Comparison of the localization of acetylcholinesterase and non‐specific cholinesterase activities in mammalian and avian retians

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Abstract
The localization of acetylcholinesterase and non‐specific cholinesterase was studied in the cone retinas of the pigeon and ground squirrel, and in the predominantly rod retinas of the rabbit, rat and cat. The enzymes were localized histochemically using the copper or gold thiocholine method. In the cone retinas, acetylcholinesterase was found in discrete bands in the inner plexiform layer. Cells corresponding in position and morphological detail to amacrine cells were stained for acetylcholinesterase. Cells of the ganglion cell layer that resembled displaced amacrine cells were also stained for acetylcholinesterase, as well as other cells that appeared to be ganglion cells. No stained processes could be followed from these latter cells, however. The horizontal cells were stained for non‐specific cholinesterase; these cells were localized to specific areas of the retina, which differed in the two species. In the predominantly rod retinas, there was no staining for non‐specific cholinesterase, but there was diffuse staining for acetylcholinesterase throughout the inner plexiform layer. In the rabbit, this staining pattern was not changed by chronic section of the optic nerve. No stained amacrine cells could be seen distinctly in any of the three species with predominantly rod retinas. After an intravenous dose of diisopropyl phosophorofluoridate sufficient to inactivate all the retinal acetylcholinesterase, however, synthesis of new enzyme could be followed in the amacrine cells and their processes. In all five species examined, therefore, the amacrine cells appeared to be the major or sole source of acetylcholinesterase for the inner plexiform layer of the retina. The possible function of this enzyme with regard to synaptic transmission in the retina is discussed.