Nitric oxide mediates differential effects in mouse retinal ganglion cells

Abstract

Purpose : The release of the neuromodulator nitric oxide (NO) is tightly modulated by a group of amacrine cells in the inner retina, but its functional role in signal processing is poorly understood. Here, we investigated how NO affects the spatio-temporal response properties of different retinal ganglion cell (RGC) types in the mouse and analyzed if NO tunes visual responses globally (across RGC channels) or differentially in a cell type-specific manner.

Methods : Mouse ex vivo whole-mount retinae (n=21) were electroporated with a Ca²⁺ indicator (OGB-1; 10μl, 5mM). Light-evoked Ca²⁺ responses from RGCs were recorded before and during NO application (DETA/NO, 100µM; n=1,838) using a two-photon microscope. As control, RGC responses were recorded twice without NO donor (n=1,590). To resolve NO-induced effects on cell type level, functional RGCs types were identified based on their chirp and moving bar responses with a classifier. Wilcoxon signed-rank test, Mann-Whitney-U-Test and Bonferroni correction were used for statistical analyses.

Results : We found that repeated recordings of the same retinal fields caused reproducible changes in the responses of some RGC types even without NO application. These control recordings allowed us to discern cell type-specific time-dependent and drug-dependent effects. Across RGC types, Off suppressed-by-contrast (SbC) 1 and 2 showed the strongest modulations: SbC1 (n_Ctrl=127; n_NO=90) lost its contrast suppression both with NO (p=3.8e-14) and in the control dataset (p=9.8e-21), indicating a time-dependent effect. SbC2 (n_Ctrl=234; n_NO=135), however, displayed significant NO-dependent loss of contrast suppression (p=7.9e-20), while being stable in the control dataset. Notably, Mixture of Gaussian clustering revealed that SbC2 RGCs likely comprise multiple types, with only some (3 of 7) displaying the NO-effect.

Conclusions : We suggest that NO affects selectively a handful of RGC types, all exhibiting contrast suppression. Interestingly, cell types with similar responses lost their contrast suppression due to time-dependent effects. Together, these findings indicate that NO may differentially tune specific response properties of distinct RGC types, rather than acting as a global neuromodulator in the inner retina.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.