Quantitative evaluation of the distribution of proliferating cells in the adult retina in three cyprinid species.

In the present study, a descriptive and quantitative analysis of all the proliferating cell populations present in the normal adult retina of three cyprinid species (goldfish, zebrafish, and tench) is reported. Evaluation of cell proliferation was performed in proliferating cell nuclear antigen (PCNA)-labeled tissue sections as well as in single-cell suspensions analyzed by flow cytometry. Our results show that the neural progenitors of the inner nuclear layer (INL) of cyprinids continue dividing in adulthood in uninjured retinas. These cells are probably related to the generation of rods in normal retinal growth, as well as in the production of any retinal cell type in regenerating processes. The distributions of both these cells and their presumptive progeny, the rod precursors, differ from one species to another, being homogeneous in zebrafish, displaced to the periphery in goldfish and to the temporal pole in tench. With regard to the cell apposition at the retinal periphery, it seems to be symmetrical in goldfish and zebrafish, based on a homogeneous extension of the peripheral growth zone (PGZ), but asymmetrical in tench, where it presents a significantly lower extension in the ventral retina. The flow cytometry analyses indicate that, overall, the proportion of proliferating cells is significantly greater in zebrafish retina despite the fact that body growth rate is lower in zebrafish than the other two species.