Characterization of Visual Responses in the Superior Colliculus of Retinal Degenerate Rats With Retinal Transplants

Abstract

Abstract: : Purpose:Visual responses to a low light stimulus were recorded from the superior colliculus (SC) to determine whether the beneficial effect of retinal transplantation is a direct effect of the transplanted photoreceptors. Methods:S334ter–3 rats received fetal retinal sheet transplants in one eye at 29–43 days of age. Controls were non–transplanted transgenic and normal pigmented rats. Visual responses were recorded in the contralateral superior colliculus (SC) at the age of 25–95 days. Light stimuli of 50 ms duration, ranging in intensity from –6.46 to 0.81 log cd/m², were presented from a fullfield white screen. Results:Normal pigmented rats had visual thresholds of –5.25 log cd/m², whereas the threshold in transgenic rats at an early age of retinal degeneration (25–28 days) was elevated to –1.6 log cd/m². When tested after 3 months of age, the threshold was considerably improved in transplanted transgenic rats (–2.8 log cd/m²). Responses were found only in an area of the SC corresponding to the placement of the graft in the retina. In all rats studied, the response onset latency (RL) was inversely proportional to the stimulus intensity, i.e. shorter latencies with higher intensities. The RL was significantly longer (180 ms) in retinal degenerate rats than in normal controls (60 ms) at the same light intensity. In contrast, the RL in the transplanted rats was closer to that of the normal rats. An abrupt transition in the latency–light response curve was apparent in pigmented normal rats at –3.42 log cd/m². This may reflect the transition between scotopic and photopic responses. Conclusions:Retinal transplantation restores visual responses in a retinal degeneration rat model. The restoration appears to be derived at least in part from the transplanted photoreceptors, since at the time of transplantation, there was a lower level of visual responses.

Keywords: retina • transplantation • electrophysiology: non-clinical