Electrophysiological evaluation of the neuromuscular junction: a brief review / Avaliação eletrofisiológica da junção neuromuscular: breve revisão

Abstract The nerve terminal and muscle membrane compose the neuromuscular junction. After opening the voltage-gated calcium channels, action potentials from the motor axons provoke a cascade for the acetylcholine release from synaptic vesicles to the synaptic cleft, where it binds to its receptor at the muscle membrane for depolarization. Low amplitude compound muscle action potential typically presents in presynaptic disorders, increasing by more than 100% after a 10-second effort in the Lambert-Eaton myasthenic syndrome and less in botulism. Needle electromyography may show myopathic motor unit action potentials and morphological instability ("jiggle") due to impulse blocking. Low-frequency repetitive nerve stimulation (RNS) is helpful in postsynaptic disorders, such as myasthenia gravis and most congenital myasthenic syndromes, where the number of functioning acetylcholine receptors is reduced. Low-frequency RNS with a decrement >10% is abnormal when comparing the 4th to the first compound muscle action potential amplitude. High-frequency RNS is helpful in presynaptic disorders like Lambert-Eaton myasthenic syndrome, botulism, and some rare congenital myasthenic syndromes. The high-frequency RNS releases more calcium, increasing the acetylcholine with a compound muscle action potential increment. Concentric needle records apparent single-fiber action potentials (spikes). A voluntary activation measures the jitter between spikes from two endplates. An electrical activation measures the jitter of one spike (one endplate). The jitter is the most sensitive test for detecting a neuromuscular junction dysfunction. Most neuromuscular junction disorders are responsive to treatment.

Resumo O nervo terminal e a membrana muscular compõem a junção neuromuscular. Após a abertura dos canais de cálcio dependentes de voltagem, os potenciais de ação do axônio motor provocam uma cascata de eventos que libera acetilcolina das vesículas para a fenda sináptica, ligando-se ao receptor na membrana muscular para despolarização. O potencial de ação muscular composto de baixa amplitude ocorre nas desordens pré-sinápticas, aumentando em mais de 100% após esforço de 10 segundos na síndrome miastênica de Lambert-Eaton e menos no botulismo. A eletromiografia pode mostrar potenciais de ação da unidade motora miopáticos e instabilidade morfológica ("jiggle") devido ao bloqueio do impulso. Estimulação nervosa repetitiva (ENR) de baixa frequência é útil nos distúrbios pós-sinápticos, como miastenia gravis e a maioria das síndromes miastênicas congênitas, quando há número reduzido de receptores de acetilcolina funcionantes. ENR de baixa frequência com decremento >10% é anormal comparando-se à amplitude do quarto com o primeiro potencial de ação muscular composto. ENR de alta frequência é útil nas doenças pré-sinápticas, como síndrome miastênica de Lambert-Eaton, botulismo e algumas síndromes miastênicas congênitas raras. ENR de alta frequência libera mais cálcio, aumenta acetilcolina, resultando em incremento do potencial de ação muscular composto. O eletrodo de agulha concêntrico registra potenciais de ação aparente de fibra única (PAAFU). Ativação voluntária mede jitter entre dois PAAFUs (duas junções neuromusculares). Ativação elétrica mede jitter de um PAAFU (uma junção neuromuscular). Jitter é o teste mais sensível para detectar disfunção de junção neuromuscular. A maioria dos distúrbios juncionais é responsiva ao tratamento.

Comparison of onset of neuromuscular blockade with electromyographic and acceleromyographic monitoring: a prospective clinical trial

Abstract Background Reliable devices that quantitatively monitor the level of neuromuscular blockade after neuromuscular blocking agents' administration are crucial. Electromyography and acceleromyography are two monitoring modalities commonly used in clinical practice. The primary outcome of this study is to compare the onset of neuromuscular blockade, defined as a Train-Of-Four Count (TOFC) equal to 0, as measured by an electromyography-based device (TetraGraph) and an acceleromyography-based device (TOFscan). The secondary outcome was to compare intubating conditions when one of these two devices reached a TOFC equal to 0. Methods One hundred adult patients scheduled for elective surgery requiring neuromuscular blockade were enrolled. Prior to induction of anesthesia, TetraGraph electrodes were placed over the forearm of patients' dominant/non-dominant hand based on randomization and TOFscan electrodes placed on the contralateral forearm. Intraoperative neuromuscular blocking agent dose was standardized to 0.5 mg.kg−1 of rocuronium. After baseline values were obtained, objective measurements were recorded every 20 seconds and intubation was performed using video laryngoscopy once either device displayed a TOFC = 0. The anesthesia provider was then surveyed about intubating conditions. Results Baseline TetraGraph train-of-four ratios were higher than those obtained with TOFscan (Median: 1.02 [0.88, 1.20] vs. 1.00 [0.64, 1.01], respectively, p < 0.001). The time to reach a TOFC = 0 was significantly longer when measured with TetraGraph compared to TOFscan (Median: 160 [40, 900] vs. 120 [60, 300] seconds, respectively, p < 0.001). There was no significant difference in intubating conditions when either device was used to determine the timing of endotracheal intubation. Conclusions The onset of neuromuscular blockade was longer when measured with TetraGraph than TOFscan, and a train-of-four count of zero in either device was a useful indicator for adequate intubating conditions. Clinical trial number and registry URL NCT05120999, https://clinicaltrials.gov/ct2/show/NCT05120999.

Myasthenia gravis in clinical practice / Miastenia gravis na prática clínica

ABSTRACT Background: Myasthenia gravis is largely a treatable disease, but it can result in significant morbidity and even mortality, which can usually be avoided, or at least mitigated, with timely diagnosis and appropriate treatment of the disease. Objective: this review aims to summarize the main practical aspects of the diagnostic approach, treatment and care of myasthenic patients. Methods: The authors performed a non-systematic critical review summarizing the main practical aspects of myasthenia gravis. Results: Most patients with myasthenia have autoantibodies targeted at acetylcholine receptors or, less commonly, muscle-specific kinase - MuSK. Electrophysiology plays an important role in the diagnosis of neuromuscular junction dysfunction. The central clinical manifestation of myasthenia gravis is fatigable muscle weakness, which can affect eye, bulbar, respiratory, and limb muscles. With rare exceptions, patients have a good response to symptomatic treatment, but corticosteroids and/or immunosuppressants are usually also necessary to obtain good control of the manifestations of the disease. Conclusion: Knowledge of the peculiar aspects of their clinical and electrophysiological presentations is important for the diagnosis. Likewise, specific treatment and response time to each drug are crucial for proper care.

RESUMO Antecedentes: A miastenia gravis é, em grande parte, uma doença tratável, mas pode resultar em significativa morbidade e até mortalidade, que geralmente pode ser evitada, ou pelo menos atenuada, com diagnóstico oportuno e tratamento adequado da doença. Objetivo: Esta revisão visa resumir os principais aspectos práticos da abordagem diagnóstica, do tratamento e dos cuidados de pacientes miastênicos. Métodos: Os autores realizaram uma revisão crítica não sistemática, resumindo os principais aspectos práticos da miastenia gravis. Resultados: A maioria dos pacientes com miastenia apresenta autoanticorpos direcionados aos receptores de acetilcolina ou, menos comumente, quinase músculo-específica - MuSK. A eletrofisiologia desempenha um papel importante no diagnóstico da disfunção da junção neuromuscular. A manifestação clínica central da miastenia gravis é a fraqueza muscular fatigável, que pode afetar os músculos oculares, bulbares, respiratórios e dos membros. Com raras exceções, os pacientes respondem bem ao tratamento sintomático, mas geralmente também são necessários corticosteroides e/ou imunossupressores para se obter um bom controle das manifestações da doença. Conclusão: O conhecimento dos aspectos peculiares de suas apresentações clínicas e eletrofisiológicas é importante para o diagnóstico. Da mesma forma, o tratamento específico e o tempo de resposta a cada medicamento são cruciais para o cuidado adequado.

Congenital Myasthenic Syndrome / 罕见病研究

Congenital Myasthenic syndrome (CMS) is a group of partially treatable genetic disorders characterized by dysfunction of neuromuscular junction signaling.With the popularization of high-throughput sequencing and in-depth understanding of the disease in recent years, more than thirty pathogenic genes have been discovered and there is a correlation between genotype and clinical phenotype.Misdiagnosis and missed diagnosis are common in clinical practice. This paper summarized the molecular mechanisms, clinical features, electrophysiologic, pathological features and treatment of main subtypes of CMS to deepen the understanding of the disease.

A morphological study of denervation and reinnervation of neuromuscular junction and muscle spindle after sciatic nerve crush in mice / 中华显微外科杂志

Objective:To observe the denervation and reinnervation of the neuromuscular junction (NMJ) and muscle spindle after sciatic nerve crush in mice.Methods:From January, 2019 to October, 2019, 18 C57BL/6 mice were randomly and evenly divided into injured groups (sciatic nerve crush group, 12 mice) and control groups (sham group, 6 mice). Mice in the injured group were sacrificed at day-1, day-2, day-3 and 4 weeks after the sciatic nerve injury. Mice in the control group were sacrificed at day-3 and 4 weeks from the day of experiment. The tibialis anterior muscles with crushed nerve were collected for immunohistochemistry staining by neurofilament (NF), synaptophysin (Syn) and α-bungarotoxin (α-BTX). Data were analysed by unpaired t-test. P<0.05 was considered significant difference. Results:The completely denervation of NMJ reached (92.4±8.85)% at day-3 after the nerve crush, compared with (5.19±1.32)% in the control group ( P<0.05). However, the muscle spindle lost γ-motor neuron innervation at day-2 after the nerve crush and completely denervated at day-3 after the surgery. For the reinnervation, no difference of no reinnervation of NMJ [(3.02±0.78)% vs. (4.22±2.08)%], partial reinnervation of NMJ [(6.44±1.91)% vs. (7.94±2.12)%] and completely reinnervation of NMJ [(90.54±10.44)% vs. (87.84±13.89)%] were observed between the control group and the injured group 4 weeks after the injury. While, for the muscle spindle, only the acetylcholine receptors at each end were partly reinnervated. The innervation of the middle part of the muscle spindle was thin and discontinued without typical spiral winding structure. Conclusion:The denervation speed of NMJ and muscle spindle was comparable after the peripheral nerve injury. The γ-motor neuron lost innervation ahead of the sensory neuron in the muscle spindle. The reinnervation of NMJ is earlier than that of the muscle spindle, and the re-innervation of the γ-motor neuron is prior to the sensory neuron in the muscle spindle.

Neurotoxical activity of Micrurus snake venom and methods for its analysis. A literature review / Actividad neurotóxica del veneno de serpientes del género Micrurus y métodos para su análisis. Revisión de la literatura

Abstract Introduction: Snakes of the genus Micrurus have fossorial habits, passive temperament and scarce production of powerful venom with neurotoxic characteristics that block the synaptic transmission at the neuromuscular junction. Objective: To present an overview of the neurotoxicity of the Micrurus snake venom, and its functional characterization by ex vivo analysis methods. Materials and methods: A literature review was conducted in MedLine and ScienceDirect using specific terms and their combinations. Search strategy: type of studies: articles on the neurotoxicity of Micrurus snake venom and techniques to determine its neurotoxic activity by in vitro, in vivo and ex vivo models; publication period: articles published until June 2018; publication language: English and Spanish. Results: Out of 88 studies identified in the initial search, 28 were excluded because they did not meet the inclusion criteria (based on reading their titles and abstracts). 8 additional articles (books and reports) were included, since, according to the authors' opinion, they complemented the information reported by the selected studies. The studies included in the review (n=68) were original research papers (n=44), review articles (n = 16), and book chapters, reports, guides and online consultations (n=8). Conclusions: Studies performed using ex vivo muscle and nerve preparations to evaluate the effect of neurotoxins provide a good model for the characterization of the pre-synaptic and post-synaptic effect of the venom produced by snakes of the genus Micrurus.

Resumen Introducción. Las serpientes del género Micrurus son animales de hábitos fosoriales, de temperamento pasivo y escasa producción de un potente veneno con características neurotóxicas que bloquean la transmisión sináptica en la placa neuromuscular. Objetivo. Presentar un panorama general de la neurotoxicidad del veneno de las serpientes Micrurus y su caracterización funcional mediante métodos de análisis ex vivo. Materiales y métodos. Se realizó una revisión de la literatura en MedLine y ScienceDirect usando términos específicos y sus combinaciones. Estrategia de búsqueda: tipo de estudios: artículos sobre la neurotoxicidad del veneno de serpientes Micrurus y técnicas para determinar su actividad neurotóxica mediante modelos in vitro, in vivo y ex vivo; periodo de publicación: sin límite inicial a junio de 2018; idiomas: inglés y español. Resultados. De los 88 estudios identificados en la búsqueda inicial, se excluyeron 28 por no cumplir los criterios de inclusión (basándose en la lectura de títulos y resúmenes); además, se incluyeron 8 documentos adicionales (libros e informes), que, a criterio de los autores, complementaban la información reportada por las referencias seleccionadas. Los estudios incluidos en la revisión (n=68) correspondieron a las siguientes tipologías: investigaciones originales (n=44), artículos de revisión (n=16) y capítulos de libros, informes, guías y consultas en internet (n=8). Conclusiones. Los estudios que describen el uso de preparaciones ex vivo de músculo y nervio para evaluar el efecto de neurotoxinas ofrecen un buen modelo para la caracterización del efecto presináptico y postsináptico del veneno producido por las serpientes Micrurus.

Miastenia gravis en la infancia: una serie de tres casos / Myasthenia gravis in infancy: a series of three cases

La miastenia gravis es una enfermedad neuromuscular crónica debida a deficiencia de transmisión nerviosa en la unión neuromuscular, de origen generalmente autoinmune en el adulto, que se caracteriza por grados variables de debilidad de los músculos esqueléticos del cuerpo, que aumenta durante los períodos de actividad y disminuye después de períodos de descanso. Sin embargo en la infancia cobran especial relevancia los síndromes miasténicos congénitos, que encuentran su origen en mutaciones de genes que codifican proteínas que juegan papeles clave en el mantenimiento de la transmisión neuromuscular, teniendo edad de inicio, distribución de debilidad y respuesta a tratamiento variables. Se presentan tres casos con el objetivo de describir el comportamiento clínico de la enfermedad y la utilidad de estudios complementarios ya que es de suma importancia su precoz identificación y tratamiento. Palabras claves: Miastenia gravis, test de estimulación repetitiva, ptosis palpebral, unión neuromuscular, pares craneanos

Myasthenia gravis is a chronic neuromuscular disease due to deficiency of nerve transmission in the neuromuscular junction, usually of an autoimmune origin in the adult, which is characterized by varying degrees of weakness of the skeletal muscles of the body, which increases during periods of activity and decreases after periods of rest. In childhood, however, congenital myasthenic syndromes, which find their origin in mutations of genes that encode proteins that play key roles in maintaining neuromuscular transmission, which may have a varying age of onset, distribution of weakness and response to treatment, are particularly relevant. Three cases are presented with the aim of describing the clinical presentation and course of the disease and the usefulness of complementary studies, since its early diagnosis and treatment is of paramount importance.Keywords: Myasthenia gravis, repetitive stimulation test, palpebral ptosis, neuromuscular junction, cranial pairs.

Reaching task performance is associated to neuromuscular junction adaptations in rats with induced diabetes mellitus

Upper limb performance is affected by diabetes mellitus (DM). Neuromuscular junction (NMJ) is a key structure to understand the relationship between performance and morphology in DM. The aim of the study was to analyze NMJ plasticity due to DM in an animal model and its relationship with the function of forelimbs in rats. Twelve Wistar rats were divided into control (C) and DM groups. Animals were trained to perform a grasping task, following procedures of habituation, shaping, and reaching task. DM was induced using streptozotocin. Forelimb neuromuscular performance for dexterity was evaluated one day before DM induction and five weeks following induction. After that, biceps, triceps, and finger flexors and extensors were removed. Connective tissue and muscle fiber cross-sectional area (CSA) were measured. NMJ was assessed by its morphometric characteristics (area, perimeter, and maximum diameter), using ImageJ software. Motor performance analyses were made using single pellet retrieval task performance test. Student's t-test was used for comparisons between groups. A significant decrease in all NMJ morphometric parameters was observed in the DM group compared with the C group. Results showed that DM generated NMJ retraction in muscles involved in a reaching task. These alterations are related to signs of muscular atrophy and to poor reaching task performance. In conclusion, induced DM caused NMJ retraction and muscular atrophy in muscles involved in reaching task performance. Induced DM caused significantly lower motor performance, especially in the final moments of evaluation, when DM compromised the tropism of the muscular tissue.

Effects of Mechanical Vibration in Neuromuscular Junctions and Fiber Type of the Soleus Muscle of Oophorectomized Wistar Rats / Efeitos da vibração mecânica nas junções neuromusculares e tipo de fibra do músculo sóleo de ratas wistar ooforectomizadas

Abstract Objective To evaluate the neuromuscular junctions (NMJs) and the type of muscle fibers of the soleus muscle of oophorectomized Wistar rats submitted to a mechanical vibration protocol. Methods A total of 36 randomized rats were used in the pseudo-oophorectomy without and with treatment and oophorectomy without and with treatment groups. The treatment was performed with a vibratory platform, frequency of 60 Hz and duration of 10 minutes, 3 times a week, for 4 weeks. At the end of the intervention period, the animals were euthanized and the soleus muscles were collected and processed for analysis of the NMJs and fiber type. The data were analyzed for normality by the Shapiro-Wilk test and analysis of the 3-way variance using the post-hoc Tukey test, when necessary, and a significance level of 5% was adopted. Results In the analysis of the NMJs, the oophorectomy group presented a smaller area than the pseudo-oophorectomy group, but the oophorectomy with treatment group was equal to the pseudo-oophorectomy with treatment group. For the larger diameter of the joints, the oophorectomy group was also different from the others; however, the oophorectomy and treatment animals were larger than those of the pseudo-oophorectomy and treatment group. There was no distinction of the types of fibers, with the muscle presenting fibers of the oxidative type. Conclusion Hormonal deprivation reduced the area and diameter of the NMJs, with reversion of this process in the groups that underwent vibratory platform treatment for 4 weeks, and both surgery and treatment did not influence the type of soleus muscle fiber, composed of oxidative fibers.

Resumo Objetivo Avaliar as junções neuromusculares (JNMs) e o tipo de fibras musculares do músculo sóleo de ratas Wistar ooforectomizadas e submetidas a um protocolo de vibração mecânica. Métodos Foram utilizadas 36 ratas randomizadas nos grupos pseudo-ooforectomia sem e com tratamento e ooforectomia sem e com tratamento. O tratamento foi realizado com plataforma vibratória, frequência de 60 Hz e duração de 10 minutos, 3 vezes por semana, durante 4 semanas. Ao término do período de intervenção, os animais foram eutanasiados e os músculos sóleos coletados e processados para análise das JNMs e tipo de fibra. Os dados foram analisados quanto à normalidade pelo teste Shapiro-Wilk e análise da variância de 3 vias, utilizando o pós-teste de Tukey quando necessário, tendo sido adotado o nível de significância de 5%. Resultados Na análise das JNMs, o grupo ooforectomia apresentou área menor que o grupo pseudo-ooforectomia, porém o grupo ooforectomia tratado igualou-se ao grupo pseudo-ooforectomia tratado. Para o maior diâmetro das junções, o grupo ooforectomia também se apresentou diferente dos demais; porém, os animais do grupo ooforectomia tratado foram maiores que o grupo pseudo-ooforectomia tratado. Não houve distinção dos tipos de fibras, com o músculo apresentando fibras do tipo oxidativo. Conclusão A privação hormonal reduziu a área e o diâmetro das JNMs, com reversão deste processo nos grupos que realizaram o tratamento com plataforma vibratória durante 4 semanas e, ainda, tanto cirurgia quanto tratamento não influenciaram no tipo de fibra do músculo sóleo, composto por fibras oxidativas.

Meralgia parestésica / Meralgia paresthetica

RESUMEN Fundamento: la meralgia parestésica es una mononeuropatía por atrapamiento que genera dolor, parestesias y pérdida de la sensibilidad en el territorio del nervio cutáneo lateral del muslo. Objetivo: profundizar y actualizar los aspectos más importantes de la meralgia parestésica. Métodos: se realizó una revisión de la literatura en idioma español e inglés disponible en PubMed Central, Hinari y SciELO. Para ello se utilizaron los siguientes descriptores: meralgia paresthetica, mononeuropathy, lateral cutaneous nerve of the thigh. A partir de la información obtenida se realizó una revisión bibliográfica de un total de 107 artículos publicados, incluídas 34 citas seleccionadas para realizar la revisión, de ellas 24 de los últimos cinco años. Desarrollo: se insistió en aquellos tópicos controversiales dentro del tema como son: reseña anatómica, factores etiológicos, presentación clínica, estudios complementarios y tratamiento. Conclusiones: la meralgia parestésica es un reto médico, debido a que puede simular enfermedades comunes como los desordenes lumbares. Es una enfermedad autolimitada cuyo diagnóstico se realiza con un alto índice de sospecha basado en el conocimiento adecuado de la anatomía, la fisiopatología, los factores etiológicos y los elementos clínicos. El tratamiento, aunque con falta de consenso, ofrece resultados favorables en la mayoría de los pacientes.

ABSTRACT Background: meralgia paresthetica is an entrapment mononeuropathy which cause pain, paresthesias and sensory loss within the distribution of the lateral cutaneous nerve of the thigh. Objective: to update and to deepen in the most important aspects of meralgia paresthetica. Methods: a revision of the literature was made in English and Spanish, available in PubMed Central, Hinari and SciELO. The following descriptors were used: meralgia paresthetica, mononeuropathy, lateral cutaneous nerve of the thigh. Base on the obtained data, a bibliographic revision was made of 107 published articles, including 34 cites selected for the research, 24 of them of the last five years. Development: it was focus in those controversial topics like: anatomic characteristics, etiological factors, clinical presentation, complementary studies and treatment. Conclusions: meralgia paresthetica is a medical challenge; due to it can simulate common illness like lumbar disorders. It is a self limited disease which is diagnosed basing on a high suspicious index with an adequate knowledge of the anatomy, physiopathology, etiological factors and clinical elements. The treatment, although with lack of consensus, offers favorable results in most of the patients.

Relationship between the Degeneration and Regeneration of Neuromuscular Junction and Wound Age during the Repair of Mouse Skeletal Muscle Contusion / 法医学杂志

Objective To investigate the morphological changes in the degeneration and regeneration of neuromuscular junctions （NMJ） during the repair of mouse skeletal muscle contusion and discuss the correlation between the degeneration and regeneration of NMJ and wound age. Methods A total of 50 healthy adult male mice were randomly divided into 10 groups, including 9 experimental groups and 1 control group. Immunofluorescent staining was applied, and neurofilament was marked with neurofilament protein-H （NF-H）, presynaptic membrane was marked with synaptophysin （Syn）, presynaptic membrane was marked with acetylcholine receptor （AChR）. Morphological changes of NMJ regeneration at different time points after mouse skeletal muscle contusion were detected. Results The neurofilament and presynaptic membrane of NMJ at the junction of contusion zones began to degrade after contusion, and completed degradation at about 3 d post-injury. Then they gradually regenerated, roughly completing the regeneration at about 21 d and basically reaching the control group level. The ratio of presynaptic membrane quantity to presynaptic membrane quantity showed a trend of decreasing then rising and finally reaching the control level. Conclusion During the repair of mouse skeletal muscle contusion, the morphological changes and wound age of the NMJ at the junction of contusion zones have a close correlation, which is expected to be one of the biological indicators for forensic skeletal muscle wound age estimation.

Methanolic extract of Rhinella schneideri (Anura: Bufonidae) poison causes ultrastructural changes in nerve terminals of phrenic nerve-diaphragm preparations in mice / Extracto metanólico de Rhinella schneideri (Anura: Bufonidae) causa cambios ultraestructurales en las terminaciones nerviosas de preparaciones de nervio frénico de ratón

Abstract Rhinella schneideri (or Bufo paracnemis), popularly known in Brazil as cururu toad, is also found in other countries in South America. The cardiovascular effects of this poison are largely known and recently was shown that it is capable to affect the neuromuscular junction on avian and mice isolated preparation. In this work, we used transmission electron microscopy to investigate the ultrastructure of the motor nerve terminal and postsynaptic junctional folds of phrenic nerve-hemidiaphragm preparations incubated for either 5 or 60 min with the methanolic extract of R. schneideri (50 µg/mL). In addition, the status of the acetylcholine receptors (AChR) was examined by TRITC-α-bungarotoxin immunofluorescence location at the endplate membrane. The results show that 5 min of incubation with the gland secretion extract significantly decreased (32 %) the number of synaptic vesicles into the motor nerve terminal, but did not decrease the electron density on the top of the junctional folds where nicotinic receptors are concentrated; however, 60 min of incubation led to significant nerve terminal reloading in synaptic vesicles whereas the AChR immunoreactivity was not as marked as in control and after 5 min incubation. Muscle fibers were well-preserved but intramuscular motor axons were not. The findings corroborated pharmacological data since the decrease in the number of synaptic vesicles (5 min) followed by recovery (60 min) is in accordance with the transient increase of MEPPs frequency meaning increased neurotransmitter release. These data support the predominant presynaptic mode of action of the R. schneideri, but do not exclude the possibility of a secondary postsynaptic action depending on the time the preparation is exposed to poison. Rev. Biol. Trop. 66(3): 1290-1297. Epub 2018 September 01.

Resumen Rhinella schneideri (o Bufo paracnemis), conocido popularmente en Brasil como sapo cururu, también se encuentra en otros países de América del Sur. Los efectos cardiovasculares de este veneno son ampliamente conocidos y recientemente se demostró que es capaz de afectar la unión neuromuscular en la preparación aislada de aves y ratones. En este trabajo, utilizamos microscopía electrónica de transmisión para investigar la ultraestructura de la terminación nerviosa motora y pliegues de unión postsináptica de preparaciones de nervio frénico-hemidiafragma incubadas durante 5 o 60 min con el extracto metanólico de R. schneideri (50 μg/mL). Además, se examinó el estado de los receptores de acetilcolina (AChR) mediante la ubicación de inmunofluorescencia de TRITC-α-bungarotoxina en la membrana de la placa terminal. Los resultados muestran que 5 min de incubación con el extracto de secreción de glándula disminuyeron significativamente (32 %) el número de vesículas sinápticas en el terminal del nervio motor, pero no disminuyeron la densidad electrónica en la parte superior de los pliegues de unión donde se concentran los receptores nicotínicos. Sin embargo, 60 min de incubación condujeron a una recarga significativa de los terminales nerviosos en las vesículas sinápticas, mientras que la inmunorreactividad del AChR no fue tan marcada como en el control y después de 5 min de incubación. Las fibras musculares estaban bien conservadas, pero los axones motores intramusculares no. Los hallazgos corroboraron los datos farmacológicos ya que la disminución en el número de vesículas sinápticas (5 min) seguida de recuperación (60 min) está de acuerdo con el aumento transitorio de la frecuencia de MEPPs, lo que significa una mayor liberación de neurotransmisores. Estos datos apoyan el modo de acción presináptico predominante de R. schneideri, pero no excluyen la posibilidad de una acción postsináptica secundaria dependiendo del tiempo en que la preparación esté expuesta al veneno.

Effects of adenosine receptor agonist on the rocuronium-induced neuromuscular block and sugammadex-induced recovery / 대한마취과학회지

BACKGROUND: Several types of receptors are found at neuromuscular presynaptic membranes. Presynaptic inhibitory A1 and facilitatory A2A receptors mediate different modulatory functions on acetylcholine release. This study investigated whether adenosine A1 receptor agonist contributes to the first twitch tension (T1) of train-of-four (TOF) stimulation depression and TOF fade during rocuronium-induced neuromuscular blockade, and sugammadex-induced recovery. METHODS: Phrenic nerve-diaphragm tissues were obtained from 30 adult Sprague-Dawley rats. Each tissue specimen was randomly allocated to either control group or 2-chloroadenosine (CADO, 10 μM) group. One hour of reaction time was allowed before initiating main experimental data collection. Loading and boost doses of rocuronium were sequentially administered until > 95% depression of the T1 was achieved. After confirming that there was no T1 twitch tension response, 15 min of resting time was allowed, after which sugammadex was administered. Recovery profiles (T1, TOF ratio [TOFR], and recovery index) were collected for 1 h and compared between groups. RESULTS: There were statistically significant differences on amount of rocuronium (actually used during experiment), TOFR changes during concentration-response of rocuronium (P = 0.04), and recovery profiles (P < 0.01) of CADO group comparing with the control group. However, at the initial phase of this experiment, dose-response of rocuronium in each group demonstrated no statistically significant differences (P = 0.12). CONCLUSIONS: The adenosine A1 receptor agonist (CADO) influenced the TOFR and the recovery profile. After activating adenosine receptor, sugammadex-induced recovery from rocuronium-induced neuromuscular block was delayed.

The present status and problems of multi-target therapy of myasthenia gravis / 中华神经科杂志

The clinical manifestation of myasthenia gravis is due to the acetylcholine transmission defect of neuromuscular junction caused by autoimmune disturbance. With the intensive understanding of the pathogenesis and the emerging of specific immunological targeting therapy, therapeutic investigations are widely expanding. A multi-target therapy pattern is now available based on treatments primed to distinct immunopathological processes and improving neuromuscular junction transmission. We will comment the status and problems in this article.

Actualización en Miastenia gravis: An Update / Myasthenia gravis

La miastenia gravis (MG) es una enfermedad autoinmune, caracterizada por fatiga y debilidad muscular localizada o generalizada, a predominio proximal y de curso fluctuante; los síntomas provienen del bloqueo post-sináptico de la transmisión neuromuscular por anticuerpos contra los receptores de acetilcolina y otras proteínas de la membrana post-sináptica. La incidencia es de 8 a 10 casos por millón de personas y la prevalencia, de 150 a 250 por millón; estas cifras, sin embargo, varían en las diferentes poblaciones estudiadas. El diagnóstico de MGse basa en el cuadro clínico y resultados positivos de tests tales como anticuerpos específicos, test neurofisiológicos o prueba terapéutica. La búsqueda de patologías asociadas es un paso importante en la evaluación. El tratamiento se sustenta en tres pilares: tratamiento con fármacos inhibidores de la acetilcolinesterasa (piridostigmina), inmunoterapia (corticoides o inmunosupresores/inmunomoduladores) e intervención quirúrgica (timectomia).

Myasthenia gravis (MG) is an autoimmune disease, characterized by fatigue and localized or generalized muscle weakness, with proximal predominance and fluctuating course; these symptoms stem from the post-synaptic blockade of neuromuscular transmission by antibodies against anti-acetylcholine antibodies and other post-synaptic membrane proteins. The incidence is 8 to 10 cases per million people, and the prevalence of 150 to 250 cases per million; however these figures vary in the different populations studied. The diagnosis of MG is based on the clinical manifestations and positive results of tests such as specific antibodies, neurophysiological tests or therapeutic interventions. The search for associated pathologies should be an important component of the evaluation. The treatment is based on three pillars: use of acetylcholinesterase inhibitors (pyridostigmine), immunotherapy (corticosteroids or immunosuppressants / immunomodulators) and surgical management (thymectomy).

Miastenia gravis de tipo bulbar en niños: un caso de difícil diagnóstico / Bulbar Myasthenia Gravis in children: a case of difficult diagnosis

La miastenia gravis (MG) es un trastorno autoinmune caracterizado por debilidad y fatigabilidad de los músculos esqueléticos debida a la disfunción de la unión neuromuscular. Se presenta el caso de una adolescente de 11 años de edad, con diagnóstico de miastenia gravis de tipo bulbar. La paciente presentó dos crisis de MG previamente diagnosticadas de manera equivocada como crisis asmáticas. Recibió tratamiento con inmunoglobulina humana, corticoides, piridostigmina y timectomía. Se discute la evolución clínica y riesgos atribuibles a situaciones sociales que pueden retrasar el diagnóstico y su manejo efectivo.

Myasthenia gravis (MG) is an autoimmune disorder characterized by weakness and fatigability of the skeletal muscles due to dysfunction of the neuromuscular junction. We report the case of an 11-year-old girl diagnosed with bulbar myasthenia gravis. The patient had two previous crises of myasthenia gravis erroneously diagnosed as asthma attacks. She received treatment with human immunoglobulin, corticosteroids, pyridostigmine and thymectomy. We discuss the clinical course and the risks attributable to social situations that can delay the diagnosis and its effective management.

Miastenia gravis seronegativa: revisión de la literatura / Seronegative Myasthenia Gravis: A Literature Review

RESUMEN En 1976 se identificaron varios anticuerpos dirigidos contra el receptor de acetil colina en el suero de los pacientes con miastenia gravis (MG). Sin embargo, luego de unos años, se evidenció que aproximadamente el 20 % de los pacientes con MG generalizada y con evidencia electrofisiológica de un trastorno de la unión neuromuscular, no expresan dichos anticuerpos por radioinmunoensayo (RIA); éstos constituyen los casos de miastenia gravis seronegativa (MGSN). El diagnóstico en estos pacientes es difícil, dada la ausencia de autoanticuerpos detectables en suero y la falta de estudios neurofisiológicos sensibles. Recientemente un nuevo método basado en ensayos celulares muestra un aumento significativo en la detección de miastenia seropositiva, en casos diagnosticados previamente como seronegativos. Este artículo pretende dar un abordaje sobre la fisiopatología de la miastenia gravis seronegativa, así como una actualización de los últimos avances sobre su diagnóstico. También busca hacer una revisión sobre el contexto general actual de esta patología en Colombia.

SUMMARY In 1976 antibodies against acetyl-choline receptor were identified on the serum of patients with myasthenia gravis. However, some years later, it became clear that about 20% of patients with generalized MG and an electro physiologic disorder on the neuromuscular junction did not express these antibodies by radioimmunoassay (RIPA). These cases represent seronegative myasthenia gravis (SNMG). The diagnosis of these patients is difficult, given the absence of detectable autoantibodies on serum and the lack of sensitive neurophysiologic tests. Recently, a new method based on cellular assays shows an increase on detection of seropositive MG from cases, which were initially diagnosed as seronegative. This article reviews the physiopathology of seronegative MG and gives an update on the latest advances concerning its diagnosis. It also hopes to approach the current general context of the illness in Colombia.

Effects of duodenal-jejunal bypass on structure of diaphragm in western diet obese rats

Abstract Purpose: To evaluate the effects of duodenal-jejunal bypass (DJB) on the diaphragm muscle of obese rats fed on a western diet (WD) . Methods: Eighteen male Wistar rats were fed a standard rodent chow diet (CTL group) or WD ad libitum. After 10 weeks, WD rats were submitted to sham (WD SHAM) or duodenal-jejunal bypass (WD DJB). The structure, ultrastructure, collagen content and the morphometry of the neuromuscular junctions (NMJs) were analyzed two months after surgery. Results: WD SHAM rats displayed an increase in body weight, the Lee index and retroperitoneal and peri-epididymal fat pads compared to the CTL group. DJB did not alter these parameters. The muscle fiber structure and NMJs were similar in the WD SHAM and CTL groups. However, the WD SHAM group showed alterations in the fiber ultrastructure, such as loosely arranged myofibrils and Z line disorganization. In addition, WD SHAM animals presented a considerable amount of lipid droplets and a reduction in the percentage of collagen compared to the CTL group. DJB did not affect the structure or ultrastructure of the muscle fibers or the NMJs in the diaphragm of the WD DJB animals. Conclusion: Duodenal-jejunal bypass did not improve the alterations observed in the diaphragm of western diet obese-rats.

Sarcopenia: Neurological Point of View

Sarcopenia is an age-related geriatric syndrome which is characterized by the gradual loss of muscle mass, muscle strength, and muscle quality. There are a lot of neurologic insults on sarcopenia at various levels from the brain to the neuromuscular junctions (NMJs) to generate a volitional task. Dopaminergic downregulation, inadequate motor programming and motor coordination impairment lead to decline of supraspinal drive. Motor unit reorganization and inflammatory changes in motor neuron decrease conduction velocity and amplitude of compound muscle action potential. Furthermore, NMJ remodeling and age related neurophysiological alterations may contribute to neuromuscular impairment. Sarcopenia is an age-associated, lifelong process which links to multiple etiological factors. Although not all the causes are completely understood, we suggest that compromised nervous system function may be one of the important contributors to the sarcopenia.

The Scaffolding Protein, Grb2-associated Binder-1, in Skeletal Muscles and Terminal Schwann Cells Regulates Postnatal Neuromuscular Synapse Maturation

The vertebrate neuromuscular junction (NMJ) is considered as a “tripartite synapse” consisting of a motor axon terminal, a muscle endplate, and terminal Schwann cells that envelope the motor axon terminal. The neuregulin 1 (NRG1)-ErbB2 signaling pathway plays an important role in the development of the NMJ. We previously showed that Grb2-associated binder 1 (Gab1), a scaffolding mediator of receptor tyrosine kinase signaling, is required for NRG1-induced peripheral nerve myelination. Here, we determined the role of Gab1 in the development of the NMJ using muscle-specific conditional Gab1 knockout mice. The mutant mice showed delayed postnatal maturation of the NMJ. Furthermore, the selective loss of the gab1 gene in terminal Schwann cells produced delayed synaptic elimination with abnormal morphology of the motor endplate, suggesting that Gab1 in both muscles and terminal Schwann cells is required for proper NMJ development. Gab1 in terminal Schwann cells appeared to regulate the number and process elongation of terminal Schwann cells during synaptic elimination. However, Gab2 knockout mice did not show any defects in the development of the NMJ. Considering the role of Gab1 in postnatal peripheral nerve myelination, our findings suggest that Gab1 is a pleiotropic and important component of NRG1 signals during postnatal development of the peripheral neuromuscular system.