Cell differentiation in the retina of the mouse during the postnatal period was studied by autoradiography. Animals were injected with 3H-thymidine at ages extending from the day of birth through postnatal day 11. Six weeks later the distribution of labeled nuclei in the cells of the mature neural retina was analyzed to determine when these cells completed their final mitosis prior to differentiating. Central and peripheral zones were analyzed separately. Cell division ceases by 5-6 days in the center of the retina and by 11 days in the periphery. Among cells produced postnatally, 73% differentiate as rods, 20% as bipolar cells, 6% as Müller cells, and 1% as amacrine and ganglion cells. At all stages of embryogenesis, the differentiation of at least three and as many as six distinct types of specialized cells is initiated simultaneously within the ventricular cell population.

The utilization of methionine-aH by retinal photorcceptor cells has been studied by radioautographic tcchnique in the rat, mouse, and frog. In all three species, the labeled amino acid is conccntratcd initially in the inner segment of the cell. Within 24 hr, the radioactive material is displaced to the base of the outer segment, where it accumulates as a distinct reaction band. The reaction band then gradually moves along the outer segment and ultimately disappears at the apex of the cell, which is in contact with the retinal pigment epithelium. These findings are interpreted to indicate that the photoreceptor ccll outer segment is continually renewed, by the repcated lamellar apposition of material (membranous discs) at the base of the outer scgment, in conjunction with a balanced removal of material at its apex. The outer segment rencwal rate is accelerated in frogs when ambient temperature is raiscd, and is elcvated in both frogs and rats when the intensity of retinal illumination is increased.

No abstract

The disposal phase of the retinal rod outer segment renewal process has been studied by radioautography in adult frogs injected with tritiated amino acids . Shortly after injection, newly formed radioactive protein is incorporated into disc membranes which are assembled at the base of the rod outer segment . During the following 2 months, these labeled discs are progressively displaced along the outer segment owing to the repeated formation of newer discs . When the labeled membranes reach the end of the outer segment, they are detached from it . They subsequently may be identified in inclusion bodies within the pigment epithelium by virtue of their content of radioactivity . These inclusions have been termed phagosomes.