Hypoprolactinemic rats under conditions of constant darkness or constant light. Effects on the sleep-wake cycle, cerebral temperature and sulfatoxymelatonin levels

In genetic hypoprolactinemic rats under light-dark (LD) conditions, the cir cadian rhythms of slow-wave (SWS) and paradoxical (PS) sleep display an alt eration of their phase relationship. The aim of our study was to investigat e the effects of constant darkness (DD) or constant light (LL) on the daily distribution and amounts of sleep-wake stages, cerebral temperature and co ncentrations of the urinary melatonin metabolite, 6-sulfatoxymelatonin, in prolactin-deficient rats. After 3 weeks of DD, the SWS period was 24 h 8 +/ - 6 min and the acrophase occurred at 15:44 +/- 1.35, while for PS, the per iod was more stable than during LD (24 h 10 +/- 8 min vs. 24 h 55 +/- 43 mi n) and the acrophase occurred at 16:44 +/- 1:54. Under LL conditions, circa dian sleep rhythms persisted during the first 3 days, then completely disap peared during the third week, to be replaced by ultradian rhythms (period o f 4-6 h). Time-series analysis showed that the two sleep states became sync hronous as early as the second day under constant conditions; The total amo unt of PS was increased under both conditions (LL and DD) at the expense of duration of waking. Under LD and constant conditions, the pattern of chang es in cerebral temperature was similar to that for wakefulness (W). Sulfato xymelatonin was rhythmically secreted under both LD and DD conditions, wher eas, under LL conditions, its rhythm was abolished. The results show that, in IPL rats in the absence of a zeitgeber, the PS and SWS rhythms recover a synchronous phase relationship and PS amounts are increased. (C) 1999 Else vier Science B.V. All rights reserved.