Autonomic thermoregulation in squirrel monkey when behavioral regulation is limited.

Squirrel monkeys (Saimiri sciureus) in a cold environment (10, 0, or -5 degrees C) learned to partially control their chamber air temperature by pulling a chain for 10-s reinforcements of 30 degrees C air. A maximal response rate of 5/min produced an average air temperature (24-27 degrees C), well below their preferred 35 degrees C. Metabolic heat production was elebtaed 0.3-1.0 W/kg. Preoptic cooling (via stereotaxically implanted thermodes) stimulated increased metabolic heat production, with a resultant rise in core temperature. Preoptic warming stimulated reduced heat production and some peripheral vasodilation, resulting in a fall in core tenperature. The metabolic response of all animals was directly related to the skin-to-air temperature difference (Tsk - TA). Usually, mean skin temperature remained essentially unchanges as a result of a steady behavioral response rate. An increase in metabolic heat production was observed in one monkey during preoptic warming. The study demonstrated that even when behavioral thermoregulation is inefficient, it is generally sustained with maximal vigor over long periods. This behavior is then supplemented by appropriate autonomic adjustments when necessary to achieve full regulation of the body temperature.