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The Journal of Neuroscience : the... Nov 1995Ganglion cell receptive field centers are small in central retina and larger toward periphery. Accompanying this expansion, the distribution of sensitivity across the...
Ganglion cell receptive field centers are small in central retina and larger toward periphery. Accompanying this expansion, the distribution of sensitivity across the centers remain Gaussian, but peak sensitivities decline. To identify circuitry that might explain this physiology, we measured the density of bipolar cell synapses on the dendritic membrane of beta (X) and alpha (Y) ganglion cells and the distribution of dendritic membrane across their dendritic fields. Both central and peripheral beta cells receive bipolar cell synapses at a density of approximately 28/100 microns2 of dendritic membrane; central and peripheral alpha cells receive approximately 13/100 microns2. The distribution of dendritic membrane across the dendritic field is dome-like; therefore, the distribution of bipolar cell synapses is also dome-like. As the dendritic field enlarges, total postsynaptic membrane increases with field radius, but only linearly. Consequently, density of postsynaptic membrane in the dendritic field declines, and so does density of synapses within the field. The results suggest a simple model in which the receptive field center's Gaussian profile and peak sensitivity are both set by the density of bipolar cell synapses across the dendritic field.
Topics: Animals; Cats; Dendrites; Microscopy, Electron; Neural Pathways; Retina; Retinal Ganglion Cells; Synapses; Synaptic Membranes
PubMed: 7472518
DOI: 10.1523/JNEUROSCI.15-11-07673.1995 -
The Journal of Biological Chemistry Jan 2017The formation of neuronal synapses and the dynamic regulation of their efficacy depend on the proper assembly of the postsynaptic neurotransmitter receptor apparatus....
The formation of neuronal synapses and the dynamic regulation of their efficacy depend on the proper assembly of the postsynaptic neurotransmitter receptor apparatus. Receptor recruitment to inhibitory GABAergic postsynapses requires the scaffold protein gephyrin and the guanine nucleotide exchange factor collybistin (Cb). In vitro, the pleckstrin homology domain of Cb binds phosphoinositides, specifically phosphatidylinositol 3-phosphate (PI3P). However, whether PI3P is required for inhibitory postsynapse formation is currently unknown. Here, we investigated the role of PI3P at developing GABAergic postsynapses by using a membrane-permeant PI3P derivative, time-lapse confocal imaging, electrophysiology, as well as knockdown and overexpression of PI3P-metabolizing enzymes. Our results provide the first in cellula evidence that PI3P located at early/sorting endosomes regulates the postsynaptic clustering of gephyrin and GABA receptors and the strength of inhibitory, but not excitatory, postsynapses in cultured hippocampal neurons. In human embryonic kidney 293 cells, stimulation of gephyrin cluster formation by PI3P depends on Cb. We therefore conclude that the endosomal pool of PI3P, generated by the class III phosphatidylinositol 3-kinase, is important for the Cb-mediated recruitment of gephyrin and GABA receptors to developing inhibitory postsynapses and thus the formation of postsynaptic membrane specializations.
Topics: Animals; Carrier Proteins; Endosomes; GABAergic Neurons; Humans; Membrane Proteins; Phosphatidylinositol 3-Kinases; Phosphatidylinositol Phosphates; Rats; Receptors, GABA-A; Rho Guanine Nucleotide Exchange Factors; Synaptic Membranes; Synaptic Potentials
PubMed: 27941024
DOI: 10.1074/jbc.M116.771592 -
The Journal of Biological Chemistry Jul 2011Homeostatic mechanisms maintaining high levels of adhesion molecules in synapses over prolonged periods of time remain incompletely understood. We used fluorescence...
Homeostatic mechanisms maintaining high levels of adhesion molecules in synapses over prolonged periods of time remain incompletely understood. We used fluorescence recovery after photobleaching experiments to analyze the steady state turnover of the immobile pool of green fluorescent protein-labeled NCAM180, the largest postsynaptically accumulating isoform of the neural cell adhesion molecule (NCAM). We show that there is a continuous flux of NCAM180 to the postsynaptic membrane from nonsynaptic regions of dendrites by diffusion. In the postsynaptic membrane, the newly delivered NCAM180 slowly intermixes with the immobilized pool of NCAM180. Preferential immobilization and accumulation of NCAM180 in the postsynaptic membrane is reduced after disruption of the association of NCAM180 with the spectrin cytoskeleton and in the absence of the homophilic interactions of NCAM180 in synapses. Our observations indicate that the homophilic interactions and binding to the cytoskeleton promote immobilization of NCAM180 and its accumulation in the postsynaptic membrane. Flux of NCAM180 from extrasynaptic regions and its slow intermixture with the immobile pool of NCAM180 in the postsynaptic membrane may be important for the continuous homeostatic replenishment of NCAM180 protein at synaptic contacts without compromising the long term synaptic contact stability.
Topics: Animals; Cells, Cultured; Mice; Mice, Knockout; Nerve Tissue Proteins; Neural Cell Adhesion Molecules; Protein Isoforms; Spectrin; Synaptic Membranes
PubMed: 21550975
DOI: 10.1074/jbc.M111.252098 -
The Journal of Neuroscience : the... Nov 1999The tubulin-binding protein gephyrin, which anchors the inhibitory glycine receptor (GlyR) at postsynaptic sites, decorates GABAergic postsynaptic membranes in various...
The tubulin-binding protein gephyrin, which anchors the inhibitory glycine receptor (GlyR) at postsynaptic sites, decorates GABAergic postsynaptic membranes in various brain regions, and postsynaptic gephyrin clusters are absent from cortical cultures of mice deficient for the GABA(A) receptor gamma2 subunit. Here, we investigated the postsynaptic clustering of GABA(A) receptors in gephyrin knock-out (geph -/-) mice. Both in brain sections and cultured hippocampal neurons derived from geph -/- mice, synaptic GABA(A) receptor clusters containing either the gamma2 or the alpha2 subunit were absent, whereas glutamate receptor subunits were normally localized at postsynaptic sites. Western blot analysis and electrophysiological recording revealed that normal levels of functional GABA(A) receptors are expressed in geph -/- neurons, however the pool size of intracellular GABA(A) receptors appeared increased in the mutant cells. Thus, gephyrin is required for the synaptic localization of GlyRs and GABA(A) receptors containing the gamma2 and/or alpha2 subunits but not for the targeting of these receptors to the neuronal plasma membrane. In addition, gephyrin may be important for efficient membrane insertion and/or metabolic stabilization of inhibitory receptors at developing postsynaptic sites.
Topics: Animals; Astrocytes; Carrier Proteins; Cells, Cultured; Culture Media, Conditioned; Dendrites; Glycine; Hippocampus; Membrane Potentials; Membrane Proteins; Mice; Mice, Inbred C57BL; Mice, Inbred Strains; Mice, Knockout; N-Methylaspartate; Nerve Tissue Proteins; Neurons; Receptors, AMPA; Receptors, GABA-A; Receptors, N-Methyl-D-Aspartate; SAP90-PSD95 Associated Proteins; Spinal Cord; Synapses
PubMed: 10531433
DOI: 10.1523/JNEUROSCI.19-21-09289.1999 -
Nature Neuroscience Apr 2014Synaptic cadherin adhesion complexes are known to be key regulators of synapse plasticity. However, the molecular mechanisms that coordinate activity-induced...
Synaptic cadherin adhesion complexes are known to be key regulators of synapse plasticity. However, the molecular mechanisms that coordinate activity-induced modifications in cadherin localization and adhesion and the subsequent changes in synapse morphology and efficacy remain unknown. We demonstrate that the intracellular cadherin binding protein δ-catenin is transiently palmitoylated by DHHC5 after enhanced synaptic activity and that palmitoylation increases δ-catenin-cadherin interactions at synapses. Both the palmitoylation of δ-catenin and its binding to cadherin are required for activity-induced stabilization of N-cadherin at synapses and the enlargement of postsynaptic spines, as well as the insertion of GluA1 and GluA2 subunits into the synaptic membrane and the concomitant increase in miniature excitatory postsynaptic current amplitude. Notably, context-dependent fear conditioning in mice resulted in increased δ-catenin palmitoylation, as well as increased δ-catenin-cadherin associations at hippocampal synapses. Together these findings suggest a role for palmitoylated δ-catenin in coordinating activity-dependent changes in synaptic adhesion molecules, synapse structure and receptor localization that are involved in memory formation.
Topics: Acyltransferases; Animals; Catenins; Female; Hippocampus; Lipoylation; Male; Membrane Proteins; Memory; Mice; Mice, Inbred C57BL; Neuronal Plasticity; Neurons; Rats; Rats, Sprague-Dawley; Synapses; Synaptic Membranes; Delta Catenin
PubMed: 24562000
DOI: 10.1038/nn.3657 -
Anesthesiology Mar 1979The dose-effectiveness of pancuronium as it relates to membrane potentials, action potentials, electrical membrane constants, miniature endplate potentials, endplate...
The dose-effectiveness of pancuronium as it relates to membrane potentials, action potentials, electrical membrane constants, miniature endplate potentials, endplate potentials, and quantal release was studied in murine phrenic nerve-diaphragm preparations in vitro. Emphasis was placed on comparison of presynaptic with postsynaptic effects of pancuronium under similar experimental conditions. At low concentrations of pancuronium (5 X 10(-8) g/ml or less), no presynaptic effect was found. At high concentration (5 X 10(-7) g/ml), pancuronium depressed quantal release to 26 per cent of control in cut-fiber preparations and 40 per cent of control in high-magnesium preparations. Postsynaptic effects as measured by the amplitude of miniature endplate potentials and relative depolarization induced by 20 microns carbachol, revealed depression to 16 and 22 per cent of control, respectively, at a pancuronium concentration of 5 X 10(-7) g/ml. Pancuronium had no effect on directly elicited action potentials and electrical membrane constants. The authors conclude that presynaptic as well as postsynaptic effects of pancuronium in paralytic doses are essential in contributing to the total efficacy of neuromuscular depression.
Topics: Action Potentials; Animals; Carbachol; Diaphragm; Dose-Response Relationship, Drug; Membrane Potentials; Mice; Neuromuscular Junction; Pancuronium; Synaptic Membranes; Time Factors
PubMed: 434503
DOI: 10.1097/00000542-197903000-00006 -
The Journal of Cell Biology Dec 2011Neuregulin (NRG)/ErbB signaling is involved in numerous developmental processes in the nervous system, including synapse formation and function in the central nervous...
Neuregulin (NRG)/ErbB signaling is involved in numerous developmental processes in the nervous system, including synapse formation and function in the central nervous system. Although intensively investigated, its role at the neuromuscular synapse has remained elusive. Here, we demonstrate that loss of neuromuscular NRG/ErbB signaling destabilized anchoring of acetylcholine receptors (AChRs) in the postsynaptic muscle membrane and that this effect was caused by dephosphorylation of α-dystrobrevin1, a component of the postsynaptic scaffold. Specifically, in mice in which NRG signaling to muscle was genetically or pharmacologically abolished, postsynaptic AChRs moved rapidly from the synaptic to the perisynaptic membrane, and the subsynaptic scaffold that anchors the AChRs was impaired. These defects combined compromised synaptic transmission. We further show that blockade of NRG/ErbB signaling abolished tyrosine phosphorylation of α-dystrobrevin1, which reduced the stability of receptors in agrin-induced AChR clusters in cultured myotubes. Our data indicate that NRG/ErbB signaling maintains high efficacy of synaptic transmission by stabilizing the postsynaptic apparatus via phosphorylation of α-dystrobrevin1.
Topics: Agrin; Animals; Cells, Cultured; Dystrophin-Associated Proteins; ErbB Receptors; Mice; Mice, Knockout; Muscle Fibers, Skeletal; Neuregulins; Neuromuscular Junction; Phosphorylation; Receptor, ErbB-2; Receptor, ErbB-4; Receptors, Cholinergic; Signal Transduction; Synaptic Membranes
PubMed: 22184199
DOI: 10.1083/jcb.201107083 -
The Journal of Physiology May 2004Mechanisms of long-term potentiation (LTP) maintenance are discussed in the light of the phenomenon of silent synapses. Evidence that LTP is associated with the... (Review)
Review
Mechanisms of long-term potentiation (LTP) maintenance are discussed in the light of the phenomenon of silent synapses. Evidence that LTP is associated with the insertion of new AMPA receptors (AMPARs) in postsynaptically silent (deaf) synapses expressing only NMDA receptors (NMDARs) before LTP induction has led to the assumption that the debate on pre- versus postsynaptic locus of LTP expression has been resolved in favour of the latter. However, recent data indicate that these synapses are mainly presynaptically silent (mute or whispering), because the probability of glutamate release (P(r)) or glutamate concentration in the cleft is too low to activate AMPARs. In this case LTP could be explained by an increase in P(r) or enhanced glutamate concentration to activate low affinity AMPARs. Optical methods to probe calcium transients in dendritic spines have revealed an increase in P(r) during LTP with concomitant postsynaptic modifications. A hypothesis is considered that accounts for the differences in both the initial failure rates between AMPAR- and NMDAR-mediated responses, and the LTP-associated decrease in failures of AMPAR-mediated responses. According to this hypothesis, glutamate release is potentiated by the strong postsynaptic depolarization used to identify NMDAR-mediated responses. We suggest that the expression of LTP may depend on coordinated pre- and postsynaptic modifications whose relative contributions vary according to the initial state of the synapse, the experimental protocol and time after induction.
Topics: Animals; Humans; Long-Term Potentiation; Neuronal Plasticity; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Synapses; Synaptic Membranes
PubMed: 15034124
DOI: 10.1113/jphysiol.2003.058966 -
The Journal of Biological Chemistry Aug 2016Protein kinase Cϵ (PKCϵ) promotes synaptic maturation and synaptogenesis via activation of synaptic growth factors such as BDNF, NGF, and IGF. However, many of the...
Protein kinase Cϵ (PKCϵ) promotes synaptic maturation and synaptogenesis via activation of synaptic growth factors such as BDNF, NGF, and IGF. However, many of the detailed mechanisms by which PKCϵ induces synaptogenesis are not fully understood. Accumulation of PSD-95 to the postsynaptic density (PSD) is known to lead to synaptic maturation and strengthening of excitatory synapses. Here we investigated the relationship between PKCϵ and PSD-95. We show that the PKCϵ activators dicyclopropanated linoleic acid methyl ester and bryostatin 1 induce phosphorylation of PSD-95 at the serine 295 residue, increase the levels of PSD-95, and enhance its membrane localization. Elimination of the serine 295 residue in PSD-95 abolished PKCϵ-induced membrane accumulation. Knockdown of either PKCϵ or JNK1 prevented PKCϵ activator-mediated membrane accumulation of PSD-95. PKCϵ directly phosphorylated PSD-95 and JNK1 in vitro Inhibiting PKCϵ, JNK, or calcium/calmodulin-dependent kinase II activity prevented the effects of PKCϵ activators on PSD-95 phosphorylation. Increase in membrane accumulation of PKCϵ and phosphorylated PSD-95 (p-PSD-95(S295)) coincided with an increased number of synapses and increased amplitudes of excitatory post-synaptic potentials (EPSPs) in adult rat hippocampal slices. Knockdown of PKCϵ also reduced the synthesis of PSD-95 and the presynaptic protein synaptophysin by 30 and 44%, respectively. Prolonged activation of PKCϵ increased synapse number by 2-fold, increased presynaptic vesicle density, and greatly increased PSD-95 clustering. These results indicate that PKCϵ promotes synaptogenesis by activating PSD-95 phosphorylation directly through JNK1 and calcium/calmodulin-dependent kinase II and also by inducing expression of PSD-95 and synaptophysin.
Topics: Animals; Bryostatins; Calcium-Calmodulin-Dependent Protein Kinase Type 2; Disks Large Homolog 4 Protein; Enzyme Activation; HEK293 Cells; Hippocampus; Humans; Intracellular Signaling Peptides and Proteins; Membrane Proteins; Mitogen-Activated Protein Kinase 8; Phosphorylation; Protein Kinase C-epsilon; Rats; Synaptic Membranes; Synaptophysin
PubMed: 27330081
DOI: 10.1074/jbc.M116.730440 -
Nature Communications Jun 2018NMDA receptors (NMDARs) are crucial for excitatory synaptic transmission and synaptic plasticity. The number and subunit composition of synaptic NMDARs are tightly...
NMDA receptors (NMDARs) are crucial for excitatory synaptic transmission and synaptic plasticity. The number and subunit composition of synaptic NMDARs are tightly controlled by neuronal activity and sensory experience, but the molecular mechanism mediating NMDAR trafficking remains poorly understood. Here, we report that RIM1, with a well-established role in presynaptic vesicle release, also localizes postsynaptically in the mouse hippocampus. Postsynaptic RIM1 in hippocampal CA1 region is required for basal NMDAR-, but not AMPA receptor (AMPAR)-, mediated synaptic responses, and contributes to synaptic plasticity and hippocampus-dependent memory. Moreover, RIM1 levels in hippocampal neurons influence both the constitutive and regulated NMDAR trafficking, without affecting constitutive AMPAR trafficking. We further demonstrate that RIM1 binds to Rab11 via its N terminus, and knockdown of RIM1 impairs membrane insertion of Rab11-positive recycling endosomes containing NMDARs. Together, these results identify a RIM1-dependent mechanism critical for modulating synaptic function by facilitating membrane delivery of recycling NMDARs.
Topics: Animals; CA1 Region, Hippocampal; Endosomes; GTP-Binding Proteins; Gene Knockdown Techniques; Hippocampus; Male; Memory; Mice; Mice, Inbred C57BL; Mice, Knockout; Neuronal Plasticity; Neurons; Protein Transport; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Synapses; Synaptic Transmission; rab GTP-Binding Proteins
PubMed: 29891949
DOI: 10.1038/s41467-018-04672-0