Dopaminergic cells of the river lamprey retina revealed by a histofluorescence study.

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Abstract
The retinas of the river lamprey (Lampetra japonica) were processed for fluorescence microscopic study with flat-mounts and cryosections. The eyes were enucleated 2hr after an intravitreous injection of a mixture of noradrenaline (2.5μg) and 5, 6-dihydroxytryptamine (2.5μg). The density (number/mm2) of dopaminergic (DA) cells was calculated for four arbitrary concentric regions of retinal flat-mounts; the central, intermediate, peripheral and marginal regions. The density was found to be higher (mean±S.D.= 131±29 cells/mm2; n=12) in the peripheral region than in the rest and extremely low (15±7cells/mm2) in the marginal region, and no DA cells existed in the circumferential edge immediately neighboring the ora terminalis. Oval or fusiform DA cells extended in various directions 2 to 3 main processes, which irregularly ramified and formed dense fiber networks in the amacrine cell and inner plexiform layers. Since no fluorescent fiber was seen in the horizontal cell layer, DA cells appeared to be a subset of amacrine cells in the lamprey retina. Differences in morphology and spatial distribution were discussed between DA cells of the lamprey and teleost fish retinas.