CIRCUITS OF NEGATIVE REINFORCEMENT IN OPIOID ADDICTION

Opioid use disorders (OUD) affect over 40 million people worldwide and cause more than 450,000 deaths annually. The high addiction liability of opioids is driven by both drug-induced euphoria (positive reinforcement) and the alleviation of aversive withdrawal symptoms (negative reinforcement). While the substrates of positive reinforcement are well characterized, our laboratory recently identified μ-opioid receptor (μOR)-expressing neurons in the central amygdala (CeA) as a key cellular determinant of negative reinforcement. However, the mechanisms by which these neurons increase addiction liability and interact with reward circuits remain unknown. To address this, we combine behavioral assays, fiber photometry, and optogenetics in freely moving animals. We validated that optogenetic inhibition of μOR neurons in the ventral tegmental area (VTA) modulates dopamine dynamics in the nucleus accumbens. Using optogenetic μOR neuron self-inhibition (oMORsi) to mimic positive reinforcement, we found that 75% of mice develop compulsive behavior, persisting despite punishment. Brain-wide mapping further identified candidate CeA pathways mediating negative reinforcement and their potential convergence with positive reinforcement circuits. Building on these findings, we will use optogenetics to test whether the concomitant engagement of both pathways promotes addiction-like behavior. We will also map CeA μOR projections engaged during withdrawal and assess synaptic plasticity in hyperactive circuits of compulsive mice, specifically the orbitofrontal–striatal pathway. This work aims to identify convergence sites between reinforcement systems and uncover therapeutic targets to treat OUD and reduce relapse.