AUTONOMIC THERMOREGULATORY EFFECTS OF ELECTRICAL-STIMULATION OF THE HYPOTHALAMUS IN THE SHEEP (OVIS-ARIES)

The effects of electrical stimulation of the preoptic region, on autonomic thermoregulatory responses, were studied in conscious sheep at ambient temperatures of 5, 20 and 40.degree. C. Stimulation of the dorsal preoptic region elicited co-ordinated thermoregulatory responses characterized by increased respiratory frequency (RF), vasodilation of the ears and lowered body temperature. Stimulation inhibited shivering in cold environments. The thermoregulatory responses were greater at 5.degree. C in unshorn than in shorn sheep. Increased RF, induced at 20 and 40.degree. C, persisted several minutes after stimulation ceased. Intraventricular injection of noradrenaline [norepinephrine, Ne] reduced both normal and electrically-induced panting. Sheep would press panels to electrically stimulate the preoptic region and this self-stimulation activated heat-loss mechanisms.