L-dopa infusion mode differentially affects corpus striatal dopamine efflux in the presence of reserpine

In the present experiment we tested the effects of L-DOPA upon dopamine (DA) efflux in vitro from superfused corpus striatal tissue fragments in medium containing reserpine. The purposes of this experiment were first, to evaluate the effects of differing infusion modes of L-DOPA upon DA efflux under conditions in which DA storage capacity has been diminished, and second, to compare this L-DOPA stimulated DA efflux with that of other putative DA secretagogues such as amphetamine and potassium. No differences were obtained in stimulated DA efflux between superfusions performed in the presence or absence of reserpine (10 microM) in the medium when L-DOPA (5 microM) was infused in a continuous (70 minute) mode during the superfusion. In contrast, a continuous infusion of either amphetamine (10 microM) or high potassium (30 mM) resulted in significantly greater stimulated DA efflux in superfusions performed with reserpine in the medium. In addition, when L-DOPA (5 microM) was administered for a brief 10-minute infusion period, a significantly greater stimulated DA efflux was obtained with superfusions containing reserpine in the medium. These results suggest that the mode of L-DOPA infusion may be an important factor in regulating DA release under conditions of diminished DA storage capacity.