Stress-induced dopamine release in the neostriatum: evaluation of the role of action potentials in nigrostriatal dopamine neurons or local initiation by endogenous excitatory amino acids.

It has been hypothesized that excitatory amino acids can initiate dopamine release in neostriatum. We examined whether the increase in extracellular dopamine in neostriatum produced by acute stress reflects presynaptic initiation of dopamine release by endogenous excitatory amino acids. Thirty minutes of intermittent tail-shock stress significantly elevated extracellular concentrations of dopamine, glutamate, aspartate, and gamma-aminobutyric acid in neostriatum of freely moving rats as measured with in vivo microdialysis. Local infusion of the N-methyl-D-aspartate receptor antagonist 2-amino-5-phosphonovalerate or the non-N-methyl-D-aspartate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione via the dialysis probe did not attenuate the stress-induced increase in extracellular dopamine. In fact, the increase was prolonged in rats treated with specific excitatory amino acid receptor antagonists. Infusion of tetrodotoxin into medial forebrain bundle increased extracellular glutamate and aspartate in neostriatum yet reduced basal dopamine in extracellular fluid to below the limit of detection of the assay and eliminated the stress-induced increase in extracellular dopamine. These findings fail to support the hypothesis that the stress-induced increase in extracellular dopamine in neostriatum is initiated locally by excitatory amino acids. Rather, the effects of stress on extracellular dopamine seem to be determined by impulse propagation in dopamine neurons.