Exogenous activated microglial transplantation into the ipsilateral SN accelerated the DA neuronal cell death. (A) TH immunohistochemistry in the contralateral (Cont) and ipsilateral SN at 7 days after vehicle (Sham) or activated microglia (aMG) implantation. Scale bar represents 300 μm. (B) Graph representing the relative percentage of the number of nigral TH-ir DA neurons. For quantitative analysis, every fourth section among 40 μm serial brain sections was immunohistochemically stained with antibodies against TH, and the number of TH-ir neurons were counted using a stereological technique in the whole SN. The percentage was analyzed by dividing the total number of TH-ir neurons in the ipsilateral SN by that of the contralateral SN. Significant reduction in the number of SN TH-ir neurons of the aMG group, compared with that of the vehicle treated group, indicates that transplantation of exogenous activated microglia into the ipsilateral SN accelerates the axotomized DA neuronal cell death. Values were expressed as the mean ± S.E.M. (n = 6). *P < 0.05 compared with value from sham control (ANOVA with post hoc Student’s t test).