Figure 4.

Operant responding for cocaine in wild-type (WT) and CB₂r overexpressing (CB₂xP) mice. (a) Average number of nose-pokes + SEM in the active hole in WT (empty circles) and CB₂xP (filled circles) mice in 1-h sessions during 10 days of training with cocaine (0.5 mg/kg/infusion); WT (n=8), CB₂xP (n=10). (b) Breaking point achieved by WT (white bar) and CB₂xP (black bar) mice under a progressive ratio schedule of reinforcement; WT (n=8), CB₂xP (n=7). (c) Average number of nose-pokes + SEM during the initial 10 sessions of extinction in the active hole in both WT (empty circles) and CB₂xP (filled circles) mice. (d) Responding in the active hole during cue-induced relapse of cocaine-seeking behavior tests in WT (white bar) and CB₂xP (black bar) mice; WT (n=8), CB₂xP (n=7). ^*P<0.05, ^**P<0.01, ^***P<0.001, CB₂xP mice vs WT mice.