An In Vivo Single-Vesicle Electrochemistry Enables Monitoring Vesicular Dopamine Dynamics and Pharmacological Rescue.

Direct single vesicle-resolved quantification of neurotransmitter storage and exocytotic dynamics in an intact living vertebrate nervous system has remained elusive. Here, we establish an in vivo single-vesicle electrochemistry platform in anesthetized living zebrafish larvae, enabling quantification of vesicular dopamine (DA) loading and quantal release dynamics in the intact neural system. By combining intracellular vesicle impact electrochemical cytometry and single-cell amperometry, we directly measure vesicular cargo and exocytotic release in dopaminergic neuron soma of the ventral diencephalon at single-vesicle resolution. Pharmacological validation with a DA elevation drug confirmed the sensitivity and robustness of the approach. Application of this platform to a chemical-induced Parkinsonian model revealed pronounced reductions in vesicular DA content, altered release patterns, and impaired exocytotic dynamics. Rasagiline treatment partially restored vesicular DA storage and release dynamics toward physiological levels, suggesting a protective modulation of vesicle function. This in vivo electrochemical method offers a single vesicle-resolved analytical platform for dissecting vesicular heterogeneity and dysfunction directly in intact neural systems, thereby bridging single-vesicle chemistry with in vivo neurobiology and opening new avenues for mechanistic studies of neurodegeneration and therapeutic intervention.