Observations on the thermoregulatory effects of preoptic warming in rats

Abstract

Experimental warming of the preoptic-anterior hypothalamic area was used to evaluate behavioral and autonomic thermoregulatory heat-loss responses. Hypothalamic warming was associated with reduced behavioral heat intake and decreased core and peripheral temperatures in rats working for radiant heat reward in a cold environment. Baseline rates of responding for external heat were determined by ambient temperature, but the magnitude of changes in core or peripheral temperatures during preoptic warming were not. Behavioral responses compensated for variations in ambient temperature so that the threshold hypothalamic temperature above which heat loss was activated by preoptic warming was not altered by changing ambient temperatures. Heat loss during hypothalamic warming was a function of both autonomic and behavioral thermoregulatory responses because the decrease in body heat content during preoptic warming could not be accounted for by the decreased behavioral heat intake alone. The threshold hypothalamic temperature for elicitation of tail vasodilation decreased systematically as ambient temperature increased when no behavioral option was available. In the rat, both behavioral and autonomic thermoregulatory responses cooperate to determine the magnitude of heat loss which is proportional to the magnitude of preoptic warming.