FIGURE 2

(a) Mean (SEM) basal dopamine concentrations sampled in the nucleus accumbens of rats chronically exposed to different doses of methadone released by osmotic minipumps implanted subcutaneously. The ^* indicates a significant difference from the 0 mg/kg/day methadone group. (b–d) Mean (SEM) percent increase in dopamine concentration in the ventral striatum caused by cocaine injections (i.p.) given to rats maintained on vehicle and different methadone doses. The ^* indicates a significant difference between rats maintained on 40 mg/kg/day methadone and vehicle. The ^** indicates a significant difference between rats maintained on 30 and 40 mg/kg/day methadone and rats maintained on vehicle.