Topography of retinal photoreceptor cells in the Jungle Crow (Corvus macrorhynchos) with emphasis on the distribution of oil droplets

摘要

Previously, we analyzed the regional specialization of ganglion cells in the retina of the Jungle Crow (Corvus macrorhynchos). The present study extends this analysis by determining the numbers and regional distribution of photoreceptor cells and thedifferent colored oil droplets. The numbers of the different colored oil droplets were counted using color microphotographs of fresh retinas. Estimation of the numbers of photoreceptor cells was made using Nissl-stained retinal whole mounts. The estimated total number of photoreceptor cells in the whole mount retina was approximately 17,933,788 (N=4). The peak density of photoreceptor cells was 92,109/mm~2 in the central area of the retina, followed by temporal and nasal areas, respectively. Four typesof oil droplet were identified on the basis of their color: red, orange, green and translucent. The central retina had a significantly higher population of oil droplets, with a density of 91,202/mm~2; this sharply declined at the peripheral retina. The lowest observed density was 13,192/mm~2 in the dorsal retina. The densities and sizes of the different colored oil droplets were inversely correlated across the retina. The average sizes of red, orange, green and translucent oil droplets had 6 mu m~2, 4 /im2, 7 mu m~2 and 4 mu m~2, respectively. At the periphery of the retina, the oil droplets were significantly larger than in the central area. The sizes of the different colored oil droplets also varied within the same area. Orange colored oil droplets (33%) were the most common type in the central area, whereas green colored oil droplets were the most frequent in other areas. The results of the present study show that photoreceptor cells and oil droplets are differentially distributed in the retina. From these results, we conclude that the area of high cell density, matched by high neuron densities of the ganglion cell layer, corresponds to the site of acute color vision in the crow retina.