Predator scent stress reduces oxycodone self-administration and the nucleus accumbens dopamine response to oxycodone in female rats

Post-traumatic stress disorder (PTSD) develops in a sub-population of people exposed to trauma and is highly comorbid with opioid use disorder (OUD). The neurobiology of comorbid PTSD+OUD, especially with respect to sex differences, is poorly understood. Here we investigated the sex-specific effects of predator scent stress on intravenous (IV) oxycodone self-administration (SA), cue-primed reinstatement, and pre- and post-stress corticosterone (CORT) concentrations. Upon detecting effects of stress on oxycodone IVSA, the nucleus accumbens (NA) dopamine response to oxycodone was assessed. Male and female rats received a single 10-minute exposure to the predator scent TMT or the control condition. One week later, rats were tested for anxiety-like behavior on the elevated plus maze and underwent oxycodone IVSA, instrumental extinction, and a cue-primed reinstatement test. In a separate cohort of only female rats, the NA core dopamine response to IV oxycodone (0, 0.25, 0.5 mg/kg) was assessed using fiber photometry. TMT increased anxiety-like behavior one week later in male and female rats. Baseline CORT was negatively correlated with anxiety-like behavior in males. TMT exposure reduced oxycodone intake exclusively in females, with no effects on instrumental extinction or cue-primed reinstatement in either sex. Female rats demonstrated a dose-dependent increase in NA core dopamine signal following oxycodone administration that was blunted by a history of TMT exposure. These results indicate that TMT exposure diminishes the NA core dopamine response to oxycodone in females, reducing oxycodone IVSA. These results are consistent with stress-induced reward insensitivity that has been observed following stress in both rodents and humans.