Effects of centrally applied drugs on pressor responses to hypothalamic stimulation
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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.
Key wordsHypothalamic Stimulation Nucleus of the Solitary Tract Cholinergic Agents Push Pull Cannula Drugs Affecting Alpha-Adrenoreceptors Arterial Blood Pressure
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