Alzheimer's disease (AD) and Parkinson's Disease (PD) are the most prevalent neurodegenerative diseases (NDD) in America, afflict several million citizens, and represent major sources of disability for the individual and substantial cost to society. The molecular causes of progressive death of cortical and diencephalic neurons in AD and dopamine neurons in PD are not known, nor ar there effective pharmacologic strategies for halting progression of either disease. A recently developed technique (cytoplasmic hybrids= "cybrids") has allowed genetic transfer of specific mitochondrial electron transport chain (ETC) defects from AD (complex IV) or PD (complex I) platelet mitochondrial DNA into clonal neuronal host cells, showing that the etiology of the ETC defects is in the mitochondrial genome. Cybrid cells provide model systems to explore hypotheses about the causes of cell death resulting from having bioenergetically impaired mitochondria. The experiments in this proposal utilize contemporary microdialysis and molecular techniques to address four Specific Aims that test four hypotheses about the causes of neuronal death in AD and PD. Aim 1 will characterize the pharmacology of brain hydroxyl free radical (OH*) production following acute, local inhibition of mitochondrial ETC complex I with MPP+ or IV with azide infusion or acute amyloid peptide infusion. Aim 2 will characterize expression of protective enzyme systems (catalase, glutathione peroxidase, superoxide dismutase) in cybrids derived from AD, PD and control subjects and will determine if exposure of cybrid cells to neurotrophin molecules (NGF, BDNF) alters ROS production and apoptosis following exposure to MPP+ or azide, transcription of genes for protective enzymes, or activities of protective enzymes. Aim 3 will measure mRNA levels with quantitative RT-PCR and protein levels with Western blotting and/or ELISA for the growth regulatory proteins p53, bcl-2, bcl-xL, and Bax in cybrid cells derived from AD, PD and control subjects during the course of MPP+ azide exposure. Aim 4 will explore the involvement of bcl- 2, bcl-xL and bax in regulating programmed cell death in cybrid cells derived from AD, PD, or control subjects. Wherever, results in cells will be extended into animals to provide correlation of in vitro with in vivo. The results of experiments in each Specific Aim have potential treatment applications and will provide knowledge applicable to other human neurodegenerative diseases.