Effects of alpha-MSH on sleep, behavior, and brain temperature: interactions with IL 1

Changes in rabbit sleep-wake activity, brain temperature (Tbr), and behavior were studied after intracerebroventricular injections of a putative endogenous antipyretic, alpha-melanocyte-stimulating hormone (alpha-MSH), and of an endogenous pyrogen, interleukin 1 (IL 1-beta). alpha-MSH (0.1-50.0 micrograms) dose dependently increased wakefulness (W) and decreased Tbr, non-rapid-eye-movement sleep (NREMS), and rapid-eye-movement sleep (REMS). NREMS was more sensitive than REMS to the suppressive effects of low alpha-MSH doses. EEG slow-wave activity in NREMS decreased after alpha-MSH treatment. alpha-MSH elicited stretching, yawning, and signs of sexual excitation. IL 1 (20 and 40 ng) induced fever and excess NREMS. alpha-MSH administered 30 min after IL 1 (40 or 20 ng IL 1 + 0.1, 0.5, or 5.0 micrograms alpha-MSH) significantly attenuated IL 1-induced fever and excess NREMS. IL 1 failed to alter the behavioral effects of alpha-MSH. Despite alpha-MSHs effect on rabbit behavior, total motor activity time did not increase, indicating that increased W after alpha-MSH cannot be attributed to behavioral activation. These results suggest that, besides acting as an endogenous antipyretic, alpha-MSH might be involved in regulation of IL 1-induced sleep.