Impact of Electrode Position on the Elicitation of Sodium Spikes in Retinal Bipolar Cells

Abstract

Bipolar cells of the magnocellular pathway in the primate retina can generate action potentials because they have an axonal segment with high sodium channel density, comparable to the sodium channel band in retinal ganglion cells or pyramidal cells. The similarity between the non-human primate and the human retina is of interest for the research on retinal implants for the blind, and especially, the conditions to elicit sodium spikes in bipolar cells using extracellular stimulation. A comparison of excitation characteristics of three model neurons, a bipolar cell, a retinal ganglion cell, and a cortical pyramidal cell, demonstrates the similarities and differences regarding stimulation with microelectrodes. Moving a microelectrode parallel to the axon of a neuron commonly allows to generate spikes for every position – and this rule holds both for cathodic and anodic pulses. However, for the simulated bipolar cell anodic pulses cannot generate sodium spikes directly. Further, there is only a small region for electrode placing where extracellular cathodic stimulation causes direct spike initiation in the sodium channel band. For all other positions, a sodium spike can only be generated by antidromic current flow originating from strongly depolarized terminals.

Stimulating electrode Design for Implantable Sub Retina Research Application: A Novel Approach

“…In visual cortex, retina and geniculate efferents, neurotransmitter released is Glutamate [11][12][13][14][15][16][17][18][19][20]. The glutamate is released by photoreceptors synaptic vesicles to the dendrites of bipolar cells.…”

“…One such prosthesis is located at missing photoreceptor spot in RP patient which communicates with the lasting bipolar cells to transfer the visual signal to ganglion cells. As earlier stated the Neurotransmitter release by photoreceptors, makes ion current to flow and depolarize dendrites and soma [11][12][13][14][15][16][17][18][19][20]. Which cause signal amplification, also enables BC to generate spike.…”

“…Several retinal research groups have already designed and fabricate different types of artificial retina [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. These devices stimulating electrode are attached to the retina space to restore vision in visually blind patients.…”

“…The vision implants are categorized as extraocular and intraocular prostheses, shown in figure 4. The Extraocular devices are externally powered and located at the surface of the eye, but the intraocular device is located in sub retinal space [10][11][12][13][14][15][16][17][18][19][20]. The vision implant gives constructive results during testing process, but some barriers still existing that have to be short out, before retinal prostheses used for human.…”

“…The vision implant gives constructive results during testing process, but some barriers still existing that have to be short out, before retinal prostheses used for human. One of the key components in vision implant is stimulating electrode [10][11][12][13][14][15][16][17][18][19][20]. Stimulating electrodes communicate with the tissue faces different electrochemical associated challenge biocompatibility, electrode-electrolyte interaction, contact impedance, charge injection ability, electrode corrosion and dynamic range.…”