The mechanism that underlies the progressive degeneration of the dopaminergic neurons in Parkinson's disease (PD) is not clear. The Zn 2+ level in the substantia nigra of Parkinson's patients is increased. However, it is unknown whether Zn 2+ has a role in the degeneration of dopaminergic neurons. This study identifies an interaction between dopamine and Zn 2+ that induces cell death. When PC12 cells were pretreated with Zn 2+ before dopamine treatment, dopamine and Zn 2+ synergistically increased cell death, while Zn 2+ and H 2O 2 had only additive effects on cell death. The synergistic effect appeared to be caused by increased apoptosis rather than necrosis. The synergistic effect was specific for Zn 2+. The synergistic effect was inhibited by thiol antioxidants but was not significantly affected by calcium channel blockers. There is a similar synergistic effect when dopamine and Zn 2+ were coinfused into the striatum, resulting in striatal dopamine content depletion in vivo. Thus, both dopamine oxidation and Zn 2+ are possibly linked to the degeneration of dopaminergic neurons.
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