The effects of L-dopa on in vitro dopamine release from striatum
Abstract
We have examined the effects of L-dihydroxyphenylalanine (L-DOPA) on endogenous dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) efflux from superfused striatal slices prepared from adult male rats. Superfusion with L-DOPA (10 microM) caused a modest elevation in the tissue levels of DA and greatly increased the basal efflux and stimulation-evoked overflow of DA. Stimulation of slices under Ca2(+)-free conditions abolished DA overflow occurring in the absence of L-DOPA, but reduced DA overflow in the presence of L-DOPA by only 56%. Ca2(+)-independent DA release was not reduced by nomifensine. Destruction of DA terminals by pretreatment with 6-hydroxydopamine did not alter the capacity of L-DOPA to elevate tissue DA content. However, it attenuated the impact of L-DOPA on DA efflux, although this effect was somewhat smaller than was the apparent loss of DA terminals. These results suggest the following conclusions: (1) L-DOPA increases both the spontaneous and depolarization-induced release of DA; (2) some of the DA formed from L-DOPA can be released in response to depolarization by a process that does not involve either Ca2(+)-dependent exocytosis or reverse transport; and (3) most but not all of the DA efflux occurring in t...Continue Reading
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