Microglial response to transient focal cerebral ischemia: an immunocytochemical study on the rat cerebral cortex using anti-phosphotyrosine antibody.

Microglial response to transient focal ischemia was examined using an immunohistochemical method with a monoclonal antibody to phosphotyrosine (P-Tyr). For this purpose, a rat model of reversible middle cerebral artery occlusion for 1 h was used. Compared with results in the noninsulted hemisphere, there was a significant increase in P-Tyr immunolabeling of the microglia in the insulted cerebral cortex 3 h postreperfusion. This microglial reaction progressed up to 24 h after ischemic insult. In the affected cerebral cortex, morphological changes of the microglial positive for P-Tyr were also observed, with shortened and thickened processes, enlarged cell bodies, and ameboid features. Cell density analysis did not show any apparent change in number of P-Tyr-positive microglia in the insulted cortex at 6, 12, and 24 h after reperfusion, suggesting that the cells with increased P-Tyr immunoreactivity were resident microglia. The present findings suggest that signal transduction mediated by tyrosine phosphorylation is involved in the microglial response to ischemic injury in the rat cerebral cortex.