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L Wang, J Dong, G Cull, GA Cioffi; Diameter Variation of Intraretinal Ganglion Axons . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2778.
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Purpose:To evaluate the diameter variation (varicosity) of individual intraretinal axons in the primate retinas and the impact on the diameter frequency distribution. Methods:Flat-mounted retinas from 7 post-mortem normal human donor eyes (age: 1 to 85) and 2 adult monekys were stained immunohistochemically with antibody of neurofilament 200 kD. Thin-sections of the retinas were cut longitudinally and transversly for electron microscope. The diameters of the axons from the two types of sections were measured and analysed statistically for frequency distrubution. Results:The unmyelinated intraretinal ganglion cell axons in all the retinas were varicose formed by a chain of bulb-shaped expansions with a mean maximum diameter of 2.7 ±0.9 µm (n=102) compared to 0.7 ±0.3 µm (n=99) of inter-varicosity fibers measured on the longitudinal cut axons. View OriginalDownload SlideView OriginalDownload Slide Pooled cumulative frequency distribution of the diameters exihibited a disctint bimodal pattern. However, the peak representing the varicosities remarkablly shifted to the left if the measurement was made on the axon cut transversely. These varicosities had no vesicle-containing chemical synaptic structures, but a large number of mitochondria. Specification of intercellular junctions with other axons and glial cells were observed in the monkey retinas. Conclusion:The varicosities of intraretinal ganglion fibers create a large variation in a single axon diameter and greatly affect the diameter distribution pattern in transversely sectioined retinas. The varicosities were likely the sites of «power stations» due to high demanding of unmyelinated fibers and junctions for intercellular communication.
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