Mapping of early neuronal activity and circuit formation during embryo development in zebrafish.

Imaging method for the characterization of the morpho-functional development of the nervous system in zebrafish. Leveraging two-photon microscopy and genetically encoded calcium indicators, we developed acquisition protocols to image differentiation, migration, and interactions that occur from the first neurons appearance to the attainment of their distinct anatomical and functional roles. We map and track early neurons, generating a high-resolution reconstruction of nervous system developmental dynamics up to 72 hpf. Concurrently, by performing whole-brain functional calcium imaging of embryos between 24 and 80 hpf, we characterized neuronal activities from their debut to the emergence of functional circuits. Our measurements revealed features of spontaneous neuronal activity at single-cell and population levels, suggesting the existence of critical phases in functional, as well as morphological, brain development. tBy designing a longitudinal study specifically tailored to zebrafish development, we underscore the potential to achieve a comprehensive characterization of brain functional and structural connectomics (i.e., the structural connectivity patterns among neurons within an assembly). Elucidating the processes through which spontaneous activity self-organizes and gives rise to specific functional networks could provide valuable insights into the role of neuronal activity in shaping the brain, as well as into the disorders associated with its dysregulation.