Excitation-contraction coupling inhibitors potentiate the actions of botulinum neurotoxin type A at the neuromuscular junction.

BACKGROUND AND PURPOSE: Botulinum neurotoxin type A1 (BoNT/A) is one of the most potent neurotoxins known. At the same time, it is also one of the safest therapeutic agents used for the treatment of several human disorders and in aesthetic medicine. Notwithstanding great effectiveness, strategies to accelerate the onset and prolong BoNT/A action would significantly ameliorate its pharmacological effects with beneficial outcomes for clinical use. EXPERIMENTAL APPROACH: Here, we combined BoNT/A with two fast-acting inhibitors of excitation-contraction coupling inhibitors (ECCI), either the µ-conotoxin CnIIIC or dantrolene, and tested the effect of their co-injection on a model of hind-limb paralysis in rodents using behavioural, biochemical, imaging and electrophysiological assays. KEY RESULTS: The BoNT/A-ECCI combinations accelerated the onset of muscle relaxation. Surprisingly, they also potentiated the peak effect and extended the duration of the three BoNT/A commercial preparations OnabotulinumtoxinA, AbobotulinumtoxinA and IncobotulinumtoxinA. ECCI co-injection increased the number of BoNT/A molecules entering motoneuron terminals, which induced a faster and greater cleavage of SNAP-25 during the onset and peak phases, and prolonged the attenuation of nerve-muscle neurotransmission during the recovery phase. We estimate that ECCI co-injection yields a threefold potentiation in BoNT/A pharmacological activity. CONCLUSIONS AND IMPLICATIONS: Overall, our results show that the pharmacological activity of BoNT/A can be combined and synergized with other bioactive molecules and uncover a novel strategy to enhance the neuromuscular effects of BoNT/A without altering the neurotoxin moiety or intrinsic activity, thus maintaining its exceptional safety profile.

Acetylcholine receptor-ß inhibition by interleukin-6 in skeletal muscles contributes to modulating neuromuscular junction during aging.

BACKGROUND: Aging-related strength decline contributes to physiological deterioration and is a good predictor of poor prognosis. However, the mechanisms underlying neuromuscular junction disorders affecting contraction in aging are not well described. We hypothesized that the autocrine effect of interleukin (IL)-6 secreted by skeletal muscle inhibits acetylcholine receptor (AChR) expression, potentially causing aging-related strength decline. Therefore, we investigated IL-6 and AChR ß-subunit (AChR-ß) expression in the muscles and sera of aging C57BL/6J mice and verified the effect of IL-6 on AChR-ß expression. METHODS: Animal experiments, in vitro studies, bioinformatics, gene manipulation, dual luciferase reporter gene assays, and chromatin immunoprecipitation experiments were used to explore the role of the transcription cofactor peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC1α) and its interacting transcription factors in the IL-6-mediated regulation of AChR-ß expression. RESULTS: IL-6 expression gradually increased during aging, inhibiting AChR-ß expression, which was reversed by tocilizumab. Both tocilizumab and the PGC1α agonist reversed the inhibiting effect of IL-6 expression on AChR-ß. Compared to inhibition of signal transducer and activator of transcription 3, extracellular signal-regulated kinases 1/2 (ERK1/2) inhibition suppressed the effects of IL-6 on AChR-ß and PGC1α. In aging mouse muscles and myotubes, myocyte enhancer factor 2 C (MEF2C) was recruited by PGC1α, which directly binds to the AChR-ß promoter to regulate its expression. CONCLUSIONS: This study verifies AChR-ß regulation by the IL-6/IL-6R-ERK1/2-PGC1α/MEF2C pathway. Hence, evaluating muscle secretion, myokines, and AChRs at an earlier stage to determine pathological progression is important. Moreover, developing intervention strategies for monitoring, maintaining, and improving muscle structure and function is necessary.

Neurological manifestations of hypermagnesemia: a narrative review.

Hypermagnesemia is a rare but potentially fatal electrolyte disorder. High serum magnesium levels have been associated with the development of neurological manifestations such as dysautonomia, muscle weakness, respiratory failure, and altered level of consciousness from drowsiness to coma. Although rare, some subjects, such as those with chronic renal failure and those taking magnesium supplements or medications, are at risk of developing this condition. Recognizing this electrolyte alteration promptly allows for an immediate initiation of a therapeutic strategy that is often resolutive when addressed in time. This paper aims to review the neurological complications associated with hypermagnesemia, their pathophysiology, and management.

Functional outcome and histologic analysis of late onset total type brachial plexus injury treated with intercostal nerve transfer to median nerve with local umbilical cord-derived mesenchymal stem cells or secretome injection: a double-blinded, randomized control study.

INTRODUCTION: Intercostal nerve transfer is a surgical technique used to restore function in patients with total brachial plexus injury. Stem cell and secretome therapy has been explored as a potential treatment for brachial plexus injuries. This study aimed to compare the functional and histologic outcome of intercostal nerve transfer to median nerve with local stem cells or secretome injection in total type brachial plexus injuries. MATERIALS AND METHODS: This was a double-blinded, randomized controlled study (RCT). We included patients with neglected total type brachial plexus injury (BPI) who underwent nerve transfer and local injection of either umbilical cord-derived mesenchymal stem cells (UC-MSC) or secretome into median nerve-flexor digitorum superficialis (FDS) neuromuscular junction (NMJ). We measured preoperative and 8-month postoperative FDS muscle strength, SF-36, DASH score, and histologic assessment. We then analyzed the difference outcome between those two groups. RESULT: A total of 15 patients were included in this study. Our study found that after nerve transfer and implantation with either UC-MSC or secretome, significant postoperative improvements were observed in physical functioning, role limitations, energy/fatigue, emotional well-being, social functioning, pain, general health, and DASH scores, particularly in the overall cohort and the secretome group. When we compared the mean difference of clinical outcome from preoperative to postoperative between UC-MSC and secretome groups, the UC-MSC group showed better improvement of health change in SF-36 subgroup compared to secretome group. From the analysis, there was no significant difference in the histologic outcomes (inflammation, regeneration, and fibrosis) in overall cohort between preoperative and postoperative cohort. There was also no significant difference in mean change of the histologic outcomes (inflammation, regeneration, and fibrosis) preoperative and postoperatively between UC-MSC and secretome groups. DISCUSSION AND CONCLUSION: Implantation of either UC-MSC or secretome along with nerve transfer may provide clinical improvement, while to achieve histologic improvement, further conditioning should be performed.

Visualization and Analysis of Neuromuscular Junctions Using Immunofluorescence.

The neuromuscular junction (NMJ) is an interface between motor neurons and skeletal muscle fibers, facilitating the transmission of signals that initiate muscle contraction. Its pivotal role lies in ensuring efficient communication between the nervous system and muscles, allowing for precise and coordinated movements essential for everyday activities and overall motor function. To provide insights into neuromuscular disease and development, understanding the physiology of NMJ is essential. We target acetylcholine receptors (AChR) by immunofluorescence assay (IFA) with α-bungarotoxin (BTX; snake venom neurotoxins binding to AChR) to visualize and quantify the NMJ. Changes in AChR distribution or structure can indicate alterations in receptor density, which may be associated with neuromuscular disorders or conditions that affect synaptic transmission. This protocol provides the methodology for isolating and longitudinally sectioning gastrocnemius muscle for AChR-targeted IFA for confocal microscopy and performing quantitative analysis of NMJs. Key features • Visualizes and quantifies NMJs using α-bungarotoxin. • Utilizes high-resolution confocal microscopy for detailed imaging.

Muscle-fiber specific genetic manipulation of Drosophila sallimus severely impacts neuromuscular development, morphology, and physiology.

The ability of skeletal muscles to contract is derived from the unique genes and proteins expressed within muscles, most notably myofilaments and elastic proteins. Here we investigated the role of the sallimus (sls) gene, which encodes a structural homologue of titin, in regulating development, structure, and function of Drosophila melanogaster. Knockdown of sls using RNA interference (RNAi) in all body-wall muscle fibers resulted in embryonic lethality. A screen for muscle-specific drivers revealed a Gal4 line that expresses in a single larval body wall muscle in each abdominal hemisegment. Disrupting sls expression in single muscle fibers did not impact egg or larval viability nor gross larval morphology but did significantly alter the morphology of individual muscle fibers. Ultrastructural analysis of individual muscles revealed significant changes in organization. Surprisingly, muscle-cell specific disruption of sls also severely impacted neuromuscular junction (NMJ) formation. The extent of motor-neuron (MN) innervation along disrupted muscles was significantly reduced along with the number of glutamatergic boutons, in MN-Is and MN-Ib. Electrophysiological recordings revealed a 40% reduction in excitatory junctional potentials correlating with the extent of motor neuron loss. Analysis of active zone (AZ) composition revealed changes in presynaptic scaffolding protein (brp) abundance, but no changes in postsynaptic glutamate receptors. Ultrastructural changes in muscle and NMJ development at these single muscle fibers were sufficient to lead to observable changes in neuromuscular transduction and ultimately, locomotory behavior. Collectively, the data demonstrate that sls mediates critical aspects of muscle and NMJ development and function, illuminating greater roles for sls/titin.

Adherence to the Mediterranean Diet: A Tool to the Therapeutic Approaches for Patients With Temporomandibular Joint Disorders.

BACKGROUND AND AIM: Temporomandibular joint disorder (TMD) is characterized by symptoms such as clenching, clicking, and locking of the jaw, often due to improper positioning affecting occlusion. Nearly half of TMD patients rarely require treatment, as symptoms typically diminish on their own within a year. Nevertheless, a significant majority of persons who are diagnosed with TMD do necessitate therapy, and it may take up to three years for complete remission to occur. This study aims to determine the extent to which a healthy nutritional model, specifically the Mediterranean diet, can enhance the effectiveness of existing therapeutic treatments, like physiotherapy with warm pads. METHODS: An interventional study design was implemented. Baseline scores were obtained pre- and post-intervention, while Mediterranean diet adherence was evaluated once at the beginning. A dependent samples t-test and a one-way multivariate analysis of covariance (MANCOVA) were used to test the experimental hypotheses. RESULTS: There is a statistically significant difference (p=0.04) between the three groups associated with Mediterranean diet adherence, as indicated by the mean differences on the Jaw Functional Limitation Scale (JFLS-20) questionnaire. Participants following a medium or high level of Mediterranean diet (≥18) reported fewer problems with jaw functionality both before and after the intervention compared to those with low (<18) adherence to the diet. CONCLUSION: Adherence to the Mediterranean diet appears to have a therapeutic effect on patients with TMD, offering a new dimension to their treatment. The primary benefit is the low cost of treatment, as the diet is easily accessible. This dietary approach could significantly enhance the management of TMD symptoms.

Fluoxetine antagonizes the acute response of LPS: Blocks K2P channels.

The channels responsible for maintaining resting membrane potential are known as K2P (two-P-domain K+ subunit) channels, a subset of which are known to be blocked by Fluoxetine. In this experiment, the compound's effects on the membrane potential were examined on muscles in larval Drosophila overexpressing a subtype of K2P channel (known in Drosophila as dORKA1 or ORKA1) and compared to larvae without overexpression. The compound was also observed in sequence and/or combination with a form of lipopolysaccharide (LPS) that transiently activates K2P channels. Different concentrations of Fluoxetine were tested, and it was also examined in cocktail with the LPS. At 25 µM Fluoxetine exposure, muscle in control larvae underwent depolarization, while muscles overexpressing K2P channels hyperpolarized; at 50 µM, however, much more variable responses were observed. The LPS caused hyperpolarization in both larval strains, but the effect was more transient in the Canton-S line than in the K2P overexpressors. Finally, LPS continued to cause hyperpolarization even in the presence of Fluoxetine, while Fluoxetine quickly depolarized the muscle during exposure to LPS. The cocktail showed a smaller effect on muscles overexpressing ORKA1 as compared to the controls, indicating that Fluoxetine does not block the ORKA1 subtype. This study is significant because it demonstrates how overexpression of K2P channels alters membrane response to LPS and Fluoxetine exposure.

Atypical Presentations of Myasthenia Gravis as Acute Respiratory Failure: A Rare Case.

Myasthenia gravis (MG) is a chronic neuromuscular disease characterized by the progressive weakness of voluntary muscles, which encompass those in the face, throat, diaphragm, and those attached to bones. Patients commonly present with specific muscle weakness, such as difficulty in eye movement, facial expression, or swallowing, rather than generalized fatigue. However, as the disease advances, the majority of patients develop respiratory symptoms, which can significantly impact their quality of life. This makes the management of respiratory comorbidities essential, as respiratory tract infections can lead to exacerbations of MG and trigger a myasthenic crisis, necessitating immediate medical intervention. This report highlights a patient who initially presented with acute respiratory distress and was subsequently diagnosed with MG, underscoring the importance of recognizing respiratory symptoms in the context of this condition.

Endocytosis of Synaptic Vesicle in Motor Nerve Endings of FUS Transgenic Mice with a Model of Amyotrophic Lateral Sclerosis.

In experiments on the motor nerve endings of the diaphragm of transgenic FUS mice with a model of amyotrophic lateral sclerosis at the pre-symptomatic stage of the disease, the processes of transmitter release and endocytosis of synaptic vesicles were studied. In FUS mice, the intensity of transmitter release during high-frequency stimulation of the motor nerve (50 imp/sec) was lowered. At the same duration of stimulation, the loading of fluorescent dye FM1-43 was lower in FUS mice. However, at the time of stimulation, during which an equal number of quanta are released in wild-type and FUS mice, no differences in the intensity of dye loading were found. Thus, endocytosis is not the key factor in the mechanism of synaptic dysfunction in FUS mice at the pre-symptomatic stage.

Integrative insights into PNI: Low-grade chronic inflammation, skeletal muscle wasting, and brain impairments.

Skeletal muscle has been recognized as an endocrine organ which communicates with different systems, including the brain. In conditions involving systemic low-grade chronic inflammation , the skeletal muscle can be negatively impacted, culminating in its quantity (mass) and quality (function) losses, referred to here as muscle wasting. The inflammatory milieu, as well known, also impairs the brain function, however there are some particularities involving skeletal muscle-brain crosstalk, including cognitive function and mental health impairments . Psychoneuroimmunology (PNI) is an important field of neuroendocrine-immune-behavior science and an approach between PNI, and the movement science, or kinesiology, field can enrich future research about the relationship between skeletal muscle wasting and brain health. Thus, in this short review, we present an overview about the interplay between skeletal muscle, inflammatory mediator markers, and brain function with the purpose to strengthen the ties between kinesiology and PNI research to enhance futures discoveries and advances in health sciences.

Clinical features of COVID-19 infection in patients with myasthenia gravis: a real-world retrospective study.

Objective: We investigated the risk factors associated with severe or critical Coronavirus disease 2019 (COVID-19) infection due to the Omicron variant in patients with myasthenia gravis (MG) and determined the potential effect of COVID-19 on myasthenic exacerbation during the Omicron pandemic. Methods: This retrospective study included 287 patients with MG in Tianjin, China. Clinical data of the patients were collected using electronic questionnaires, databases, and clinical records. Results: The overall infection rate was 84.7%. Advanced age, comorbidities, generalized phenotype, and MG instability were drivers of COVID-19 severity, and post-COVID-19 myasthenic exacerbation. The concurrent use of a steroid-sparing agent did not affect COVID-19 susceptibility or severity. It did lower the risk of myasthenic exacerbation after COVID-19 infection. Patients with severe COVID-19 experienced myasthenic exacerbation earlier than patients with non-severe infection (p < 0.001). The severity of COVID-19 (Hazards Ratio = 3.04, 95% CI: 1.41-6.54, p = 0.004) and the clinical phenotype (Hazards Ratio = 3.29, 95% CI: 1.63-6.63, p < 0.001) emerged as independent risk factors for early MG exacerbation. Conclusion: Generally, patients with MG appear to be susceptible to the Omicron strains. Immunotherapy for MG did not increase COVID-19 susceptibility or severity. We do not advocate an immediate cessation of ongoing immunosuppressive treatments once a COVID-19 infection is diagnosed. Instead, a judicious evaluation of the risks and benefits, tailored to each individual, is recommended.

Isolation and Pharmacological Characterisation of Pre-Synaptic Neurotoxins from Thai and Javanese Russell's Viper (Daboia siamensis) Venoms.

The widespread geographical distribution of Russell's vipers (Daboia spp.) is associated with marked variations in the clinical outcomes of envenoming by species from different countries. This is likely to be due to differences in the quantity and potency of key toxins and, potentially, the presence or absence of some toxins in venoms across the geographical spectrum. In this study, we aimed to isolate and pharmacologically characterise the major neurotoxic components of D. siamensis venoms from Thailand and Java (Indonesia) and explore the efficacy of antivenom and a PLA2 inhibitor, Varespladib, against the neuromuscular activity. These data will provide insights into the link between venom components and likely clinical outcomes, as well as potential treatment strategies. Venoms were fractionated using RP-HPLC and the in vitro activity of isolated toxins assessed using the chick biventer cervicis nerve-muscle preparation. Two major PLA2 fractions (i.e., fractions 8 and 10) were isolated from each venom. Fraction 8 from both venoms produced pre-synaptic neurotoxicity and myotoxicity, whereas fraction 10 from both venoms was weakly neurotoxic. The removal of the two fractions from each venom abolished the in vitro neurotoxicity, and partially abolished myotoxicity, of the whole venom. A combination of the two fractions from each venom produced neurotoxic activity that was equivalent to the respective whole venom (10 µg/mL), but the myotoxic effects were not additive. The in vitro neurotoxicity of fraction 8 (100 nM) from each venom was prevented by the pre-administration of Thai Russell's viper monovalent antivenom (2× recommended concentration) or preincubation with Varespladib (100 nM). Additionally, the neurotoxicity produced by a combination of the two fractions was partially reversed by the addition of Varespladib (100-300 nM) 60 min after the fractions. The present study demonstrates that the in vitro skeletal muscle effects of Thai and Javanese D. siamensis venoms are primarily due to key PLA2 toxins in each venom.

Angiotensin-converting enzyme inhibitors attenuate circulating CAF22 and physical decline in congestive heart failure: Diagnostic implications of CAF22.

AIMS: Age-associated muscle loss, termed sarcopenia is the major cause of physical disability in patients with congestive heart failure (CHF). Angiotensin-converting enzyme inhibitors (ACEi) are commonly used to treat CHF patients; however, their impacts on the neuromuscular junction (NMJ) and sarcopenia in CHF patients remain poorly understood. We aim to investigate the potential impact of ACEi on NMJ and CHF-induced sarcopenia. METHODS: The cardiac function, short physical performance battery, handgrip strength (HGS), appendicular skeletal mass index, gait speed (GS) and plasma c-terminal agrin fragment-22 (CAF22), a marker of NMJ degradation, were assessed in controls (n = 81) and CHF patients treated with (n = 134) or without (n = 145) ACEi. RESULTS: Irrespective of treatment, HGS and GS, indicators of sarcopenia, were profoundly declined in the patients with CHF vs. controls. However, patients on ACEi demonstrated significantly better HGS and GS compared to non-ACEi patients (P < .001). The level of CAF22 was significantly lower (P < .0001) in the ACEi-treated compared to non-ACEi CHF patients. Further, the level of CAF22 was inversely correlated (R2 = .33, P < .0001) with HGS in both ACEi and non-ACEi CHF patients, while CAF22 was inversely correlated with GS and short physical performance battery only in ACEi-treated but not in patients on other therapies without ACEi. The receiver operating characteristic curve analysis revealed CAF22 as a potential diagnostic marker (95% confidence interval: 0.785-0.883; P < .0001) for CHF. CONCLUSION: Collectively, these findings strongly suggest that ACEi limits CHF-induced neuromuscular disjunction and physical disability in CHF. CAF22 has shown diagnostic implications for CHF.

Unacylated Ghrelin Protects Against Age-Related Loss of Muscle Mass and Contractile Dysfunction in Skeletal Muscle.

Sarcopenia, the progressive loss of muscle mass and function, universally affects older adults and is closely associated with frailty and reduced quality of life. Despite the inevitable consequences of sarcopenia and its relevance to healthspan, no pharmacological therapies are currently available. Ghrelin is a gut-released hormone that increases appetite and body weight through acylation. Acylated ghrelin activates its receptor, growth hormone secretagogue receptor 1a (GHSR1a), in the brain by binding to it. Studies have demonstrated that acyl and unacylated ghrelin (UnAG) both have protective effects against acute pathological conditions independent of receptor activation. Here, we investigated the long-term effects of UnAG in age-associated muscle atrophy and contractile dysfunction in mice. Four-month-old and 18-month-old mice were subjected to either UnAG or control treatment for 10 months. UnAG did not affect food consumption or body weight. Gastrocnemius and quadriceps muscle weights were reduced by 20%-30% with age, which was partially protected against by UnAG. Specific force, force per cross-sectional area, measured in isolated extensor digitorum longus muscle was diminished by 30% in old mice; however, UnAG prevented the loss of specific force. UnAG also protected from decreases in mitochondrial respiration and increases in hydrogen peroxide generation of skeletal muscle of old mice. Results of bulk mRNA-seq analysis and our contractile function data show that UnAG reversed neuromuscular junction impairment that occurs with age. Collectively, our data revealed the direct role of UnAG in mitigating sarcopenia in mice, independent of food consumption or body weight, implicating UnAG treatment as a potential therapy against sarcopenia.

Neuromuscular impairment at different stages of human sarcopenia.

BACKGROUND: Degeneration of the motoneuron and neuromuscular junction (NMJ) and loss of motor units (MUs) contribute to age-related muscle wasting and weakness associated with sarcopenia. However, these features have not been comprehensively investigated in humans. This study aimed to compare neuromuscular system integrity and function at different stages of sarcopenia, with a particular focus on NMJ stability and MU properties. METHODS: We recruited 42 young individuals (Y) (aged 25.98 ± 4.6 years; 57% females) and 88 older individuals (aged 75.9 ± 4.7 years; 55% females). The older group underwent a sarcopenia screening according to the revised guidelines of the European Working Group on Sarcopenia in Older People 2. In all groups, knee extensor muscle force was evaluated by isometric dynamometry, muscle morphology by ultrasound and MU potential properties by intramuscular electromyography (iEMG). MU number estimate (iMUNE) and blood samples were obtained. Muscle biopsies were collected in a subgroup of 16 Y and 52 older participants. RESULTS: Thirty-nine older individuals were non-sarcopenic (NS), 31 pre-sarcopenic (PS) and 18 sarcopenic (S). A gradual decrease in quadriceps force, cross-sectional area and appendicular lean mass was observed across the different stages of sarcopenia (for all P < 0.0001). Handgrip force and the Short Physical Performance Battery score also showed a diminishing trend. iEMG analyses revealed elevated near fibre segment jitter in NS, PS and S compared with Y (Y vs. NS and S: P < 0.0001; Y vs. PS: P = 0.0169), suggestive of age-related impaired NMJ transmission. Increased C-terminal agrin fragment (P < 0.0001) and altered caveolin 3 protein expression were consistent with age-related NMJ instability in all the older groups. The iMUNE was lower in all older groups (P < 0.0001), confirming age-related loss of MUs. An age-related increase in MU potential complexity was also observed. These observations were accompanied by increased muscle denervation and axonal damage, evinced by the increase in neural cell adhesion molecule-positive fibres (Y vs. NS: P < 0.0001; Y vs. S: P = 0.02) and the increase in serum concentration of neurofilament light chain (P < 0.0001), respectively. Notably, most of these MU and NMJ parameters did not differ when comparing older individuals with or without sarcopenia. CONCLUSIONS: Alterations in MU properties, axonal damage, an altered innervation profile and NMJ instability are prominent features of the ageing of the neuromuscular system. These neuromuscular alterations are accompanied by muscle wasting and weakness; however, they appear to precede clinically diagnosed sarcopenia, as they are already detectable in older NS individuals.

Distinct input-specific mechanisms enable presynaptic homeostatic plasticity.

Synapses are endowed with the flexibility to change through experience, but must be sufficiently stable to last a lifetime. This tension is illustrated at the Drosophila neuromuscular junction (NMJ), where two motor inputs that differ in structural and functional properties co-innervate most muscles to coordinate locomotion. To stabilize NMJ activity, motor neurons augment neurotransmitter release following diminished postsynaptic glutamate receptor functionality, termed presynaptic homeostatic potentiation (PHP). How these distinct inputs contribute to PHP plasticity remains enigmatic. We have used a botulinum neurotoxin to selectively silence each input and resolve their roles in PHP, demonstrating that PHP is input-specific: Chronic (genetic) PHP selectively targets the tonic MN-Ib, where active zone remodeling enhances Ca2+ influx to promote increased glutamate release. In contrast, acute (pharmacological) PHP selectively increases vesicle pools to potentiate phasic MN-Is. Thus, distinct homeostatic modulations in active zone nanoarchitecture, vesicle pools, and Ca2+ influx collaborate to enable input-specific PHP expression.

Elevated serum levels of C-terminal agrin fragment in acetylcholine receptor antibody-positive myasthenia gravis.

Agrin is essential for neuromuscular junction (NMJ) formation and maintenance. The C-terminal agrin fragment (CAF), generated by neurotrypsin-mediated cleavage of agrin, has been gaining attention as a potential biomarker for sarcopenia. We investigated serum CAF levels in myasthenia gravis (MG), a NMJ disorder. Compared to healthy controls, serum CAF levels were significantly elevated in acetylcholine receptor antibody-positive MG (AChR-MG) patients, but not in muscle-specific kinase antibody-positive MG patients. In AChR-MG, baseline and post-treatment CAF levels inversely correlated with post-treatment MG activities of daily living scores, suggesting that elevated CAF levels may reflect protective mechanisms against AChR-MG pathogenesis, such as improved NMJ regeneration.

Application of Electrophysiological Techniques in Assessing of Neuromuscular Junction-Related Disorders.

This review aims to comprehensively summarize the application of electrophysiological methods, specifically repetitive nerve stimulation (RNS) and single fiber electromyography (SFEMG), in the diagnosis of neuromuscular junction (NMJ) disorders, including myasthenia gravis, Lambert-Eaton syndrome, and sarcopenia in the elderly. Both RNS and SFEMG have demonstrated high sensitivity and specificity in detecting NMJ abnormalities. RNS aids in distinguishing presynaptic from postsynaptic lesions, while SFEMG provides direct evidence of NMJ function by assessing single motor unit action potentials. Key parameters in SFEMG, such as fiber density, jitter, and pulse blocking, are crucial for evaluating NMJ function. Increased fiber density and jitter value, along with pulse blocking, are often observed in patients with NMJ disorders. However, despite the extensive application of these techniques in various NMJ-related diseases, their role in aging, particularly in sarcopenic patients, remains underexplored, highlighting the need for future research.

Ocular versus generalized myasthenia gravis: a continuum associated with acetylcholine receptor antibody titers.

The aim of this study was to evaluate clinical and serological differences between the ocular myasthenia gravis (oMG) and generalized MG (gMG). This study is a retrospective chart review, in which data was collected from patients fulfilling 2 of 3 diagnostic MG criteria (positive antibodies, evidence of neuromuscular transmission defect on neurophysiological examination, positive effect of pyridostigmine treatment). 350 patients were included and data concerning demographics and MG medical history were collected. Patients with oMG accounted for 15.7 % of the included patients. The two subgroups differed significantly in oMG having a later age at onset, lower AChR antibody-titers, longer doctor-to-diagnosis delay and less intensive MG treatment. Additionally, patients with oMG were faster at reaching a well-controlled disease state. Thymus pathology, number of antibody-positive (95.9 % of gMG and 94.5 % of oMG), sex, number of other autoimmune diseases and delay before drug stability did not differ between oMG and gMG. In conclusion, oMG is presumably a milder form of gMG characterized by lower AChR antibody-titers, a milder phenotype, and a quicker response to a less aggressive treatment. But otherwise, oMG and gMG show very similar characteristics, including the same frequency of positive AChR antibodies, which seems new compared to previous reports.