Histochemical and cytochemical localization of acetylcholinesterase in retina and optic tectum of teleost fish.

The activity of cholinesterase and its cellular and subcellular localization were investigated in the retina and optic tectum of Eugerres plumieri and in the retina of Carassius carassius by means of radiometric, histochemical, and cytochemical procedures. In both fishes only the presence of acetylcholinesterase could be demonstrated. This study, besides confirming previous findings that acetylcholinesterase is located in the ganglion and amacrine cells of the retina as well as in the inner plexiform layer, in addition provides evidence that the enzyme is also present at the region of photoreceptor synapses between the cell bodies and apposing extensions of the horizontal cells of the same layer. The latter localization may indicate the involvement of a cholinergic mechanism at the functional contacts (transferapses) between the horizontal cells. In the optic tectum of Eugerres plumieri, histochemistry reveals fine distinguishable bands of acetylcholinesterase activity; two of the bands are quite sharply defined, whereas three others have rather a more diffuse appearance. The presence of these bands and their distribution may suggest a widespread distribution of cholinergic elements in the optic tectum.