Serotonin containing neurons in the retina of the teleost Eugerres plumieri

The concentration and localization of serotonin was determined in the retina of the teleost Eugerres plumieri by using high performance liquid chromatography (HPLC) and immunohistochemical techniques. Serotonin and dopamine were measured simultaneously, their concentrations in the retina being77 ± 8 and516 ± 23 ng/mg tissue respectively. Treatment of the animals with pargyline significantly increased the levels of dopamine and serotonin. When retinas were treated with the neurotoxin 5,6-dihydroxytryptamine, the level of serotonin was reduced by more than 90% while the dopamine content only diminished by 20% when compared to controls. By using immunohistochemistry with a monoclonal anti-serotonin antibody it was possible to localize this amine in cell bodies of a population of amacrine cells with processes extending mainly into a thin layer of the most external lamina of the inner plexiform layer. Very few ramifications were seen projecting to the internal lamina of this layer. When visualized in flat mount preparations, dense arborization of fluorescent processes was observed. This is the first direct evidence that serotonin is apparently present in amacrine cells of the retina of E. plumieri with a distribution of the serotonergic terminals similar to goldfish but somewhat different when compared to other species.