Abstract
To restore the sight of individuals blinded by outer retinal degeneration, numerous retinal prostheses have been developed. However, the performance of those implants is still hampered by some factors including the lack of comprehensive understanding of the electrically-evoked responses arising in various retinal ganglion cell (RGC) types. In this study, we characterized the electrically-evoked network-mediated responses (hereafter referred to as electric responses) of ON-OFF direction-selective (DS) RGCs in rabbit and mouse retinas for the first time. Interestingly, both species in common demonstrated strong negative correlations between spike counts of electric responses and direction selective indices (DSIs), suggesting electric stimulation activates inhibitory presynaptic neurons that suppress null direction responses for high direction tuning in their light responses. The DS cells of the two species showed several differences including different numbers of bursts. Also, spiking patterns were more heterogeneous across DS RGCs of rabbits than those of mice. The electric response magnitudes of rabbit DS cells showed positive and negative correlations with ON and OFF light response magnitudes to preferred direction motion, respectively. But the mouse DS cells showed positive correlations in both comparisons. Our Fano Factor (FF) and spike time tiling coefficient (STTC) analyses revealed that spiking consistencies across repeats were reduced in late electric responses in both species. Moreover, the response consistencies of DS RGCs were lower than those of non-DS RGCs. Our results indicate the species-dependent retinal circuits may result in different electric response features and therefore suggest a proper animal model may be crucial in prosthetic researches.
Highlights
OUTER degenerative retinal diseases, such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP), are the leading causes of irreversible vision loss in Western countries [1, 2]
ON-OFF DS retinal ganglion cell (RGC) are known to evoke a robust burst response to elongated bars of light moving in preferred direction while weak or almost no spikes to bars moving in the opposite direction [16, 3236, 45]
In case of the DS RGC which showed no spike in response to the null direction, both ON and OFF responses resulted in high direction selective indices (DSIs) (Fig. 1Ai)
Summary
OUTER degenerative retinal diseases, such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP), are the leading causes of irreversible vision loss in Western countries [1, 2]. Those diseases cause gradual loss of photoreceptors that can lead to synaptic remodeling of the complex retinal circuitries [3, 4]. For those blinded by these ailments, retinal prostheses could be a promising option for vision restoration [5,6,7,8,9,10,11,12,13,14]. The recent work reported 7-8 seconds to identify letters [13], suggesting artificiallyelicited neural signals may be less decipherable
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