Dendrite Morphology Minimally Influences the Synaptic Distribution of Excitation and Inhibition in Retinal Direction-Selective Ganglion Cells

Abstract

Throughout the nervous system, the organization of excitatory and inhibitory synaptic inputs within a neuron’s receptive field shapes its output computation. In some cases, multiple motifs of synaptic organization can contribute to a single computation. Here, we compare two of these mechanisms performed by two morphologically distinct retinal direction-selective ganglion cells (DSGCs): directionally tuned inhibition and spatially offset inhibition. Using drifting stimuli, we found that DSGCs that have asymmetric dendrites exhibited stronger directionally tuned inhibition than symmetric DSGCs. Using stationary stimuli to map receptive fields, we found that DSGCs with both symmetric and asymmetric dendrites exhibited similar spatially offset inhibition. Interestingly, we observed that excitatory and inhibitory synapses for both cell types were locally correlated in strength. This result indicates that in the mouse retina, dendritic morphology influences the amount of tuned inhibition attained through asymmetric wiring but does not dictate the synaptic organization of excitation relative to inhibition.

Rejection of inappropriate synaptic partners mediated by transcellular FLRT2-UNC5 signaling

“…Identification, dye loading and imaging of GFP + ooDSGCs was performed as described previously (El-Quessny and Feller, 2021). In brief, GFP + cells were identified using a custom-modified two-photon microscope (Fluoview 300; Olympus America) tuned to 920 nm to minimize activation and bleaching of photoreceptors.…”

“…Next, morphological reconstruction and dendritic segmentation were performed as described previously (El Quessny & Feller, 2021). Briefly, 480 x 480 µm Image stacks were acquired at z intervals of 1.0 µm and resampled fifteen times for each stack using a 20X objective (Olympus LUMPlanFl/IR 2x digital zoom, 1.0 NA) and 30kHz resonance scanning mirrors covering the entire dendritic fields of the ooDSGCs.…”