A) Time course of regeneration of cone and rod photoreceptors. The number of BrdU+ rod and cone photoreceptors per section at 31 dpl is plotted as a function of time of BrdU injection (in days post-lesion). Each bar is the mean number per section calculated by combining data from counts on two retinas and 4 to 17 sections per retina. The data were pooled after an ANOVA showed that there was no significant difference between the average counts between retinas at each time point. The error bars represent one SEM. Comparison of means with a single factor ANOVA showed that slightly more cones are born at 3 dpl than at 4 dpl (p < 0.05), fewer at 7 dpl (p < 0.001) and almost none at 10 dpl (data not shown). In contrast, significantly fewer rods than cones are born at 3 and 4 dpl (p < 0.001), but many more rods than cones are born at 7 (p < 0.001) and 10 dpl (data not shown). B) Most of the proliferating cells at 2 dpl are Müller glia. Fish with heat lesioned retinas were exposed to a 4 h pulse of BrdU at 2, 3 or 4 dpl. Retinas were processed for in situ hybridization with an apoE probe to label cell bodies of Müller glia and for BrdU immunocytochemistry. Each bar represents one lesion, and 2 to 9 sections were counted for each lesion. All BrdU+ nuclei were counted and scored for apoE. The mean number of BrdU+ nuclei per section is given above each bar. Statistical analysis of the data by single factor ANOVA indicates that the percent apoE+ cells in the BrdU+ population at 2 dpl greater than at 3 dpl (p < 0.01) or at 4 dpl (p < 0.01) but 3 dpl does not differ from 4 dpl.