Fig. 5.

Effects of the FAAH inhibitor URB597 (URB; 0.1 mg/kg, i.p., 2 h before test) and the opioid receptor agonist morphine (MOR; 1 mg/kg, s.c., 1 h before test) on social play behavior in adolescent rats tested in a familiar (a–f) or an unfamiliar environment (g–n). In a familiar environment, when social play behavior was assessed per 15 min, both URB597 and morphine increased pinning (a) and pouncing (b), without affecting social exploration (c). Both URB597 and morphine increased pinning in the first and last 5 min periods of the test (d), increased pouncing in the first 5 min period (e) and did not affect social exploration (f). In an unfamiliar environment, when social play behavior was assessed per 15 min, both URB597 and morphine increased pinning (g) and pouncing (h), without affecting social exploration (i). When behavior was analyzed per 5 min intervals, pinning (l) and pouncing (m) were significantly increased during the first 5 min of the test in both URB597- and morphine-treated rats. During the second 5 min period, morphine increased both pinning (l) and pouncing (m), whereas URB597 significantly increased pouncing only (m). Data represent mean ± SEM frequency of pinning and pouncing and mean ± SEM duration of social exploration. *p<0.05, **p<0.01 vs. vehicle treatment, ^$$p<0.01 vs. URB597 treatment (Tukey’s post hoc test, n = 13–14 per treatment group).