HYPOTHALAMIC SUPERFUSION WITH MUSCARINIC DRUGS - THEIR EFFECTS ON PRESSOR-RESPONSES TO HYPOTHALAMIC-STIMULATION

The posterior hypothalamus of cats anaesthetized with pentobarbital sodium was superfused with artificial cerebrospinal fluid through a push-pull canula and electrically stimulated with the noninsulated tip of the canula. The effects of muscarinic drugs on the pressor response to stimulation of the hypothalamus were investigated. Superfusion with muscarine, oxotremorine or N-benzyl-3-pyrrolidyl acetate methobromide (AHR 602) decreased the pressor responses to hypothalamic stimulation. Superfusion with methylatropine did not influence the pressor responses to hypothalamic stimulation; superfusion with methylatropine 60 min prior to and during superfusion with the muscarinic drugs abolished the inhibitory effects of muscarine and oxotremorine and temporarily reversed that of AHR 602 on the pressor responses. Superfusion of the posterior hypothalamus with arecoline enhanced the rise of blood pressure elicited by hypothalamic stimulation. When the hypothalamus was superfused with hexamethonium 60 min prior to and during superfusion with arecoline, arecoline reduced the pressor responses to electrical stimulation of the hypothalamus. Superfusion with methylatropine prior to and together with an ineffective concentration of arecoline increased the rise of blood pressure elicited by hypothalamic stimulation. Only oxotremorine caused a fall of the resting arterial blood pressure; it was abolished by the i.v. injection of methylatropine. Superfusion of the posterior hypothalamus with muscarinic drugs impairs the pressor responses to hypothalamic stimulation. Drugs possessing both nicotinic and muscarinic properties either enhance or diminish the pressor responses according to their relative potencies on the 2 types of receptor.