Lipopolysaccharide causes deficits in spatial learning in the watermaze but not in BDNF expression in the rat dentate gyrus

We investigated the effects of a single injection and a daily injection of lipopolysaccharide (LPS) on spatial learning and brain-derived neurotrophic factor (BDNF) expression in the rat dentate gyrus. LPS is derived from the cell wall of Gram-negative bacteria and is a potent endotoxin that causes the release of cytokines such as interleukin-1 and tumour necrosis factor. LPS is thought to activate both the neuroimmune and neuroendocrine systems; it also blocks long-term potentiation in the hippocampus. Here, we examine d the effects of LPS on a form of hippocampal-dependent learning-spatial le arning in the water maze. Rats were injected with LPS intraperitoneally (10 0 mug/kg) and trained in the water maze. The first group of rats were injec ted on day 1 of training, 4 h prior to learning the water maze task. Groups 2 and 3 were injected daily, again 4 h prior to the water-maze task; group 2 with LPS and group 3 with saline. A number of behavioural variables were recorded by a computerised tracking system for each trial. The behavioural . results showed a single injection of LPS (group 1) impaired escape latenc y in both the acquisition and retention phases of the study, whereas a dail y injection of LPS did not significantly impair acquisition or retention. B DNF expression was analysed in the dentate gyrus of all animals. No signifi cant differences in BDNF expression were found between the three groups. (C ) 2001 Elsevier Science BY. All rights reserved.