Cells projecting out of retinal transplants placed over the tectum of newborn rats were studied by labelling with horseradish peroxidase 1 month or more after transplantation. Using this technique, it was found that only cells with the dendritic characteristics of ganglion cells were labelled and, furthermore, that the major classes of ganglion cells seen in normal retinae were also present in the transplants. The cell body size histograms of ganglion cells in normal and transplanted retinae compared closely with each other. Dendritic trees were closely confined by the limits of the inner plexiform layer, and if that layer was folded or distorted, they were themselves frequently abnormal. While axons usually coursed over the surface of the retinal transplants, they quite often followed an anomalous course crossing the individual layers. It appears, therefore, that this transplantation procedure has relatively little impact on the ability of ganglion cells to develop many of their characteristic morphological features. Whether the different functional responses of the various ganglion cell classes are also preserved after transplantation is a matter for further investigation.
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