Research Article

Postnatal connectomic development of inhibition in mouse barrel cortex

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Science  03 Dec 2020:
eabb4534
DOI: 10.1126/science.abb4534

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Abstract

Brain circuits in the neocortex develop from diverse types of neurons that migrate and form synapses. Here we quantify the circuit patterns of synaptogenesis for inhibitory interneurons in the developing mouse somatosensory cortex. We studied synaptic innervation of cell bodies, apical dendrites and axon initial segments using 3D electron microscopy focusing on the first four weeks postnatally (postnatal days 5 to 28). We found that innervation of apical dendrites occurs early and specifically: target preference is already almost at adult levels at the fifth postnatal day (P5). Axons innervating cell bodies, on the other hand, gradually acquire specificity from P5 to P9 likely via synaptic overabundance followed by antispecific synapse removal. Chandelier axons show first target preference by P14 but develop full target specificity almost completely by P28, consistent with a combination of axon outgrowth and off-target synapse removal. This connectomic developmental profile reveals how inhibitory axons in mouse cortex establish brain circuitry during development.

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