Functional heterogeneity of vasoactive intestinal peptide-expressing interneurons in the anterior cingulate cortex - PROJECT SUMMARY Cortical subregions are often implicated in a variety of behavioral functions, but it is not well understood how these areas encode such diverse information. The anterior cingulate cortex (ACC) is necessary for emotional processing and social cognition, but how it encodes stimuli relevant to both processes is unknown. The goal of this proposal is to understand the functional heterogeneity of ACC circuits, and how this impacts encoding of diverse stimuli and cognitive function. In Aim 1, we will determine the functional heterogeneity of ACC inhibitory circuits during social and anxiety-like behaviors. To monitor interneuron activity, we will first inject an adeno- associated virus (AAV) that expresses GCaMP6f, a fluorescent Ca2+ indicator, in a Cre-dependent manner into the ACC of somatostatin (SST)- or parvalbumin (PV)-cre transgenic mice. Next, we will use the 3D-printed miniature miniscopes to perform in vivo single-cell resolution calcium imaging in either somatostatin or parvalbumin interneurons in the ACC to investigate their functional heterogeneity while mice performed tasks to assay anxiety-like behaviors, general sociability and social novelty. In Aim 2, we will determine whether specific populations of excitatory pyramidal cells (Pyr) in the ACC encode particular behavioral stimuli. First, to target specific populations of Pyr in the ACC, we will inject an AAV that expresses Cre recombinase and can retrogradely label cells into either the contralateral ACC, anterior thalamic nucleus, or the retrosplenial cortex. Next, we will inject an AAV that expresses GCaMP6 in a cre-dependent manner to label Pyr in the ACC and project to either the contralateral ACC, anterior thalamic nucleus or retrosplenial cortex. Three weeks later, we will use approaches described in Aim 1 to monitor the activity of specific populations of Pyr during particular behaviors. We will also determine the laminar sources of synaptic input to VIP interneurons in the ACC. To test this, we will first cross VIP-cre mice to a cre-dependent fluorescent reporter line. Next, we will inject an AAV expressing ChETA, a light-activated channel, into the contralateral ACC, anterior thalamic nucleus or retrosplenial cortex. Four weeks after viral injections, we will combine electrophysiological recordings in acute brain slices with optogenetic stimulation to characterize the laminar organization of specific projections unto VIP interneurons in the ACC. In addition to determining the connectivity probability of these inputs, we will correlate the cortical depth of the soma to morphological, and electrophysiological properties and molecular markers. While reductionist and simplified models of cortical networks have established a framework to understand their function, it is now evident that to understand the role of cortical networks in complex, adaptive behavior, optimized models will need to incorporate the functional heterogeneity of these circuits. Completion of these aims will dissect the functional heterogeneity of inhibitory circuits in the ACC.
