Activation of retinal ganglion cells in wild-type and rd1 mice through electrical stimulation of the retinal neural network

We compared the thresholds and response properties of extracellularly recorded retinal ganglion cells (RGCs) in wild-type and rd1 mouse retinas to electrical stimulation of the retinal neural network. Retinas were stimulated in vitro with biphasic current pulses (1 ms/phase) applied with a 400-μm diameter, subretinal electrode. Three types of responses were observed in both wild-type and rd1 RGCs. Type I cells elicited a single burst of spikes within 20 ms following application of the electrical stimulus, type II cells elicited a single burst of spikes with a latency greater than 37 ms, and type III cells elicited two and occasionally three bursts of spikes. For all ages examined, ranging from postnatal day (P) 25 to P186, the thresholds of RGCs were overall consistently higher in rd1 mice. Median threshold values were 14 and 50 μA in wild-type and rd1 mice, respectively. We propose that photoreceptors lower the thresholds for activation of RGCs whereas postreceptoral neurons determine the response properties of RGCs to electrical stimuli.