Expression of Tumor Necrosis Factor-alpha, Interleukin-1beta and Inducible Nitric Oxide Synthase after Stereotaxic Injection of Lipopolysaccharide in Rat Hippocampus

ABSTRACT

BACKGROUND: Brain inducible nitric oxide synthase (iNOS) might be detectable in several pathologic conditions, and it is thought to play an important role in their pathophysiology. Tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta are believed to be essential factors of iNOS induction of the brain. METHODS: After intrahippocampal stereotaxic injection of lipopoly-saccharide (LPS), the rat brains were removed at 6, 12 and 24 h. The rat brain tissues were examined to clarify the expression patterns of TNF-alpha, IL-1beta and iNOS. RESULTS: The inflammatory cells which were stained with anti-TNF-alpha antibody, appeared in 6 h and increased for 24 h after LPS injection. The iNOS positive cells appeared after 12 h of LPS injection. A semiquantitative analysis of reverse transcription-polymerase chain reaction (RT-PCR) revealed that the TNF-alpha and IL-1beta mRNA arose at 1 h, peaked at 6 h and then declined until 48 h after LPS injection. The iNOS mRNA arose after 6 h, peaked at 12 h, and declined until 48 h after LPS injection. CONCLUSIONS: We conclude that the induction of inflammatory events by intrahippocampal injection of LPS activates TNF-alpha and IL-1beta secretion, and this is followed by an induction of iNOS expression. TNF-alpha and IL-1beta seem to be related with iNOS expression in brain inflammation.