Lipopolysaccharide effects on neuronal activity in rat basal forebrain andhypothalamus during sleep and waking

Peripheral administration of lipopolysaccharide (LPS) is associated with al terations in sleep and the electroencephalogram. To evaluate potential neur onal mechanisms for the somnogenic effects of LPS administration, we used u nanesthetized rats to survey the firing patterns of neurons in various regi ons of rat basal forebrain (BF) and hypothalamus during spontaneous sleep a nd waking and during the epochs of sleep and waking that occurred after the intraperitoneal administration of LPS. In the brain regions studied, LPS a dministration was associated with altered firing rates in 39% of the neuron s examined. A larger proportion of LPS-responsive units showed vigilance-re lated alterations in firing rates compared with nonresponsive units. Approx imately equal proportions of LPS-responsive neurons showed increased and de creased firing rates after LPS administration, with some units in the later al preoptic area of the hypothalamus showing particularly robust increases. These findings are consistent with other studies showing vigilance-related changes in neuronal activity in various regions of BF and hypothalamus and further demonstrate that peripheral LPS administration alters neuronal fir ing rates in these structures during both sleep and waking.