These lesions accumulate in small numbers during normal aging of the brain but occur in excess in AD.> Neuritic plaques contain a central core that includes A p amyloid, proteoglycans, Apo E4, a1 antichymotrypsin, and other proteins.> A amyloid is a protein of 39 to 42 amino acids that is derived proteolytically from a larger transmembrane protein, amyloid precursor protein (APP), which has neurotrophic and neuroprotective activity.> The normal function of A p amyloid is unknown.> Soluble amyloid fibrils may represent the initial pathologic event in AD leading to formation of neuritic plaques.> The plaque core is surrounded by the debris of degenerating neurons, microglia, and macrophages.> The accumulation of amyloid in cerebral arterioles, termed amyloid angiopathy, may lead to cerebral lobar hemorrhages.">