Figure 2.

Dose-response curves for the number of responses made during CS+drug reinstatement tests in rats with a history of self-administering MDPV (black open circles; n=10) or a mixture of MDPV+caffeine (gray open squares; n=8–10). Experimentally determined dose-response curves (circle or square symbols) for MDPV (panel A), caffeine (panel B) alone, as well as mixtures of MDPV+caffeine at 3 fixed-dose ratios, (panel C [3:1], panel D [1:1], and panel E [1:3]) represent the mean (± 1 S.E.M.) number of responses, whereas the predicted dose-response curves (red lines, no symbols) represent the mean (± 1 S.E.M.) number of responses calculated for an additive interaction. Abscissa: S represents saline pretreatment (CS test), whereas the numbers refer to doses of MDPV (panel A), caffeine (panel B), or MDPV equivalents (panels C-E) administered intravenously 5-min before the CS or CS+drug test session. Ordinates: total number of responses made on the active lever during the 90-min session. Filled symbols represent responding significantly greater than saline (CS test).