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M. Tanito, S. Kaidzu, A. Ohira, R. E. Anderson; Impaired Choroidal Circulation and Delayed Loss of Cone and Remaining Rod Photoreceptor Cells Following Acute Light Exposure in Rats. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4496.
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To examine the long-term effects of acute light exposure in the retina, and retinal pigment epithelial (RPE) and choroidal layers.
Albino rats injected with either the protective antioxidant phenyl-N-tert-butylnitrone (PBN) or saline 30 min prior to exposure with 5 k lux white fluorescent light for 6 h were kept for up to 3 months. Electroretinograms were recorded and the outer nuclear layer (ONL) and the choroidal thickness were measured. The expression of rod, cone, and RPE cell-specific markers was detected by Western blotting, and apoptosis was analyzed by TUNEL staining. Oxidative stress was analyzed by immunohistochemistry of 4-hydroxynonenal (HNE)-modified proteins. Retinal and choroidal ultrastructure was observed by transmission electron microscopy. Choroidal circulation was determined by in vivo staining of the choroidal layer by trypan blue.
In saline-injected animals, TUNEL- and 4-HNE-labeling in the ONL, RPE, and choroid was greater 24 h and 7 days after light exposure, and ERG amplitudes, ONL and choroidal thickness, and the expression of rhodopsin and RPE65 were lower 7 days after light exposure and later, compared to PBN-injected animals. In saline-injected animals, the expression of mid-wavelength opsin and the presence of cone nuclei in the ONL, and the choroidal circulation were preserved 7 days after light exposure, but started to decrease by 1 month and continued to decrease for 3 months following light exposure. An increase in TUNEL-positive cells was observed in the ONL at the inferior peripheral retina just behind the iris by 3 months after light exposure. Delayed loss of cone cells and remaining rod cells, and reduction in choroidal circulation, were counteracted by PBN treatment.
Although cone cells are resistant to cell damage induced by acute photo-oxidative stress, progressive slow loss of cone cells continued for up to 3 months after light exposure. Impaired choroidal circulation may be involved in the mechanism of delayed photoreceptor cell death. Therefore, preserving choroidal circulation may provide a novel target for retarding loss of cone and rod cells in patients with retinal degeneration such as retinitis pigmentosa.
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