Electron microscopical localization of the zinc in hippocampal mossy fibre synapses by a modified sulfide silver procedure

Vesicular Zinc Regulates the Ca2+Sensitivity of a Subpopulation of Presynaptic Vesicles at Hippocampal Mossy Fiber Terminals

“…Amplitude distribution of spontaneous (s) and miniature (m) EPSCs recorded from CA3 pyramidal cells are known to be skewed toward larger values (Haug, 1967;Jonas et al, 1993) (Fig. 1 B, C).…”

Ultrastructural localization of zinc transporter-3 (ZnT-3) to synaptic vesicle membranes within mossy fiber boutons in the hippocampus of mouse and monkey

“…In addition, Timm's-stainable zinc is also present in nonneuronal cells in the brain, e.g., in the choroid plexus. Earlier ultrastructural investigations demonstrated that the zinc in synaptic boutons is localized in the vicinity of presynaptic vesicles (1,12) and more recent studies indicate that the zinc is within individual vesicles (2,19). However, previous work indicated that only a small fraction of clear, round vesicles in MFBs were reactive for zinc (1)(2)(3), suggesting that a subclass of vesicles might contain zinc.…”

“…Earlier ultrastructural investigations demonstrated that the zinc in synaptic boutons is localized in the vicinity of presynaptic vesicles (1,12) and more recent studies indicate that the zinc is within individual vesicles (2,19). However, previous work indicated that only a small fraction of clear, round vesicles in MFBs were reactive for zinc (1)(2)(3), suggesting that a subclass of vesicles might contain zinc. In contrast, our study of Timm's-stained material demonstrates that the majority of SVs in MFBs contain zinc, consistent with the observation that all SVs were ZnT-3 positive, and thus presumably capable of facilitating zinc uptake.…”

“…Most of the zinc in the mammalian brain is associated with metalloproteins; however, there is also a pool of histochemically reactive zinc that exists in synaptic vesicles (SVs) of a subset of glutamatergic neurons, which has led to classification of these neurons as zinc-containing or zinc-ergic (1)(2)(3)(4). Pathways utilizing this vesicular form of zinc have been mapped using histochemical stains such as the neo-Timm's sulfidesilver method (5), selenium stain (6,7), and the fluorescent compound, TSQ (8).…”

“…One of the best described zinc-ergic systems is found in the rodent hippocampal formation, where vesicular zinc can be detected in each component of the trisynaptic circuit that includes (i) perforant path projections from the entorhinal cortex to the outer molecular layer of the dentate gyrus, (ii) mossy fiber (MF) projections from granule cells in the dentate gyrus to hilar neurons and pyramidal cells in the CA3 region (4, 9-11), (iii) projections from CA3 pyramidal neurons to neurons in the CA1 region, and (iv) projections from CA1 to subiculum (3,4). Electron microscopy (EM) has revealed that the Timm's stain precipitate is present within SVs in the giant axonal boutons of the MFs in the hilus and stratum (s.) lucidum (1,2,12). However, only Ϸ10-15% of the SVs within a given bouton have been shown to contain Timm's precipitate (2); thus, it has been difficult to ascertain whether zinc is present in a subset of vesicles or if it is present in the same vesicles as glutamate.…”