Abstract
Various homeostatic systems are under the control of the circadian clock. Recently we found that fasted rats kept under a light-dark cycle showed a decrease in body temperature (Tcore) only during the light phase. In the fasting condition, in the dark phase Tcore was maintained normal by a suppression of heat loss mechanism despite the reduction of metabolic heat production. In contrast, the response was weakened in the light phase, decreasing Tcore greatly, but in this period cold escape behavior is facilitated, probably for the compensation of Tcore decrease. These modulations of thermoregulatory effectors, depending on the time of the day, are considered as adaptive responses to the lack of food. Interestingly, in the rats with the lesion of the hypothalamic suprachiasmatic nucleus in which daily rhythms of Tcore and activity were abolished, body temperature was unchanged by food deprivation. Very similar loss of Tcore modulation was observed in those mice lacking the criptochrome genes (Cry1−/-/Cry2−/-) during food restriction. These results suggest that the circadian clock is a key structure for coordinating the controls of body temperature, energy metabolism, and behavior. [Jpn J Physiol 54 Suppl:S7 (2004)]
