PURPOSE:To further characterize the retinas of Pro3471Leu rhodopsin transgenic pigs, a model for human retinitis pigmentosa.METHODS:Retinas from normal and transgenic pigs, newborn to 20 months old, were processed for light and electron microscopic immunocytochemical examination.RESULTS:At birth, rod numbers were normal in the transgenic retinas, but their outer segments were short and disorganized and their inner segments contained stacks of rhodopsin-positive membranes. The newborn rod synapses lacked synaptic vesicles and ribbons and had numerous rhodopsin-positive, filopodia-like processes that extended past the cone synapses into the outer plexiform layer. Rod cell death was apparent by 2 weeks and was pronounced in the mid periphery and central regions by 6 weeks. Far peripheral rods were initially better preserved, but by 9 months virtually all rods had degenerated. Cones degenerated more slowly than rods, but by 4 weeks the cone synapses were shrunken and some mid peripheral cones had lost their immunoreactivity for phosphodiesterase-gamma, arrestin, and recoverin. From 9 months to 20 months, the cone outer segments shortened progressively, and more cones lost immunoreactivity for these proteins.CONCLUSIONS:The rhodopsin transgenic pig retina shares many cytologic features with human retinas with retinitis pigmentosa and provides an opportunity to examine the earliest stages in photoreceptor degeneration, about which little is known in humans. The finding of abnormal rhodopsin localization in newborn rods is consistent with misrouting of mutant rhodopsin as an early process leading to rod cell death. Novel changes in the photoreceptor synapses may correlate with early electrophysiological abnormalities in these retinas.

PURPOSE:In an unpublished study, the authors found that immunoreactivity for basic fibroblast growth factor (bFGF) is increased in rod photoreceptors adjacent to long-standing laser burns in human diabetic retinas. The goal of this study was to determine whether laser photocoagulation produces a similar increase in photoreceptor bFGF and promotes survival of these cells in dystrophic rodent retinas.METHODS:Threshold (whitening) and subthreshold (nonwhitening) laser burns were made in retinas of normal and Royal College of Surgeons (RCS) rats and normal and rds mice. The retinas were processed for immunocytochemical and morphometric analyses.RESULTS:In nonlasered normal rat and mouse retinas, bFGF immunoreactivity was prominent in the nuclei of Müller cells and astrocytes. Photoreceptors were bFGF negative except for a zone of bFGF-immunoreactive rods near the ora serrata. Some photoreceptors in nonlasered retinas of RCS rats and rds mice became bFGF immunoreactive. After laser treatment, bFGF immunoreactivity was markedly increased in all photoreceptors flanking the threshold burns and within the subthreshold burns in normal and mutant rats and mice. In RCS rat retinas, photoreceptor bFGF immunoreactivity remained elevated within subthreshold burns and flanking the threshold burns, and photoreceptor survival was prolonged. In rds mouse retinas, increased bFGF immunoreactivity in photoreceptors was not sustained and their degeneration was not retarded.CONCLUSIONS:Laser treatment of RCS rat retinas produced a sustained increase in bFGF immunoreactivity in photoreceptors and prolonged their survival, but laser treatment of rds mouse retinas did not have a long-term effect on photoreceptor bFGF immunoreactivity or survival. Although species differences in laser effects on photoreceptor bFGF and survival are apparent, the finding that rods flanking laser burns in human retinas have sustained increases in bFGF immunoreactivity suggests that laser treatment may be useful for prolonging survival of mutant photoreceptors in retinas of patients with retinitis pigmentosa.

Retinitis pigmentosa (RP) is an inherited disease that causes primary degeneration of rod photoreceptors in the retina. Although the causal gene (e.g. rhodopsin) is thought to be expressed in all rods across the retina, the degeneration is typically nonuniform, with rods in the far periphery surviving significantly longer than those in the midperiphery and macula. Basic fibroblast growth factor (bFGF) is a putative survival factor for photoreceptors, and the characteristic regional pattern of rod cell survival in RP suggested that bFGF might be distributed nonuniformly in the human retina. We performed double-label immunocytochemistry on 15 normal human retinas, using anti-bFGF and other antibody markers for retinal neurons and glia. Immunoreactivity for bFGF was consistently absent from cones but was present in rods, populations of cone bipolar and amacrine cells, Müller glial cells, and astrocytes. In the macula, the percentage of bFGF-reactive rods was very low (approximately 0.5%) but it increased in a central to peripheral gradient, accounting for up to approximately 88% of the rods in the far periphery. These findings suggest that a central to peripheral gradient of rod bFGF is present in normal human retina and may influence the pattern of photoreceptor degeneration in RP. The absence of bFGF in cones and the low number of bFGF-positive rods in the macula may correlate with the vulnerability of these cells in RP, age-related macular degeneration, and other retinal diseases.