RESTRICTION AND FUNCTIONAL-CHANGES OF DOPAMINE RELEASE IN RAT STRIATUM FROM YOUNG-ADULT AND OLD RATS

In order to investigate the age-related changes in dopaminergic activi ty in rats, we have utilized the K+- and veratridine-stimulated [C-14] dopamine release from striatum in vitro as a functional index of respo nsiveness to these stimuli in aging. We found that the K+-stimulated d opamine release from old (12 months) rats decreased by more than 50% c ompared to that from young adult rats (3 months). Reserpine (5 mg/kg) led to a pronounced decrease of the K+-stimulated dopamine release of young adult as well as old rats. Whereas ouabain (10 mu mol/l) decreas ed the K+-stimulated dopamine release from young adult rats, in old ra ts the K+-induced dopamine release was increased up to 250%. However, in old rats which were reserpine pretreated, ouabain was unable to sti mulate the K+-induced dopamine release. In contrast, the veratridine-s timulated dopamine release of old rats was increased up to 200% compar ed to that of young adult rats and was highly sensitive to reserpine p retreatment but not to ouabain. However, reserpine did not alter this veratridine-stimulated dopamine release from young adult rats. The pre sent data indicate that the age-related reduction of exocytosis-relate d, Ca2+-dependent release mechanisms (K+) are probably compensated via an increase in Ca2+-independent, uptake carrier-mediated release proc esses (veratridine).