MORPHOLOGY AND NEUROCHEMICAL CHARACTERISTICS OF THE VULNERABLE NEURONS IN BRAIN AGING AND ALZHEIMERS-DISEASE

Since the classical descriptions of the symptomatology and neuropathol ogic characteristics of Alzheimer's disease (AD), we have witnessed a considerable increase in the knowledge of the morphologic and molecula r features not only of AD, but also of normal brain aging. In spite of this progress, the pathogenetic events that differentiate normal brai n aging from the early stages of dementia and may lead eventually to A D are not completely understood. This article reviews the possible rel ationships between the localization of cellular pathologic changes in AD and the distribution of neuronal components of the hippocampal and neocortical circuitry that are affected by these alterations. The rela tive vulnerability or resistance of a given neuronal type to the degen erative process is discussed in order to provide correlates of the dis tribution of cellular pathologic changes, neurochemical phenotype rela ted to vulnerability, and affected hippocampal and neocortical circuit s.