Specifi cation of gabaergic neocortical interneurons

Inhibitory GABAergic interneurons within the cerebral cortex are critical for fi ne-tuning the activity of cortical circuits and thus are thought to be involved in generating the distinct oscillatory patterns that underlie higher brain functions such as consciousness and memory. Understanding how cortical interneurons are specifi ed during development is important not just from the standpoint of basic research but also is likely to provide key insights into how cognitive disorders emerge. Although interneurons only consist of around 20 % of the neurons within the neocortex, they are extremely diverse with regard to their morphologies, molecular expression profi les, intrinsic electrophysiological properties, and synaptic connections. In rodents, most neocortical interneurons originate during embryogenesis from ventrally located structures, primarily the gang ionic eminences, and therefore must migrate over long distances following discrete pathways to reach the appropriate cortical areas. Thus, proper coordination of the distinct migration programs followed by pyramidal cells and interneuron precursors during development is crucial for the assembly of functional microcircuits within the cerebral cortex. Here, we review and discuss emerging views of how cortical GABAergic interneuron specifi cation, migration, and integration occur from embryonic to early postnatal stages.