Dopaminergic mechanisms of reinstatement of MDMA-seeking behaviour in rats.
Animal models of drug-seeking suggest that exposure to cues associated with self-administered drugs and drug primes might precipitate relapse via activation of central dopaminergic substrates. The effects of priming injections of dopamine and 5-HT agonists on drug-seeking and effects of dopamine antagonists on methylenedioxymethamphetamine (MDMA)-produced potentiation of drug-seeking following extinguished MDMA self-administration were examined. Drug-seeking was produced by exposure to a light stimulus that had been paired with self-administered MDMA infusions and this effect was potentiated by experimenter-administered injections of the dopamine D(2) -like receptor agonist, quinpirole, the indirect agonist, amphetamine and the uptake inhibitor, GBR 12909. Drug-seeking was not elicited by the dopamine D(1) -like receptor agonist, SKF 81297 or the non-selective agonist, apomorphine. The 5-HT receptor agonists DOI or mCPP also failed to elicit drug-seeking. The 5-HT uptake inhibitor, clomipramine, attenuated drug-seeking produced by the MDMA-associated stimulus but failed to alter the potentiated response produced by GBR 12909. The D(1) receptor antagonist, SCH 23390 or the D(2) receptor antagonist, eticlopride attenuated the potentiation of drug-seeking produced by MDMA. These data provide evidence of dopaminergic mechanisms in drug-seeking following extinction of MDMA self-administration. Because tissue levels of 5-HT were significantly decreased following MDMA self-administration, we suggest that MDMA begins to preferentially activate dopaminergic substrates to potentiate the drug-seeking response.