Differential effects of amphetamine and dopamine uptake blockers (cocaine, nomifensine) on caudate and accumbens dialysate dopamine and 3-methoxytyramine.

Evidence suggests that some amphetamine-like stimulants may enhance accumbens dialysate dopamine to the greater extent than caudate dopamine. To test our hypothesis that the difference in transmitter response may derive, in part, from the degree to which released dopamine in the two regions is metabolized to 3-methoxytyramine, we compared the effects of amphetamine with the uptake blockers, nomifensine and cocaine, on caudate and accumbens dialysate concentrations of dopamine, its acid metabolites and 3-methoxytyramine. The percentage increases in accumbens dopamine were significantly greater than in caudate only after the uptake blockers. All three drugs promoted dose-dependent increases in dialysate 3-methoxytyramine which, although temporally delayed, generally paralleled the increases in dopamine. However, after the administration of uptake blockers, the ratio of dialysate 3-methoxytyramine to dopamine was greater in caudate than in accumbens. In addition, the acid metabolite patterns were the same in the two regions after amphetamine, but were qualitatively different after the uptake blockers. These results indicate that the relative degree of metabolism of released dopamine to 3-methoxytyramine in caudate and accumbens may contribute to the regional differences in dopamine response to uptake blockers.