Fig. 2.

Dose-response curves for the percent of responding that occurred on the cocaine-appropriate lever during test sessions in which cumulative doses of binary mixtures of cocaine and caffeine (top row), MDPV and caffeine (middle row), or cocaine and MDPV (bottom row) were administered. Each mixture was tested at three fixed-dose ratios [3:1 (left column), 1:1 (center column), and 1:3 (right column)] relative to the ED₅₀ for each constituent drug. Experimentally determined dose-response curves (black lines, open symbols) represent the mean (± 1 S.E.M.) for seven rats, with all dose-response curves determined in triplicate for each rat. Predicted, additive dose-response curves represent the mean (± 1 S.E.M.) for seven rats and are depicted as gray lines (no symbols). Because total cocaine equivalents were calculated for individual rats, cumulative total cocaine equivalents (mg/kg) represent the mean (± 1 S.E.M.) for seven rats.