The role of the pigment epithelium in the etiology of inherited retinal dystrophy in the rat

Inherited retinal dystrophy: primary defect in pigment epithelium determined with experimental rat chimeras

Chimeric rats were produced by the aggregation of embryos of the pinkeyed, retinal dystrophic RCS strain with those of pigmented, normal rats. In the mosaic eyes, patches of neural retina with abnormal and degenerated photoreceptors were present only opposite patches of nonpigmented, mutant pigment epithelium. This indicates that the retinal dystrophy gene acts in the pigment epithelial cell rather than in the photoreceptor cell.

Retinitis pigmentosa

The authors review the symptomatic and genetic aspects of the various entities of isolated retinitis pigmentosa (R.P), both in its typical form and in the forms associated with the affection of other ocular tissues. Syndromes in which R. P. is associated with the affection of other organs and systemic disorders are also cconsidered. Origin, diagnosis and the course of the disease are discussed with regard to electrophysiology, histopathology, fluorescein angiography and biochemistry. Animal research has provided new realizations about the ultrastructure and physiological mechanisms of retinal photoreceptors, and better understanding of abnormal changes. The possible pathogenesis of the human disease, based on research findings, is onsidered. Although R.P. is generally thought to be to be an "untreatable" disease, therapy may be effective in several pathological entities. Methods and results of therapy with vitamins, light deprivation and vision aids are discussed.

Pathology of the pigment epithelium and retina in rabbits poisoned with lead

Multifocal lesions of the retinal pigment epithelium were observed in rabbits fed a diet contaning 0.5% lead subacetate for periods of up to 2 years. Groups of pigment epithelial cells became congested with a lipofuscin pigment which was apparently derived from phagosomes of rod outer segments. Lipofuscin granules displaced melanin granules from the apical surface of the retinal pigment epithelial cells and resulted in conspicuous brown pigmentation of these cells in albino animals. Migration of macrophages and pigment epithelial cells into the subretinal space was common in affected areas. This pathology was not observed in the pigment epithelium of the ora serrata, or ciliary body. At the latest time periods, the abnormal lipofuscin pigmentation subsided, and degeneration of photoreceptors occurred. The pathogenesis of the lesions is discussed.

Electron microscopic histochemical studies of cyclic 3', 5'-nucleotide phosphodiesterase in the developing retina of normal mice and mice with hereditary retinal degeneration

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Kinetics of rod outer segment renewal in the developing mouse retina

The kinetics of rod outer segment renewal in the developing retina have been investigated in C57BL/6J mice. Litters of mice were injected with [(3)H]amino acids at various ages and killed at progressively later time intervals. Plastic 1.5 microm sections of retina were studied by light microscope autoradiography. The rate of outer segment disk synthesis, as judged by labeled disk displacement away from the site of synthesis, is slightly greater than the adult level at 11-13 days of age; it rises to more than 1.6 times the adult rate between days 13 and 17, after which it falls to the adult level at 21-25 days. The rate of disk disposal, as measured by labeled disk movement toward the site of disposal, is less than 15% of the adult level at 11-13 days of age; it rises sharply to almost 70% of the adult level by days 13-15 and then more gradually approaches the adult rate. The net difference in rates of synthesis and disposal accounts for the rapid elongation of rod outer segments in the mouse between days 11 and 17 and the subsequent, more gradual elongation to the adult equilibrium length reached between days 19 and 25. The changing rate of outer segment disk synthesis characterizes the late stages of cytodifferentiation of the rod photoreceptor cells.

Photoreceptor-pigment epithelial cell relationships in rats with inherited retinal degeneration. Radioautographic and electron microscope evidence for a dual source of extra lamellar material

Protein synthesis and displacement in photoreceptor and pigment epithelial cells of inbred normal (Fisher) and mutant (RCS) rats with inherited retinal degeneration has been studied by light and electron microscope radioautography. Groups of animals 14, 15, 17, 19, 27, 35, and 50 days of age were injected with amino acids-H(3) and killed at subsequent time intervals. In normal rats, radioactive protein synthesized in the rod inner segments was incorporated into outer segment saccules and displaced outward; the total renewal time of outer segments at all ages was approximately 9 days. In RCS photoreceptors, outer segment displacement was slowed from the normal rate before day 17 and at all subsequent stages. Most of the newly synthesized protein appeared to migrate only into the basal third of the outer segments. Labeling of pigment epithelial cells in RCS rats was always heavier than in controls. Labeled protein was displaced as early as 1 hr postinjection from pigment epithelial cell somas into the apical processes, and by 2 hr postinjection was located in the adjacent lamellar whorls characteristic of the mutant rat retina. After 1 day, radioactivity was present in the 14, 15, 17, and 19 day series of RCS rats in the apical third of the outer segment layer (occupied mainly by extra lamellar material) while there were few silver grains in the middle third of the layer (occupied mainly by distal parts of outer segments). The RCS pigment epithelial cells thus have an unusual synthetic role and appear to be a source of the extra lamellar material. Electron microscope examination revealed that many intact pigment epithelial cell processes were incorporated into the large whorls of extra lamellae. In addition, many disorganized outer segment saccules were observed in continuity with longer membranous lamellae and large lamellar whorls. The extra lamellar material therefore appears to be derived from both rod outer segments and pigment epithelial cells.