Topographic mapping of retinal neurons in the European anchovy by nuclear staining and immunohistochemistry.

The anchovy retina is unique among vertebrates in being designed for polarization-contrast vision and has a marked cone area in the ventrotemporal quadrant for acute vision in the frontal field of view. Whereas cone topography and fine structure have been well examined in the European anchovy, the morphological organization of its inner retina is poorly understood so far. Using fluorescence staining of cell nuclei in combination with antibody stainings, the 3D pattern of cell nuclei was recorded coevally in all three retinal cell layers by confocal laser scanning microscopy, and the topographies of several neuron types were mapped separately across the retina. Cell classification and quantification succeeded for rods, cones, three types of horizontal cells (H1-3), rod and cone bipolars, amacrines, ganglion cells, and displaced amacrines as well as Müller cells; moreover, the morphology of H1 horizontal cells (calretinin-positive), rod bipolars (protein kinase C-positive), and a subtype of cone bipolars (parvalbumin-positive) is shown. Most cell types follow the cone topography, with a cell density maximum in the ventrotemporal quadrant (e.g., 730 cones, 2,800 cone bipolars, 230 GCL cells per 10(4) μm(2) ), showing their affiliation to the photopic system, except rods and rod bipolars (showing a cell density minimum in the cone area). The correlation of density maps of different cell types provides insight into convergence and divergence patterns in cone and rod pathways.