THE INFLUENCE OF A HEAVY THERMAL LOAD ON REM-SLEEP IN THE RAT

This study was carried out in order to further test the hypothesis tha t the occurrence of REM sleep in the rat in the form of episodes separ ated by long intervals (single REM sleep episodes) and by short interv als (sequential REM sleep episodes) is differently influenced by chang es in both sleep and ambient related processes. Rats were studied duri ng the exposure to Ta -10 degrees C for 24 or 48 h and during a 12 h r ecovery period at laboratory Ta (23 degrees C) following either the fi rst or the second 24 h of cold exposure. The exposure to such a low Ta induced an almost complete abolition of REM sleep which was followed, during recovery, by a marked REM sleep rebound. However, in spite of the larger REM sleep deprivation, the REM sleep rebound was weaker fol lowing the 48 h-exposure than that following the exposure for 24 h. Th e increase in the amount of REM sleep during the recovery period was d ue to an increase in the amount of that occurring in the form of seque ntial episodes, whilst that in the form of single episodes did not cha nge with respect to control levels. However, the occurrence of REM sle ep in the form of sequential episodes was partially impaired during th e REM sleep rebound observed in the recovery period following the 48 h -exposure. These results would suggest that the homeostatic regulation of physiological variables may conflict with that of REM sleep occurr ence and that the degree of such a contrast is indicated, at low Ta, b y the amount of REM sleep in the form of single episodes and, during t he following recovery, by the amount of REM sleep in the form of seque ntial episodes. (C) 1998 Elsevier Science B.V.