Wide‐field amacrine cell inputs to ON parasol ganglion cells in macaque retina. Issue 9 (27th December 2019) - Patterson, Sara S.
Abstract: Parasol cells are one of the major types of primate retinal ganglion cells. The goal of this study was to describe the synaptic inputs that shape the light responses of the ON type of parasol cells, which are excited by increments in light intensity. A connectome from central macaque retina was generated by serial blockface scanning electron microscopy. Six neighboring ON parasol cells were reconstructed, and their synaptic inputs were analyzed. On average, they received 21% of their input from bipolar cells, excitatory local circuit neurons receiving input from cones. The majority of their input was from amacrine cells, local circuit neurons of the inner retina that are typically inhibitory. Their contributions to the neural circuit providing input to parasol cells are not well‐understood, and the focus of this study was on the presynaptic wide‐field amacrine cells, which provided 17% of the input to ON parasol cells. These are GABAergic amacrine cells with long, relatively straight dendrites, and sometimes also axons, that run in a single, narrow stratum of the inner plexiform layer. The presynaptic wide‐field amacrine cells were reconstructed, and two types were identified based on their characteristic morphology. One presynaptic amacrine cell was identified as semilunar type 2, a polyaxonal cell that is electrically coupled to ON parasol cells. A second amacrine was identified as wiry type 2, a type known to be sensitive to motion. These inputs likely make ON parasol cells more sensitive to stimuli that are rapidly changing outside their classical receptive fields. Abstract : Parasol cells are one of the major types of retinal ganglion cells, and they give rise to the magnocellular stream of visual information processing. They respond well to moving and other rapidly changing stimuli in their receptive field. They also respond to stimuli outside of their classical receptive fields, and this article is about the inhibitory local circuits that mediate those responses, wide‐field amacrine cells. The parasol cells (orange, light blue, yellow, and pink) were reconstructed from a connectome of central macaque retina, as were dendrites of the presynaptic wide field amacrine cells. Three wide field amacrine cells were wiry type 2 cells (dark blue, salmon, and green), amacrine cells with active dendrites. The locations of their synapses onto parasol cells are circled.