Late-born (E15.5) interneurons in p35 mutant brains are properly layered despite layer inversion of projection neurons. A, In the wild-type cortex, double-labeling for GABA (green) and BrdU (red) reveals that the vast majority of double-labeled interneurons at E15.5 (yellow) are in the upper layers. B, Higher magnification of boxed area in A indicating that the majority of double-labeled interneurons (arrows) are in the upper layers of the cortex. C, Histogram depicting the layer positions of GABA–BrdU interneurons (n = 2 animals, 257 cells; mean ± SEM percentage) indicating that the majority of late-born interneurons in wild-type cortices are distributed in the upper layers. D, In the p35 mutant cortex, double-labeled interneurons (yellow) born at E15.5 are also found in the upper layers. E, Higher magnification of boxed area in D indicating that double-labeled interneurons (arrows) are in the upper layers of the p35 mutant cortex. F, Histogram depicting the layer positions of GABA–BrdU interneurons (n = 2 animals, 345 cells; mean ± SEM percentage) indicating that the majority of late-born interneurons in p35 mutant cortex are situated in the upper layers of the cortex. G, Early-born interneurons (BrdU at E12.5) in the mutant p35 cortex are inverted. Double-labeled interneurons (GABA–BrdU) (n = 3 animals, 364 cells; mean ± SEM percentage) indicate that the majority of early-born interneurons in p35 mutant cortices are situated in the upper layers of the cortex. H, Global analysis of all interneurons in p35 mutant cortex (both early- and late-born interneurons) (n = 2 animals, 3731 cells; mean ± SEM percentage) shows a biased distribution of interneurons to the upper half of the mutant cortex. I, In contrast, a relatively even distribution of interneurons to all cortical layers was seen in wild-type cortex (n = 2 animals, 3795 cells; mean ± SEM percentage). Scale bar: A, D, 160 μm; B, E, 80 μm. WM, White matter.