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M. Djavari, A. Polosa, V, S. Chemtob, P. Lachapelle; Dark Rearing Protects From Oxygen-induced Retinopathy (OIR). Invest. Ophthalmol. Vis. Sci. 2009;50(13):3608.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies of ours have shown that the retina of newborn albino rats exposed to hyperoxia in a normal light environment during the first two weeks of life sustains permanent functional and structural impairments. Given that the metabolic demand of the retina is increased in the dark, we examined whether dark rearing could protect the developing retina from OIR.
Dark reared albino Sprague-Dawley (SD) pups exposed to 80% oxygen from P0-P14 (DRO2) were compared to normal pups dark reared from P0-P14 (DR14) or P0-P28 (DR28). At the end of the dark rearing period the pups were placed in a normal light environment (80 lux). All groups were compared to age matched pups raised in normal light conditions (NC). Scotopic (-6.3 to 0.9 log cd.m-2.sec), photopic (intensity: 0.9 log cd.m-2.sec; background: 30 cd.m-2) electroretinograms (ERG) and histology were performed at P 30.
The DR28 group disclosed significant (p<. 05) increases of all scotopic ERG parameters compared to the DR14 and NC groups [rod a-wave (166% and 146%), mix rod cone b wave (113% and 136%) and rod V max (142% and 143%), respectively]. No significant changes were observed between DR14 and NC groups (p>. 05). Compared to the DR28 group, the DRO2 group showed important loss of function (p<. 05) [mix rod cone a wave (56%), mix rod cone b wave (59%), rod V max (66%) and cone b wave (52%). The only significant (p<. 05) structural alteration resulting from oxygen exposure were observed at the outer segment layer (OSL) where the DRO2 OSL was 168% and 144% larger than DR14 and DR28 respectively and at the inner plexiform layer (IPL) where the DRO2 IPL was 24% and 22% smaller that DR14 and DR28 respectively.
Compared to previous results of ours, the OIR observed in dark-reared rat pups yields structural (OPL not obliterated) and functional (ERG amplitude 20% larger) consequences that are significantly less severe compared to normally reared OIR. Dark rearing also appears to be beneficial to the development of the normal retina. Taken together our results would suggest that the increase in retinal metabolic rate (and possibly increased synaptic activity to explain ERG effect in DR28) triggered by the dark-rearing period, would protect (or mask) some of the deleterious effect of postnatal hyperoxia.
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