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R Leal, A Tsin, R Glickman, R Elliott, H Rentmeister-Bryant; Ocular Retinoids in Cornsnake (Elaphe g. guttata) . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3602.
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Purpose: The purpose of this study is to determine the type and the amount of retinoids in the retina and retinal pigment epithelium of the Cornsnake (Elaphe g. gutata). Cornsnake and garter snake (Thamnophis) are both in the family Colubridae, which are crepuscular/nocturnal species with apparently good dim light (scotopic) vision. However, their photoreceptors exhibit morphology of cone (photopic) rather than rod (scotopic) cells. In previous studies, we reported that 11-cis retinoids (such as 11-cis retinyl ester) predominate in the retina and retinal pigment epithelium of cone species. Therefore, analysis of ocular retinoids in the Cornsnake may yield novel biochemical insights into scotopic vs. photopic vision. Methods: Animals were light-adapted and anesthetized before eye dissection. Retina and retinal pigment epithelium were isolated under a dissecting microscope. Retinoids were extracted by acetone. Retinyl esters, retinal and retinol were separated by an alumina column before HPLC analyses. Retinoids were identified by retention time and on-line scan using a photodiode array detector. Quantitations were carried out by comparison with known amount of authentic standards. Results: The Cornsnake retina had 0.036 nmol of all-trans retinyl palmitate/eye, 0.218 nmol of all-trans retinal/eye and no detectable amount of retinol. The snake retinal pigment epithelium had 0.147 nmol of all-trans retinyl palmitate/eye, 0.042 nmol of all-trans retinal per eye and no retinol. Similar results were observed from two animals analyzed separately. Conclusion: Cornsnake retina and RPE had no detectable level of 11-cis retinoid. Although this finding is atypical in a cone dominated eye, it is consistent with crepuscular behavior and scotopic vision of the Cornsnake. Therefore, it is possible that their photoreceptors have cone morphology but rod functions.
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