Comparative studies of retinal morphology of Bothrops jararaca and Crotalus durissus terrificus (Serpentes, Viperidae): density and topography of photoreceptors and ganglion cell, and estimation of visual acuity
The snake group had great evolutionary success and the different species present morphological and physiological adaptations associated to the environment in which they live.The Viperidae snakes Bothrops jararaca and Crotalus durissus occupy predominantly the Atlantic forest and the cerrado biomes, respectively. Unlike C. durissus, the B. jararaca snake presents ontogenetic variations in diet and in the use of the environment. In the juvenile phase it feeds on small ectodermal vertebrates and occupies arboreal extract, while adult individuals preferentially feed on rodents and occupy extract terrestrial, as well as young individuals and adults of C. durissus. Such variations between the two species may indicate adaptations of the visual system. Visual processing begins in the retina, fine nerve tissue located deep in the eyes, responsible for capturing the light energy of the environment and converting this energy into electrochemical signals that are transmitted to the higher visual centers. Differences in the density and distribution of retinal cells are associated with the ecological characteristics of the species. Therefore, B. jararaca and C. durissus snakes represent an interesting model for the comparative study of retinal morphology and the understanding of adaptive mechanisms of the visual system. For this study will be collected the eyes of eight adult individuals and eight juveniles of each of the two species. The snakes will be obtained from the Animal Reception of the Butantan Institute and will be euthanized with a lethal dose of the anesthetic Thionembutal (active principle thiobarbiturate ethyl sodium, dosage 100 mg / kg). The eyes will then be enucleated and fixed in 4% paraformaldehyde diluted in 0.1M PB phosphate buffer for three hours. The retinas will be dissected and maintained in 0.1 M PB, at 4 ° C. Flat retinas of the retinas will be used to label photoreceptors and cells of the ganglion cell layer (GCC), using the techniques of immunohistochemistry and Nissl, respectively. The analysis of the density and distribution of retinal cells will be performed using the stereological method, Stereo Investigator (MicroBrightField, Colchester, VT). Visual acuity will be estimated based on the peak of CCG cell density and posterior nodal distance from the center of the lens to the retina. Based on previous studies of retinas of different species of vertebrates, it is expected to find differences in the distribution of retinal neurons in young and adult snakes of the B. jararaca species. These results will bring greater understanding on the behavioral and evolutionary aspects of these species of high medical interest in Brazil.
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