Body temperature and sleep in intact and ovariectomized female rats

The present study examined intact and ovariectomized adult rats to assess the effects of removal of sex hormones on body temperature (Tb) and sleep. Subjects were 12 female rats, aged 5-8 mo, half of which were bilaterally ovariectomized (OVX). Sleep or waking and Tb were recorded under a 12:12-h light-dark cycle. There was a strong coupling between level of Tb and the three conditions of waking, slow-wave sleep (SWS), and rapid eye movement sleep (REMS): Tb was significantly positively correlated with waking and significantly negatively correlated with SWS and REMS. These correlations were even higher in OVX rats. In the light, OVX rats had more SWS and stayed awake less than did the intact rats. OVX rats had more REMS than did intact rats in both light and dark. Mean Tb and daily Tb amplitude were the same in both groups. These results suggest that ovariectomy increases and, by extension, gonadal steroids decrease, the coupling between Tb and sleep.