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1.
Science ; 372(6540): 385-393, 2021 04 23.
Artigo em Inglês | MEDLINE | ID: mdl-33888637

RESUMO

Motor and sensory functions of the spinal cord are mediated by populations of cardinal neurons arising from separate progenitor lineages. However, each cardinal class is composed of multiple neuronal types with distinct molecular, anatomical, and physiological features, and there is not a unifying logic that systematically accounts for this diversity. We reasoned that the expansion of new neuronal types occurred in a stepwise manner analogous to animal speciation, and we explored this by defining transcriptomic relationships using a top-down approach. We uncovered orderly genetic tiers that sequentially divide groups of neurons by their motor-sensory, local-long range, and excitatory-inhibitory features. The genetic signatures defining neuronal projections were tied to neuronal birth date and conserved across cardinal classes. Thus, the intersection of cardinal class with projection markers provides a unifying taxonomic solution for systematically identifying distinct functional subsets.


Assuntos
Vias Neurais , Neurônios/fisiologia , Medula Espinal/citologia , Transcriptoma , Animais , Medula Cervical/citologia , Feminino , Masculino , Camundongos , Neurônios Motores/fisiologia , Propriocepção , RNA-Seq , Células Receptoras Sensoriais/fisiologia , Análise de Célula Única , Análise Espacial , Medula Espinal/embriologia , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo
2.
Int J Mol Sci ; 22(5)2021 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-33800863

RESUMO

The ability to sense and move within an environment are complex functions necessary for the survival of nearly all species. The spinal cord is both the initial entry site for peripheral information and the final output site for motor response, placing spinal circuits as paramount in mediating sensory responses and coordinating movement. This is partly accomplished through the activation of complex spinal microcircuits that gate afferent signals to filter extraneous stimuli from various sensory modalities and determine which signals are transmitted to higher order structures in the CNS and to spinal motor pathways. A mechanistic understanding of how inhibitory interneurons are organized and employed within the spinal cord will provide potential access points for therapeutics targeting inhibitory deficits underlying various pathologies including sensory and movement disorders. Recent studies using transgenic manipulations, neurochemical profiling, and single-cell transcriptomics have identified distinct populations of inhibitory interneurons which express an array of genetic and/or neurochemical markers that constitute functional microcircuits. In this review, we provide an overview of identified neural components that make up inhibitory microcircuits within the dorsal and ventral spinal cord and highlight the importance of inhibitory control of sensorimotor pathways at the spinal level.


Assuntos
Vias Aferentes/fisiologia , Interneurônios/fisiologia , Movimento/fisiologia , Inibição Neural/fisiologia , Sensação/fisiologia , Filtro Sensorial/fisiologia , Medula Espinal/citologia , Animais , Células do Corno Anterior/química , Células do Corno Anterior/classificação , Células do Corno Anterior/fisiologia , Humanos , Interneurônios/química , Interneurônios/classificação , Modelos Neurológicos , Neurônios Motores/fisiologia , Transtornos dos Movimentos/fisiopatologia , Fibras Nervosas/fisiologia , Proteínas do Tecido Nervoso/análise , Neuropeptídeos/análise , Células do Corno Posterior/química , Células do Corno Posterior/classificação , Transtornos das Sensações/fisiopatologia , Células Receptoras Sensoriais/fisiologia , Medula Espinal/fisiologia , Sinapses/fisiologia
3.
J Vis Exp ; (168)2021 02 10.
Artigo em Inglês | MEDLINE | ID: mdl-33645560

RESUMO

Sensory systems gather cues essential for directing behavior, but animals must decipher what information is biologically relevant. Locomotion generates reafferent cues that animals must disentangle from relevant sensory cues of the surrounding environment. For example, when a fish swims, flow generated from body undulations is detected by the mechanoreceptive neuromasts, comprising hair cells, that compose the lateral line system. The hair cells then transmit fluid motion information from the sensor to the brain via the sensory afferent neurons. Concurrently, corollary discharge of the motor command is relayed to hair cells to prevent sensory overload. Accounting for the inhibitory effect of predictive motor signals during locomotion is, therefore, critical when evaluating the sensitivity of the lateral line system. We have developed an in vivo electrophysiological approach to simultaneously monitor posterior lateral line afferent neuron and ventral motor root activity in zebrafish larvae (4-7 days post fertilization) that can last for several hours. Extracellular recordings of afferent neurons are achieved using the loose patch clamp technique, which can detect activity from single or multiple neurons. Ventral root recordings are performed through the skin with glass electrodes to detect motor neuron activity. Our experimental protocol provides the potential to monitor endogenous or evoked changes in sensory input across motor behaviors in an intact, behaving vertebrate.


Assuntos
Sistema da Linha Lateral/inervação , Neurônios Aferentes/fisiologia , Natação/fisiologia , Peixe-Zebra/fisiologia , Animais , Eletrodos , Fenômenos Eletrofisiológicos , Larva/fisiologia , Neurônios Motores/fisiologia
4.
Int J Mol Sci ; 22(5)2021 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-33670886

RESUMO

Deficient intracellular transport is a common pathological hallmark of many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Mutations in the fused-in-sarcoma (FUS) gene are one of the most common genetic causes for familial ALS. Motor neurons carrying a mutation in the nuclear localization sequence of FUS (P525L) show impaired axonal transport of several organelles, suggesting that mislocalized cytoplasmic FUS might directly interfere with the transport machinery. To test this hypothesis, we studied the effect of FUS on kinesin-1 motility in vitro. Using a modified microtubule gliding motility assay on surfaces coated with kinesin-1 motor proteins, we showed that neither recombinant wildtype and P525L FUS variants nor lysates from isogenic ALS-patient-specific iPSC-derived spinal motor neurons expressing those FUS variants significantly affected gliding velocities. We hence conclude that during ALS pathogenesis the initial negative effect of FUS (P525L) on axonal transport is an indirect nature and requires additional factors or mechanisms.


Assuntos
Esclerose Amiotrófica Lateral/metabolismo , Transporte Axonal , Microtúbulos/metabolismo , Neurônios Motores/metabolismo , Mutação , Proteína FUS de Ligação a RNA/genética , Esclerose Amiotrófica Lateral/genética , Esclerose Amiotrófica Lateral/fisiopatologia , Linhagem Celular , Humanos , Cinesina , Neurônios Motores/fisiologia , Proteína FUS de Ligação a RNA/metabolismo
5.
Neuron ; 109(7): 1188-1201.e7, 2021 04 07.
Artigo em Inglês | MEDLINE | ID: mdl-33577748

RESUMO

Proprioception is essential for behavior and provides a sense of our body movements in physical space. Proprioceptor organs are thought to be only in the periphery. Whether the central nervous system can intrinsically sense its own movement remains unclear. Here we identify a segmental organ of proprioception in the adult zebrafish spinal cord, which is embedded by intraspinal mechanosensory neurons expressing Piezo2 channels. These cells are late-born, inhibitory, commissural neurons with unique molecular and physiological profiles reflecting a dual sensory and motor function. The central proprioceptive organ locally detects lateral body movements during locomotion and provides direct inhibitory feedback onto rhythm-generating interneurons responsible for the central motor program. This dynamically aligns central pattern generation with movement outcome for efficient locomotion. Our results demonstrate that a central proprioceptive organ monitors self-movement using hybrid neurons that merge sensory and motor entities into a unified network.


Assuntos
Retroalimentação Sensorial/fisiologia , Movimento/fisiologia , Propriocepção/fisiologia , Peixe-Zebra/fisiologia , Animais , Geradores de Padrão Central/fisiologia , Feminino , Interneurônios/fisiologia , Canais Iônicos/fisiologia , Locomoção/fisiologia , Masculino , Mecanotransdução Celular , Neurônios Motores/fisiologia , Rede Nervosa/citologia , Rede Nervosa/fisiologia , RNA/genética , Células Receptoras Sensoriais/fisiologia , Medula Espinal/diagnóstico por imagem , Medula Espinal/fisiologia , Tomografia Computadorizada por Raios X , Proteínas de Peixe-Zebra/fisiologia
6.
Muscle Nerve ; 63(4): 546-552, 2021 04.
Artigo em Inglês | MEDLINE | ID: mdl-33452679

RESUMO

BACKGROUND: The most common subtypes of Guillain-Barré syndrome (GBS) are acute inflammatory demyelinating polyneuropathy (AIDP) and acute motor axonal neuropathy (AMAN). In the first days after the onset of weakness, standard nerve conduction studies (NCS) may not distinguish GBS subtypes. Reduced nerve excitability may be an early symptom of nerve dysfunction, which can be determined with the compound muscle action potential (CMAP) scan. The aim of this study was to explore whether early changes in motor nerve excitability in GBS patients are related to various subtypes. METHODS: Prospective case-control study in 19 GBS patients from The Netherlands and 22 from Bangladesh. CMAP scans were performed within 2 days of hospital admission and NCS 7-14 days after onset of weakness. CMAP scans were also performed in age- and country-matched controls. RESULTS: CMAP scan patterns of patients who were classified as AMAN were distinctly different compared to the CMAP scan patterns of the patients who were classified as AIDP. The most pronounced differences were found in the stimulus intensity parameters. CONCLUSIONS: CMAP scans made at hospital admission demonstrate several characteristics that can be used as an early indicator of GBS subtype.


Assuntos
Tecido Nervoso/fisiopatologia , Condução Nervosa/fisiologia , Sistema Nervoso Periférico/diagnóstico por imagem , Sistema Nervoso Periférico/fisiopatologia , Adulto , Estudos de Casos e Controles , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Neurônios Motores/fisiologia , Países Baixos , Exame Neurológico/métodos
7.
Nat Commun ; 12(1): 391, 2021 01 15.
Artigo em Inglês | MEDLINE | ID: mdl-33452250

RESUMO

Spinal cord injury (SCI) often causes severe and permanent disabilities due to the regenerative failure of severed axons. Here we report significant locomotor recovery of both hindlimbs after a complete spinal cord crush. This is achieved by the unilateral transduction of cortical motoneurons with an AAV expressing hyper-IL-6 (hIL-6), a potent designer cytokine stimulating JAK/STAT3 signaling and axon regeneration. We find collaterals of these AAV-transduced motoneurons projecting to serotonergic neurons in both sides of the raphe nuclei. Hence, the transduction of cortical neurons facilitates the axonal transport and release of hIL-6 at innervated neurons in the brain stem. Therefore, this transneuronal delivery of hIL-6 promotes the regeneration of corticospinal and raphespinal fibers after injury, with the latter being essential for hIL-6-induced functional recovery. Thus, transneuronal delivery enables regenerative stimulation of neurons in the deep brain stem that are otherwise challenging to access, yet highly relevant for functional recovery after SCI.


Assuntos
Terapia Genética/métodos , Interleucina-6/genética , Locomoção/fisiologia , Regeneração Nervosa/fisiologia , Traumatismos da Medula Espinal/terapia , Animais , Axônios/fisiologia , Córtex Cerebral/citologia , Córtex Cerebral/fisiologia , Dependovirus/genética , Modelos Animais de Doenças , Feminino , Vetores Genéticos/administração & dosagem , Vetores Genéticos/genética , Humanos , Janus Quinases/metabolismo , Masculino , Camundongos , Camundongos Knockout , Microinjeções , Neurônios Motores/fisiologia , PTEN Fosfo-Hidrolase/genética , Núcleos da Rafe/citologia , Núcleos da Rafe/fisiologia , Recuperação de Função Fisiológica , Fator de Transcrição STAT3/metabolismo , Neurônios Serotoninérgicos/fisiologia , Índice de Gravidade de Doença , Transdução de Sinais , Medula Espinal/citologia , Medula Espinal/fisiopatologia , Traumatismos da Medula Espinal/diagnóstico , Traumatismos da Medula Espinal/fisiopatologia , Transdução Genética
8.
Nat Commun ; 12(1): 435, 2021 01 19.
Artigo em Inglês | MEDLINE | ID: mdl-33469022

RESUMO

Epidural electrical stimulation (EES) of lumbosacral sensorimotor circuits improves leg motor control in animals and humans with spinal cord injury (SCI). Upper-limb motor control involves similar circuits, located in the cervical spinal cord, suggesting that EES could also improve arm and hand movements after quadriplegia. However, the ability of cervical EES to selectively modulate specific upper-limb motor nuclei remains unclear. Here, we combined a computational model of the cervical spinal cord with experiments in macaque monkeys to explore the mechanisms of upper-limb motoneuron recruitment with EES and characterize the selectivity of cervical interfaces. We show that lateral electrodes produce a segmental recruitment of arm motoneurons mediated by the direct activation of sensory afferents, and that muscle responses to EES are modulated during movement. Intraoperative recordings suggested similar properties in humans at rest. These modelling and experimental results can be applied for the development of neurotechnologies designed for the improvement of arm and hand control in humans with quadriplegia.


Assuntos
Medula Cervical/fisiopatologia , Neurônios Motores/fisiologia , Quadriplegia/terapia , Recrutamento Neurofisiológico/fisiologia , Traumatismos da Medula Espinal/terapia , Estimulação da Medula Espinal/métodos , Vias Aferentes/fisiopatologia , Animais , Medula Cervical/citologia , Medula Cervical/diagnóstico por imagem , Medula Cervical/lesões , Simulação por Computador , Modelos Animais de Doenças , Eletrodos Implantados , Espaço Epidural , Feminino , Gânglios Espinais/citologia , Gânglios Espinais/diagnóstico por imagem , Gânglios Espinais/fisiopatologia , Humanos , Macaca fascicularis , Imagem por Ressonância Magnética , Masculino , Modelos Neurológicos , Músculo Esquelético/inervação , Quadriplegia/etiologia , Quadriplegia/fisiopatologia , Traumatismos da Medula Espinal/complicações , Traumatismos da Medula Espinal/diagnóstico , Traumatismos da Medula Espinal/fisiopatologia , Estimulação da Medula Espinal/instrumentação , Extremidade Superior/inervação
9.
J Electromyogr Kinesiol ; 56: 102510, 2021 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-33341461

RESUMO

It is necessary to decompose the intra-muscular EMG signal to extract motor unit action potential (MUAP) waveforms and firing times. Some algorithms were proposed in the literature to resolve superimposed MUAPs, including Peel-Off (PO), branch and bound (BB), genetic algorithm (GA), and particle swarm optimization (PSO). This study aimed to compare these algorithms in terms of overall accuracy and running time. Two sets of two-to-five MUAP templates (set1: a wide range of energies, and set2: a high degree of similarity) were used. Such templates were time-shifted, and white Gaussian noise was added. A total of 1000 superpositions were simulated for each template and were resolved using PO (also, POI: interpolated PO), BB, GA, and PSO algorithms. The generalized estimating equation was used to identify which method significantly outperformed, while the overall rank product was used for overall ranking. The rankings were PSO, BB, GA, PO, and POI in the first, and BB, PSO, GA, PO, POI in the second set. The overall ranking was BB, PSO, GA, PO, and POI in the entire dataset. Although the BB algorithm is generally fast, there are cases where the BB algorithm is too slow and it is thus not suitable for real-time applications.


Assuntos
Potenciais de Ação/fisiologia , Algoritmos , Eletromiografia/métodos , Neurônios Motores/fisiologia , Recrutamento Neurofisiológico/fisiologia , Processamento de Sinais Assistido por Computador , Humanos , Músculo Esquelético/fisiologia
10.
J Neurosci ; 41(7): 1443-1454, 2021 02 17.
Artigo em Inglês | MEDLINE | ID: mdl-33334866

RESUMO

Renshaw cells mediate recurrent inhibition between motoneurons within the spinal cord. The function of this circuit is not clear; we previously suggested based on computational modeling that it may cancel oscillations in muscle activity around 10 Hz, thereby reducing physiological tremor. Such tremor is especially problematic for dexterous hand movements, yet knowledge of recurrent inhibitory function is sparse for the control of the primate upper limb, where no direct measurements have been made to date. In this study, we made intracellular penetrations into 89 motoneurons in the cervical enlargement of four terminally anesthetized female macaque monkeys, and recorded recurrent IPSPs in response to antidromic stimulation of motor axons. Recurrent inhibition was strongest to motoneurons innervating shoulder muscles and elbow extensors, weak to wrist and digit extensors, and almost absent to the intrinsic muscles of the hand. Recurrent inhibitory connections often spanned joints, for example from motoneurons innervating wrist and digit muscles to those controlling the shoulder and elbow. Wrist and digit flexor motoneurons sometimes inhibited the corresponding extensors, and vice versa. This complex connectivity presumably reflects the flexible usage of the primate upper limb. Using trains of stimuli to motor nerves timed as a Poisson process and coherence analysis, we also examined the temporal properties of recurrent inhibition. The recurrent feedback loop effectively carried frequencies up to 100 Hz, with a coherence peak around 20 Hz. The coherence phase validated predictions from our previous computational model, supporting the idea that recurrent inhibition may function to reduce tremor.SIGNIFICANCE STATEMENT We present the first direct measurements of recurrent inhibition in primate upper limb motoneurons, revealing that it is more flexibly organized than previous observations in cat. Recurrent inhibitory connections were relatively common between motoneurons controlling muscles that act at different joints, and between flexors and extensors. As in the cat, connections were minimal for motoneurons innervating the most distal intrinsic hand muscles. Empirical data are consistent with previous modeling: temporal properties of the recurrent inhibitory feedback loop are compatible with a role in reducing physiological tremor by suppressing oscillations around 10 Hz.


Assuntos
Inibição Neural/fisiologia , Extremidade Superior/fisiologia , Animais , Axônios/fisiologia , Estimulação Elétrica , Potenciais Pós-Sinápticos Excitadores/fisiologia , Retroalimentação Fisiológica , Feminino , Macaca mulatta , Neurônios Motores/fisiologia , Músculo Esquelético/inervação , Músculo Esquelético/fisiologia , Neurônios/fisiologia , Células de Renshaw/fisiologia , Medula Espinal/citologia , Medula Espinal/fisiologia , Extremidade Superior/inervação
11.
Neurosci Lett ; 743: 135583, 2021 01 19.
Artigo em Inglês | MEDLINE | ID: mdl-33352279

RESUMO

There are isolated instances in the literature that suggest the 'onion skin' phenomenon is not always present. That is, newly recruited high threshold motor units (MU) have higher discharge rates than previously recruited low threshold MUs. Therefore, the purpose of this paper was to investigate the presence of the 'onion skin' phenomenon in a large sample of intramuscular myoelectric recordings from low to maximal force outputs. Forty-eight participants performed rapid isometric dorsiflexion contractions at 20, 40, 60, 80 and 100 % MVC while intramuscular electrical activity was recorded. A bivariate frequency-distribution of the motor unit discharge rate and motor unit action potential peak-to-peak (P-P) amplitude was assessed. There was a significant difference in bivariate frequency-distribution across force levels (D's = 0.1083-0.3094, p's < 0.001). Newly recruited high threshold MUs did have lower discharge rates, but there was an increase in the presence of high threshold, large P-P amplitude MUs with higher discharge rates than lower threshold MUs (reverse onion skin) during the stable portion of the force output. The recruitment of high threshold MUs with higher discharge rates decreased the level of common drive from the cross-correlation (Rxy) = 0.79 at 20 % MVC to Rxy = 0.68 at 100 % MVC (p < 0.01), but it remained high. As the interference pattern becomes more complex with the recruitment of more motor units at higher force outputs, intramuscular electrodes may be more discriminating while recording motor unit activity leading to the identification of both the 'reverse onion skin' and 'onion skin' phenomenon being present.


Assuntos
Eletromiografia/métodos , Contração Isométrica/fisiologia , Neurônios Motores/fisiologia , Músculo Esquelético/fisiologia , Complexo Mioelétrico Migratório/fisiologia , Recrutamento Neurofisiológico/fisiologia , Adolescente , Adulto , Feminino , Humanos , Masculino , Adulto Jovem
12.
Science ; 369(6510)2020 09 18.
Artigo em Inglês | MEDLINE | ID: mdl-32943498

RESUMO

Although many molecular mechanisms controlling developmental processes are evolutionarily conserved, the speed at which the embryo develops can vary substantially between species. For example, the same genetic program, comprising sequential changes in transcriptional states, governs the differentiation of motor neurons in mouse and human, but the tempo at which it operates differs between species. Using in vitro directed differentiation of embryonic stem cells to motor neurons, we show that the program runs more than twice as fast in mouse as in human. This is not due to differences in signaling, nor the genomic sequence of genes or their regulatory elements. Instead, there is an approximately two-fold increase in protein stability and cell cycle duration in human cells compared with mouse cells. This can account for the slower pace of human development and suggests that differences in protein turnover play a role in interspecies differences in developmental tempo.


Assuntos
Desenvolvimento Embrionário/fisiologia , Neurônios Motores/fisiologia , Neurogênese/fisiologia , Estabilidade Proteica , Animais , Desenvolvimento Embrionário/genética , Regulação da Expressão Gênica no Desenvolvimento , Humanos , Masculino , Neurônios Motores/citologia , Células-Tronco Neurais/citologia , Células-Tronco Neurais/fisiologia , Tubo Neural/embriologia , Neurogênese/genética , Especificidade da Espécie
13.
Muscle Nerve ; 62(4): 516-521, 2020 10.
Artigo em Inglês | MEDLINE | ID: mdl-32710682

RESUMO

INTRODUCTION: We evaluated the association between muscle ultrasound, number of motor units, and clinical parameters, and assessed their utility for distinguishing amyotrophic lateral scleorisis (ALS) patients from healthy individuals. METHODS: Three muscle pairs (abductor pollicis brevis, abductor digiti minimi, and tibialis anterior) of 18 ALS patients and 18 controls underwent muscle ultrasound (echointensity and thickness) and assessment of motor unit number index (MUNIX). The clinical and functional status of participants were also assessed. RESULTS: Mean age of the patients was 53.8 ± 12.1 years, and score on the ALS Functional Rating Scale-Revised was 38.9 ± 4.1. Echointensity of all tested muscles of ALS participants was significantly higher than that of controls, but there was no significant difference in muscle thickness. Muscle echointensity correlated significantly with clinical and electrophysiological parameters. CONCLUSION: Echointensity of muscles was highly associated with clinical scales and MUNIX, confirming its relevance as an ancillary diagnostic test in ALS patients.


Assuntos
Esclerose Amiotrófica Lateral/diagnóstico por imagem , Neurônios Motores/fisiologia , Músculo Esquelético/diagnóstico por imagem , Adulto , Idoso , Esclerose Amiotrófica Lateral/fisiopatologia , Estudos Transversais , Eletromiografia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Músculo Esquelético/fisiopatologia , Ultrassonografia
14.
Exerc Sport Sci Rev ; 48(4): 151-162, 2020 10.
Artigo em Inglês | MEDLINE | ID: mdl-32658038

RESUMO

Including a brief overview of current investigative approaches, the present Perspectives for Progress article offers an overview of potential future experiments in the field of exercise-related neuroplasticity to strength training. It is proposed that the combination of specific experimental approaches and recently developed techniques holds the potential for unraveling spinal and supraspinal mechanisms involved in the adaptation to strength training.


Assuntos
Plasticidade Neuronal , Treinamento de Resistência , Adaptação Fisiológica , Animais , Potenciais Evocados , Humanos , Neurônios Motores/fisiologia , Contração Muscular , Músculo Esquelético/fisiologia , Tratos Piramidais/fisiologia , Sinapses
15.
Exerc Sport Sci Rev ; 48(4): 209-216, 2020 10.
Artigo em Inglês | MEDLINE | ID: mdl-32658041

RESUMO

This review discusses evidence suggesting that group III/IV muscle afferents affect locomotor performance by influencing neuromuscular fatigue. These neurons regulate the hemodynamic and ventilatory response to exercise and, thus, assure appropriate locomotor muscle O2 delivery, which optimizes peripheral fatigue development and facilitates endurance performance. In terms of central fatigue, group III/IV muscle afferents inhibit motoneuronal output and thereby limit exercise performance.


Assuntos
Exercício Físico/fisiologia , Neurônios Motores/fisiologia , Músculo Esquelético/inervação , Neurônios Aferentes/fisiologia , Resistência Física/fisiologia , Fadiga/fisiopatologia , Hemodinâmica , Humanos , Fadiga Muscular/fisiologia , Músculo Esquelético/metabolismo , Consumo de Oxigênio , Respiração
16.
J Electromyogr Kinesiol ; 53: 102442, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32659610

RESUMO

The monoaminergic bulbospinal pathways from the brainstem are central to motor functions by regulating the gains of spinal motoneurons and represent, in that respect, probably the primary control system for motoneuron excitability. Yet, the efficiency of this system is few, if not never, assessed in the fields of sports and exercise sciences. In this review paper, we propose a methodological approach intended to assess how this neuromodulatory system affects motoneuron excitability. This approach is based on the use of tendon vibration which can, in certain circumstances, induce the generation of the so-called tonic vibration reflex through the stimulation of muscle spindles. Force and EMG responses to tendon vibration are indeed indicative of how this descending system modulates the gain of the ionotropic inputs from Ia afferents and thus of the strength of the monoaminergic drive. After a brief presentation of the neuromodulatory system and of the mechanisms involved in the generation of the tonic vibration reflex, we address some important methodological considerations regarding the use of the TVR to probe this neuromodulatory gain control system. Hopefully, this paper will encourage sports and exercise scientists to investigate this system.


Assuntos
Exercício Físico/fisiologia , Neurônios Motores/fisiologia , Tratos Piramidais/fisiologia , Esportes/fisiologia , Eletromiografia/métodos , Eletromiografia/tendências , Humanos , Contração Muscular/fisiologia , Fusos Musculares/fisiologia , Músculo Esquelético/fisiologia , Reflexo/fisiologia
17.
PLoS One ; 15(6): e0233843, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32497147

RESUMO

The vestibular system is essential to produce adequate postural responses enabling voluntary movement. However, how the vestibular system influences corticospinal output during postural tasks is still unknown. Here, we examined the modulation exerted by the vestibular system on corticospinal output during standing. Healthy subjects (n = 25) maintained quiet standing, head facing forward with eyes closed. Galvanic vestibular stimulation (GVS) was applied bipolarly and binaurally at different delays prior to transcranial magnetic stimulation (TMS) which triggered motor evoked potentials (MEPs). With the cathode right/anode left configuration, MEPs in right Soleus (SOL) muscle were significantly suppressed when GVS was applied at ISI = 40 and 130ms before TMS. With the anode right/cathode left configuration, no significant changes were observed. Changes in the MEP amplitude were then compared to changes in the ongoing EMG when GVS was applied alone. Only the decrease in MEP amplitude at ISI = 40ms occurred without change in the ongoing EMG, suggesting that modulation occurred at a premotoneuronal level. We further investigated whether vestibular modulation could occur at the motor cortex level by assessing changes in the direct corticospinal pathways using the short-latency facilitation of the SOL Hoffmann reflex (H-reflex) by TMS. None of the observed modulation occurred at the level of motor cortex. Finally, using the long-latency facilitation of the SOL H-reflex, we were able to confirm that the suppression of MEP at ISI = 40ms occurred at a premotoneuronal level. The data indicate that vestibular signals modulate corticospinal output to SOL at both premotoneuronal and motoneuronal levels during standing.


Assuntos
Eletromiografia/métodos , Tratos Piramidais/fisiologia , Posição Ortostática , Vestíbulo do Labirinto/fisiologia , Adulto , Potencial Evocado Motor/fisiologia , Feminino , Lateralidade Funcional/fisiologia , Reflexo H/fisiologia , Voluntários Saudáveis , Humanos , Masculino , Córtex Motor/fisiologia , Neurônios Motores/fisiologia , Músculo Esquelético/fisiologia , Estimulação Transcraniana por Corrente Contínua , Estimulação Magnética Transcraniana , Adulto Jovem
18.
Muscle Nerve ; 62(4): 555-558, 2020 10.
Artigo em Inglês | MEDLINE | ID: mdl-32564387

RESUMO

INTRODUCTION: M Scan-Fit, an automated method for motor unit number estimation (MUNE), was assessed in muscles innervated by the facial nerve. METHODS: Healthy volunteers were recruited. M Scans were recorded twice from nasalis and depressor anguli oris (DAO) muscles, and then fitted to a probabilistic model. RESULTS: Twenty-one subjects were evaluated; 38% were females and 62% were males, with a mean age of 34.71 years. The average number of MUs was 38.57 on both testing occasions (t ≤ 0.0001; P = 1.0) for the nasalis. For the DAO, results were 20.62 MUs for the first and 23.48 for the second (t = -2.12; P = .04). Pearson's interrater correlation coefficients were 0.96 (P < .0001) for nasalis and 0.87 (P ≤ .01) for DAO. Intraclass correlation coefficients were 0.88 (P ≤ .01) for nasalis and 0.39 (P = .37) for DAO. DISCUSSION: M Scan-Fit MUNE is an automated, accurate, reliable method of estimating MU number and size from facial muscles.


Assuntos
Músculos Faciais/fisiologia , Neurônios Motores/fisiologia , Adulto , Eletromiografia , Feminino , Voluntários Saudáveis , Humanos , Masculino , Pessoa de Meia-Idade , Adulto Jovem
19.
J Electromyogr Kinesiol ; 53: 102429, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32505088

RESUMO

Unfused tetanic contractions evoked in fast motor units exhibit extra-efficient force production at the onset of contraction, an effect called "boost". Boost is diminished in subsequent contractions if there is a short rest period between contractions, but can be re-established with a longer period of rest. We tested the hypothesis that contractile activity and rest could enhance boost-related metrics. Two sets of 3 unfused tetani were evoked 3 min apart in fast fatigable (FF) and fast fatigue-resistant (FR) motor units of the rat medial gastrocnemius. The greatest changes occurred in the first unfused tetanic contractions. Relative to the first contraction in the first set, the first contraction in the second set exhibited higher peak force during boost in a subset of motor units (76% of FF and 48% of FR). Enhanced force during boost was influenced by interaction of slowing of twitch contraction time (up to 20% and 25%, for FF and FR motor units, respectively), half-relaxation time (up to 37% and 49% for FF and FR motor units, respectively), and potentiation of the first twitch (up to 13% and 5% for FF and FR motor units, respectively). Examination of twitches evoked between sets suggested opportunity for greater enhancement of boost with shorter intervening rest periods. The phenomenon of enhanced boost following motor unit activity may interest sports scientists.


Assuntos
Contração Muscular/fisiologia , Fadiga Muscular/fisiologia , Músculo Esquelético/fisiologia , Recrutamento Neurofisiológico/fisiologia , Descanso/fisiologia , Animais , Estimulação Elétrica/métodos , Feminino , Neurônios Motores/fisiologia , Ratos , Ratos Wistar , Fatores de Tempo
20.
J Electromyogr Kinesiol ; 52: 102421, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32353708

RESUMO

This study included spike trigger averaging (STA) procedures to examine the acceptability of the Precision Decomposition (PD) III derived motor unit action potential (MUAP) trains that met the >90% accuracy criteria from the reconstruct-and-test. MUs met the >90% accuracy criteria from the reconstruct-and-test with STA procedures then applied. Y-intercepts and slopes were calculated for the firing rate- and MUAP amplitude-recruitment threshold relationships. Gaussian noise (1% of the SD of the mean interspike interval) was added to the firing times with the changes in MUAPs quantified. A total of 455 MUs were decomposed with 155 MUs removed as a result of the reconstruct-and-test. Five additional MUs were excluded via the STA criteria. The MUAP waveforms deteriorated with the inclusion of Gaussian noise. There were differences in the derived action potentials amplitudes of higher-threshold MUs between the PD III algorithm and the STA procedure. There was excellent agreement among the slopes and y-intercepts between the relationships that included or excluded MUs that did not meet the STA criteria. There was good agreement between the MUAP amplitude-recruitment threshold relationships derived from the PD III and STA procedure. The addition of the STA procedures did not alter the MU-derived relationships.


Assuntos
Potenciais de Ação , Neurônios Motores/fisiologia , Músculo Esquelético/fisiologia , Adulto , Eletromiografia/métodos , Eletromiografia/normas , Humanos , Masculino , Músculo Esquelético/inervação , Tempo de Reação , Reprodutibilidade dos Testes
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