Abstract
Previously we reported that endotoxin-dependent induction of tumor necrosis factor alpha (TNFexpression in microglia was significantly suppressed by the superoxide anion scavenger N-acetyl cysteine (NAC), and that microglia induced TNF in response to a superoxide anion donor 3-(4-morpholinyl)sydnonimine (SIN-1) in vitro. Those findings strongly suggested that superoxide anion is associated with the induction of TNF in microglia. However, whether TNF is actually induced in microglia in vivo remains to be determined. In the present study, we confirmed the ability of microglia to induce TNF in vitro and examined the effects of SIN-1 on microglial induction of TNF in vivo. The accumulation of SIN-1 solution in rat cerebral cortex led to the induction of TNF on the ipsilateral, but not the contralateral side. The levels of TNF in the ipsilateral cortex peaked at 6-12 h post-accumulation. Immunohistochemical study revealed that anti-TNF antibody-positive cells in the SIN-1-injected region were mainly anti-ionized Ca 2+ binding adapter molecule-1 (Iba-1) antibody-positive, suggesting that microglia are a major cell type for inducing TNF. On the other hand, interleukin 1beta (IL-1) and IL-6 were not detected in the SIN-1-injected cortex. Together, these results indicate that microglia induced TNF in vivo in response to superoxide anion.