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Einat Hauzman, Daniela Maria O. Bonci, Andre Mauricio P. Liber, Sonia L. Martins, Sonia R. Grotzner, Maritana Mela, Dora F. Ventura; A Comparative Study Of The Photoreceptor And Ganglion Cell Topography In Arboreal And Terrestrial Snakes. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3492. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To compare photoreceptor and ganglion cell densities and topography of two species of Dipsadidae Snakes that live in different habitats - the arboreal Philodryas olfersii and the terrestrial P. patagoniensis.
Photoreceptor types were labeled with antibodies JH455 and JH492 (against human S and L/M cones, respectively) in sections and wholemount retinas. Ganglion cells were labeled with Nissl stain in wholemount retinas. Mean cell density was calculated from counts made in photographs of the retinas and used to obtain isodensity maps. Visual acuity was estimated from the ganglion cell peak density. Morphology of photoreceptor types was viewed with Scanning EM (JEOL JSM 6360LV).
EM scans revealed four distinct photoreceptor subtypes, three of which were labeled. Radial sections showed large single and double cones labeled by the antibody JH492, and small single cones labeled by the antibody JH455. Densities of the total photoreceptor population were obtained in 10 retinas of P. olfersii (11,183 ± 1,107 cells/mm2) and 13 retinas of P. patagoniensis (11,531 ± 1,237 cells/mm2). Small cones comprised 3% of the photoreceptor population in P. olfersii and 5% in P. patagoniensis. Large single and double cones represented 83% in P. olfersii and 85% in P. patagoniensis. The mean density of presumed ganglion cells was obtained in 5 retinas of P. olfersii (10,118 ± 1,026 cells/mm2) and 7 retinas of P. patagoniensis (9,835 ± 2,772 cells/mm2). The maximal spatial resolution was 3 cpd in both species. P. olfersii ganglion cells and photoreceptors isodensity maps revealed a horizontal streak and two areae of higher density, one central and the other caudal. P. patagoniensis retinas presented an area centralis located in the ventro-rostral region.
The two species have L/M and S (or UV) type photoreceptors plus a non identified type, suggesting a potential for trichromacy. The different specialization retinal areas might be related to specific habitat and life style. The visual streak and the two areae in P. olfersii retinas may be relevant for locomotion and hunting in the arboreal layer, while the area in the rostro-ventral quadrant in P. patagoniensis retinas provides better spatial resolution in the superior visual field, important for the survival of terrestrial snakes.
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