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M. E. Guido, D. J. Valdez, D. M. Verra, N. Diaz, B. S. Betts, A. R. Trevino, A. T. Tsin; Photosensitivity and Chromophores in the Chicken Inner Retina. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1299. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
We demonstrated the presence of intrinsically photosensitive retinal ganglion cells (ipRGCs) in the wild type (WT) chicken retina as well as light responses mediated by the inner retina of GUCY1* (blind) birds (Contin et al., 2006; Valdez et al., 2009). Here, we investigated the presence of photopigments, photoisomerases and retinal chromophores (11-cis RAL and all-trans RAL) in the inner retina and RGCs that could be responsible for the photosensitivity observed.
Chicken embryonic retinas from days 4 to 18 (E4 to E18) and post hatching P5-10 were processed for RNA extraction and RT-PCR. Primary cultures of chicken RGCs were obtained at E8byanti-Thy-1 immunopanning and processed. Young (15-20 day-old) and adult (2 month-old) WT and GUCY1* birds were exposed to a 30 min white light pulse (2000 lux) or kept in the dark and sacrificed under dim red light. Eyes were dissected and lyophilized, and the inner retina or different cell layers (RGC, inner nuclear layer:INL and photoreceptor cell: PRC) obtained by the Scotch tape method. Retinoids from the different samples were then extracted and subjected to HPLC.
During development, we observed the early expression of melanopsin m (Opn4m), RPE65, RGR and peropsin in the whole retina from E4, and in primary cultures of RGCs at E8. These cultures also present detectable levels of Opn4x mRNA which increased until day 5; cultures showed 15% of Opn4x-immunopositive cells and traces of the vitamin A1-based chromophores. In the inner retinas of dark-adapted young and adult GUCY1* chickens, we found basal levels of 11-cis RAL and all-trans RAL increasing with age whereas 11-cis RAL was significantly elevated in light-adapted birds. Similar results were observed in RGCs and INL cells of WT animals with a 2-fold increase in levels of 11-cis RAL after light-adaptation. By contrast, PRCs showed the typical elevation of 11-cis RAL in the dark and decrease by light exposure.
The results demonstrate that RGCs and the inner retina of GUCY1* and WT birds contain different components of the photoreceptive machinery including non-visual photopigments, photoisomerases and retinal chromophores likely responsible for the photosensitivity previously reported. However, the differential light effects on retinoids observed and the elements present in the inner retina strongly suggest that the mechanisms triggered by light differ from those described in the classical and cone-visual cycles.
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