Fig. 1.

Dose-dependent changes in the frequency of reinforcers and responses induced by the adenosine A₁ receptor agonist CHA (0.0156–0.125 mg/kg i.p.) for rats performing under a DRL 72-s schedule (n = 8). For the vehicle condition, the mean (± S.E.M.) number of reinforcers obtained was 7.9 (± 1.49) while the mean number of total responses was 86.8 (± 11.20). Rats were injected 1 h before a 1-h behavioral session. Significant changes from the vehicle control are indicated: *, p < 0.05, and **, p < 0.01, using the Dunnett test. Dotted lines indicate graphical continuation of the vehicle control value.