Electron microscopy of human first trimester and rat mid-term retinal cell transplants with long development time

Abstract

The ultrastructure of rat to rat and human to rat long-term transplants of retinal cell transplants has been investigated. The human transplants were examined at 30 to 41 weeks of total age after conception. Rat homotransplants were nine to ten weeks of age after conception in four cases and 20 weeks in one case. Xenotransplanted rats were immunosuppressed with Cyclosporin A.Both xeno-and homotransplants can develop in the epiretinal or the subretinal space. The development is often heterogeneous. Photoreceptor cells can form both inner and outer segments as well as synaptic terminals. In regions corresponding to the inner plexiform layer, the adult complement of synapses has been seen, including advanced features like serial synapses as well as reciprocal synapses at bipolar cell dyads. Incompletely differentiated synapses of both amacrine and bipolar cell types have been observed, especially in rat epiretinal transplants. Ganglion cell processes have not been identified with certainty. Transplants from ...