Abstract
Purpose :
While Orientation Selectivity (OS) is a fundamental computation in the visual system, a comprehensive characterization of OS ganglion cell types (OSGCs) in the retina is lacking, the cellular and circuit mechanisms that generate the OS response are incompletely understood, and contributions of OSGCs to subsequent stages of visual processing remain unknown. The purpose of this study was to identify OSGC types in mouse, to investigate the mechanisms that generate their orientation selective selective response, and to identify the contribution of OSGCs to visual processing in downstream thalamic nuclei.
Methods :
This study used two-photon fluorescence calcium imaging to survey ganglion cell populations with a genetically encoded calcium indicator in Thy1-GCaMP6f mice, followed by cluster analysis to identify functional types. Innovative intra-experimental analysis of visually-evoked responses allowed targeting of OSGCs for detailed study using electrophysiology and morphological reconstruction. To identify OSGC targets to downstream visual centers, we used state-of-the-art retrograde rabies tracing from thalamus and superior colliculus followed by calcium imaging in the retina.
Results :
Our calcium imaging surveys identified six apparent OS types with selectivity for both horizontal and vertically oriented drifting gratings. We identified types that have not been previously described as OS, including a horizontal-preferring RGC matching the 4on type from the Seung Eyewire museum. Amongst these types we identified cells with tuned excitation and tuned inhibition — some with a combination of the two — demonstrating sources for the OS tuning. Preliminary data from retrograde tracing studies implicated one of the vertical-preferring types as synapsing with Wide Field Vertical Cells in superior colliculus (SC), potentially driving OS tuning in SC.
Conclusions :
This study identified multiple OSGC types in mouse and provides new insight into the circuit-level tuning mechanisms of these cells. We have begun to resolve correspondences between reported OS RGCs from our dataset and incompletely categorized cell types from previous studies, contributing to a more complete understanding of RGC types and their functional role in the mouse retina. Our novel identification of central targets of OSGCs is an important step toward understanding the role of retinal OS in visual processing of downstream visual centers.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.