Brain temperature changes coupled to sleep states persist during interleukin 1-enhanced sleep

The effects of human interleukin 1 (IL 1) on the architecture of rabbit sleep-wake cycles and brain temperature (Tbr) changes coupled to states of vigilance were examined. Cerebral intraventricular infusion of IL 1 induced increased slow-wave sleep (SWS), increased electroencephalographic slow-wave (0.5-4 Hz) amplitudes, and fever. Heat-inactivated IL 1 failed to elicit these responses. IL 1 also significantly inhibited rapid-eye-movement (REM) sleep; however, inactivated IL 1 also reduced REM sleep; thus some of the IL 1-induced REM reduction may be related to the infusion process. The duration and number of sleep cycles (REM-to-REM interval) were unaffected by IL 1. Similarly, Tbr changes that normally occur during the transition from one arousal state to another remained unchanged after IL 1 infusion, even though rabbits were simultaneously febrile. We conclude that IL 1 selectively enhances SWS while leaving sleep cycles and Tbr changes coupled to states of vigilance undisturbed.