Abstract
Circadian sleep-wake and temperature rhythm of the domestic cat were examined by EEG polygraphic method under constant light (LL) with different light intensities and under shifted light-dark (LD) conditions. Under LD 12 : 12, a total sleep time (TST), as an index of sleep-wake rhythm, demonstrated a nocturnal bi-modal circadian rhythm, which was also shown in brain temperature (Tb), being higher in the dark period. These circadian rhythms were entrained to the phase shift of LD period with a short term transition period. The free-running rhythm was observed at the beginning of both bright and dim LL. Under bright LL (65 lux), the freerunning circadian rhythms diminished in amplitude and disappeared shortly after the beginning of the LL condition. Yet it persisted longer in dim LL (1.0 lux) for approximately 2 weeks. Tb rhythm also showed the similar alteration. From these and our previous report of constant darkness (DD), we discussed that the cats have circadian rhythms driven by endogenous oscillators and their appearances fairly depend on the external timing cue. Further, Tb altered slower than TST in any lighting condition, suggesting that Tb rhythm does not depend on TST rhythm.
