MDMA-induced impairment in primates: antagonism by a selective norepinephrine or serotonin, but not by a dopamine/norepinephrine transport inhibitor

Human MDMA ( R, S-3,4-methylenedioxymethamphetamine) users display selective cognitive deficits after acute MDMA exposure, frequently attributed to serotonin deficits. We postulated that MDMA will compromize executive function in primates and that an inhibitor of the serotonin transporter (SERT) and the norepinephrine transporter ( NET) but not the dopamine (DAT) transporter, will prevent impairment. The potencies of DAT/NET, NET and SERT inhibitors to block transport of [H-3] MDMA and [H-3] monoamines were compared in vitro. Subsequently, cynomolgus monkeys ( Macaca fasicularis) were trained to stable performance in a reversal learning task. Effects of once-weekly oral or i.m. dose of MDMA (1.5 mg/kg, n=4 ) on performance were monitored, alone or after pretreatment with inhibitors of the SERT, DAT or NET ( prior to i.m. MDMA). 1) Drug potencies for blocking [ 3H] MDMA or [ 3H] monoamine transport were not consistent; 2) Oral MDMA increased error rates in a cognitive task for up to three days following exposure, whereas intramuscular MDMA prevented subjects from performing the cognitive task on the day of administration, but not on subsequent days; 3) The SERT inhibitor citalopram and the NET inhibitor desipramine, but not the DAT/NET inhibitor methylphenidate, reversed the effects of MDMA on task performance and mandibular movements induced by i.m. MDMA and 4) MDMA altered sleep latency. Oral MDMA impairs executive function in monkeys for several days, a finding of potential relevance to MDMA consumption by humans. Reversal of impaired executive function by a NET inhibitor implicates the NET and norepinephrine in MDMA-induced cognitive impairment and may be relevant to therapeutic strategies.