Brain and core temperatures and peripheral vasomotion during sleep and wakefulness at various ambient temperatures in the rat

Changes in brain, core and tail skin temperatures (T_br, T_c and T_t) associated with transitions in the arousal states were recorded in rats throughout the 24-h diurnal cycle at 10 °C, 21 °C and 29 °C. Falling asleep was accompanied by decreases in both T_br and T_c and vasodilation at 10 C and 21 °C. At 29 °C, tail vessels were permanently dilated, and further dilation was not found on sleep onset. T_br and T_c, however, continued to decrease during non-rapid-eye-movement sleep (NREMS); these changes are likely to result from reductions in heat production and increased conductive heat loss. The changes in T_br, T_c and T_t on awakening mirrored those on falling asleep. It is suggested that the suppression of sleep in the cold and the enhancement of NREMS in the heat promote thermoregulation. Rapid-eye-movement sleep (REMS) was associated with sharp rises in T_br. The rise in T_br was the largest in the cold and was attenuated at 29 °C. T_c decreased and T_t increased in the cold, whereas T_c tended to increase and T_t to decrease in the heat. The paradoxical peripheral vasomotion during REMS supports previous suggestions on severe thermoregulatory impairment during REMS in other species.