The role of the cholinergic systems in the central control of thermoregulation in rats

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Abstract
Systemic and central administration of methacholine (a synthetic choline derivative) both produced dose-dependent decreases in rectal temperature in rats at all the ambient temperatures studied. At room temperature (22.degree. C) and in the cold (8.degree. C), the hypothermia in response to methacholine application was brought about by a decrease in metabolic heat production and an increase in cutaneous circulation. In the heat (29.degree. C), the hypothermia was due solely to an increase in respiratory evaporative heat loss. The methacholine-induced hypothermia was antagonized by central pretreatment of atropine (a selective blocker of cholinergic receptors), but not by the central administration of 6-hydroxydopamine (a relative depletor of catecholaminergic nerve fibers) or 5,6-dihydroxytryptamine (predominately a serotonin depletor). Apparently, activation of the cholinergic receptors within brain with methacholine decreases heat production and (or) increases heat loss which leads to hypothermia in rats.