Cortical PV and VIP interneurons similarly influence SST neuron output despite distinct unitary properties

Somatostatin (SST) expressing cells are powerful inhibitors of excitatory pyramidal neurons. It has been shown that SST cells are targeted by other inhibitory interneurons, namely parvalbumin- (PV) and vasoactive intestinal polypeptide- (VIP) expressing cells in various cortical regions. Subcellular distribution of PV and VIP synapses suggests differences in their modulation of action potential generation in postsynaptic SST cells. However, functional analyses if and to what extent individual neurons are able to change the output of postsynaptic targets are sparse. To test this, we use paired patch clamp recordings to analyze SST cell firing with and without presynaptic PV or VIP cell stimulation. Despite their enormous differences in unitary synaptic properties, individual PV and VIP cells both are able to significantly decrease action potential output in postsynaptic SST cells. However, testing two different action potential firing durations (1 s and 100 ms) in presynaptic cells, we do not observe significant differences in overall spike loss of PV to SST versus VIP to SST cell connections. Morphological analysis of putative contact sites (PCS) does not reveal differences in PCS location. We propose that individual GABAergic neurons are indeed able to modulate the firing output of SST neurons without principled cell type specificity.