PROJECT SUMMARY The COVID-19 pandemic has had a palpable impact on mental health, and maladaptive coping strategies, such as excessive alcohol consumption, have seen a marked increase in recent years. Binge drinking is the most common pattern of excessive drinking behavior and is associated with an increased risk for the development of an alcohol use disorder (AUD). Presently, pharmacotherapies for the treatment of AUD are limited, creating a pressing need for novel therapeutic interventions. A more thorough understanding of the neurobiological processes that govern excessive, uncontrolled alcohol drinking is necessary to meet this goal. The Drinking in the Dark (DID) model serves as a robust and reproducible platform for molecular and circuit level interrogation of systems that promote binge-like alcohol consumption. The endogenous opioid-like peptide nociceptin/orphanin FQ (N/OFQ) and the nociceptin receptor (NOP) is one molecular target of interest and selective NOP antagonists have shown great promise in attenuating excessive drinking behavior. For example, a NOP antagonist was found to decrease number of heavy drinking days and amount consumed per week in treatment-seeking patients with an AUD. My preliminary results support this therapeutic target in that a NOP antagonist decreased alcohol intake in the DID model, which is consistent with the literature. Together, these findings point to NOP as a clear candidate for AUD pharmacotherapies, and yet no studies to date have explored the endogenous N/OFQ populations that are involved in alcohol drinking behavior and only one has probed the site of NOP action. To this end, my preliminary studies have identified the lateral septum (LS) as rich in N/OFQ (LSN/OFQ) and that this discrete population plays a causal role in binge-like alcohol consumption. More specifically, cell-type specific chemogenetic activation of LSN/OFQ increased alcohol intake while silencing LSN/OFQ decreased drinking. In addition, I have found this effect to be specific to alcohol, since LSN/OFQ manipulation did not affect sucrose intake nor locomotion. The finding of selective LSN/OFQ bidirectional control over binge drinking behavior is highly exciting and paves the way for this proposal. Here, I aim to take a multifaceted approach to interrogate the functional consequence of a history of binge drinking on the electrophysiological profile of LSN/OFQ and determine the activity patterns of these neurons in vivo during alcohol drinking behavior with fiber photometry. Lastly, I will determine the molecular profile of LSN/OFQ and map the downstream projection sites, and determine the effect of genetic NOP deletion therein on alcohol intake. Thus, this proposal aims to thoroughly interrogate activity in the novel LSN/OFQ population and seeks to identify mechanistic processes by which this system promotes excessive drinking through the NOP receptor. In summary, this grant proposal targets an understudied population and neuropeptide...