Cell migration from the ganglionic eminences is required for the development of hippocampal GABAergic interneurons

GABAergic interneurons have major roles in hippocampal function and dysfunc tion. Here we provide evidence that, in mice, virtually all of these cells originate from progenitors in the basal telencephalon. Immature interneuron s tangentially migrate from the basal telencephalon through the neocortex t o take up their final positions in the hippocampus. Disrupting differentiat ion in the embryonic basal telencephalon (lateral and medial ganglionic emi nences) through loss of Dlx1/2 homeobox function blocks the migration of vi rtually ail GABAergic interneurons to the hippocampus. On the other hand, d isrupting specification of the medial ganglionic eminence through loss of N kw2.1 homeobox function depletes the hippocampus of a distinct subset of hi ppocampal interneurons. Loss of hippocampal interneurons does not appear to have major effects on the early development of hippocampal projection neur ons nor on the pathfinding of afferrent tracts.