Retinal dystrophy in the RCS rat: in vivo and in vitro studies of phagocytic action of the pigment epithelium on the shed rod outer segments

The ability of the pigment epithelium (PE) of dystrophic and control RCS rats to phagocytize rod outer segment (ROS) material was examined in vivo and in vitro. In the in vivo studies of animals with fully developed ROS, the number of phagosomes found in the PE increased between 1 and 2 hr after the onset of light in both groups, although at all times the dystrophic animals demonstrated substantially smaller numbers than the controls. During the postnatal development of ROS, the number of phagosomes found at the daily peak increased steadily in the control rats until adult levels were reached at 35 days. In the dystrophic animals the maximum number was observed by 15 days and showed no further increase with age. Organ culture of contro retina-PE explants caused a burst of ROS shedding and phagocytosis, with the maximum number of phagosomes appearing at 2 hr of incubation. The dystrophic retina-PE explants exhibited a very small peak at 4 hr. Recombinations of dystrophic retina with control PE and control retina with dystrophic PE revealed extensive phagocytosis by the control PE but not by the dystrophic PE. These results confirm the previous observation in chimeric rats that the retina of the RCS dystrophic rat is apparently normal while the PE carries the genetic expression of the defect.