Reward-related behavior in Cnr1 MT and WT animals. Limited-access SCM intake was significantly increased in adult MT (p = 0.00002) (a), but not adolescent MT rats (p = 0.083), compared with age-matched WT animals, indicating a ceiling effect in adolescent rats (b). During PR responding, the highest completed ratio (p = 0.0001) and the inactivity ratio (p = 0.000002) were significantly enhanced in MT rats (c). Social play, a highly rewarding social activity most pronounced during mid-adolescence, was strongly enhanced in MT rats compared with WT controls (attacks received: p = 0.0005; attacks initiated: p = 0.0002; pinning: p = 0.014) (d). Morever, impulsive choice was increased in MT compared with WT animals during delay discounting testing (interaction effect: F_(5,100) = 4.9, p < 0.001) (e). MT rats were also found to show increased reward sensitivity toward the rewarding effects of cocaine. CPP for cocaine (p = 0.007) (f), cocaine-induced sensitization (genotype effect: F_(1,24) = 13.1, p = 0.003) (g) and the acute stimulatory effects of cocaine (h) were also increased in MT rats compared with WT controls (interaction effect: F_(2,34) = 5.3, p = 0.01). Data are indicated as means ± SEM (SCM intake, PR: MT: n = 13, WT n = 10; social play: MT: n = 11, WT n = 9; delay discounting: MT: n = 13, WT n = 9; cocaine CPP: MT: n = 6, WT n = 8; cocaine sensitization: MT: n = 6, WT n = 8; cocaine dose–response curve: MT: n = 7, WT n = 12; *p ≤ 0.05).