Nociceptin Orphanin F/Q Pathways are Dysregulated by Stress and Modulate Reward Learning and Motivation Across Species.

Nociceptin orphanin F/Q has been implicated in stress-related depressive phenotypes. Specifically, exposure to chronic stressors upregulates nociceptin receptors (NOPR), whereas NOPR antagonism has anti-depressant/anti-anhedonic effects. The mechanisms underlying these effects remain, however, unclear. Here, we investigated the role of NOPR in depressive phenotypes alongside potentially prohedonic effects of NOPR antagonism across species. In Study 1, we evaluated whether exposure to early-life adversity (ELA) upregulated ventral tegmental area (VTA) and striatal prepronociceptin ( ) gene expression in adult mice. In Study 2, we tested whether chronic social defeat altered gene expression in reward-related regions. To establish whether direct NOPR modulation is implicated in reward-related behaviors, in Study 3, we assessed whether NOPR antagonism alters reward learning in rats. Finally, in Study 4, we tested whether NOPR antagonism boosts motivation among depressed humans. ELA induced anhedonic behavior and increased expression in the VTA; in females (but not males), ELA increased expression in the dorsal striatum (Study 1). Furthermore, chronic stress reduced -expressing cells in the VTA, dorsal striatum and prefrontal cortex and susceptible rats showed reduced VTA NOPR gene ( expressing cells (Study 2). In a behavioral assay, a single 30-mg dose of a NOPR antagonist (BTRX-246040) boosted reward learning in rats (Study 3). Finally, in depressed humans, relative to placebo, 8-week treatment with BTRX-246040 increased incentive motivation (Study 4). Collectively, our findings indicate that chronic stressors alter and mRNA levels of -expressing cells in a sex-selective and region-specific manner impacting reward structures, and that NOPR antagonism shows anti-anhedonic properties.