Dexamethasone and nitric oxide synthase gene expression in brain

Systemic administration of lipopolysaccharide (LPS), which causes endotoxemia and systemic inflammation, has been reported to induce expression of the gene for type II inducible nitric oxide synthase (iNOS) in peripheral organs. This study was carried out to examine whether intraperitoneally injected LPS elicits the expression of iNOS messenger ribonucleic acid (mRNA) in the rat brain. We also investigated whether intraperitoneal treatment with dexamethasone (DEX) prevents this induction. To determine levels of iNOS mRNA, a quantitative reverse transcription-polymerase chain reaction (RT-PCR) method was employed. Treatment with LPS induced the expression of iNOS mRNA in various brain regions, accounting for approximately 1 x 10⁵ to 4 x 10⁵ molecules per μg of poly A⁺ RNA, and these inductions were markedly suppressed by DEX. The results suggest that, during systemic inflammation, iNOS mRNA induction occurs in brain through a DEX-sensitive mechanism.