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. 2020 Aug 5;6(32):eabc0413. doi: 10.1126/sciadv.abc0413

Fig. 4. Mice escalate fentanyl vapor self-administration.

Fig. 4

(A) The long-access fentanyl (LgA-Fen) group escalated their intake over time. Linear regression analysis shows a positive slope for the LgA-Fen group (a = 4.04; CI, 2.46 to 5.62), which is significantly greater than 0 (F1,158 = 25.53; r2 = 0.14; P < 0.0001). The calculated slopes for the short-access fentanyl (ShA-Fen) group (a = −0.058; CI, −0.33 to 0.22) and long-access vehicle (LgA-Veh) group (a = −0.64; CI, −1.92 to 0.63) were not different from 0. The slopes from the three groups were different from each other (test of equal slopes; F2,434 = 18.77; P < 0.0001). (B) In the LgA-Fen group, the number of VD during the first hour of self-administration increased across escalation days (slope a = 0.56; CI, 0.31 to 0.82; F1,158 = 18.82; r2 = 0.11; P < 0.0001). n, number of mice. The data are expressed as means ± SEM. *P < 0.05.