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. 2022 May 30;10(6):1127. doi: 10.3390/microorganisms10061127

Figure 2.

Figure 2

Fentanyl intravenous self-administration. (A) Mean number of infusions across 2 days at fixed ratio (FR) 1, FR2, and FR5 schedules of reinforcement, reinforced (Reinf, filled bars and circles) vs. non-reinforced (NonReinf, empty bars and circles) responses, at 0, 1.25, and 2.5 μg/kg/infusion (error bars represent S.E.M., ** p < 0.01, * p < 0.05, n = 10–16/group). (B) Mean infusion breakpoint over 2 days at a progressive ratio schedule of reinforcement at 0, 1.25, and 2.5 μg/kg/infusion (error bars represent S.E.M., **** p < 0.0001, ** p < 0.01, n = 10–16/group). Data are collapsed by sex.