Mean ± SEM a active and b inactive lever presses for amphetamine (0.03 mg/kg/infusion) between EC, IC, and SC rats under a PR schedule of reinforcement following MTEP (0.3, 1.0, 3.0 mg/kg) or saline treatment. a Final ratio completed is included in the right y-axis. Asterisk (*) indicates that SC rats administered MTEP (3.0 mg/kg) exhibited significantly fewer active lever presses than SC rats administered saline (p<.05). b There were no significant differences in inactive lever responding between EC, IC, or SC rats under any MTEP dose