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M Watanabe, H Maki, M Katoh; Growth Rate Of Transected Axons Of Retinal Ganglion Cells In Adult Cat . Invest. Ophthalmol. Vis. Sci. 2002;43(13):761.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Although transected axons of retinal ganglion cells (RGCs) regenerate into a transplanted peripheral nerve segment (PN), the numbers of RGCs with regenerated axons are fewer than 5000 in the cat retina (Watanabe et al., 1993). Enhancing axonal regrowth would be one of promising methods to obtain more regenerated RGCs. We estimated the rate of growth of RGC axons regenerating in a PN as the control value. Methods: The left transected ON of anesthetized cats was connected with a PN segment. After 4, 6, and 8 week survival, RGCs with regenerated axons were doubly labeled with two fluorescent dyes (dextran-fluorescein & -rhodamine) injected at 10 mm (2 day before enucleation) and 20 mm (4 day before enucleation) from the ON connection. Numbers of single- and double-labeled RGCs were counted. Proportions of alpha, beta and not alpha/beta (NAB) were estimated by Lucifer yellow (LY)injection. Results: Average numbers of RGCs with 10 mm-regenerated axons were 2250 on 4 wk, 4009 on 6 wk, and 2871 on 8 wk. Percentages of RGCs with 10 & 20 mm-regenerated axons were 17% (4 wk), 65% (6 wk), and 66% (8 wk) of RGCs with 10 mm-regenerated axons. These values indicate that most RGCs extended their axons to 10 mm by 6 wk. From a scatter diagram of ratios of double-labeling vs surviving weeks, we obtained a formula: Y= 73.6 ln(X)-78.3, where Y is double labeling ratio (%), X survival (week). The formula indicates that the fastest axon reached at 20 mm by 2.9 wk, the slowest one did by 11.1 wk. Supposing a lag of regrowth as 4.5 days (Cho & So, 1989), ratios of axonal growth were: 1.3 mm/day for the fastest, 0.27 mm/day for the slowest. LY injections did not show clear difference in rates among cell types so far. Conclusion: The value 1.3 mm/day is close to that in hamster RGCs, 2 mm/day. The present experiment provides a model system to search for methods to enhance regrowth of damaged CNS axons.
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