Comparative morphology of the rat optic nerve using light and electron microscopy

Abstract

Optic nerve fibers are the axons of retinal ganglion cells, and as such they can provide information about the visual acuity and sensitivity capabilities of an animal. Consistent optic nerve fiber counts are not currently available for most animals. In this study, using light microscopy, we counted optic nerve fibers for 7 nerves from 4 adult Sprague‐Dawley rats. Using unbiased stereology we counted 4 adjacent sections of each nerve at 1000X, each using a different staining technique, including Bielschowsky's silver impregnation, Bodian's protagarol, Luxol Fast Blue stain, and a combination Bodian's protagarol and Luxol Fast Blue. We obtained counts of 75,000 to 90,000 fibers, with a fiber size range of 0.1μm to 5μm. We also examined preliminary electron micrographs of one Sprague‐Dawley rat optic nerve at magnifications up to 10,000X. Published counts of the pigmented rat optic nerve fibers using electron microscopy are 120,000, with a size range of 0.4μm to 5μm. This is significantly higher than our light microscopy counts. However, using EM at 10,000X we observe myelinated fibers as small as 0.02.μm. This discrepancy in fiber numbers calls into question which methodology is most suitable for counting myelinated fibers within the optic nerve.Grant Funding Source: Kenneth A. Suarez fellowship