British Journal of Pharmacology
December 30, 2010
Susan Schenk, David Gittings, Joyce Colussi‐mas
61 citations
In rats trained to self-administer MDMA (ecstasy), a light cue previously paired with the drug triggered drug-seeking behavior. This effect was amplified by priming injections of drugs that activate dopamine D2-like receptors (quinpirole, amphetamine, GBR 12909) but not by a D1-like receptor agonist (SKF 81297), the non-selective dopamine agonist apomorphine, or serotonin (5-HT) receptor agonists. A serotonin uptake inhibitor reduced cue-induced drug-seeking but did not block the potentiation caused by a dopamine uptake inhibitor. Blocking either D1 or D2 receptors attenuated the MDMA-enhanced drug-seeking. The findings suggest that after repeated MDMA use, dopamine pathways become more influential in driving relapse to drug-seeking, partly because MDMA reduces brain serotonin levels.
Addiction Biology
June 14, 2013
Sarah Bradbury, Judith Bird, Joyce Colussi‐mas et al.
59 citations
About half of rats fail to acquire MDMA self-administration, and the difference is not due to how the drug is metabolized. MDMA triggers greater release of serotonin than dopamine in the brain. Rats that did acquire self-administration showed lower serotonin overflow than those that did not. Destroying serotonin neurons with a toxin made more rats acquire MDMA self-administration and speeded acquisition of cocaine self-administration. These findings suggest that serotonin limits initial sensitivity to MDMA's rewarding effects and delays reliable self-administration.
The International Journal of Neuropsychopharmacology
March 25, 2010
Joyce Colussi‐mas, Richard J. Wise, Alex Howard et al.
51 citations
In rats that learned to self-administer MDMA, a later injection of the drug triggered renewed drug-seeking behavior. The strength of this drug seeking was greater in rats that had acquired self-administration more quickly and in those that showed larger MDMA-induced increases in dopamine in the dorsal striatum. Rats that never learned to self-administer MDMA or that received the drug passively did not show this effect. The findings suggest that individual differences in initial sensitivity to MDMA's reinforcing effects and in the drug's ability to elevate striatal dopamine influence the propensity to seek the drug after a period of abstinence.
Journal of Drug and Alcohol Research
January 1, 2012
Susan Schenk, Joyce Colussi‐mas, Jennifer Do et al.
38 citations
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.