Morphology, physiology and connectivity of genetically specified VIP neurons in mouse barrel cortex

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Genetic access via Cre-driver lines have made vasoactive intestinal polypeptide (VIP) expressing neurons a subject of major discoveries, like for instance their brain-wide signaling of reward or punishment in the context of learning. Also an abundant disinhibitory circuit motif was disclosed, in which VIP neurons inhibit somatostatin (SST) expressing neurons, which in consequence relieves their inhibition from pyramidal cells’ dendritic arbors. However, there is also ample evidence of VIP neurons directly participating in sensory information processing, possibly by mediating feedforward inhibition. How these functions relate to putative specific subtypes of VIP neurons remains to be shown since it was so far not possible to identify these, if there are any. Recently, a novel intersectional approach of studying genetically defined neurons has been published, which led to the making of Cre- and Flp-dependent driver lines that showed as VIP/Calretinin and VIP/Cholecystokinin cells only little overlapping distributions, and were suggested to represent interneuron-specific interneurons and small basket cells, respectively. Here, we will multimodally characterize these (and other) cells and test, via paired and triple recordings, if their connectivity motifs are in agreement with this hypothesis. Furthermore, with patch-seq we will provide a thorough molecular characterization of the VIP neurons. This study has the potential to substantially improve our knowledge on VIP neuron diversity and their putative involvement in sensory information processing.