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

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 (Tbr) responses of rabbits induced by mild increases in ambient temperature (Tamb) were determined. Each rabbit was recorded under three conditions: (1) 21 degrees C Tamb plus pyrogen-free saline (PFS); (2) 27 degrees C Tamb plus PFS; (3) 27 degrees C Tamb plus the IL-1RF. The higher Tamb significantly increased Tbr during the warming period; this effect was attenuated by pretreatment with the IL-1RF. The higher Tamb 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-1 RF treatment, were not significantly different from those obtained from PFS-treated animals at 27 degrees C Tamb. The ability of the IL-1 RF to block Tamb-induced changes in Tbr and the failure of the IL-1RF to block Tamb-induced NREMS responses is different from previous results which indicated that a tumor necrosis factor receptor fragment (TNF-RF) inhibits warm Tamb-induced sleep but not Tbr responses. Thus, brain IL-1 and TNF sleep and thermo mechanisms are, in part, different.