AGE-RELATED DISTRIBUTION OF CONES AND ON-BIPOLAR CELLS IN THE RD MOUSE RETINA

Purpose. Retinal dystrophic (rd) mice lose most of their rod photorece ptors within the first three weeks after birth. We determined the age- related distribution of peanut agglutinin lectin (PNA)-labeled cones d uring the first 12 months of age. We also investigated whether the den sity of ON-bipolar cells expressing L7 protein was affected by their l oss of photoreceptor inputs. Methods. rd mice were selected from a tra nsgenic strain which expresses an L7-beta-galactosidase fusion gene lo calized to ON-bipolar cells. Cones were stained with PNA and ON-bipola r cells with blue-gal (halogenated indolyl-beta-D-galactoside). Retina s were flat-mounted and observed at 1, 2, 3, 6, and 12 months of age. Results. PNA-labeled cones are distributed unevenly across the retina at 1 month postnatal. Their concentration decreases first in the centr al and far peripheral retina, leaving a ring of labeled cells in the m idperipheral region. At 3 months, a larger patch of cones remains in t he supero-temporal midperipheral region and a smaller patch in the inf ero-nasal retina. By 6 months, few cones remain in the infero-nasal re tina; by 1 year approximately 100 cones remain in the entire retina, l ocalized to the superior midperipheral region. ON-bipolar cells appear evenly distributed at 1 month. By 2-3 months, relatively more blue-ga l staining is seen in the midperipheral regions underlying dense cone populations. At 6-12 months, blue-gal label is distributed in a spotty pattern with little or no staining seen in areas of apparent neovascu larization. Conclusions. (1) PNA-labeling of cones in the rd retina de teriorates in a distinct spatial pattern with the longest cone surviva l in the midperipheral superior retina. (2) ON-bipolar cells are more densely labeled in regions of high cone density during the early month s of cone degeneration and, in later stages, show relative decreases i n regions of apparent neovascularization.