THE ROLE OF N-METHYL-D-ASPARTATE RECEPTORS IN THE REGULATION OF PHYSIOLOGICALLY RELEASED DOPAMINE

In vivo voltammetry was used to measure changes in ascorbate, which are an index of changes in the release of glutamate, and microdialysis was used to measure changes in dopamine in the striatum of freely moving rats. A 5 min tail pinch produced a rapid rise in striatal ascorbate paralleled by an increase in motor activity and a slower, more prolonged rise in dopamine. Systemic administration of ketamine or dizocilpine maleate, non-competitive antagonists of the N-methyl-D-aspartate glutamate receptor, produced an increase in the basal level of ascorbate but not dopamine; however the tail pinch-evoked rise in both ascorbate and dopamine was completely abolished by these drugs. The rise in dopamine was also abolished by local infusion of dizocilpine maleate into the striatum. Local application of N-methyl-D-aspartate produced a dose-dependent increase in dopamine, which was partially reduced in the presence of tetrodotoxin. The results show that the tail pinch-evoked increase in motor activity involves an increase in the release of striatal dopamine which requires the activation of N-methyl-D-aspartate receptors in the striatum. This suggests that phasic increases in striatal dopamine release are triggered by the action of glutamate on dopaminergic nerve terminals.