Behavioural pharmacologyTime course of the effects of lipopolysaccharide on prepulse inhibition and brain nitrite content in mice

The systemic administration of lipopolysaccharide (LPS) induces time-dependent behavioral alterations, which are related to sickness behavior and depression. The time-course effects of LPS on prepulse inhibition (PPI) remain unknown. Furthermore, the time-dependent effects of LPS on central nitrite content had not been investigated. Therefore, we studied alterations induced by single LPS (0.5 mg/kg, i.p.) administration to mice on parameters, such as PPI, depressive- and anxiety-like behaviors, working memory, locomotor activity and motor coordination, 1.5 and 24 h post-LPS administration. IL-1β and TNFα in the blood and brain as well as brain nitrite levels were evaluated in the prefrontal cortex (PFC), hippocampus (HC) and striatum (ST). An overall hypolocomotion was observed 1.5 h post-LPS, along with depressive-like behaviors and deficits in working memory. Increments in IL-1β content in plasma and PFC, TNFα in plasma and decreases in nitrite levels in the ST and PFC were also verified. Twenty-four hours post-LPS treatment, depressive-like behaviors and working memory deficits persisted, while PPI levels significantly reduced along with increases in IL-1β content in the PFC and a decrease in nitrite levels in the HC, ST and PFC. Our data demonstrate that a delayed increase (i.e., 24 h post-LPS) in PPI levels ensue, which may be useful behavioral parameter for LPS-induced depression. A decrease in nitrergic neurotransmission was associated with these behavioral findings.