Effects of MDMA, methamphetamine and methylphenidate on repeated acquisition and performance in rats.

Repeated-acquisition procedures that include performance controls for effects not specific to acquisition permit the assessment of drug effects on learning on a within-subject, within-session basis. Despite the advantages of this methodology, few studies have examined effects of psychomotor stimulants on repeated acquisition in rodents. The purpose of the present study was to investigate the effects of methylenedioxymethamphetamine (MDMA, 0.3-10mg/kg), methamphetamine (MA, 0.1-3mg/kg) and methylphenidate (MPD,1-17 mg/kg) using repeated-acquisition procedures with performance controls in rats using a touch-screen apparatus. Rats were presented a 2x3 array of stimuli using a computer touch-screen and nose-pokes to target locations within the array were reinforced. In the acquisition component, the correct location changed across sessions, whereas during the performance component, the correct location was constant across sessions. All three drugs reduced accuracy of responding to target locations in a dose-dependent fashion. None of the compounds enhanced learning at any dose. MPD and MA produced significant disruptions of acquisition accuracy only at doses that also disrupted performance, but the 3mg/kg dose of MDMA impaired acquisition of target responding without affecting performance. The selective impairment of acquisition found in the present study adds to the evidence of learning and memory disruption produced by acute MDMA administration and raise questions about the mechanisms for these actions.