Retinal transplants restore visually evoked responses in rats with photoreceptor degeneration

To assess whether transplantation of intact sheets of fetal retina with retinal pigment epithelium (RPE) into a retina with photoreceptor degeneration restores visually evoked responses.

Sheets of fetal retina with RPE were transplanted into the subretinal 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 responses were recorded in the superior colliculus (SC) of transplanted rats, age-matched untransplanted rats, and rats with sham surgery.

In 19 of 29 RCS rats with transplants, visually evoked responses were 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 placed. Outside of this area, no visual responses were evoked. Visually evoked responses were never recorded in age-matched, nontransplanted RCS rats. Visually evoked responses were recorded in 6 of 13 RCS rats with sham surgery, but these responses were significantly different from responses in rats with transplants.

These results demonstrate that this transplantation technique restores visually evoked responses in the brain. Although the underlying mechanism is unknown, we propose that the central visual response results from increased synaptic efficacy within the host retina. If it can be established that functional connections between the transplant and the host retina produce the effect, then it would indicate that the technique could be explored as a therapeutic strategy in some diseases of retinal degeneration.