Fig. 4

Cellular origin of U-fibers revealed with in utero electroporation. GFP was introduced into lower-layer neurons and upper-layer neurons using in utero electroporation at E31 (a-c) and E37 (d-f), respectively. Coronal sections were prepared at P16. a, d Lower magnification images of the coronal sections. The boxed areas were magnified and are shown in (b, c, e, f). b, e Higher magnification images of the cerebral cortex. c, f Higher magnification images of the white matter. At both E31 and E37, GFP-positive fibers were observed in the white matter immediately deep to the cerebral cortex (square brackets). Numbers indicate layers in the cerebral cortex. GM, gray matter; WM, white matter. Scale bars = 2 mm (a, d) and 300 μm (b, c, e and f)