Multiple Presynaptic and Postsynaptic Sites of Inhibitory Modulation by Myomodulin at ARC Neuromuscular Junctions ofAplysia

2003 ◽  
Vol 89 (3) ◽  
pp. 1488-1502 ◽  
Author(s):  
Irina V. Orekhova ◽  
Vera Alexeeva ◽  
Paul J. Church ◽  
Klaudiusz R. Weiss ◽  
Vladimir Brezina
Keyword(s):  
Motor Neuron ◽  
Motor Neurons ◽  
Neuromuscular Junctions ◽  
Definitive Evidence ◽  
Multiple Parameters ◽  
Intact Muscle ◽  
Single Arc ◽  
Excitatory Junction Potentials ◽  
K Current ◽  
Neuron Terminals

The functional activity of even simple cellular ensembles is often controlled by surprisingly complex networks of neuromodulators. One such network has been extensively studied in the accessory radula closer (ARC) neuromuscular system of Aplysia. The ARC muscle is innervated by two motor neurons, B15 and B16, which release modulatory peptide cotransmitters to shape ACh-mediated contractions of the muscle. Previous analysis has shown that key to the combinatorial ability of B15 and B16 to control multiple parameters of the contraction is an asymmetry in their peptide modulatory actions. B16, but not B15, releases myomodulin, which, among other actions, inhibits the contraction. Work in single ARC muscle fibers has identified a distinctive myomodulin-activated K current as a candidate postsynaptic mechanism of the inhibition. However, definitive evidence for this mechanism has been lacking. Here, working with the single fibers and then motor neuron-elicited excitatory junction potentials (EJPs) and contractions of the intact ARC muscle, we have confirmed two central predictions of the K-current hypothesis: the myomodulin inhibition of contraction is associated with a correspondingly large inhibition of the underlying depolarization, and the inhibition of both contraction and depolarization is blocked by 4-aminopyridine (4-AP), a potent and selective blocker of the myomodulin-activated K current. However, in the intact muscle, the experiments revealed a second, 4-AP-resistant component of myomodulin inhibition of both B15- and B16-elicited EJPs. This component resembles, and mutually occludes with, inhibition of the EJPs by another peptide modulator released from both B15 and B16, buccalin, which acts by a presynaptic mechanism, inhibition of ACh release from the motor neuron terminals. Direct measurements of peptide release showed that myomodulin also inhibits buccalin release from B15 terminals. At the level of contractions, nevertheless, the postsynaptic K-current mechanism is responsible for much of the myomodulin inhibition of peak contraction amplitude. The presynaptic mechanism, which is most evident during the initial build-up of the EJP waveform, underlies instead an increase of contraction latency.

Motor organization in pharynx of Helix pomatia

1984 ◽  
Vol 52 (3) ◽  
pp. 389-409 ◽  
Author(s):  
M. Peters ◽  
U. Altrup
Keyword(s):  
Motor Neuron ◽  
Motor Neurons ◽  
Neuromuscular Junctions ◽  
Muscle Tension ◽  
Helix Pomatia ◽  
Single Motor ◽  
Cobalt Staining ◽  
Excitatory Junction Potentials ◽  
Individual Motor ◽  
Phase Relationships

Identified motor neurons in the buccal ganglia of Helix pomatia and pharynx muscles innervated by them were studied with intracellular recording and cobalt staining. Retrograde cobalt staining via the buccal nerves indicated that neurons occupy relatively constant positions within the ganglia. With intracellular cobalt staining it was shown that the shape of a representative motor neuron (B4) is similar in different preparations. In some cases, however, deviations from the normal pattern of axon distribution were found. Presumed motor endings of neuron B4 in the muscle were also visualized with intracellular staining. Recordings from individual motor neurons show typical phase relationships of spontaneous spike activity. Most motor neurons are active in the retraction phase of the radula. Only excitatory motor neurons were found. Most neurons directly supply more than one muscle. Amplitude of excitatory junction potentials (EJP) and plasticity at neuromuscular junctions from one neuron are similar in different muscles. Single muscle fibers receive polyneuronal innervation. Activity of single motor neurons already leads to muscle contraction even without spiking of the muscle cells. Muscle tension depends on integrated EJP size. Most motor neurons supply typical combinations of a set of muscles. Thus, several muscles can be activated synchronously by activity of a single motor neuron. In this way muscle combinations are predetermined morphologically by the peripheral branching patterns of the respective neurons.

FRF peptides in the ARC neuromuscular system of Aplysia: purification and physiological actions

1994 ◽  
Vol 72 (5) ◽  
pp. 2181-2195 ◽  
Author(s):  
E. C. Cropper ◽  
V. Brezina ◽  
F. S. Vilim ◽  
O. Harish ◽  
D. A. Price ◽  
...  
Keyword(s):  
Motor Neuron ◽  
Motor Neurons ◽  
Muscle Contractions ◽  
Contraction Duration ◽  
Peptide Family ◽  
Voltage Dependent ◽  
Excitatory Junction Potentials ◽  
K Current ◽  
High Doses ◽  
Antagonistic Muscles

1. One preparation that has proven to be advantageous for the study of neuromuscular modulation is the accessory radula closer (ARC) muscle of Aplysia californica and its motor neurons B15 and B16. In this study three members of a new peptide family have been purified from this well-characterized preparation. Because these peptides terminate in Phe-Arg-Phe-amide, we have named them FRFA, FRFB, and FRFC. The FRFs are thus RFamide peptides and are related to the widely studied neuropeptide FMRFamide. 2. The FRFs are present in the ARC motor neuron B15 in small quantities. 3. When they are exogenously applied, the FRFs decrease the size of ARC muscle contractions elicited by stimulation of either motor neuron B15 or B16. They appear to do this by a combination of presynaptic and postsynaptic actions. 4. Presynaptically, the FRFs appear to act like the buccalins, another family of inhibitory ARC neuropeptides. Both families of peptides reduce the size of motor neuron-elicited excitatory junction potentials (EJPs) presumably by decreasing presynaptic acetylcholine (ACh) release. 5. Postsynaptically, the FRFs appear to depress contractions because they activate a characteristic voltage-dependent, 4-amino-pyridine-sensitive K current in the ARC muscle. The same current is activated by a second class of ARC modulators: those that exert potentiating actions at low doses and inhibitory actions at high doses, i.e., serotonin, the small cardioactive peptides (SCPs), and particularly the myomodulins. Receptors mediating activation of the K current by the FRFs and the other modulators do, however, appear to be different. 6. We hypothesize that the inhibitory actions of the FRFs prevent excessively large muscle contractions. If contraction size is limited, then contraction duration is also limited. This may allow faster and more energetically favorable switching between contractions of antagonistic muscles.

scholarly journals Myomirnas Role in Als Suggest a Crosstalk between Muscle and Motor Neuron

2018 ◽  
Author(s):  
Valentina Pegoraro ◽  
Antonio Merico ◽  
Corrado Angelini
Keyword(s):  
Skeletal Muscle ◽  
Motor Neuron ◽  
Aerobic Exercise ◽  
Muscle Atrophy ◽  
Motor Neurons ◽  
Neuromuscular Junctions ◽  
Neurodegenerative Disorder ◽  
Disease Process ◽  
Muscle Fibres ◽  
Wide Range

Amyotrophic lateral sclerosis (ALS) is a rare, progressive, neurodegenerative disorder caused by degeneration of upper and lower motor neurons. The disease process leads from lower motor neuron involvement to progressive muscle atrophy, weakness, fasciculations for the upper motor neuron involvement to spasticity. Muscle atrophy in ALS is caused by a dysregulation in the molecular network controlling fast and slow muscle fibres. Denervation and reinnervation processes in skeletal muscle occur in the course of ALS and are modulated by rehabilitation. MicroRNAs (miRNAs) are small non-coding RNAs that modulate a wide range of biological functions under various pathophysiological conditions. MiRNAs can be secreted by various cell types and they are markedly stable in body fluids. MiR-1, miR-133 a, miR-133b, and miR-206 are called “myomiRs” and are considered markers of myogenesis during muscle regeneration and neuromuscular junction stabilization or sprouting. We observed a positive effect of a standard aerobic exercise rehabilitative protocol conducted for six weeks in 18 ALS patients during hospitalization in our center. We correlated clinical scales with molecular data on myomiRs. After six weeks of moderate aerobic exercise, myomiRNAs were down-regulated, suggesting an active proliferation of satellite cells in muscle and increased neuromuscular junctions. Our data suggest that circulating miRNAs modulate during skeletal muscle recovery in response to physical rehabilitation in ALS.

Nine members of the myomodulin family of peptide cotransmitters at the B16-ARC neuromuscular junction of Aplysia

1995 ◽  
Vol 74 (1) ◽  
pp. 54-72 ◽  
Author(s):  
V. Brezina ◽  
B. Bank ◽  
E. C. Cropper ◽  
S. Rosen ◽  
F. S. Vilim ◽  
...  
Keyword(s):  
Motor Neuron ◽  
Relaxation Rate ◽  
Motor Neurons ◽  
Physiological Effects ◽  
Ca Current ◽  
Good Opportunity ◽  
Contraction Amplitude ◽  
K Current ◽  
High Concentrations ◽  
K Currents

1. Neuromodulation by multiple related peptides with different spectra of physiological effects appears an effective way to integrate complex physiological functions. A good opportunity to examine this issue occurs in the accessory radula closer (ARC) neuromuscular circuit of Aplysia, where, extensive previous work has shown, acetylcholine-induced contractions of the muscle are variously modulated by several families of peptide cotransmitters released under appropriate behavioral circumstances from the muscle's own two motor neurons. 2. In this work we focused on the myomodulins (MMs) released from motor neuron B16. Previous work has characterized MMA (PMSMLRLamide) and MMB (GSYRMMRLamide). We now similarly purified from ARC neuromuscular material and sequenced MMC (GWSMLRLamide), MMD (GLSMLRLamide), MME (GLQMLRLamide), and MMF (SLNMLRLamide). Three additional MMs, MMG (TLSMLRLamide), MMH (GLHMLRLamide), and MMI (SLSMLRLamide), are encoded by a known MM gene. B16 probably synthesizes, and coreleases, all nine MMs. Further MMs have been found in other mollusks. All evidence indicates that the MMs are a major, widely distributed family of molluscan neuropeptides important as neuromuscular modulators and probably also central transmitters or modulators. 3. MM effects on motor neuron B16-elicited ARC muscle contractions were best analyzed as the sum of three distinct actions: potentiation, depression of the amplitude of the contractions, and acceleration of their relaxation rate. We compared the effectiveness of all nine MMs in these respects. We correlated this with their effectiveness in enhancing the L-type Ca current and activating a specific K current in voltage-clamped dissociated ARC muscle fibers, effects we previously proposed to underlie, respectively, the potentiation and the depression of contractions. 4. All nine MMs were similarly effective in enhancing the Ca current and, as far as it was possible to determine, potentiating the amplitude as well as accelerating the relaxation rate of the contractions. 5. In contrast, the MMs' ability to activate the K current and depress the contractions varied greatly. MMB and MMC, in particular, were weak, whereas the other seven MMs were considerably more effective in both respects. 6. Altogether, we were able to explain the potentiating and depressing strengths of the MMs by the magnitude of their modulation of the Ca and K currents, providing further support for our hypothesis that the effects on contraction amplitude are mediated by the effects on the two currents. 7. The net effect on contraction amplitude was determined by the balance between the potentiation and depression. Although most MM concentrations had both potentiating and depressing actions, potentiated contractions predominated at low and depressed contractions (but with accelerated relaxation rate) at high concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Dynamic neuromuscular remodeling precedes motor-unit loss in a mouse model of ALS

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Éric Martineau ◽  
Adriana Di Polo ◽  
Christine Vande Velde ◽  
Richard Robitaille
Keyword(s):  
Motor Neuron ◽  
Motor Neurons ◽  
Axonal Degeneration ◽  
Synapse Formation ◽  
Neuromuscular Junctions ◽  
Motor Units ◽  
Early Event ◽  
Motor Neuron Degeneration ◽  
Single Motor Units

Despite being an early event in ALS, it remains unclear whether the denervation of neuromuscular junctions (NMJ) is simply the first manifestation of a globally degenerating motor neuron. Using in vivo imaging of single axons and their NMJs over a three-month period, we identify that single motor-units are dismantled asynchronously in SOD1G37R mice. We reveal that weeks prior to complete axonal degeneration, the dismantling of axonal branches is accompanied by contemporaneous new axonal sprouting resulting in synapse formation onto nearby NMJs. Denervation events tend to propagate from the first lost NMJ, consistent with a contribution of neuromuscular factors extrinsic to motor neurons, with distal branches being more susceptible. These results show that NMJ denervation in ALS is a complex and dynamic process of continuous denervation and new innervation rather than a manifestation of sudden global motor neuron degeneration.

scholarly journals Human motor units in microfluidic devices are impaired by FUS mutations and improved by HDAC6 inhibition

2020 ◽  
Author(s):  
Katarina Stoklund Dittlau ◽  
Emily N. Krasnow ◽  
Laura Fumagalli ◽  
Tijs Vandoorne ◽  
Pieter Baatsen ◽  
...  
Keyword(s):  
Motor Neuron ◽  
Neurite Outgrowth ◽  
Motor Neurons ◽  
Neuromuscular Junctions ◽  
Induced Pluripotent Stem Cell ◽  
Microfluidic Devices ◽  
Motor Units ◽  
Human Motor ◽  
Induced Pluripotent

AbstractNeuromuscular junctions (NMJs) ensure proper communication between motor neurons and muscle through the release of neurotransmitters. In motor neuron disorders, such as amyotrophic lateral sclerosis (ALS), NMJs degenerate resulting in muscle atrophy, paralysis and respiratory failure. The aim of this study was to establish a versatile and reproducible in vitro model of a human motor unit to study the effect of ALS-causing mutations. Therefore, we generated a co-culture of human induced pluripotent stem cell-derived motor neurons and human primary mesoangioblast-derived myotubes in microfluidic devices. A chemotactic and volumetric gradient facilitated the growth of motor neuron neurites through microgrooves resulting in the interaction with myotubes and the formation of NMJs. We observed that ALS-causing FUS mutations resulted in a reduced neurite outgrowth and in a decreased NMJ number. Interestingly, the selective HDAC6 inhibitor, Tubastatin A, improved the neurite outgrowth and the NMJ morphology of FUS-ALS co-cultures, further prompting HDAC6 inhibition as a potential therapeutic strategy for ALS.

scholarly journals Assessment of motor neuron pathology and potential compensatory mechanisms in phenotypically normal mice with reduced Survival Motor Neuron levels.

2015 ◽  
Vol 8 (1) ◽  
Author(s):  
Rebecca Xu Xu ◽  
Lyndsay M. Murray M. Murray Murray ◽  
Yves De Repentigny De Repentigny ◽  
Rashmi Kothary Kothary
Keyword(s):  
Motor Neuron ◽  
Mouse Models ◽  
Motor Neurons ◽  
Neuromuscular Junctions ◽  
Muscular Atrophy ◽  
Neuromuscular Disorder ◽  
Survival Motor Neuron ◽  
Compensatory Mechanisms ◽  
Protein Levels ◽  
Smn Protein

Spinal muscular atrophy (SMA) is a destructive pediatric neuromuscular disorder caused by low survival motor neuron (Smn) protein levels due to mutations and deletions within the survival motor neuron 1 (SMN1) gene. Motor neurons are the main pathological targets, and along with neuromuscular junctions (NMJs), they play an early significant role in the pathogenesis of SMA. Previous studies demonstrate that a pathological reduction in Smn levels can lead to significant remodeling defects in both the outgrowth of axonal sprouts and in the nerve-directed clustering of AChRs in mouse models. However, whether this pathological reduction in Smn leads to ubclinical features has not been investigated. Here, we have employed the Smn2B/2B and Smn+/- mouse models to study whether similar SMA pathology is present sub-clinically, and if so whether there is any compensation present. We show a decrease in the motor neuron number in the mouse models, no change in myelin thickness and modest NMJ pathology in both mouse models. Additionally, compensation through the expansion of the motor unit size is suggested.L’amyotrophie spinale (AMS) est un trouble neuromusculaire pédiatrique destructif causé par le niveau bas de protéine du neurone de moteur de survie (NMS) en raison des mutations et des effacements dans le neurone de moteur de survie 1 gène (NMS1). Des neurones du moteur sont les cibles pathologiques principales, et ce, avec des jonctions neuromusculaires (JNMs), ils jouent, en avance, un rôle significatif dans la pathogénie de AMS. Des études précédentes démontrent qu’une réduction pathologique de niveaux de NMS peut mener aux défauts importants de réorganisation tant dans l’excroissance axonale que dans l’agrégation du récepteur de l’acétylcholine (AChR) sous la terminaison nerveuse dans des modèles de souris. Cependant, si cette reduction pathologique de NMS mène aux caractéristiques infracliniques n’a pas été à l’étude. Ici, nous avons employé le NMS2B/2B et NMS +/- des modèles de souris afin de déterminer si une pathologie semblable à l’AMS est présente infracliniquement, ainsi s’il y a présence de quelconque compensation. Nous montrons une diminution dans le nombre des neurones du moteur dans les modèles de souris, aucun changement de l’épaisseur du myelin et une pathologie modeste de JNM dans les deux modèles de souris. De plus, une compensation par l’expansion de la taille d’unité du moteur est suggérée.

scholarly journals Skeletal Muscle in ALS: An Unappreciated Therapeutic Opportunity?

Cells ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 525
Author(s):  
Silvia Scaricamazza ◽  
Illari Salvatori ◽  
Alberto Ferri ◽  
Cristiana Valle
Keyword(s):  
Skeletal Muscle ◽  
Motor Neuron ◽  
Motor Neurons ◽  
Skeletal Muscles ◽  
Neuromuscular Junctions ◽  
Neurodegenerative Disorder ◽  
Incurable Disease ◽  
Genetic Modifications ◽  
Therapeutic Opportunity ◽  
Metabolic Dysfunctions

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the selective degeneration of upper and lower motor neurons and by the progressive weakness and paralysis of voluntary muscles. Despite intense research efforts and numerous clinical trials, it is still an incurable disease. ALS had long been considered a pure motor neuron disease; however, recent studies have shown that motor neuron protection is not sufficient to prevent the course of the disease since the dismantlement of neuromuscular junctions occurs before motor neuron degeneration. Skeletal muscle alterations have been described in the early stages of the disease, and they seem to be mainly involved in the “dying back” phenomenon of motor neurons and metabolic dysfunctions. In recent years, skeletal muscles have been considered crucial not only for the etiology of ALS but also for its treatment. Here, we review clinical and preclinical studies that targeted skeletal muscles and discuss the different approaches, including pharmacological interventions, supplements or diets, genetic modifications, and training programs.

scholarly journals Distinct roles for motor neuron autophagy early and late in the SOD1G93A mouse model of ALS

2017 ◽  
Vol 114 (39) ◽  
pp. E8294-E8303 ◽  
Author(s):  
Noam D. Rudnick ◽  
Christopher J. Griffey ◽  
Paolo Guarnieri ◽  
Valeria Gerbino ◽  
Xueyong Wang ◽  
...  
Keyword(s):  
Mouse Model ◽  
Motor Neuron ◽  
Disease Progression ◽  
Motor Neurons ◽  
Neuromuscular Junctions ◽  
Tibialis Anterior Muscle ◽  
Sporadic Amyotrophic Lateral Sclerosis ◽  
Related Transcription Factor ◽  
Factor C ◽  
Autophagy Inhibition

Mutations in autophagy genes can cause familial and sporadic amyotrophic lateral sclerosis (ALS). However, the role of autophagy in ALS pathogenesis is poorly understood, in part due to the lack of cell type-specific manipulations of this pathway in animal models. Using a mouse model of ALS expressing mutant superoxide dismutase 1 (SOD1G93A), we show that motor neurons form large autophagosomes containing ubiquitinated aggregates early in disease progression. To investigate whether this response is protective or detrimental, we generated mice in which the critical autophagy gene Atg7 was specifically disrupted in motor neurons (Atg7 cKO). Atg7 cKO mice were viable but exhibited structural and functional defects at a subset of vulnerable neuromuscular junctions. By crossing Atg7 cKO mice to the SOD1G93A mouse model, we found that autophagy inhibition accelerated early neuromuscular denervation of the tibialis anterior muscle and the onset of hindlimb tremor. Surprisingly, however, lifespan was extended in Atg7 cKO; SOD1G93A double-mutant mice. Autophagy inhibition did not prevent motor neuron cell death, but it reduced glial inflammation and blocked activation of the stress-related transcription factor c-Jun in spinal interneurons. We conclude that motor neuron autophagy is required to maintain neuromuscular innervation early in disease but eventually acts in a non–cell-autonomous manner to promote disease progression.

scholarly journals Modelling functional human neuromuscular junctions in a differentially-perturbable microfluidic environment, validated through recombinant monosynaptic pseudotyped ΔG-rabies virus tracing

2019 ◽  
Author(s):  
Ulrich Stefan Bauer ◽  
Rosanne van de Wijdeven ◽  
Rajeevkumar Nair Raveendran ◽  
Vegard Fiskum ◽  
Clifford Kentros ◽  
...  
Keyword(s):  
Neuromuscular Junction ◽  
Motor Neuron ◽  
Rabies Virus ◽  
Motor Neurons ◽  
Microfluidic Chip ◽  
Neuromuscular Junctions ◽  
Patient Specific ◽  
Human Myotubes ◽  
Virus Tracing

AbstractCompartmentalized microfluidic culture systems provide new perspectives in in vitro disease modelling as they enable co-culture of different relevant cell types in interconnected but fluidically isolated microenvironments. Such systems are thus particularly interesting in the context of in vitro modelling of mechanistic aspects of neurodegenerative diseases such as amyotrophic lateral sclerosis, which progressively affect the function of neuromuscular junctions, as they enable the co-culture of motor neurons and muscle cells in separate, but interconnected compartments. In combination with cell reprogramming technologies for the generation of human (including patient-specific) motor neurons, microfluidic platforms can thus become important research tools in preclinical studies. In this study, we present the application of a microfluidic chip with a differentially-perturbable microenvironment as a platform for establishing functional neuromuscular junctions using human induced pluripotent stem cell derived motor neurons and human myotubes. As a novel approach, we demonstrate the functionality of the platform using a designer pseudotyped ΔG-rabies virus for retrograde monosynaptic tracing.Graphical abstractFunctional neuromuscular junction in a microfluidic chip(a) Overview of microfluidic chip. Human iPS cell-derived motor neuron aggregates (spheroids indicated by black arrows) are seeded in the three lateral compartments of the chip, while human myotubes (white arrows) are seeded in the middle compartment.(b) Directed connectivity and retrograde virus tracing. Outgrowing axons (yellow arrow) from the motor neuron aggregate enter the directional axon tunnels (grey rectangles) and form connections with the myotubes (white arrow) within the opposite compartment. Addition of a designer monosynaptic pseudotyped ΔG-rabies virus to the myotube compartment, infects the myotubes (green) expressing an exogenous receptor (TVA) and rabies glycoprotein (G), subsequently making infectious viruses that are retrogradely transported through the motor neuron axons (green arrow) back to the neuronal cell bodies within the aggregate, validating neuromuscular junction functionality.

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