A.: A three-lever operant procedure differentiates the stimulus effects of R(2)MDA from S(1)MDA

1-(3,4-Methylenedioxyphenyl)-2-aminopropane (MDA) pro-duces an effect in humans that is somewhat similar to both a hallucinogen and a central stimulant. We have previously shown that R(-)-MDA but not S(+)-MDA produces a stimulus effect in animals similar to that of the hallucinogen 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM), whereas S(+)-MDA but not R(-)-MDA produces a stimulus effect similar to that of the stimulant amphetamine. Others have suggested that the stimulus effects of the two MDA isomers may be much more similar than our results would indicate. To help clarify this issue, we have shown that rats (n = 8) can be trained to discriminate 1.25 mg/kg of R(-)-MDA (ED5O = 0.99 mg/kg) from 1.25 mg/kg of S(+)-MDA (ED50 = 0.80 mg/kg) versus 0.9 % saline with use of a three-lever operant procedure. T