Morphological changes of retinal pigment epithelium and choroid in rd-mice

The sequence of degenerative changes in the retinal pigment epithelium (RPE ) and the choroid of retinal degeneration (rd)-mice was studied in correlat ion with photoreceptor changes. Three weeks to 26-month-old animals were in vestigated using light and transmission electron microscopy, enzyme histoch emistry and quantitative morphology. Changes in the choriocapillaris (CC) w ere additionally studied by scanning electron microscopy of corrosion cast preparations. In 3-week-old mice, in which most of the outer segments of ph otoreceptors in the central portion of the retina had disappeared but remna nts of the cells were still present, the RPE was enlarged and showed elonga ted microvilli. In 8-week-old animals, the photoreceptors were completely a bsent in large areas of the posterior pole region. In these areas the RPE w as also completely lost. Quantitative evaluation performed in histological serial sections showed that loss of RPE measured as length of RPE-free Bruc h's membrane, continuously increased up to the age of 20 months. In 8-week- old animals, CC adjacent to degenerating RPE showed loss of fenestration. I n 10-week-old animals, the CC disappeared in those areas where the RPE was already lacking. The loss of CC increased with increasing age and in 20-mon th-old animals 5-10 % of the entire CC was lacking. Loss of the related art erioles and nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d )-positive nerve fibers occurred only in similar to 2-year-old rd-mice. Com pared to other animal models, RPE and CC defects in rd-mice are relatively large. The rd-mice might therefore provide a good tool to study factors inv olved in CC degeneration. (C) 1999 Academic Press.