Late emergence of pathological oscillatory activity in the retina of the Retinitis pigmentosa model RCS (Royal College of Surgeons) rat

Retinitis pigmentosa (RP) is a leading cause of blindness. The best studied models of human RP are the rd1 and rd10 mouse and the RCS rat (Royal College of Surgeons). In many models after degeneration of the photoreceptors, a pathological rhythmic activity of the retina as well as lowered efficiency of electrical stimulation were observed. In rd10 retina, both events were shown to be intimately linked. Surprisingly, to our knowledge no retinal oscillations have been reported in RCS retina. As oscillations might interfere with the performance of therapeutic approaches to restore vision, e.g., retinal prostheses, it is important to know, whether they are a common feature of retinal degeneration. Electrical activity was recorded in retinae of 3-19 months (M3-19) old RCS rats in vitro using planar and penetrating multi-electrode-arrays. Short deflections in the local field potential resembling those observed in oscillations in rd1 and rd10 retinae were only sporadically found in M3 RCS retinae. Oscillations at appr. 2 Hz occurred more often and were more pronounced the older the animals were. Yet, even at M18-19 oscillatory periods were short and separated by long periods of non-oscillatory activity. In summary, in advanced stages of degeneration, RCS retinae display oscillations similar to rd1 and rd10 retinae. However, in RCS retina oscillatory periods are shorter than in mouse models and may, therefore, have escaped detection in earlier studies. These results together with results observed in non-rodent models suggest that pathological rhythmic activity is a common feature in RP models.