ROLE OF THE CHOLINERGIC SYSTEMS IN THE CENTRAL CONTROL OF THERMOREGULATION IN RATS

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. Both at room temperature (22°C) and in the cold (8°C), the hypothermia in response to methacholine application was brought about by both a decrease in metabolic heat production and an increase in cutaneous circulation. In the heat (29°C), the hypothermia was due solely to an increase in respiratory evaporative heat loss. Furthermore, the methacholine-induced hypothermia was antagonized by central pretreatment of atropine (a selective blocker of cholinergic receptors), but not by the central administration of either 6-hydroxy-dopamine (a relative depletor of catecholaminergic nerve fibers) or 5,6-dihydroxytryptamine (predominately a serotonin depletor). The data indicate that activation of the cholinergic receptors within brain with methacholine decreases heat production and (or) increases heat loss which leads to hypothermia in rats.