Spike desensitisation as a mechanism for high-contrast selectivity in retinal ganglion cells

Abstract

In the vertebrate retina, several dozens of parallel channels relay information about the visual world to the brain. These channels are represented by the different types of retinal ganglion cells (RGCs), whose responses are rendered selective for distinct sets of visual features by various mechanisms. These mechanisms can be roughly grouped into synaptic interactions and cell-intrinsic mechanisms, with the latter including dendritic morphology as well as ion channel complement and distribution. Here, we investigate how strongly ion channel complement can shape RGC output by comparing two mouse RGC types, the well-described ON alpha cell and a little-studied ON cell that is EGFP-labelled in the Igfbp5 mouse line and displays an unusual selectivity for high-contrast stimuli. Using patch-clamp recordings and computational modelling we show that in ON Igfbp5 cells - but not in the ON alpha cells - a higher activation threshold and a pronounced slow inactivation of the voltage-gated Na+ channels are responsible for the distinct contrast tuning and transient responses of ON Igfbp5 RGCs, respectively. This study provides an example for the powerful role that the last stage of retinal processing can play in shaping RGC responses. SIGNIFICANCE STATEMENTHere, we investigated, how voltage-gated sodium channels contribute to shaping the light responses of mouse retinal ganglion cells. Using single-cell electrophysiology and computational modelling, we studied a ganglion cell type that displays highly transient responses and an unusual selectivity for visual high-contrast stimuli. We found that the cells characteristic responses were largely determined by intrinsic mechanisms, notably, a high activation threshold and a pronounced slow inactivation of its voltage-gated sodium channels. Therefore, our study demonstrates how sodium channels at the last stage of retinal signal processing can contribute to shape retinal output to higher visual areas the brain; it also adds a rare example for how channel complement can be directly linked to feature selectivity.