Dexamethasone Modulates Lipopolysaccharide-Induced Expression of Proinflammatory Cytokines in Rat Hippocampus

The effects of intrahippocampal injection of dexamethasone on the expression of proinflammatory cytokines in the dorsal and ventral parts of the hippocampus were studied. We evaluated mRNA expression of interleukin-1b (Il1b), interleukin-6 (Il6), and tumor necrosis factor (Tnf) 3 days after injection of dexamethasone (DEX), bacterial lipopolysaccharide (LPS), and their combination in the dorsal hippocampus. Phosphate buffered saline administered to control animals did not affect the expression of the cytokines studied. In the dorsal hippocampus, LPS induced a significant increase in the level of Tnf and a trend to an increase in Il1b and Il6 mRNA expression. DEX alone induced a trend to an increase in the expression of Il1b. A DEX + LPS combination also tended to increase Il1b expression and a significant increase in Tnf. In addition, we observed a considerable decrease in Il6 mRNA level after DEX + LPS as compared to LPS group. In the ventral hippocampus, we observed a trend to an increase in the level of Il1b after DEX + LPS and a trend to an increase in Tnf after DEX alone. The data suggest that DEX by itself is able to induce weak neuroinflammation in the hippocampal tissue, and, when applied during LPS-induced neuroinflammation, evokes differential effects on proinflammatory cytokines expression indicating a complex DEX-mediated regulation of cytokine balance in the hippocampus.