Fig. 5

Development of U-fibers revealed with in utero electroporation. GFP was introduced into cortical neurons using in utero electroporation at E31, and coronal sections were prepared at P0 (a), P6 (b) and P16 (c). Lower magnification images are shown on the left. Higher magnification images of the boxed areas are shown on the right. Note that GFP-positive fibers in the white matter immediately deep to the cerebral cortex were rarely observed at P0 and increased between P0 and P16 (square bracket). In contrast, abundant GFP-positive fibers in the deep white matter were clearly visible even at P0 (asterisks). d The ratios of GFP signal intensities in the U-fiber regions relative to those in the deep white matter. The ratios of GFP signals in the U-fiber regions to those in the deep white matter significantly increased between P1 and P16. Bars present mean ± SD. **p < 0.01; Welch’s t-test; n = 3 animals for each condition. GM, gray matter; WM, white matter. Scale bars = 2 mm (left) and 300 μm (right)