Wide‐field amacrine cell inputs to ON parasol ganglion cells in macaque retina

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.

Synaptic inputs to broad thorny ganglion cells in macaque retina

“…Although the synaptic inputs and outputs of the amacrine cells presynaptic to broad thorny cell 103 were not analyzed completely, it was apparent that they also made synaptic contacts with one another and with parasol cells identified previously (Patterson, Bordt, et al, 2020). Wiry Type 2 cell 182 made nine synapses onto four ON parasol cells and one onto another wiry amacrine cell, 4315.…”

A Color Vision Circuit for Non-Image-Forming Vision in the Primate Retina

“…Data analysis and 3D rendering were performed using SBFSEM-tools, an open-source MATLAB (Mathworks) program developed in the Neitz lab (https://github.com/neitzlab/sbfsem-tools) [17,49]. Final figures were compiled in Adobe Illustrator.…”

Conserved Circuits for Direction Selectivity in the Primate Retina

“…For proximal dendrites, criteria included thin dendritic diameters, sparse radial branching, an absence of synaptic output sites and bipolar cell input, often at the end of short dendritic spine-like branches. Dendritic diameter and branching frequency in particular distinguished SACs from other S4 amacrine cells, such as the semilunar and wiry amacrine cells 56 . These morphological features reported previously and confirmed in our full SAC reconstructions served as a guide for confirming isolated branches as SACs 3,22,30,31 .…”

“…Stratification depth within in the inner plexiform layer (IPL) was calculated as previously described 56 . Briefly, markers were placed throughout the volume at the borders between the INL-IPL and IPL-GCL.…”