Pattern of REM sleep occurrence in continuous darkness following the exposure to low ambient temperature in the rat

The occurrence of REM sleep episodes, separated by intervals > 3 min (singl e episodes) and less than or equal to 3 min (sequential episodes), was dete rmined in the rat during the recovery (ambient temperature (Ta) 23 degreesC , L period of the LD [12 h:12 h]-cycle), which followed the exposure to low Ta (0 and - 10 degreesC) during the D period of the previous LD-cycle, eit her in normal light (DL) or in continuous darkness (DD). Both exposures wer e characterized by an almost complete disappearance of REM sleep, whilst th e recoveries showed an increase in the amount of REM sleep in the form of s equential episodes, which in DD was particularly prominent and concomitant with a decrease in the amount of REM sleep in the form of single episodes. The initial 2 h-rate of REM sleep occurrence was lower following the exposu re to Ta - 10 degreesC, than to Ta 0 degreesC. In DD, such an effect was du e to the large reduction in the occurrence of sequential REM sleep episodes . A functional correlate of this finding is that the accumulation capacity of a second messenger (cAMP) was found to be lower at the end of the exposu re to Ta - 10 degreesC, with respect to both the control (Ta 23 degreesC) a nd the end of exposure to Ta 0 degreesC, in the preoptic-anterior hypothala mus, but not in the cerebral cortex. (C) 2001 Elsevier Science B.V. All rig hts reserved.