Temporal properties of dual-peak responses of mouse retinal ganglion cells and effects of inhibitory pathways

Abstract

Dual-peak responses of retinal ganglion cells (RGCs) are observed in various species, previous researches suggested that both response peaks were involved in retinal information coding. In the present study, we investigated the temporal properties of the dual-peak responses recorded in mouse RGCs elicited by spatially homogeneous light flashes and the effect of the inhibitory inputs mediated by GABAergic and/or glycinergic pathways. We found that the two peaks in the dual-peak responses exhibited distinct temporal dynamics, similar to that of short-latency and long-latency single-peak responses respectively. Pharmacological studies demonstrated that the application of exogenous GABA or glycine greatly suppressed or even eliminated the second peak of the cells' firing activities, while little change was induced in the first peak. Co-application of glycine and GABA led to complete elimination of the second peak. Moreover, application of picrotoxin or strychnine induced dual-peak responses in some cells with transient responses by unmasking a second response phase. These results suggest that both GABAergic and glycinergic pathways are involved in the dual-peak responses of the mouse RGCs, and the two response peaks may arise from distinct pathways that would converge on the ganglion cells.

Coding Properties of Mouse Retinal Ganglion Cells with Dual-Peak Patterns with Respect to Stimulus Intervals

“…The RGCs studied here responded to light-ON stimuli with two components: one transient component and another following component occurring shortly after the initial one, resulting in two peaks in the PSTH (Figure 1 ). The second component could be either transient or sustained (Zhou et al, 2007 ; Yan et al, 2016 ).…”

“…Thus the occurrence of dual-peak response might be stimulus independent, with its properties modulated by different stimulus parameters. According to one of our previous works, the dual-peak response might originate from the convergence of two pathways related to the short-latency response and long-latency response respectively (Yan et al, 2016 ).…”

“…In the present study, we focused on the stimulus-interval-dependent response changes and information coding for dual-peak cells. Here only the encoding of different preceding light-OFF intervals was investigated, because the dual-peak responses recorded were mostly ON responses, observed in ON RGCs and light-ON part of ON-OFF RGCs (Soucy et al, 1998 ; Yan et al, 2016 ). In previous study, it has been reported that the latency and firing rate of ON responses were modulated by preceding light-OFF intervals, but independent on the following light-ON durations (Xiao et al, 2014b ).…”

“…From a recent work in our lab, it was found that the two response peaks in the dual-peak pattern may originate from two different pathways related to brisk response and sluggish response respectively (Yan et al, 2016 ). Our present study added to the point by showing that taking dual-peak pattern as two discrete spike events instead of as a single event led to better discrimination performance: C(T1 + R1 + T2 + R2) > C(T1 + R total ) (data not shown).…”

“…In response to spatially homogeneous light flashes, a particular pattern termed “dual-peak” response has been observed. The dual-peak response consists of two response components: a transient component occurring within a short interval (50–100 ms) relative to the stimulus onset, and another following component occurring tens to hundreds of milliseconds after the initial one, thus resulting in two peaks in the peri-stimulus time histogram (PSTH) (Soucy et al, 1998 ; Segev et al, 2006 ; Thiel et al, 2006 ; Zhou et al, 2007 ; Yan et al, 2016 ), possible generating mechanism for this particular pattern was also suggested (Yan et al, 2016 ). However the coding properties of dual-peak pattern, particularly the contribution of the second peak to stimulus information coding, still remained largely unknown.…”