Light and electron microscopic radioautography of glucose‐6‐H³ incorporation in the retina of the adult newt, Triturus viridescens dorsalis

Tritiated glucose was administered to fasted newts to study glucose incorporation in the retina and particularly the photoreceptor cells. Incorporation of glucose into glycogen throughout the retina commenced at 30 minutes after injection. The first silver grain concentrations were observed over the photoreceptor myoid at two hours. Incorporation of glucose into glycogen reached a maximum at six hours with grains concentrated over photoreceptor paraboloids, the apices of Müller cells and the inner and outer plexiform layers. By 24 hours there was a reduction of the label in glycogen but silver grains were now visible over mitochondria in the photoreceptor ellipsoids and in increased amounts in the outer and inner plexiform layers and the nerve fiber layer. After three weeks, most radioactive material was observed over the photoreceptor cell outer segments. These results suggest that glycogen is added at the inner aspect of the photoreceptor paraboloid and then moves outward in a scleral direction, where it is metabolized by the ellipsoidal mitochondria.