Simultaneous determination of circadian rhythms of locomotor activity and body temperature in the rat.

Stimultaneous determination of the circadian rhythms of locomotor activity and body temperature was carried out in the rat. Deep body temperature was monitored continuously using a telemetric device. The circadian rhythm of locomotor activity was characterized by clustering of several bursts of activity during the dark period. The circadian rhythm of body temperature was also characterized by bursts of small fluctuations which were well correlated with those of locomotor activity. Correlation between the two functions was such that the regression line expressing body temperature as a function of locomotor activity had approximately the same slope for dark and light periods, but a body temperature for a given amount of locomotor activity was significantly higher during the dark period than during the light one. After a prolonged exposure to constant light, the circadian rhythm disappeared in both functions. Both showed bursts of fluctuations which were correlated with each other. These results indicate that the bursts of body temperature increment were dependent on those of the locomotor activity. However, manifestation of the circadian rhythm per se of body temperature could not be explained as resulting exclusively from the circadian fluctuation of locomotor activity.