In vivo long-term voltage imaging by genetically encoded voltage indicator reveals spatiotemporal dynamics of neuronal populations during development

A central question in brain development lies in how individual neurons emerge and organize communities to acquire various functions. Voltage imaging provides unique approaches to addressing this by enabling simultaneous, non-invasive, in vivo recording of voltage dynamics from a population of cells. Recently, genetically encoded voltage indicators (GEVIs) facilitate cell-type specific imaging of voltage dynamics. However, it has not been applied to brain development. Here, we applied ArcLight, a GEVI utilizing voltage-sensitive domain, to zebrafish and established experimental approaches for analyzing voltage and morphology of neuron populations during development, focusing on the spinal cord and cerebellum. We initially demonstrated that Arclight was widely distributed in the neural tissues. With voltage imaging, we successfully visualized the coordinated, spontaneous activity of spinal cord neurons in their early stage of development at a high spatiotemporal resolution, at subcellular and population levels. Hyperpolarization and subthreshold signals were also detected. Finally, long-term voltage imaging during development revealed the process of changes in voltage dynamics in neuron populations, accompanied by axonal outgrowth. Voltage imaging could greatly contribute to our understanding of the functional organization of the nervous system during development. ### Competing Interest Statement The authors have declared no competing interest.