Reduced number of microglia and apoptotic cells in early and middle stages of corticogenesis in Robo1−/− mice. A–F, Immunohistochemistry in the cortices of Robo1+/+ (A, C, E) and Robo1−/− (B, D, F) mice for Iba1 (green) and CC3 (red) at E12.5 (A, B), E13.5 (C, D), and E15.5 (E, F). G, H, Counts revealed significantly reduced numbers of Iba1- (G) and CC3-positive (H) cells in the cortices of Robo1−/− at E13.5–E15.5 compared with control littermates; *p < 0.04, **p < 0.004.