SST interneurons facilitate dendritic calcium signaling via tonic activation of α5-GABA receptors

Rs mediate tonic currents in cortical pyramidal neurons that paradoxically enhance action potential-evoked dendritic calcium influx. Experimental and computational data indicate that the increased calcium influx arises via deinactivation of low-threshold voltage-gated channels. Tonic α5-mediated GABAergic currents and dendritic calcium signals are both enhanced by optogenetic activation of somatostatin-expressing interneurons (SST-INs). In addition, α5-mediated GABAergic facilitation of postsynaptic calcium signaling modulates the short-term plasticity of GABAergic transmission at SST-IN synapses. Our results demonstrate unexpected diversity in the function of both SST-INs and GABAergic signaling to influence dendritic activity and synaptic transmission in the cortex.