A morphometric study of age changes in the rat optic nerve

Age-related changes of the optic nerve fibres were studied in 3-month-old ( young), 12-month-old (adult) and 24-month-old (aged) male Sprague-Dawley ra ts. The optic nerve was harvested with particular care from the intracrania l portion. Cross sections from the optic nerve of animals of different age groups were stained with toluidine blue and examined under a light microsco pe at low and high magnification. Other sections were stained for the demon stration of glial cells using the method described by Holzer. A third group of sections were stained by the immunohistochemical method to detect glial fibrillary acidic protein, which is a marker for localising and characteri sing astrocytes. All these morphological results were subjected to the quan titative analysis of images and to statistical analysis of the values to id entify significant morphometric data. Biochemical dosages of proteins were also performed on homogenised fragments of the optic nerve. Our results dem onstrate that the following age-related changes can be observed: (1) an inc rease in meningeal membranes, (2) an increased number of astrocytes, (3) an increase in areal density of glial fibrillary acidic protein immunoreactiv ities, (4) an increased thickness of the entire optic nerve and an increase d area of the nerve, (5) a decreased number of nerve fibres and (6) a decre ase in the nerve fibre/meningeal membrane ratio from 3:1 to 1:1. Moreover, the amount of protein does not change with age. The rat optic nerve, theref ore, appears sensitive to aging processes. Copyright (C) 2001 S. Karger AG, Basel.