Treatment with naltrexone (NTX), a nonselective µ, d, k (MOP, DOP, KOP) classical opioid receptor antagonist, is considered a gold standard of care for alcohol use disorder (AUD). Nonetheless, there is an urgent need for novel and more efficacious pharmacological approaches to AUD since only a minority of patients benefit from NTX. Findings of the previous funding periods suggest that both innate and chronic EtOH-induced overexpression of classical opioid receptors contribute to enhanced motivation for EtOH whereas activation of the antiopioid nociceptin/orphanin (N/OFQ) receptor (NOP) system reduces EtOH intake and seeking. Preliminary data supporting this renewal suggest that simultaneous blockade of classical opioid receptors with concurrent activation of NOP has superior efficacy compared to classical opioid receptor antagonists such as NTX or manipulation of single receptor subtypes. These findings provide a solid foundation for a systematic investigation of the therapeutic potential of a novel pharmacological agent (BU10119) that blocks MOP, DOP, and KOP receptors while activating NOP receptors. The major objective of this project, therefore, is to establish the efficacy of BU10119 (and, by inference, mixed nonselective classical opioid antagonists/NOP agonists) for AUD treatment as well as the neurobiological basis of BU10119’s actions. Specific Aim 1 will establish the effects of acute BU10119 vs. NTX on EtOH drinking and context or stress-induced EtOH seeking in rats with intact NOP function [nondependent Wistar rats (ndW)] compared to both rats with innate [Marchigian Sardinian alcohol preferring rats (msP)] and chronic EtOH-induced [(postdependent Wistar rats (pdW)] NOP overexpression and rats with deficient NOP function [NOP-knockout (NOP-KO) rats]. Specific Aim 2 is designed to characterize the effects of BU10119 in the context of chronic treatment. This objective is translationally relevant as well as necessary given the known sensitivity of N/OFQ-NOP function to adaptive changes with repeated pharmacological manipulation and will establish the direction in which such possible changes modify the effects of BU10119 vs. NTX. Specific Aim 3 will elucidate how recruitment of the N/OFQ system contributes to the efficacy BU10119 by establishing the effects of concurrent classical opioid receptor blockade and NOP activation and by identifying the brain site(s) in which NOP activation conveys enhanced efficacy to mixed MOP, DOP, KOP antagonists / NOP agonists. Successful completion of this project is expected (a) to define the therapeutic potential of drugs acting as classical opioid receptor antagonists / NOP agonists for AUD treatment while directly informing the development of BU10119 as an AUD therapeutic, and (b) to generate novel information on the neural basis of the “anti-addiction” effects of this class of pharmacological agents.