Abstract
Syntaxins are a family of membrane-integrated proteins that are instrumental in exocytosis of vesicles. Syntaxin-1 is an essential component of the presynaptic exocytotic fusion machinery in the brain and interacts with several other proteins. Syntaxin-1 forms a four-helical bundle complex with proteins SNAP-25 and VAMP2 that drives fusion of vesicles with the plasma membrane in the active zone (AZ). Little is known, however, about the ultrastructural localization of syntaxin-1 at the synapse. We have analyzed the intrasynaptic expression of syntaxin-1 in glutamatergic hippocampal synapses in detail by using quantitative postembedding immunogold labeling. Syntaxin-1 was present in highest concentrations at the presynaptic AZ, supporting its role in transmitter release. Presynaptic plasma membrane lateral to the AZ, as well as presynaptic cytoplasmic (PreCy) vesicles were also labeled. However, syntaxin-1 was also significantly expressed in postsynaptic spines, where it was localized at the postsynaptic density (PSD), at postsynaptic lateral membranes and in postsynaptic cytoplasm. Postsynaptically, syntaxin-1 colocalized in the nanometer range with the N-methyl-D-aspartate (NMDA) receptor subunit NR2B, but only weakly with the AMPA receptor subunits GluA2/3. This observation points to the possibility that syntaxin-1 may be involved with NR2B vesicular trafficking from cytoplasmic stores to the postsynaptic plasma membrane, thus facilitating synaptic plasticity. Confocal immunofluorescence double labeling with PSD-95 and ultrastructural fractionation of synaptosomes also confirm localization of syntaxin-1 at the PSD.
Highlights
Individuals adapt to changes in the environment through synaptic plasticity
Syntaxin in Postsynaptic Spines involves vesicular insertion or retraction of AMPA receptors in the postsynaptic plasma membrane, regulated by calcium influx through glutamate receptors of the NMDA (N-methyl-Daspartate) class, which seem to be inserted in the synapse through vesicular mechanisms (Lu et al, 2001; Hanley, 2008)
The cerebellum showed the highest concentration of syntaxin-1 next to hippocampus
Summary
Individuals adapt to changes in the environment through synaptic plasticity. Synapses are junctions between neurons where the flow of information can be modified (Pozo and Goda, 2010). Glutamatergic transmission mainly occurs through activation of postsynaptic receptors of the AMPA (α-Amino-3-hydroxy-5-methyl-4isoxazolepropionic acid) class (Rosenmund et al, 1998). Syntaxin in Postsynaptic Spines involves vesicular insertion or retraction of AMPA receptors in the postsynaptic plasma membrane, regulated by calcium influx through glutamate receptors of the NMDA (N-methyl-Daspartate) class, which seem to be inserted in the synapse through vesicular mechanisms (Lu et al, 2001; Hanley, 2008). For the first time, the presence of small, cytoplasmic vesicles in postsynaptic spines (Hussain and Davanger, 2015). The existence of such vesicles is a necessary condition for vesicular regulation of synaptic strength
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