Analysis of the Acquisition of Drug Discrimination Reveals Differences Between a High Versus Low Training Dose of ±3,4-methylenedioxymethamphetamine (MDMA)

Abstract

Background. Studies of the discriminative stimulus effects of the recreational drug, ±3,4- methylenedioxymethamphetamine (MDMA), typically use a dose of 1.5 mg/kg during training. This dose is relatively low compared to those used in other behavioral paradigms. Purpose. The present study assessed the ability of this low dose of MDMA and a higher dose of 3.0 mg/kg to support drug- discrimination learning in rats. Procedures. Daily training sessions were preceded by an injection of either MDMA (1.5 mg/kg or 3.0 mg/kg) or saline. Injections alternated in a pseudorandom fashion for a total of 63 sessions. Criteria for the acquisition of the MDMA/saline discrimination were increased from 4 to 10 successive, and successful, discriminations. As the acquisition criteria became more stringent, the impact on the low dose discrimination was greater than the impact on the high dose discrimination. Conclusions. These results suggest that the drug discrimination produced by 1.5 mg/kg MDMA may be less reliable than when a higher dose is employed, especially when the number of training sessions is limited. The data further suggest that 3.0 mg/kg MDMA produced a robust discriminative stimulus effect which may be better suited to experiments of this nature.