Peripheral lipopolysaccharide stimulation induces interleukin-1β messenger RNA in rat brain microglial cells

The inflammatory cytokine interleukin-1 acts as an endogenous pyrogenin organisms affected by infectious diseases and has been shown to influence the activity of the central nervous system. Using in situ hybridization histochemistry, we have examined the cellular source of interleukin-1β in rat brain after peripheral stimulation with the bacterial lipopolysaccharide, a potent inducer of interleukin-1. Whereas no interleukin-1β messenger RNA could be detected in brains in unstimulated rats, lipopolysaccharide induced a transient, high and widespread expression of interleukin-1β messenger RNA in the entire brain. The highest levels of interleukin-1β messenger RNA were observed 6-8 h after stimulation with lipopolysaccharide. Using a combination of non-radioactive in situ hybridization and immunocytochemistry with the microglial-specific antibody OX-42, interleukin-1β messenger RNA-positive cells could be identified as microglia. We conclude that brain microglial cells are the major source of interleukin-1β messenger RNA after peripheral administration of lipopolysaccharide