Fig. 5. GABAergic neurons in the dorsal mesencephalon are not induced. In situ hybridization with the Gad67 riboprobe of coronal (A-I) and sagittal (J-O) sections, showing the mesencephalon of E10.5 (A-C), the anterior of E11.5 (D-F) and the caudal regions of E11.5 (G-I), 13.5 (J-L) and E18.5 (M-O) of wild-type (B,E,H,K,N) and Mgn^tZ/tZ (C,F,I,L,O) embryos. (A,D,G,J,M) Bright-field images of wild type. (B,E) Gad67 expression is prominent in the mantle zone of the developing ventral midbrain of wild-type embryo. (C,F) Gad67 expression is reduced in the developing ventral midbrain of homozygous mutant mice, and dorsal expression is not detectable. Arrows in E,F indicate the presence (E) and absence (F) of dorsal Gad67-expressing cells. (H,I) Gad67 expression is also reduced in the caudal region of the mutant SC at E11.5. (K) Expression of Gad67 is present in the dorsal mesencephalic vesicle of wild-type (arrows), while the Gad67 expression in the mutant (L) is completely absent in the dorsal mesencephalic vesicle (arrows); it is also reduced in the pretectal area (arrowheads) and slightly reduced in the ventral midbrain. Gad67 expression in other areas of the brain (spinal cord, ventral hindbrain, cerebellum, thalamus, hypothalamus and the ventral telencephalon) is not affected. Arrows in K,L indicate the presence (K) and absence (L) of Gad67-expressing cells in the dorsal midbrain at E13.5 of the indicated genotype. (N-O) The mid/hindbrain region. Strong Gad67 expression can be observed in the SC of the wild-type mouse (N). (O) In the mutant mouse, Gad67 expression is completely absent in the dorsal midbrain, weaker in the ventral midbrain and not affected in the cerebellum and ventral hindbrain. Abbreviations: Cb, cerebellum; IC, inferior colliculus; SC, superior colliculus; vMB, ventral midbrain.