PROJECT SUMMARY / ABSTRACT The transition from opioid use to abuse and, eventually, to dependence may be governed by distinct genetic mechanisms that alter the molecular pathways that mediate opioid use disorder (OUD). The identity of these genetic/genomic mechanisms is unknown, in part, because the majority of OUD studies have been done in substance-dependent individuals where the dissociation between susceptibility and consequence is ambiguous and genetic/environmental factors are equivocal. One potential strategy for investigating the genetic mechanisms underlying differences in opiate-use trajectories that we have been pursuing in rats is to examine the neurobiology of complex behavioral phenotypes that are associated with different phases of drug use. Our work has identified a decision-making phenotype (e.g., ¨+ parameter) that predicts opiate-taking behaviors in rats, which differs from the decision-making phenotype that is affected by opiate use (e.g., ¨0 parameter). We have found that these distinct phenotypes are controlled by different orbitofrontal circuits that involve the amygdala and nucleus accumbens, and our preliminary proteomic data indicates that these phenotypes are mediated by divergent signaling pathways. We posit, therefore, that these computationally-derived phenotypes could serve as a powerful tool for dissociating the genomic/genetic mechanisms of opioid use susceptibility from those that are consequential to drug use. Here, we propose to use state-of-the-art genomic approaches to identify genes that mediate susceptibility to opiate-taking behaviors and those that mediate drug-induced behavioral changes. In Aim 1, we will investigate the genomic mechanisms underlying susceptibility to oxycodone use. Decision making will be assessed in rats (N=300) to identify individuals who either have low or high ¨+ parameter (N=60/group) that predicts susceptibility to opiate-taking behaviors. RNA sequencing will be performed on tissue from the orbitofrontal cortex, nucleus accumbens and amygdala to identify genes whose expression differs between rats with a low or high ¨+ parameter. We will then perform ATAC sequencing to identify the open chromatin regions associated with the genes that differ between rats with a low or high ¨+ parameter. In Aim 2, we will investigate the genomic mechanisms underlying the decision-making consequences of oxycodone self- administration. Decision making will be assessed in rats (N=300) before and after they self-administer oxycodone to identify individuals who either have low or high ¨0 parameter (N=60/group) following drug exposure. Tissue collected from the orbitofrontal cortex, nucleus accumbens and amygdala will be sequenced using next- generation RNA sequence to identify genes whose expression differs between rats with a low or high ¨0 parameter. We will then perform ATAC sequencing to identify the open chromatin regions associated with the differentially expressed genes. Our results – integrating...