Inhibitory interneurons of the cerebral cortex. (A) Coronal section from a GAD67-green fluorescent protein (GFP) transgenic mouse at E13.5. GFP-labeled γ-aminobutyric acid (GABA) neurons (green) are born in the subcortical basal ganglia and tangentially migrate to the cortex. Yellow arrows indicate the leading group of migrating GABA neurons. (B) Transcription factor genes that specify medial ganglionic eminence (MGE) neuronal cell types. Neural “stem cells” in the MGE express Olig2, Sox2, and Nkx2-1. In migrating intermediate neural progenitors, Dlx genes and Ascl1 specify differentiation into GABAergic interneurons. MGE cells that migrate to the cortex down-regulate Nkx2.1 and express Lhx6, as well as other genes and transcription factors. (C) Schematic showing the main interneuron subtypes originating in the MGE (parvalbumin [PV]-, somatostatin [SST]-, and neuronal nitric oxide synthase [nNOS]-positive interneurons) and caudal ganglionic eminence (CGE) (vasoactive peptide [VIP]-, calretinin [CR]-, and reelin-positive interneurons). Ctx, Neocortex; HC, hippocampus; LGE, lateral ganglionic eminence; POA, preoptic area.