Similarity in spatial distribution between dopaminergic cells and indoleamine-accumulating cells of carp retina.

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Abstract
Carp (Cyprinus carpio) retinas were processed for fluorescence-microscopic studies with flat-mounts. When the fish were injected intravitreally with noradrenaline (NA; 20μg) 2hr before enucleation, the number of visible cells was approximately double that of endogenously fluorescent cells due to the additional appearance of smaller and weakly fluorescent cells. By injecting a mixture of NA (5μg) and 5, 6-dihydroxytryptamine (5, 6-DHT; 5μg) intravitreally 2hr prior to enucleation, simultaneous visualization of greenish and yellowish fluorescent cells was achieved. It was found that the former was larger in size and certainly belonged to a class of dopaminergic (DA-) cells, while the latter was smaller and corresponded to another class of cells, indoleamine-accumulating (IA-) cells. These findings were further confirmed by selective destruction of DA-or IA-cells with intravitreal injection of 6-hydroxydopamine (6-OHDA; 15μg) plus pargyline (15μg) or of 5, 7-dihydroxytryptamine (5, 7-DHT; 15μg) once daily on two succesive days, one week before enucleation. The density ratio of DA-cells to IA-cells was found to be 1:1, and they were similarly distributed in space in a mixed fashion. Their densities were higher in the peripheral region than in the rest, and extremely high at the retinal margin. Where the densities were higher, the size of cell bodies tended to be smaller. Those cells, located in the intermediate and peripheral regions, appeared to be arranged in radial rows originating at the optic disc and fanning out towards the retinal margin.