This study will focus on the fundamental question of whether reactive metabolites of dopamine, may be contributing to the pathogenesis of neurodegenerative disorders such as Parkinson's disease. Dopamine has been shown to be toxic to cells both in vitro and in vivo. However, the exact mechanism associated with the toxicity is not known. Because mitochondria play a critical role in mechanisms of cell death, the proposed studies are designed to increase our understanding of the interplay between reactive metabolites of dopamine and mitochondrial function, and their ability to enhance the vulnerability of dopaminergic neurons to injury. In Aim 1, we will characterize the temporal relationship between loss of mitochondrial function and cell death following exposure to dopamine. In Aim 2, using striatonigral organotypic cultures, we will examine whether dopaminergic neurons exhibit an increased vulnerability to mitochondrial inhibition and whether dopamine contributes to this effect. Finally, in Aim 3, we will determine the identity of critical proteins modified and inactivated by dopamine quinones using mass spectrometry, with a focus on mitochondrial proteins. The outcome of these studies has potential for identifying new therapeutic targets for stopping and preventing the neurodegenerative process in Parkinson's disease.