Fig. 2.

(Upper panel, left side) Self-administration of 0.032 mg/kg/infusion MDPV (n = 32, squares) and 0.32 mg/kg/infusion cocaine (n = 16, circles) during the last 3 days of the FR1 and FR5 schedules of reinforcement. Abscissa: numbers refer to the final three sessions of FR1 and FR5 training. (Upper panel, right side) Self-administration dose-response curves obtained under the FR5 schedule of reinforcement in MDPV-trained high-responders (n = 7) and low-responders (n = 9) using dose substitution. Abscissa: SAL represents infusions of saline, while the numbers refer to dose of MDPV available during each session, expressed as mg/kg/infusion on a log scale. Ordinate: total infusions obtained during the 90-minute session. Error bars represent ±S.E.M. (Lower panel, left side) Distribution of MDPV-trained (n = 32) and cocaine-trained (n = 16) rats based on timeout responding. Abscissa: percent of total responses emitted on the active lever occurring during the postinfusion timeout, presented in 10% bins. Ordinate: proportion of MDPV- or cocaine-trained rats. (Lower panel, right side) Correlation between timeout responding and infusions obtained under FR5/5-second TO. Abscissa: average number of infusions of 0.032 mg/kg/infusion MDPV obtained over the last 3 days of FR5 conditions. Ordinate: percent responses made on the active lever during timeouts versus total active lever responses. Asterisks and pound signs indicate statistical significance: *P < 0.05 versus low-responders during same FR; #P < 0.05 versus same group during FR1.