Induction of pro-inflammatory cytokine mRNAs in the brain after peripheral injection of subseptic doses of lipopolysaccharide in the rat.

Abstract Although it is generally accepted that pro-inflammatory cytokines produced by cells of the central nervous system play important roles in the communication between the central nervous system and the immune system during sepsis, it is not clear whether these cytokines are produced in the brain under subseptic conditions. In this study, we used in situ hybridization to examine the mRNA expression of the pro-inflammatory cytokines IL-1β and TNFα in the brains of rats 2 and 12 h after they were challenged by peripheral injections of lipopolysaccharide (LPS) ranging from 0.01 to 1000 μg/kg. Unlike septic doses of LPS (>500 μg/kg), which induce global expression of pro-inflammatory cytokines in the brain, subseptic doses of LPS (0.01–10 μg/kg) induced IL-1β and TNFα mRNA expression only in the choroid plexus, the circumventricular organs, and meninges. The expression of the cytokine-responsive immediate early gene IκBα was induced in the brain after doses of LPS as low as 0.1 μg/kg. IκBα mRNA expression was confined to sites where IL-1β and TNFα were expressed. These results indicate that the induction and action of pro-inflammatory cytokines during subseptic infection occur at the blood–brain barrier and at circumventricular organs, which may be sites for elaboration of signal molecules that communicate peripheral immune status to the brain.