Heat-escape behavior in the rat following intrahypothalamic injection of acetylcholine.

The effects of preoptic/anterior hypothalamic injections of acetylcholine on heat-escape behavior and hypothalamic temperature were investigated in unrestrained rats implanted with bilateral cannulae. Two types of responses were observed, either a fall in hypothalamic temperature coupled with an increase in behavioral responses to escape heat or a rise in hypothalamic temperature associated with little or no change in behavioral heat-escape responses. The fall in hypothalamic temperature observed in one group of rats was significant and was associated with a dose-dependent increase in heat-escape responding. The rise in hypothalamic temperature noted in the other group of rats was nonsignificant, and the associated behavioral responses were variable. Distinct anatomical differences in cannulae loci between the 2 groups were not apparent. It is concluded that acetylcholine activates the heat-dissipating control system of the rat hypothalamus and that the hyperthermic effects of acetylcholine are nonspecific.