Contextual unfamiliarity during drug intake induces transient AMPA receptors linked to relapse vulnerability

Relapse to drug use remains a challenge in treating substance use disorders (SUDs). In rodent models of SUDs, Ca2+-permeable AMPA receptors (CP-AMPARs) in nucleus accumbens (NAc) medium spiny neurons enhance cue-drug memories after prolonged withdrawal from some forms of drug-conditioned training. Inhibition or removal of these receptors dampens drug-seeking behavior. However, it remains unclear which contextual variables associated with drug use govern CP-AMPAR expression and whether these receptors exhibit the long-term persistence expected of a reliable addiction-related biomarker. Here, we compared three fentanyl-conditioning settings in mice: conditioned place preference (CPP), open-field (OF), and home-cage (HC). Contrary to the HC condition, synaptic CP-AMPAR recruitment was observed in the NAc shell of both CPP and OF groups, which involved exposure to an unfamiliar context following drug administration. CPP and OF training produced comparable increases in CP-AMPAR expression, while CPP mice displayed heightened fentanyl-seeking behavior and OF mice showed locomotor sensitization. After more than 100 days of withdrawal, neither CP-AMPAR expression nor fentanyl-seeking behavior was detected following context re-exposure alone. However, fentanyl re-exposure reinstated drug-seeking behavior despite the absence of CP-AMPAR recruitment, which re-emerged only hours after drug administration. These findings indicate that contextual unfamiliarity drives CP-AMPAR recruitment after drug conditioning and suggest that these receptors transiently govern relapse in consecutive synaptic adaptations during withdrawal. The habituation or avoidance of contextual novelty during opioid treatments may therefore represent a previously underappreciated strategy to limit the recruitment of these maladaptive plasticity mechanisms and reduce relapse risk.