About half of a large sample of rats learned to self-administer MDMA, taking an average of 16 daily sessions before meeting the initial criterion. When the dose was reduced, the rats increased their responding in a compensatory manner. Over an additional 14 days of self-administration, daily intake rose from 8.5 to 15.25 mg/kg. These results indicate that MDMA acts as a reliable reinforcer for roughly half of rats, and that acquiring self-administration requires more sessions than is typical for other abused drugs.
MDMA use is rising worldwide, and high doses reduce serotonin (5HT) markers in the brain. This study examined whether self-administered MDMA causes lasting serotonin deficits in rats. Rats self-administered MDMA infusions until reaching total doses of either 165 or 315 mg/kg. Serotonin levels in the frontal cortex, striatum, and hippocampus were measured 2 or 10 weeks later. The lower dose did not significantly reduce serotonin in any brain region. The higher dose decreased serotonin by 30–35% in all three regions at 2 weeks, but levels recovered by 10 weeks. These dose- and time-dependent deficits suggest similar effects may occur in humans who use MDMA.