Microscopic details of age related changes in rat optic nerve

Age-related changes in the number and density of optic nerve fibres were studied in 12-month-old (adult) and 24- month-old (aged) male Wistar rats. Methods: Two-micrometer-thick resin-embedded optic nerve cross-sections obtained from two different age groups were stained with toluidine blue and examined under a light microscope at low (5x) and high (500x) magnification. The optic nerve cross-sectional area, and the number of nerve fibres with diameters less or higher than 1 μm were evaluated by means of computerized image analysis and statistical analysis of results. Results: Retrobulbar optic nerve cross-sectional area decreased in relation to ageing. The number of optic nerve fibres with a diameter of less than 1 μm decreased by about 39% in 24-month-old rats versus 12 month-old animals (P < 0.05) while only a swelling was observed in nerve fibres with diameters higher than 1 μm ( P > 0.05). Conclusions: Data suggest that age-related impairment of nerve cell population also occurs at the optic nerve level. Our data allow us to hypothesize that all major components of the rat optic paths are sensitive to the aging process