Figure 5.

Acquisition of operant responding for water in wild-type (WT) and CB₂r overexpressing (CB₂xP) mice. (a) Average number of nose-pokes + SEM in the active hole in both WT (empty circles) and CB₂xP (filled circles) mice in 1-h sessions during 10 days of training with water under a fixed ratio 1 (FR1) schedule of reinforcement (10 μl of water in 10 s.); WT (n=7), CB₂xP (n=8). (b) Breaking point achieved by WT (white bar) and CB₂xP (black bar) mice under a progressive ratio schedule of reinforcement; WT (n=6), CB₂xP (n=8).