Interleukin 1 alters rat sleep: temporal and dose-related effects

Rats received various doses of interleukin 1 (IL-1) (range, 0.5-25.0 ng) or pyrogen-free saline intracerebroventricularly during the rest (light) and the active (dark) cycles of the day, and sleep-wake activity and brain temperature were determined for 6 h. Low doses of IL-1 (0.5 ng at night, 2.5 ng during the day) increased both the duration of non-rapid-eye-movement sleep (NREMS) and electroencephalogram (EEG) slow-wave activity during NREMS episodes. Increasing doses of IL-1 had divergent effects on NREMS duration and EEG slow-wave activity, and the direction of the changes depended on the diurnal cycle. Thus NREMS duration was promoted at night and EEG slow-wave amplitudes during the day, whereas NREMS duration during the day and EEG slow-wave amplitudes at night were suppressed after higher doses of IL-1. High doses of IL-1 also induced decreases in rapid-eye-movement sleep during both phases of the day. Each dose of IL-1 that promoted NREMS also tended to increase brain temperature. These results demonstrate that IL-1 promotes NREMS in the rat. However, unlike previously reported findings in rabbits, the circadian rhythm of sleep regulation strongly interferes with the sleep-promoting activity of IL-1 in rats.