Involvement of intraterminal dopamine compartments in the amine release in the cat striatum

A push-pull superfusion technique has been used in the anesthetized cat to study the simultaneous release of tritiated and total dopamine (DA) during continuous labelling with tritiated tyrosine. The concentration of tritiated and total DA (1.3 and 70 nM respectively) and dihydroxyphenylacetic acid (1 microM) have been measured in the extracellular space under our experimental conditions. The specific activity of spontaneously released DA was found to be 0.76 Ci/mmol. The release of tritiated and total amine following 3 h superfusion with [3H]tyrosine did not occur in parallel in response to the local application of either alpha-methyl-p-tyrosine (0.1 mM) or amphetamine (1 microM). Amphetamine induced an increase followed by a decrease in the specific activity of released DA which reflects an initial release of newly synthesized DA followed by the release of stored amine. The transfer between intraterminal pools of the amine is thus clearly evidenced. The results show that the simultaneous determination of tritiated and total DA release allows the relative contribution of the two intraterminal pools to the amine release to be monitored.