Side Of Synapses Research Articles

PCDH19 interplay with GABA(A) receptors: a window to DEE9 pathogenetic mechanisms.

PCDH19 interplay with GABA(A) receptors: a window to DEE9 pathogenetic mechanisms.

Postsynaptic Y654 dephosphorylation of β‐catenin modulates presynaptic vesicle turnover through increased n‐cadherin‐mediated transsynaptic signaling

Synaptic adhesion molecules, which coordinately control structural and functional changes at both sides of synapses, are important for synaptogenesis and synaptic plasticity. Because they physically form homophilic or heterophilic adhesions across synaptic junctions, these molecules can initiate transsynaptic communication in both anterograde and retrograde directions. Using optical imaging approaches, we investigated whether an increase in postsynaptic N-cadherin could correspondingly alter the function of connected presynaptic terminals. Postsynaptic expression of β-catenin Y654F, a phosphorylation-defective form with enhanced binding to N-cadherin, is sufficient to increase postsynaptic surface levels of N-cadherin and consequently promote presynaptic reorganizations. Such reorganizations include increases in the densities of the synaptic vesicle protein, Synaptotagmin 1 and the active zone scaffold protein, Bassoon, the number of active boutons and the size of the total recycling vesicle pool. In contrast, synaptic vesicle turnover is significantly impaired, preventing the exchange of synaptic vesicles with adjacent boutons. Together, N-cadherin-mediated retrograde signaling, governed by phosphoregulation of postsynaptic β-catenin Y654, coordinately modulates presynaptic vesicle dynamics to enhance synaptic communication in mature neurons. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 61-74, 2017.

Presynaptic and Postsynaptic Roles of NO, cGK, and RhoA in Long-Lasting Potentiation and Aggregation of Synaptic Proteins

Recent results suggest that long-lasting potentiation at hippocampal synapses involves the rapid formation of clusters or puncta of presynaptic as well as postsynaptic proteins, both of which are blocked by antagonists of NMDA receptors and an inhibitor of actin polymerization. We have investigated whether the increase in puncta involves retrograde signaling through the NO-cGMP-cGK pathway and also examined the possible roles of two classes of molecules that regulate the actin cytoskeleton: Ena/VASP proteins and Rho GTPases. Our results suggest that NO, cGMP, cGK, actin, and Rho GTPases including RhoA play important roles in the potentiation and act directly in both the presynaptic and postsynaptic neurons, where they contribute to the increase in puncta of synaptic proteins. cGK phosphorylates synaptic VASP during the potentiation, whereas Rho GTPases act both in parallel and upstream of cGMP, in part by maintaining the synaptic localization of soluble guanylyl cyclase.

NMDA receptor blockade in intact adult cortex increases trafficking of NR2A subunits into spines, postsynaptic densities, and axon terminals

Past in vitro studies have used immunofluorescence to show increased clustering of the NR1 subunits of NMDA receptors (NMDAR) following NMDAR blockade, indicating that NMDARs self-regulate trafficking to and from spines. However, since a substantial portion of spinous NMDAR subunits can reside at sites removed from plasma membranes, whether or not these immunofluorescent clusters are synaptic remains to be shown. Also, the NR2A/B subunits undergo activity-dependent switching at synapses, indicating that their subcellular distribution may be regulated differently from the NR1 subunits. We examined the issue of NMDAR autoregulation by determining whether in vivo NMDAR blockade enhances trafficking of the NR2A subunits toward spines and more specifically to postsynaptic densities (PSDs) of already mature synapses. Seven adult rats received unilateral intra-cortical infusion of the NMDAR antagonist, d-AP5 for 1/2–2 h and the inactive enantiomer or the solvent, alone, in the contralateral cortex. Using an electron microscope, ∼5600 cortical spines originating from the two hemispheres of the seven adult animals were analyzed for the location of NR2A subunits. In six out of the seven cases analyzed, the d-AP5-treated neuropil exhibited increased immunolabeling at PSDs and a concomitantly great increase at non-synaptic sites within spines. NR2A subunits also increased presynaptically within 1/2 h but not after 1 h. These findings indicate that NR2A subunits in intact, adult cortical neurons are prompted to become trafficked into spines and axon terminals by NMDAR inactivity, yielding an increase of a readily available reserve pool and greater localization at both sides of synapses.