Role of histamine receptor in mesencephalic nucleus dorsalis raphe in cardiovascular regulation

Abstract

The effects of microinjection of histamine and its antagonists into mesencephalic nucleus dorsalis raphe, were investigated on mean arterial pressure and heart rate in cats to elucidate the nature and role of histaminergic receptors in cardiovascular regulation. Microinjection of histamine (5 and 10 micrograms) into nucleus dorsalis raphe elicited both inhibitory and excitatory cardiovascular responses respectively. On the other hand, microinjection of H2-receptor blocker, cimetidine (10 micrograms) resulted in hypertension and tachycardia while H1-receptor antagonist, mepyramine (10 micrograms) microinjection evoked hypotension and bradycardia. Furthermore, local pretreatment with cimetidine and mepyramine blocked the inhibitory and excitatory cardiovascular responses of graded doses of histamine microinjection. These H1 and H2 receptors are localized in nucleus dorsalis raphe since microinjection of histamine into adjoining neural structures did not evoke any cardiovascular change. Furthermore, both the inhibitory and excitatory cardiovascular responses to histamine microinjection could not be observed in animals with spinal cord transection and in animals pretreated with p-chlorophenylalanine while they could be observed in bilateral cervical vagotomized animals. Thus, it appears that these cardiovascular responses to microinjection of histamine into nucleus dorsalis raphe, are due to modulation of serotonergic bulbospinal influence on sympathetic preganglionic neurones in the spinal cord. Moreover, the excitatory cardiovascular responses of high dose of histamine (10 micrograms) seem to result from a local release of noradrenaline since they were blocked by prior microinjection of guanethidine and piperoxan into nucleus dorsalis raphe. A release of noradrenaline in turn, modulates the activity of the neurones of the nucleus by acting on alpha adrenoceptors and thereby alters the activity of sympathetic preganglionic neurones.(ABSTRACT TRUNCATED AT 250 WORDS)

Histamine Excites Neonatal Rat Sympathetic Preganglionic Neurons In Vitro Via Activation of H1 Receptors

“…Ba: samples of a continuous wholecell current-clamp recording from another SPN, showing increased firing frequency in the presence of the H 1 receptor-specific agonist HTMT. indicate that activation of the central histamine system leads to elevated levels of plasma catecholamines (Akins and Bealer 1993;Knigge et al 1990;Matzen et al 1992;Okuma et al 1997) and changes in blood pressure and heart rate (Gatti and Gertner 1983;Klein andGertner 1981, 1983;Singewald and Phillippu 1996;Tangri et al 1989). Thus histamine has a role in regulating autonomic function, both peripherally and centrally.…”