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Engisch KL, Wang X, Rich MM. Homeostatic Plasticity of the Mammalian Neuromuscular Junction. ADVANCES IN NEUROBIOLOGY 2022; 28:111-130. [PMID: 36066823 DOI: 10.1007/978-3-031-07167-6_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The mammalian neuromuscular junction (NMJ) is an ideal preparation to study synaptic plasticity. Its simplicity- one input, one postsynaptic target- allows experimental manipulations and mechanistic analyses that are impossible at more complex synapses. Homeostatic synaptic plasticity attempts to maintain normal function in the face of perturbations in activity. At the NMJ, 3 aspects of activity are sensed to trigger 3 distinct mechanisms that contribute to homeostatic plasticity: Block of presynaptic action potentials triggers increased quantal size secondary to increased release of acetylcholine from vesicles. Simultaneous block of pre- and postsynaptic action potentials triggers an increase in the probability of vesicle release. Block of acetylcholine binding to acetylcholine receptors during spontaneous fusion of single vesicles triggers an increase in the number of releasable vesicles as well as increased motoneuron excitability. Understanding how the NMJ responds to perturbations of synaptic activity informs our understanding of its response to diverse neuromuscular diseases.
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Affiliation(s)
- Kathrin L Engisch
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, USA
| | - Xueyong Wang
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, USA
| | - Mark M Rich
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, USA.
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2
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Zheng JJ, Zhang TY, Liu HT, Huang ZX, Teng JM, Deng JX, Zhong JG, Qian X, Sheng XW, Ding JQ, He SQ, Zhao X, Ji WD, Qi DF, Li W, Zhang M. Cytisine Exerts an Anti-Epileptic Effect via α7nAChRs in a Rat Model of Temporal Lobe Epilepsy. Front Pharmacol 2021; 12:706225. [PMID: 34248648 PMCID: PMC8263902 DOI: 10.3389/fphar.2021.706225] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Accepted: 06/09/2021] [Indexed: 11/13/2022] Open
Abstract
Background and Purpose: Temporal lobe epilepsy (TLE) is a common chronic neurological disease that is often invulnerable to anti-epileptic drugs. Increasing data have demonstrated that acetylcholine (ACh) and cholinergic neurotransmission are involved in the pathophysiology of epilepsy. Cytisine, a full agonist of α7 nicotinic acetylcholine receptors (α7nAChRs) and a partial agonist of α4β2nAChRs, has been widely applied for smoking cessation and has shown neuroprotection in neurological diseases. However, whether cytisine plays a role in treating TLE has not yet been determined. Experimental Approach: In this study, cytisine was injected intraperitoneally into pilocarpine-induced epileptic rats for three weeks. Alpha-bungarotoxin (α-bgt), a specific α7nAChR antagonist, was used to evaluate the mechanism of action of cytisine. Rats were assayed for the occurrence of seizures and cognitive function by video surveillance and Morris water maze. Hippocampal injuries and synaptic structure were assessed by Nissl staining and Golgi staining. Furthermore, levels of glutamate, γ-aminobutyric acid (GABA), ACh, and α7nAChRs were measured. Results: Cytisine significantly reduced seizures and hippocampal damage while improving cognition and inhibiting synaptic remodeling in TLE rats. Additionally, cytisine decreased glutamate levels without altering GABA levels, and increased ACh levels and α7nAChR expression in the hippocampi of TLE rats. α-bgt antagonized the above-mentioned effects of cytisine treatment. Conclusion and Implications: Taken together, these findings indicate that cytisine exerted an anti-epileptic and neuroprotective effect in TLE rats via activation of α7nAChRs, which was associated with a decrease in glutamate levels, inhibition of synaptic remodeling, and improvement of cholinergic transmission in the hippocampus. Hence, our findings not only suggest that cytisine represents a promising anti-epileptic drug, but provides evidence of α7nAChRs as a novel therapeutic target for TLE.
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Affiliation(s)
- Jing-Jun Zheng
- Key Laboratory of Molecular Target and Clinical Pharmacology, Department of Clinical Pharmacology, School of Pharmaceutical Sciences and the Fifth Affiliated Hospital, Guangzhou Medical University, Guangzhou, China.,Department of Pharmacy, Shenzhen Kangning Hospital, Shenzhen Mental Health Center, Shenzhen, China
| | - Teng-Yue Zhang
- Key Laboratory of Molecular Target and Clinical Pharmacology, Department of Clinical Pharmacology, School of Pharmaceutical Sciences and the Fifth Affiliated Hospital, Guangzhou Medical University, Guangzhou, China
| | - Hong-Tao Liu
- Key Laboratory of Molecular Target and Clinical Pharmacology, Department of Clinical Pharmacology, School of Pharmaceutical Sciences and the Fifth Affiliated Hospital, Guangzhou Medical University, Guangzhou, China
| | - Ze-Xin Huang
- Key Laboratory of Molecular Target and Clinical Pharmacology, Department of Clinical Pharmacology, School of Pharmaceutical Sciences and the Fifth Affiliated Hospital, Guangzhou Medical University, Guangzhou, China
| | - Jing-Mei Teng
- Key Laboratory of Molecular Target and Clinical Pharmacology, Department of Clinical Pharmacology, School of Pharmaceutical Sciences and the Fifth Affiliated Hospital, Guangzhou Medical University, Guangzhou, China
| | - Jing-Xian Deng
- Key Laboratory of Molecular Target and Clinical Pharmacology, Department of Clinical Pharmacology, School of Pharmaceutical Sciences and the Fifth Affiliated Hospital, Guangzhou Medical University, Guangzhou, China
| | - Jia-Gui Zhong
- Department of Neurosurgery, The First Affiliated Hospital of Jinan University, Guangzhou, China
| | - Xu Qian
- Key Laboratory of Molecular Target and Clinical Pharmacology, Department of Clinical Pharmacology, School of Pharmaceutical Sciences and the Fifth Affiliated Hospital, Guangzhou Medical University, Guangzhou, China
| | - Xin-Wen Sheng
- Key Laboratory of Molecular Target and Clinical Pharmacology, Department of Clinical Pharmacology, School of Pharmaceutical Sciences and the Fifth Affiliated Hospital, Guangzhou Medical University, Guangzhou, China
| | - Ji-Qiang Ding
- Department of Neurosurgery, The First Affiliated Hospital of Jinan University, Guangzhou, China
| | - Shu-Qiao He
- Department of Pharmacy, Maoming People's Hospital, Maoming, China
| | - Xin Zhao
- Key Laboratory of Molecular Target and Clinical Pharmacology, Department of Clinical Pharmacology, School of Pharmaceutical Sciences and the Fifth Affiliated Hospital, Guangzhou Medical University, Guangzhou, China
| | - Wei-Dong Ji
- Center for Translational Medicine, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - De-Feng Qi
- Department of Urology, Minimally Invasive Surgery Center, The First Affiliated Hop-ital of Guangzhou Medical University, Guangdong Key Laboratory of Urology, Guangzhou, China
| | - Wei Li
- Department of Neurosurgery, The First Affiliated Hospital of Jinan University, Guangzhou, China
| | - Mei Zhang
- Key Laboratory of Molecular Target and Clinical Pharmacology, Department of Clinical Pharmacology, School of Pharmaceutical Sciences and the Fifth Affiliated Hospital, Guangzhou Medical University, Guangzhou, China
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Vilquin JT, Bayer AC, Le Panse R, Berrih-Aknin S. The Muscle Is Not a Passive Target in Myasthenia Gravis. Front Neurol 2020; 10:1343. [PMID: 31920954 PMCID: PMC6930907 DOI: 10.3389/fneur.2019.01343] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Accepted: 12/05/2019] [Indexed: 12/22/2022] Open
Abstract
Myasthenia gravis (MG) is a rare autoimmune disease mediated by pathogenic antibodies (Ab) directed against components of the neuromuscular junction (NMJ), mainly the acetylcholine receptor (AChR). The etiological mechanisms are not totally elucidated, but they include a combination of genetic predisposition, triggering event(s), and hormonal components. MG disease is associated with defective immune regulation, chronic cell activation, inflammation, and the thymus is frequently abnormal. MG is characterized by muscle fatigability that is very invalidating and can be life-threatening when respiratory muscles are affected. MG is not cured, and symptomatic treatments with acetylcholinesterase inhibitors and immunosuppressors are life-long medications associated with severe side effects (especially glucocorticoids). While the muscle is the ultimate target of the autoimmune attack, its place and role are not thoroughly described, and this mini-review will focus on the cascade of pathophysiologic mechanisms taking place at the NMJ and its consequences on the muscle biology, function, and regeneration in myasthenic patients, at the histological, cellular, and molecular levels. The fine structure of the synaptic cleft is damaged by the Ab binding that is coupled to focal complement-dependent lysis in the case of MG with anti-AChR antibodies. Cellular and molecular reactions taking place in the muscle involve several cell types as well as soluble factors. Finally, the regenerative capacities of the MG muscle tissue may be altered. Altogether, the studies reported in this review demonstrate that the muscle is not a passive target in MG, but interacts dynamically with its environment in several ways, activating mechanisms of compensation that limit the pathogenic mechanisms of the autoantibodies.
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Affiliation(s)
- Jean-Thomas Vilquin
- Sorbonne Université, INSERM, Association Institut de Myologie (AIM), Paris, France
| | | | - Rozen Le Panse
- Sorbonne Université, INSERM, Association Institut de Myologie (AIM), Paris, France
| | - Sonia Berrih-Aknin
- Sorbonne Université, INSERM, Association Institut de Myologie (AIM), Paris, France
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Ouanounou G, Baux G, Bal T. A novel synaptic plasticity rule explains homeostasis of neuromuscular transmission. eLife 2016; 5. [PMID: 27138195 PMCID: PMC4854514 DOI: 10.7554/elife.12190] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2015] [Accepted: 04/07/2016] [Indexed: 11/13/2022] Open
Abstract
Excitability differs among muscle fibers and undergoes continuous changes during development and growth, yet the neuromuscular synapse maintains a remarkable fidelity of execution. Here we show in two evolutionarily distant vertebrates (Xenopus laevis cell culture and mouse nerve-muscle ex-vivo) that the skeletal muscle cell constantly senses, through two identified calcium signals, synaptic events and their efficacy in eliciting spikes. These sensors trigger retrograde signal(s) that control presynaptic neurotransmitter release, resulting in synaptic potentiation or depression. In the absence of spikes, synaptic events trigger potentiation. Once the synapse is sufficiently strong to initiate spiking, the occurrence of these spikes activates a negative retrograde feedback. These opposing signals dynamically balance the synapse in order to continuously adjust neurotransmitter release to a level matching current muscle cell excitability. DOI:http://dx.doi.org/10.7554/eLife.12190.001 Nerve cells communicate with each other, and with targets such as muscle cells, at junctions called synapses. The nerve cell before the synapses releases a chemical called a neurotransmitter, which binds to receptors on the cell after the synapses. However, the first cell cannot determine by itself whether it is releasing the correct amount of neurotransmitter to activate its partner. For this, it requires feedback from the second cell. This feedback is particularly important at synapses between nerve cells and muscle cells, which are known as neuromuscular junctions. The likelihood that a given amount of transmitter will activate a muscle cell can vary with age and after exercise. Muscle cells must therefore be able to instruct their nerve cell partners to increase or decrease neurotransmitter release to accommodate these changes. Ouanounou et al. have now identified the mechanism by which muscle cells determine whether nerve cells are releasing an appropriate amount of neurotransmitter. Experiments in two distantly related animals – mice and embryos from a frog called Xenopus – revealed that muscle cells use two calcium-based signals. The first is the flow of calcium ions into the muscle cell in response to binding of neurotransmitter to receptors at the synapses: this tells the muscle cell how active the nerve cell is. The second is the release of calcium ions from internal stores inside the muscle cell: this occurs whenever neurotransmitter release is sufficient to activate the muscle cell. In response to the first calcium signal, the muscle cell sends positive feedback to the neuron, telling it to increase neurotransmitter release further. In response to the second signal, the muscle cell sends negative feedback to reduce neurotransmitter release. Thus, when neurotransmitter release is not enough to activate the muscle, positive feedback dominates and neurotransmitter release increases. However, when the muscle is activated, the two types of feedback act in balance to maintain efficient communication across the synapse. The next steps are to identify the cell signaling cascades that are mobilized by the two calcium signals, including the specific molecule (or molecules) that regulate neurotransmitter release. DOI:http://dx.doi.org/10.7554/eLife.12190.002
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Affiliation(s)
- Gilles Ouanounou
- Unité de Neuroscience Information et Complexité, Centre National de la Recherche Scientifique, FRE 3693, Gif-sur-Yvette, France
| | - Gérard Baux
- Unité de Neuroscience Information et Complexité, Centre National de la Recherche Scientifique, FRE 3693, Gif-sur-Yvette, France
| | - Thierry Bal
- Unité de Neuroscience Information et Complexité, Centre National de la Recherche Scientifique, FRE 3693, Gif-sur-Yvette, France
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Marshall AG, Watson JA, Hallengren JJ, Walters BJ, Dobrunz LE, Francillon L, Wilson JA, Phillips SE, Wilson SM. Genetic background alters the severity and onset of neuromuscular disease caused by the loss of ubiquitin-specific protease 14 (usp14). PLoS One 2013; 8:e84042. [PMID: 24358326 PMCID: PMC3865287 DOI: 10.1371/journal.pone.0084042] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2013] [Accepted: 11/11/2013] [Indexed: 12/14/2022] Open
Abstract
In this study, we identified and characterized an N-ethyl-N-nitrosourea (ENU) induced mutation in Usp14 (nmf375) that leads to adult-onset neurological disease. The nmf375 mutation causes aberrant splicing of Usp14 mRNA, resulting in a 95% reduction in USP14. We previously showed that loss of USP14 in ataxia (ax (J)) mice results in reduced ubiquitin levels, motor endplate disease, Purkinje cell axonal dystrophy and decreased hippocampal paired pulse facilitation (PPF) during the first 4-6 weeks of life, and early postnatal lethality by two months of age. Although the loss of USP14 is comparable between the nmf375 and ax (J) mice, the nmf375 mice did not exhibit these ax (J) developmental abnormalities. However, by 12 weeks of age the nmf375 mutants present with ubiquitin depletion and motor endplate disease, indicating a continual role for USP14-mediated regulation of ubiquitin pools and neuromuscular junction (NMJ) structure in adult mice. The observation that motor endplate disease was only seen after ubiquitin depletion suggests that the preservation of NMJ structure requires the stable maintenance of synaptic ubiquitin pools. Differences in genetic background were shown to affect ubiquitin expression and dramatically alter the phenotypes caused by USP14 deficiency.
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Affiliation(s)
- Andrea G. Marshall
- Department of Neurobiology, Evelyn F. McKnight Brain Institute, Civitan International Research Center, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Jennifer A. Watson
- Department of Neurobiology, Evelyn F. McKnight Brain Institute, Civitan International Research Center, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Jada J. Hallengren
- Department of Neurobiology, Evelyn F. McKnight Brain Institute, Civitan International Research Center, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Brandon J. Walters
- Department of Neurobiology, Evelyn F. McKnight Brain Institute, Civitan International Research Center, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Lynn E. Dobrunz
- Department of Neurobiology, Evelyn F. McKnight Brain Institute, Civitan International Research Center, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Ludwig Francillon
- Department of Neurobiology, Evelyn F. McKnight Brain Institute, Civitan International Research Center, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Julie A. Wilson
- Department of Neurobiology, Evelyn F. McKnight Brain Institute, Civitan International Research Center, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Scott E. Phillips
- Department of Neurobiology, Evelyn F. McKnight Brain Institute, Civitan International Research Center, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Scott M. Wilson
- Department of Neurobiology, Evelyn F. McKnight Brain Institute, Civitan International Research Center, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
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Abstract
In this study we demonstrate that myasthenia gravis, an autoimmune disease strongly identified with deficient acetylcholine receptor transmission at the post-synaptic neuromuscular junction, is accompanied by a profound loss of olfactory function. Twenty-seven MG patients, 27 matched healthy controls, and 11 patients with polymiositis, a disease with peripheral neuromuscular symptoms analogous to myasthenia gravis with no known central nervous system involvement, were tested. All were administered the University of Pennsylvania Smell Identification Test (UPSIT) and the Picture Identification Test (PIT), a test analogous in content and form to the UPSIT designed to control for non-olfactory cognitive confounds. The UPSIT scores of the myasthenia gravis patients were markedly lower than those of the age- and sex-matched normal controls [respective means (SDs) = 20.15 (6.40) & 35.67 (4.95); p<0.0001], as well as those of the polymiositis patients who scored slightly below the normal range [33.30 (1.42); p<0.0001]. The latter finding, along with direct monitoring of the inhalation of the patients during testing, implies that the MG-related olfactory deficit is unlikely due to difficulties sniffing, per se. All PIT scores were within or near the normal range, although subtle deficits were apparent in both the MG and PM patients, conceivably reflecting influences of mild cognitive impairment. No relationships between performance on the UPSIT and thymectomy, time since diagnosis, type of treatment regimen, or the presence or absence of serum anti-nicotinic or muscarinic antibodies were apparent. Our findings suggest that MG influences olfactory function to the same degree as observed in a number of neurodegenerative diseases in which central nervous system cholinergic dysfunction has been documented.
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Ribchester RR. Quantal Analysis of Endplate Potentials in Mouse Flexor Digitorum Brevis Muscle. ACTA ACUST UNITED AC 2011; 1:429-44. [PMID: 26068999 DOI: 10.1002/9780470942390.mo110127] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The isolated flexor digitorum brevis (FDB) muscle from mice is extremely well suited to rapid acquisition of data and analysis of neurotransmitter release and action at neuromuscular junctions, because the muscle and its tibial nerve supply are simple to dissect and its constituent muscle fibers are short (<1 mm) and isopotential along their length. Methods are described here for dissection of FDB, stimulation of the tibial nerve, microelectrode recording from individual muscle fibers, and quantal analysis of endplate potentials (EPPs) and miniature endplate potentials (MEPPs). Curr. Protoc. Mouse Biol. 1:429-444 © 2011 by John Wiley & Sons, Inc.
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Affiliation(s)
- Richard R Ribchester
- Euan MacDonald Centre for Motor Neurone Disease Research, University of Edinburgh, George Square, Edinburgh, Scotland, United Kingdom
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8
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Noronha-Matos JB, Morais T, Trigo D, Timóteo MA, Magalhães-Cardoso MT, Oliveira L, Correia-de-Sá P. Tetanic failure due to decreased endogenous adenosine A(2A) tonus operating neuronal Ca(v) 1 (L-type) influx in Myasthenia gravis. J Neurochem 2011; 117:797-811. [PMID: 21323926 DOI: 10.1111/j.1471-4159.2011.07216.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
In healthy motor endplates, tetanic depression is overcome by tonic adenosine A(2A) -receptor-mediated facilitation of transmitter release. The A(2A) receptor operates a coordinated shift from fast-desensitizing Ca(v) 2.1 (P/Q) calcium influx to long-lasting Ca(V) 1 (L) channels on motor nerve terminals. This study aimed at investigating whether A(2A) receptors-operated Ca(2+) influx via Ca(V) 1 (L)-type channels contribute to sustain acetylcholine release evoked by 50 Hz-bursts in toxin-induced Myasthenia gravis (TIMG) rats. In contrast to control animals, inhibition of [(3) H]acetylcholine (ACh) release by the Ca(V) 2.1 (P/Q) channel blocker, ω-Agatoxin IVA (100 nM), in TIMG rats had a higher magnitude than that observed with the Ca(V) 1 (L) channel blocker, nifedipine (1 μM). Adenosine deaminase (0.5 U/mL) and the A(2A) receptor antagonist, ZM 241385 (50 nM), decreased [(3) H]ACh release by a similar amount in control rats, but their effects were smaller in magnitude in myasthenic animals. The adenosine precursor, AMP (100 μM), increased (~40%) ACh release in both control and TIMG animals. Blockade of A(2A) , but not of A(1) , receptors prevented AMP-induced facilitation of transmitter release; nifedipine (1 μM) mimicked the effect of the A(2A) receptor antagonist. Video-microscopy studies designed to measure real-time transmitter exocytosis using the FM4-64 fluorescent dye fully supported radiochemical data. Thus, impairment of the adaptive shift from Ca(V) 2.1 (P/Q) to Ca(V) 1 (L) channels may contribute to tetanic failure in myasthenic rats. This parallels the reduction of adenosine A(2A) receptor tonus in TIMG animals, which might be restored by exogenous application of AMP.
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Affiliation(s)
- J B Noronha-Matos
- Laboratório de Farmacologia e Neurobiologia/UMIB, Instituto de Ciências Biomédicas de Abel Salazar, Universidade do Porto, L. Prof. Abel Salazar 2, Porto, Portugal
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9
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Mann MA, Das S, Zhang J, Wagner M, Fischbach GD. Neuregulin effect on quantal content dissociated from effect on miniature endplate potential amplitude. J Neurophysiol 2006; 96:671-6. [PMID: 16835362 DOI: 10.1152/jn.00225.2006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Members of the neuregulin family of signaling proteins increase transcription of acetylcholine receptor (AChR) subunit genes in muscle fibers and the number of AChRs in the muscle membrane. In adult mice heterozygous for targeted deletion of type I neuregulins (Ig-NRG(+/-)), postsynaptic AChR density was decreased and transmitter release was increased. We examined the relationship between functional AChR density and ACh release in postnatal day 7 (P7), P14, and adult NRG-deficient mice. Here we report that changes in postsynaptic sensitivity and transmitter release are not temporally coupled during postnatal development in Ig-NRG-deficient mice. Although miniature endplate potential (MEPP) amplitude was decreased compared with control in P7 Ig-NRG(+/-) mice, quantum content was not increased. Quantum content was increased in adult heterozygotes despite normal MEPP amplitudes. Thus, during postnatal maturation, both quantal size and quantum content were influenced by decreased Ig-NRG expression, although the effects were dissociated in time.
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Affiliation(s)
- Mary Anne Mann
- Department of Pharmacology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
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Abstract
Ion channels are crucial elements in neuronal signaling and synaptic transmission, and defects in their function are known to underlie rare genetic disorders, including some forms of epilepsy. A second class of channelopathies, characterized by autoantibodies against ligand- and voltage-gated ion channels, cause a variety of defects in peripheral neuromuscular and ganglionic transmission. There is also emerging evidence for autoantibody-mediated mechanisms in subgroups of patients with central nervous system disorders, particularly those involving defects in cognition or sleep and often associated with epilepsy. In all autoimmune channelopathies, the relationship between autoantibody specificity and clinical phenotype is complex. But with this new information, autoimmune channelopathies are detected and treated with increasing success, and future research promises new insights into the mechanisms of dysfunction at neuronal synapses and the determinants of clinical phenotype.
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Affiliation(s)
- Angela Vincent
- Neurosciences Group, Department of Clinical Neurology, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford OX3 9DS, United Kingdom.
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Santafé MM, Lanuza MA, Garcia N, Tomàs J. Calcium inflow-dependent protein kinase C activity is involved in the modulation of transmitter release in the neuromuscular junction of the adult rat. Synapse 2005; 57:76-84. [PMID: 15906390 DOI: 10.1002/syn.20159] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Using intracellular recording, we studied how protein kinase C activity affected miniature endplate potentials (MEPPs) and evoked endplate potentials (EPPs) in the neuromuscular junctions of the levator auris longus muscle from adult rats. The protein kinase C activator phorbol 12-myristate 13-acetate (PMA, 10 nM) increased the quantal content by approximately 150% (P<0.05). On the other hand, the quantal content decreased by approximately 40% (P<0.05) for all the protein kinase C inhibitors tested (Calphostin-C, 10 microM; Chelerythrine, 1 microM; Staurosporine, 200 nM). These changes in acetylcholine release were maintained at plateau for 1 to 7 h. Moreover, none of the protein kinase C activators or inhibitors used could modify the spontaneous MEPP mean size (P>0.05). We reduced the calcium influx in nerve terminals using the P/Q-type channel blocker omega-Aga-IVA(100 nM) or with 5 mM magnesium in physiological solution. In neither situation was the quantal content modified by PMA or by CaC. However, when high Ca2+ (5 mM) was added to a preparation that was previously blocked with omega-Aga-IVA, PMA and CaC had their full effect. We conclude that under physiological conditions PKC is dependent on the calcium inflow through the P/Q-type voltage-dependent calcium channels during evoked activity and works near the maximum rate at normal external calcium concentration.
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Affiliation(s)
- M M Santafé
- Unitat d'Histologia i Neurobiologia (UHN), Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, 43201-Reus, Spain.
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12
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Lorenzo SD, Veggetti M, Muchnik S, Losavio A. Presynaptic inhibition of spontaneous acetylcholine release induced by adenosine at the mouse neuromuscular junction. Br J Pharmacol 2004; 142:113-24. [PMID: 15066904 PMCID: PMC1574912 DOI: 10.1038/sj.bjp.0705656] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
1. At the mouse neuromuscular junction, adenosine (AD) and the A(1) agonist 2-chloro-N(6)-cyclopentyl-adenosine (CCPA) induce presynaptic inhibition of spontaneous acetylcholine (ACh) release by activation of A(1) AD receptors through a mechanism that is still unknown. To evaluate whether the inhibition is mediated by modulation of the voltage-dependent calcium channels (VDCCs) associated with tonic secretion (L- and N-type VDCCs), we measured the miniature end-plate potential (mepp) frequency in mouse diaphragm muscles. 2. Blockade of VDCCs by Cd(2+) prevented the effect of the CCPA. Nitrendipine (an L-type VDCC antagonist) but not omega-conotoxin GVIA (an N-type VDCC antagonist) blocked the action of CCPA, suggesting that the decrease in spontaneous mepp frequency by CCPA is associated with an action on L-type VDCCs only. 3. As A(1) receptors are coupled to a G(i/o) protein, we investigated whether the inhibition of PKA or the activation of PKC is involved in the presynaptic inhibition mechanism. Neither N-(2[p-bromocinnamylamino]-ethyl)-5-isoquinolinesulfonamide (H-89, a PKA inhibitor), nor 1-(5-isoquinolinesulfonyl)-2-methyl-piperazine (H-7, a PKC antagonist), nor phorbol 12-myristate 13-acetate (PHA, a PKC activator) modified CCPA-induced presynaptic inhibition, suggesting that these second messenger pathways are not involved. 4. The effect of CCPA was eliminated by the calmodulin antagonist N-(6-aminohexil)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7) and by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid-acetoxymethyl ester epsilon6TDelta-BM, which suggests that the action of CCPA to modulate L-type VDCCs may involve Ca(2+)-calmodulin. 5. To investigate the action of CCPA on diverse degrees of nerve terminal depolarization, we studied its effect at different external K(+) concentrations. The effect of CCPA on ACh secretion evoked by 10 mm K(+) was prevented by the P/Q-type VDCC antagonist omega-agatoxin IVA. 6. CCPA failed to inhibit the increases in mepp frequency evoked by 15 and 20 mm K(+). We demonstrated that, at high K(+) concentrations, endogenous AD occupies A1 receptors, impairing the action of CCPA, since incubation with 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, an A(1) receptor antagonist) and adenosine deaminase (ADA), which degrades AD into the inactive metabolite inosine, increased mepp frequency compared with that obtained in 15 and 20 mm K(+) in the absence of the drugs. Moreover, CCPA was able to induce presynaptic inhibition in the presence of ADA. It is concluded that, at high K(+) concentrations, the activation of A(1) receptors by endogenous AD prevents excessive neurotransmitter release.
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Affiliation(s)
- Silvana De Lorenzo
- Instituto de Investigaciones Médicas Alfredo Lanari, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires 1427, Argentina
| | - Mariela Veggetti
- Instituto de Investigaciones Médicas Alfredo Lanari, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires 1427, Argentina
| | - Salomón Muchnik
- Instituto de Investigaciones Médicas Alfredo Lanari, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires 1427, Argentina
| | - Adriana Losavio
- Instituto de Investigaciones Médicas Alfredo Lanari, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires 1427, Argentina
- Author for correspondence:
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Mantilla CB, Zhan WZ, Sieck GC. Neurotrophins improve neuromuscular transmission in the adult rat diaphragm. Muscle Nerve 2004; 29:381-6. [PMID: 14981737 DOI: 10.1002/mus.10558] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Neurotrophins modulate acute and sustained synaptic plasticity. In cultured Xenopus laevis neuromuscular junctions, neurotrophins improve neuromuscular transmission. Whether this influence exists at the mammalian neuromuscular junction is unknown. We hypothesized that neurotrophins improve neuromuscular transmission at neuromuscular junctions of adult rat diaphragm muscle fibers. A diaphragm muscle-phrenic nerve preparation was used to determine the effects of brain-derived neurotrophic factor (BDNF), neurotrophin-4 (NT-4) and K252a [tyrosine kinase (Trk) receptor inhibitor] on the extent of neuromuscular transmission failure induced by repetitive nerve stimulation. We found significant enhancement of neuromuscular transmission with BDNF or NT-4 treatment, whereas K252a treatment worsened neuromuscular transmission. In contrast, diaphragm muscle contractile and fatigue properties were unaffected by neurotrophin or K252a treatment. These results demonstrate that BDNF and NT-4 improve synaptic transmission in the adult rat diaphragm muscle, likely in a Trk-dependent fashion. Neurotrophins may constitute a novel therapeutic target to improve neuromuscular function in the diaphragm.
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Affiliation(s)
- Carlos B Mantilla
- Department of Anesthesiology, Mayo Clinic, 200 First Street SW, Rochester, Minnesota 55905, USA
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Abstract
Reliable transmission of activity from nerve to muscle is necessary for the normal function of the body. The term 'safety factor' refers to the ability of neuromuscular transmission to remain effective under various physiological conditions and stresses. This is a result of the amount of transmitter released per nerve impulse being greater than that required to trigger an action potential in the muscle fibre. The safety factor is a measure of this excess of released transmitter. In this review we discuss the practical difficulties involved in estimating the safety factor in vitro. We then consider the factors that influence the safety factor in vivo. While presynaptic transmitter release may be modulated on a moment to moment basis, the postsynaptic features that determine the effect of released transmitter are not so readily altered to meet changing demands. Different strategies are used by different species to ensure reliable neuromuscular transmission. Some, like frogs, rely on releasing a large amount of transmitter while others, like man, rely on elaborate postsynaptic specialisations to enhance the response to transmitter. In normal adult mammals, the safety factor is generally 3-5. Both pre- and postsynaptic components change during development and may show plasticity in response to injury or disease. Thus, both acquired autoimmune and inherited congenital diseases of the neuromuscular junction (NMJ) can significantly reduce, or even transiently increase, safety factor.
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Affiliation(s)
- S J Wood
- Department of Physiology, School of Medical Sciences, University of Bristol, University Walk, BS8 1TD, Bristol, UK.
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Costanzo EM, Barry JA, Ribchester RR. Co-regulation of synaptic efficacy at stable polyneuronally innervated neuromuscular junctions in reinnervated rat muscle. J Physiol 1999; 521 Pt 2:365-74. [PMID: 10581308 PMCID: PMC2269663 DOI: 10.1111/j.1469-7793.1999.00365.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. Intracellular recordings and quantal analysis of synaptic transmission were made at neuromuscular junctions receiving stable convergent innervation in reinnervated rat lumbrical muscles, following recovery from chronic nerve conduction block. The polyneuronally innervated motor endplates (pi-junctions) were identified by vital staining of lateral plantar nerve (LPN) and sural nerve (SN) motor terminals, using the activity-dependent staining properties of the aminostyryl dyes RH414 and FM1-43, respectively. 2. Endplate depolarisation and quantal content per unit area varied by more than a factor of ten ( approximately 0.1-1. 4 quanta microm-2) between fibres. However, the stable pi-junctions produced nearly equivalent endplate depolarisations and quantal content per unit area, suggesting that synaptic strengths were co-regulated at these motor endplates. Quantal content per unit area was also independent of the size of individual synaptic inputs, or whether one, both or neither input was judged sufficient to produce suprathreshold or subthreshold endplate depolarisations. 3. Simultaneous excitation of convergent LPN and SN inputs from some pi-junctions resulted in profound non-linear summation, and in some cases complete occlusion of the response of the smaller input. The amplitude of the smaller, test responses recovered with a time constant of 2.1 +/- 0.5 ms (mean +/- s.e.m.) on varying the interval between paired stimuli, of similar order to the time constant of repolarisation of the conditioning endplate potential. 4. The data show that it is not necessary for a motor nerve terminal to occupy most of an endplate, or to produce a suprathreshold response in order to become stable. The occlusion of linear summation, similar to that described previously at polyneuronal junctions in neonates, suggests that convergent inputs comprising interdigitated synaptic boutons evoke self-contained synaptic responses at endplates, and that these are non-co-operative with respect to overall endplate depolarisation or safety margin for synaptic transmission.
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Affiliation(s)
- E M Costanzo
- Department of Neuroscience, University Medical School, Edinburgh EH1 9LE, UK
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Ribchester RR, Thomson D, Haddow LJ, Ushkaryov YA. Enhancement of spontaneous transmitter release at neonatal mouse neuromuscular junctions by the glial cell line-derived neurotrophic factor (GDNF). J Physiol 1998; 512 ( Pt 3):635-41. [PMID: 9769409 PMCID: PMC2231231 DOI: 10.1111/j.1469-7793.1998.635bd.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/1998] [Accepted: 07/29/1998] [Indexed: 11/30/2022] Open
Abstract
1. The acute effects of neurotrophic factors on the frequency of spontaneous transmitter release (miniature endplate potentials (MEPPs)) from motor nerve terminals has been examined in skeletal muscles of neonatal mice aged between 9 and 20 days. The following factors were tested at a concentration of 50 ng ml-1: brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), ciliary neuronotrophic factor (CNTF), leukaemia inhibitory factor (LIF), insulin-like growth factors 1 and 2 (IGF-1 and IGF-2), and glial cell line-derived neurotrophic factor (GDNF). In some experiments, the responses to 2 microM LaCl3 and 10 mM K+, or to 2-5 nM purified alpha-latrotoxin (alpha-LTX) were also measured. 2. Neither BDNF, NT-3, NT-4, LIF, IGF-1 or IGF-2 - singly or in combination - caused any significant change in MEPP frequency. GDNF, however, produced a highly significant, 2-fold increase in neurotransmitter release that was reproduced in fourteen muscles. 3. Potentiation of MEPP frequency in GDNF was of the same order as that induced by tetanic stimulation or substitution of the bathing medium with hypertonic saline; but substantially less than that induced either by lanthanum ions or alpha-latrotoxin. 4. The data suggest that concentrations of GDNF that produce maximal enhancement of motoneurone survival in vitro and in vivo also produce acute, non-saturating enhancement in transmitter release at immature mammalian neuromuscular synapses. Taken together with other reports, these findings suggest that GDNF may mediate both functional and structural plasticity of neonatal neuromuscular junctions.
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Affiliation(s)
- R R Ribchester
- Department of Physiology, University Medical School, Teviot Place, Edinburgh EH8 9AG, UK.
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Abstract
The phosphorylation of proteins on tyrosine residues, initially believed to be primarily involved in cell growth and differentiation, is now recognized as having a critical role in regulating the function of mature cells. The brain exhibits one of the highest levels of tyrosine kinase activity in the adult animal and the synaptic region is particularly rich in tyrosine kinases and tyrosine phosphorylated proteins. Recent studies have described the effects of tyrosine phosphorylation on the activities of a number of proteins which are potentially involved in the regulation of synaptic function. Furthermore, it is becoming apparent that tyrosine phosphorylation is involved in the modification of synaptic activity, such as occurs during depolarization, the induction of long-term potentiation or long-term depression, and ischemia. Changes in the activities of tyrosine kinases and/or protein tyrosine phosphatases which are associated with synaptic structures may result in altered tyrosine phosphorylation of proteins located at the synapse leading to both short-term and long-lasting changes in synaptic and neuronal function.
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Affiliation(s)
- J W Gurd
- Division of Life Sciences, University of Toronto at Scarborough, Ontario, Canada.
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