Function and structure in retinal transplants

Embryonic mammalian donor retina transplanted into the subretinal space of a mature host develops into a graft with well-organized, but atypical retinal structure. We tested the effect of this organization on rabbit-to-rabbit graft functional properties, isolating the graft to avoid contamination of graft responses by host retinal activity. Transient ON or ON-OFF spike-like responses and local electroretinograms (L-ERGs) were recorded simultaneously via a single electrode on the graft surface. These response components depended on stimulus diameter, sometimes in a way indicating antagonistic center-surround receptive field organization and spatial tuning (43%). Other times, the responses were an increasing function of stimulus diameter which saturated for large spots (57%). Response amplitudes were a monotonically-increasing function of light intensity over the narrow range tested. The L-ERGs were reminiscent of the proximal negative response or M-wave seen in normal retinas, which reflect light-induced amacrine cell activity. Thus, for the first time, we have shown that these subretinal grafts possess light-transduction and complex functional properties like those in normal retinas. They also possess the cellular complement and synaptic microcircuitry needed to form these physiological properties, Therefore, these results demonstrate a functional ability and capacity in transplants that is required if nerve cell transplantation surgery is to be done with therapeutic aims.