Transient preservation of photoreceptors on the flanks of argon laser lesions in the RCS rat.

In the RCS rat there is a progressive degeneration of the photoreceptors which starts at two to three weeks after birth. We have demonstrated that there is prolonged survival of photoreceptors on the flanks of argon laser lesions made at post-natal day 23, just as degeneration begins. The cells in the outer nuclear layer retained a relatively normal appearance on the flanks of the lesions for the first two weeks and there was a very low percentage of pyknotic cells. By one month some cell loss occurred but much less than in non-irradiated regions where very few cells remained. At two months after lesion there were still elevated numbers on the flanks but only 2-3 rows of cells remained. The prolonged survival correlated with disruption to the pigment epithelial layer, increased migration of phagocytic cells into the outer segment/debris layer and a reduction in thickness of the debris layer at late stages. The mechanisms of this effect are unknown however laser lesions provide a well controlled and reproducible situation in which to study these mechanisms.