Influence of various cholinergic and anticholinergic drugs on rectal temperature in rats.

The influence of various cholinergic drugs on rectal temperature of rats under controlled laboratory conditions was examined. Animals were anaesthetized by intraperitoneal injection of thiopental. Three hours later acetylcholine, methacholine, arecoline, nicotine, neostigmine, atropine, methylatropine, mecamylamine or hemicholinium were injected intrahypothalamically (i.h.), intracerebroventricularly (i.c.v.) or intraperitoneally (i.p.). Rectal temperature was measured at 15 min-intervals for 1 hr after the substances were injected. Our results indicate that the cholinergic mechanisms play an important role in thermoregulatory processes in rats. Cholinergic activation decreases rectal temperature, due to an increased activity of central, and not of peripheral cholinergic neurotransmission. The hypothermic effect of cholinomimetics is mediated through an activation of muscarinic cholinergic receptors.