Light-induced photoreceptor cell degeneration has been studied in several species, but not extensively in the teleost fish. Furthermore, the continual production of rods and cones throughout the teleost's life may result in regeneration of lost rods and cones. We exposed adult albino zebrafish to 7 days of constant darkness, followed by 7 days of constant 8000 lux light, followed by 28 days of recovery in a 14-h light:10-h dark cycle. We characterized the resulting photoreceptor layer cell death and subsequent regeneration using immunohistochemistry and light microscopy. Within the first 24 h of constant light, the zebrafish retina exhibited widespread rod and cone cell apoptosis. High levels of cell proliferation within the inner nuclear layer (INL) were observed within the first 3 days of constant light, as assessed by immunodetection of proliferating cell nuclear antigen and BrdU labeling. The proliferating cells within the INL were closely associated with the radial processes of Müller glia, similar to the pluripotent retinal stem cells observed during embryonic development. Using antibodies generated against the individual zebrafish opsins, we determined that rods and the green, blue, and ultraviolet cone cells were replaced within the 28 day recovery period. While both rods and cones were replaced, the well-ordered cone cell mosaic was not reestablished.
Copyright 2000 John Wiley & Sons, Inc.