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Two-photon imaging of Zn2+ dynamics in mossy fiber boutons of adult hippocampal slices


Khan, Mustafa
Goldsmith, Christian R.
Huang, Zhen
Georgiou, John
Luyben, Thomas T.
Roder, John C.
Lippard, Stephen J.
Okamoto, Kenichi


Mossy fiber termini in the hippocampus accumulate Zn2+, which is released with glutamate from synaptic vesicles upon neural excitation. Understanding the spatiotemporal regulation of mobile Zn2+ at the synaptic level is challenging owing to the difficulty of visualizing Zn2+ at individual synapses. Here we describe the use of zinc-responsive fluorescent probes together with two-photon microscopy to image Zn2+ dynamics mediated by NMDA receptor-dependent long-term potentiation induction at single mossy fiber termini of dentate gyrus neurons in adult mouse hippocampal slices. The membrane-impermeant fluorescent Zn2+ probe, 6-CO2H-ZAP4, was loaded into presynaptic vesicles in hippocampal mossy fiber termini upon KCl-induced depolarization, which triggers subsequent endocytosis and vesicular restoration. Local tetanic stimulation decreased the Zn2+ signal observed at individual presynaptic sites, indicating release of the Zn2+ from vesicles in synaptic potentiation. This synapse-level two-photon Zn2+ imaging method enables monitoring of presynaptic Zn2+ dynamics for improving the understanding of physiological roles of mobile Zn2+ in regular and aberrant neurologic function.