Differences in the stimulus properties of 3,4-methylenedioxyamphetamine and 3,4- methylenedioxymethamphetamine in animals trained to discriminate hallucinogens from saline.

The stimulus properties of 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxymethamphetamine (MDMA) and several related compounds were compared to those of (+)-lysergic acid diethylamide (LSD) and mescaline (3,4,5-trimethoxyphenylethylamine) in a two-lever, water-reinforced, drug discrimination task. In animals trained to discriminate LSD (0.08 mg/kg) from saline (n = 8), LSD-like responding occurred during substitution (generalization) tests with sufficiently high doses of (+/- )-2,5-dimethoxy-4-methylamphetamine, LSD, mescaline, psilocybin and (-)-MDA; saline appropriate responding occurred after (+)-MDA and both (+)- and (+)- and (-)-MDMA. In animals trained to discriminate mescaline (10 mg/kg; n = 8), (-)-MDA, (+)-MDA, (-)-MDMA and (+)-MDMA as well as (+/- )-2,5-dimethoxy-4-methylamphetamine, LSD, mescaline and psilocybin mimicked the training drug. Neither (+)-amphetamine nor cocaine produced mescaline-like responding; fenfluramine substituted partially for mescaline but not LSD. Because all of the phenylisopropylamine enantiomers mimicked the potent hallucinogen mescaline (10 mg/kg), these results do not support suggestions that similarities in the behavioral effects of "designer" drugs such as MDA and MDMA to those of hallucinogens are limited to (-)-MDA. They also indicate that, although LSD and mescaline may be pharmacologically similar (in other assays), these compounds do not have identical stimulus properties.