Mac-1 immunoreactivity in the hippocampus. The age, phenotype and treatment of the animals are indicated in the upper right corners. T-: control and T+: TGF-β1 mice; PIO: treated with pioglitazone for 2 months; 4 m and 9 m: 4 and 9-month-old mice. Each row shows images taken at increasing magnifications (bars are 50 μM). Microglia cells were "activated" in TGF-β1 mice at 4 months, revealed by increased Mac-1 immunoreactivity, retraction of processes, and increased soma size (compare B to A and E to D). Microglia activation decreased with age (compare C to B) and with PIO (compare F to E). G-I are high magnification images of single microglia cells. The insets illustrate the soma surfaces as determined for the quantification of microglia activation. DG: dentate gyrus; HiF: hippocampal fissure.