Distinct maturation profiles of perisomatic and dendritic targeting GABAergic interneurons in the mouse primary visual cortex during the critical period of ocular dominance plasticity

In the rodent primary visual cortex, maturation of GABA inhibitory circuitry is regulated by visual input and contributes to the onset and progression of ocular dominance (OD) plasticity. Cortical inhibitory circuitry consists of diverse groups of GABAergic interneurons, which display distinct physiological properties and connectivity patterns. Whether different classes of interneurons mature with similar or distinct trajectories and how their maturation profiles relate to experience dependent development are not well understood. We used green fluorescent protein reporter lines to study the maturation of two broad classes of cortical interneurons: parvalbumin-expressing (PV) cells, which are fast spiking and innervate the soma and proximal dendrites, and somatostatin-expressing (SOM) cells, which are regular spiking and target more distal dendrites. Both cell types demonstrate extensive physiological maturation, but with distinct trajectories, from eye opening to the peak of OD plasticity. Typical fast-spiking characteristics of PV cells became enhanced, and synaptic signaling from PV to pyramidal neurons became faster. SOM cells demonstrated a large increase in input resistance and a depolarization of resting membrane potential, resulting in increased excitability. While the substantial maturation of PV cells is consistent with the importance of this source of inhibition in triggering OD plasticity, the significant increase in SOM cell excitability suggests that dendrite-targeted inhibition may also play a role in OD plasticity. More generally, these results underscore the necessity of cell type-based analysis and demonstrate that distinct classes of cortical interneurons have markedly different developmental profiles, which may contribute to the progressive emergence of distinct functional properties of cortical circuits.