Abstract: The existence of both nitric oxide synthase (NOS) immunoreactive interneurons and amino acid neurotransmitter-mediated nitric oxide (NO) release in the striatum suggests a role for NO in modulating striatal function. To explore the potential interaction between NO and dopaminergic neurotransmission, the NO-releasing agent (±)-S-nitroso-N-acetylpenicillamine (SNAP) was administered locally into the anterior medial striatum of chloral hydrate-anesthetized rats. SNAP, at 0.5, 1, and 2 mM concentrations, elevated striatal extracellular (EC) dopamine (DA) to 200 ± 42, 472 ± 120, and 2,084 ± 496%, respectively, above baseline levels. Perfusion with (±)-penicillamine (PEN, 1 mM), the non-NO-containing carrier component of SNAP, was ineffective, indicating that PEN is not responsible for SNAP-mediated DA release. Additional microdialysis experiments suggest SNAP-mediated DA release is not due to NO-induced neurotoxicity or blockade of the DA transporter. The DA-releasing effect of SNAP was attenuated under calcium-free conditions and abolished in rats pretreated with reserpine (5 mg/kg), implicating a calcium-sensitive vesicular-dependent release process. To determine the mechanism of SNAP-mediated DA release, the guanylyl cyclase (GC) inhibitor LY 83583 (100 µM) was administered 100 min before and during the SNAP pulse. LY 83583 elevated EC DA levels approximately fivefold and potentiated the DA-releasing effect of SNAP to 2,598 ± 551% above basal DA levels. Similar pretreatments with both the noncompetitive N-methyl-d-aspartate (NMDA) antagonist MK-801 (10 µM) and the competitive NMDA-receptor antagonist (±)-3-(carboxypiperazin-4-yl)propyl-1-phosphonic acid [(±)-CPP, 100 µM] blocked SNAP-mediated DA release. SNAP-mediated DA release was also significantly blunted by pretreatment and coperfusion with MgSO4 (10 mM) and 6,7-dinitroquinoxaline-2,3-dione (DNQX, 10 µM) but not (+)-2-amino-3-phosphonopropionic acid (AP-3, 10 µM). These results suggest that NO releases DA via a calcium-sensitive vesicular-dependent process that is independent of GC activation. In addition, NMDA and kainate/(±)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated mechanisms are implicated in NO-induced DA release.