a Timeline of Exp. 2. b Oxycodone self-administration training: Number of oxycodone infusions and inactive and active lever presses during the 6-h sessions. c Electric barrier-induced abstinence: Number of oxycodone infusions and inactive and active lever presses during the 2-h sessions. d Relapse (incubation) tests: Total responding. Number of active lever presses during the 90-min test sessions after (−)-OSU6162 pretreatment (0, 7.5, 15 mg/kg). e, f Relapse (incubation) tests: Time course day 1 and 15. 30-min time course of active lever presses 1 day after oxycodone self-administration training and after 13 days of electric barrier-induced voluntary abstinence. * Different from day 1 within each dose condition; # Different from the vehicle group on day 15, p < 0.05. Data are mean ± SEM; Day 1, 9–10 males/dose and 9 females/dose; Day 15, 10–13 males/dose and 10–15 females/dose. See Fig. S1 for individual data.