EFFECT OF INTERLEUKIN-1-BETA ON EEG POWER-DENSITY DURING SLEEP DEPENDS ON CIRCADIAN PHASE

The cytokine interleukin (IL)-1 is a key mediator of the somnogenic re sponse to immune challenge. In this vehicle-controlled study we evalua ted circadian interference with the sleep-promoting effects of IL-1 be ta. In two randomized experiments, rats mere injected intracerebrovent ricularly with 5 ng IL-1 beta either at the beginning of the rest phas e or at the beginning of the activity phase. Recordings were made duri ng the 24 h preceding the injections (baseline) and during the first 1 2 postinjection hours. To avoid masking effects of light, the rats wer e maintained under a skeleton photoperiod during recording. During bot h the rest and activity phase, IL-1 beta induced fever and initially p romoted non-rapid eye movement sleep (non-REMS) and suppressed rapid e ye movement sleep (REMS). The effect of IL-1 beta on the duration of n on-REMS and electroencephalogram (EEG) power densities within non-REMS was related to circadian phase. During the rest phase, IL-1 beta resu lted in a minor increase in non-REMS duration but a prominent enhancem ent in EEG activity in the delta (0.5-4 Hz) and most other frequency b ands. During the activity phase, IL-1 beta evoked a larger increase in the duration of non-REMS but hardly affected EEG activity within this state. Thus the effects of IL-1 beta on non-REMS are strongly influen ced by diurnal phase. The alterations in EEG power density are in cont rast to those elicited by sleep deprivation, which are largely indepen dent of time of day. It is concluded that IL-1 beta activates EEG regu latory mechanisms mediated by processes that depend on circadian phase .