The effects of MDMA and other methylenedioxy-substituted phenylalkylamines on the structure of rat locomotor activity.

The effects of acute subcutaneous injections of methylenedioxy-substituted phenylalkylamines in rats were tested in an unconditioned motor behavior paradigm using the Behavioral Pattern Monitor (BPM). Based on a previously developed scaling hypothesis and the associated temporal and spatial scaling exponents (alpha and d), the effects of racemic and S(+) 3,4-methylenedioxyamphetamine (MDA), racemic, S(+) and R(-) 3,4-methylenedioxymethamphetamine (MDMA), racemic N-methyl-1-(1,3-benzodioxol-5yl)-2-butanamine (MBDB), racemic N-ethyl-3,4-methylenedioxyamphetamine (MDEA), 2,5-dimethoxy-4-iodoamphetamine, and methamphetamine were characterized using the d-alpha plane. Three distinct dose-response patterns were observed. 1) S(+) and (+/-)MDA had pronounced dose-dependent effects on the structure of motor behavior, which were characterized by long-straight path movements and minimal changes in the amount of motor behavior. 2) (+/-)MDMA and (+/-)MBDB dose-dependently changed patterns of movements towards long-straight paths together with dose-dependent increases in the amount of motor activity. 3) S(+)MDMA and (+/-)MDEA produced dose-related increases in the amount of motor activity with minimal changes of the movement patterns in the BPM. Comparisons with the existing drug discrimination, operant, and biochemical literature on these compounds lead to the conclusion that the observed effects in the d-alpha plane do not simply reflect the different effects of these compounds as dopamine or serotonin (5-HT) releasers or reuptake inhibitors and do not parallel their different abilities to exhibit hallucinogen-like effects. Instead, indirect 5-HT1 effects appear to contribute substantially to the differential changes in the amount and structure of motor behavior induced by the phenylalkylamines. This conclusion may provide an encouraging rationale to develop postsynaptically effective "entactogens," a potential new drug category as adjunctive psychotherapeutics.