An interleukin-1 receptor fragment blocks ambient temperature-induced increases in brain temperature but not sleep in rabbits

Abstract

The effects of intracerebroventricular injection (i.c.v.) of an interleukin-1 (IL-1) inhibitor, a soluble IL-1 receptor fragment (IL-1RF), on sleep and brain temperature (T br) responses of rabbits induced by mild increases in ambient temperature (T amb) were determined. Each rabbit was recorded under three conditions: (1) 21°C T amb plus pyrogen-free saline (PFS); (2) 27°C T amb plus PFS; (3) 27°C T amb plus the IL-1RF. The higher T amb significantly increased T br during the warming period; this effect was attenuated by pretreatment with the IL-1RF. The higher T amb alone (6 h exposure) significantly increased non-rapid eye movement sleep (NREMS) across the 23-h recording period. However, during the 6-h warming period NREMS values, obtained after IL-1RF treatment, were not significantly different from those obtained from PFS-treated animals at 27°C T amb. The ability of the IL-1RF to block T amb-induced changes in T br and the failure of the IL-1RF to block T amb-induced NREMS responses is different from previous results which indicated that a tumor necrosis factor receptor fragment (TNF-RF) inhibits warm T amb-induced sleep but not T br responses. Thus, brain IL-1 and TNF sleep and thermo mechanisms are, in part, different.