Vigilance state episodes and cortical temperature in the Djungarian hamster: the influence of photoperiod and ambient temperature.

The electroencephalogram, electromyogram and cortical temperature (TCRT) were recorded in seven Djungarian hamsters adapted to a short photoperiod at 16 degrees C ambient temperature (TA; SP16). A baseline day was followed by 4 h sleep deprivation (SD) and 20 h recovery. The analysis included data obtained in earlier experiments at 22 degrees C TA in a long (LP22) and short photoperiod (SP22). In all three conditions the changes in TCRT during vigilance state episodes were a function of episode duration and, for waking and non-rapid eye movement (NREM) sleep, of TCRT at episode onset. The increase in TCRT during REM sleep became progressively larger from LP22 to SP22 to SP16. After SD the mean TCRT decreased below baseline in the LP22 and stayed above baseline in the SP22. This difference in the effect of SD on TCRT was reflected in its increase during REM sleep, which was attenuated during recovery in LP22, but was enhanced in SP22. The time course of TCRT during NREM sleep or waking episodes was unaffected by SD. Therefore, the overall difference in TCRT between baseline and recovery in the LP22 and SP22 is due to changes in the increase in TCRT during REM sleep.