Abstract
Purpose :
One of the key challenges remaining in the field of retinal prosthetics would be a lack of comprehensive understanding of electrically-evoked responses of various types of retinal ganglion cells (RGCs). For example, directionally selective (DS) RGCs are known to encode motion information from the visual world; interestingly however, no study has been reported regarding characteristics of network-mediated responses arising in those RGCs. In the present work, for the first time, we have explored the electrically-elicited network-mediated responses of ON-OFF DS RGCs in rabbit and mouse retinas.
Methods :
Cell-attached patch-clamp technique was used to record spikes from DS RGCs in retinal explants from rabbits (n = 8) and mice (n = 6), both widely-studied species in retinal researches. ON-OFF DS RGCs were identified by their robust spiking at both onsets and offsets of stationary spot flashes and white bars moving in twelve different directions. Their direction selectivity index (DSI) was computed from moving bar responses. A monophasic half-sinusoidal pulse (4 ms duration, -100 µA amplitude) was delivered from the epiretinal side. The stimulus was repeated at least 5 times.
Results :
Unlike network-mediated responses of non-DS RGCs in our previous works, electric pulse evoked remarkably heterogeneous spiking patterns across DS RGCs in each species. Also, Fano Factors (FFs) of their spike counts were quite high in both species (0.84 ± 0.50 and 0.72 ± 0.40 for rabbits and mice), indicating unreliable responses across repeats of electric pulses. Intriguingly, the two species showed a contrasting difference in the relationship between electrically- and light-evoked responses: the peak firing rates of the rabbit DS RGCs were in a strong inverse correlation with their DSIs (r = -0.839). On the contrary, the peak firing rates of the mouse DS RGCs appeared to have a weaker correlation with their DSIs (r = 0.161).
Conclusions :
Given the critical role in the dynamic visual perception, the natural responses of DS RGCs may be crucial for improved artificial vision. However, the heterogeneous and inconsistent network-mediated responses (i.e. high FFs) suggest it may be difficult. Also, the different correlations with light-evoked responses suggest the species-specific DS circuits should be better understood.
This is a 2021 ARVO Annual Meeting abstract.