Confocal reconstruction of immunofluorescent staining for the axonal marker L1 on 100-μm–thick horizontal sections taken at 400-μm intervals of a wild-type (A–D) and a Netrin-1 knockout (E–H) E17.5 mouse embryo. L1 stains both TC axons as well as other axon tracts such as the corpus callosum (CC), but not other corticofugal axons ([25]; A. Powell and F. Polleux, unpublished data). Red arrowheads indicate the internal capsule, and green arrows indicate the thalamic peduncle. CC and anterior commissure projection defects can be observed in the Netrin-1 knockout embryos as described previously [27]. However, no gross TC axon pathfinding defect can be detected at this level. VTh, ventral thalamus. Scale bar represents 1 mm. (1.39 MB TIF)