Hippocampal and Parahippocampal Somatostatin 28 and Neuropeptide Y Containing Neurons in Alzheimer's Disease (Part 2 of 2)

Abstract

The somatostatinergic innervation, and by comparison that of neuropeptide Y, was examined by immunocytochemistry, in the hippocampal formation of 6 patients with clinically and neuropathologically confirmed diagnosis of Alzheimer's disease (AD) and 4 matched controls. The quantitative assessment of the somatostatin and neuropeptide Y immunoreactive cell perikarya was conducted on regularly spaced sections covering the span of the whole hippocampus and parahippocampal cortex. The estimated total number of somatostatin or neuropeptide Y containing neurons was similar in the hippocampal formation of patients with AD and controls. By contrast, the density of the somatostatinergic fibers and terminals as estimated by the optical density of the somatostatin neuropil, significantly decreased by 30-45% in all the hippocampal subregions and the parahippocampal cortex, whereas the density of the neuropeptide Y immunoreactive neuropil significantly decreased (45%) only in the parahippocampal cortex. Numerous enlarged fibers containing somatostatin or neuropeptide Y, some of which were observed within senile plaques, were detected in the brain of patients with AD. These data suggest that in AD, somatostatin and neuropeptide Y containing cell bodies in the hippocampus and parahippocampal gyrus are anatomically preserved, in spite of an altered terminal field.