Regional difference in density of monoamine‐accumulating cells of carp and catfish retinas

By means of a histofluorescence technique, a comparative study was conducted on the regional density of dopaminergic (DA) and indoleamine‐accumulating (IA) cells in carp (Cyprinus carpio) and catfish (Ictaluruspunctatus) retinas. In order to enhance detection of fluorescent cells, noradrenaline (NA; 5.0 μg) or a mixture of NA (2.5 μg) and 5,6‐dihydroxytryptamine (5,6‐DHT; 2.5 μg) was intravitreally injected into the eyes 2–3 hr before enucleation. DA and IA cells were counted systematically in space on flat‐mounted preparations. Both classes of cells were found to be distributed similarly in the two species of fish; the cell density is highest in the circumferential margin of the retina, and is slightly higher in a region dorsal to the optic disc than in the surrounding area. Differences in the distribution pattern of the cells between carp and catfish retinas were as follows: (a) the DA cell density is higher over the whole retinal field in carp (the mean density ± SD = 34 ± 16 cells/mm²) than in catfish (13 ± 7 cells/mm²); (b) the region where the density is slightly higher than in the surrounding area is restricted to a small area immediately dorsolateral to the optic disc in carp, while it is relatively broadly placed dorsal to the optic discs, forming a horizontal band in catfish; (c) the density ratio of DA cells to IA cells is 1:l in carp but 1:2 in catfish; and (d) catfish DA cells seem to be more irregular than carp DA cells in shape, size, dendritic arborization, uptake preference for monoamines intravitreally injected, and also in depth location seen in radial cryosections.