Imaging Electrical Activity of Retinal Ganglion Cells with Fluores-cent Voltage and Calcium Indicator Proteins in Retinal Degenera-tive rd1 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 voltage and calcium indicators, Bongwoori-R3 and GCaMP6f, to visualize membrane voltage and calcium dynamics in the form of the spatial map within retinal ganglion cells from retina tissues of the photoreceptor degenerated rd1 mice. Retinal voltage imaging confirmed current-evoked responses from somatic spiking and intercellular conduction, while calcium imaging showed current evoked changes in calcium concentrations of presynaptic neurons. These results indicate that the combination of fluorescent protein sensors and high-speed imaging methods permits imaging 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.