Abstract

Previous studies have shown that the dopamine (DA) reuptake inhibitor 1-(2-[bis(4-fluorophenyl)-[methoxy]ethyl)-4-(3-phenylpropyl) piperazine (GBR12909) antagonizes the increase in extracellular DA evoked by local perfusion of cocaine into the striatum. In the present work, in vivo microdialysis methods were used to examine the effects of i.v. cocaine, GBR12909 and combinations of the two drugs on DA overflow in the nucleus accumbens of awake rats. Both cocaine and GBR12909 (0.3, 1.0 and 3.0 mg/kg) caused dose-related elevations in extracellular DA when given alone. However, the temporal profile of DA overflow was different with each drug. Cocaine caused a rapid and short-lived increase in DA, whereas GBR12909 caused a slow and sustained elevation of transmitter. In drug combination studies, the rise in extracellular DA after a modest dose of cocaine (1.0 mg/kg) was significantly reduced from 250% to 175% of baseline by pretreatment with a subthreshold dose of GBR12909 (0.3 mg/kg). A high dose of cocaine (3.0 mg/kg) increased dialysate DA by 600%; this rise in DA was decreased to 450% and 325% of baseline by pretreatment with 0.3 and 1.0 mg/kg of GBR12909, respectively. The neurochemical effect of the combination of GBR12909 plus cocaine was clearly not additive. GBR12909 also blocked the DA-releasing action of amphetamine (1.0 mg/kg). Our findings show that GBR12909 antagonizes the rise in extracellular DA produced by systemic cocaine and these results provide further evidence that DA reuptake inhibitors may be useful pharmacological adjuncts in the treatment of cocaine addiction and withdrawal in human patients.