Four rhesus monkeys trained to press levers for intravenous cocaine infusions were tested with saline and (+/-)-3,4-methylenedioxymethamphetamine (MDMA; 3-300 micrograms/kg per infusion) during daily 1-h sessions. From four to over nine times more cocaine infusions were obtained than saline infusions during baseline sessions. When MDMA was substituted for cocaine, at least one dose was self-administered in 3 of the 4 monkeys at rates that exceeded the range of saline infusions. In fact, two of the monkeys self-administered a dose of MDMA at a greater rate than cocaine. These results demonstrate that MDMA can serve as a positive reinforcer for rhesus monkeys and, taken together with other preclinical behavioral studies, suggest a potential for recreational use of MDMA by humans.
