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D. Ji, N. Osborne; Evidence That Light Can Affect Ganglion Cell Parameters in situ. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4934.
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To test the hypothesis that mitochondria-rich retinal ganglion cells within the globe are susceptible to light injury.
Female Hooded Pigmented rats were anesthetised, their pupils dilated with topical cyclopentolate and one eye exposed to 2000 lux of white light (400-760 nm). : source of light consisted of four peaks at around 400, 420, 550 and 590 nm) or red light (550-760 nm, filter used to exclude 400 and 420 nm peaks of wave light) for 70-90 minutes. Rats were positioned on their side so that only one eye received light. This process was repeated every second day over a period of 8 days. Rats were otherwise maintained in normal 12 hour light (50 lux)/dark cycle. Two days after the last light insult, animals were killed and retinas and optic nerves from both eyes analysed for specific mRNAs in the case of the retina and neurofilament-light (NF-L) and tubulin proteins in the optic nerve.
White light caused a significant reduction in retinal NF-L and Thy-1 mRNAs by 18% and 22%, respectively (relative to GAPDH) in the retina receiving light when compared with the retina of the other eye (n=8). Moreover, the mRNA for retinal GFAP was significantly elevated while that for rhodopsin was surprisingly unaffected. In addition, the NF-L and tubulin proteins, relative to actin, in the optic nerve of the eye receiving light were significantly reduced. In contrast, an identical intensity of red light to had no significant influence on retinal mRNAs or optic nerve proteins when compared with the untreated eye.
Blue/violet light is known to affect certain mitochondrial enzymes to cause a generation of reactive oxygen species. Since, ganglion axons within the globe are laden with mitochondria we have hypothesised that light is a risk factor to these cells under certain circumstances (BJO 90, 237-241, 2006). For technical reasons we were not able to use 2000 lux of blue/violet light in the present experiments. We show here that white light with two light peaks (400 and 420 nm) in the blue/violet range affects ganglion cell parameters but an identical intensity of red light has no measurable influence. We conclude that the changes in retinal Thy-1 and NF-L mRNAs and optic nerve proteins (NF-L and tubulin) induced by white light shows that ganglion cells are being affected, and suggest that the blue/violet light peaks are the major cause.
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