Retinal degenerations in the dog III abnormal cyclic nucleotide metabolism in rod-cone dysplasia

In dogs bred to develop rod-cone dysplasia, retinal development is normal until 13 days of age.Afterwards, there is an arrest of visual cell differentiation. Rod inner segments remain diminutive and outer segments fail to elongate as in controls; the outer segments show lamellar disorientation and disorganization. Affected visual cells degenerate, but the degeneration process is more rapid and extensive for rods than cones. Cyclic GMP levels become elevated in affected retinas early during the postnatal differentiation of visual cells; this elevation precedes any morphological evidence of photoreceptor disease. Retinal protein synthesis is normal during the time that retinal cGMP levels are rising above control values. The results indicate that the biochemical abnormality which results in elevated retinal cGMP levels is the earliest recognized defect in rod-cone dysplasia.