Whole brain fluorescence imaging in Drosophila reveals spreading depolarization and its initiation, propagation, and resilience dynamics

Spreading depolarization (SD) is a propagating wave of neural depression associated with migraine, stroke, and brain injury. We develop high-throughput, whole-brain fluorescence imaging assays in Drosophila melanogaster ideal for observing and mechanistically understanding SD. We reveal key characteristics of SD, including that it originates at multiple, variable sites across and within individuals, and that it spreads throughout the nervous systems of adults and larvae. This reveals that SD is a fundamental phenomenon not restricted to specific brain regions, neuronal populations, or developmental stages. Furthermore, we demonstrate that single SD events cause a depolarization-independent transient refractory period with elevated SD threshold, suggesting an alteration of homeostatic processes following SD. This work and others, combined with Drosophila's extensive genetic toolkit, establishes the fly as a high-throughput model for understanding conserved cellular and circuit-level mechanisms relevant to human neurological disorders involving SD.