Figure 2. Aged rats present a different microglial phenotype than young adult rats following MCAO.

At 24 h following MCAO, microglia in the ipsilateral hemisphere of young adult and aged rats exhibited different phenotypes as revealed by Iba-1 immunohistochemistry. In the contralateral cortex of young adult rats, microglia expressed the resting or ramified phenotype with many long, thin, and highly branched processes extending into three-dimensional cortical parenchyma (A). In the ipsilateral cortex of young adult rats, microglial processes appeared swollen and contained clumps of phagocytosed material (B). In the contralateral cortex of aged rats, microglia appeared in the resting phenotype (C). In aged rats, MCAO resulted in the transformation of microglia into the fully phagocytic phenotype: round or oval cell soma with few processes extending from the cell body (D). Arrows denote different microglial phenotypes in young and old rats following MCAO. Bar = 50 μ.