Electron histochemical and developmental study of glycogen metabolism in the retina of the chick fetus.

The activities of glycogen synthetase and phosphorylase were electron histochemically examined in the retina of the fetal chick. These enzyme activities appeared in the cytoplasmic matrices of the developing paraboloid in the photoreceptor inner segment almost simultaneously at the 17th day of incubation. After the appearance of these 2 enzyme activities, glycogen particles were found in the developing paraboloid. It is concluded that glycogen is synthesized through the enzymatic pathway in the fetal retina and that glycogen is not found before the enzymes related to glycogen metabolism appear in the cell except the appearance of native glycogen in the egg. Branching glycosyltransferase seemed to appear after phosphorylase was activated and these enzymes became higher in their activity with the differentiation in the paraboloid in the fetal and early postnatal periods.