AMYLOID, NEUROFIBRILLARY TANGLES AND ARGYROPHILIC PLAQUES - NEUROPATHOLOGY OF ALZHEIMERS-DISEASE

Alzheimer's disease (AD) is morphologically characterized by different types of lesions including neurofibrillary tangles and argyrophilic plaques. The former are present in the neocortex, hippocampus, nucleus basalis of Meynert and brainstem nuclei. Tangles are seen in large and medium sized neurons and, under transmission electron microscopy, they appear as paired helical filaments. Immunohistochemical studies reveal that the major antigenic component of these filaments is the abnormally phosphorylated Tau protein. Argyrophilic plaques are formed by degenerated neurites, and are observed in the neocortex and the hippocampus. They can be classified Into three types; early, mature and burnt-out. In the latter two types, amyloid is progressively deposited until it totally obscures the original structures, Neurites that participate in the formation of plaques belong to different neurotransmitter systems that include vasoactive intestinal polypeptides, encephalins, neurotensin, somatostin and substance P. Whereas neurofibrillary tangles can be found in several different types of encephalopaties aside from AD, plaques are a characteristic of this entity and are also part of normal aging. For this reason, it is of the utmost importance to be able to quantify the pathological findings in order to diagnose AD with a greater degree of certainty.