Mechanisms of nicotinic acetylcholine receptor modulation of cocaine reward

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PROJECT SUMMARY Large-scale human genome-wide association studies have identified alleles in CHRNA5, the gene that encodes for the α5 nicotinic acetylcholine receptor (nAChR) subunit, that are protective against developing cocaine use disorder. Preliminary data from our group show that α5 knockout mice are less sensitive than wild-type mice to the rewarding effects of cocaine as measured using intravenous self-administration and intracranial self- stimulation procedures. Cholinergic interneurons (CINs) in the nucleus accumbens (NAc) shape reward-related behaviors, and inhibitory effects of cocaine on CIN activity are considered critical to its rewarding properties. Preliminary electrophysiology data collected in support of this application show that inhibitory GABAergic transmission onto CINs in the NAc is deficient in α5 knockout mice, which results in increased spontaneous firing activity of CINs. Further, CINs in α5 knockout mice are refractory to the inhibitory actions of cocaine. While Chrna5 transcript is not expressed in CINs or any other cell type in the NAc, Chrna5 transcripts are detected in the medial prefrontal cortex (mPFC) and a small number of other brain sites that provide long-range input to the NAc. Based on these exciting findings, I hypothesize that CIN-derived cholinergic transmission in the NAc stimulates α5-containing (α5*) nAChRs located on the terminals of long-range inputs from the mPFC, which enhances GABAergic transmission back onto CINs to inhibit their activity. Further, I propose that α5* nAChR- mediated feedback inhibition plays a permissive role in cocaine reward. I propose to rigorously test this hypothesis using two specific aims. In AIM 1, I will determine how α5* nAChRs contribute to cholinergic mechanisms of cocaine reward. In vivo fiber photometry with a fluorescence-based reporter of acetylcholine signaling will be used to monitor cholinergic transmission in the NAc following acute cocaine to confirm that feedback inhibition of cholinergic signaling evoked by cocaine is deficient in α5 knockout mice. I will then use a chemogenetic approach to determine how inhibiting CINs influences cocaine self-administration in wild-type and α5 knockout mice. AIM 2 will directly test the role of α5 nAChR- expressing inputs to the NAc on cocaine reward and physiology. First, slice electrophysiology combined with targeted optogenetic manipulation will be used to assess how α5 nAChR-expressing inputs from mPFC regulate the activity of CINs as well as the actions of cocaine. Finally, I will use a CRISPR/Cas9 approach to cleave CHRNA5 in α5* nAChR-expressing mPFC→NAc inputs followed by an intravenous self-administration paradigm to assess the consequences of CHRNA5 knockout on cocaine reward in mice. This innovative research proposal will generate important new data relevant to cholinergic mechanisms of cocaine reward with direct relevance to genetic mechanisms of vulnerability to CUD in humans. Further, the tailored career development plan will provide me with training in cutting-edge methodologies and position me to submit a highly competitive application for a K99/R00 Pathway to Independence Award.