Imaging Electrical Activity of Retinal Ganglion Cells with Fluorescent Voltage and Calcium Indicator Proteins in Retinal Degenerative <i>rd1</i> Blind Mice

In order to understand the retinal network, it is essential to identify functional connectivity among retinal neurons. For this purpose, imaging neuronal activity through fluorescent indicator proteins has been a promising approach, offering simultaneous measurements of neuronal activities from different regions of the circuit. In this study, we used genetically encoded indicators─Bongwoori-R3 for voltage or GCaMP6f for calcium─to visualize membrane voltage or calcium dynamics, respectively, as spatial maps within individual retinal ganglion cells from retinal tissues of photoreceptor-degenerated <i>rd1</i> mice. Retinal voltage imaging was able to show current-evoked somatic spiking as well as subthreshold voltage changes, while calcium imaging showed changes in calcium concentrations evoked by current pulses in retinal ganglion cells. These results indicate that the combination of fluorescent protein sensors and high-speed imaging methods permits the imaging of electrical activity with cellular precision and millisecond resolution. Hence, we expect our method will provide a potent experimental platform for the study of retinal signaling pathways, as well as the development of retinal stimulation strategies in visual prosthesis.