Retinal transplants restore visually evoked responses in rats with photoreceptor degeneration

PURPOSE. To assess whether transplantation of intact sheets of fetal retina with retinal pigment epithelium (RPE) into a retina with photoreceptor deg eneration restores visually evoked responses. METHODS. Sheets of fetal retina with RPE were transplanted into the subreti nal space of Royal College of Surgeons (RCS) rats at 37 to 69 days of age. Sixty-three days to 10 months after transplantation, multiunit visual respo nses were recorded in the superior colliculus (SC) of transplanted rats, ag e-matched untransplanted rats, and rats with sham surgery. RESULTS. In 19 of 29 RCS rats with transplants, visually evoked responses w ere recorded from and restricted to a small area of the SC that corresponds topographically to the portion of the retina in which the transplant was p laced. Outside of this area, no visual responses were evoked. Visually evok ed responses were never recorded in age-matched, nontransplanted RCS rats. Visually evoked responses were recorded in 6 of 13 RCS rats with sham surge ry, but these responses were significantly different from responses in rats with transplants. CONCLUSIONS. These results demonstrate that this transplantation technique restores visually evoked responses in the brain. Although the underlying me chanism is unknown, we propose that the central visual response results fro m increased synaptic efficacy within the host retina. If it can be establis hed that functional connections between the transplant and the host retina produce the effect, then it would indicate that the technique could be expl ored as a therapeutic strategy in some diseases of retinal degeneration.