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A. Giddabasappa, W.R. Hamilton, W. Xiao, S. Chaney, J.E. Johnson, D.A. Fox; Kinetics of Apoptosis and Increased Cell Proliferation in the Developing Mouse Retina During Gestational Lead Exposure . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2791.
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© ARVO (1962-2015); The Authors (2016-present)
Previously we observed that low–to–moderate level gestational lead (Pb) exposure produces a dose–dependent increase in the thickness of the adult retinal outer and inner nuclear layers. This increase appeared specific for rods and bipolar cells (BCs) as Müller glial cells did not appear changed, and the number of cones was slightly decreased. The aims of the present study were to quantify the changes and to determine the kinetics of this unique retinal phenotype during development.
Female C57BL/6 mice were exposed to water or one of three different Pb solutions throughout pregnancy and until postnatal day 10 (PN10): equivalent to human gestation period. At PN60, fixed retinas were stained with nuclear and molecular markers that define various retinal cell classes and Western blots were performed. To assess the kinetics of retinal cell proliferation, dams or mice were injected with BrdU (ip; 2 hr survival) on embryonic days 16.5 (E16.5), 18.5 and on PN1, 3, 5, 7 and 10. Fixed retinas were stained for BrdU, the mitotic marker anti–PH3 antibody and for apoptosis using TUNEL. Retinal sections were examined by light or laser scanning confocal microscopy and cell counts were obtained using stereological techniques.
At PN60 there was a Pb–dependent increase (10–30%) in the number of rods (rhodopsin+ve), rod BCs (PKC+ve & chx10+ve), and cone BCs (PKC–ve & chx10+ve); decrease (5–15%) in the number of cones (M– and S–opsin+ve); and no change in number of Müller glial cells (glutamine synthetase+ve). These results were confirmed by Western blots. The number of BrdU+ve cells was increased in the center and periphery of Pb retinas at all ages examined. The largest increase was at E16.5 and PN1. PH3+ve cells were slightly increased in central and peripheral retina at E16.5 and PN1, respectively. At E16.5 and E18.5 there is minimal apoptosis in the control neuroblastic layer (NBL), however, it was decreased in Pb retinas. During postnatal development, apoptosis slowly increases in the NBL and inner retina: as published. Pb slightly increased the NBL apoptosis at PN1 and PN3.
Low–level gestational Pb exposure produces a novel phenotype characterized by a significantly increased proliferation of both late–born rods and bipolar cells. The increased number of cells in the rod signaling pathway likely produces the Pb–induced supernormal scotopic ERGs observed in gestationally Pb–exposed children, monkeys and rodents. Our future work will focus on determining the birth date of the proliferating neurons and molecular mechanisms underlying this Pb–induced proliferation.
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