Fig. 9. Cell migration defects in the forebrain of Robo1 knockout brains. (A) Quantification of the total number of calbindin labelled cells that entered the cortex of control and Robo1 knockout brains at E12.5 showed that the latter contained roughly twice as many cells (*P<0.001, Student's t-test; error bars represent s.e.m.). (B) Histogram depicts the average number of calbindin cells in a 200 µm wide radial strip of dorsomedial cortex (DMC) in control and Robo1 knockout brain sections at E18.5. More calbindin-positive cells were observed in the knockout cortex (*P<0.01, Student's t-test; error bars represent s.e.m.). (C) At E18.5, the average number of calbindin cells in rostral and middle regions (200 µm wide strip) of DMC is higher in Robo1 knockout brains compared with control (*P<0.01 for both rostral and middle regions, Student's t-test; error bars represent s.e.m.), whereas no difference was observed in caudal regions. Calbindin staining in representative coronal sections taken from rostral cortex at E12.5 (D,E) and middle (parietal) cortex at E18.5 (F-G') of control (D,F) and Robo1 knockout (E,G) mouse brains. The cortex of the knockout brains appeared to contain a greater number of calbindin-labelled cells. The arrows in F,G indicate the striatal region, shown at higher magnification at F' and G', which is populated by calbindin cells in Robo1 knockout brains (G,G'), but not in controls (F,F'). Scale bars: in E, 200 µm in D,E; in G', 400 µm in F,G and 200 µm in F',G'.