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B. A. Berkowitz, U. B. Kompella, D. Bissig, C. Durairaj, R. Roberts; Examining a Role for Melanin in Retinal Ion Regulation and Neovascularization in Experimental ROP. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4460.
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Coordinated retinal ion flux is critical for proper vision, whereas retinal ion dysregulation is linked with neovascularization (NV). We tested the hypothesis that the ion buffer melanin in RPE/choroid, influences intraretinal uptake of manganese, a biomarker of regulation of ions like calcium, in control rats, as well as NV severity in retinopathy of prematurity (ROP) rats.
In dark adapted, awake and freely moving control rats (Brown Norway (BN, postnatal day 50 (P50)), Long Evans (LE, P20, P50), and Sprague Dawley (SD, P14, P20, P50)), and experimental rats (LE rats 6 and 36 days after 50/10 oxygen exposure, and SD rats 0, 6, and 36 days after 50/10) central retinal ion regulation was measured using manganese-enhanced MRI (MEMRI, MnCl2 ip). In select groups, RPE/choroid melanin content, NV incidence and severity, and visual performance (optokinetic tracking) were evaluated.
In P50 controls, manganese uptake in RPE/choroid correlated with melanin content (BN > LE > SD); uptake in ONL and inner retina (BN > SD >> LE) did not. In experimental ROP, NV severity (LE > SD ~ BN) did not correlate with melanin levels. 50/10 LE, but not SD, pups had supernormal inner and outer retinal uptake through P50. Supernormal intraretinal uptake in LE rats was associated with subnormal visual performance.
As expected, melanin content and manganese uptake were linked in RPE/choroid. Melanin levels were not correlated with ion regulation in the rest of the retina, or with NV. NV severity and visual performance impairment were closely associated with apparent intraretinal depolarization.
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