RESUMEN
The modular control of muscles in groups, often referred to as muscle synergies, has been proposed to provide a motor repertoire of actions for the robust control of movement. However, it is not clear whether muscle synergies identified in one task are also recruited by different neural pathways subserving other motor behaviors. We tested the hypothesis that voluntary and reactive modifications to walking in humans result from the recruitment of locomotor muscle synergies. We recorded the activity of 16 muscles in the right leg as subjects walked a 7.5 m path at two different speeds. To elicit a second motor behavior, midway through the path we imposed ramp and hold translation perturbations of the support surface in each of four cardinal directions. Variations in the temporal recruitment of locomotor muscle synergies could account for cycle-by-cycle variations in muscle activity across strides. Locomotor muscle synergies were also recruited in atypical phases of gait, accounting for both anticipatory gait modifications before perturbations and reactive feedback responses to perturbations. Our findings are consistent with the idea that a common pool of spatially fixed locomotor muscle synergies can be recruited by different neural pathways, including the central pattern generator for walking, brainstem pathways for balance control, and cortical pathways mediating voluntary gait modifications. Together with electrophysiological studies, our work suggests that muscle synergies may provide a library of motor subtasks that can be flexibly recruited by parallel descending pathways to generate a variety of complex natural movements in the upper and lower limbs.
Asunto(s)
Actividad Motora/fisiología , Músculo Esquelético/fisiología , Equilibrio Postural/fisiología , Reclutamiento Neurofisiológico/fisiología , Caminata/fisiología , Adolescente , Adulto , Tronco Encefálico/fisiología , Corteza Cerebral/fisiología , Electromiografía/métodos , Femenino , Humanos , Masculino , Músculo Esquelético/inervación , Vías Nerviosas/fisiología , Adulto JovenRESUMEN
Although cats that have been spinalized can also be trained to stand and step with full weight support, directionally appropriate long-latency responses to perturbations are impaired, suggesting that these behaviors are mediated by distinct neural mechanisms. However, it remains unclear whether these responses reflect an attenuated postural response using the appropriate muscular coordination patterns for balance or are due to fundamentally different neural mechanisms such as increased muscular cocontraction or short-latency stretch responses. Here we used muscle synergy analysis on previously collected data to identify whether there are changes in the spatial organization of muscle activity for balance within an animal after spinalization. We hypothesized that the modular organization of muscle activity for balance control is disrupted by spinal cord transection. In each of four animals, muscle synergies were extracted from postural muscle activity both before and after spinalization with nonnegative matrix factorization. Muscle synergy number was reduced after spinalization in three animals and increased in one animal. However, muscle synergy structure was greatly altered after spinalization with reduced direction tuning, suggesting little consistent organization of muscle activity. Furthermore, muscle synergy recruitment was correlated to subsequent force production in the intact but not spinalized condition. Our results demonstrate that the modular structure of sensorimotor feedback responses for balance control is severely disrupted after spinalization, suggesting that the muscle synergies for balance control are not accessible by spinal circuits alone. Moreover, we demonstrate that spinal mechanisms underlying weight support are distinct from brain stem mechanisms underlying directional balance control.
Asunto(s)
Músculo Esquelético/fisiología , Equilibrio Postural , Médula Espinal/fisiología , Animales , Gatos , Desnervación , Retroalimentación Sensorial , Músculo Esquelético/inervación , Médula Espinal/cirugíaRESUMEN
We investigated muscle activity, ground reaction forces, and center of mass (CoM) acceleration in two different postural behaviors for standing balance control in humans to determine whether common neural mechanisms are used in different postural tasks. We compared nonstepping responses, where the base of support is stationary and balance is recovered by returning CoM back to its initial position, with stepping responses, where the base of support is enlarged and balance is recovered by pushing the CoM away from the initial position. In response to perturbations of the same direction, these two postural behaviors resulted in different muscle activity and ground reaction forces. We hypothesized that a common pool of muscle synergies producing consistent task-level biomechanical functions is used to generate different postural behaviors. Two sets of support-surface translations in 12 horizontal-plane directions were presented, first to evoke stepping responses and then to evoke nonstepping responses. Electromyographs in 16 lower back and leg muscles of the stance leg were measured. Initially (â¼100-ms latency), electromyographs, CoM acceleration, and forces were similar in nonstepping and stepping responses, but these diverged in later time periods (â¼200 ms), when stepping occurred. We identified muscle synergies using non-negative matrix factorization and functional muscle synergies that quantified correlations between muscle synergy recruitment levels and biomechanical outputs. Functional muscle synergies that produce forces to restore CoM position in nonstepping responses were also used to displace the CoM during stepping responses. These results suggest that muscle synergies represent common neural mechanisms for CoM movement control under different dynamic conditions: stepping and nonstepping postural responses.
Asunto(s)
Movimiento/fisiología , Músculo Esquelético/fisiología , Equilibrio Postural/fisiología , Tiempo de Reacción/fisiología , Adulto , Electromiografía/métodos , Femenino , Humanos , Masculino , Postura/fisiología , Adulto JovenRESUMEN
Coronaviruses rely on host membranes for entry, establishment of replication centers, and egress. Compounds targeting cellular membrane biology and lipid biosynthetic pathways have previously shown promise as antivirals and are actively being pursued as treatments for other conditions. Here, we test small molecule inhibitors that target the PI3 kinase VPS34 or fatty acid metabolism for anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) activity. Our studies determine that compounds targeting VPS34 are potent SARS-CoV-2 inhibitors. Mechanistic studies with compounds targeting multiple steps up- and downstream of fatty acid synthase (FASN) identify the importance of triacylglycerol production and protein palmitoylation as requirements for efficient viral RNA synthesis and infectious virus production. Further, FASN knockout results in significantly impaired SARS-CoV-2 replication that can be rescued with fatty acid supplementation. Together, these studies clarify roles for VPS34 and fatty acid metabolism in SARS-CoV-2 replication and identify promising avenues for the development of countermeasures against SARS-CoV-2.
Asunto(s)
Antivirales/farmacología , COVID-19/virología , Fosfatidilinositol 3-Quinasas Clase III/antagonistas & inhibidores , Metabolismo de los Lípidos/efectos de los fármacos , SARS-CoV-2/efectos de los fármacos , SARS-CoV-2/fisiología , Replicación Viral/efectos de los fármacos , Aminopiridinas/farmacología , Animales , Células CACO-2 , Línea Celular , Chlorocebus aethiops , Fosfatidilinositol 3-Quinasas Clase III/metabolismo , Ácido Graso Sintasas/efectos de los fármacos , Ácido Graso Sintasas/genética , Técnicas de Inactivación de Genes , Humanos , Lipoilación/efectos de los fármacos , Pirimidinas/farmacología , ARN Viral/metabolismo , Triglicéridos/metabolismo , Células VeroRESUMEN
Therapeutics targeting replication of SARS coronavirus 2 (SARS-CoV-2) are urgently needed. Coronaviruses rely on host membranes for entry, establishment of replication centers and egress. Compounds targeting cellular membrane biology and lipid biosynthetic pathways have previously shown promise as antivirals and are actively being pursued as treatments for other conditions. Here, we tested small molecule inhibitors that target membrane dynamics or lipid metabolism. Included were inhibitors of the PI3 kinase VPS34, which functions in autophagy, endocytosis and other processes; Orlistat, an inhibitor of lipases and fatty acid synthetase, is approved by the FDA as a treatment for obesity; and Triacsin C which inhibits long chain fatty acyl-CoA synthetases. VPS34 inhibitors, Orlistat and Triacsin C inhibited virus growth in Vero E6 cells and in the human airway epithelial cell line Calu-3, acting at a post-entry step in the virus replication cycle. Of these the VPS34 inhibitors exhibit the most potent activity.
RESUMEN
The cardiac action potential (AP) is vital for understanding healthy and diseased cardiac biology and drug safety testing. However, techniques for high throughput cardiac AP measurements have been limited. Here, we introduce a novel technique for reliably increasing the coupling of cardiomyocyte syncytium to planar multiwell microelectrode arrays, resulting in a stable, label-free local extracellular action potential (LEAP). We characterized the reliability and stability of LEAP, its relationship to the field potential, and its efficacy for quantifying AP morphology of human induced pluripotent stem cell derived and primary rodent cardiomyocytes. Rise time, action potential duration, beat period, and triangulation were used to quantify compound responses and AP morphology changes induced by genetic modification. LEAP is the first high throughput, non-invasive, label-free, stable method to capture AP morphology from an intact cardiomyocyte syncytium. LEAP can accelerate our understanding of stem cell models, while improving the automation and accuracy of drug testing.
Asunto(s)
Potenciales de Acción/fisiología , Corazón/fisiología , Microelectrodos , Animales , Animales Recién Nacidos , Electroporación , Humanos , Células Madre Pluripotentes Inducidas/citología , Canales Iónicos/antagonistas & inhibidores , Canales Iónicos/metabolismo , Miocitos Cardíacos/fisiología , Ratas , Procesamiento de Señales Asistido por Computador , Factores de TiempoRESUMEN
Methylprednisolone (MP) has been shown to reduce acute inflammation resulting from a secondary damage cascade initiated by the primary physical injury to the spinal cord. The current clinical practice for delivering systemic MP is inefficient, and high doses are required, resulting in adverse, undesired, dose-related side effects in patients. Here, we report a novel, minimally invasive, localized drug delivery system for delivering MP to the contused adult rat spinal cord that potentially side-steps the deleterious consequences of systemic cortico-steroid therapy. MP was encapsulated in biodegradable PLGA based nanoparticles (NP), and these nanoparticles were embedded in an agarose hydrogel for localization to the site of contusion injury. To visualize and quantify its spatial distribution within the injured spinal cord, MP was conjugated to Texas-red cadaverine prior to encapsulation in nanoparticles. When delivered via the hydrogel-nanoparticle system, MP entered the injured spinal cord and diffused up to 1.5mm deep and up to 3mm laterally into the injured spinal cord within 2 days. Furthermore, topically delivered MP significantly decreased early inflammation inside the contusion injured spinal cord as evidenced by a significant reduction in the number of ED-1(+) macrophages/activated microglia. This decreased early inflammation was accompanied by a significantly diminished expression of pro-inflammatory proteins including Calpain and iNOS. Additionally, topically delivered MP significantly reduced lesion volume 7 days after contusion injury. The minimally invasive MP delivery system reported in this study has the potential to enhance the effectiveness of MP therapy after contusion injury to the spinal cord and avoid the side effects arising from high dose cortico-steroid therapy.
Asunto(s)
Preparaciones de Acción Retardada/administración & dosificación , Metilprednisolona/administración & dosificación , Metilprednisolona/farmacocinética , Sefarosa/química , Traumatismos de la Médula Espinal/tratamiento farmacológico , Traumatismos de la Médula Espinal/metabolismo , Enfermedad Aguda , Animales , Antiinflamatorios/administración & dosificación , Portadores de Fármacos/administración & dosificación , Portadores de Fármacos/química , Masculino , Ratas , Ratas Sprague-Dawley , Traumatismos de la Médula Espinal/patología , Distribución Tisular , Resultado del TratamientoRESUMEN
OBJECTIVE: Incomplete spinal cord injury (iSCI) disrupts motor control and limits the ability to coordinate muscles for overground walking. Inappropriate muscle activity has been proposed as a source of clinically observed walking deficits after iSCI. We hypothesized that persons with iSCI exhibit lower locomotor complexity compared to able-body (AB) controls as reflected by fewer motor modules, as well as, altered module composition and activation. METHODS: Eight persons with iSCI and eight age-matched AB controls walked overground at prescribed cadences. Electromyograms of fourteen single leg muscles were recorded. Non-negative matrix factorization was used to identify the composition and activation of motor modules, which represent groups of consistently co-activated muscles that accounted for 90% of variability in muscle activity. RESULTS: Motor module number, composition, and activation were significantly altered in persons with iSCI as compared to AB controls during overground walking at self-selected cadences. However, there was no significant difference in module number between persons with iSCI and AB controls when cadence and assistive device were matched. CONCLUSIONS: Muscle coordination during overground walking is impaired after chronic iSCI. SIGNIFICANCE: Our results are indicative of neuromuscular constraints on muscle coordination after iSCI. Altered muscle coordination contributes to person-specific gait deficits during overground walking.
Asunto(s)
Pierna/fisiopatología , Trastornos del Movimiento/fisiopatología , Músculo Esquelético/fisiopatología , Traumatismos de la Médula Espinal/fisiopatología , Caminata/fisiología , Adulto , Electromiografía , Femenino , Humanos , Masculino , Persona de Mediana Edad , Trastornos del Movimiento/etiología , Traumatismos de la Médula Espinal/complicaciones , Adulto JovenRESUMEN
Little is known about the integration of neural mechanisms for balance and locomotion. Muscle synergies have been studied independently in standing balance and walking, but not compared. Here, we hypothesized that reactive balance and walking are mediated by a common set of lower-limb muscle synergies. In humans, we examined muscle activity during multidirectional support-surface perturbations during standing and walking, as well as unperturbed walking at two speeds. We show that most muscle synergies used in perturbations responses during standing were also used in perturbation responses during walking, suggesting common neural mechanisms for reactive balance across different contexts. We also show that most muscle synergies using in reactive balance were also used during unperturbed walking, suggesting that neural circuits mediating locomotion and reactive balance recruit a common set of muscle synergies to achieve task-level goals. Differences in muscle synergies across conditions reflected differences in the biomechanical demands of the tasks. For example, muscle synergies specific to walking perturbations may reflect biomechanical challenges associated with single limb stance, and muscle synergies used during sagittal balance recovery in standing but not walking were consistent with maintaining the different desired center of mass motions in standing vs. walking. Thus, muscle synergies specifying spatial organization of muscle activation patterns may define a repertoire of biomechanical subtasks available to different neural circuits governing walking and reactive balance and may be recruited based on task-level goals. Muscle synergy analysis may aid in dissociating deficits in spatial vs. temporal organization of muscle activity in motor deficits. Muscle synergy analysis may also provide a more generalizable assessment of motor function by identifying whether common modular mechanisms are impaired across the performance of multiple motor tasks.
RESUMEN
Muscle coordination may be difficult or impossible to predict accurately based on biomechanical considerations alone because of redundancy in the musculoskeletal system. Because many solutions exist for any given movement, the role of the nervous system in further constraining muscle coordination patterns for movement must be considered in both healthy and impaired motor control. On the basis of computational neuromechanical analyses of experimental data combined with modeling techniques, we have demonstrated several such neural constraints on the temporal and spatial patterns of muscle activity during both locomotion and postural responses to balance perturbations. We hypothesize that subject-specific and trial-by-trial differences in muscle activation can be parameterized and understood by a hierarchical and low-dimensional framework that reflects the neural control of task-level goals. In postural control, we demonstrate that temporal patterns of muscle activity may be governed by feedback control of task-level variables that represent the overall goal-directed motion of the body. These temporal patterns then recruit spatially-fixed patterns of muscle activity called muscle synergies that produce the desired task-level biomechanical functions that require multijoint coordination. Moreover, these principles apply more generally to movement, and in particular to locomotor tasks in both healthy and impaired individuals. Overall, understanding the goals and organization of the neural control of movement may provide useful reduced dimension parameter sets to address the degrees-of-freedom problem in musculoskeletal movement control. More importantly, however, neuromechanical analyses may lend insight and provide a framework for understanding subject-specific and trial-by-trial differences in movement across both healthy and motor-impaired populations.