Different Aging Patterns of the Neuronal and Inducible Isoforms of Nitric Oxide Synthase in Mouse Hippocampus by Immunohistochemistry

Abstract

Background: Nitric oxide synthase (NOS) produces nitric oxide (NO) from arginine, and both NOS and NO play important roles in the normal aging of the hippocampus. Aim: To study the age-related distribution patterns of the neuronal (nNOS) and the inducible (iNOS) isoforms of NOS in the mouse hippocampus, and their roles in the aging mechanism. Result: The nNOS significantly decreased in the aged hippocampus whereas iNOS increased significantly. The nNOS expressed in interneuron-like cells distributed mainly in the dentate gyrus and the pyramidal layer. iNOS was possibly expressed in both old and newly proliferated astrocytes mainly found in the stratum oriens, stratum lacunosum-moleculare and to a lesser extent in the fimbria and dentate gyrus. The astrocyte number also significantly increased in the aged hippocampus. In fact, iNOS was almost absent in the young hippocampus. Those cells expressing the two isoforms were not apoptotic. Conclusion: The results suggested different expression patterns for nNOS and iNOS during aging in terms of the localization, expression levels and cell types involved. These changes were unlikely to involve apoptosis. This might signify an alteration in the normal functions of the hippocampus during aging such as long-term potentiation.