Endogenous thermoregulatory rhythms of squirrel monkeys in thermoneutrality and cold

Section of Neurobiology, Physiology and Behavior, University of California, Davis, California 95616-8519 Whole body heat production (HP) and heat loss (HL) were examined to determine if the free-running circadian rhythm in body temperature (T b ) results from coordinated changes in HP and HL rhythms in thermoneutrality (27°C) as well as mild cold (17°C). Squirrel monkey metabolism ( n = 6) was monitored by both indirect and direct calorimetry, with telemetered measurement of T b and activity. Feeding was also measured. Rhythms of HP, HL, and conductance were tightly coupled with the circadian T b rhythm at both ambient temperatures (T A ). At 17°C, increased HP compensated for higher HL at all phases of the T b rhythm, resulting in only minor changes to T b . Parallel compensatory changes of HP and HL were seen at all rhythm phases at both T A . Similar time courses of T b , HP, and HL in their respective rhythms and the relative stability of T b during both active and rest periods suggest action of the circadian timing system on T b set point. body temperature; direct calorimetry; indirect calorimetry; metabolism; heat production; heat loss; nonhuman primates; conductance