Effect of epiretinal electrical stimulation on the glial cells in a rabbit retinal eyecup model

Introduction We examined how pulse train electrical stimulation of the inner surface of the rabbit retina effected the resident glial cells. We used a rabbit retinal eyecup preparation model, transparent stimulus electrodes, and optical coherence tomography (OCT). The endfeet of Muller glia processes line the inner limiting membrane (ILM).Methods To examine how epiretinal electrode stimulation affected the Muller glia, we labeled them post stimulation using antibodies against soluble glutamine synthetase (GS). After 5 min 50 Hz pulse train stimulation 30 mu m from the surface, the retina was fixed, immunostained for Muller glia, and examined using confocal microscopic reconstruction. Stimulus pulse charge densities between 133-749 mu C/cm2/ph were examined.Results High charge density stimulation (442-749 mu C/cm2/ph) caused significant losses in the GS immunofluorescence of the Muller glia endfeet under the electrode. This loss of immunofluorescence was correlated with stimuli causing ILM detachment when measured using OCT. Muller cells show potassium conductances at rest that are blocked by barium ions. Using 30 msec 20 mu A stimulus current pulses across the eyecup, the change in transretinal resistance was examined by adding barium to the Ringer. Barium caused little change in the transretinal resistance, suggesting under low charge density stimulus pulse conditions, the Muller cell radial conductance pathway for these stimulus currents was small. To examine how epiretinal electrode stimulation affected the microglia, we used lectin staining 0-4 h post stimulation. After stimulation at high charge densities 749 mu C/cm2/ph, the microglia under the electrode appeared rounded, while the local microglia outside the electrode responded to the stimulated retina by process orientation inwards in a ring by 30 min post stimulation.Discussion Our study of glial cells in a rabbit eyecup model using transparent electrode imaging suggests that epiretinal electrical stimulation at high pulse charge densities, can injure the Muller and microglia cells lining the inner retinal surface in addition to ganglion cells.