The circadian system alters thermoregulation depending on the time of day and feeding condition

Abstract

The circadian rhythm of body temperature (Tb) is a well-known phenomenon. However, it is unknown how the circadian system affects thermoregulation. Food deprivation in mice induces a greater reduction of Tb particularly in the light phase. We examined the role of the clock gene and the suprachiasmatic nucleus (SCN) during induced hypothermia. At 20C with fasting, mice increased their metabolic heat production in the dark phase and maintained T~b~, whereas in the light phase, heat production was less, resulting in hypothermia. Under these conditions, neuronal activity in the SCN, assessed by cFos expression, increased only in the light phase. The differences between the phases in Clock mutant mice were less marked. The neural network between the SCN and paraventricular nucleus appeared to be important in hypothermia. These findings suggest that the circadian system per se is influenced by both the feeding condition and environmental temperature and that it modulates thermoregulation.