Retinal degenerations in the dog II. Development of the retina in rod-cone dysplasia

The kinetics of rod outer segment production and turnover were studied in Irish setter dogs with a recessively inherited photoreceptor degeneration (rod-cone dysplasia). Affected and littermate control (heterozygote) dogs, 16–50 days of age, were injected intravitreally with [ 3H]leucine after electroretinographic studies. Normal age-matched mongrel dogs were also used as controls. Between 6 hr and 8 days following intravitreal injection, eyes were removed and processed for microscopic and radioautographic studies. In affected dogs, the rod components of the electroretinogram were not recordable. Cone components were recordable but failed to develop normally. Morphologically, rod inner segments were diminutive and the outer segments short and contained disorganized and disoriented disc material. Cone inner segments became broad and club-shaped. Radio-autography showed label accumulation within inner segments, but only sporadic and randomly distributed label in the narrow outer segment layer. These results suggest that in Irish setters with rod-cone dysplasia, there is a defect in the morphogenesis of the rod outer segments during postnatal retinal differentiation.