Differential electrical responses in retinal ganglion cell subtypes : effects of synaptic blockade and stimulating electrode location

Objective. Visual prostheses have shown promising results in restoring visual perception to blind patients. The ability to differentially activate retinal ganglion cell (RGC) subtypes could further improve the efficacy of these medical devices. Approach. Using whole-cell patch clamp, we investigated membrane potential differences between ON and OFF RGCs in the mouse retina when their synaptic inputs were blocked by synaptic blockers, and examined the differences in stimulation thresholds under such conditions. By injecting intracellular current, we further confirmed the relationship between RGC stimulation thresholds and resting membrane potentials (RMPs). In addition, we investigated the effects of stimulating electrode location on the differences in stimulation thresholds between ON and OFF RGCs. Main results. With synaptic blockade, ON RGCs became significantly more hyperpolarized (from -61.8 ± 1.4 mV to -70.8 ± 1.6 mV), while OFF RGCs depolarized slightly (from -60.5 ± 0.7 mV to -58.6 ± 0.9 mV). RGC stimulation thresholds were negatively correlated with their RMPs (Pearson r value: -0.5154; p-value: 0.0042). Thus, depriving ON RGCs of synaptic inputs significantly increased their thresholds (from 14.7 ± 1.3 μA to 22.3 ± 2.1 μA) over those of OFF RGCs (from 13.2 ± 0.7 μA to 13.1 ± 1.1 μA). However, with control solution, ON and OFF RGC stimulation thresholds were not significantly different. Finally, placement of the stimulating electrode away from the axon enhanced differences in stimulation thresholds between ON and OFF RGCs, facilitating preferential activation of OFF RGCs. Significance. Since ON and OFF RGCs have antagonistic responses to natural light, achieving differential RGC activation could convey more natural visual information, leading to better visual prosthesis outcomes.