Dark-adapted albino zebrafish were exposed to constant intense light for 0 (A, F, K), 31 (B, G, L), 51 (C, H, M), 68 (D, I, N) and 96 hours (E, J, O) and eyes were collected and processed for immunolabeling of glutamine synthetase (A-E, green), PCNA (F-J, red), or the two labels merged (K-O). At 0 hours, the glutamine synthetase evenly labeled the Müller glia and PCNA was not present. At 31 hours, the single PCNA-positive cells in the INL colocalized with a subset of glutamine synthetase-positive Müller glia (arrow), while the remaining glutamine synthetase-positive Müller glia remained PCNA-negative (arrowhead). By 51 hours, the Müller glia that were associated with clusters of PCNA-positive cells had hypertrophied and were expressing reduced levels of glutamine synthetase relative to the remaining Müller glia (arrow and arrowhead, respectively). At 68 and 96 hours, the Müller glia that were associated with clusters of PCNA-positive cells reached a maximal level of hypertrophy (dashed outline and arrow, respectively). Scale bar in Panel A is 25 microns. PCNA, proliferating cell nuclear antigen; GS, glutamine synthetase; ONL, outer nuclear layer; INL, inner nuclear layer; GCL, ganglion cell layer.