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1.
J Rehabil Med ; 52(4): jrm00042, 2020 04 14.
Artigo em Inglês | MEDLINE | ID: mdl-32253444

RESUMO

OBJECTIVE: Impairment of physical function is the main determinant of morbidity/mortality in sarcopenia and frailty. Physical function tests are performed by the movement around the joints, and skeletal muscles are the main generators of the forces required to perform these functional tasks. However, the central nervous system, which initiates and coordinates muscle movements, controls the magnitude and temporal parameters of muscle forces. METHODS: Non-systematic literature review was performed about the effects of aging on neuromotor control. RESULT: The ability of a muscle to produce force by aging is deteriorated not only by muscle structural changes, but also by neuromotor control dysfunction. With aging, changes in muscle structure and loss of volumes in brain structures related with movement and cognition have been shown. Age-related cognitive impairment can have considerable negative effects on the force generating capacity of skeletal muscles. In this sense, the relationship has been found between handgrip strength, gait speed, and cognition. CONCLUSION: Treatments targeting muscle mass only would be insufficient unless we address the impairment of neurocognitive functions. It is essential that prescribing life-long exercise is important for healthy aging including the preservation of muscle mass/strength, physical and cognitive functioning, and independent living.


Assuntos
Envelhecimento/fisiologia , Neurônios Motores/fisiologia , Sarcopenia/fisiopatologia , Idoso , Envelhecimento/patologia , Envelhecimento/psicologia , Encéfalo/fisiopatologia , Cognição/fisiologia , Disfunção Cognitiva/fisiopatologia , Idoso Fragilizado/psicologia , Força da Mão/fisiologia , Humanos , Vida Independente , Força Muscular/fisiologia , Músculo Esquelético/fisiologia , Velocidade de Caminhada
2.
Science ; 367(6484): 1372-1376, 2020 03 20.
Artigo em Inglês | MEDLINE | ID: mdl-32193327

RESUMO

The structural and functional complexity of multicellular biological systems, such as the brain, are beyond the reach of human design or assembly capabilities. Cells in living organisms may be recruited to construct synthetic materials or structures if treated as anatomically defined compartments for specific chemistry, harnessing biology for the assembly of complex functional structures. By integrating engineered-enzyme targeting and polymer chemistry, we genetically instructed specific living neurons to guide chemical synthesis of electrically functional (conductive or insulating) polymers at the plasma membrane. Electrophysiological and behavioral analyses confirmed that rationally designed, genetically targeted assembly of functional polymers not only preserved neuronal viability but also achieved remodeling of membrane properties and modulated cell type-specific behaviors in freely moving animals. This approach may enable the creation of diverse, complex, and functional structures and materials within living systems.


Assuntos
Compostos de Anilina/química , Ascorbato Peroxidases/genética , Engenharia Genética , Neurônios/fisiologia , Nitrocompostos/química , Fenilenodiaminas/química , Polímeros/química , Potenciais de Ação , Animais , Ascorbato Peroxidases/metabolismo , Caenorhabditis elegans , Membrana Celular/metabolismo , Sobrevivência Celular , Células Cultivadas , Condutividade Elétrica , Células HEK293 , Hipocampo , Humanos , Potenciais da Membrana , Camundongos , Neurônios Motores/fisiologia , Células Musculares/fisiologia , Neurônios/enzimologia , Técnicas de Patch-Clamp , Polímeros/metabolismo , Ratos , Transdução Genética
3.
Muscle Nerve ; 61(4): 480-484, 2020 04.
Artigo em Inglês | MEDLINE | ID: mdl-31998973

RESUMO

INTRODUCTION: Immobility of the upper limbs has been associated with reduction of F-wave frequency. However, there are no similar studies on lower limb (LL) F-waves. We investigated the impact of LL rest on F-wave and H-reflex parameters. METHODS: The LLs of 14 healthy participants were studied after 90 minutes rest. F-waves (frequency, latencies, chronodispersion, and mean amplitude) and H-reflexes (latency and recruitment curve) were investigated bilaterally. In seven participants the protocol was repeated, but the temperature of one limb was reduced. RESULTS: Immobility only changed F-wave latencies, which increased significantly (mean value of 2 ms, P < .01). Limb cooling did not influence results. DISCUSSION: Contrary to what occurred in cervical lower motor neurons (LMN), LL LMNs did not show a reduced F-wave response to immobility, but their latency increased significantly. This could have been due to reduced Renshaw inhibition of small LMNs, thus facilitating their response to antidromic stimulation and causing delayed late responses.


Assuntos
Reflexo H/fisiologia , Extremidade Inferior/fisiologia , Neurônios Motores/fisiologia , Músculo Esquelético/fisiologia , Adulto , Estimulação Elétrica , Eletromiografia , Feminino , Humanos , Imobilização , Masculino , Pessoa de Meia-Idade , Nervo Tibial/fisiologia , Adulto Jovem
4.
Muscle Nerve ; 61(3): 387-390, 2020 03.
Artigo em Inglês | MEDLINE | ID: mdl-31875989

RESUMO

INTRODUCTION: Motor unit hyperexcitability (MUH) may become manifest in needle electromyography (EMG) recordings as fasciculation potentials, myokymic discharges, or neuromyotonic discharges. Here, we describe a further MUH phenomenon. METHODS: Needle EMG recordings of the Neurology Hospital of Halle (Saale) stored in a video mode as .wav data between 2000 and 2015 were screened for spontaneous continuous motor unit single discharges (SCMUSD). RESULTS: We identified 23 video needle EMG waveforms from 14 patients with SCMUSD. The corresponding motor units discharged at a rate of about 6 H Z (6.3 ± 4.0; range, 1.3-18.1). The coefficient of variation of the discharge rate was 3.5% ± 1.7%. Neurogenic disorders were diagnosed in 12 patients, limb girdle muscle dystrophy was diagnosed in one patient, and stiff-limb syndrome was diagnosed in one patient. DISCUSSION: Spontaneous continuous motor unit single discharge, as described here, widens the spectrum of MUH phenomena.


Assuntos
Potenciais de Ação , Neurônios Motores/fisiologia , Doenças Neuromusculares/fisiopatologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Eletrodos , Eletromiografia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Doença dos Neurônios Motores , Músculo Esquelético/inervação , Doenças Neuromusculares/diagnóstico
5.
Nat Commun ; 10(1): 5815, 2019 12 20.
Artigo em Inglês | MEDLINE | ID: mdl-31862889

RESUMO

Locomotor function, mediated by lumbar neural circuitry, is modulated by descending spinal pathways. Spinal cord injury (SCI) interrupts descending projections and denervates lumbar motor neurons (MNs). We previously reported that retrogradely transported neurotrophin-3 (NT-3) to lumbar MNs attenuated SCI-induced lumbar MN dendritic atrophy and enabled functional recovery after a rostral thoracic contusion. Here we functionally dissected the role of descending neural pathways in response to NT-3-mediated recovery after a T9 contusive SCI in mice. We find that residual projections to lumbar MNs are required to produce leg movements after SCI. Next, we show that the spared descending propriospinal pathway, rather than other pathways (including the corticospinal, rubrospinal, serotonergic, and dopaminergic pathways), accounts for NT-3-enhanced recovery. Lastly, we show that NT-3 induced propriospino-MN circuit reorganization after the T9 contusion via promotion of dendritic regrowth rather than prevention of dendritic atrophy.


Assuntos
Locomoção/fisiologia , Neurônios Motores/fisiologia , Fatores de Crescimento Neural/metabolismo , Traumatismos da Medula Espinal/fisiopatologia , Medula Espinal/fisiopatologia , Animais , Atrofia/patologia , Atrofia/fisiopatologia , Dendritos/patologia , Modelos Animais de Doenças , Feminino , Humanos , Camundongos , Neurônios Motores/patologia , Vias Neurais/fisiopatologia , Recuperação de Função Fisiológica , Traumatismos da Medula Espinal/patologia
6.
Sheng Li Xue Bao ; 71(6): 809-823, 2019 Dec 25.
Artigo em Inglês | MEDLINE | ID: mdl-31879736

RESUMO

Spinal α-motoneurons directly innervate skeletal muscles and function as the final common path for movement and behavior. The processes that determine the excitability of motoneurons are critical for the execution of motor behavior. In fact, it has been noted that spinal motoneurons receive various neuromodulatory inputs, especially monoaminergic one. However, the roles of histamine and hypothalamic histaminergic innervation on spinal motoneurons and the underlying ionic mechanisms are still largely unknown. In the present study, by using the method of intracellular recording on rat spinal slices, we found that activation of either H1 or H2 receptor potentiated repetitive firing behavior and increased the excitability of spinal α-motoneurons. Both of blockage of K+ channels and activation of Na+-Ca2+ exchangers were involved in the H1 receptor-mediated excitation on spinal motoneurons, whereas the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels were responsible for the H2 receptor-mediated excitation. The results suggest that, through switching functional status of ion channels and exchangers coupled to histamine receptors, histamine effectively biases the excitability of the spinal α-motoneurons. In this way, the hypothalamospinal histaminergic innervation may directly modulate final motor outputs and actively regulate spinal motor reflexes and motor execution.


Assuntos
Histamina , Neurônios Motores , Animais , Histamina/farmacologia , Canais Disparados por Nucleotídeos Cíclicos Ativados por Hiperpolarização/metabolismo , Neurônios Motores/efeitos dos fármacos , Neurônios Motores/fisiologia , Ratos , Receptores Histamínicos H2/metabolismo , Trocador de Sódio e Cálcio/metabolismo
7.
PLoS Comput Biol ; 15(10): e1007437, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31609992

RESUMO

In computational modelling of sensory-motor control, the dynamics of muscle contraction is an important determinant of movement timing and joint stiffness. This is particularly so in animals with many slow muscles, as is the case in insects-many of which are important models for sensory-motor control. A muscle model is generally used to transform motoneuronal input into muscle force. Although standard models exist for vertebrate muscle innervated by many motoneurons, there is no agreement on a parametric model for single motoneuron stimulation of invertebrate muscle. Although several different models have been proposed, they have never been evaluated using a common experimental data set. We evaluate five models for isometric force production of a well-studied model system: the locust hind leg tibial extensor muscle. The response of this muscle to motoneuron spikes is best modelled as a non-linear low-pass system. Linear first-order models can approximate isometric force time courses well at high spike rates, but they cannot account for appropriate force time courses at low spike rates. A linear third-order model performs better, but only non-linear models can account for frequency-dependent change of decay time and force potentiation at intermediate stimulus frequencies. Some of the differences among published models are due to differences among experimental data sets. We developed a comprehensive toolbox for modelling muscle activation dynamics, and optimised model parameters using one data set. The "Hatze-Zakotnik model" that emphasizes an accurate single-twitch time course and uses frequency-dependent modulation of the twitch for force potentiation performs best for the slow motoneuron. Frequency-dependent modulation of a single twitch works less well for the fast motoneuron. The non-linear "Wilson" model that optimises parameters to all data set parts simultaneously performs better here. Our open-access toolbox provides powerful tools for researchers to fit appropriate models to a range of insect muscles.


Assuntos
Biologia Computacional/métodos , Gafanhotos/fisiologia , Animais , Simulação por Computador , Estimulação Elétrica , Feminino , Membro Posterior/fisiologia , Insetos/fisiologia , Contração Isométrica/fisiologia , Modelos Lineares , Masculino , Modelos Biológicos , Simulação de Dinâmica Molecular , Neurônios Motores/fisiologia , Movimento , Contração Muscular/fisiologia , Músculo Esquelético/fisiologia , Dinâmica não Linear
8.
Elife ; 82019 10 09.
Artigo em Inglês | MEDLINE | ID: mdl-31596230

RESUMO

Motor cortex (M1) has lateralized outputs, yet neurons can be active during movements of either arm. What is the nature and role of activity across the two hemispheres? We recorded muscles and neurons bilaterally while monkeys cycled with each arm. Most neurons were active during movement of either arm. Responses were strongly arm-dependent, raising two possibilities. First, population-level signals might differ depending on the arm used. Second, the same population-level signals might be present, but distributed differently across neurons. The data supported this second hypothesis. Muscle activity was accurately predicted by activity in either the ipsilateral or contralateral hemisphere. More generally, we failed to find signals unique to the contralateral hemisphere. Yet if signals are shared across hemispheres, how do they avoid impacting the wrong arm? We found that activity related to each arm occupies a distinct subspace, enabling muscle-activity decoders to naturally ignore signals related to the other arm.


Assuntos
Braço/inervação , Lateralidade Funcional , Córtex Motor/fisiologia , Neurônios Motores/fisiologia , Movimento , Animais , Macaca mulatta , Masculino
9.
Elife ; 82019 10 15.
Artigo em Inglês | MEDLINE | ID: mdl-31612855

RESUMO

Prior expectations of movement instructions can promote preliminary action planning and influence choices. We investigated how action priors affect action-goal encoding in premotor and parietal cortices and if they bias subsequent free choice. Monkeys planned reaches according to visual cues that indicated relative probabilities of two possible goals. On instructed trials, the reach goal was determined by a secondary cue respecting these probabilities. On rarely interspersed free-choice trials without instruction, both goals offered equal reward. Action priors induced graded free-choice biases and graded frontoparietal motor-goal activity, complementarily in two subclasses of neurons. Down-regulating neurons co-encoded both possible goals and decreased opposite-to-preferred responses with decreasing prior, possibly supporting a process of choice by elimination. Up-regulating neurons showed increased preferred-direction responses with increasing prior, likely supporting a process of computing net likelihood. Action-selection signals emerged earliest in down-regulating neurons of premotor cortex, arguing for an initiation of selection in the frontal lobe.


Assuntos
Antecipação Psicológica , Comportamento de Escolha/fisiologia , Tomada de Decisões/fisiologia , Macaca mulatta/fisiologia , Córtex Motor/fisiologia , Lobo Parietal/fisiologia , Potenciais de Ação/fisiologia , Animais , Sinais (Psicologia) , Eletrodos Implantados , Funções Verossimilhança , Macaca mulatta/anatomia & histologia , Macaca mulatta/psicologia , Córtex Motor/anatomia & histologia , Neurônios Motores/citologia , Neurônios Motores/fisiologia , Movimento/fisiologia , Lobo Parietal/anatomia & histologia , Reconhecimento Visual de Modelos/fisiologia , Desempenho Psicomotor , Recompensa , Técnicas Estereotáxicas
10.
PLoS Biol ; 17(10): e3000480, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31613896

RESUMO

Many species execute ballistic escape reactions to avoid imminent danger. Despite fast reaction times, responses are often highly regulated, reflecting a trade-off between costly motor actions and perceived threat level. However, how sensory cues are integrated within premotor escape circuits remains poorly understood. Here, we show that in zebrafish, less precipitous threats elicit a delayed escape, characterized by flexible trajectories, which are driven by a cluster of 38 prepontine neurons that are completely separate from the fast escape pathway. Whereas neurons that initiate rapid escapes receive direct auditory input and drive motor neurons, input and output pathways for delayed escapes are indirect, facilitating integration of cross-modal sensory information. These results show that rapid decision-making in the escape system is enabled by parallel pathways for ballistic responses and flexible delayed actions and defines a neuronal substrate for hierarchical choice in the vertebrate nervous system.


Assuntos
Reação de Fuga/fisiologia , Córtex Motor/fisiologia , Neurônios Motores/fisiologia , Reconhecimento Fisiológico de Modelo/fisiologia , Ponte/fisiologia , Peixe-Zebra/fisiologia , Animais , Tomada de Decisões/fisiologia , Larva/fisiologia , Córtex Motor/citologia , Neurônios Motores/citologia , Ponte/citologia , Tempo de Reação/fisiologia
11.
Nat Neurosci ; 22(10): 1669-1676, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31477898

RESUMO

Visual attention dramatically improves individuals' ability to see and modulates the responses of neurons in every known visual and oculomotor area, but whether such modulations can account for perceptual improvements is unclear. We measured the relationship between populations of visual neurons, oculomotor neurons and behavior during detection and discrimination tasks. We found that neither of the two prominent hypothesized neuronal mechanisms underlying attention (which concern changes in information coding and the way sensory information is read out) provide a satisfying account of the observed behavioral improvements. Instead, our results are more consistent with the hypothesis that attention reshapes the representation of attended stimuli to more effectively influence behavior. Our results suggest a path toward understanding the neural underpinnings of perception and cognition in health and disease by analyzing neuronal responses in ways that are constrained by behavior and interactions between brain areas.


Assuntos
Atenção/fisiologia , Neurônios/fisiologia , Animais , Tomada de Decisões/fisiologia , Macaca mulatta , Masculino , Neurônios Motores/fisiologia , Rede Nervosa/fisiologia , Desempenho Psicomotor/fisiologia , Psicofísica
12.
Invest Ophthalmol Vis Sci ; 60(12): 3970-3979, 2019 09 03.
Artigo em Inglês | MEDLINE | ID: mdl-31560371

RESUMO

Purpose: Pattern strabismus is characterized by a cross-axis pattern of horizontal and vertical misalignments. In A-pattern strabismus, for example, a divergent change in the horizontal misalignment occurs on downgaze. Work with nonhuman primate models has provided evidence that this disorder is associated with abnormal cross-talk between brainstem pathways that normally encode horizontal and vertical eye position and velocity. Neurons in the interstitial nucleus of Cajal (INC) are normally sensitive to vertical eye position; in the present study, we test the hypothesis that, in monkeys with pattern strabismus, some INC neurons will show an abnormal sensitivity to horizontal eye position. Methods: Monkeys were rewarded for fixating a visual target that stepped to various locations on a tangent screen. Single neurons were recorded from INC in one normal monkey, and two with A-pattern strabismus. Multiple linear regression analysis was used to estimate the preferred direction for each neuron. Results: In the normal monkey, all INC neurons had preferred directions within 20° of pure vertical (either up or down). The preferred directions were significantly more variable in the monkeys with pattern strabismus, with a minority being more sensitive to horizontal eye position than vertical eye position. In addition, the vertical eye position sensitivity was significantly less in the monkeys with strabismus. Conclusions: In pattern strabismus, neurons in INC show neurophysiological abnormalities consistent with a failure to develop normal tuning properties. Results were consistent with the hypothesis that, in pattern strabismus, INC receives an abnormally strong signal related to horizontal eye position.


Assuntos
Neurônios Motores/fisiologia , Transtornos da Motilidade Ocular/fisiopatologia , Estrabismo/fisiopatologia , Tegmento Mesencefálico/fisiopatologia , Animais , Movimentos Oculares/fisiologia , Fixação Ocular/fisiologia , Macaca mulatta , Macaca nemestrina
13.
Nat Commun ; 10(1): 4095, 2019 09 10.
Artigo em Inglês | MEDLINE | ID: mdl-31506439

RESUMO

Animals must slow or halt locomotion to integrate sensory inputs or to change direction. In Caenorhabditis elegans, the GABAergic and peptidergic neuron RIS mediates developmentally timed quiescence. Here, we show RIS functions additionally as a locomotion stop neuron. RIS optogenetic stimulation caused acute and persistent inhibition of locomotion and pharyngeal pumping, phenotypes requiring FLP-11 neuropeptides and GABA. RIS photoactivation allows the animal to maintain its body posture by sustaining muscle tone, yet inactivating motor neuron oscillatory activity. During locomotion, RIS axonal Ca2+ signals revealed functional compartmentalization: Activity in the nerve ring process correlated with locomotion stop, while activity in a branch correlated with induced reversals. GABA was required to induce, and FLP-11 neuropeptides were required to sustain locomotion stop. RIS attenuates neuronal activity and inhibits movement, possibly enabling sensory integration and decision making, and exemplifies dual use of one cell across development in a compact nervous system.


Assuntos
Caenorhabditis elegans/fisiologia , Cálcio/metabolismo , Neurônios GABAérgicos/metabolismo , Locomoção/fisiologia , Neuropeptídeos/metabolismo , Sono/fisiologia , Animais , Axônios/metabolismo , Caenorhabditis elegans/citologia , Neurônios Colinérgicos/fisiologia , Junções Comunicantes/metabolismo , Luz , Modelos Biológicos , Neurônios Motores/fisiologia , Músculos/citologia , Fenótipo , Transdução de Sinais , Ácido gama-Aminobutírico/metabolismo
14.
Elife ; 82019 09 16.
Artigo em Inglês | MEDLINE | ID: mdl-31524598

RESUMO

Neurexophilins are secreted neuropeptide-like glycoproteins, and neurexophilin1 and neurexophilin3 are ligands for the presynaptic cell adhesion molecule α-neurexin. Neurexophilins are more selectively expressed in the brain than α-neurexins, however, which led us to ask whether neurexophilins modulate the function of α-neurexin in a context-specific manner. We characterized the expression and function of neurexophilin4 in mice and found it to be expressed in subsets of neurons responsible for feeding, emotion, balance, and movement. Deletion of Neurexophilin4 caused corresponding impairments, most notably in motor learning and coordination. We demonstrated that neurexophilin4 interacts with α-neurexin and GABAARs in the cerebellum. Loss of Neurexophilin4 impaired cerebellar Golgi-granule inhibitory neurotransmission and synapse number, providing a partial explanation for the motor learning and coordination deficits observed in the Neurexophilin4 null mice. Our data illustrate how selectively expressed Neurexophilin4, an α-neurexin ligand, regulates specific synapse function and modulates cerebellar motor control.


Assuntos
Cerebelo/fisiologia , Glicoproteínas/metabolismo , Atividade Motora , Neurônios Motores/fisiologia , Neuropeptídeos/metabolismo , Animais , Deleção de Genes , Regulação da Expressão Gênica , Glicoproteínas/deficiência , Camundongos Endogâmicos C57BL , Camundongos Knockout , Neuropeptídeos/deficiência
15.
Elife ; 82019 09 10.
Artigo em Inglês | MEDLINE | ID: mdl-31502540

RESUMO

How circuits assemble starting from stem cells is a fundamental question in developmental neurobiology. We test the hypothesis that, in neuronal stem cells, temporal transcription factors predictably control neuronal terminal features and circuit assembly. Using the Drosophila motor system, we manipulate expression of the classic temporal transcription factor Hunchback (Hb) specifically in the NB7-1 stem cell, which produces U motor neurons (MNs), and then we monitor dendrite morphology and neuromuscular synaptic partnerships. We find that prolonged expression of Hb leads to transient specification of U MN identity, and that embryonic molecular markers do not accurately predict U MN terminal features. Nonetheless, our data show Hb acts as a potent regulator of neuromuscular wiring decisions. These data introduce important refinements to current models, show that molecular information acts early in neurogenesis as a switch to control motor circuit wiring, and provide novel insight into the relationship between stem cell and circuit.


Assuntos
Proteínas de Ligação a DNA/biossíntese , Proteínas de Drosophila/biossíntese , Expressão Gênica , Neurônios Motores/fisiologia , Vias Neurais/embriologia , Junção Neuromuscular/fisiologia , Células-Tronco/fisiologia , Fatores de Transcrição/biossíntese , Animais , Drosophila , Neurônios Motores/citologia , Junção Neuromuscular/citologia , Células-Tronco/citologia
16.
Exp Brain Res ; 237(10): 2653-2664, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31396644

RESUMO

It is common practice to examine motor unit (MU) activity according to mean firing rate (MFR) and action potential amplitude (MUAPAMP) vs. recruitment threshold (RT) relationships during isometric trapezoidal contractions. However, it is unknown whether the rate of torque development during the linearly increasing torque phase affects the activity of MUs during such contractions. Sixteen healthy males and females performed two isometric trapezoidal muscle actions at 40% of maximum voluntary contraction (MVC), one at a rate of torque development of 5% MVC/s (SLOW40) and one at 20% MVC/s (FAST40) during the linearly increasing torque phase. Surface electromyography (EMG) was recorded from the vastus lateralis (VL) via a 5-pin surface array sensor and decomposed into action potential trains of individual MUs, yielding MFRs and MUAPAMP which were regressed against RT separately for each contraction. Surface EMG amplitude recorded from leg extensors and flexors was used to quantify muscle activation and coactivation. MFR vs. RT relationship slopes were more negative (P = 0.003) for the SLOW40 (- 0.491 ± 0.101 pps/%MVC) than FAST40 (- 0.322 ± 0.109 pps/%MVC) and the slopes of the MUAPAMP vs. RT relationships (P = 0.022, SLOW40 = 0.0057 ± 0.0021 mV/%MVC, FAST40 = 0.0041 ± 0.0023 mV/%MVC) and muscle activation of the extensors (P < 0.001, SLOW40 = 36.3 ± 7.82%, FAST40 = 34.0 ± 6.26%) were greater for SLOW40 than FAST40. MU firing rates were lower and action potential amplitudes were larger in relation to recruitment thresholds for a contraction performed at a slower rate compared to a faster rate of isometric torque development. Differences in MU activity can exist as a function of rate of torque development during commonly performed isometric trapezoidal contractions.


Assuntos
Contração Isométrica/fisiologia , Neurônios Motores/fisiologia , Músculo Esquelético/fisiologia , Recrutamento Neurofisiológico/fisiologia , Potenciais de Ação/fisiologia , Adulto , Feminino , Humanos , Masculino , Músculo Quadríceps/fisiologia , Torque , Adulto Jovem
17.
Brain Struct Funct ; 224(8): 2717-2731, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31375981

RESUMO

Medial rectus motoneurons are innervated by two main pontine inputs. The specific function of each of these two inputs remains to be fully understood. Indeed, selective partial deafferentation of medial rectus motoneurons, performed by the lesion of either the vestibular or the abducens input, initially induces similar changes in motoneuronal discharge. However, at longer time periods, the responses to both lesions are dissimilar. Alterations on eye movements and motoneuronal discharge induced by vestibular input transection recover completely 2 months post-lesion, whereas changes induced by abducens internuclear lesion are more drastic and permanent. Functional recovery could be due to some kind of plastic process, such as reactive synaptogenesis, developed by the remaining intact input, which would occupy the vacant synaptic spaces left after lesion. Herein, by means of confocal microscopy, immunocytochemistry and retrograde labeling, we attempt to elucidate the possible plastic processes that take place after partial deafferentation of medial rectus motoneuron. 48 h post-injury, both vestibular and abducens internuclear lesions produced a reduced synaptic coverage on these motoneurons. However, 96 h after vestibular lesion, there was a partial recovery in the number of synaptic contacts. This suggests that there was reactive synaptogenesis. This recovery was preceded by an increase in somatic neurotrophin content, suggesting a role of these molecules in presynaptic axonal sprouting. The rise in synaptic coverage might be due to terminal sprouting performed by the remaining main input, i.e., abducens internuclear neurons. The present results may improve the understanding of this apparently redundant input system.


Assuntos
Neurônios Motores/fisiologia , Plasticidade Neuronal , Músculos Oculomotores/fisiologia , Animais , Denervação/métodos , Movimentos Oculares , Masculino , Neurônios Motores/citologia , Vias Neurais/fisiologia , Músculos Oculomotores/inervação , Ratos Wistar
18.
Int J Mol Sci ; 20(16)2019 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-31394733

RESUMO

Motor neuron circuitry is one of the most elaborate circuitries in our body, which ensures voluntary and skilled movement that requires cognitive input. Therefore, both the cortex and the spinal cord are involved. The cortex has special importance for motor neuron diseases, in which initiation and modulation of voluntary movement is affected. Amyotrophic lateral sclerosis (ALS) is defined by the progressive degeneration of both the upper and lower motor neurons, whereas hereditary spastic paraplegia (HSP) and primary lateral sclerosis (PLS) are characterized mainly by the loss of upper motor neurons. In an effort to reveal the cellular and molecular basis of neuronal degeneration, numerous model systems are generated, and mouse models are no exception. However, there are many different levels of complexities that need to be considered when developing mouse models. Here, we focus our attention to the upper motor neurons, which are one of the most challenging neuron populations to study. Since mice and human differ greatly at a species level, but the cells/neurons in mice and human share many common aspects of cell biology, we offer a solution by focusing our attention to the affected neurons to reveal the complexities of diseases at a cellular level and to improve translational efforts.


Assuntos
Neurônios Motores/fisiologia , Condução Nervosa , Plasticidade Neuronal , Animais , Modelos Animais de Doenças , Suscetibilidade a Doenças , Ligação Genética , Predisposição Genética para Doença , Humanos , Camundongos , Camundongos Transgênicos , Doença dos Neurônios Motores/etiologia , Doença dos Neurônios Motores/metabolismo , Doença dos Neurônios Motores/fisiopatologia , Neurônios Motores/citologia , Neurônios Motores/ultraestrutura
19.
PLoS One ; 14(7): e0218738, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31260485

RESUMO

C. elegans neuronal system constitutes the ideal framework for studying simple, yet realistic, neuronal activity, since the whole nervous system is fully characterized with respect to the exact number of neurons and the neuronal connections. Most recent efforts are devoted to investigate and clarify the signal processing and functional connectivity, which are at the basis of sensing mechanisms, signal transmission, and motor control. In this framework, a refined modelof whole neuron dynamics constitutes a key ingredient to describe the electrophysiological processes, both at thecellular and at the network scale. In this work, we present Hodgkin-Huxley-based models of ion channels dynamics black, built on data available both from C. elegans and from other organisms, expressing homologous channels. We combine these channel models to simulate the electrical activity oftwo among the most studied neurons in C. elegans, which display prototypical dynamics of neuronal activation, the chemosensory AWCON and the motor neuron RMD. Our model properly describes the regenerative responses of the two cells. We analyze in detail the role of ion currents, both in wild type and in in silico knockout neurons. Moreover, we specifically investigate the behavior of RMD, identifying a heterogeneous dynamical response which includes bistable regimes and sustained oscillations. We are able to assess the critical role of T-type calcium currents, carried by CCA-1 channels, and leakage currents in the regulation of RMD response. Overall, our results provide new insights in the activity of key C. elegans neurons. The developed mathematical framework constitute a basis for single-cell and neuronal networks analyses, opening new scenarios in the in silico modeling of C. elegans neuronal system.


Assuntos
Proteínas de Caenorhabditis elegans/genética , Caenorhabditis elegans/fisiologia , Modelos Neurológicos , Neurônios Motores/fisiologia , Rede Nervosa/fisiologia , Células Receptoras Sensoriais/fisiologia , Transmissão Sináptica/fisiologia , Animais , Caenorhabditis elegans/citologia , Proteínas de Caenorhabditis elegans/metabolismo , Canais de Cálcio/genética , Canais de Cálcio/metabolismo , Simulação por Computador , Expressão Gênica , Transporte de Íons , Neurônios Motores/citologia , Rede Nervosa/citologia , Canais de Potássio/genética , Canais de Potássio/metabolismo , Células Receptoras Sensoriais/citologia , Análise de Célula Única/métodos , Canais de Sódio/genética , Canais de Sódio/metabolismo
20.
Handb Clin Neurol ; 160: 217-224, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31277849

RESUMO

Nerve conduction studies (NCSs) are an essential tool in the evaluation of the peripheral nervous system. The sensory nerve action potential (SNAP) provides information on the sensory nerve axon and its pathway from the distal receptors in the skin to the dorsal root ganglia, while the compound muscle action potential (CMAP) is an assessment of the motor nerve fibers from their origins in the anterior horn cell to their termination along muscle fibers. Various parameters of the SNAP and CMAP waveforms are used to determine the number of functioning nerve fibers and the speed of conduction. Similarly, specific electrodiagnostic patterns involving SNAP and CMAP amplitudes, latencies and other measurements can help discern the underlying nerve pathophysiology as either axon loss or demyelinating in nature. Numerous technical and environmental factors can affect the NCS and should be recognized and corrected if possible. Finally, while basic NCSs are a noninvasive and low-risk procedure, safety issues for patients with implanted electrical devices should be considered.


Assuntos
Eletromiografia/métodos , Neurônios Motores/fisiologia , Condução Nervosa/fisiologia , Células Receptoras Sensoriais/fisiologia , Potenciais de Ação/fisiologia , Axônios/fisiologia , Humanos
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