Fig. 7. A caudal shift of thalamic axons is detected inside the internal capsule of Ebf1^-/- embryos. Horizontal hemisections of E16.5 wild-type (left) and Ebf1^-/- mutant (right) brains in which one crystal of DiI and one of DiA were introduced in: (1) the frontal and parietal neocortex (A-C); (2) the occipital and parietal neocortex (D-F); and (3) in two putative thalamic nuclei — the dorsal lateral geniculate nucleus (dLGN) and ventrobasal complex (VB) (G-K). Schematic diagrams show the locations of DiI and DiA injection sites (A,D,G). (A-F) Horizontal sections of either frontal and parietal neocortex double injections (A-C) or occipital and parietal neocortex double injections (D-F). In wild-type embryos, bundles of labeled axons are restricted to regions of the internal capsule. The position of neocortical axons was not detectably altered in Ebf1 mutants (compare B with C and E with F). (G-K) Horizontal sections at ventral levels (H,I) and more dorsal levels (J,K) of brains following a thalamic double injection. Even though the tracer crystals were relatively small, a large number of axons were stained in our experiments because of the small size of the thalamus. In wild-type animals, putative dLGN axons (red) and VB axons (green) turn into the striatum (H) and remain as two separate bundles in the caudal and intermediate regions of the internal capsule, respectively (J). In Ebf1^-/- mutant embryos, dLGN axons are detected as an abnormal tract going towards the amygdala (white arrowhead in I). In dorsal sections, only VB axons are detected (green) and they are located in a more caudal region of the internal capsule than in controls (compare J with K). dTH, dorsal thalamus; Fr, frontal neocortex; Ncx, neocortex; Occ, occipital neocortex; Par, parietal neocortex; Str, striatum.