Figure 3.

Evaluation of PZM21 effects on intravenous self‐administration in rats. (a) Rats that self‐administered oxycodone (0.06 mg·kg⁻¹ per infusion, i.v.), but not PZM21 (0.05 and 0.5 mg·kg⁻¹ per infusion, i.v.), presented an increasing number of infusions over time. (b) Only rats from the oxycodone group presented an increasing number of active lever responses. (c) No differences between groups were observed in inactive lever presses during self‐administration training. (d) Unlike the oxycodone group, rats in the saline and PZM21 groups did not present drug‐seeking behaviour after abstinence period, as they did not discriminate between active and inactive levers and made a similar number of responses on both levers. Data are presented as the mean ± SEM. In (a), * P < .05, within group effects significantly different from the first day of experiment; in (b–d), active and inactive lever responses significantly different within experimental groups. Numbers of animals used in experiments presented in Table S5. Oxy, oxycodone; Sal, saline