Circadian, sleep and brain temperature rhythms in cats under sustained daily light-dark cycles and constant darkness.

In adult cats, sleep-wake states and brain temperatures were determined under experimental LD cycles and prolonged DD. Convincing rhythms had not previously been well-established for this animal. The present results demonstrated daily fluctuation in total sleep time (TST) and in brain temperature (Tb). These comprise predominantly nocturnal wakefulness and high temperatures but include a bi-modal component marking dawn and dusk peaks. In addition there are ultradian variations with a period of 2-4 hour superimposed on the circadian rhythm. The latter continued at the beginning of prolonged DD, but gradually diminished and disappeared after about ten days. The TST circadian rhythm diminished more quickly than the Tb rhythm. This result suggests that the former is coupled more strongly to the circadian oscillator than the latter, and that the brain temperature rhythm could not depend on the circadian rhythm of sleep-wakefulness. These results encourage use of cats in further chronobiological studies of sleep and other physiological rhythms.