Showing papers on "Solitary tract published in 1974"

Effects of centrally applied drugs on pressor responses to hypothalamic stimulation.

Abstract: The posterior hypothalamus of anaesthetized cats was superfused through a push-pull cannula with artificial cerebrospinal fluid and electrically stimulated with the non-insulated tip of the cannula. The hypothalamus was superfused with drugs, and their effects on the pressor responses to hypothalamic stimulation were studied. Superfusion with low concentrations of clonidine (1×10−5 M or 5×10−5 M) enhanced the pressor responses to hypothalamic stimulation, while the rise of blood pressure caused by stimulation of the hypothalamus was reduced during superfusion with high concentrations of clonidine (1×10−3 M or 1×10−2 M). A moderate concentration of clonidine (1×10−4 M) was ineffective. Superfusion with carbachol or DMPP (1×10−3 M or 1×10−2 M) elicited a dose-dependent enhancement of the pressor responses to hypothalamic stimulation. Hexamethonium (1×10−2 M) did not affect the rise of blood pressure but abolished the enhancing effects of carbachol and DMPP. In some experiments the nucleus of the solitary tract was superfused with the push-pull cannula and the posterior hypothalamus was stimulated electrically with a monopolar electrode. Superfusion of the nucleus of the solitary tract with tolazoline (1×10−1 M) enhanced the pressor responses to hypothalamic stimulation. The present results are compatible with the following views: 1. Low concentrations of clonidine enhance the pressor responses to hypothalamic stimulation by activating the alpha-adrenoceptors of the hypothalamic area; high concentrations of clonidine inhibit the pressor responses by reducing the noradrenaline release via a feed-back mechanism and/or by inhibiting the release of acetylcholine from cholinergic nerve endings of the hypothalamus. 2. Nicotine agents enhance the rise of blood pressure caused by hypothalamic stimulation; their effects are mediated by nicotinic receptors. 3. More than one neurotransmitter seems to be involved in the central modulation of the arterial blood pressure.

Central regulation of arterial blood pressure.

Abstract: 1. Cats were anaesthetized with pentobarbitone sodium. The hypothalamus was superfused with drugs through a push-pull cannula and electrically stimulated with the non-insulated tip of the cannula. In another series of experiments, the hypothalamus was stimulated with a monopolar electrode and the nucleus of the solitary tract superfused with drugs through a push-pull cannula. 2. Superfusion of the hypothalamus with alpha-adrenoreceptor blocking agents (piperoxan or tolazoline) decreased the pressor responses to hypothalamic stimulation. Superfusion with low concentrations of clonidine increased, whereas superfusion with higher concentrations of this drug diminished, the rise of blood pressure during hypothalamic stimulation. Muscarinic agents (oxotremorine, muscarine or AHR 602) decreased the pressor responses to hypothalamic stimulation. The inhibitory effects of the muscarinic compounds were abolished by superfusing the hypothalamus with methylatropine. Superfusion with nicotinic agents (1,1-dimethyl-4-phenylpiperazinium, or carbachol) enhanced the pressor responses to hypothalamic stimulation. The enhancement of the pressor responses by these drugs was completely inhibited by superfusion of the hypothalamus with hexamethonium. 3. Superfusion of the nucleus of the solitary tract with tolazoline enhanced the pressor responses to hypothalamic stimulation. The pressor responses were reduced during superfusion of the nucleus of the solitary tract with clonidine.