Sleep deprivation in the rat: XX. Differences in wake and sleep temperatures during recovery

We examined the relationship between wake and sleep peritoneal temperature (T(ip)) during recovery from short-term (five rats, 5 days of deprivation) and long-term (nine rats, 14-21 days) total sleep deprivation (TSD). Mammalian body temperature normally declines in the passage from wakefulness to sleep. Recovery from TSD featured reductions of the typical wake-sleep T(ip) differences. Previous studies from our laboratory have shown that chronic TSD in the rat produces a progressive rise in energy production and an initial rise in wake T(ip), followed by a later fall in T(ip) to below baseline that becomes more acute as death becomes imminent. During recovery from both short-term TSD (wherein pre-recovery wake T(ip) was still above baseline) and long-term TSD (wherein pre-recovery wake T(ip) had fallen to below baseline), wake T(ip) and energy production quickly returned towards baseline. On the first recovery day, both short- and long-term TSD rats showed mean non-rapid eye movement (NREM) and paradoxical sleep (PS) T(ip) values that were slightly, although not significantly, above mean wake T(ip). In short-term TSD rats, wake-NREM and wake-PS T(ip) differences were reduced from baseline significantly (p < 0.0025) on the first recovery day and nonsignificantly on the remaining three recovery days. In long-term TSD rats, wake-NREM and wake-PS T(ip) differences were significantly (p < 0.001) reduced from baseline on the first four recovery day block. On the last four recovery day block, wake-sleep T(ip) differences tended to return toward baseline. Hypothalamic wake-sleep temperature differences in long-term TSD rats showed similar reductions during recovery. The reduction of wake-sleep temperature differences in recovery does not support either energy reduction or cooling functions for sleep.