LIPOPOLYSACCHARIDE INCREASES EEG DELTA-ACTIVITY WITHIN NON-REM SLEEP AND DISRUPTS SLEEP CONTINUITY IN RATS

Activation of the immune system by microorganisms or specific microbial constituents promotes non-rapid-eye-movement (REM) sleep (non-REMS). In this study, we assessed the effects of lipopolysaccharide (LPS) on sleep duration, electroencephalogram (EEG) power spectra, and brain temperature (Tbr) in rats. Twenty-four hour recordings were made before and after intraperitoneal injection of vehicle or 30 or 100 mu g/kg LPS at lights on. During the first 12 h after administration of both doses of LPS, Tbr was elevated, REMS duration was reduced, and non-REMS duration was unchanged, whereas the non-REMS episodes were shortened. EEG activity within non-REMS from 0.5 to 7 Hz was enhanced during hours 3-12. During the second 12-h period, the number of non-REMS and REMS episodes and the total time in both states were increased. EEG activity within non-REMS was mainly reduced in the entire frequency range (0.5-25.5 Hz). The effects of LPS did not differ between the doses. The effects of LPS on EEG power spectra are similar to those observed after sleep deprivation, i.e., a physiological intensification of non-REMS, indicating that both manipulations may activate common sleep EEG regulatory mechanisms. However, the disruption of non-REMS continuity following LPS administration at light onset contrasts the changes induced by sleep deprivation and may reflect an effect of a systemic inflammatory response on sleep maintenance.