Abstract A diverse set of GABA A receptors (GABA A Rs) enable synaptic plasticity adaptations at inhibitory postsynaptic sites in collaboration with the scaffolding protein gephyrin. Early studies helped to identify distinctions between GABA A R subtypes allocated within specific functional circuits, but their contribution to the changing dynamics of a microcircuit remains unclear. Here, using the whisker-barrel system in mouse, we assessed the contribution of specific synaptic GABA A R subtypes and gephyrin scaffolding changes to sensory processing in vivo . We monitored spontaneous and evoked Ca 2+ transients in layer 2/3 pyramidal cells with the genetically encoded Ca 2+ sensor RCaMP1.07. Using Gabra1 or Gabra2 global and conditional knockout mice, we uncovered that α1- and α2-GABA A Rs determine the sparseness of L2/3 pyramidal neuron encoding. In a cell-type dependent manner, α1-GABA A Rs and α2-GABA A Rs affected neuronal excitability and the reliability of neuronal responses after whisker stimulation. We also discerned that gephyrin with its diverse post-translational modifications (PTMs) shows preference for specific GABA A R subtype to facilitate microcircuit activity. Our results underscore the relevance of the diversity of GABA A Rs within a cortical microcircuit. Key points While GABAergic inhibition from interneuron subtypes regulates cortical microcircuit activity the molecular determinants have remain unclear. We demonstrate that specific-GABA A receptor subtypes contribute differentially to layer 2/3 neuronal activities in mouse barrel cortex. Importantly, we link the GABAAR contributions to the scaffolding properties of its important postsynaptic density protein gephyrin. We show that different PTMs on gephyrin determines neuronal excitability via GABAAR recruitment and modulation of inhibition within layer 2/3 neurons. Specifically, α1 and α2 subunits containing GABA A receptors, along with their scaffolding protein gephyrin determine the distribution of high, medium and low activity pyramidal neurons during sensory encoding, whereby controlling the total activity of cortical microcircuit.

Differential impact of GABA<sub>A</sub> receptors and gephyrin post-translational modifications on layer 2/3 pyramidal neuron responsiveness <i>in vivo</i>

Differential impact of GABAA receptors and gephyrin post-translational modifications on layer 2/3 pyramidal neuron responsiveness in vivo