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. Author manuscript; available in PMC: 2023 Mar 1.
Published in final edited form as: Addict Neurosci. 2022 Dec 9;5:100057. doi: 10.1016/j.addicn.2022.100057

Fig. 2. Escalation and re-escalation of fentanyl vapor self-administration.

Fig. 2.

Male and female C57BL/6J mice were trained to lever press for fentanyl vapor deliveries on an FR1 schedule of reinforcement. Upon stable lever pressing, the mice were split in short-access (ShA; 1 h) and long-access (LgA; 6 h) conditions. (A) Mice in the LgA condition escalated their intake in the first hour of the session across days. The data are expressed as the mean ± SEM and were analyzed using two-way repeated-measures ANOVA. #p < 0.05, compared with session 1; *p < 0.05, compared with LgA. (B) Mice in the LgA condition escalated their fentanyl intake across the 6 h sessions. The data are expressed as the mean ± SEM and were analyzed using two-way repeated-measures ANOVA. #p < 0.05, compared with session 1; *p < 0.05, compared with LgA. (C) Mice in the LgA condition had higher calculated slopes of the escalation curve compared with mice in the ShA condition. The data are expressed as the mean ± SEM and were analyzed using unpaired Student’s t-test. *p < 0.05, compared with ShA. (D) Fentanyl intake on the first re-escalation self-administration sessions. The data are expressed as the mean ± SEM and were analyzed using two-way repeated-measures ANOVA. #p < 0.05, compared with session 1. (E) Mice in the LgA condition maintained higher fentanyl intake across sessions in the re-escalation phase. The data are expressed as the mean ± SEM and were analyzed using two-way repeated-measures ANOVA. # p < 0.05, compared with session 1; *p < 0.05, compared with LgA. (F) The calculated re-escalation slope did not differ between ShA and LgA conditions. The data are expressed as the mean ± SEM and were analyzed using unpaired Student’s t-test. (n = 8/sex/group).