Figure 2.
Intermittent access (IntA) is associated with the emergence of negative emotional states following 4 weeks of abstinence. (A) IntA animals spent less time swimming on the forced swim test (F2,18 = 4.265, p = .0305) compared with long access (LgA) (t18 = 2.348, p = .0305; Holm-Sidak post hoc test) or short access (ShA) (t18 = 3.132, p = .0263; Holm-Sidak post hoc test) control animals. On the same test, IntA animals spent more time immobile (F2,18 = 5.285, p = .0156) compared with LgA (t18 = 2.462, p = .0242; Holm-Sidak post hoc test) or ShA (t18 = 3.132, p = .0115; Holm-Sidak post hoc test) control rats. There was no significant difference between LgA and ShA animals in these measures (p > .05). IntA, n = 6; LgA, n = 7; ShA, n = 8. (B) IntA animals showed lower preference for saccharin (F2,19 = 4.027, p = .0348) compared with LgA (t19 = 2.121, p = .0473; Holm-Sidak post hoc test) or ShA (t19 = 2.757, p = .0249; Holm-Sidak post hoc test) rats, which may reflect anhedonia in IntA rats. There was no significant difference between LgA and ShA animals in this measure (p > .05). IntA, n = 6; LgA, n = 7; ShA, n = 7 (one ShA animal included in the forced swim test did not complete saccharin preference test or open field test). (C) IntA animals spent less time in the center square during a 15-minute open field test (F2,16 = 3.857, p = .0429) compared with LgA (t16 = 2.412, p = .0445; Holm-Sidak post hoc test) or ShA (t16 = 2.525, p = .0445; Holm-Sidak post hoc test) rats, indicating an enhanced anxiety-like state in these animals. There was no significant difference between LgA and ShA animals in this measure (p > .05). IntA, n = 5 (one animal excluded, see Statistical Analyses in Supplemental Methods and Materials); LgA, n = 7; ShA, n = 7. All analyses represent Holm-Sidak post hoc comparisons. Error bars are SEM. *p < .05.