Some cytological and initial biochemical observations on photoreceptors in retinas of rds mice.

As a control for biochemical studies in progress, an ultrastructural study has been carried out on the deteriorating, 21-day photoreceptors of the 020/Cpb strain of mice, homozygous for retinal degeneration, slow (rds). At 21 postnatal days, outer segments were essentially lacking, but cilia erupting from the inner segments were common. A low percentage of cilia bore small cytoplasmic masses containing a few layered membranes, and rare inner segments possessed spherical aggregations of multilayered membranes. Pigment epithelial cells also possessed membranous aggregations in presumed phagosomes. While other parts of photoreceptors possessed the usual organelles of normal rods, inner segments were reduced in volume, and the layer of photoreceptor synaptic terminals was thinner. Mutant 21-day retinas possessed about two-thirds of the protein of normal 21-day retinas but 50% more protein than "rodless" (rd/rd) 21-day retinas. Surprisingly, while dark-adapted rds retinas possessed markedly lower levels of cyclic GMP as compared to controls, light-adaptation significantly reduced cyclic GMP and cyclic AMP levels, and biochemical data point to persistent light-modulated cyclic nucleotide levels in the photoreceptors.