THE DISTRIBUTION OF CHOLINE ACETYLTRANSFERASE ACTIVITY IN VERTEBRATE RETINA1

Abstract— Choline acetyltransferase (ChAc) activity was determined in retinal layers from 10 vertebrates. In all animals, the highest activity was in the inner plexiform layer, intermediate activity in the inner nuclear and ganglion cell layers, and very low activity in the photoreceptor and outer plexiform layers and optic nerve. The pattern of distribution of enzyme activity within the inner nuclear layer corresponds quantitatively to the distribution of amacrine cells within that layer. A species difference of almost 90‐fold was found between the lowest and highest values for ChAc activity in inner plexiform layer. The variation in enzyme activity found among homeotherms in inner nuclear and inner plexiform layers is related to the number of amacrine cell synapses in the inner plexiform layer. But the differences in enzyme activity are generally greater than those which have been found in numbers of amacrine cell synapses between species. The data suggest that cholinergic neurons in retina are to be found predominantly among the amacrine cell types and that not all amacrine cells will be found to be cholinergic.