Forced desynchrony of circadian rhythms of body temperature and activity in rats

The daily rhythm in body temperature is thought to be the result of the dir ect effects of activity and the effects of an endogenous circadian clock. F orced desynchrony (FD) is a tool used in human circadian rhythm research to disentangle endogenous and activity-related effects on daily rhythms. In t he present study, we applied an FD protocol to rats. We subjected 8 rats fo r 5 days to a 20h forced activity cycle consisting of 10h of forced wakeful ness and 10h for rest and sleep. The procedure aimed to introduce a 10h sle ep/ 10h wake cycle, which period was different from the endogenous circadia n (about 24h) rhythm. Of the variation in the raw body temperature data, 68 -77% could be explained by a summation of estimated endogenous circadian cy cle and forced activity cycle components of body temperature. Free-running circadian periods of body temperature during FD were similar to free-runnin g periods measured in constant conditions. The applied forced activity cycl e reduced clock-related circadian modulation of activity. This reduction of circadian modulation of activity did not affect body temperature. Also, th e effects of the forced activity on body temperature were remarkably small.