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SHASHA LV, Anna Polosa, Pierre Lachapelle; Cellular Response Following Bright Light Exposure in the Retina of Juvenile Rats. Invest. Ophthalmol. Vis. Sci. 2018;59(9):968.
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© ARVO (1962-2015); The Authors (2016-present)
We have previously shown that the retina of juvenile Sprague-Dawley (SD) rats has a remarkable intrinsic resistance to light-induced damage compared to adults. While in the juvenile rats, the photoreceptor rapidly reaches a 50% loss 3 days following the onset of exposure and then plateaus at that level for the remainder of the exposure duration, in adult rats we see a dose-response effect which results in a near complete destruction of the photoreceptors at the end of the same exposure duration. We investigated the cellular and molecular mechanisms that could explain the higher resistance of the juvenile retina to light-induced damage.
SD rats (12 adults+12 juvenile) were exposed to a bright luminous environment (12 hours ON/OFF) for 1, 3, 6 or 14 consecutive days. Protein expression was analyzed immediately post-light exposure by immunohistochemistry (IHC) with the following biomarkers: 1- Ionized Calcium-binding Adapter Molecule 1(Iba1) - activity of microglial cell, 2- Glial Fibrillary Acidic Protein (GFAP) - active Müller cells, 3- Ciliary Neurotrophic Factor (CNTF) - protective activity of tissue destruction and 4- Basic Fibroblast Growth Factor (FGF2) - activity of tissue wound healing.
IHC revealed a migration of microglial cells from the inner retina to the outer retina starting (in a dose-dependent manner) after 3 days light exposure in juvenile rats compared to 1 day in adult rats. The GFAP positive Müller cells were observed after 3 days of exposure in both group and their staining increased proportionally with the exposure duration. The expression of CNTF was stronger in adults compared to juvenile rats which is consistent with the GFAP. FGF2 was gradually expressed in the ONL of exposed adults compared to control who only have expression in INL. However, the expression of FGF2 in the INL of juvenile rats only started after 14 days of exposure.
We believe that the immature immune system of juvenile rats explains the delayed and reduced inflammatory response compared to adult rats. Given that in juvenile rats there is no further damage following the onset of the inflammatory response, this would suggest a protective anti-inflammatory response. In contrast, results obtained in adult either suggest a destructive pro-inflammatory reaction or that the light damage is simply too severe for the immune system to deal with it efficiently.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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