A possible postsynaptic role for SNAP-25 in hippocampal synapses
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The SNARE protein SNAP-25 is well documented as regulator of presynaptic vesicle exocytosis. Increasing evidence suggests roles for SNARE proteins in postsynaptic trafficking of glutamate receptors as a basic mechanism in synaptic plasticity. Despite these indications, detailed quantitative subsynaptic localization studies of SNAP-25 have never been performed. Here, we provide novel electron microscopic data of SNAP-25 localization in postsynaptic spines. In addition to its expected presynaptic localization, we show that the protein is also present in the postsynaptic density (PSD), the postsynaptic lateral membrane and on small vesicles in the postsynaptic cytoplasm. We further investigated possible changes in synaptic SNAP-25 protein expression after hippocampal long-term potentiation (LTP). Quantitative analysis of immunogold-labeled electron microscopy sections did not show statistically significant changes of SNAP-25 gold particle densities 1 h after LTP induction, indicating that local trafficking of SNAP-25 does not play a role in the early phases of LTP. However, the strong expression of SNAP-25 in postsynaptic plasma membranes suggests a function of the protein in postsynaptic vesicle exocytosis and a possible role in hippocampal synaptic plasticity.
KeywordsSNARE proteins Electron microscopy LTP Synaptic plasticity Hippocampus
We thank Karen Marie Gujord, Jorunn Knutsen, Bjørg Riber, Johannes Helm and Bashir Hakim for their expert technical assistance. We thank Finn-Mogens S. Haug for assistance with immunogold quantification and statistics. The University of Oslo, and the European Union Projects QLG3-CT-2001-02089 (KARTRAP) and LSCHM-CT-2005-005320 (GRIPANNT) supported this work. The authors declare that they have no competing interests.
Compliance with ethical standards
Experimental protocols were approved by the Institutional Animal Care and Use Committee and conform to National Institutes of Health guidelines for the care and use of animals, as well as international laws on protection of laboratory animals, with the approval of a local bioethical committee and under the supervision of a veterinary commission for animal care and comfort of the University of Oslo and the University of Copenhagen. The animals were treated in accordance with the guidelines of the Norwegian Committees and Danish Animal Health Inspectorate on Animal Experimentation (Norwegian/Danish Animal Welfare Act and European Communities Council, Directive of 24 November 1986–86/609/EEC). Every effort was made to minimize the number of animals used and their sufferings. This article does not contain any studies with human participants performed by any of the authors.
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