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Chen JJ, Kaufmann WA, Chen C, Arai I, Kim O, Shigemoto R, Jonas P. Developmental transformation of Ca 2+ channel-vesicle nanotopography at a central GABAergic synapse. Neuron 2024; 112:755-771.e9. [PMID: 38215739 DOI: 10.1016/j.neuron.2023.12.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2022] [Revised: 07/12/2023] [Accepted: 12/05/2023] [Indexed: 01/14/2024]
Abstract
The coupling between Ca2+ channels and release sensors is a key factor defining the signaling properties of a synapse. However, the coupling nanotopography at many synapses remains unknown, and it is unclear how it changes during development. To address these questions, we examined coupling at the cerebellar inhibitory basket cell (BC)-Purkinje cell (PC) synapse. Biophysical analysis of transmission by paired recording and intracellular pipette perfusion revealed that the effects of exogenous Ca2+ chelators decreased during development, despite constant reliance of release on P/Q-type Ca2+ channels. Structural analysis by freeze-fracture replica labeling (FRL) and transmission electron microscopy (EM) indicated that presynaptic P/Q-type Ca2+ channels formed nanoclusters throughout development, whereas docked vesicles were only clustered at later developmental stages. Modeling suggested a developmental transformation from a more random to a more clustered coupling nanotopography. Thus, presynaptic signaling developmentally approaches a point-to-point configuration, optimizing speed, reliability, and energy efficiency of synaptic transmission.
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Affiliation(s)
- Jing-Jing Chen
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Walter A Kaufmann
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Chong Chen
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Itaru Arai
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Olena Kim
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Ryuichi Shigemoto
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Peter Jonas
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria.
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2
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Ojala KS, Kaufhold CJ, Davey MR, Yang D, Liang M, Wipf P, Badawi Y, Meriney SD. Potentiation of neuromuscular transmission by a small molecule calcium channel gating modifier improves motor function in a severe spinal muscular atrophy mouse model. Hum Mol Genet 2023; 32:1901-1911. [PMID: 36757138 DOI: 10.1093/hmg/ddad019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Revised: 01/03/2023] [Accepted: 01/24/2023] [Indexed: 02/10/2023] Open
Abstract
Spinal muscular atrophy (SMA) is a monogenic disease that clinically manifests as severe muscle weakness owing to neurotransmission defects and motoneuron degeneration. Individuals affected by SMA experience neuromuscular weakness that impacts functional activities of daily living. We have used a mouse model of severe SMA (SMNΔ7) to test whether a calcium channel gating modifier (GV-58), alone or in combination with a potassium channel antagonist (3,4-diaminopyridine; 3,4-DAP), can improve neuromuscular function in this mouse model. Bath application of GV-58 alone or in combination with 3,4-DAP significantly restored neuromuscular transmission to control levels in both a mildly vulnerable forearm muscle and a strongly vulnerable trunk muscle in SMNΔ7 mice at postnatal days 10-12. Similarly, acute subcutaneous administration of GV-58 to postnatal day 10 SMNΔ7 mice, alone or in combination with 3,4-DAP, significantly increased a behavioral measure of muscle strength. These data suggest that GV-58 may be a promising treatment candidate that could address deficits in neuromuscular function and strength and that the addition of 3,4-DAP to GV-58 treatment could aid in restoring function in SMA.
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Affiliation(s)
- Kristine S Ojala
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Cassandra J Kaufhold
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Mykenzie R Davey
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Donggyun Yang
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Mary Liang
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Peter Wipf
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Yomna Badawi
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Stephen D Meriney
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
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3
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Bykhovskaia M. Probabilities of evoked and spontaneous synaptic transmission at individual active zones: Lessons from Drosophila. Front Mol Neurosci 2023; 15:1110538. [PMID: 36683858 PMCID: PMC9846329 DOI: 10.3389/fnmol.2022.1110538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Accepted: 12/12/2022] [Indexed: 01/05/2023] Open
Abstract
Nerve terminals release neuronal transmitters at morphological specializations known as active zones (AZs). Synaptic vesicle fusion at individual AZs is probabilistic, and this property is fundamental for the neuronal information transfer. Until recently, a lack of appropriate tools limited the studies of stochastic properties of neuronal secretion at individual AZs. However, Drosophila transgenic lines that express postsynaptically tethered Ca2+ sensor GCaMP enabled the visualization of single exocytic event at individual AZs. The present mini-review discusses how this powerful approach enables the investigation of the evoked and spontaneous transmission at single AZs and promotes the understanding of the properties of both release components.
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4
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Laghaei R, Meriney SD. Microphysiological Modeling of the Structure and Function of Neuromuscular Transmitter Release Sites. Front Synaptic Neurosci 2022; 14:917285. [PMID: 35769072 PMCID: PMC9236679 DOI: 10.3389/fnsyn.2022.917285] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Accepted: 05/12/2022] [Indexed: 11/13/2022] Open
Abstract
The general mechanism of calcium-triggered chemical transmitter release from neuronal synapses has been intensely studied, is well-known, and highly conserved between species and synapses across the nervous system. However, the structural and functional details within each transmitter release site (or active zone) are difficult to study in living tissue using current experimental approaches owing to the small spatial compartment within the synapse where exocytosis occurs with a very rapid time course. Therefore, computer simulations offer the opportunity to explore these microphysiological environments of the synapse at nanometer spatial scales and on a sub-microsecond timescale. Because biological reactions and physiological processes at synapses occur under conditions where stochastic behavior is dominant, simulation approaches must be driven by such stochastic processes. MCell provides a powerful simulation approach that employs particle-based stochastic simulation tools to study presynaptic processes in realistic and complex (3D) geometries using optimized Monte Carlo algorithms to track finite numbers of molecules as they diffuse and interact in a complex cellular space with other molecules in solution and on surfaces (representing membranes, channels and binding sites). In this review we discuss MCell-based spatially realistic models of the mammalian and frog neuromuscular active zones that were developed to study presynaptic mechanisms that control transmitter release. In particular, these models focus on the role of presynaptic voltage-gated calcium channels, calcium sensors that control the probability of synaptic vesicle fusion, and the effects of action potential waveform shape on presynaptic calcium entry. With the development of these models, they can now be used in the future to predict disease-induced changes to the active zone, and the effects of candidate therapeutic approaches.
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Affiliation(s)
- Rozita Laghaei
- Biomedical Applications Group, Pittsburgh Supercomputing Center, Carnegie Mellon University, Pittsburgh, PA, United States
| | - Stephen D. Meriney
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA, United States
- *Correspondence: Stephen D. Meriney
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5
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Machamer JB, Vazquez-Cintron EJ, O'Brien SW, Kelly KE, Altvater AC, Pagarigan KT, Dubee PB, Ondeck CA, McNutt PM. Antidotal treatment of botulism in rats by continuous infusion with 3,4-diaminopyridine. Mol Med 2022; 28:61. [PMID: 35659174 PMCID: PMC9164507 DOI: 10.1186/s10020-022-00487-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Accepted: 05/17/2022] [Indexed: 11/10/2022] Open
Abstract
Botulinum neurotoxins (BoNTs) are highly potent, select agent toxins that inhibit neurotransmitter release at motor nerve terminals, causing muscle paralysis and death by asphyxiation. Other than post-exposure prophylaxis with antitoxin, the only treatment option for symptomatic botulism is intubation and supportive care until recovery, which can require weeks or longer. In previous studies, we reported the FDA-approved drug 3,4-diaminopyridine (3,4-DAP) reverses early botulism symptoms and prolongs survival in lethally intoxicated mice. However, the symptomatic benefits of 3,4-DAP are limited by its rapid clearance. Here we investigated whether 3,4-DAP could sustain symptomatic benefits throughout the full course of respiratory paralysis in lethally intoxicated rats. First, we confirmed serial injections of 3,4-DAP stabilized toxic signs and prolonged survival in rats challenged with 2.5 LD50 BoNT/A. Rebound of toxic signs and death occurred within hours after the final 3,4-DAP treatment, consistent with the short half-life of 3,4-DAP in rats. Based on these data, we next investigated whether the therapeutic benefits of 3,4-DAP could be sustained throughout the course of botulism by continuous infusion. To ensure administration of 3,4-DAP at clinically relevant doses, three infusion dose rates (0.5, 1.0 and 1.5 mg/kg∙h) were identified that produced steady-state serum levels of 3,4-DAP consistent with clinical dosing. We then compared dose-dependent effects of 3,4-DAP on toxic signs and survival in rats intoxicated with 2.5 LD50 BoNT/A. In contrast to saline vehicle, which resulted in 100% mortality, infusion of 3,4-DAP at ≥ 1.0 mg/kg∙h from 1 to 14 d after intoxication produced 94.4% survival and full resolution of toxic signs, without rebound of toxic signs after infusion was stopped. In contrast, withdrawal of 3,4-DAP infusion at 5 d resulted in re-emergence of toxic sign and death within 12 h, confirming antidotal outcomes require sustained 3,4-DAP treatment for longer than 5 d after intoxication. We exploited this novel survival model of lethal botulism to explore neurophysiological parameters of diaphragm paralysis and recovery. While neurotransmission was nearly eliminated at 5 d, neurotransmission was significantly improved at 21 d in 3,4-DAP-infused survivors, although still depressed compared to naïve rats. 3,4-DAP is the first small molecule to reverse systemic paralysis and promote survival in animal models of botulism, thereby meeting a critical treatment need that is not addressed by post-exposure prophylaxis with conventional antitoxin. These data contribute to a growing body of evidence supporting the use of 3,4-DAP to treat clinical botulism.
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Affiliation(s)
- James B Machamer
- U.S. Army Medical Research Institute of Chemical Defense, Gunpowder, MD, 21010, USA
- BASF, Research Triangle, Durham, NC, 27709, USA
| | | | - Sean W O'Brien
- U.S. Army Medical Research Institute of Chemical Defense, Gunpowder, MD, 21010, USA
- Wake Forest Institute for Regenerative Medicine, Wake Forest School of Medicine, Winston-Salem, NC, 27101, USA
| | - Kyle E Kelly
- U.S. Army Medical Research Institute of Chemical Defense, Gunpowder, MD, 21010, USA
| | - Amber C Altvater
- U.S. Army Medical Research Institute of Chemical Defense, Gunpowder, MD, 21010, USA
| | - Kathleen T Pagarigan
- U.S. Army Medical Research Institute of Chemical Defense, Gunpowder, MD, 21010, USA
| | - Parker B Dubee
- U.S. Army Medical Research Institute of Chemical Defense, Gunpowder, MD, 21010, USA
| | - Celinia A Ondeck
- U.S. Army Medical Research Institute of Chemical Defense, Gunpowder, MD, 21010, USA
- Wake Forest Institute for Regenerative Medicine, Wake Forest School of Medicine, Winston-Salem, NC, 27101, USA
| | - Patrick M McNutt
- U.S. Army Medical Research Institute of Chemical Defense, Gunpowder, MD, 21010, USA.
- Wake Forest Institute for Regenerative Medicine, Wake Forest School of Medicine, Winston-Salem, NC, 27101, USA.
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6
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Ginebaugh SP, Badawi Y, Tarr TB, Meriney SD. Neuromuscular Active Zone Structure and Function in Healthy and Lambert-Eaton Myasthenic Syndrome States. Biomolecules 2022; 12:biom12060740. [PMID: 35740866 PMCID: PMC9221282 DOI: 10.3390/biom12060740] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Revised: 05/16/2022] [Accepted: 05/18/2022] [Indexed: 12/02/2022] Open
Abstract
The mouse neuromuscular junction (NMJ) has long been used as a model synapse for the study of neurotransmission in both healthy and disease states of the NMJ. Neurotransmission from these neuromuscular nerve terminals occurs at highly organized structures called active zones (AZs). Within AZs, the relationships between the voltage-gated calcium channels and docked synaptic vesicles govern the probability of acetylcholine release during single action potentials, and the short-term plasticity characteristics during short, high frequency trains of action potentials. Understanding these relationships is important not only for healthy synapses, but also to better understand the pathophysiology of neuromuscular diseases. In particular, we are interested in Lambert-Eaton myasthenic syndrome (LEMS), an autoimmune disorder in which neurotransmitter release from the NMJ decreases, leading to severe muscle weakness. In LEMS, the reduced neurotransmission is traditionally thought to be caused by the antibody-mediated removal of presynaptic voltage-gated calcium channels. However, recent experimental data and AZ computer simulations have predicted that a disruption in the normally highly organized active zone structure, and perhaps autoantibodies to other presynaptic proteins, contribute significantly to pathological effects in the active zone and the characteristics of chemical transmitters.
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7
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Camargo WL, Kushmerick C, Pinto E, Souza N, Cavalcante W, Souza-Neto FP, Guatimosim S, Prado M, Guatimosim C, Naves LA. Homeostatic plasticity induced by increased acetylcholine release at the mouse neuromuscular junction. Neurobiol Aging 2021; 110:13-26. [PMID: 34844076 DOI: 10.1016/j.neurobiolaging.2021.10.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Revised: 10/21/2021] [Accepted: 10/22/2021] [Indexed: 02/07/2023]
Abstract
At the neuromuscular junction (NMJ), changes to the size of the postsynaptic potential induce homeostatic compensation. At the Drosophila NMJ, increased glutamate release causes a compensatory decrease in quantal content, but it is unknown if this mechanism operates at the cholinergic mammalian NMJ. We addressed this question by recording endplate potentials (EPP) and muscle contraction in 3-month and 24-month ChAT-ChR2-EYFP mice that overexpress vesicular acetylcholine transporter and release more acetylcholine per vesicle. At 3 months, the quantal content of EPPs from ChAT-ChR2-EYFP mice were not different from WT controls, however tetanic depression was greater, and quantal size during high-frequency stimulation and the size of the readily releasable pool (RRP) were decreased. At 24 months of age, quantal content was reduced in ChAT-ChR2-EYFP mice, which normalized synaptic depression despite smaller RRP. The effect of pancuronium on indirect evoked muscle twitch was not different between groups. These results indicate that an increase in the amount of acetylcholine per vesicle induces two distinct age-dependent homeostatic mechanisms compensating excessive acetylcholine release.
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Affiliation(s)
| | | | | | | | | | | | | | - Mam Prado
- Robarts Research Institute and Department of Physiology and Pharmacology and Anatomy & Cell Biology, University of Western Ontario, London, ON, Canada
| | | | - L A Naves
- Departments of Physiology and biophysics
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8
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Ojala KS, Ginebaugh SP, Wu M, Miller EW, Ortiz G, Covarrubias M, Meriney SD. A high-affinity, partial antagonist effect of 3,4-diaminopyridine mediates action potential broadening and enhancement of transmitter release at NMJs. J Biol Chem 2021; 296:100302. [PMID: 33465376 PMCID: PMC7949096 DOI: 10.1016/j.jbc.2021.100302] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Revised: 01/12/2021] [Accepted: 01/14/2021] [Indexed: 12/03/2022] Open
Abstract
3,4-Diaminopyridine (3,4-DAP) increases transmitter release from neuromuscular junctions (NMJs), and low doses of 3,4-DAP (estimated to reach ∼1 μM in serum) are the Food and Drug Administration (FDA)-approved treatment for neuromuscular weakness caused by Lambert–Eaton myasthenic syndrome. Canonically, 3,4-DAP is thought to block voltage-gated potassium (Kv) channels, resulting in prolongation of the presynaptic action potential (AP). However, recent reports have shown that low millimolar concentrations of 3,4-DAP have an off-target agonist effect on the Cav1 subtype (“L-type”) of voltage-gated calcium (Cav) channels and have speculated that this agonist effect might contribute to 3,4-DAP effects on transmitter release at the NMJ. To address 3,4-DAP’s mechanism(s) of action, we first used the patch-clamp electrophysiology to characterize the concentration-dependent block of 3,4-DAP on the predominant presynaptic Kv channel subtypes found at the mammalian NMJ (Kv3.3 and Kv3.4). We identified a previously unreported high-affinity (1–10 μM) partial antagonist effect of 3,4-DAP in addition to the well-known low-affinity (0.1–1 mM) antagonist activity. We also showed that 1.5-μM DAP had no effects on Cav1.2 or Cav2.1 current. Next, we used voltage imaging to show that 1.5- or 100-μM 3,4-DAP broadened the AP waveform in a dose-dependent manner, independent of Cav1 calcium channels. Finally, we demonstrated that 1.5- or 100-μM 3,4-DAP augmented transmitter release in a dose-dependent manner and this effect was also independent of Cav1 channels. From these results, we conclude that low micromolar concentrations of 3,4-DAP act solely on Kv channels to mediate AP broadening and enhance transmitter release at the NMJ.
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Affiliation(s)
- Kristine S Ojala
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Scott P Ginebaugh
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Man Wu
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Evan W Miller
- Departments of Chemistry and Molecular & Cell Biology, University of California, Berkeley, Berkeley, California, USA
| | - Gloria Ortiz
- Departments of Chemistry and Molecular & Cell Biology, University of California, Berkeley, Berkeley, California, USA
| | - Manuel Covarrubias
- Department of Neuroscience, Thomas Jefferson University, Philadelphia, Pennsylvania, USA
| | - Stephen D Meriney
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
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9
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Tsentsevitsky AN, Zakyrjanova GF, Petrov AM. Cadmium desynchronizes neurotransmitter release in the neuromuscular junction: Key role of ROS. Free Radic Biol Med 2020; 155:19-28. [PMID: 32445865 DOI: 10.1016/j.freeradbiomed.2020.05.017] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Revised: 05/18/2020] [Accepted: 05/18/2020] [Indexed: 12/11/2022]
Abstract
Cd2+ is one of the most widespread environmental pollutants and its accumulation in central and peripheral nervous systems leads to neurotoxicity as well as aggravation of common neurodegenerative diseases. Mechanism of the Cd2+ toxicity is far from being resolved. Here, using microelectrode recordings of postsynaptic responses and fluorescent redox indicators we studied the effect of Cd2+ in the submicromolar range on timing of neurotransmitter release and oxidative status in two functionally different compartments of the same frog motor nerve terminal. Cd2+ (0.1-1 μM) acting as typical voltage-gated Ca2+channel (VGCC) antagonist decreased neurotransmitter release in both distal and proximal parts of the nerve terminal, but in contrast to the VGCC blockers Cd2+(0.1-0.5 μM) desynchronized the release selectively in the distal region. The latter action of Cd2+ was completely prevented by inhibitor of NADPH-oxidase and antioxidants, including mitochondrial specific, as well as redox-sensitive TRPV1 channel blocker. Cd2+ markedly increased levels of mitochondrial reactive oxygen species (ROS) in both the distal and proximal compartments of the nerve terminal, which was associated with lipid peroxidation mainly in the distal region. Zn2+, whose transport systems translocate Cd2+, markedly enhanced the effects of Cd2+ on both the mitochondrial ROS levels and timing of neurotransmitter release. Furthermore, in the presence of Zn2+ ions, Cd2+ also desynchronized the neurotransmitter release in the proximal region. Thus, in synapses Cd2+ at very low concentrations can increase mitochondrial ROS, lipid peroxidation and disturb the timing of neurotransmitter release via a ROS/TRPV-dependent mechanism. Desynchronization of neurotransmitter release and synaptic oxidative stress could be early events in Cd2+ neurotoxicity.
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Affiliation(s)
- A N Tsentsevitsky
- Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Federal Research Center ''Kazan Scientific Center of RAS", 2/31 Lobachevsky Street, Box 30, Kazan, 420111, Russia
| | - G F Zakyrjanova
- Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Federal Research Center ''Kazan Scientific Center of RAS", 2/31 Lobachevsky Street, Box 30, Kazan, 420111, Russia; Institute of Neuroscience, Kazan State Medial University, 49 Butlerova Street, Kazan, 420012, Russia
| | - A M Petrov
- Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Federal Research Center ''Kazan Scientific Center of RAS", 2/31 Lobachevsky Street, Box 30, Kazan, 420111, Russia; Institute of Neuroscience, Kazan State Medial University, 49 Butlerova Street, Kazan, 420012, Russia.
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10
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Rusakov DA, Savtchenko LP, Latham PE. Noisy Synaptic Conductance: Bug or a Feature? Trends Neurosci 2020; 43:363-372. [PMID: 32459990 PMCID: PMC7902755 DOI: 10.1016/j.tins.2020.03.009] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2019] [Revised: 03/10/2020] [Accepted: 03/23/2020] [Indexed: 12/31/2022]
Abstract
More often than not, action potentials fail to trigger neurotransmitter release. And even when neurotransmitter is released, the resulting change in synaptic conductance is highly variable. Given the energetic cost of generating and propagating action potentials, and the importance of information transmission across synapses, this seems both wasteful and inefficient. However, synaptic noise arising from variable transmission can improve, in certain restricted conditions, information transmission. Under broader conditions, it can improve information transmission per release, a quantity that is relevant given the energetic constraints on computing in the brain. Here we discuss the role, both positive and negative, synaptic noise plays in information transmission and computation in the brain.
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Affiliation(s)
- Dmitri A Rusakov
- Queen Square UCL Institute of Neurology, University College London, Queen Square, London, WC1N 3BG, UK.
| | - Leonid P Savtchenko
- Queen Square UCL Institute of Neurology, University College London, Queen Square, London, WC1N 3BG, UK.
| | - Peter E Latham
- Gatsby Computational Neuroscience Unit, University College London, 25 Howland Street, London, W1T 4JG, UK.
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11
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Gundersen CB. Cysteine string proteins. Prog Neurobiol 2020; 188:101758. [DOI: 10.1016/j.pneurobio.2020.101758] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Revised: 01/06/2020] [Accepted: 01/13/2020] [Indexed: 12/17/2022]
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12
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Dittrich M, Homan AE, Meriney SD. Presynaptic mechanisms controlling calcium-triggered transmitter release at the neuromuscular junction. CURRENT OPINION IN PHYSIOLOGY 2018; 4:15-24. [PMID: 30272045 DOI: 10.1016/j.cophys.2018.03.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Calcium-triggered neurotransmission underlies most communication in the nervous system. Yet, despite the conserved and essential nature of this process, the molecular underpinnings of calcium-triggered neurotransmission have been difficult to study directly and our understanding to this date remains incomplete. Here we frame more recent efforts to understand this process with a historical perspective of the study of neurotransmitter release at the neuromuscular junction. We focus on the role of calcium channel distribution and organization relative to synaptic vesicles, as well as the nature of the calcium sensors that trigger release. Importantly, we provide a framework for understanding how the function of neurotransmitter release sites, or active zones, contributes to the function of the synapse as a whole.
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Affiliation(s)
| | - Anne E Homan
- Department of Neuroscience, A210 Langley Hall, University of Pittsburgh, Pittsburgh, PA 15260
| | - Stephen D Meriney
- Department of Neuroscience, A210 Langley Hall, University of Pittsburgh, Pittsburgh, PA 15260
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13
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Bradford AB, Machamer JB, Russo TM, McNutt PM. 3,4-diaminopyridine reverses paralysis in botulinum neurotoxin-intoxicated diaphragms through two functionally distinct mechanisms. Toxicol Appl Pharmacol 2018; 341:77-86. [PMID: 29366638 DOI: 10.1016/j.taap.2018.01.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Revised: 01/15/2018] [Accepted: 01/18/2018] [Indexed: 01/11/2023]
Abstract
Botulinum neurotoxins (BoNTs) are exceedingly potent neurological poisons that prevent neurotransmitter release from peripheral nerve terminals by cleaving presynaptic proteins required for synaptic vesicle fusion. The ensuing neuromuscular paralysis causes death by asphyxiation. Although no antidotal treatments exist to block toxin activity within the nerve terminal, aminopyridine antagonists of voltage-gated potassium channels have been proposed as symptomatic treatments for botulism toxemia. However, clinical evaluation of aminopyridines as symptomatic treatments for botulism has been inconclusive, in part because mechanisms responsible for reversal of paralysis in BoNT-poisoned nerve terminals are not understood. Here we measured the effects of 3,4-diaminopyridine (DAP) on phrenic nerve-elicited diaphragm contraction and end-plate potentials at various times after intoxication with BoNT serotypes A, B, or E. We found that DAP-mediated increases in quantal content promote neurotransmission from intoxicated nerve terminals through two functionally distinguishable mechanisms. First, DAP increases the probability of neurotransmission at non-intoxicated release sites. This mechanism is serotype-independent, becomes less effective as nerve terminals become progressively impaired, and remains susceptible to ongoing intoxication. Second, DAP elicits persistent production of toxin-resistant endplate potentials from nerve terminals fully intoxicated by BoNT/A, but not serotypes B or E. Since this effect appears specific to BoNT/A intoxication, we propose that DAP treatment enables BoNT/A-cleaved SNAP-25 to productively engage in fusogenic release by increasing the opportunity for low-efficiency fusion events. These findings have important implications for DAP as a botulism therapeutic by defining conditions under which DAP may be clinically effective in reversing botulism symptoms.
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Affiliation(s)
- Aaron B Bradford
- Department of Neuroscience, United States Army Medical Research Institute of Chemical Defense, 2900 Ricketts Point Road, Gunpowder, MD 21010, USA
| | - James B Machamer
- Department of Neuroscience, United States Army Medical Research Institute of Chemical Defense, 2900 Ricketts Point Road, Gunpowder, MD 21010, USA
| | - Trisha M Russo
- Department of Neuroscience, United States Army Medical Research Institute of Chemical Defense, 2900 Ricketts Point Road, Gunpowder, MD 21010, USA
| | - Patrick M McNutt
- Department of Neuroscience, United States Army Medical Research Institute of Chemical Defense, 2900 Ricketts Point Road, Gunpowder, MD 21010, USA.
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14
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Laghaei R, Ma J, Tarr TB, Homan AE, Kelly L, Tilvawala MS, Vuocolo BS, Rajasekaran HP, Meriney SD, Dittrich M. Transmitter release site organization can predict synaptic function at the neuromuscular junction. J Neurophysiol 2017; 119:1340-1355. [PMID: 29357458 DOI: 10.1152/jn.00168.2017] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
We have investigated the impact of transmitter release site (active zone; AZ) structure on synaptic function by physically rearranging the individual AZ elements in a previously published frog neuromuscular junction (NMJ) AZ model into the organization observed in a mouse NMJ AZ. We have used this strategy, purposefully without changing the properties of AZ elements between frog and mouse models (even though there are undoubtedly differences between frog and mouse AZ elements in vivo), to directly test how structure influences function at the level of an AZ. Despite a similarly ordered ion channel array substructure within both frog and mouse AZs, frog AZs are much longer and position docked vesicles in a different location relative to AZ ion channels. Physiologically, frog AZs have a lower probability of transmitter release compared with mouse AZs, and frog NMJs facilitate strongly during short stimulus trains in contrast with mouse NMJs that depress slightly. Using our computer modeling approach, we found that a simple rearrangement of the AZ building blocks of the frog model into a mouse AZ organization could recapitulate the physiological differences between these two synapses. These results highlight the importance of simple AZ protein organization to synaptic function. NEW & NOTEWORTHY A simple rearrangement of the basic building blocks in the frog neuromuscular junction model into a mouse transmitter release site configuration predicted the major physiological differences between these two synapses, suggesting that transmitter release site structure and organization is a strong predictor of function.
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Affiliation(s)
- Rozita Laghaei
- Biomedical Applications Group, Pittsburgh Supercomputing Center, Carnegie Mellon University , Pittsburgh, Pennsylvania
| | - Jun Ma
- Biomedical Applications Group, Pittsburgh Supercomputing Center, Carnegie Mellon University , Pittsburgh, Pennsylvania
| | - Tyler B Tarr
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Anne E Homan
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Lauren Kelly
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Megha S Tilvawala
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Blake S Vuocolo
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Harini P Rajasekaran
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Stephen D Meriney
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Markus Dittrich
- Biomedical Applications Group, Pittsburgh Supercomputing Center, Carnegie Mellon University , Pittsburgh, Pennsylvania.,Department of Neuroscience, Center for Neuroscience, University of Pittsburgh , Pittsburgh, Pennsylvania.,BioTeam Inc., Middleton , Massachusetts
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15
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Badawi Y, Nishimune H. Presynaptic active zones of mammalian neuromuscular junctions: Nanoarchitecture and selective impairments in aging. Neurosci Res 2017; 127:78-88. [PMID: 29221906 DOI: 10.1016/j.neures.2017.11.014] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Revised: 11/17/2017] [Accepted: 11/27/2017] [Indexed: 12/16/2022]
Abstract
Neurotransmitter release occurs at active zones, which are specialized regions of the presynaptic membrane. A dense collection of proteins at the active zone provides a platform for molecular interactions that promote recruitment, docking, and priming of synaptic vesicles. At mammalian neuromuscular junctions (NMJs), muscle-derived laminin β2 interacts with presynaptic voltage-gated calcium channels to organize active zones. The molecular architecture of presynaptic active zones has been revealed using super-resolution microscopy techniques that combine nanoscale resolution and multiple molecular identification. Interestingly, the active zones of adult NMJs are not stable structures and thus become impaired during aging due to the selective degeneration of specific active zone proteins. This review will discuss recent progress in the understanding of active zone nanoarchitecture and the mechanisms underlying active zone organization in mammalian NMJs. Furthermore, we will summarize the age-related degeneration of active zones at NMJs, and the role of exercise in maintaining active zones.
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Affiliation(s)
- Yomna Badawi
- Department of Anatomy and Cell Biology, University of Kansas School of Medicine, Kansas City, KS, 66160, USA
| | - Hiroshi Nishimune
- Department of Anatomy and Cell Biology, University of Kansas School of Medicine, Kansas City, KS, 66160, USA.
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16
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Abstract
At each of the brain's vast number of synapses, the presynaptic nerve terminal, synaptic cleft, and postsynaptic specialization form a transcellular unit to enable efficient transmission of information between neurons. While we know much about the molecular machinery within each compartment, we are only beginning to understand how these compartments are structurally registered and functionally integrated with one another. This review will describe the organization of each compartment and then discuss their alignment across pre- and postsynaptic cells at a nanometer scale. We propose that this architecture may allow for precise synaptic information exchange and may be modulated to contribute to the remarkable plasticity of brain function.
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Affiliation(s)
- Thomas Biederer
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA.
| | - Pascal S Kaeser
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
| | - Thomas A Blanpied
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
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17
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Biederer T, Kaeser PS, Blanpied TA. Transcellular Nanoalignment of Synaptic Function. Neuron 2017; 96:680-696. [PMID: 29096080 PMCID: PMC5777221 DOI: 10.1016/j.neuron.2017.10.006] [Citation(s) in RCA: 213] [Impact Index Per Article: 30.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2017] [Revised: 09/29/2017] [Accepted: 10/03/2017] [Indexed: 12/21/2022]
Abstract
At each of the brain's vast number of synapses, the presynaptic nerve terminal, synaptic cleft, and postsynaptic specialization form a transcellular unit to enable efficient transmission of information between neurons. While we know much about the molecular machinery within each compartment, we are only beginning to understand how these compartments are structurally registered and functionally integrated with one another. This review will describe the organization of each compartment and then discuss their alignment across pre- and postsynaptic cells at a nanometer scale. We propose that this architecture may allow for precise synaptic information exchange and may be modulated to contribute to the remarkable plasticity of brain function.
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Affiliation(s)
- Thomas Biederer
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA.
| | - Pascal S Kaeser
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
| | - Thomas A Blanpied
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
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18
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Ge D, Lavidis N. Seasonal factors influence quantal transmitter release and calcium dependence at amphibian neuromuscular junctions. Am J Physiol Regul Integr Comp Physiol 2017. [PMID: 28637657 DOI: 10.1152/ajpregu.00070.2017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Amphibian neuromuscular junctions (NMJs) are composed of hundreds of neurotransmitter release sites that exhibit nonuniform transmitter release probabilities and demonstrated seasonal modulation. We examined whether recruitment of release sites is variable when the extracellular calcium concentration ([Ca2+]o) is increased in the wet and dry seasons. The amount of transmitter released from the entire nerve terminal increases by approximately the fourth power as [Ca2+]o is increased. Toad (Bufo marinus) NMJs were visualized using 3,3'-diethyloxardicarbocyanine iodide [DiOC2(5)] fluorescence, and focal loose patch extracellular recordings were used to record the end-plate currents (EPCs) from small groups of release sites. Quantal content (m̄e ), average probability of quantal release (pe ), and the number of active release sites (ne ) were determined for different [Ca2+]o Our results indicated that the recruitment of quantal release sites with increasing [Ca2+]o differs spatially (between different groups of release sites) and also temporally (in different seasons). These differences were reflected by the nonuniform alterations in pe and ne Most release site groups demonstrated an increase in both pe and ne when [Ca2+]o increased. In ~30% of release site groups examined, pe decreased while ne increased only during the active period (wet season). Although the dry season induced parallel right shift in the quantal release versus extracellular calcium concentration when compared with the wet season, the dependence of quantal content on [Ca2+]o was not changed. These results demonstrate the flexibility, reserve, and adaptive capacity of neuromuscular junctions in maintaining appropriate levels of neurotransmission.
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Affiliation(s)
- Dengyun Ge
- School of Biomedical Sciences, The University of Queensland, St. Lucia, Australia
| | - Nickolas Lavidis
- School of Biomedical Sciences, The University of Queensland, St. Lucia, Australia
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19
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Stanley EF. Single calcium channel domain gating of synaptic vesicle fusion at fast synapses; analysis by graphic modeling. Channels (Austin) 2016; 9:324-33. [PMID: 26457441 PMCID: PMC4826128 DOI: 10.1080/19336950.2015.1098793] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
At fast-transmitting presynaptic terminals Ca2+ enter through voltage gated calcium channels (CaVs) and bind to a synaptic vesicle (SV) -associated calcium sensor (SV-sensor) to gate fusion and discharge. An open CaV generates a high-concentration plume, or nanodomain of Ca2+ that dissipates precipitously with distance from the pore. At most fast synapses, such as the frog neuromuscular junction (NMJ), the SV sensors are located sufficiently close to individual CaVs to be gated by single nanodomains. However, at others, such as the mature rodent calyx of Held (calyx of Held), the physiology is more complex with evidence that CaVs that are both close and distant from the SV sensor and it is argued that release is gated primarily by the overlapping Ca2+ nanodomains from many CaVs. We devised a 'graphic modeling' method to sum Ca2+ from individual CaVs located at varying distances from the SV-sensor to determine the SV release probability and also the fraction of that probability that can be attributed to single domain gating. This method was applied first to simplified, low and high CaV density model release sites and then to published data on the contrasting frog NMJ and the rodent calyx of Held native synapses. We report 3 main predictions: the SV-sensor is positioned very close to the point at which the SV fuses with the membrane; single domain-release gating predominates even at synapses where the SV abuts a large cluster of CaVs, and even relatively remote CaVs can contribute significantly to single domain-based gating.
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Affiliation(s)
- Elise F Stanley
- a Toronto Western Research Institute ; Toronto , Ontario Canada
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20
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Tang AH, Chen H, Li TP, Metzbower SR, MacGillavry HD, Blanpied TA. A trans-synaptic nanocolumn aligns neurotransmitter release to receptors. Nature 2016; 536:210-4. [PMID: 27462810 PMCID: PMC5002394 DOI: 10.1038/nature19058] [Citation(s) in RCA: 425] [Impact Index Per Article: 53.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Accepted: 06/27/2016] [Indexed: 12/29/2022]
Abstract
Synaptic transmission is maintained by a delicate, sub-synaptic molecular architecture, and even mild alterations in synapse structure drive functional changes during experience-dependent plasticity and pathological disorders. Key to this architecture is how the distribution of presynaptic vesicle fusion sites corresponds to the position of receptors in the postsynaptic density. However, while it has long been recognized that this spatial relationship modulates synaptic strength, it has not been precisely described, owing in part to the limited resolution of light microscopy. Using localization microscopy, here we show that key proteins mediating vesicle priming and fusion are mutually co-enriched within nanometre-scale subregions of the presynaptic active zone. Through development of a new method to map vesicle fusion positions within single synapses in cultured rat hippocampal neurons, we find that action-potential-evoked fusion is guided by this protein gradient and occurs preferentially in confined areas with higher local density of Rab3-interacting molecule (RIM) within the active zones. These presynaptic RIM nanoclusters closely align with concentrated postsynaptic receptors and scaffolding proteins, suggesting the existence of a trans-synaptic molecular 'nanocolumn'. Thus, we propose that the nanoarchitecture of the active zone directs action-potential-evoked vesicle fusion to occur preferentially at sites directly opposing postsynaptic receptor-scaffold ensembles. Remarkably, NMDA receptor activation triggered distinct phases of plasticity in which postsynaptic reorganization was followed by trans-synaptic nanoscale realignment. This architecture suggests a simple organizational principle of central nervous system synapses to maintain and modulate synaptic efficiency.
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21
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Abstract
The priming of a docked synaptic vesicle determines the probability of its membrane (VM) fusing with the presynaptic membrane (PM) when a nerve impulse arrives. To gain insight into the nature of priming, we searched by electron tomography for structural relationships correlated with fusion probability at active zones of axon terminals at frog neuromuscular junctions. For terminals fixed at rest, the contact area between the VM of docked vesicles and PM varied >10-fold with a normal distribution. There was no merging of the membranes. For terminals fixed during repetitive evoked synaptic transmission, the normal distribution of contact areas was shifted to the left, due in part to a decreased number of large contact areas, and there was a subpopulation of large contact areas where the membranes were hemifused, an intermediate preceding complete fusion. Thus, fusion probability of a docked vesicle is related to the extent of its VM-PM contact area. For terminals fixed 1 h after activity, the distribution of contact areas recovered to that at rest, indicating the extent of a VM-PM contact area is dynamic and in equilibrium. The extent of VM-PM contact areas in resting terminals correlated with eccentricity in vesicle shape caused by force toward the PM and with shortness of active zone material macromolecules linking vesicles to PM components, some thought to include Ca(2+) channels. We propose that priming is a variable continuum of events imposing variable fusion probability on each vesicle and is regulated by force-generating shortening of active zone material macromolecules in dynamic equilibrium.
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22
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Affiliation(s)
- Markus Dittrich
- a Department of Neuroscience , Center for Neuroscience, University of Pittsburgh , Pittsburgh , PA , USA.,b Pittsburgh Supercomputing Center , Carnegie Mellon University , Pittsburgh , PA , USA
| | - Stephen D Meriney
- a Department of Neuroscience , Center for Neuroscience, University of Pittsburgh , Pittsburgh , PA , USA
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23
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Beske PH, Bradford AB, Grynovicki JO, Glotfelty EJ, Hoffman KM, Hubbard KS, Tuznik KM, McNutt PM. Botulinum and Tetanus Neurotoxin-Induced Blockade of Synaptic Transmission in Networked Cultures of Human and Rodent Neurons. Toxicol Sci 2015; 149:503-15. [PMID: 26615023 DOI: 10.1093/toxsci/kfv254] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Clinical manifestations of tetanus and botulism result from an intricate series of interactions between clostridial neurotoxins (CNTs) and nerve terminal proteins that ultimately cause proteolytic cleavage of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins and functional blockade of neurotransmitter release. Although detection of cleaved SNARE proteins is routinely used as a molecular readout of CNT intoxication in cultured cells, impaired synaptic function is the pathophysiological basis of clinical disease. Work in our laboratory has suggested that the blockade of synaptic neurotransmission in networked neuron cultures offers a phenotypic readout of CNT intoxication that more closely replicates the functional endpoint of clinical disease. Here, we explore the value of measuring spontaneous neurotransmission frequencies as novel and functionally relevant readouts of CNT intoxication. The generalizability of this approach was confirmed in primary neuron cultures as well as human and mouse stem cell-derived neurons exposed to botulinum neurotoxin serotypes A-G and tetanus neurotoxin. The sensitivity and specificity of synaptic activity as a reporter of intoxication was evaluated in assays representing the principal clinical and research purposes of in vivo studies. Our findings confirm that synaptic activity offers a novel and functionally relevant readout for the in vitro characterizations of CNTs. They further suggest that the analysis of synaptic activity in neuronal cell cultures can serve as a surrogate for neuromuscular paralysis in the mouse lethal assay, and therefore is expected to significantly reduce the need for terminal animal use in toxin studies and facilitate identification of candidate therapeutics in cell-based screening assays.
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Affiliation(s)
- Phillip H Beske
- Cellular and Molecular Biology Branch, Research Division, United States Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, Maryland
| | - Aaron B Bradford
- Cellular and Molecular Biology Branch, Research Division, United States Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, Maryland
| | - Justin O Grynovicki
- Cellular and Molecular Biology Branch, Research Division, United States Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, Maryland
| | - Elliot J Glotfelty
- Cellular and Molecular Biology Branch, Research Division, United States Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, Maryland
| | - Katie M Hoffman
- Cellular and Molecular Biology Branch, Research Division, United States Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, Maryland
| | - Kyle S Hubbard
- Cellular and Molecular Biology Branch, Research Division, United States Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, Maryland
| | - Kaylie M Tuznik
- Cellular and Molecular Biology Branch, Research Division, United States Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, Maryland
| | - Patrick M McNutt
- Cellular and Molecular Biology Branch, Research Division, United States Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, Maryland
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24
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Abstract
The first synapses transmitting visual information contain an unusual organelle, the ribbon, which is involved in the transport and priming of vesicles to be released at the active zone. The ribbon is one of many design features that allow efficient refilling of the active zone, which in turn enables graded changes in membrane potential to be transmitted using a continuous mode of neurotransmitter release. The ribbon also plays a key role in supplying vesicles for rapid and transient bursts of release that signal fast changes, such as the onset of light. We increasingly understand how the physiological properties of ribbon synapses determine basic transformations of the visual signal and, in particular, how the process of refilling the active zone regulates the gain and adaptive properties of the retinal circuit. The molecular basis of ribbon function is, however, far from clear.
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Affiliation(s)
- Leon Lagnado
- School of Life Sciences, University of Sussex, Brighton BN1 9QG, United Kingdom;
| | - Frank Schmitz
- Department of Neuroanatomy, Institute for Anatomy and Cell Biology, Medical School Saarland University, Homburg/Saar, Germany;
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25
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Slater CR. The functional organization of motor nerve terminals. Prog Neurobiol 2015; 134:55-103. [DOI: 10.1016/j.pneurobio.2015.09.004] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Revised: 08/28/2015] [Accepted: 09/05/2015] [Indexed: 12/19/2022]
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26
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Stanley EF. PresyNaptic calcium channels: why is P selected before N? Biophys J 2015; 108:451-2. [PMID: 25650909 DOI: 10.1016/j.bpj.2014.12.021] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Revised: 12/05/2014] [Accepted: 12/08/2014] [Indexed: 11/30/2022] Open
Affiliation(s)
- Elise F Stanley
- Toronto Western Research Institute, Toronto, Ontario, Canada.
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27
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Wichmann C. Molecularly and structurally distinct synapses mediate reliable encoding and processing of auditory information. Hear Res 2015; 330:178-90. [PMID: 26188105 DOI: 10.1016/j.heares.2015.07.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/12/2015] [Revised: 06/21/2015] [Accepted: 07/10/2015] [Indexed: 01/20/2023]
Abstract
Hearing impairment is the most common human sensory deficit. Considering the sophisticated anatomy and physiology of the auditory system, disease-related failures frequently occur. To meet the demands of the neuronal circuits responsible for processing auditory information, the synapses of the lower auditory pathway are anatomically and functionally specialized to process acoustic information indefatigably with utmost temporal precision. Despite sharing some functional properties, the afferent synapses of the cochlea and of auditory brainstem differ greatly in their morphology and employ distinct molecular mechanisms for regulating synaptic vesicle release. Calyceal synapses of the endbulb of Held and the calyx of Held profit from a large number of release sites that project onto one principal cell. Cochlear inner hair cell ribbon synapses exhibit a unique one-to-one relation of the presynaptic active zone to the postsynaptic cell and use hair-cell-specific proteins such as otoferlin for vesicle release. The understanding of the molecular physiology of the hair cell ribbon synapse has been advanced by human genetics studies of sensorineural hearing impairment, revealing human auditory synaptopathy as a new nosological entity.
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Affiliation(s)
- Carolin Wichmann
- Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience & InnerEarLab, University Medical Center, Göttingen, Germany.
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28
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Saveliev A, Khuzakhmetova V, Samigullin D, Skorinkin A, Kovyazina I, Nikolsky E, Bukharaeva E. Bayesian analysis of the kinetics of quantal transmitter secretion at the neuromuscular junction. J Comput Neurosci 2015; 39:119-29. [PMID: 26129670 DOI: 10.1007/s10827-015-0567-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Revised: 06/15/2015] [Accepted: 06/19/2015] [Indexed: 11/29/2022]
Abstract
The timing of transmitter release from nerve endings is considered nowadays as one of the factors determining the plasticity and efficacy of synaptic transmission. In the neuromuscular junction, the moments of release of individual acetylcholine quanta are related to the synaptic delays of uniquantal endplate currents recorded under conditions of lowered extracellular calcium. Using Bayesian modelling, we performed a statistical analysis of synaptic delays in mouse neuromuscular junction with different patterns of rhythmic nerve stimulation and when the entry of calcium ions into the nerve terminal was modified. We have obtained a statistical model of the release timing which is represented as the summation of two independent statistical distributions. The first of these is the exponentially modified Gaussian distribution. The mixture of normal and exponential components in this distribution can be interpreted as a two-stage mechanism of early and late periods of phasic synchronous secretion. The parameters of this distribution depend on both the stimulation frequency of the motor nerve and the calcium ions' entry conditions. The second distribution was modelled as quasi-uniform, with parameters independent of nerve stimulation frequency and calcium entry. Two different probability density functions for the distribution of synaptic delays suggest at least two independent processes controlling the time course of secretion, one of them potentially involving two stages. The relative contribution of these processes to the total number of mediator quanta released depends differently on the motor nerve stimulation pattern and on calcium ion entry into nerve endings.
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Affiliation(s)
- Anatoly Saveliev
- Kazan Federal University, Kremlevskaya St. 18, Kazan, 420008, Russia
| | - Venera Khuzakhmetova
- Kazan Federal University, Kremlevskaya St. 18, Kazan, 420008, Russia.,Laboratory of the Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, P.O. Box 30, Kazan, 420111, Russia
| | - Dmitry Samigullin
- Kazan Federal University, Kremlevskaya St. 18, Kazan, 420008, Russia.,Laboratory of the Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, P.O. Box 30, Kazan, 420111, Russia.,Kazan National Research Technical University named after A. N. Tupolev, K. Marx St. 10, Kazan, 420111, Russia
| | - Andrey Skorinkin
- Kazan Federal University, Kremlevskaya St. 18, Kazan, 420008, Russia.,Laboratory of the Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, P.O. Box 30, Kazan, 420111, Russia
| | - Irina Kovyazina
- Kazan Federal University, Kremlevskaya St. 18, Kazan, 420008, Russia.,Laboratory of the Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, P.O. Box 30, Kazan, 420111, Russia
| | - Eugeny Nikolsky
- Kazan Federal University, Kremlevskaya St. 18, Kazan, 420008, Russia.,Laboratory of the Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, P.O. Box 30, Kazan, 420111, Russia.,Kazan State Medical University, Butlerov St. 49, Kazan, 420012, Russia
| | - Ellya Bukharaeva
- Kazan Federal University, Kremlevskaya St. 18, Kazan, 420008, Russia. .,Laboratory of the Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, P.O. Box 30, Kazan, 420111, Russia.
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29
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Luo F, Dittrich M, Cho S, Stiles JR, Meriney SD. Transmitter release is evoked with low probability predominately by calcium flux through single channel openings at the frog neuromuscular junction. J Neurophysiol 2015; 113:2480-9. [PMID: 25652927 DOI: 10.1152/jn.00879.2014] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2014] [Accepted: 01/31/2015] [Indexed: 01/07/2023] Open
Abstract
The quantitative relationship between presynaptic calcium influx and transmitter release critically depends on the spatial coupling of presynaptic calcium channels to synaptic vesicles. When there is a close association between calcium channels and synaptic vesicles, the flux through a single open calcium channel may be sufficient to trigger transmitter release. With increasing spatial distance, however, a larger number of open calcium channels might be required to contribute sufficient calcium ions to trigger vesicle fusion. Here we used a combination of pharmacological calcium channel block, high-resolution calcium imaging, postsynaptic recording, and 3D Monte Carlo reaction-diffusion simulations in the adult frog neuromuscular junction, to show that release of individual synaptic vesicles is predominately triggered by calcium ions entering the nerve terminal through the nearest open calcium channel. Furthermore, calcium ion flux through this channel has a low probability of triggering synaptic vesicle fusion (∼6%), even when multiple channels open in a single active zone. These mechanisms work to control the rare triggering of vesicle fusion in the frog neuromuscular junction from each of the tens of thousands of individual release sites at this large model synapse.
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Affiliation(s)
- Fujun Luo
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; Center for the Neural Basis of Cognition, Pittsburgh, Pennsylvania
| | - Markus Dittrich
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; Biomedical Applications Group, Pittsburgh Supercomputing Center, Carnegie Mellon University, Pittsburgh, Pennsylvania; and Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Soyoun Cho
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Joel R Stiles
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; Biomedical Applications Group, Pittsburgh Supercomputing Center, Carnegie Mellon University, Pittsburgh, Pennsylvania; and Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Stephen D Meriney
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; Center for the Neural Basis of Cognition, Pittsburgh, Pennsylvania;
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30
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Ma J, Kelly L, Ingram J, Price TJ, Meriney SD, Dittrich M. New insights into short-term synaptic facilitation at the frog neuromuscular junction. J Neurophysiol 2014; 113:71-87. [PMID: 25210157 DOI: 10.1152/jn.00198.2014] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Short-term synaptic facilitation occurs during high-frequency stimulation, is known to be dependent on presynaptic calcium ions, and persists for tens of milliseconds after a presynaptic action potential. We have used the frog neuromuscular junction as a model synapse for both experimental and computer simulation studies aimed at testing various mechanistic hypotheses proposed to underlie short-term synaptic facilitation. Building off our recently reported excess-calcium-binding-site model of synaptic vesicle release at the frog neuromuscular junction (Dittrich M, Pattillo JM, King JD, Cho S, Stiles JR, Meriney SD. Biophys J 104: 2751-2763, 2013), we have investigated several mechanisms of short-term facilitation at the frog neuromuscular junction. Our studies place constraints on previously proposed facilitation mechanisms and conclude that the presence of a second class of calcium sensor proteins distinct from synaptotagmin can explain known properties of facilitation observed at the frog neuromuscular junction. We were further able to identify a novel facilitation mechanism, which relied on the persistent binding of calcium-bound synaptotagmin molecules to lipids of the presynaptic membrane. In a real physiological context, both mechanisms identified in our study (and perhaps others) may act simultaneously to cause the experimentally observed facilitation. In summary, using a combination of computer simulations and physiological recordings, we have developed a stochastic computer model of synaptic transmission at the frog neuromuscular junction, which sheds light on the facilitation mechanisms in this model synapse.
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Affiliation(s)
- Jun Ma
- Biomedical Applications Group, Pittsburgh Supercomputing Center, Carnegie Mellon University, Pittsburgh, Pennsylvania; Joint Carnegie Mellon-University of Pittsburgh PhD Program in Computational Biology, School of Computer Science, Carnegie Mellon University, Pittsburgh, Pennsylvania
| | - Lauren Kelly
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; and
| | - Justin Ingram
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; and
| | - Thomas J Price
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; and
| | - Stephen D Meriney
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; and
| | - Markus Dittrich
- Biomedical Applications Group, Pittsburgh Supercomputing Center, Carnegie Mellon University, Pittsburgh, Pennsylvania; Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; and Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
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31
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Tarr TB, Wipf P, Meriney SD. Synaptic Pathophysiology and Treatment of Lambert-Eaton Myasthenic Syndrome. Mol Neurobiol 2014; 52:456-63. [PMID: 25195700 DOI: 10.1007/s12035-014-8887-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2014] [Accepted: 08/29/2014] [Indexed: 12/12/2022]
Abstract
Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease that disrupts the normally reliable neurotransmission at the neuromuscular junction (NMJ). This disruption is thought to result from an autoantibody-mediated removal of a subset of the P/Q-type Ca(2+) channels involved with neurotransmitter release. With less neurotransmitter release at the NMJ, LEMS patients experience debilitating muscle weakness. The underlying cause of LEMS in slightly more than half of all patients is small cell lung cancer, and cancer therapy is the priority for these patients. In the remaining cases, the cause of LEMS is unknown, and these patients often rely on symptomatic treatment options, as there is no cure. However, current symptomatic treatment options, such as 3,4-diaminopyridine (3,4-DAP), can have significant dose-limiting side effects; thus, additional treatment approaches would benefit LEMS patients. Recent studies introduced a novel Ca(2+) channel agonist (GV-58) as a potential therapeutic alternative for LEMS. Additionally, this work has shown that GV-58 and 3,4-DAP interact in a supra-additive manner to completely restore the magnitude of neurotransmitter release at the NMJs of a LEMS mouse model. In this review, we discuss synaptic mechanisms for reliability at the NMJ and how these mechanisms are disrupted in LEMS. We then discuss the current treatment options for LEMS patients, while also considering recent work demonstrating the therapeutic potential of GV-58 alone and in combination with 3,4-DAP.
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Affiliation(s)
- Tyler B Tarr
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA, 15260, USA
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32
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Meriney SD, Umbach JA, Gundersen CB. Fast, Ca2+-dependent exocytosis at nerve terminals: shortcomings of SNARE-based models. Prog Neurobiol 2014; 121:55-90. [PMID: 25042638 DOI: 10.1016/j.pneurobio.2014.07.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Revised: 04/14/2014] [Accepted: 07/03/2014] [Indexed: 11/30/2022]
Abstract
Investigations over the last two decades have made major inroads in clarifying the cellular and molecular events that underlie the fast, synchronous release of neurotransmitter at nerve endings. Thus, appreciable progress has been made in establishing the structural features and biophysical properties of the calcium (Ca2+) channels that mediate the entry into nerve endings of the Ca2+ ions that trigger neurotransmitter release. It is now clear that presynaptic Ca2+ channels are regulated at many levels and the interplay of these regulatory mechanisms is just beginning to be understood. At the same time, many lines of research have converged on the conclusion that members of the synaptotagmin family serve as the primary Ca2+ sensors for the action potential-dependent release of neurotransmitter. This identification of synaptotagmins as the proteins which bind Ca2+ and initiate the exocytotic fusion of synaptic vesicles with the plasma membrane has spurred widespread efforts to reveal molecular details of synaptotagmin's action. Currently, most models propose that synaptotagmin interfaces directly or indirectly with SNARE (soluble, N-ethylmaleimide sensitive factor attachment receptors) proteins to trigger membrane fusion. However, in spite of intensive efforts, the field has not achieved consensus on the mechanism by which synaptotagmins act. Concurrently, the precise sequence of steps underlying SNARE-dependent membrane fusion remains controversial. This review considers the pros and cons of the different models of SNARE-mediated membrane fusion and concludes by discussing a novel proposal in which synaptotagmins might directly elicit membrane fusion without the intervention of SNARE proteins in this final fusion step.
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Affiliation(s)
- Stephen D Meriney
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Joy A Umbach
- Department of Molecular and Medical Pharmacology, UCLA David Geffen School of Medicine, Los Angeles, CA 90095, USA
| | - Cameron B Gundersen
- Department of Molecular and Medical Pharmacology, UCLA David Geffen School of Medicine, Los Angeles, CA 90095, USA.
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33
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Wong FK, Nath AR, Chen RHC, Gardezi SR, Li Q, Stanley EF. Synaptic vesicle tethering and the CaV2.2 distal C-terminal. Front Cell Neurosci 2014; 8:71. [PMID: 24639630 PMCID: PMC3945931 DOI: 10.3389/fncel.2014.00071] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2013] [Accepted: 02/18/2014] [Indexed: 01/18/2023] Open
Abstract
Evidence that synaptic vesicles (SVs) can be gated by a single voltage sensitive calcium channel (CaV2.2) predict a molecular linking mechanism or "tether" (Stanley, 1993). Recent studies have proposed that the SV binds to the distal C-terminal on the CaV2.2 calcium channel (Kaeser et al., 2011; Wong et al., 2013) while genetic analysis proposed a double tether mechanism via RIM: directly to the C terminus PDZ ligand domain or indirectly via a more proximal proline rich site (Kaeser et al., 2011). Using a novel in vitro SV pull down binding assay, we reported that SVs bind to a fusion protein comprising the C-terminal distal third (C3, aa 2137-2357; Wong et al., 2013). Here we limit the binding site further to the last 58 aa, beyond the proline rich site, by the absence of SV capture by a truncated C3 fusion protein (aa 2137-2299). To test PDZ-dependent binding we generated two C terminus-mutant C3 fusion proteins and a mimetic blocking peptide (H-WC, aa 2349-2357) and validated these by elimination of MINT-1 or RIM binding. Persistence of SV capture with all three fusion proteins or with the full length C3 protein but in the presence of blocking peptide, demonstrated that SVs can bind to the distal C-terminal via a PDZ-independent mechanism. These results were supported in situ by normal SV turnover in H-WC-loaded synaptosomes, as assayed by a novel peptide cryoloading method. Thus, SVs tether to the CaV2.2 C-terminal within a 49 aa region immediately prior to the terminus PDZ ligand domain. Long tethers that could reflect extended C termini were imaged by electron microscopy of synaptosome ghosts. To fully account for SV tethering we propose a model where SVs are initially captured, or "grabbed," from the cytoplasm by a binding site on the distal region of the channel C-terminal and are then retracted to be "locked" close to the channel by a second attachment mechanism in preparation for single channel domain gating.
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Affiliation(s)
- Fiona K Wong
- Laboratory of Synaptic Transmission, Toronto Western Research Institute Toronto, ON, Canada
| | - Arup R Nath
- Laboratory of Synaptic Transmission, Toronto Western Research Institute Toronto, ON, Canada
| | - Robert H C Chen
- Laboratory of Synaptic Transmission, Toronto Western Research Institute Toronto, ON, Canada
| | - Sabiha R Gardezi
- Laboratory of Synaptic Transmission, Toronto Western Research Institute Toronto, ON, Canada
| | - Qi Li
- Laboratory of Synaptic Transmission, Toronto Western Research Institute Toronto, ON, Canada
| | - Elise F Stanley
- Laboratory of Synaptic Transmission, Toronto Western Research Institute Toronto, ON, Canada
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Dittrich M, Pattillo JM, King JD, Cho S, Stiles JR, Meriney SD. An excess-calcium-binding-site model predicts neurotransmitter release at the neuromuscular junction. Biophys J 2014; 104:2751-63. [PMID: 23790384 DOI: 10.1016/j.bpj.2013.05.023] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Revised: 05/02/2013] [Accepted: 05/06/2013] [Indexed: 10/26/2022] Open
Abstract
Despite decades of intense experimental studies, we still lack a detailed understanding of synaptic function. Fortunately, using computational approaches, we can obtain important new insights into the inner workings of these important neural systems. Here, we report the development of a spatially realistic computational model of an entire frog active zone in which we constrained model parameters with experimental data, and then used Monte Carlo simulation methods to predict the Ca(2+)-binding stoichiometry and dynamics that underlie neurotransmitter release. Our model reveals that 20-40 independent Ca(2+)-binding sites on synaptic vesicles, only a fraction of which need to bind Ca(2+) to trigger fusion, are sufficient to predict physiological release. Our excess-Ca(2+)-binding-site model has many functional advantages, agrees with recent data on synaptotagmin copy number, and is the first (to our knowledge) to link detailed physiological observations with the molecular machinery of Ca(2+)-triggered exocytosis. In addition, our model provides detailed microscopic insight into the underlying Ca(2+) dynamics during synapse activation.
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Affiliation(s)
- Markus Dittrich
- National Resource for Biomedical Supercomputing, Pittsburgh Supercomputing Center, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA.
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Bosch-Bouju C, Hyland BI, Parr-Brownlie LC. Motor thalamus integration of cortical, cerebellar and basal ganglia information: implications for normal and parkinsonian conditions. Front Comput Neurosci 2013; 7:163. [PMID: 24273509 PMCID: PMC3822295 DOI: 10.3389/fncom.2013.00163] [Citation(s) in RCA: 147] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Accepted: 10/24/2013] [Indexed: 12/23/2022] Open
Abstract
Motor thalamus (Mthal) is implicated in the control of movement because it is strategically located between motor areas of the cerebral cortex and motor-related subcortical structures, such as the cerebellum and basal ganglia (BG). The role of BG and cerebellum in motor control has been extensively studied but how Mthal processes inputs from these two networks is unclear. Specifically, there is considerable debate about the role of BG inputs on Mthal activity. This review summarizes anatomical and physiological knowledge of the Mthal and its afferents and reviews current theories of Mthal function by discussing the impact of cortical, BG and cerebellar inputs on Mthal activity. One view is that Mthal activity in BG and cerebellar-receiving territories is primarily "driven" by glutamatergic inputs from the cortex or cerebellum, respectively, whereas BG inputs are modulatory and do not strongly determine Mthal activity. This theory is steeped in the assumption that the Mthal processes information in the same way as sensory thalamus, through interactions of modulatory inputs with a single driver input. Another view, from BG models, is that BG exert primary control on the BG-receiving Mthal so it effectively relays information from BG to cortex. We propose a new "super-integrator" theory where each Mthal territory processes multiple driver or driver-like inputs (cortex and BG, cortex and cerebellum), which are the result of considerable integrative processing. Thus, BG and cerebellar Mthal territories assimilate motivational and proprioceptive motor information previously integrated in cortico-BG and cortico-cerebellar networks, respectively, to develop sophisticated motor signals that are transmitted in parallel pathways to cortical areas for optimal generation of motor programmes. Finally, we briefly review the pathophysiological changes that occur in the BG in parkinsonism and generate testable hypotheses about how these may affect processing of inputs in the Mthal.
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Affiliation(s)
- Clémentine Bosch-Bouju
- 1Department of Anatomy, Otago School of Medical Science, University of Otago Dunedin, New Zealand ; 2Brain Health Research Centre, Otago School of Medical Science, University of Otago Dunedin, New Zealand
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36
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Evaluation of a novel calcium channel agonist for therapeutic potential in Lambert-Eaton myasthenic syndrome. J Neurosci 2013; 33:10559-67. [PMID: 23785168 DOI: 10.1523/jneurosci.4629-12.2013] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
We developed a novel calcium (Ca(2+)) channel agonist that is selective for N- and P/Q-type Ca(2+) channels, which are the Ca(2+) channels that regulate transmitter release at most synapses. We have shown that this new molecule (GV-58) slows the deactivation of channels, resulting in a large increase in presynaptic Ca(2+) entry during activity. GV-58 was developed as a modification of (R)-roscovitine, which was previously shown to be a Ca(2+) channel agonist, in addition to its known cyclin-dependent kinase activity. In comparison with the parent molecule, (R)-roscovitine, GV-58 has a ∼20-fold less potent cyclin-dependent kinase antagonist effect, a ∼3- to 4-fold more potent Ca(2+) channel agonist effect, and ∼4-fold higher efficacy as a Ca(2+) channel agonist. We have further evaluated GV-58 in a passive transfer mouse model of Lambert-Eaton myasthenic syndrome and have shown that weakened Lambert-Eaton myasthenic syndrome-model neuromuscular synapses are significantly strengthened following exposure to GV-58. This new Ca(2+) channel agonist has potential as a lead compound in the development of new therapeutic approaches to a variety of disorders that result in neuromuscular weakness.
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Meriney SD, Dittrich M. Organization and function of transmitter release sites at the neuromuscular junction. J Physiol 2013; 591:3159-65. [PMID: 23613535 PMCID: PMC3717219 DOI: 10.1113/jphysiol.2012.248625] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Accepted: 04/09/2013] [Indexed: 12/18/2022] Open
Abstract
The neuromuscular junction is known as a strong and reliable synapse. It is strong because it releases an excess of chemical transmitter, beyond what is required to bring the postsynaptic muscle cell to threshold. Because the synapse can sustain suprathreshold muscle activation during short trains of action potentials, it is also reliable. The presynaptic mechanisms that lead to reliability during short trains of activity have only recently been elucidated. It appears that there are relatively few calcium channels in individual active zones, that channels open with a low probability during action potential stimulation and that even if channels open the resulting calcium flux only rarely triggers vesicle fusion. Thus, each synaptic vesicle may only associate with a small number of calcium channels, forming an unreliable single vesicle release site. Strength and reliability of the neuromuscular junction emerge as a result of its assembly from thousands of these unreliable single vesicle release sites. Hence, these synapses are strong while at the same time only releasing a small subset of available docked vesicles during each action potential, thus conserving transmitter release resources. This prevents significant depression during short trains of action potential activity and confers reliability.
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Affiliation(s)
- Stephen D Meriney
- Department of Neuroscience, University of Pittsburgh, A210 Langley Hall, Pittsburgh, PA 15260, USA.
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