[Effect of avitaminosis A on retinal photoreceptor ultrastructure in adult hens]

A-avitaminosis has been shown to provoke important ultrastructural changes in the external segments of the rods whose membrane disks disorient and disappear. No changes in the external segments of the cones were observed. The ellipsoid and paraboloid of visual cells, both rods and cones, undergo changes. The increase in the number and length of mitochondrial cristae and also the increase in the number of mitochondria themselves is noted in the ellipsoid. In the paraboloid, on the membranes of elements of endoplasmic reticulum, the number of ribosomes increase, and the number of polyribosome complexes increases in the cytoplasm. By means of the colorimetrical method, a decrease in the quantity of vitamin A is shown in the liver and retina of the sick hens. Their feedings on vitamin A provokes a restoration of the ultrastructure of membrane disks of the external segments of the rods.