Spatial distribution of catecholaminergic cells in the fish retina

The cell density, distribution pattern, and morphology of catecholaminergic (CA) cells have been studied by fluorescence microscopy of retinal flatmounted preparations from various species of fresh water, estuary, and marine fishes, and the toad. In all fish retinas examined the CA‐cell density (cells/mm 2 ) is lowest in the central region surrounding the optic disc, slightly higher in the intermediate region, and highest in the periphery. The size of CA‐cells is smaller the higher their density. Following administration of L‐Dopa, dompamine, or noradrenaline, the density of CA‐cells approximately doubled, due to the appearance of small fluorescent cells. CA‐cells are arranged in rows along radial lines which fan out from the optic disc. In large cells of the central and intermediate regions three to five processes arise from the soma and extend and ramify irregularly in the inner plexiform layer, while in small cells from the intermediate and peripheral regions two processes arise from opposite poles and extend regularly in a direction perpendicular to the rows of cells and parallel to the retinal margin. In the retina of the marine fish Holocentrus sp CA‐cells are fewer in number compared to other fish studied and their processes extend without any regular pattern. In the toad their size and density are homogenous throughout the retina, and their processes show a regular arrangement.