Comparison of the effects of abstinence on MDMA and cocaine self-administration in rats.
3,4-Methylenedioxymethamphetamine (MDMA) preferentially increases synaptic serotonin (5HT). This response was attenuated following repeated exposure but there was recovery as a result of abstinence. Effects of abstinence on self-administration of many drugs have been documented but the impact on MDMA self-administration is unknown. This study compared the effects of abstinence on MDMA and cocaine self-administration. Six-hour daily MDMA or cocaine sessions were conducted until a total of 350 mgkg had been self-administered. Following this, rats were randomly assigned to either a 0- or 14-day abstinence group. Self-administration testing then continued for an additional 7 days. The latency to self-administer 350 mgkg was shorter for rats that self-administered cocaine. The temporal distribution of responding within each test session also differed MDMA self-administration was high during the first hour of each session, and decreased during subsequent hours, whereas cocaine self-administration was evenly distributed throughout each hour of the session. Abstinence decreased MDMA but not cocaine self-administration. The selective reduction of MDMA self-administration following abstinence is consistent with the idea that MDMA-stimulated 5-HT release is inhibitory to MDMA self-administration.