Photoreceptors in experimental retinal cell transplants

Abstract: The main objective of this thesis was to investigate the fate of photoreceptor cells when using different strategies for retinal cell transplantation. Comparing transplantation of fragments of embryonic retina with cell suspensions of the same tissue we found that transplantation of fragments of embryonic retina result in mature transplants with a higher degree of cellular organization than transplantation of cell suspensions of embryonic retina. However, photoreceptor cells appeared to develop outer segments only when using the fragment method. In transplanted fragments of embryonic retina, four components of the extracellular matrix surrounding photoreceptor cells were studied. Chondroitin-6-sulfate and F22 antigen appeared with a normal distribution, whereas immunoreactivity for interphotoreceptor retinoid binding protein was absent and peanut agglutinin binding appeared increased, indicating that the interphotoreceptor matrix of these retinal transplants is not entirely normal. In the same type of transplants we also found an unexpectedly high proportion of shortwave sensitive cones. The shortwave-/middlewave-sensitive cone ratio was found to be reversed in the transplants compared to normal retina. We also developed a new technique with which it is possible to transplant a coherent sheet of both photoreceptor cells and retinal pigment epithelium to the subretinal space in rats. With this method, photoreceptor cell organization can be preserved. Previous preliminary results by others have shown a rescue effect on host cones in the rd mouse by transplantation. This could not be confirmed. The survival rate of the transplants was low and host cone survival could have been affected by the large amount of retinal detachment in the transplanted eyes. As a basis for our transplantation studies, the distribution of the different cone types were studied in mouse and rabbit retinas. Unexpectedly we found that both have areas containing exclusively shortwave sensitive cones in the ventral part of the retina.