The effect of MDMA ("Ecstasy") and its optical isomers on schedule-controlled responding in mice.

Eleven mice were trained to respond under an FR 20 schedule of reinforcement and, after learning the schedule, were administered doses of saline and the following phenylisopropylamines: (+/-)-MDMA, S(+)-MDMA, R(-)-MDMA and (+)-amphetamine. Each of the phenylisopropylamines decreased rates of operant responding in a dose-dependent manner. S(+)-MDMA (ED50 = 3.1 mg/kg) was nearly equipotent with racemic MDMA and four times more potent than R(-)-MDMA (ED50 = 4.1 and 11.6 mg/kg, respectively), but less potent than (+)-amphetamine (ED50 = 0.74 mg/kg). The present study constitutes the first enantiomeric behavioral-potency comparison for the optical isomers of MDMA.