Inhibition by atropine of the increased turnover of noradrenaline in the hypothalamus of rats exposed to cold

Abstract

Summary1. Small doses of (-)-[3H] noradrenaline were injected into the lateral cerebral ventricles in rats to label radioactively the endogenous noradrenaline (NA) stores.2. Intraventricular injection of 25 1ug atropine methonitrate at the same time inhibited the increased rate of disappearance of [3H] NA from the hypothalamus at an environmental temperature of 90 C, when compared with the values at 240 C, without impairing temperature regulation. 3. At 320 C, 25 jtg atropine methonitrate caused a lethal hyperthermia. A dose of 5 yg was not lethal and did not inhibit the increased rate of disappearance of [3H] NA from the hypothalamus. 4. It is concluded that the pathway which stimulates an increased turnover of NA in the cold contains an atropine sensitive synapse but is not the principal pathway of heat production. The increased turnover of NA in the heat probably does not involve an atropine sensitive synapse.

Effects of capsaicin on central monoaminergic mechanisms in the rat

“…In accordance with these assumptions, the 5-HT turnover increased in rats exposed to a warm environment (Reid et al, 1968;Corrodi et al, 1967;Sheard and Aghajanian, 1967;Weiss and Aghajanian, 1971). The NA turnover was activated in the cold and, though it may also be increased in heat, the latter is regarded as a non-specific stress reaction (Corrodi et al, 1967;Reid et al, 1968;Simmonds and Iversen, 1969;Simmonds, 1971). With all this in mind, it might be expected that capsaicin, a stimulant for warm receptors, would possibly increase the serotonergic activity and decrease the noradrenergic activity, which is exactly opposite to what was found in our experiments.…”