Spreading depression and related events are significant sources of neuronal Zn²⁺ release and accumulation

Spreading depression (SD) involves coordinated depolarizations of neurons and glia that propagate through the brain tissue. Repetitive SD-like events are common following human ischemic strokes, and are believed to contribute to the enlargement of infarct volume. Accumulation of Zn²⁺ is also implicated in ischemic neuronal injury. Synaptic glutamate release contributes to SD propagation, and because Zn²⁺ is costored with glutamate in some synaptic vesicles, we examined whether Zn²⁺ is released by SD and may therefore provide a significant source of Zn²⁺ in the postischemic period. Spreading depression-like events were generated in acutely prepared murine hippocampal slices by deprivation of oxygen and glucose (OGD), and Zn²⁺ release was detected extracellularly by a Zn ²⁺-selective indicator FluoZin-3. Deprivation of oxygen and glucose-SD produced large FluoZin-3 increases that propagated with the event, and signals were abolished in tissues from ZnT3 knockout animals lacking synaptic Zn²⁺. Synaptic Zn²⁺ release was also maintained with repetitive SDs generated by microinjections of KCl under normoxic conditions. Intracellular Zn²⁺ accumulation in CA1 neurons, assessed using microinjection of FluoZin-3, showed significant increases following SD that was attributed to synaptic Zn²⁺ release. These results suggest that Zn²⁺ is released during SDs and could provide a significant source of Zn²⁺ that contributes to neurodegeneration in the postischemic period.