Visual processing in snakes: morphological analysis of the inner retina and neural circuitry aspects

• Grant number: 20/16377-0
• Support Opportunities: Scholarships in Brazil - Doctorate
• Start date: September 01, 2022
• End date: February 28, 2025
• Field of knowledge: Biological Sciences - Morphology - Histology
• Principal Investigator: Dora Selma Fix Ventura
• Grantee: Juliana Hiromi Tashiro
• Host Institution: Instituto de Psicologia (IP). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Snakes have high ecophysiological diversity, with different circadian rhythms and the use of different habitats, which is reflected in important variations in retinal structures. The retina is organized into layers of cells and nerve plexuses that process visual information. The types and organization of retinal neurons vary between species. In snakes, some studies have described photoreceptors and ganglion cells, but nothing is known about the visual information processing pathways. Photoreceptors connect to different types of bipolar cells, which act at the beginning of post-receptor processing of the luminance and chromatic information pathways. In some vertebrates, bipolar cells may receive input from S photoreceptors, M photoreceptors, or both. The first two types can contribute to chromatic opponency, while the third type can contribute to the luminance channel if the signals add up, or opposition if they have opposite signs. Nothing about this architecture is known in snakes. The objective of this project is to characterize a specific type of bipolar cell, the PKC±, using immunohistochemistry in the retinas of nocturnal snakes, with cones and rods, and of diurnal, with only cones, and to verify the patterns of convergence of photoreceptors for bipolar cells, and from these to ganglion cell layer cells. The snakes (n=16) will be euthanized (thionembutal, 100 mg/Kg), the eyes enucleated and fixed to obtain histological sections or for wholemount retinas. Bipolar PKC± cells will be marked to verify distribution patterns and connection with photoreceptors. This project will provide the first comparative report on neural convergence patterns in snake retinas. (AU)