An analysis of urodelian retinal regeneration: I. Studies of the cellular source of retinal regeneration in Notophthalmus viridescens utilizing 3H‐thymidine and colchicine

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Abstract
The process of retinal degeneration and regeneration in retinectomized or enucleated and reimplanted eyes of adult Notophthalmus viridescens has been studied following staged administrations of tritiated thymidine or colchicine. In control left eyes, no labeled cells were observed in either the retina, pigment epithelium, or ora serrata. In retinectomized or enucleated eyes, retinal degeneration proceeded from the posterior central pole circumferentially to the ora serrata, with complete retinal degeneration being consistently observed. Retinal replacement originated from two cellular sources: the posterior pigment epithelium and the anterior complex, consisting of cells in the ora serrata and pars ciliaris retina.The posterior pigment epithelium gave rise to an initial central retinal portion which differentiated in an annular pattern which extended from the optic nerve to the vortex veins. Cellular addition from the pigment epithelium became restricted to these two regions by day 25. The anterior retinal mass was regenerated from the anterior elements (ora serrata/pars ciliaris retina) with a minor contribution from the underlying anterior pigment epithelium. Data concerning the relative numbers of cellular types involved in the regenerative sequence and the times of their function are presented. Peak labeling occurred in the posterior pigment epithelium at day 20, the pars ciliaris retina at days 18 and 40, and the new retina at days 28 and 41. By 30 days regional sites of cellular proliferation became established that coincided with the pattern of ocular blood vessels. Retinal differentiation followed the pattern commonly observed during retinal development.The significance of these observations with respect to earlier work demonstrating a different sequence for retinal restoration is discussed.