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

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Abstract
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 δC 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.