Effects of elevated ambient temperatures on the sleep-waking activity of rats with impaired warm reception.

The sleep-waking activities of intact and of capsaicin-desensitized rats (animals with damaged peripheral and central warm receptors) were studied at room temperature and at the warm ambient temperatures of 32 and 34 degrees C. At 32 degrees C, the time spent in sleep increased significantly in the desensitized animals, while a decrease in the amount of deep slow wave sleep was found in the controls. At 34 degrees C, the amount of the sleep-waking stages returned to the levels observed at room temperature in the desensitized rats. A further decrease in sleep and a significantly increased wakefulness was found in the controls. At both warm ambient temperatures, the body temperature of the desensitized rats was significantly higher than that of the controls. We suggest that warm environments exert a dual effect on the sleep-waking activity. The activating effect abolished by desensitization seems to be in connection with capsaicin-sensitive thermoreceptors, while the deactivation brought about by heat is not influenced by capsaicin.