Regulation of the Vesicular Monoamine Transporter-2: A Novel Mechanism for Cocaine and Other Psychostimulants

Abstract

The plasmalemmal dopamine (DA) transporter (DAT) is a principal site of action for cocaine. This report presents the novel finding that in addition to inhibiting DAT function, cocaine administration rapidly alters vesicular DA transport. Specifically, cocaine treatment abruptly and reversibly increased both the V_max of DA uptake and the B_max of vesicular monoamine transporter-2 (VMAT-2) ligand (dihydrotetrabenazine) binding, as assessed ex vivo in purified rat striatal synaptic vesicles. Selective inhibitors of the DAT (amfonelic acid and GBR12935), but not the plasmalemmal serotonin transporter (fluoxetine), also increased vesicular DA uptake. Moreover, DA depletion resulting from administration of the tyrosine hydroxylase inhibitor α-methyl-p-tyrosine had cocaine-like effects. Conversely, administration of the DA-releasing agent methamphetamine rapidly decreased vesicular uptake. Taken together, these data demonstrate for the first time ex vivo that cocaine treatment rapidly alters vesicular monoamine transport, and suggest that alterations in cytoplasmic DA concentrations contribute to stimulant-induced changes in vesicular DA uptake. Hence, the VMAT-2 may be an important target for developing strategies to treat not only cocaine addiction but also other disorders involving alterations in neuronal DA disposition, including Parkinson's disease.