Rod cell activity in retinal degenerative rats.

The Royal College of Surgeons (RCS) rat is a good model for the study of the early onset of retinal degenerative disorders. RCS retinal disease is often associated with the loss of rhodopsin in outer segment membranes and the progressive degeneration of photoreceptor cells. This study was conducted to investigate the possible mechanisms of the loss of photoreceptor sensitivity. The electroretinographic responses were recorded in RCS and control rats, age 15, 25 and 35 days, as well as in adult control rats. The a-waves were analyzed using the Hood and Birch model of activation of photoresponse. Photoresponse latency in the RCS rats was prolonged as the disease progressed. The maximum recorded a-wave amplitudes were significantly lower for the RCS rats compared to the control rats. The sensitivity of a-waves as indicated by Ka, the semi-saturation constant, varied and depended on the age of the rats and degenerative stage of the disease. The model's time to peak response increased more than twofold as the degeneration advanced. The changes in a-waves indicate that RCS disease causes progressive impairment of the rod photoresponse. It also suggests that in addition to the phagocytic defect of the retinal pigment epithelium, the abnormal composition of the membrane lipids and the interphotoreceptor matrix and the rhodopsin loss may also cause abnormal photoresponses in RCS rats.