Análise do eletrorretinograma de campo total e histologia da retina do peixe Oscar (Astronotus ocellatus - Agassiz, 1831)

Abstract

Fish have been increasingly used as experimental models in the most diverse areas, due to structural and cellular similarities, ability to regenerate tissues and easy handling. Astronotus ocellatus is a cichlid that lives in clear environments of calm, shallow water, feeding on crustaceans, molluscs and smaller fish. Its ecosystem matches its complex visual structure. Promising specimen for clinical and experimental studies of vision. Electroretinography (ERG) is a non-invasive method that, through electrodes, captures the electrical activity of the retina when stimulated by light. Allied to it, the histological analysis of the retina and the morphometric description of each layer provides a structural basis for the cells analyzed in the exam. Two groups were used, the first with 16 fish, for the electrophysiological analysis and the other with 3 fish for histomorphometry. The ERG was performed with the fish under general anesthesia with 10% lidocaine (5μg/ml) and 1% propofol (50 μg/ml) and recordings with a frequency of 2Hz and 30Hz with a white light LED with an intensity of 3cds/m2. Four fish recorded multifrequency responses, stimuli with a frequency of 2 Hz and wavelength ranging from ultraviolet to infrared. For histomorphometry, the fish were euthanized, their eyes enucleated, fixed in Davidson's solution, stained with Hematoxylin and Eosin, and some depigmented with potassium permanganate and oxalic acid to visualize the outer segments of the photoreceptors, covered by the melanin present in the villi of the pigment epithelium. In the ERG results, it was possible to obtain the main components, waves A and B. The tracings obtained with the multifrequency stimuli showed greater variation in the responses to ultraviolet and no records were obtained to the infrared stimulus. In Histomorphometry, the total retinal thickness was 187.55±21μm. The present studies demonstrated a simple and fast protocol for obtaining retinal responses in anesthetized Astronotus ocellatus, allowing the recovery of all animals after examinations and the description and histological analysis of the retina and its associated structures.