Thermoregulatory changes to cholinomimetics and angiotensin II, but not to the monoamines microinjected into the brain stem of the rabbit

Abstract

A brain mapping study that assessed the sites of drug action was carried out by microinjecting the monoamines (dopamine, norepinephrine, epinephrine, 5-hydroxytryptamine), carbachol, acetylcholine, eserine and angiotensin II into several basal forebrain and brain stem sites in the restrained and unrestrained rabbit. The monoamines (0.75–100 μg) failed to evoke a consistent change in either brain or colonic temperature when microinjected in several preoptic, diencephalic, mesencephalic and lower brain stem sites. Carbachol (0.375–6 μg) produced a dose-dependent rise in temperature when microinjected into the medial and lateral preoptic areas, the bed nucleus of the stria terminalis, the anterior and posterior hypothalamic area and the mesencephalic and pontine central gray. In a few experiments, microinjections of the cholinomimetics into the fourth ventricle evoked a consistent fall in temperature. Angiotensin II (0.05–1.5μg) produced a dose-dependent fall in body temperature when microinjected in the lateral basal forebrain and medial aspects of the hypothalamus, thalamus, midbrain and pons. Neither the restraint nor changes in behavioral and physiological responses contributed significantly to the temperature changes following microinjections of cholinomimetics and angiotensin II. These results suggest that the central monoamines serve either no role or a minor one, in the central control of themoregulation in the rabbit. Central cholinergic systems appear to function in heat-gain and possibly heat-loss mechanisms. The angiotensin II-induced hypothermia supports the involvement of angiotensin II in the activation of heat-loss mechanisms.