scholarly journals DEVELOPMENT OF THE NEUROMUSCULAR JUNCTION

1970 ◽  
Vol 47 (2) ◽  
pp. 423-436 ◽  
Author(s):  
Thomas L. Lentz
Keyword(s):  
Neuromuscular Junction ◽  
Synaptic Vesicles ◽  
Neuromuscular Junctions ◽  
Morphological Changes ◽  
Muscle Fibers ◽  
Lead Nitrate ◽  
Synaptic Function ◽  
Axon Termination ◽  
Nerve Muscle ◽  
Thiolacetic Acid

Following amputation of the limb of the newt, Triturus viridescens, muscle fibers dedifferentiate giving rise to mesenchymal cells. The earliest changes detected in neuromuscular junctions of dedifferentiating muscle fibers are the appearance of a few vacuoles and decrease in density of the terminal axoplasm. Later, synaptic vesicles become tightly clustered in the axon termination, and their content appears denser than normal. Then, vesicles diminish in number until few are seen in the ending. While these changes are occurring, the area of contact of nerve with muscle becomes smaller. Junctional folds persist only where the nerve maintains contact with muscle, but these are shorter than normal and appear as slight ridges on the muscle surface. Subsequently, the nerve withdraws from the muscle cell and is completely invested by Schwann cell cytoplasm, and all traces of junctional folds are lost at the former region of contact. Cholinesterase activity was localized with the thiolacetic acid-lead nitrate method. Even before marked morphological changes occur in the junction, DFP- and physostigmine-sensitive activity in the cleft between nerve and muscle is decreased in intensity. Activity continues to decrease as the area of nerve-muscle contact diminishes and junctional folds disappear. When the nerve has withdrawn from the muscle surface, only a few small deposits of lead are left in the intervening region. These results show that as muscle becomes less specialized during dedifferentiation, the neuromuscular junction also loses the cytological and cytochemical specializations associated with synaptic function.

scholarly journals Regulatory Function of Sympathetic Innervation on the Endo/Lysosomal Trafficking of Acetylcholine Receptor

2021 ◽  
Vol 12 ◽  
Author(s):  
Tatjana Straka ◽  
Charlotte Schröder ◽  
Andreas Roos ◽  
Laxmikanth Kollipara ◽  
Albert Sickmann ◽  
...  
Keyword(s):  
Neuromuscular Junction ◽  
Acetylcholine Receptor ◽  
Ribosomal Proteins ◽  
Neuromuscular Junctions ◽  
Sympathetic Neurons ◽  
Sympathetic Innervation ◽  
Regulatory Function ◽  
Hindlimb Muscles ◽  
Nerve Muscle

Recent studies have demonstrated that neuromuscular junctions are co-innervated by sympathetic neurons. This co-innervation has been shown to be crucial for neuromuscular junction morphology and functional maintenance. To improve our understanding of how sympathetic innervation affects nerve–muscle synapse homeostasis, we here used in vivo imaging, proteomic, biochemical, and microscopic approaches to compare normal and sympathectomized mouse hindlimb muscles. Live confocal microscopy revealed reduced fiber diameters, enhanced acetylcholine receptor turnover, and increased amounts of endo/lysosomal acetylcholine-receptor-bearing vesicles. Proteomics analysis of sympathectomized skeletal muscles showed that besides massive changes in mitochondrial, sarcomeric, and ribosomal proteins, the relative abundance of vesicular trafficking markers was affected by sympathectomy. Immunofluorescence and Western blot approaches corroborated these findings and, in addition, suggested local upregulation and enrichment of endo/lysosomal progression and autophagy markers, Rab 7 and p62, at the sarcomeric regions of muscle fibers and neuromuscular junctions. In summary, these data give novel insights into the relevance of sympathetic innervation for the homeostasis of muscle and neuromuscular junctions. They are consistent with an upregulation of endocytic and autophagic trafficking at the whole muscle level and at the neuromuscular junction.

scholarly journals The p75NTR neurotrophin receptor is required to organize the mature neuromuscular synapse by regulating synaptic vesicle availability

2019 ◽  
Vol 7 (1) ◽  
Author(s):  
Viviana Pérez ◽  
Francisca Bermedo-Garcia ◽  
Diego Zelada ◽  
Felipe A. Court ◽  
Miguel Ángel Pérez ◽  
...  
Keyword(s):  
Neuromuscular Junction ◽  
Motor Neurons ◽  
Neuromuscular Junctions ◽  
Neuronal Damage ◽  
Neuromuscular Synapse ◽  
Force Production ◽  
Synaptic Function ◽  
Neurotrophin Receptor ◽  
Acetylcholinesterase Inhibition ◽  
Pharmacological Intervention

Abstract The coordinated movement of organisms relies on efficient nerve-muscle communication at the neuromuscular junction. After peripheral nerve injury or neurodegeneration, motor neurons and Schwann cells increase the expression of the p75NTR pan-neurotrophin receptor. Even though p75NTR targeting has emerged as a promising therapeutic strategy to delay peripheral neuronal damage progression, the effects of long-term p75NTR inhibition at the mature neuromuscular junction have not been elucidated. We performed quantitative neuroanathomical analyses of the neuromuscular junction in p75NTR null mice by laser confocal and electron microscopy, which were complemented with electromyography, locomotor tests, and pharmacological intervention studies. Mature neuromuscular synapses of p75NTR null mice show impaired postsynaptic organization and ultrastructural complexity, which correlate with altered synaptic function at the levels of nerve activity-induced muscle responses, muscle fiber structure, force production, and locomotor performance. Our results on primary myotubes and denervated muscles indicate that muscle-derived p75NTR does not play a major role on postsynaptic organization. In turn, motor axon terminals of p75NTR null mice display a strong reduction in the number of synaptic vesicles and active zones. According to the observed pre and postsynaptic defects, pharmacological acetylcholinesterase inhibition rescued nerve-dependent muscle response and force production in p75NTR null mice. Our findings revealing that p75NTR is required to organize mature neuromuscular junctions contribute to a comprehensive view of the possible effects caused by therapeutic attempts to target p75NTR.

scholarly journals Basal lamina directs acetylcholinesterase accumulation at synaptic sites in regenerating muscle.

1985 ◽  
Vol 101 (3) ◽  
pp. 735-743 ◽  
Author(s):  
L Anglister ◽  
U J McMahan
Keyword(s):  
Plasma Membrane ◽  
Neuromuscular Junction ◽  
Basal Lamina ◽  
Acetylcholine Receptors ◽  
Skeletal Muscles ◽  
Ache Activity ◽  
Neuromuscular Junctions ◽  
Muscle Fibers ◽  
Synaptic Cleft

In skeletal muscles that have been damaged in ways which spare the basal lamina sheaths of the muscle fibers, new myofibers develop within the sheaths and neuromuscular junctions form at the original synaptic sites on them. At the regenerated neuromuscular junctions, as at the original ones, the muscle fibers are characterized by junctional folds and accumulations of acetylcholine receptors and acetylcholinesterase (AChE). The formation of junctional folds and the accumulation of acetylcholine receptors is known to be directed by components of the synaptic portion of the myofiber basal lamina. The aim of this study was to determine whether or not the synaptic basal lamina contains molecules that direct the accumulation of AChE. We crushed frog muscles in a way that caused disintegration and phagocytosis of all cells at the neuromuscular junction, and at the same time, we irreversibly blocked AChE activity. New muscle fibers were allowed to regenerate within the basal lamina sheaths of the original muscle fibers but reinnervation of the muscles was deliberately prevented. We then stained for AChE activity and searched the surface of the new muscle fibers for deposits of enzyme they had produced. Despite the absence of innervation, AChE preferentially accumulated at points where the plasma membrane of the new muscle fibers was apposed to the regions of the basal lamina that had occupied the synaptic cleft at the neuromuscular junctions. We therefore conclude that molecules stably attached to the synaptic portion of myofiber basal lamina direct the accumulation of AChE at the original synaptic sites in regenerating muscle. Additional studies revealed that the AChE was solubilized by collagenase and that it remained adherent to basal lamina sheaths after degeneration of the new myofibers, indicating that it had become incorporated into the basal lamina, as at normal neuromuscular junctions.

scholarly journals Cytoskeletal components of the vertebrate neuromuscular junction: vinculin, alpha-actinin, and filamin.

1983 ◽  
Vol 97 (1) ◽  
pp. 217-223 ◽  
Author(s):  
R J Bloch ◽  
Z W Hall
Keyword(s):  
Neuromuscular Junction ◽  
Neuromuscular Junctions ◽  
Muscle Fibers ◽  
Cytoskeletal Proteins ◽  
Rat Muscle ◽  
Normal Rat ◽  
Specific Affinity

We have used immunocytochemical methods to investigate the cytoskeletal constituents of the vertebrate neuromuscular junction. Specific, affinity-purified antibodies to three cytoskeletal proteins, vinculin, alpha-actinin, and filamin, bound to neuromuscular junctions in sections of normal rat, mouse, chick, and Xenopus muscles. All three antibodies bound to the synaptic regions of denervated rat muscle fibers, indicating that the proteins recognized by these antibodies are associated with postsynaptic structures. The three proteins are present at the neuromuscular junction in muscle fibers of embryonic and neonatal animals, and therefore, may play an important role in its differentiation.

scholarly journals Cytoplasmic actin in postsynaptic structures at the neuromuscular junction.

1981 ◽  
Vol 90 (3) ◽  
pp. 789-792 ◽  
Author(s):  
Z W Hall ◽  
B W Lubit ◽  
J H Schwartz
Keyword(s):  
Neuromuscular Junction ◽  
Mammalian Cells ◽  
Acetylcholine Receptors ◽  
Body Wall ◽  
Neuromuscular Junctions ◽  
Muscle Fibers ◽  
Adult Rat ◽  
Rat Muscle ◽  
Cytoplasmic Actin ◽  
Immunocytochemical Studies

We used an antibody prepared against Aplysia (mollusc) body-wall actin that specifically reacts with certain forms of cytoplasmic actin in mammalian cells to probe for the presence of actin at the neuromuscular junction. Immunocytochemical studies showed that actin or an actinlike molecule is concentrated at neuromuscular junctions of normal and denervated adult rat muscle fibers. Actin is present at the neuromuscular junctions of fibers of developing diaphragm muscles as early as embryonic day 18, well before postsynaptic folds are formed. These results suggest that cytoplasmic actin may play a role in the clustering or stabilization of acetylcholine receptors at the neuromuscular junction.

scholarly journals Targeting of the ETS Factor Gabpα Disrupts Neuromuscular Junction Synaptic Function

2007 ◽  
Vol 27 (9) ◽  
pp. 3470-3480 ◽  
Author(s):  
Debra A. O'Leary ◽  
Peter G. Noakes ◽  
Nick A. Lavidis ◽  
Ismail Kola ◽  
Paul J. Hertzog ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Transcription Factor ◽  
Neuromuscular Junction ◽  
Acetylcholine Receptor ◽  
Neuromuscular Junctions ◽  
Binding Protein ◽  
Synaptic Function ◽  
Single Point Mutation ◽  
Structural Formation ◽  
Ga Binding Protein

ABSTRACT The GA-binding protein (GABP) transcription factor has been shown in vitro to regulate the expression of the neuromuscular proteins utrophin, acetylcholine esterase, and acetylcholine receptor subunits δ and ε through the N-box promoter motif (5′-CCGGAA-3′), but its in vivo function remains unknown. A single point mutation within the N-box of the gene encoding the acetylcholine receptor ε subunit has been identified in several patients suffering from postsynaptic congenital myasthenic syndrome, implicating the GA-binding protein in neuromuscular function and disease. Since conventional gene targeting results in an embryonic-lethal phenotype, we used conditional targeting to investigate the role of GABPα in neuromuscular junction and skeletal muscle development. The diaphragm and soleus muscles from mutant mice display alterations in morphology and distribution of acetylcholine receptor clusters at the neuromuscular junction and neurotransmission properties consistent with reduced receptor function. Furthermore, we confirmed decreased expression of the acetylcholine receptor ε subunit and increased expression of the γ subunit in skeletal muscle tissues. Therefore, the GABP transcription factor aids in the structural formation and function of neuromuscular junctions by regulating the expression of postsynaptic genes.

Effect of depolarization by potassium proprionate on synaptic vesicle diameter and distribution of the snake motor endplate

1989 ◽  
Vol 47 ◽  
pp. 946-947
Author(s):  
Gregory Hendricks ◽  
Lisa Coniglio ◽  
Ian Marshall ◽  
Tim Searl ◽  
Rodney Parsons
Keyword(s):  
Synaptic Vesicles ◽  
Neuromuscular Junctions ◽  
Muscle Fibers ◽  
Average Diameter ◽  
Uranyl Acetate ◽  
Release Agent ◽  
High K ◽  
Microscope Slides ◽  
Whole Mounts

The morphological effects of elevated potassium (K+) at the neuromuscular junction of garter snake twitch muscle fibers were examined in vitro. Elevated K+ depolarizes the motor neuron terminals and causes quantal release of acetylcholine. It has been shown in amphibians that prolonged (30-60 min) depolarization with high K+ depletes terminals of synaptic vesicles ; but causes no change in the average diameter of the vesicles. In the snake, however, we have shown previously that miniature endplate currents (MEPCs) are present at high frequency even after 1-2 hours of exposure to high K+ . This indicates that in the snake, synaptic vesicles are not totally depleted by depolarization with high K+. In this study, we examined the effect of depolarization with high K+ on the distribution and diameter of synaptic vesicles.Intercostal muscle preparations were exposed for 15 minutes to Ringer's + solution containing either a control (1.2mM) or high (70mM) concentration of K+ Preparations were fixed immediately in 1% glutaraldehyde for 15 minutes and washed with Millonig's buffer. The whole mount muscle preparations were then fixed for 1 h in 2.5% glutaraldehyde in 0.1 M phosphate buffer, pH 7.2; rinsed three times in fresh buffer and post-fixed in 2% OsO4 in the same buffer for 30 min, rinsed in fresh buffer and dehydrated in a graded ethanol series to 100% and then transferred into a 2% solution of uranyl acetate for 20 min to en-block stain the whole mounts. The preps were then transferred back to 100% ethanol to complete the dehydration and embedded in a mixture of Embed 812/Araldite 502 (Hard) between two microscope slides that had been precoated with Formen- Trennmittel Liquid Release Agent and polymerized overnight at 70°C.The whole mounts were then removed from the microscope slides and examined on a compound light microscope where the neuromuscular junctions on the twitch muscle fibers could be identified, marked and cut out of the preps. These pieces of the whole mounts were then remounted into a slot on the end of a pre-cast Embed-Araldite block with a drop of fresh resin and polymerized.

scholarly journals Nucleus-specific translation and assembly of acetylcholinesterase in multinucleated muscle cells.

1990 ◽  
Vol 110 (3) ◽  
pp. 715-719 ◽  
Author(s):  
R L Rotundo
Keyword(s):  
Skeletal Muscle ◽  
Cell Surface ◽  
Neuromuscular Junctions ◽  
Muscle Fibers ◽  
Structural Basis ◽  
Multinucleated Cells ◽  
Skeletal Muscle Fibers ◽  
Nuclear Domains ◽  
Nerve Muscle ◽  
Polypeptide Chains

Multinucleated skeletal muscle fibers synthesize cell surface and secreted oligomeric forms of acetylcholinesterase (AChE) that accumulate at specialized locations on the cell surface, such as sites of nerve-muscle contact. Using allelic variants of the AChE polypeptide chains as genetic markers, we show that nuclei homozygous for either the alpha or beta alleles residing in chimeric myotubes preferentially translate their AChE mRNAs on their respective ERs. These results indicate that the events of transcription, translation, and assembly of this membrane protein are compartmentalized into nuclear domains in multinucleated cells, and provide the structural basis for the possible localized expression and regulation of synaptic components at the neuromuscular junctions of vertebrate skeletal muscle fibers.

scholarly journals Neuromuscular Junctions in Flight and Tymbal Muscles of the Cicada

1958 ◽  
Vol 4 (3) ◽  
pp. 251-256 ◽  
Author(s):  
George A. Edwards ◽  
Helmut Ruska ◽  
Étienne de Harven
Keyword(s):  
Endoplasmic Reticulum ◽  
Neuromuscular Junction ◽  
Muscle Fiber ◽  
High Frequency ◽  
Plasma Membranes ◽  
Flight Muscle ◽  
Neuromuscular Junctions ◽  
Muscle Fibers ◽  
Membrane System ◽  
Indirect Flight Muscle

The tymbal muscle fiber in the cicada closely resembles the indirect flight muscle fiber in its structural detail. We agree with other authors that the tymbal muscle is a modified indirect flight muscle. The peripheral nerve branches to the tymbal and flight muscle fibers are similar to those in the wasp leg. The axon is loosely mantled by irregular turns of the mesaxon, enclosing cytoplasm. The nerve is therefore a tunicated nerve. The neuromuscular junction in the high frequency muscle fibers shows direct apposition of plasma membranes of axon and muscle fiber, large numbers of mitochondria and synaptic vesicles in the axon, and concentrations of mitochondria, aposynaptic granules, and endoplasmic reticulum in the postsynaptic area of the muscle fiber. Of special interest is the multitude of intracellular, opposing membranes in the postsynaptic area. They form laminated stacks and whorls, vesicles, cysternae, and tubules. They occasionally show continuity with the plasma membrane, the outer nuclear envelope, and the circumfibrillar endoplasmic reticulum. The membrane system in this area is designated "rete synapticum." It is believed to add to the electrical capacity of the neuromuscular junction, to serve in transmission of potentials, and possibly is the site of the oscillating mechanism in high-frequency muscle fibers.

scholarly journals TrkB kinase activity maintains synaptic function and structural integrity at adult neuromuscular junctions

2014 ◽  
Vol 117 (8) ◽  
pp. 910-920 ◽  
Author(s):  
Carlos B. Mantilla ◽  
Jessica M. Stowe ◽  
Dylan C. Sieck ◽  
Leonid G. Ermilov ◽  
Sarah M. Greising ◽  
...  
Keyword(s):  
Neuromuscular Transmission ◽  
Kinase Activity ◽  
Structural Integrity ◽  
Neuromuscular Junctions ◽  
Morphological Changes ◽  
Synaptic Function ◽  
Diaphragm Muscle ◽  
Presynaptic Terminals ◽  
Reversible Inactivation ◽  
Motor End Plates

Activation of the tropomyosin-related kinase receptor B (TrkB) by brain-derived neurotrophic factor acutely regulates synaptic transmission at adult neuromuscular junctions (NMJs). The role of TrkB kinase activity in the maintenance of NMJ function and structure at diaphragm muscle NMJs was explored using a chemical-genetic approach that permits reversible inactivation of TrkB kinase activity in TrkB F616A mice by 1NMPP1. Inhibiting TrkB kinase activity for 7 days resulted in significant, yet reversible, impairments in neuromuscular transmission at diaphragm NMJs. Neuromuscular transmission failure following 2 min of repetitive phrenic nerve stimulation increased from 42% in control to 59% in 1NMPP1-treated TrkB F616A mice ( P = 0.010). Recovery of TrkB kinase activity following withdrawal of 1NMPP1 treatment improved neuromuscular transmission ( P = 0.006). Electrophysiological measurements at individual diaphragm NMJs documented lack of differences in quantal content in control and 1NMPP1-treated mice ( P = 0.845). Morphological changes at diaphragm NMJs were modest following inhibition and recovery of TrkB kinase activity. Three-dimensional reconstructions of diaphragm NMJs revealed no differences in volume at motor end plates (labeled by α-bungarotoxin; P = 0.982) or presynaptic terminals (labeled by synaptophysin; P = 0.515). Inhibition of TrkB kinase activity by 1NMPP1 resulted in more compact NMJs, with increased apposition of presynaptic terminals and motor end plates ( P = 0.017) and reduced fragmentation of motor end plates ( P = 0.005). Recovery of TrkB kinase activity following withdrawal of 1NMPP1 treatment resulted in postsynaptic remodeling likely reflecting increased gutter depth ( P = 0.007), without significant presynaptic changes. These results support an essential role for TrkB kinase activity in maintaining synaptic function and structural integrity at NMJs in the adult mouse diaphragm muscle.

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