Adolescent pre-exposure to ethanol and 3,4-methylenedioxymethylamphetamine (MDMA) increases conditioned rewarding effects of MDMA and drug-induced reinstatement.
Many adolescents often take ethanol (EtOH) in combination with 3,4-methylenedioxymethylamphetamine (MDMA). In the present work, we used a mouse model to study the effect of repeated pre-exposure during adolescence to EtOH (2 gkg), MDMA (10 or 20 mgkg) or EtOH MDMA on the rewarding and reinstating effects of MDMA in the conditioned place preference (CPP) paradigm. Pre-exposure to EtOH, MDMA or both increased the rewarding effects of a low dose of MDMA (1.25 mgkg). These pre-treatments did not affect the acquisition of the CPP induced by 5 mgkg of MDMA. However, the CPP was more persistent in mice pre-exposed to both doses of MDMA or to EtOH MDMA20. After extinction of the CPP induced by 5 mgkg of MDMA, reinstatement was observed in all groups with a priming dose of 2.5 mgkg of MDMA, in the groups pre-exposed to EtOH or MDMA alone with a priming dose of 1.25 mgkg, and in the groups pre-treated with MDMA alone with a priming dose of 0.625 mgkg. Pre-treatment during adolescence with MDMA or EtOH induced long-term changes in the level of biogenic amines dihydroxyphenyl acetic acid, homovanillic acid, dopamine turnover, serotonin (5-hydroxytryptamine, 5-HT) and 5-hydroxyindole acetic acid (5-HIAA) in the striatum, and 5-HT and 5-HIAA in the cortex after the first reinstatement test, although these effects depended on the dose used during conditioning. These results suggest that exposure to EtOH and MDMA during adolescence reinforces the addictive properties of MDMA.