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Ye Zhou, Xiaopeng Zhao, Xiang-Run Huang; Relationship between Axonal Subtypes and Size of Retinal Nerve Fiber Bundles. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2289.
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© ARVO (1962-2015); The Authors (2016-present)
The axons of retinal ganglion cells (RGCs) consist of cytoskeletal components, including actin filaments (F-actin), microtubules (MTs) and neurofilaments (NFs). In this study, we classified axonal subtypes based on the relative contents of these components and studied the relationship between each subtype and the sizes of retinal nerve fibers bundles. Knowledge gained will be useful for understanding selective damage of the nerve fiber bundles in glaucoma.
Normal Wistar rats were used in this study. Whole-mounted retinas were simultaneously stained with fluorescence to label F-actin, MTs and NFs. Strands of these components, running along the axons, were identified by confocal imaging of the tissues. To determine the relative content of cytoskeletal components, lines across cytoskeletal strands were defined within nerve fiber bundles. Intensity profiles along the lines were obtained for each cytoskeletal component. Axons were classified by relative intensities of these components. For instance, axons with intensely stained F-actin, MTs and NFs were classified as FMN subtype. A linear density of each subtype was calculated as the number of the subtype found along a line divided by the line length. Bundle size was determined by multiplying bundle width with its thickness. The density was studied for different sizes of nerve fiber bundles.
Normal axons could be classified as the subtypes of FMN, FM, FN, and MN, in which three or two cytoskeletal components were nearly colocalized. Also there were subtypes, F, M, N, of which one structure dominated the content of axons. The linear densities of the axonal subtypes, FMN, FM and FN, decreased with increasing of the bundle size, while the density of MN did not change very much with the bundle size.
Normal axons of retinal ganglion cells contain different proportions of cytoskeletal components. Because cytoskeleton provides support for axonal structure and function, the lower cytoskeletal density in larger nerve fiber bundles may offer an explanation of selectively greater loss of large nerve fiber bundles found in glaucomatous eyes.
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