Fig. 1.

Dose-response curves for the percent of responding that occurred on the cocaine-appropriate lever (top panel) during test sessions in which cumulative doses of cocaine, caffeine, MDPV, methamphetamine, or midazolam were administered, as well as when saline (S) was administered before each of six cycles. Data represent the mean (± 1 S.E.M.) for seven rats, with each dose-response curve determined in triplicate for MDPV, methamphetamine, midazolam, and saline, or doubly determined in triplicate for cocaine and caffeine. Bottom panel shows the mean (± 1 S.E.M.) rate of responding observed during test sessions. Response-rate data reflect data from all cycles of each test session; however, data for the percent cocaine-appropriate responding were included only for doses/cycles in which a rat earned at least one reinforcer.