All but two D1 and D2 facial whiskers were trimmed, as shown in the schematic drawing, and cortical d4EGFP expression was analyzed 24 hours later. Anti-GFP immunostaining visualized with FITC-conjugated secondary antibodies revealed prominent induction of d4EGFP expression in the D1 and D2 columns in the trimmed, but not in the control untrimmed, animal. The scale bar = 1 mm. Cytochrome oxidase (co) staining (left in two panels) was used to visualize individual columns in the barrel cortex, which are organized in rows A though D; position of the D1 and D2 columns are marked in the image.