-
Journal of Neurophysiology Jan 2007The M-type K(+) current (M-current), encoded by Kv7.2/3 (KCNQ2/3) K(+) channels, plays a critical role in regulating neuronal excitability because it counteracts...
The M-type K(+) current (M-current), encoded by Kv7.2/3 (KCNQ2/3) K(+) channels, plays a critical role in regulating neuronal excitability because it counteracts subthreshold depolarizations. Here we have characterized the functions of pre- and postsynaptic M-channels using a novel Kv7.2/3 channel opener, NH6, which we synthesized as a new derivative of N-phenylanthranilic acid. NH6 exhibits a good selectivity as it does not affect Kv7.1 and I(KS) K(+) currents as well as NR1/NR2B, AMPA, and GABA(A) receptor-mediated currents. Superfusion of NH6 increased recombinant Kv7.2/3 current amplitude (EC(50) = 18 muM) by causing a hyperpolarizing shift of the voltage activation curve and by markedly slowing the deactivation kinetics. Activation of native M-currents by NH6 robustly reduced the number of evoked and spontaneous action potentials in cultured cortical, hippocampal and dorsal root ganglion neurons. In hippocampal slices, NH6 decreased somatically evoked spike after depolarization of CA1 pyramidal neurons and induced regular firing in bursting neurons. Activation of M-channels by NH6, potently reduced the frequency of spontaneous excitatory and inhibitory postsynaptic currents. Activation of M-channels also decreased the frequency of miniature excitatory (mEPSC) and inhibitory (mIPSC) postsynaptic currents without affecting their amplitude and waveform, thus suggesting that M-channels presynaptically inhibit glutamate and GABA release. Our results suggest a role of presynaptic M-channels in the release of glutamate and GABA. They also indicate that M-channels act pre- and postsynaptically to dampen neuronal excitability.
Topics: Action Potentials; Animals; Animals, Newborn; CHO Cells; Cells, Cultured; Cricetinae; Cricetulus; Excitatory Postsynaptic Potentials; Inhibitory Postsynaptic Potentials; Ionophores; KCNQ2 Potassium Channel; Mice; Mice, Inbred ICR; Molecular Structure; Nervous System; Neurotransmitter Agents; Organ Culture Techniques; Presynaptic Terminals; Rats; Rats, Sprague-Dawley; Synaptic Membranes; Synaptic Transmission; ortho-Aminobenzoates
PubMed: 17050829
DOI: 10.1152/jn.00634.2006 -
Neuroscience Jan 2009Activity dependent modification of receptors in the post-synaptic density is a key determinant in regulating the strength of synaptic transmission during development and... (Review)
Review
Activity dependent modification of receptors in the post-synaptic density is a key determinant in regulating the strength of synaptic transmission during development and plasticity. A major mechanism for this recruitment and removal of postsynaptic proteins is the lateral diffusion in the plane of the plasma membrane. Therefore, the processes that regulate this lateral mobility are of fundamental importance. In recent years significant progress has been achieved using optical approaches such as single particle tracking (SPT) and fluorescence recovery after photobleach (FRAP). Here, we provide an overview of the principles and methodology of these techniques and highlight the contributions they have made to current understanding of protein mobility in the plasma membrane.
Topics: Animals; Diffusion; Fluorescence Recovery After Photobleaching; Humans; Image Cytometry; Microscopy, Video; Protein Transport; Receptors, Neurotransmitter; Spectrometry, Fluorescence; Synapses; Synaptic Membranes; Synaptic Transmission
PubMed: 18455319
DOI: 10.1016/j.neuroscience.2008.01.075 -
Neuron Jun 2008The cellular basis of brain imaging is emerging as a new frontier in current neuroscience. In this issue of Neuron, Petzold et al. analyze a model system, the olfactory... (Review)
Review
The cellular basis of brain imaging is emerging as a new frontier in current neuroscience. In this issue of Neuron, Petzold et al. analyze a model system, the olfactory glomerulus, to show how neurovascular coupling involves an elaborate dance between axon terminals, presynaptic and postsynaptic dendrites, glial cells, and the capillary network.
Topics: Animals; Humans; Models, Animal; Neuroglia; Olfactory Bulb; Olfactory Receptor Neurons; Smell
PubMed: 18579073
DOI: 10.1016/j.neuron.2008.06.005 -
Journal of Neurocytology 2003Neuromuscular synapse formation is brought about by a complex bi-directional exchange of information between the innervating motor neuron and its target skeletal muscle... (Review)
Review
Neuromuscular synapse formation is brought about by a complex bi-directional exchange of information between the innervating motor neuron and its target skeletal muscle fiber. Agrin, a heparin sulfate proteoglycan, is released from the motor nerve terminal to activate its muscle-specific kinase (MuSK) receptor that leads to a second messenger cascade requiring rapsyn to ultimately bring about AChR clustering in the muscle membrane. Rapsyn performs many functions in skeletal muscle. First, rapsyn and AChRs co-target to the postsynatic apparatus. Second, rapsyn may self associate to stabilize and promote AChR clustering. Third, rapsyn is essential for AChR cluster formation. Fourth, rapsyn is required to transduce the agrin-evoked MuSK phosphorylation signal to AChRs. Finally, rapsyn links AChRs to the utrophin-associated complex, which appears to be required for AChR stabilization as well as maturation of the neuromuscular junction. Proteins within the utrophin-associated complex such as alpha-dystrobrevin and alpha-syntrophin are also important for signaling events that affect neuromuscular synapse stability and function. Here we review our current understanding of the role of the postsynaptic-submembrane machinery involving rapsyn and the utrophin-associated complex at the neuromuscular synapse. In addition we briefly review how these studies of the neuromuscular junction relate to GABAergic and glycinergic synapses in the CNS.
Topics: Animals; Cytoskeletal Proteins; Humans; Membrane Proteins; Muscle Proteins; Neuromuscular Junction; Synapses; Synaptic Membranes; Utrophin
PubMed: 15034263
DOI: 10.1023/B:NEUR.0000020619.24681.2b -
The Journal of Cell Biology Jul 1979The receptor-rich postsynaptic membrane of the elasmobranch electric organ was fixed by quick-freezing and then viewed by freeze-fracture, deep-etching and...
The receptor-rich postsynaptic membrane of the elasmobranch electric organ was fixed by quick-freezing and then viewed by freeze-fracture, deep-etching and rotary-replication. Traditional freeze-fracture revealed a distinct, geometrical pattern of shallow 8.5-nm bumps on the E fracture-face, similar to the lattice which has been seen before in chemically fixed material, but seen less clearly than after quick-freezing. Fracture plus deep-etching brought into view on the true outside of this membrane a similar geometrical pattern of 8.5-nm projections rising out of the membrane surface. The individual projections looked like structures that have been seen in negatively stained or deep-etched membrane fragments and have been identified as individual acetylcholine receptor molecules. The surface protrusions were twice as abundant as the large intramembrane particles that characterize the fracture faces of this membrane, which have also been considered to be receptor molecules. Particle counts have always been too low to match the estimates of postsynaptic receptor density derived from physiological and biochemical studies; counts of surface projections, however, more closely matched these estimates. Rotary-replication of quick-frozen, etched postsynaptic membranes enhanced the visibility of these surface protuberances and illustrated that they often occur in dimers, tetramers, and ordered rows. The variations in these surface patterns suggested that in vivo, receptors in the postsynaptic membrane may tend to pack into "liquid crystals" which constantly appear, flow, and disappear in the fluid environment of the membrane. Additionally, deep-etching revealed a distinct web of cytoplasmic filaments beneath the postsynaptic membrane, and revealed the basal lamina above it; and delineated possible points of contact between these structures and the membrane proper.
Topics: Acetylcholine; Animals; Electric Organ; Fishes; Freeze Etching; Freeze Fracturing; Receptors, Cholinergic; Synaptic Membranes
PubMed: 479296
DOI: 10.1083/jcb.82.1.150 -
Medecine Sciences : M/S Jan 2004A family of anchoring proteins named MAGUK (for membrane associated guanylate kinase) has emerged as a key element in the organization of protein complexes in... (Review)
Review
A family of anchoring proteins named MAGUK (for membrane associated guanylate kinase) has emerged as a key element in the organization of protein complexes in specialized membrane regions. These proteins are characterized by the presence of multipe protein-protein interaction domains including PDZ and SH3 domains. The MAGUK family comprises the post-synaptic density 95 (PSD-95) protein and closely related molecules such as chapsyn-110, synapse-associated protein 102 (SAP-102), and SAP-97. These are located either on the pre- and/or post-synaptic sides of synapses or at cell-cell adhesion sites of epithelial cells. MAGUK proteins interact with glutamate receptors and various ionic channels. For instance, an interaction has been reported between the first two PDZ domains of MAGUK proteins and several channels via a consensus sequence Thr/Ser-X-Val/Leu usually located at their carboxy terminus. The role of these anchoring proteins in channel function is not fully understood. MAGUK proteins enhance the current density by increasing the number of functional channels to the sarcolemma. They can also facilitate signaling between channels and several enzymes or G protein-dependent signaling pathways. In the heart also, MAGUK proteins are abundantly expressed and they interact with various channels including Shaker Kv1.5 and connexins.
Topics: Animals; Guanylate Kinases; Ion Channels; Nucleoside-Phosphate Kinase; Synaptic Membranes
PubMed: 14770369
DOI: 10.1051/medsci/200420184 -
The Japanese Journal of Physiology Dec 1998Neuron requires a continual supply of materials synthesized in the cell body, for example a wide range of soluble proteins, membranous components, and various... (Review)
Review
Neuron requires a continual supply of materials synthesized in the cell body, for example a wide range of soluble proteins, membranous components, and various organelles. The transported materials are needed to replace constituents that turn over in the membrane and organelles of the fiber and also are needed to bring substances participating in energy metabolism. Other transported components are neurotransmitters or transmitter-related components supplied to the nerve terminals for the release and subsequent excitation of postsynaptic cells. Moreover, neurotropic substances and modulators are released from the nerve terminals to affect the functional state of the neuron. Conversely, some materials are conveyed back to the cell body. These include organelles, lysosomes, nerve growth factor, and selected small molecules such as adenosine, Ca2+, and some neurotransmitters. Axoplasmic transport is thought to be fundamental for a variety of neuronal cell functions. Thus it may be considered that axoplasmic transport relates to the dynamic physiological activity of neurons; in other words, axoplasmic transport is supposed to express the physiological activity of neurons. In turn, as in the case for many other physiological functions, axoplasmic transport is possibly controlled by neuronal, hormonal, and immunological systems. Since axoplasmic transport supplies neuron materials toward the synapses and back to the cell body, a feedback system of regulatory mechanisms of a variety of neuronal functions might be operated through axoplasmic transport pathways. Although axoplasmic transport is the important neuronal function, its regulation is poorly understood. In this review, we focus on the dynamics of organelle transport and its regulatory mechanisms mediated by neurotransmitters.
Topics: Animals; Axonal Transport; Humans; Microscopy, Video; Mitochondria; Models, Biological; Signal Transduction
PubMed: 10021495
DOI: 10.2170/jjphysiol.48.413 -
The EMBO Journal Apr 2006Intracellular membrane trafficking of glutamate receptors at excitatory synapses is critical for synaptic function. However, little is known about the specialized...
Intracellular membrane trafficking of glutamate receptors at excitatory synapses is critical for synaptic function. However, little is known about the specialized trafficking events occurring at the postsynaptic membrane. We have found that two components of the exocyst complex, Sec8 and Exo70, separately control synaptic targeting and insertion of AMPA-type glutamate receptors. Sec8 controls the directional movement of receptors towards synapses through PDZ-dependent interactions. In contrast, Exo70 mediates receptor insertion at the postsynaptic membrane, but it does not participate in receptor targeting. Thus, interference with Exo70 function accumulates AMPA receptors inside the spine, forming a complex physically associated, but not yet fused with the postsynaptic membrane. Electron microscopic analysis of these complexes indicates that Exo70 mediates AMPA receptor insertion directly within the postsynaptic density, rather than at extrasynaptic membranes. Therefore, we propose a molecular and anatomical model that dissects AMPA receptor sorting and synaptic delivery within the spine, and uncovers new functions of the exocyst at the postsynaptic membrane.
Topics: Animals; Carrier Proteins; Cells, Cultured; Dendritic Spines; Hippocampus; Membrane Fusion; Membrane Proteins; Mice; Mutation; Neurons; Organ Culture Techniques; Patch-Clamp Techniques; Protein Transport; Rats; Receptors, AMPA; Synapses; Synaptic Membranes; Synaptic Transmission; Synaptosomes; Vesicular Transport Proteins
PubMed: 16601687
DOI: 10.1038/sj.emboj.7601065 -
Nature Protocols Jan 2014This protocol describes how to image the trafficking of glutamate receptors around excitatory postsynaptic membrane formed on an adhesion protein-coated glass surface....
This protocol describes how to image the trafficking of glutamate receptors around excitatory postsynaptic membrane formed on an adhesion protein-coated glass surface. The protocol was developed to clarify how receptors move during the induction of synaptic plasticity. Dissociated neurons are cultured on a coverslip coated with neurexin, which induces the formation of postsynaptic membrane-like structures on the glass surface. A glutamate receptor tagged with a fluorescent protein is then transfected into neurons, and it is observed with total internal reflection fluorescence microscopy. The whole process takes about 3 weeks. Changes in the amount of cell-surface receptors caused by neuronal activities can be quantified, and individual exocytosis events of receptors can be clearly observed around the pseudo-postsynaptic membrane. This protocol has potential applications for studies of movements of membrane proteins around other specialized regions of the cell membrane, such as the inhibitory postsynaptic membrane, the presynaptic membrane or the immunological synapses.
Topics: Cell Culture Techniques; Cell Membrane; Disks Large Homolog 4 Protein; HEK293 Cells; Humans; Intracellular Signaling Peptides and Proteins; Membrane Proteins; Nerve Tissue Proteins; Neuronal Plasticity; Optical Imaging; Receptors, Glutamate
PubMed: 24336472
DOI: 10.1038/nprot.2013.171 -
The EMBO Journal Sep 2018Hippocampal GABAergic interneurons are crucial for cortical network function and have been implicated in psychiatric disorders. We show here that Neuregulin 3 (Nrg3), a...
Hippocampal GABAergic interneurons are crucial for cortical network function and have been implicated in psychiatric disorders. We show here that Neuregulin 3 (Nrg3), a relatively little investigated low-affinity ligand, is a functionally dominant interaction partner of ErbB4 in parvalbumin-positive (PV) interneurons. Nrg3 and ErbB4 are located pre- and postsynaptically, respectively, in excitatory synapses on PV interneurons Additionally, we show that ablation of Nrg3 results in a similar phenotype as the one described for ErbB4 ablation, including reduced excitatory synapse numbers on PV interneurons, altered short-term plasticity, and disinhibition of the hippocampal network. In culture, presynaptic Nrg3 increases excitatory synapse numbers on ErbB4 interneurons and affects short-term plasticity. Nrg3 mutant neurons are poor donors of presynaptic terminals in the presence of competing neurons that produce recombinant Nrg3, and this bias requires postsynaptic ErbB4 but not ErbB4 kinase activity. Furthermore, when presented by non-neuronal cells, Nrg3 induces postsynaptic membrane specialization. Our data indicate that Nrg3 provides adhesive cues that facilitate excitatory neurons to synapse onto ErbB4 interneurons.
Topics: Animals; Hippocampus; Interneurons; Intracellular Signaling Peptides and Proteins; Mice; Mice, Transgenic; Nerve Net; Neuregulins; Neuronal Plasticity; Receptor, ErbB-4; Synapses
PubMed: 30049711
DOI: 10.15252/embj.201798858