Interleukin-1 induces changes in sleep, brain temperature, and serotonergic metabolism

Simultaneous recordings of sleep-wake activity and of serotonergic metabolism in the medial preoptic area were performed in freely moving rats after the intracerebroventricular injection of interleukin-1 (IL-1) at dark onset. IL-1 (2.5 ng) induced a biphasic increase in slow-wave sleep and an early increase in serotonergic metabolism starting 30 min postinjection. Phasic, state-specific changes (which have been described in spontaneous sleep) were superimposed on this tonic, overall increase in serotonergic metabolism. IL-1 (25 ng) induced an increase in wakefulness and a delayed increase in serotonergic metabolism, which started 120 min postinjection. This suggests that the time course of the serotonergic activation could play a role in mediating IL-1 effects on sleep. Both doses of IL-1 induced a similar and significant increase in brain cortical temperature, suggesting that IL-1 effects on sleep are not a secondary effect of the increase in cortical temperature and that the serotonergic system is not involved in IL-1-induced fever.