Rostral hypothalamus: a new neuroanatomical site of neurochemically-induced emesis in the cat.
The localized effect of noradrenergic agonists administered directly in the anterior hypothalamic preoptic area (AH/POA) in inducing emesis in the cat was investigated. Of the noradrenergic agonists tested, which included norepinephrine, clonidine, phenylephrine and methoxamine, only clonidine in doses of 5.0-50.0 micrograms was found to evoke emesis consistently when micro-injected in a volume of 1.0 microliter into AH/POA of the unrestrained cat. The emetic response to clonidine was short-lasting, generally dose-dependent in terms of latency and frequency, and occurred in bouts of one to three episodes. The sequence of the vomiting response, beginning with licking and retching, functionally resembled a normal pattern of an emetic response. The clonidine-induced emesis was not antagonized by the following antagonists micro-injected in AH/POA just prior to clonidine: alpha-adrenergic blocking agents, yohimbine, RX 781094 and phentolamine; the antimuscarinic drug, atropine; the serotonin antagonist, methysergide; the opioid antagonist, naloxone; and the dopamine antagonist, chlorpromazine. Therefore, it would appear that clonidine-induced emesis is not mediated by alpha noradrenergic, serotonergic, dopaminergic, muscarinic and opiate receptor systems within the AH/POA of the cat. Finally, the obtained results show that apart from the area postrema and a circumscribed zone of the brain-stem reticular formation, the hypothalamus is now implicated as a neuroanatomical site in the central nervous system mechanism underlying neurochemically-induced emesis.
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002415:Cats; D003000:Clonidine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D005260:Female; D007031:Hypothalamus / Q000033:anatomy & histology / Q000378:metabolism / Q000502:physiology*; D007035:Hypothermia / Q000139:chemically induced / Q000517:prevention & control; D009638:Norepinephrine / Q000378:metabolism / Q000502:physiology*; D014839:Vomiting / Q000139:chemically induced*
D000317:Adrenergic alpha-Antagonists; D003000:Clonidine; D009638:Norepinephrine