GBR 12783, a potent and selective inhibitor of dopamine uptake: biochemical studies in vivo and ex vivo

The effects of GBR 12783, an aryl 1,4-dialk(en)ylpiperazine derivative, were studied on the in vivo and ex vivo neuronal uptake of dopamine (DA), norepinephrine (NE) and serotonin (5HT). The drug inhibited potently (IC50 = 1.8 nM) and competitively the [3H]DA uptake by rat striatal synaptosomes. It produced significant [14C]DA release only at much higher concentrations (in the micromolar range). Depending on the animal species (rat or mouse) and the experimental conditions, GBR 12783 was 18-90 times and 85-300 times less effective against NE and 5HT uptake respectively than against DA uptake. In synaptosomes preloaded with [3H]DA, GBR 12783 added to the superfusion medium prevented the (+)amphetamine-induced DA release. The total binding of [3H]GBR 12783 to a membranal fraction prepared from striatum was lower than the binding to a synaptosomal fraction, suggesting its entry in synaptosomes. In addition, the concentration-dependent release of [3H]DA produced by GBR 12783 from a striatal vesicular fraction may account for the synaptosomal DA release promoted by micromolar concentrations of the drug. In ex vivo experiments, the ID50 for DA uptake inhibition (30 min after i.p. administration) was 8.1 mg/kg. After a dose of 10 mg/kg i.p., the striatal DA uptake inhibition occurred quickly (less than 10 min) and was long-lasting (greater than 5 h). The specificity of the drug for the DA uptake relative to NE and 5HT uptakes was also seen after i.p. administration of GBR 12783.