Neuronal degeneration is a major histopathologic finding in Alzheimer's disease (AD). Selective vulnerability of subpopulations of subcortical neurons has previously been described. We recently described retinal ganglion cell loss and optic neuropathy, all in the absence of neuritic plaques, neurofibrillary tangles and amyloid angiopathy. Clinically, some AD patients show changes in visual evoked responses. Although the CNS contains heterogeneous cell populations, a monoclonal antibody marker (MAb 3F12) has identified some of the vulnerable neurons in the neocortex, hippocampus, and possibly the axons of retinal ganglion cells undergoing degeneration. Little is known of the molecular specificities of these cells in normal or AD brain or retina. IN this study we propose to analyze neuronal-specific function at three levels: clinical, histologic, and molecular. For the clinical studies we shall focus on the visual system, integrating the neurologic and psychometric database with specific visual function studies. Patients will be followed to autopsy and retinal ganglion cell loss assessed. A parallel histologic assessment of auditory system neuronal changes will be made. Temporal progression of neuronal loss in AD will be examined. With use of neuron-specific monoclonal probes, the architectonic differences in neuronal changes in AD will also be compared to other dementing diseases (Pick's, Parkinson's). The AD-vulnerable neurons will be further defined by: (1) immunocytochemical identification of their associated neurotransmitter and neuropeptides, (2) molecular characterization of Ag3F12, and (3) development of a neuron-enriched cDNA library. MAb 3F12 will be used to isolate clones from a human brain cDNA expression library, localization confirmed by combined in situ hybridization and immunoperoxidase staining. Isolated 3F12 cDNA clones will be useful as markers of pyramidal cell enrichment in preparation of a new neuron-enriched cDNA library. To enhance isolation of rare or low abundance mRNA species, we shall use subtraction hybridization methods. Transcripts will be screened by Northern and Southern blot analyses, and positives by in situ hybridization in normal and AD neocortex, hippocampus and retina. Proteins and/or transcripts of interest will be sequenced to determine if they are of known molecular specificity. Development of this neuronal subset-specific molecular panel may contribute to the understanding of regulatory mechanisms operative in these cells in AD.
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