Proposed studies will examine archival and fresh human temporal bones as well as brains to examine and characterize age-related mitochondrial DNA mutations and correlate these with changes in proteins related to the mitochondrial function of oxidative phosphorylation as well as to histopathology. A hypothesis is, that there will be a relation between regions with the highest oxidative phosphorylation (e.g. spiral ganglion cells and stria vascularis) and age- related mitochondrial changes and cell loss. The characterization of mitochondrial DNA will involve DNA extraction and quantitative PCR. The experiments also involve cloning, amplification and analysis for point mutations and deletions in mitochondrial DNA. Oxidative phosphorylation will be assessed with immunocytochemistry for different cytochrome oxidase subunits and histochemical assessment of cytochrome oxidase and succinate dehydrogenase. Cochlear histopathology also will be assessed in the same region of each cochlea both in archival and fresh material. The first specific aim will be to compare changes in the cochlea with changes in specific brain regions with varying susceptibilities to acquired mitochondrial DNA damage. The second specific aim is to characterize changes in the cochlea of aged subjects with normal appearing cochlear histology. The third and final specific aim is to characterize changes in the cochlea of subjects whose cochlea show age-related histopathology.