Influence of ambient temperature on the sleep-wakefulness cycle in the golden hamster

The sleep-wakefulness cycle (SWC) of euthermic golden hamsters (Mesocricetus auratus) after 5 weeks of warm (30 degrees C) and of cold (5 degrees C) acclimation, was recorded at ambient temperatures between 5 degrees and 35 degrees C. Significant influences both of acclimation and of recording temperature were detected. Amount of paradoxical sleep (P%) after warm acclimation was maximal at 30 degrees C decreasing markedly at lower and higher temperatures. Variations in P% were mainly consequent to alterations in the frequency of occurrence of paradoxical sleep (PS) episodes. After cold acclimation (CA) P% was maximal at 20 degrees C but no strong decreases occurred at lower temperatures. Influences of CA upon SWC were already detectable after 3 days of cold exposure. Significant individual differences as well as strong fluctuations in P% during CA occurred. Acute oscillations in abdominal temperature along the SWC were recorded. Reductions in abdominal temperature during PS episodes, in relation to ambient temperature and to the length of the episode tended to occur.