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      Activation of group II metabotropic glutamate receptors blocks zinc release from hippocampal mossy fibers

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          Abstract

          Background

          The hippocampal CA3 area contains large amounts of vesicular zinc in the mossy fiber terminals which is released during synaptic activity, depending on presynaptic calcium. Another characteristic of these synapses is the presynaptic localization of high concentrations of group II metabotropic glutamate receptors, specifically activated by DCG-IV. Previous work has shown that DCG-IV affects only mossy fiber-evoked responses but not the signals from associational-commissural afferents, blocking mossy fiber synaptic transmission. Since zinc is released from mossy fibers even for single stimuli and it is generally assumed to be co-released with glutamate, the aim of the work was to investigate the effect of DCG-IV on mossy fiber zinc signals.

          Results

          Studies were performed using the membrane-permeant fluorescent zinc probe TSQ, and indicate that DCG-IV almost completely abolishes mossy fiber zinc changes as it does with synaptic transmission.

          Conclusions

          Zinc signaling is regulated by the activation of type II metabotropic receptors, as it has been previously shown for glutamate, further supporting the corelease of glutamate and zinc from mossy fibers.

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          Most cited references98

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          The biochemical basis of zinc physiology.

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            Zinc at glutamatergic synapses.

            It has long been known that the mammalian forebrain contains a subset of glutamatergic neurons that sequester zinc in their synaptic vesicles. This zinc may be released into the synaptic cleft upon neuronal activity. Extracellular zinc has the potential to interact with and modulate many different synaptic targets, including glutamate receptors and transporters. Among these targets, NMDA receptors appear particularly interesting because certain NMDA receptor subtypes (those containing the NR2A subunit) contain allosteric sites exquisitely sensitive to extracellular zinc. The existence of these high-affinity zinc binding sites raises the possibility that zinc may act both in a phasic and tonic mode. Changes in zinc concentration and subcellular zinc distribution have also been described in several pathological conditions linked to glutamatergic transmission dysfunctions. However, despite intense investigation, the functional significance of vesicular zinc remains largely a mystery. In this review, we present the anatomy and the physiology of the glutamatergic zinc-containing synapse. Particular emphasis is put on the molecular and cellular mechanisms underlying the putative roles of zinc as a messenger involved in excitatory synaptic transmission and plasticity. We also highlight the many controversial issues and unanswered questions. Finally, we present and compare two widely used zinc chelators, CaEDTA and tricine, and show why tricine should be preferred to CaEDTA when studying fast transient zinc elevations as may occur during synaptic activity.
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              The metabotropic glutamate receptors: structure and functions.

              Glutamate is the main excitatory neurotransmitter in the brain. For many years it has been considered to act only on ligand-gated receptor channels--termed NMDA, AMPA and kainate receptors--involved in the fast excitatory synaptic transmission. Recently, glutamate has been shown to regulate ion channels and enzymes producing second messengers via specific receptors coupled to G-proteins. The existence of these receptors, called metabotropic glutamate receptors, is changing our views on the functioning of fast excitatory synapses.
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                Author and article information

                Contributors
                cmatias@utad.pt
                jose.dionisio@netcabo.pt
                peters@alleninstitute.org
                emilia@ci.uc.pt
                Journal
                Biol Res
                Biol. Res
                Biological Research
                BioMed Central (London )
                0716-9760
                0717-6287
                18 December 2014
                18 December 2014
                2014
                : 47
                : 1
                : 73
                Affiliations
                [ ]Center for Neurosciences of Coimbra, University of Coimbra, 3004-516 Coimbra, Portugal
                [ ]Department Animal Biology, FCUL, University Lisbon, Campo Grande, Lisbon, Portugal
                [ ]Allen Institute for Brain Science, 551 N 34th Street, Seattle, USA
                [ ]Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal
                [ ]Department of Physics, School of Science and Technology, University of Trás-os-montes and Alto Douro (UTAD), Quinta dos Prados, 5000-911 Vila Real, Portugal
                Article
                60
                10.1186/0717-6287-47-73
                4289587
                4ef03f2a-a7cc-4b52-a632-258ed02d748a
                © Matias et al.; licensee BioMed Central. 2014

                This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                History
                : 25 July 2014
                : 25 November 2014
                Categories
                Research Article
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                © The Author(s) 2014

                zinc,neurotransmission,glutamatergic,co-release,metabotropic fluorescence,inhibition

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