Intracranial self-administration of MDMA into the ventral striatum of the rat: differential roles of the nucleus accumbens shell, core, and olfactory tubercle.

Abstract

Behavioral and anatomical data suggest that the ventral striatum, consisting of the nucleus accumbens and olfactory tubercle, is functionally heterogeneous. Cocaine and D: -amphetamine appear to be more rewarding when administered into the medial olfactory tubercle or medial accumbens shell than into their lateral counterparts, including the accumbens core. We sought to determine whether rats self-administer the popular recreational drug (+/-)-3,4-methylenedioxymethamphetamine (MDMA) into ventrostriatal subregions and whether the medial olfactory tubercle and medial accumbens shell mediate MDMA's positive reinforcing effects more effectively than their lateral counterparts. Rats receiving 30 mM MDMA into the medial olfactory tubercle, medial accumbens shell, or accumbens core, but not the lateral tubercle or lateral shell, showed higher self-administration rates than rats receiving vehicle. The medial shell supported more vigorous self-administration of MDMA at higher concentrations than the core or medial olfactory tubercle. In addition, intra-medial shell MDMA self-administration was disrupted by co-administration of the D1 or D2 receptor antagonists SCH 23390 (1-3 mM) or raclopride (3-10 mM). Our data suggest that the ventral striatum is functionally heterogeneous. The medial accumbens shell appears to be more important than other ventrostriatal subregions in mediating the positive reinforcing effects of MDMA via both D1- and D2-type receptors. Together with previous data, our data also suggest that unidentified actions of MDMA interfere with the positive reinforcing effects of dopamine in the medial olfactory tubercle.