Fig. 7. Ultrastructure of the PSPB in wild-type and Pax6^-/- brains at E15.5 (A-J) and E18.5 (K-U). Electron microscopy was performed in coronal sections of wild-type (E-G,O-Q) and Pax6^-/- (H-J,R-U) brains. Boxes on the camera lucida drawings (A,C), in the light microscopy images of resin-embedded sections (K,M) and in the Toluidine Blue-stained semithin sections (B,D,L,N) indicate the areas examined. (E-G,O-Q) At E15.5 and E18.5, wild-type axons (ax) are observed at the level of the intermediate zone (iz) of the cortex (ctx) (Q) and crossing the PSPB (E,O). (F,G) Higher magnifications of wild-type PSPB cells. (P) High-power view showing the ultrastructure of the ventricular zone (vz) in wild-type brains. (H-J,R-U). At both ages, the lateral telencephalon of the Pax6^-/- brain was abundant in axon bundles (J,R) and less of them are seen crossing the PSPB (H,S) (compare with E or O). The ultrastructure of the PSPB is characterized by densely packed cells in the Pax6^-/- brains (H,S). This ultrastructural abnormality was more evident at E18.5 than at early stages (asterisk in S). (T) Clusters of abnormal cells with loss of organelles on the cytoplasm are observed at the vz in Pax6^-/- brains at both ages. str, striatum; dt, dorsal thalamus; ht, hypothalamus. Scale bars: 400 µm in A,C,K,M; 2 µm in E-F,J; 3 µm in H; 1 µm in G,I; 5 µm in O,Q-S,U; 2 µm in P; 1 µm in T.