Quantification of Neurotransmitter Release Dynamics in a Hindlimb Unloading Model via Multi-Spatiotemporal...

Spaceflight induces multifaceted physiological adaptations, yet the molecular mechanisms underlying microgravity-associated neurological dysfunction remain poorly defined. Although microgravity is known to influence the dopaminergic system, most existing studies have relied on surrogate markers such as the expression of dopamine (DA) biosynthetic enzymes and transport proteins rather than direct measurements of neurotransmission. To address this gap, we employ a 14-day hindlimb unloading (HU) mouse model to simulate microgravity conditions and utilize fast-scan cyclic voltammetry (FSCV) to directly quantify stimulus-evoked DA release in the dorsolateral striatum. Our results reveal a significant reduction in DA levels under HU conditions. Immunofluorescence analysis further indicates that the observed deficits are associated with a decrease in the expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in DA synthesis. To elucidate the underlying mechanisms, we use high spatiotemporal resolution single-cell amperometry (SCA) to analyze exocytotic kinetics at the vesicular level and observe marked impairments in neurotransmitter release dynamics including reduced quantal size, narrowed initial fusion pore diameter, and delayed fusion pore closure. These alterations in vesicle fusion behavior are correlated to behavioral deficits in motor coordination and cognitive performance. This finding essentially establishes a direct mechanistic link between simulated microgravity-induced dopaminergic dysfunction and neurobehavioral impairments, guiding the development of targeted neuroprotective strategies for spaceflight missions.