Change of phosphotyrosine immunoreactivity on microglia in the rat substantia nigra following striatal ischemic injury.

Using immunohistochemistry, we investigated changes in phosphotyrosine (P-Tyr) immunoreactivity on the microglia of the rat substantia nigra (SN) following striatal ischemic injury produced by transient middle cerebral artery (MCA) occlusion. Anterograde axonal degeneration in the SN due to striatal ischemic injury was detected by depletion of calcineurin immunoreactivity in that region from 1 day after operation. From 3 days to 1 month (the longest period examined in this study) after MCA occlusion, there was a significant increase in P-Tyr immunoreactivity in the SN ipsilateral to the MCA occlusion. Also, light microscopic observation showed that the microglia exhibited an increased immunoreactivity for P-Tyr and characteristic morphological changes in the ipsilateral SN. The present results indicate that a signal transducing cascade(s) associated with tyrosine phosphorylation may be involved in the activation of the microglia in the SN responding to anterograde degeneration of the striatonigral pathway.