Roles of the histaminergic receptors in the locus ceruleus in stress-induced carotid baroreflex resetting in rats / 中国应用生理学杂志

<p><b>AIM</b>To explore the roles of H1 and H2 receptors in the locus ceruleus (LC) in the carotid baroreflex (CBR) resetting resulted from foot-shock stress.</p><p><b>METHODS</b>Male SD rats were divided into two groups (n=18) at random: unstressed and stressed group. The latter were subjected to unavoidable electric foot-shock twice daily for a week and each session of foot-shock lasted 2 hours. The left and right carotid sinus regions were isolated from the systemic circulation in all animals anesthetized with pentobarbital sodium. The intracarotid sinus pressure (ISP) was altered in a stepwise manner in vivo. ISP-mean arterial pressure (MAP), ISP-Gain relationship curves and reflex characteristic parameters were constructed by fitting to the logistic function with five parameters. The changes in CBR performance induced by stress and the effects of microinjection with histaminergic receptors antagonists into the LC on the responses of CBR to stress were examined.</p><p><b>RESULTS</b>Stress significantly shifted the ISP-MAP relationship curve upwards (P < 0.05) and obviously moved the middle part of ISP-Gain relationship curve downwards (P < 0.05), and decreased the value of the MAP range and maximum gain (P < 0.05), but increased the threshold pressure, saturation pressure, set point and ISP at maximum gain (P < 0.05). Microinjection of selective H1 or H2 receptor antagonist, chlorpheniramine (CHL, 0.5 microg/microl) or cimetidine (CIM, 1.5 microg/microl) into the LC, significantly attenuated the above-mentioned changes in CBR performance induced by stress and the alleviate effect of CIM was less remarkable than that of CHL (P < 0.05). The responses of CBR under stress to H1 or H2 receptor antagonist generally occurred 20 min after the administration and lasted approximately for 16 min. Microinjection with the same dose of CHL or CIM into the LC in the unstressed group did not change CBR performance significantly (P > 0.05). However, microinjection of CHL or CIM into the LC could not completely abolish the stress-induced changes in CBR.</p><p><b>CONCLUSION</b>The stress results in a resetting of CBR and a decrease in reflex sensitivity. The stress-induced changes in CBR may be mediated, at least in part, by activating the brain histaminergic system. The H1 and H2 receptors in the LC, especially, Hi receptors may play an important role in the resetting of CBR under stress. The descending histaminergic pathway from the hypothalamus to LC may be involved in these effects. Moreover, the effects of stress on CBR also have other mechanisms.</p>

A receptors in the NTS modulate depression of carotid baroreflex induced by intracerebroventricular injection of histamine in rats / 中国应用生理学杂志

<p><b>AIM</b>To investigate the roles of alpha1 and alpha2 receptors in the nucleus tractus solitarius (NTS) in the carotid baroreflex (CBR) resetting induced by the intracerebroventricular injection (ICV) of histamine (HA).</p><p><b>METHODS</b>The left and right carotid sinus regions were isolated from the systemic circulation in 25 Sprague-Dawley rats anesthetized with pentobarbital sodium. The intracarotid sinus pressure (ISP) was altered in a stepwise manner. ISP-mean arterial pressure (MAP) relationship curve and its characteristic parameters were constructed by fitting to the logistic function with five parameters. The changes in CBR performance induced by ICV HA and the effects of pretreatment with alpha1 or alpha2 receptor antagonist into the NTS on the responses of CBR to HA were examined.</p><p><b>RESULTS</b>ICV HA (60 micromol x L(-1) in 5 microl) significantly shifted the ISP-MAP relationship curve upwards (P < 0.05) and moved the middle part of ISP-Gain relationship curve downwards (P < 0.05), and reduced the MAP range and maximum gain (P < 0.05). The pretreatment with phenoxybenzamine (PBZ, a selective antagonist of alpha1 receptor, 3 micromol x L(-1) in 500 nl) or yohimbine (YOH, a selective antagonist of alpha2 receptor, 2.5 micromol x L(-1) in 500 nl) into the NTS could obviously intensify the above-mentioned changes in CBR performance induced by HA, but the intensive effect of PBZ was less remarkable than that of YOH (P < 0.05).</p><p><b>CONCLUSION</b>The intracerebroventricular administration of HA results in a rapid resetting of CBR and a decrease in reflex sensitivity, and the functions of alpha1 and alpha2 receptors in the NTS might weaken CBR resetting induced by ICV HA. Furthermore, alpha2 receptor in the NTS might play an more important role in modulating the responses of CHR to HA.</p>

H(1) and H(2) receptors in the locus ceruleus are involved in the intracerebroventricular histamine-induced carotid sinus baroreceptor reflex resetting in rats / 神经科学通报·英文版

Objective To investigate the role of H(1) and H(2) receptors in the locus ceruleus (LC) in carotid sinus baroreceptor reflex (CSR) resetting induced by intracerebroventricular (i.c.v.) injection of histamine (HA). Methods The left and right carotid sinus regions were isolated from the systemic circulation in 18 male Sprague-Dawley rats anesthetized with pentobarbital sodium. The intracarotid sinus pressure (ISP) was altered in a stepwise manner in vivo. ISP-mean arterial pressure (MAP) relationship curve and its characteristic parameters were constructed by fitting to the logistic function with five parameters. The changes in CSR performance induced by i.c.v. HA and the effects of pretreatment with H(1) or H(2) receptors selective antagonist, chlorpheniramine (CHL) or cimetidine (CIM) into the LC, on the responses of CSR to HA were examined. Results I.c.v. HA (100 ng in 5 mu l) significantly shifted the ISP-MAP relationship curve upwards (P < 0.05) and obviously decreased the value of the reflex parameters such as MAP range and maximum gain (P < 0.05), but increased the threshold pressure, saturation pressure and ISP at maximum gain (P < 0.05). The pretreatment with CHL (0.5 mu g in 1 mu l) or CIM (1.5 mu g in 1 mu l) into the LC could obviously attenuate the changes mentioned above in CSR performance induced by HA, but the alleviative effect of CIM was less remarkable than that of CHL (P < 0.05). Respective microinjection of CHL or CIM alone into the LC with the corresponding dose and volume did not change CSR performance significantly (P > 0.05). Conclusion Intracerebroventricular administration of HA results in a rapid resetting of CSR and a decrease in reflex sensitivity, and the responses of CSR to HA may be mediated, at least in part, by H(1) and H(2) receptors activities in the LC, especially by H(1) receptors. Moreover, the effects of the central HA on CSR might be related to a histaminergic descending pathway from the hypothalamus to LC.