GABAergic interneurons form transient layer-specific circuits in early postnatal neocortex

Anastasiades, Paul G. and Marques-Smith, Andre and Lyngholm, Daniel and Lickiss, Tom and Raffiq, Sayda and Kätzel, Dennis and Miesenböck, Gero and Butt, Simon J.B. (2016) GABAergic interneurons form transient layer-specific circuits in early postnatal neocortex. Nature Communications, 7. 10584. ISSN 2041-1723 (https://doi.org/10.1038/ncomms10584)

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Abstract

GABAergic interneurons play key roles in cortical circuits, yet little is known about their early connectivity. Here we use glutamate uncaging and a novel optogenetic strategy to track changes in the afferent and efferent synaptic connections of developing neocortical interneuron subtypes. We find that Nkx2-1-derived interneurons possess functional synaptic connections before emerging pyramidal cell networks. Subsequent interneuron circuit maturation is both subtype and layer dependent. Glutamatergic input onto fast spiking (FS), but not somatostatin-positive, non-FS interneurons increases over development. Interneurons of both subtype located in layers (L) 4 and 5b engage in transient circuits that disappear after the somatosensory critical period. These include a pathway mediated by L5b somatostatin-positive interneurons that specifically targets L4 during the first postnatal week. The innervation patterns of immature cortical interneuron circuits are thus neither static nor progressively strengthened but follow a layer-specific choreography of transient connections that differ from those of the adult brain.