メスラットの視床下部室傍核と海馬歯状回のc-Fos発現に及ぼす細菌性内毒素の影響

LPS, a bacterial endotoxin, is known to affect various functions of the central nervous system, including stimulation of the hypothalamo-pituitary-adorenal axis. We have previously reported that LPS increased immunoreactivity of corticotropin-releasing hormone (CRH) in the PVN in association with inhibition of gonadotropin secretion. LPS also produces deficits in learning and memory. In the present study, we examined whether LPS treatment may differentially influence c-Fos expression in the PVN and the hippocampus which is believed to be crucial for learning and memory. We also examined whether the LPS-induced change in c-Fos expression in the hippocampus may be mediated by the LPS-induced release of glucocorticoid. Ovariectomized rats were treated with an intravenous (iv) injection of LPS (40 μg/kg) or saline. Two hours after the injection, the brains were fixed and immunohistochemistry against c-Fos was performed. In the PVN, LPS treatment induced a dramatic increase in the number of c-Fos immunoreactive cells as reported previously. By contrast, LPS treatment significantly decreased c-Fos expression in the DG. In the CA3, there was no difference in c-Fos immunoreactive cell number between LPS treated rats and their controls. Pretreatment with metyrapone (75 mg/kg), an inhibitor of glucocorticoid synthesis, had no effect on LPS induced decline in c-Fos expression in the DG. These results show that LPS treatment selectively decreases c-Fos expression in the DG in a glucocorticoid independent manner. [J Physiol Sci. 2007;57 Suppl:S174]