of chronic inhibition of upright standing behaviour on the baroreceptor reflex function in rats.