L-dopa administration enhances exocytotic dopamine release in vivo in the rat striatum.

Peripheral administration of L-3,4-dihydroxyphenylalanine (L-DOPA) methylester increased extracellular levels of DOPA and dopamine (DA) in the rat striatum monitored by in vivo brain microdialysis. The increase in DA levels persisted after inhibition of DA reuptake by nomifensine. Administration of blockers of voltage-dependent Na+ (tetrodotoxin) or Ca2+ (NKY-722) channels through the dialysis membrane completely eliminated the increase in DA levels. These results demonstrate that the L-DOPA-induced DA release is exocytotic in nature and hence, derived from neurons in the striatum.