Internal temperature variations during the sleep-wake cycle in the rat.

This study attempted to explain the variations of internal (brain and subcutaneous) temperature in the rat as a function of sleeping and waking. Temperature variations in cerebellum and hypothalamus were related to the changes in local cerebral blood flow (CBF) measured chronically with a thermal clearance method. CBF was stable and at a high level during slow wave sleep (SWS), decreased at the beginning of each wake (W) and paradoxical sleep (PS) phase, but tended to overshoot at the end of the PS phase. Subcutaneous temperature was related to the whole body thermogenesis (VO2) and to the sensible heat loss by radiation, convection and conduction. VO2 increased during W, decreased and plateaued during SWS, and was at a minimum level during PS. Sensible heat loss decreased during W, increased during SWS, and generally rose abruptly during PS. These variations in body and brain heat gain and heat loss are in agreement with the local temperature variations during sleeping and waking. The concomitant variations in vigilance states and internal temperature led to an apparent close relationship between the circadian rhythms of these variables, although their exact degree of liaison was not established.