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Kumar Abhiram Jha, Tapas C Nag, Pankaj Kumar, Tara S Roy, Shashi Wadhwa; Photoreceptor degenerative changes in neonatal chick retina exposed to intense visible light of variable photoperiods. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4384.
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© ARVO (1962-2015); The Authors (2016-present)
PURPOSE: The aim of the present study was to see the effects of intense visible light of variable photoperiods on photoreceptor cells and associated molecular changes in neonatal chick retina.
Post-hatch day 1 chicks (N=18) were reared in 12 hour light (L): 12 hour dark (D) photoperiod for 7 days at 500 lux. After acclimatization, they were divided into three groups: 12L: 12D (Normal Light and Dark; NLD), 18L: 6D, and 24L: 0D (continuous light; CL), and reared in light of intensity 2000 lux (at the base of cage) for 23 days. After completion of experiment, eyes were enucleated and processed for immunofluorescence and western blot studies. Cell death was examined by TUNEL labeling. Quantitative protein expression of rhodopsin, s-opsin, synaptophysin, PSD95, glutamine synthetase (GS), and glutamate aspartate transporter (GLAST) was determined by Western blot and qualitative expression was evaluated using immunofluorescence studies.
CL group showed significantly higher TUNEL positive cells compared to NLD and 18L: 6D groups. Immunolabelling of rhodopsin and S-opsin were remarkably reduced in photoreceptor outer segments as was the case with synaptophysin in synaptic layers in CL group compared to NLD and 18L: 6D groups. Similarly, reduced expressions of synaptophysin, PSD-95, rhodopsin and S-opsin were observed by Western blot in CL group. Moreover, in CL group staining of GS was significantly lesser in Müller cell processes throughout the retina. Also, a decreased expression of GLAST was observed in inner and outer plexiform layers and in Müller cell processes of inner nuclear layer in CL group compared to NLD and 18L: 6D groups. Further, Western blot analysis showed significantly decreased expression of GS and GLAST in CL group compared to NLD group (p≤0.001). Although GS and GLAST expressions increased in 18L: 6D group compared to the NLD group, the data were not statistically significant.
The present data clearly suggest that continuous light causes degeneration of rod and cone outer segments, and apoptosis of retinal cells. Based on our observations, it can be stated that continuous light leads to glutamate induced neurotoxicity, as seen by reduced expressions of GS and GLAST.
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