Distribution of altered hippocampal neurons and axons immunoreactive with antisera against neuropeptide Y in Alzheimer's‐type dementia

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Abstract
This paper provides detailed information on the distribution of neuropeptide tyrosine (neuropeptide Y; NPY) immunoreactive neurons and fibers in the hippocampal region of eight neuropathologically confirmed cases of Alzheimer's‐type dementia (ATD) at postmortem. These neuronal networks are detected by a polyclonal antibody raised against the unconjugated peptide and controls were obtained by using liquid phase absorption immunocytochemistry. The description covers the subfields area dentata, CA3 and CA1, the subicular complex, and the entorhinal area. The hippocampal regions in which the NPY‐i neuron networks are most severely affected are the hilus, CA1, the parasubiculum, and the entorhinal cortex. Less obvious reductions occurred in CA3, subiculum, and the presubiculum. Parallel semiquantitative estimates were made of the numbers of neuritic plaques and neurofibrillary tangles in the other hippocampus of the brains in every ATD case. The areas of heaviest pathological changes by these indices are CA1 and the entorhinal cortex. The subicular complex CA3 and the area dentata are less affected. These findings show that the areas with the most severe loss of NPY‐i neurons and axons, CA1 and the entorhinal cortex, are the same as those areas most severely affected by the other indices of ATD. Thus NPY‐i networks are involved in the ATD disease process. However, other NPY‐i networks survive, in some subfields better than in others. The cumulative evidence suggests a population of hippocampal peptide neurons that are remarkably resistant in terminal neurological disease. These neurons have the capability to participate in the maintenance of minimal functioning circuits in target areas of the disease and as such hold significant links for our understanding of synaptic plasticity in disease.