THE OCCURRENCE OF DOPAMINERGIC INTERPLEXIFORM CELLS CORRELATES WITH THE PRESENCE OF CONES IN THE RETINAE OF FISH

Using light-microscopic immunocytochemistry against tyrosine hydroxyla se, we have investigated the morphology of dopaminergic cells in 23 sp ecies of fishes representing various systematic classes and subclasses and which live in very different habitats. We have, for the first tim e, observed teleosts with dopaminergic amacrine cells. Thus, in both b ony and cartilaginous fishes, dopaminergic cells are differentiated as interplexiform and amacrine cells. The differentiation of dopaminergi c cells into amacrine or interplexiform cells in fishes correlates wit h the absence or presence of cones. In pure-rod retinae, they occur as amacrine cells, and in mixed rod/cone retinae, they occur as interple xiform cells. We conclude therefore that the differentiation of retina l dopaminergic cells in fish does not depend on the evolutionary or sy stematic classification of a given species. Rather, it is correlated w ith the occurrence of rods and/or cones, and thus linked more closely to the habitat. We argue that, in fish, the presence of cones and cone -specific horizontal cells may be responsible for inducing dopaminergi c cells to differentiate as interplexiform cells. Possible functions o f dopamine in all-rod retinae, which may not require adaptation, may i nclude neuromodulation in the inner plexiform layer for the sensitizat ion of the rod pathway, the shaping of biological rhythms, and the con trol of eye growth.