ULTRASTRUCTRAL LOCALIZATION OF ZINC TRANSPORTER-3 (ZNT-3) TO SYNAPTICVESICLE MEMBRANES WITHIN MOSSY FIBER BOUTONS IN THE HIPPOCAMPUS OF MOUSE AND MONKEY

Zinc transporter-3 (ZnT-3), a member of a growing family of mammalian zinc transporters, is expressed in regions of the brain that are rich in histochemically reactive zinc (as revealed by the Timm's stain), in cluding entorhinal cortex, amygdala, and hippocampus. ZnT-3 protein is most abundant in the zinc enriched messy fibers that project from the dentate granule cells to hilar and CA3 pyramidal neurons. We show her e by electron microscopy that ZnT-3 decorates the membranes of all cle ar, small, round synaptic vesicles (SVs) in the messy fiber boutons of both mouse and monkey, Furthermore, up to 60-80% of these SVs contain Timm's-stainable zinc, The coincidence of ZnT-3 on the membranes of S Vs that accumulate zinc, and its homology with known zinc transporters , suggest that ZnT-3 is responsible for the transport of zinc into SVs , and hence for the ability of these neurons to release zinc upon exci tation.