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Effects of central histaminergic receptor activation on carotid sints baroreceptor reflex resetting in stressed rats

WANG Guo- Qing, ZHOU Xi-Ping, H UANG Wei- Qiu

Department of Physiology，Medical School，Soochow University，Suzhou 215007

Abstract

To determine the effect of stress on carotid sinus baroreceptor reflex(CS助and whether or not central histaminergic receptors modulate the CSR under stress，the characteristics of CSR were analyzed by using an isolated carotid sinus preparation in Wistar rats .Animals were divided into two groups
at random:unstressed group(n一42) and stressed group(n一41).According to the site of microinjec tion of histaminergic receptor antagonists，each group was subdivided into a group of intracerebroventricular injection(i. c. v.)and a group of microinjection into the nucleus of the solitary tract(NTS).The volume of injection into the lateral cerebroventricle and NTS was 5 p1 and 1 p1，respective1y.Stressed groups were su匀ected to unavoidable electric foot-shock twice daily for a week，each session of foot shock lasted 2 hours .The left and right carotid sinus regions were isolated from the systemic cir
culation under anesthesia with pentobarbital sodium in all rats .The intracarotid sinus pressure(ISP) was altered in a stepwise manner to trigger CS R from 0 to 280 m m Hg at every step of 40 m m Hg and 4 s，and
then returned to 0 m m Hg in similar steps.ISP and mean arterial pressure(MAP) were recorded simultaneously .ISP- MAP relationship curve was constructed by fitting to the logistic function with five parameters .The CSR parameters and the ISP- MAP relationship curve were separately compared statistically.
The main results obtained are as follows.(1) Stress significantly shifted the ISP- MAP relationship curve upwards and obviously moved the middle part of ISP- Gain relationship curve downwards，and decreased the value of the MAP range and maximum gain(Gmax)，but increased the threshold pressure(T P)，sat-
uration pressure(S P)，set point and ISP at Gmax( ISPcmax).(2) I. c. v. of H, receptor antagonist chlorpheniramine(CHL，5 pg) or HZ receptor antagonist cimetidine(CI M，1 5 pg) significantly diminished the above mentioned changes in CSR performance induced by stress;the alleviative effect of CI M was
less re markable than that of CHL .The responses of CS R in stressed rats to H, or HZ receptor antagonists generally occurred 20 min after the administration and lasted approximately for 15 min.(3)After microinjection of CHL(0. 5 pg) or CI M(1 .5 pg) into the NTS，the responses of CSR in stressed groups were similar to those after i. c. v. injection of CHL or CI M.(4) However，microinjection of CHL or CI M into the lateral cerebroventricle or the NTS could not completely abolish the stress-induced changes
in CSR .These findings suggest that stress results in a resetting of CSR，a decrease in reflex sensitivity.The stress-induced changes in CSR may be mediated，at least in part，by activating the brain histamines
gic syste m .The central histaminergic receptors(H, and HZ receptors) may play an important role in the resetting of CSR under stress .The descending histaminergic pathway from the hypothalamus to NTS may be involved in these effects.

Key words: Carotid sinus baroreceptor reflex;Stress;;;;;

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Citing This Article：

WANG Guo- Qing, ZHOU Xi-Ping, H UANG Wei- Qiu. Effects of central histaminergic receptor activation on carotid sints baroreceptor reflex resetting in stressed rats. Acta Physiol Sin 2003; 55 (1): (in Chinese with English abstract).