The Morphology of Amacrine Cells Coupled to the OFF Alpha Ganglion Cell in the Rabbit Retina

Abstract

Abstract: : Purpose: Injection of Neurobiotin into an OFF alpha ganglion cell reveals the somas of other alpha ganglion cells and a variety of amacrine cells. We have stained the coupled amacrine cells more fully in order to characterize the types which are coupled to OFF alpha ganglion cells. Methods: OFF alpha ganglion cells of rabbit retina were visualized with acridine orange, injected with Neurobiotin and subsequently fixed, permeabilized with Tween20 and visualized with streptavidin linked to Cy3 or Alexa488. Amacrine cells targeted by this method were injected with DiI or DiO. Results: The most well–coupled amacrine cell found by this method is an axon–bearing amacrine cell which descends through the region in which the alpha ganglion cell processes stratified, slightly above the level of cholinergic processes in sublamina a, and terminates just below this cholinergic band. At least two other types of amacrine cell were frequently stained by this method. A fourth type (ND2) was sometimes stained both by an antibody to nitric oxide synthase (NOS) and Neurobiotin–coupling. Conclusions: The amacrine cells coupled to OFF alpha ganglion cells, as revealed by Neurobiotin–coupling, are comprised of at least 4 types. The strongest Neurobiotin–coupling was to an axon–bearing type whose output synapses may lie in another layer. This could provide inhibition from OFF alpha ganglion cells to a different ganglion cell type. Gap junctions from the alpha ganglion cell to the NOS–positive amacrine cell, although inconsistently found, might proved a mechanism for release of nitric oxide under conditions of high OFF alpha ganglion cell activity. The other two types were not axon–bearing and presumably provide local inhibition, although their targets have not yet been identified.

Keywords: gap junctions/coupling • amacrine cells • ganglion cells