Studies On Age-related Morphological Changes In The Optic Nerve Of Cat

The optic nerve is the sole pathway for visual information input from the retinae to visual precessing center. An age related morphological change of the optic nervemay impact the conduction property of visual information. In this paper,the optic nerve morphology ofyoung adult and old cats was compared in order to disclose the characteristics of it's age dependent changes and accumulate morphological data for elucidating the neural mechanism underlying visual function degradation during senescence.1. Consecutive cross-sections from two age groups were stained with hematoxylin-eosin to observe the structure of the optic nerve. Adjacent sections were stained with crystal violet to demonstrate glial cells. Neurofilament (NF) immunoreaction was used for locating and characterizing optic nerve axons, and glial fibrillary acidic protein (GFAP) was applied to visualize astrocytes. All the data was subjected to the statistical analysis, and the diameter spectrum for both age groups was drawn. The results indicated that the myelin sheath's thickness, diameter and area of optic nerves in old cats were significantly increased when compared with that of young adults. However, the density and number of optic nerve fibers were considerably decreased in old cats in comparison with young cats, especially in the center of optic nerve. As indicated by the diameter spectrum of optic nerve fibers, the peak diameter range of optic nerve fibers in two age groups was quite similar, but the value of peak and mean diameter in old cats were significant less than in young adults. Additionally, astrocytes in old cats showed considerably hypertrophic and occupied a higher proportion in total glial cells when compared with that in young adult ones. Our results suggested a significant loss of optic nerve fibres, especially thicker fibres, and a declined diameter of nerve fibers in senile cats, which might be an important cause that underlies the degradation of visual processing speed during senescence. An age-related activity enhancement of glial cells in the optic nerve of old cats may provide protective effects on nerve...