PROJECT SUMMARY Opioid use disorder (OUD) is an escalating public health concern that has resulted in over 570,000 overdose deaths between 1999 and 2020. Exposure to prescription opioids (such as oxycodone) is frequently an initiating factor in OUD, with 9.9 million people reporting misusing prescription opioids annually (Centers for Disease Control). While many individuals can use opioids as prescribed, a subset of individuals transition to problematic drug use, which is defined as continued drug intake despite negative consequences and is a hallmark feature of OUD. These individual differences have been modeled in rodents: most subjects will readily self-administer opioids but will suppress drug intake when drug seeking is paired with punishment such as a foot shock (punishment-sensitive). Conversely, ~20-30% of individuals will persist in drug seeking despite this punishment (punishment-resistant). Elucidating the neural mechanisms underlying individual differences in punishment-resistant drug seeking is critical for understanding susceptibility to compulsive drug use in OUD. The ventral pallidum (VP) has emerged as a central brain area for encoding the relative value and motivation for rewards and translating this motivation into action. Recent work has also established that VP activity is necessary for drug seeking and relapse, and critically modulates reward seeking under conflict. The VP is an incredibly heterogeneous nucleus, with distinct neurochemically- and anatomically-defined populations playing discrete and dissociable roles in behavior. However, our understanding of how the VP subpopulations work in concert to orchestrate motivated behavior in the context of OUD is severely limited by the inability to identify functionally-relevant VP populations. Here we will use state-of-the-art omics platform to obtain high resolution cellular information of comprehensive cell types in the VP and their role in OUD. Our long-term goal is to elucidate the molecular and neural circuit basis of punishment-resistant opioid self- administration, and to leverage this understanding to develop targeted therapies to prevent or reverse the transition to punishment-resistant opioid intake in patients with OUD. The outcomes of this proposal will lay the foundation for this goal by creating a comprehensive cellular atlas of the VP and characterizing transcriptional adaptations induced by self-administration of oxycodone (Aim 1), and by profiling ensembles of VP neurons that are activated in the context of oxycodone self-administration (Aim 2). By profiling transcription factor binding using cutting edge “calling card” technology, we will establish whether transcriptional profiles distinguishing punishment sensitive- and resistant- individuals emerge with repeated self-administration, or whether these differences are antecedent to opioid exposure and only revealed upon introduction of punishment (Aim 3). This work will help inform future therapies for OUD and ...