Development, maintenance and temporal pattern of self-administration maintained by ecstasy (MDMA) in rats.
BACKGROUND
+/-3,4-Methylenedioxymethamphetamine (MDMA; "ecstasy") use is increasing around the globe but there is a paucity of studies examining the abuse liability of this drug.


OBJECTIVE
The ability of drugs to reinforce operant responding in laboratory animals is a valid and reliable predictor of abuse potential. MDMA is self-administered by humans, but there have been few reports of reliable self-administration by drug-naive laboratory animals. The present study sought to examine the acquisition and maintenance of MDMA self-administration by laboratory rats. The influence of prior training with cocaine self-administration on the acquisition of MDMA self-administration was also examined.


METHODS
MDMA self-administration (0.25-2.0 mg/kg per infusion) was examined in rats that were first trained to self-administer cocaine as well as by those that were drug-naive. The dose-dependency of MDMA self-administration and the temporal pattern of responding maintained by various doses of MDMA were examined. In some rats, self-administration of MDMA during a 24-h session was also examined.


RESULTS
MDMA was self-administered by laboratory rats that were experienced with self-administration of cocaine as well as by rats that were initially drug naive. For drug naive rats, the acquisition of MDMA self-administration (1.0 mg/kg per infusion) developed gradually during daily test sessions. The latency to acquisition of self-administration was shorter in cocaine-trained rats. Self-administration was dose-dependent, extinguished when saline was substituted for MDMA and, was reinstated when MDMA was reintroduced. During a 24-h self-administration session, a high rate of responding was produced during the first hour of the test session followed by a steady and lower rate of two to four responses per hour during subsequent hours of the test.


CONCLUSIONS
These results suggest that prior experience with cocaine self-administration facilitates the acquisition of MDMA self-administration. The results also suggest that MDMA has abuse liability and that increased use of the drug should raise concern of a growing and widespread potential for chronic abuse.
Schenk
Susan
S
School of Psychology, Victoria University of Wellington, PO Box 600, Wellington, New Zealand. susan.schenk@vuw.ac.nz
Gittings
David
D
Johnstone
Malcolm
M
Daniela
Evangeline
E
D000818:Animals; D003042:Cocaine / Q000008:administration & dosage; D018765:Dopamine Uptake Inhibitors / Q000008:administration & dosage; D004305:Dose-Response Relationship, Drug; D006213:Hallucinogens / Q000008:administration & dosage*; D008297:Male; D018817:N-Methyl-3,4-methylenedioxyamphetamine / Q000008:administration & dosage*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012646:Self Administration
D018765:Dopamine Uptake Inhibitors; D006213:Hallucinogens; D003042:Cocaine; D018817:N-Methyl-3,4-methylenedioxyamphetamine