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

Abstract

Changes in brain, core and tail skin temperatures (Tbr, Tc and Tt) associated with transitions in the arousal states were recorded in rats throughout the 24-h diurnal cycle at 10 degrees C, 21 degrees C and 29 degrees C. Falling asleep was accompanied by decreases in both Tbr and Tc and vasodilation at 10 degrees C and 21 degrees C. At 29 degrees C, tail vessels were permanently dilated, and further dilation was not found on sleep onset. Tbr and Tc, 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 Tbr, Tc and Tt 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 Tbr. The rise in Tbr was the largest in the cold and was attenuated at 29 degrees C. Tc decreased and Tt increased in the cold, whereas Tc tended to increase and Tt to decrease in the heat. The paradoxical peripheral vasomotion during REMS supports previous suggestions on severe thermoregulatory impairment during REMS in other species.

Heat Synch: Inter- and Independence of Body-Temperature Fluctuations and Brain-State Alternations in Urethane-Anesthetized Rats

“…Within sleep itself, alternations between rapideye-movement (REM) and non-REM states (Aserinsky and Kleitman 1955) are accompanied by smaller, ultradian fluctuations in body temperature. In the rabbit, rat, and cat, brain temperature has been shown to increase sharply during REM sleep and decrease during non-REM sleep (Alfoldi et al 1990; Kawamura and Sawyer 1965;Kovalzon 1973;Obal et al 1985;Satoh 1968). In humans, ultradian oscillations of rectal temperature have been similarly correlated with sleep stages (Almirall et al 1997).…”

Orexins and the cardiovascular events of awakening

“…3) revealed that at 21 C ambient temperature, the tail skin temperature sharply decreased upon awakening from NREM sleep in the face of increasing core body temperature. 53 These data may reflect the rapid return of SNA to waking values, in light of the previously discussed observations that skin SNA is lower during NREM sleep than during wakefulness. 10,11,13 The resultant distal skin vasoconstriction may contribute to increase core body temperature by promoting heat conservation.…”

“…3 also shows that in rats, differences in core body temperature and tail skin temperature upon awakening were much less marked at 29 C than at 21 C ambient temperature. 53 This may indicate that at 29 C ambient temperature, the tail skin of rats is already maximally vasodilated during NREM sleep. 53 Replication of these findings at different skin sites and in different species, including mice, would improve our understanding of the link between the cardiovascular events of awakening and thermoregulation.…”

“…53 This may indicate that at 29 C ambient temperature, the tail skin of rats is already maximally vasodilated during NREM sleep. 53 Replication of these findings at different skin sites and in different species, including mice, would improve our understanding of the link between the cardiovascular events of awakening and thermoregulation. The thermoregulatory responses of the distal/hairless (tail) skin and the proximal/hairy (back) skin of rats are controlled by independent neural pathways that originate from the rostral medullary raphe.…”

“…3 indicate that the decrease in tail skin temperature upon awakening from NREM sleep was much smaller and shorter lasting at 29 C than at 21 C ambient temperature. 53 Conversely, work on mice indicated that the difference in ABP between NREM sleep and wakefulness was greater at 30 C than at 20 C ambient temperature. 42 Notably, the cardiovascular effects of changes in ambient temperature are even greater in mice than in rats, likely because mice have a higher ratio between body surface area and volume.…”