Alzheimer's disease: The density of amygdalar neuritic plaques is associated with the severity of neurofibrillary pathology and the degree of beta-amyloid protein deposition in the cerebral cortex

The gradual development of Alzheimer-related neurofibrillary changes and β-amyloid deposits have been investigated in the amygdala and cerebral cortex with advanced silver methods. Neurofibrillary tangles occur within the somata of nerve cells, while neuropil threads are located in nerve cell processes. In neuritic plaques, there are both neuronal processes containing neurofibrillary changes and extracellular deposits of β-amyloid protein. The amygdala early displays Alzheimer-type pathology and is typically rich in neuritic plaques. Neuritic plaques do not occur in the amygdala in the absence of neuropil threads and neurofibrillary tangles in the entorhinal region and amygdala. In contrast to the gradual increase in the number of neurofibrillary tangles and neuropil threads, neuritic plaques grow in size and number along with advancement in the neurofibrillary and β-amyloid pathology. The findings indicate that neuropil threads and neurofibrillary tangles in the entorhinal region and amygdala precede neuritic plaques in the amygdala, and the density of neuritic plaques is related both to the degree of neurofibrillary and β-amyloid pathology in the cerebral cortex.