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Blazevich AJ, Mesquita RNO, Pinto RS, Pulverenti T, Ratel S. Reduction and recovery of self-sustained muscle activity after fatiguing plantar flexor contractions. Eur J Appl Physiol 2024; 124:1781-1794. [PMID: 38340155 PMCID: PMC11130039 DOI: 10.1007/s00421-023-05403-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Accepted: 12/11/2023] [Indexed: 02/12/2024]
Abstract
PURPOSE Persistent inward calcium and sodium currents (PICs) are crucial for initiation and maintenance of motoneuron firing, and thus muscular force. However, there is a lack of data describing the effects of fatiguing exercise on PIC activity in humans. We simultaneously applied tendon vibration and neuromuscular electrical stimulation (VibStim) before and after fatiguing exercise. VibStim induces self-sustained muscle activity that is proposed to result from PIC activation. METHODS Twelve men performed 5-s maximal isometric plantar flexor contractions (MVC) with 5-s rests until joint torque was reduced to 70%MVC. VibStim trials consisted of five 2-s trains of neuromuscular electrical stimulation (20 Hz, evoking 10% MVC) of triceps surae with simultaneous Achilles tendon vibration (115 Hz) without voluntary muscle activation. VibStim was applied before (PRE), immediately (POST), 5-min (POST-5), and 10-min (POST-10) after exercise completion. RESULTS Sustained torque (Tsust) and soleus electromyogram amplitudes (EMG) measured 3 s after VibStim were reduced (Tsust: -59.0%, p < 0.001; soleus EMG: -38.4%, p < 0.001) but largely recovered by POST-5, and changes in MVC and Tsust were correlated across the four time points (r = 0.69; p < 0.001). After normalisation to values obtained at the end of the vibration phase to control for changes in fibre-specific force and EMG signal characteristics, decreases in Tsust (-42.9%) and soleus EMG (-22.6%) remained significant and were each correlated with loss and recovery of MVC (r = 0.41 and 0.46, respectively). CONCLUSION The parallel changes observed in evoked self-sustained muscle activity and force generation capacity provide motivation for future examinations on the potential influence of fatigue-induced PIC changes on motoneuron output.
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Affiliation(s)
- Anthony J Blazevich
- School of Medical and Health Sciences, Centre for Human Performance, Edith Cowan University, Joondalup, Australia.
| | - Ricardo N O Mesquita
- School of Medical and Health Sciences, Centre for Human Performance, Edith Cowan University, Joondalup, Australia
- Department of Electrical Engineering, Chalmers University of Technology, Gothenburg, Sweden
- Neuroscience Research Australia, Sydney, Australia
| | - Ronei S Pinto
- Exercise Research Laboratory, School of Physical Education, Physiotherapy and Dance, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
| | - Timothy Pulverenti
- Department of Physical Therapy, College of Staten Island, Staten Island, NY, USA
| | - Sébastien Ratel
- UFR STAPS - Laboratoire AME2P, Université Clermont Auvergne, Campus Universitaire des Cézeaux, 3 Rue de la Chebarde, 63170, Clermont-Ferrand, France
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Amiez N, Martin A, Gaveau J, Julliand S, Papaxanthis C, Paizis C. Local vibration induces changes in spinal and corticospinal excitability in vibrated and antagonist muscles. J Neurophysiol 2024; 131:379-393. [PMID: 38198664 DOI: 10.1152/jn.00258.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Revised: 12/21/2023] [Accepted: 01/09/2024] [Indexed: 01/12/2024] Open
Abstract
Local vibration (LV) applied over the muscle tendon constitutes a powerful stimulus to activate the muscle spindle primary (Ia) afferents that project to the spinal level and are conveyed to the cortical level. This study aimed to identify the neuromuscular changes induced by a 30-min LV-inducing illusions of hand extension on the vibrated flexor carpi radialis (FCR) and the antagonist extensor carpi radialis (ECR) muscles. We studied the change of the maximal voluntary isometric contraction (MVIC, experiment 1) for carpal flexion and extension, motor-evoked potentials (MEPs, experiment 2), cervicomedullary motor-evoked potentials (CMEPs, experiment 2), and Hoffmann's reflex (H-reflex, experiment 3) for both muscles at rest. Measurements were performed before (PRE) and at 0, 30, and 60 min after LV protocol. A lasting decrease in strength was only observed for the vibrated muscle. The reduction in CMEPs observed for both muscles seems to support a decrease in alpha motoneurons excitability. In contrast, a slight decrease in MEPs responses was observed only for the vibrated muscle. The MEP/CMEP ratio increase suggested greater cortical excitability after LV for both muscles. In addition, the H-reflex largely decreased for the vibrated and the antagonist muscles. The decrease in the H/CMEP ratio for the vibrated muscle supported both pre- and postsynaptic causes of the decrease in the H-reflex. Finally, LV-inducing illusions of movement reduced alpha motoneurons excitability for both muscles with a concomitant increase in cortical excitability.NEW & NOTEWORTHY Spinal disturbances confound the interpretation of excitability changes in motor areas and compromise the conclusions reached by previous studies using only a corticospinal marker for both vibrated and antagonist muscles. The time course recovery suggests that the H-reflex perturbations for the vibrated muscle do not only depend on changes in alpha motoneurons excitability. Local vibration induces neuromuscular changes in both vibrated and antagonist muscles at the spinal and cortical levels.
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Affiliation(s)
- Nicolas Amiez
- Inserm UMR 1093-CAPS, UFR des Sciences du Sport, Institut National de la Santé et de la Recherche Médicale: UMR 1093, Université de Bourgogne, Dijon, France
| | - Alain Martin
- Inserm UMR 1093-CAPS, UFR des Sciences du Sport, Institut National de la Santé et de la Recherche Médicale: UMR 1093, Université de Bourgogne, Dijon, France
| | - Jérémie Gaveau
- Inserm UMR 1093-CAPS, UFR des Sciences du Sport, Institut National de la Santé et de la Recherche Médicale: UMR 1093, Université de Bourgogne, Dijon, France
| | - Sophie Julliand
- Inserm UMR 1093-CAPS, UFR des Sciences du Sport, Institut National de la Santé et de la Recherche Médicale: UMR 1093, Université de Bourgogne, Dijon, France
| | - Charalambos Papaxanthis
- Inserm UMR 1093-CAPS, UFR des Sciences du Sport, Institut National de la Santé et de la Recherche Médicale: UMR 1093, Université de Bourgogne, Dijon, France
| | - Christos Paizis
- Inserm UMR 1093-CAPS, UFR des Sciences du Sport, Institut National de la Santé et de la Recherche Médicale: UMR 1093, Université de Bourgogne, Dijon, France
- Centre d'Expertise de la Performance, UFR des Sciences du Sport, Université de Bourgogne, Dijon, France
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Lapole T, Mesquita RNO, Baudry S, Souron R, Brownstein CG, Rozand V. Can local vibration alter the contribution of persistent inward currents to human motoneuron firing? J Physiol 2023; 601:1467-1482. [PMID: 36852473 DOI: 10.1113/jp284210] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2022] [Accepted: 02/23/2023] [Indexed: 03/01/2023] Open
Abstract
The response of spinal motoneurons to synaptic input greatly depends on the activation of persistent inward currents (PICs), which in turn are enhanced by the neuromodulators serotonin and noradrenaline. Local vibration (LV) induces excitatory Ia input onto motoneurons and may alter neuromodulatory inputs. Therefore, we investigated whether LV influences the contribution of PICs to motoneuron firing. This was assessed in voluntary contractions with concurrent, ongoing LV, as well as after a bout of prolonged LV. High-density surface electromyograms (HD-EMG) of the tibialis anterior were recorded with a 64-electrode matrix. Twenty males performed isometric, triangular, dorsiflexion contractions to 20% and 50% of maximal torque at baseline, during LV of the tibialis anterior muscle, and after 30-min of LV. HD-EMG signals were decomposed, and motor units tracked across time points to estimate PICs through a paired motor unit analysis, which quantifies motor unit recruitment-derecruitment hysteresis (ΔF). During ongoing LV, ΔF was lower for both 20% and 50% ramps. Although significant changes in ΔF were not observed after prolonged LV, a differential effect across the motoneuron pool was observed. This study demonstrates that PICs can be non-pharmacologically modulated by LV. Given that LV leads to reflexive motor unit activation, it is postulated that lower PIC contribution to motoneuron firing during ongoing LV results from decreased neuromodulatory inputs associated with lower descending corticospinal drive. A differential effect in motoneurons of different recruitment thresholds after prolonged LV is provocative, challenging the interpretation of previous observations and motivating future investigations. KEY POINTS: Neuromodulatory inputs from the brainstem influence motoneuron intrinsic excitability through activation of persistent inward currents (PICs). PICs make motoneurons more responsive to excitatory input. We demonstrate that vibration applied on the muscle modulates the contribution of PICs to motoneuron firing, as observed through analysis of the firing of single motor units. The effects of PICs on motoneuron firing were lower when vibration was concurrently applied during voluntary ramp contractions, likely due to lower levels of neuromodulation. Additionally, prolonged exposure to vibration led to differential effects of lower- vs. higher-threshold motor units on PICs, with lower-threshold motor units tending to present an increased and higher-threshold motor units a decreased contribution of PICs to motoneuron firing. These results demonstrate that muscle vibration has the potential to influence the effects of neuromodulation on motoneuron firing. The potential of using vibration as a non-pharmacological neuromodulatory intervention should be further investigated.
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Affiliation(s)
- T Lapole
- Université Jean Monnet Saint-Etienne, Lyon 1, Université Savoie Mont-Blanc, Laboratoire Interuniversitaire de Biologie de la Motricité, Saint-Etienne, France
| | - R N O Mesquita
- Department of Electrical Engineering, Chalmers University of Technology, Gothenburg, Sweden
- School of Medical and Health Sciences, Edith Cowan University, Perth, Australia
- Neuroscience Research Australia, Sydney, Australia
| | - S Baudry
- Laboratory of Applied Biology, Research Unit in Applied Neurophysiology (LABNeuro), Faculty of Motor Sciences, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - R Souron
- Movement-Interactions-Performance, MIP, UR 4334, Nantes Université, 44000 Nantes, France
| | - C G Brownstein
- Université Jean Monnet Saint-Etienne, Lyon 1, Université Savoie Mont-Blanc, Laboratoire Interuniversitaire de Biologie de la Motricité, Saint-Etienne, France
| | - V Rozand
- Université Jean Monnet Saint-Etienne, Lyon 1, Université Savoie Mont-Blanc, Laboratoire Interuniversitaire de Biologie de la Motricité, Saint-Etienne, France
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Amann M, Sidhu SK, McNeil CJ, Gandevia SC. Critical considerations of the contribution of the corticomotoneuronal pathway to central fatigue. J Physiol 2022; 600:5203-5214. [PMID: 36326193 PMCID: PMC9772161 DOI: 10.1113/jp282564] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Accepted: 10/31/2022] [Indexed: 11/06/2022] Open
Abstract
Neural drive originating in higher brain areas reaches exercising limb muscles through the corticospinal-motoneuronal pathway, which links the motor cortex and spinal motoneurones. The properties of this pathway have frequently been observed to change during fatiguing exercise in ways that could influence the development of central fatigue (i.e. the progressive reduction in voluntary muscle activation). However, based on differences in motor cortical and motoneuronal excitability between exercise modalities (e.g. single-joint vs. locomotor exercise), there is no characteristic response that allows for a categorical conclusion about the effect of these changes on functional impairments and performance limitations. Despite the lack of uniformity in findings during fatigue, there is strong evidence for marked 'inhibition' of motoneurones as a direct result of voluntary drive. Endogenous forms of neuromodulation, such as via serotonin released from neurones, can directly affect motoneuronal output and central fatigue. Exogenous forms of neuromodulation, such as brain stimulation, may achieve a similar effect, although the evidence is weak. Non-invasive transcranial direct current stimulation can cause transient or long-lasting changes in cortical excitability; however, variable results across studies cast doubt on its claimed capacity to enhance performance. Furthermore, with these studies, it is difficult to establish a cause-and-effect relationship between brain responsiveness and exercise performance. This review briefly summarizes changes in the corticomotoneuronal pathway during various types of exercise, and considers the relevance of these changes for the development of central fatigue, as well as the potential of non-invasive brain stimulation to enhance motor cortical excitability, motoneuronal output and, ultimately, exercise performance.
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Affiliation(s)
- Markus Amann
- Department of Anesthesiology, University of Utah, Salt Lake City, UT, USA
| | - Simranjit K. Sidhu
- School of Biomedicine, The University of Adelaide, South Australia, Australia
| | - Chris J McNeil
- School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | - Simon C Gandevia
- Neuroscience Research Australia and University of New South Wales, Sydney, Australia
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5
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Kavanagh JJ, Taylor JL. Voluntary activation of muscle in humans: does serotonergic neuromodulation matter? J Physiol 2022; 600:3657-3670. [PMID: 35864781 PMCID: PMC9541597 DOI: 10.1113/jp282565] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Accepted: 07/12/2022] [Indexed: 11/08/2022] Open
Abstract
Ionotropic inputs to motoneurones have the capacity to depolarise and hyperpolarise the motoneurone, whereas neuromodulatory inputs control the state of excitability of the motoneurone. Intracellular recordings of motoneurones from in vitro and in situ animal preparations have provided extraordinary insight into the mechanisms that underpin how neuromodulators regulate neuronal excitability. However, far fewer studies have attempted to translate the findings from cellular and molecular studies into a human model. In this review, we focus on the role that serotonin (5-HT) plays in muscle activation in humans. 5-HT is a potent regulator of neuronal firing rates, which can influence the force that can be generated by muscles during voluntary contractions. We firstly outline structural and functional characteristics of the serotonergic system, and then describe how motoneurone discharge can be facilitated and suppressed depending on the 5-HT receptor subtype that is activated. We then provide a narrative on how 5-HT effects can influence voluntary activation during muscle contractions in humans, and detail how 5-HT may be a mediator of exercise-induced fatigue that arises from the central nervous system.
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Affiliation(s)
- Justin J. Kavanagh
- Neural Control of Movement laboratoryMenzies Health Institute QueenslandGriffith UniversityGold CoastAustralia
| | - Janet L. Taylor
- Centre for Human Performance, School of Medical and Health SciencesEdith Cowan UniversityPerthAustralia
- Neuroscience Research AustraliaSydneyAustralia
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6
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Goodlich BI, Horan SA, Kavanagh JJ. Blockade of 5-HT 2 receptors suppresses rate of torque development and motor unit discharge rate during rapid contractions. J Neurophysiol 2021; 127:150-160. [PMID: 34936830 DOI: 10.1152/jn.00470.2021] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Serotonin (5-HT) is a neuromodulator that is critical for regulating the excitability of spinal motoneurons and the generation of muscle torque. However, the role of 5-HT in modulating human motor unit activity during rapid contractions has yet to be assessed. Nine healthy participants (23.7 ± 2.2 yr) ingested 8 mg of the competitive 5-HT2 antagonist cyproheptadine in a double-blinded, placebo-controlled, repeated-measures experiment. Rapid dorsiflexion contractions were performed at 30%, 50% and 70% of maximal voluntary contraction (MVC), where motor unit activity was assessed by high-density surface electromyographic decomposition. A second protocol was performed where a sustained, fatigue-inducing dorsiflexion contraction was completed prior to undertaking the same 30%, 50% and 70% MVC rapid contractions and motor unit analysis. Motor unit discharge rate (p < 0.001) and rate of torque development (RTD; p = 0.019) for the unfatigued muscle were both significantly lower for the cyproheptadine condition. Following the fatigue inducing contraction, cyproheptadine reduced motor unit discharge rate (p < 0.001) and RTD (p = 0.024), where the effects of cyproheptadine on motor unit discharge rate and RTD increased with increasing contraction intensity. Overall, these results support the viewpoint that serotonergic effects in the central nervous system occur fast enough to regulate motor unit discharge rate during rapid powerful contractions.
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Affiliation(s)
| | - Sean A Horan
- Menzies Health Institute Queensland, Griffith University, Gold Coast, Australia
| | - Justin J Kavanagh
- Menzies Health Institute Queensland, Griffith University, Gold Coast, Australia
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7
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Martinez-Valdes E, Negro F, Falla D, Dideriksen JL, Heckman CJ, Farina D. Inability to increase the neural drive to muscle is associated with task failure during submaximal contractions. J Neurophysiol 2020; 124:1110-1121. [DOI: 10.1152/jn.00447.2020] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Motor unit firing and contractile properties during a submaximal contraction until failure were assessed with a new tracking technique. Two distinct phases in firing behavior were observed, which compensated for changes in twitch area and predicted time to failure. However, the late increase in firing rate was below the rates attained in the absence of fatigue, which points to an inability of the central nervous system to sufficiently increase the neural drive to muscle with fatigue.
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Affiliation(s)
- Eduardo Martinez-Valdes
- Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Francesco Negro
- Department of Clinical and Experimental Sciences, Research Centre for Neuromuscular Function and Adapted Physical Activity “Teresa Camplani,” Università degli Studi di Brescia, Brescia, Italy
| | - Deborah Falla
- Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Jakob Lund Dideriksen
- Center for Sensory-Motor Interaction, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
| | - C. J. Heckman
- Department of Physiology, Northwestern University, Chicago, Illinois
| | - Dario Farina
- Department of Bioengineering, Imperial College London, Royal School of Mines, London, United Kingdom
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8
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Pearcey GEP, Heckman CJ. Serotonin affects our perception of fatigue when performing submaximal efforts - but is it all in our heads? J Physiol 2020; 598:2533-2534. [PMID: 32390162 DOI: 10.1113/jp279883] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- Gregory E P Pearcey
- Physiology, Physical Medicine and Rehabilitation, Physical Therapy and Human Movement Sciences, Shirley Ryan AbilityLab, Northwestern University, Chicago, IL, USA
| | - C J Heckman
- Physiology, Physical Medicine and Rehabilitation, Physical Therapy and Human Movement Sciences, Shirley Ryan AbilityLab, Northwestern University, Chicago, IL, USA
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9
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Thorstensen JR, Taylor JL, Tucker MG, Kavanagh JJ. Enhanced serotonin availability amplifies fatigue perception and modulates the TMS‐induced silent period during sustained low‐intensity elbow flexions. J Physiol 2020; 598:2685-2701. [DOI: 10.1113/jp279347] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Accepted: 03/26/2020] [Indexed: 11/08/2022] Open
Affiliation(s)
| | - Janet L. Taylor
- School of Medical and Health SciencesEdith Cowan University Perth Australia
- Neuroscience Research Australia Sydney Australia
| | - Murray G. Tucker
- Mental HealthDrugs and Alcohol ServiceBarwon HealthUniversity Hospital Geelong Geelong Victoria Australia
| | - Justin J. Kavanagh
- Menzies Health Institute QueenslandGriffith University Gold Coast Australia
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10
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Souron R, Baudry S, Millet GY, Lapole T. Vibration‐induced depression in spinal loop excitability revisited. J Physiol 2019; 597:5179-5193. [DOI: 10.1113/jp278469] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Accepted: 08/14/2019] [Indexed: 01/24/2023] Open
Affiliation(s)
- Robin Souron
- Univ LyonUJM Saint‐EtienneInter‐university Laboratory of Human Movement Biology EA 7424 F‐42023 Saint‐Etienne France
| | - Stéphane Baudry
- Laboratory of Applied BiologyResearch Unit in Applied NeurophysiologyULB Neuroscience InstituteUniversité Libre de Bruxelles Brussels Belgium
| | - Guillaume Y. Millet
- Univ LyonUJM Saint‐EtienneInter‐university Laboratory of Human Movement Biology EA 7424 F‐42023 Saint‐Etienne France
| | - Thomas Lapole
- Univ LyonUJM Saint‐EtienneInter‐university Laboratory of Human Movement Biology EA 7424 F‐42023 Saint‐Etienne France
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11
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Thompson CK, Johnson MD, Negro F, Mcpherson LM, Farina D, Heckman CJ. Exogenous neuromodulation of spinal neurons induces beta-band coherence during self-sustained discharge of hind limb motor unit populations. J Appl Physiol (1985) 2019; 127:1034-1041. [PMID: 31318619 PMCID: PMC6850985 DOI: 10.1152/japplphysiol.00110.2019] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The spontaneous or self-sustained discharge of spinal motoneurons can be observed in both animals and humans. Although the origins of this self-sustained discharge are not fully known, it can be generated by activation of persistent inward currents intrinsic to the motoneuron. If self-sustained discharge is generated exclusively through this intrinsic mechanism, the discharge of individual motor units will be relatively independent of one another. Alternatively, if increased activation of premotor circuits underlies this prolonged discharge of spinal motoneurons, we would expect correlated activity among motoneurons. Our aim is to assess potential synaptic drive by quantifying coherence during self-sustained discharge of spinal motoneurons. Electromyographic activity was collected from 20 decerebrate animals using a 64-channel electrode grid placed on the isolated soleus muscle before and following intrathecal administration of methoxamine, a selective α1-noradrenergic agonist. Sustained muscle activity was recorded and decomposed into the discharge times of ~10-30 concurrently active individual motor units. Consistent with previous reports, the self-sustained discharge of motor units occurred at low mean discharge rates with low-interspike variability. Before methoxamine administration, significant low-frequency coherence (<2 Hz) was observed, while minimal coherence was observed within higher frequency bands. Following intrathecal administration of methoxamine, increases in motor unit discharge rates and strong coherence in both the low-frequency and 15- to 30-Hz beta bands were observed. These data demonstrate beta-band coherence among motor units can be observed through noncortical mechanisms and that neuromodulation of spinal/brainstem neurons greatly influences coherent discharge within spinal motor pools.NEW & NOTEWORTHY The correlated discharge of spinal motoneurons is often used to describe the input to the motor pool. We demonstrate spinal/brainstem neurons devoid of cortical input can generate correlated motor unit discharge in the 15- to 30-Hz beta band, which is amplified through neuromodulation. Activity in the beta band is often ascribed to cortical drive in humans; however, these data demonstrate the capability of the mammalian segmental motor system to generate and modulate this coherent state of motor unit discharge.
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Affiliation(s)
| | | | - Francesco Negro
- 3Department of Clinical and Experimental Sciences, Research Centre for Neuromuscular Function and Adapted Physical Activity “Teresa Camplani,” Università degli Studi di Brescia, Bescia, Italy
| | | | - Dario Farina
- 5Department of Bioengineering, Imperial College London, London, United Kingdom
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Noga BR, Turkson RP, Xie S, Taberner A, Pinzon A, Hentall ID. Monoamine Release in the Cat Lumbar Spinal Cord during Fictive Locomotion Evoked by the Mesencephalic Locomotor Region. Front Neural Circuits 2017; 11:59. [PMID: 28912689 PMCID: PMC5582069 DOI: 10.3389/fncir.2017.00059] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Accepted: 08/09/2017] [Indexed: 01/28/2023] Open
Abstract
Spinal cord neurons active during locomotion are innervated by descending axons that release the monoamines serotonin (5-HT) and norepinephrine (NE) and these neurons express monoaminergic receptor subtypes implicated in the control of locomotion. The timing, level and spinal locations of release of these two substances during centrally-generated locomotor activity should therefore be critical to this control. These variables were measured in real time by fast-cyclic voltammetry in the decerebrate cat's lumbar spinal cord during fictive locomotion, which was evoked by electrical stimulation of the mesencephalic locomotor region (MLR) and registered as integrated activity in bilateral peripheral nerves to hindlimb muscles. Monoamine release was observed in dorsal horn (DH), intermediate zone/ventral horn (IZ/VH) and adjacent white matter (WM) during evoked locomotion. Extracellular peak levels (all sites) increased above baseline by 138 ± 232.5 nM and 35.6 ± 94.4 nM (mean ± SD) for NE and 5-HT, respectively. For both substances, release usually began prior to the onset of locomotion typically earliest in the IZ/VH and peaks were positively correlated with net activity in peripheral nerves. Monoamine levels gradually returned to baseline levels or below at the end of stimulation in most trials. Monoamine oxidase and uptake inhibitors increased the release magnitude, time-to-peak (TTP) and decline-to-baseline. These results demonstrate that spinal monoamine release is modulated on a timescale of seconds, in tandem with centrally-generated locomotion and indicate that MLR-evoked locomotor activity involves concurrent activation of descending monoaminergic and reticulospinal pathways. These gradual changes in space and time of monoamine concentrations high enough to strongly activate various receptors subtypes on locomotor activated neurons further suggest that during MLR-evoked locomotion, monoamine action is, in part, mediated by extrasynaptic neurotransmission in the spinal cord.
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Affiliation(s)
- Brian R Noga
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of MedicineMiami, FL, United States
| | - Riza P Turkson
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of MedicineMiami, FL, United States
| | - Songtao Xie
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of MedicineMiami, FL, United States
| | - Annette Taberner
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of MedicineMiami, FL, United States
| | - Alberto Pinzon
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of MedicineMiami, FL, United States
| | - Ian D Hentall
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of MedicineMiami, FL, United States
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13
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Carroll TJ, Taylor JL, Gandevia SC. Recovery of central and peripheral neuromuscular fatigue after exercise. J Appl Physiol (1985) 2017; 122:1068-1076. [DOI: 10.1152/japplphysiol.00775.2016] [Citation(s) in RCA: 117] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Revised: 12/02/2016] [Accepted: 12/02/2016] [Indexed: 12/29/2022] Open
Abstract
Sustained physical exercise leads to a reduced capacity to produce voluntary force that typically outlasts the exercise bout. This “fatigue” can be due both to impaired muscle function, termed “peripheral fatigue,” and a reduction in the capacity of the central nervous system to activate muscles, termed “central fatigue.” In this review we consider the factors that determine the recovery of voluntary force generating capacity after various types of exercise. After brief, high-intensity exercise there is typically a rapid restitution of force that is due to recovery of central fatigue (typically within 2 min) and aspects of peripheral fatigue associated with excitation-contraction coupling and reperfusion of muscles (typically within 3–5 min). Complete recovery of muscle function may be incomplete for some hours, however, due to prolonged impairment in intracellular Ca2+ release or sensitivity. After low-intensity exercise of long duration, voluntary force typically shows rapid, partial, recovery within the first few minutes, due largely to recovery of the central, neural component. However, the ability to voluntarily activate muscles may not recover completely within 30 min after exercise. Recovery of peripheral fatigue contributes comparatively little to the fast initial force restitution and is typically incomplete for at least 20–30 min. Work remains to identify what factors underlie the prolonged central fatigue that usually accompanies long-duration single joint and locomotor exercise and to document how the time course of neuromuscular recovery is affected by exercise intensity and duration in locomotor exercise. Such information could be useful to enhance rehabilitation and sports performance.
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Affiliation(s)
- T. J. Carroll
- Centre for Sensorimotor Performance, School of Human Movement and Nutrition Sciences, University of Queensland; and
| | - J. L. Taylor
- Neuroscience Research Australia and University of New South Wales
| | - S. C. Gandevia
- Neuroscience Research Australia and University of New South Wales
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Taylor JL, Amann M, Duchateau J, Meeusen R, Rice CL. Neural Contributions to Muscle Fatigue: From the Brain to the Muscle and Back Again. Med Sci Sports Exerc 2016; 48:2294-2306. [PMID: 27003703 PMCID: PMC5033663 DOI: 10.1249/mss.0000000000000923] [Citation(s) in RCA: 295] [Impact Index Per Article: 36.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
: During exercise, there is a progressive reduction in the ability to produce muscle force. Processes within the nervous system as well as within the muscles contribute to this fatigue. In addition to impaired function of the motor system, sensations associated with fatigue and impairment of homeostasis can contribute to the impairment of performance during exercise. This review discusses some of the neural changes that accompany exercise and the development of fatigue. The role of brain monoaminergic neurotransmitter systems in whole-body endurance performance is discussed, particularly with regard to exercise in hot environments. Next, fatigue-related alterations in the neuromuscular pathway are discussed in terms of changes in motor unit firing, motoneuron excitability, and motor cortical excitability. These changes have mostly been investigated during single-limb isometric contractions. Finally, the small-diameter muscle afferents that increase firing with exercise and fatigue are discussed. These afferents have roles in cardiovascular and respiratory responses to exercise, and in the impairment of exercise performance through interaction with the motor pathway, as well as in providing sensations of muscle discomfort. Thus, changes at all levels of the nervous system, including the brain, spinal cord, motor output, sensory input, and autonomic function, occur during exercise and fatigue. The mix of influences and the importance of their contribution vary with the type of exercise being performed.
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Affiliation(s)
- Janet L Taylor
- 1Neuroscience Research Australia, Sydney, AUSTRALIA; 2School of Medical Sciences, the University of New South Wales, Sydney, AUSTRALIA; 3Department of Medicine, University of Utah, Salt Lake City, UT; 4Laboratory of Applied Biology and Neurophysiology, ULB Neuroscience Institute, Université Libre de Bruxelles, Brussels, BELGIUM; 5Human Physiology Research Group Vrije Universiteit Brussel, Brussels, BELGIUM; 6School of Public Health, Tropical Medicine and Rehabilitation Sciences, James Cook University, Queensland, AUSTRALIA; and 7School of Kinesiology, and Department of Anatomy and Cell Biology, The University of Western Ontario, London, CANADA
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15
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Lyamin OI, Lapierre JL, Kosenko PO, Kodama T, Bhagwandin A, Korneva SM, Peever JH, Mukhametov LM, Siegel JM. Monoamine Release during Unihemispheric Sleep and Unihemispheric Waking in the Fur Seal. Sleep 2016; 39:625-36. [PMID: 26715233 PMCID: PMC4763370 DOI: 10.5665/sleep.5540] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 10/31/2015] [Indexed: 11/03/2022] Open
Abstract
STUDY OBJECTIVES Our understanding of the role of neurotransmitters in the control of the electroencephalogram (EEG) has been entirely based on studies of animals with bilateral sleep. The study of animals with unihemispheric sleep presents the opportunity of separating the neurochemical substrates of waking and sleep EEG from the systemic, bilateral correlates of sleep and waking states. METHODS The release of histamine (HI), norepinephrine (NE), and serotonin (5HT) in cortical and subcortical areas (hypothalamus, thalamus and caudate nucleus) was measured in unrestrained northern fur seals (Callorhinus ursinus) using in vivo microdialysis, in combination with, polygraphic recording of EEG, electrooculogram, and neck electromyogram. RESULTS The pattern of cortical and subcortical HI, NE, and 5HT release in fur seals is similar during bilaterally symmetrical states: highest in active waking, reduced in quiet waking and bilateral slow wave sleep, and lowest in rapid eye movement (REM) sleep. Cortical and subcortical HI, NE, and 5HT release in seals is highly elevated during certain waking stimuli and behaviors, such as being sprayed with water and feeding. However, in contrast to acetylcholine (ACh), which we have previously studied, the release of HI, NE, and 5HT during unihemispheric sleep is not lateralized in the fur seal. CONCLUSIONS Among the studied neurotransmitters most strongly implicated in waking control, only ACh release is asymmetric in unihemispheric sleep and waking, being greatly increased on the activated side of the brain. COMMENTARY A commentary on this article appears in this issue on page 491.
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Affiliation(s)
- Oleg I. Lyamin
- Department of Psychiatry and Biobehavioral Sciences, and Brain Research Institute, University of California Los Angeles, Los Angeles, CA
- Severtsov Institute of Ecology and Evolution, RAS, Moscow, Russia
- Utrish Dolphinarium Ltd., Moscow, Russia
| | - Jennifer L. Lapierre
- Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada
| | - Peter O. Kosenko
- Utrish Dolphinarium Ltd., Moscow, Russia
- Southern Federal University, Rostov-on-Don, Russia
| | - Tohru Kodama
- Department of Dementia and Higher Brain Function, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Adhil Bhagwandin
- School of Anatomical Sciences, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | | | - John H. Peever
- Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada
| | - Lev M. Mukhametov
- Severtsov Institute of Ecology and Evolution, RAS, Moscow, Russia
- Utrish Dolphinarium Ltd., Moscow, Russia
| | - Jerome M. Siegel
- Department of Psychiatry and Biobehavioral Sciences, and Brain Research Institute, University of California Los Angeles, Los Angeles, CA
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Changes of 5-hydroxytryptamine and tryptophan hydroxylase expression in the ventral horn of spinal cord. Neurosci Bull 2014; 24:29-33. [PMID: 18273073 DOI: 10.1007/s12264-008-1031-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
OBJECTIVE To investigate changes of 5-hydroxytryptamine (5-HT) and its synthesis rate-limiting enzyme tryptophan hydroxylase (TPH) in the ventral horn of spinal cord after exercise-induced fatigue, and to further discuss the mechanism of exercise-induced central fatigue at spinal level. METHODS Sixteen healthy adult Wistar rats were randomly divided into 2 groups: exercise-induced fatigue group and control group. Immunohistochemical staining for 5-HT and TPH in the ventral horn were performed and analyzed quantitatively. The mean optic densities of 5-HT and TPH positive fibers or terminals were measured by computerized image analyzer. RESULTS Both 5-HT and TPH positive fibers/terminals decreased in the exercise-induced fatigue group. The immunohistochemical staining was weaker and the mean optic densities decreased obviously in the fatigue group compared with those in the control group (P< 0.05). CONCLUSION 5-HT and TPH in the ventral horn of spinal cord might be involved in exercise-induced fatigue.
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Foley TE, Brooks LR, Gilligan LJ, Burghardt PR, Koch LG, Britton SL, Fleshner M. Brain activation patterns at exhaustion in rats that differ in inherent exercise capacity. PLoS One 2012; 7:e45415. [PMID: 23028992 PMCID: PMC3444461 DOI: 10.1371/journal.pone.0045415] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Accepted: 08/22/2012] [Indexed: 11/18/2022] Open
Abstract
In order to further understand the genetic basis for variation in inherent (untrained) exercise capacity, we examined the brains of 32 male rats selectively bred for high or low running capacity (HCR and LCR, respectively). The aim was to characterize the activation patterns of brain regions potentially involved in differences in inherent running capacity between HCR and LCR. Using quantitative in situ hybridization techniques, we measured messenger ribonuclease (mRNA) levels of c-Fos, a marker of neuronal activation, in the brains of HCR and LCR rats after a single bout of acute treadmill running (7.5-15 minutes, 15° slope, 10 m/min) or after treadmill running to exhaustion (15-51 minutes, 15° slope, initial velocity 10 m/min). During verification of trait differences, HCR rats ran six times farther and three times longer prior to exhaustion than LCR rats. Running to exhaustion significantly increased c-Fos mRNA activation of several brain areas in HCR, but LCR failed to show significant elevations of c-Fos mRNA at exhaustion in the majority of areas examined compared to acutely run controls. Results from these studies suggest that there are differences in central c-Fos mRNA expression, and potential brain activation patterns, between HCR and LCR rats during treadmill running to exhaustion and these differences could be involved in the variation in inherent running capacity between lines.
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Affiliation(s)
- Teresa E. Foley
- Department of Integrative Physiology and The Center for Neuroscience, University of Colorado, Boulder, Colorado, United States of America
| | - Leah R. Brooks
- Department of Integrative Physiology and The Center for Neuroscience, University of Colorado, Boulder, Colorado, United States of America
| | - Lori J. Gilligan
- Department of Anesthesiology, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Paul R. Burghardt
- Department of Psychiatry and the Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Lauren G. Koch
- Department of Anesthesiology, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Steven L. Britton
- Department of Anesthesiology, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Monika Fleshner
- Department of Integrative Physiology and The Center for Neuroscience, University of Colorado, Boulder, Colorado, United States of America
- * E-mail:
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18
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Sluka KA, Danielson J, Rasmussen L, DaSilva LF. Exercise-induced pain requires NMDA receptor activation in the medullary raphe nuclei. Med Sci Sports Exerc 2012; 44:420-7. [PMID: 21795998 DOI: 10.1249/mss.0b013e31822f490e] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
PURPOSE Pain in response to physical activity is common in people with chronic musculoskeletal pain and is likely a barrier to regular exercise, which would lead to a sedentary lifestyle. We recently developed a model of exercise-induced pain that is associated with increased activation of neurons in the medullary raphe nuclei, i.e., the nucleus raphe obscurus (NRO) and nucleus raphe pallidus (NRP). Because the NRO and NRP not only modulate motor output but also respond to noxious stimuli, we hypothesized that the NRO and NRP were key nuclei in the interaction between pain and exercise. We tested whether exercise enhances hyperalgesia through activation of N-methyl D-aspartate (NMDA) receptors in the NRO/NRP. METHODS Muscle insult was induced by two injections of pH 5.0 saline 5 d apart into one gastrocnemius muscle. We initially tested whether hyperalgesia developed in mice injected with acidic saline (pH 5.0) into the gastrocnemius muscle immediately after a 30-min or 2-h exercise task or 2 h after a 2-h exercise task. Next, we tested whether blockade of NMDA receptors in the NRO/NRP during the exercise task prevented the development of exercise-induced hyperalgesia. Finally, we evaluated changes in phosphorylation of the NR1 subunit of the NMDA receptor (pNR1) after the exercise task at times in which muscle insult was given in behavioral experiments, i.e., immediately after a 30-min or 2-h exercise task or 2 h after the 2-h exercise task. RESULTS All exercise conditions enhanced nociception (hyperalgesia) after combining with two injections of pH 5.0 saline. Microinjection of AP5 (1.0-0.1 nmol; 2-amino-5-phophonopenanoate) dose-dependently prevented the development of exercise-induced hyperalgesia. All exercise conditions increased pNR1 in the NRO and NRP. CONCLUSIONS Thus, exercise-induced pain in sedentary mice is associated with increased phosphorylation and activation of NMDA receptors in the NRO/NRP, suggesting that changes in central excitability mediate an interaction between unaccustomed exercise and pain.
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Affiliation(s)
- Kathleen A Sluka
- Physical Therapy and Rehabilitation Science Graduate Program, The University of Iowa, Iowa City, IA 52242-1190, USA.
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Activity of Brain Serotonergic Neurons in Relation to Physiology and Behavior. ACTA ACUST UNITED AC 2010. [DOI: 10.1016/s1569-7339(10)70076-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Korb A, Bonetti LV, da Silva SA, Marcuzzo S, Ilha J, Bertagnolli M, Partata WA, Faccioni-Heuser MC. Effect of treadmill exercise on serotonin immunoreactivity in medullary raphe nuclei and spinal cord following sciatic nerve transection in rats. Neurochem Res 2009; 35:380-9. [PMID: 19774460 DOI: 10.1007/s11064-009-0066-x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/12/2009] [Indexed: 10/20/2022]
Abstract
The serotoninergic system modulates nociceptive and locomotor spinal cord circuits. Exercise improves motor function and changes dopaminergic, noradrenergic, and serotonergic central systems. However, the direct relationship between serotonin, peripheral nerve lesion and aerobic treadmill exercise has not been studied. Using immunohistochemistry and optic densitometry, this study showed that the sciatic nerve transection increased the serotoninergic immunoreactivity in neuronal cytoplasm of the magnus raphe nuclei of trained and sedentary rats. In the dorsal raphe nucleus the increase only occurred in sedentary-sham-operated rats. In the spinal cord of trained, transected rats, the ventral horn showed significant changes, while the change in dorsal horn was insignificant. Von Frey's test indicated analgesia in all exercise-trained rats. The sciatic nerve functional index indicated recovery in the trained group. Thus, both the aerobic treadmill exercise training and the nervous lesion appear to contribute to changes in serotonin immunoreactivity.
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Affiliation(s)
- Arthiese Korb
- Programa de Pós-Graduação em Neurociências, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil
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22
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Sluka KA, Rasmussen LA. Fatiguing exercise enhances hyperalgesia to muscle inflammation. Pain 2009; 148:188-197. [PMID: 19632780 DOI: 10.1016/j.pain.2009.07.001] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2009] [Revised: 06/09/2009] [Accepted: 07/02/2009] [Indexed: 12/20/2022]
Abstract
Since many people with chronic fatigue present with pain and many people with chronic pain present with fatigue, we tested if fatigue would enhance the response to pain in male and female mice. We further tested for the activation of brainstem nuclei by the fatigue task using c-fos as a marker. Fatigue was induced by having mice spontaneously run in running wheel for 2h. Carrageenan (0.03%) was injected into the gastrocnemius muscle either 2h before or 2h after the fatigue task. The mechanical sensitivity of the paw (von Frey filaments), muscle (tweezers), grip force and running wheel activity was assessed before and 24h after injection of carrageenan. Both male and female mice that performed the fatigue task, either before or after intramuscular injection of carrageenan, showed an enhanced mechanical sensitivity of the paw, but not the muscle. Ovariectomized mice showed a similar response to male mice. There was a decrease in running wheel activity after carrageenan injection, but no change in grip force suggesting that mice had no deficit in motor performance induced by the carrageenan. C-fos expression was observed in the nucleus raphe pallidus, obscurus, and magnus after the fatigue task suggesting an increased activity in the raphe nuclei in response to the fatigue task. Therefore, widespread hyperalgesia is enhanced by the fatigue response but not hyperalgesia at the site of insult. We suggest that this effect is sex-dependent and involves mechanisms in the brainstem to result in an enhanced hyperalgesia.
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Affiliation(s)
- Kathleen A Sluka
- Physical Therapy and Rehabilitation Science Graduate Program, Pain Research Program, University of Iowa, #1-252 MEB, Iowa City, IA 52241, USA
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23
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Shevchuk NA. Possible use of repeated cold stress for reducing fatigue in chronic fatigue syndrome: a hypothesis. Behav Brain Funct 2007; 3:55. [PMID: 17958903 PMCID: PMC2164952 DOI: 10.1186/1744-9081-3-55] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2007] [Accepted: 10/24/2007] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Physiological fatigue can be defined as a reduction in the force output and/or energy-generating capacity of skeletal muscle after exertion, which may manifest itself as an inability to continue exercise or usual activities at the same intensity. A typical example of a fatigue-related disorder is chronic fatigue syndrome (CFS), a disabling condition of unknown etiology and with uncertain therapeutic options. Recent advances in elucidating pathophysiology of this disorder revealed hypofunction of the hypothalamic-pituitary-adrenal axis and that fatigue in CFS patients appears to be associated with reduced motor neurotransmission in the central nervous system (CNS) and to a smaller extent with increased fatigability of skeletal muscle. There is also some limited evidence that CFS patients may have excessive serotonergic activity in the brain and low opioid tone. PRESENTATION OF THE HYPOTHESIS This work hypothesizes that repeated cold stress may reduce fatigue in CFS because brief exposure to cold may transiently reverse some physiological changes associated with this illness. For example, exposure to cold can activate components of the reticular activating system such as raphe nuclei and locus ceruleus, which can result in activation of behavior and increased capacity of the CNS to recruit motoneurons. Cold stress has also been shown to reduce the level of serotonin in most regions of the brain (except brainstem), which would be consistent with reduced fatigue according to animal models of exercise-related fatigue. Finally, exposure to cold increases metabolic rate and transiently activates the hypothalamic-pituitary-adrenal axis as evidenced by a temporary increase in the plasma levels of adrenocorticotropic hormone, beta-endorphin and a modest increase in cortisol. The increased opioid tone and high metabolic rate could diminish fatigue by reducing muscle pain and accelerating recovery of fatigued muscle, respectively. TESTING THE HYPOTHESIS To test the hypothesis, a treatment is proposed that consists of adapted cold showers (20 degrees Celsius, 3 minutes, preceded by a 5-minute gradual adaptation to make the procedure more comfortable) used twice daily. IMPLICATIONS OF THE HYPOTHESIS If testing supports the proposed hypothesis, this could advance our understanding of the mechanisms of fatigue in CFS.
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Affiliation(s)
- Nikolai A Shevchuk
- Molecular Radiobiology Section, the Department of Radiation Oncology, Virginia Commonwealth University School of Medicine, 401 College St, Richmond, VA 23298, USA.
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Benarroch EE, Schmeichel AM, Sandroni P, Parisi JE, Low PA. Rostral raphe involvement in Lewy body dementia and multiple system atrophy. Acta Neuropathol 2007; 114:213-20. [PMID: 17639427 DOI: 10.1007/s00401-007-0260-3] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2007] [Revised: 06/05/2007] [Accepted: 06/21/2007] [Indexed: 11/26/2022]
Abstract
Depression is a feature of both Lewy body disorders and multiple system atrophy (MSA). Since serotonergic neurons of the rostral raphe have been implicated in depression, we sought to determine whether there is a differential involvement of these neurons in cases with clinically diagnosed dementia with Lewy bodies (DLB) or MSA. We studied the brainstem obtained at autopsy from fourteen patients with diagnosis of DLB and pathological limbic or neocortical stage Lewy body disease, 13 patients with clinical and neuropathological diagnosis of MSA, and 12 controls with no history of neurologic disease. The clinical features of these patients were analyzed retrospectively by reviewing their medical records. Serial sections were immunostained for tryptophan hydroxylase (TrOH) and alpha-synuclein and cell counts were performed in the dorsal raphe (DR), median raphe (MR) and medullary raphe nuclei. There was loss of serotonergic cells in both the DR and MR in DLB compared to control cases: For the DR, the number of cells/section were 53 +/- 6 in DLB versus 159 +/- 13 (P < 0.001) respectively, and for the MR 70 +/- 11 in DLB versus 173 +/- 23 (P < 0.001) respectively. In contrast, these cells were relatively preserved in MSA. The caudal raphe groups were affected both in MSA and in DLB. There is a differential involvement of raphe neurons in DLB and MSA. Although loss of rostral raphe neurons may contribute to depression in DLB, this appears to be less likely in MSA. Factors other than the neurochemical phenotype determine neuronal vulnerability in MSA.
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Affiliation(s)
- E E Benarroch
- Department of Neurology, Mayo Clinic, 811 Guggenheim Building, 200 First Street SW, Rochester, MN 55905, USA.
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Windhorst U. Muscle proprioceptive feedback and spinal networks. Brain Res Bull 2007; 73:155-202. [PMID: 17562384 DOI: 10.1016/j.brainresbull.2007.03.010] [Citation(s) in RCA: 197] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2007] [Accepted: 03/15/2007] [Indexed: 12/19/2022]
Abstract
This review revolves primarily around segmental feedback systems established by muscle spindle and Golgi tendon organ afferents, as well as spinal recurrent inhibition via Renshaw cells. These networks are considered as to their potential contributions to the following functions: (i) generation of anti-gravity thrust during quiet upright stance and the stance phase of locomotion; (ii) timing of locomotor phases; (iii) linearization and correction for muscle nonlinearities; (iv) compensation for muscle lever-arm variations; (v) stabilization of inherently unstable systems; (vi) compensation for muscle fatigue; (vii) synergy formation; (viii) selection of appropriate responses to perturbations; (ix) correction for intersegmental interaction forces; (x) sensory-motor transformations; (xi) plasticity and motor learning. The scope will at times extend beyond the narrow confines of spinal circuits in order to integrate them into wider contexts and concepts.
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Affiliation(s)
- U Windhorst
- Center for Physiology and Pathophysiology, University of Goettingen, Humboldtallee 23, D-37073 Goettingen, Germany.
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Nordstrom MA, Gorman RB, Laouris Y, Spielmann JM, Stuart DG. Does motoneuron adaptation contribute to muscle fatigue? Muscle Nerve 2007; 35:135-58. [PMID: 17195169 DOI: 10.1002/mus.20712] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
To help reduce the gap between the cellular physiology of motoneurons (MNs) as studied "bottom-up" in animal preparations and the "top-down" study of the firing patterns of human motor units (MUs), this article addresses the question of whether motoneuron adaptation contributes to muscle fatigue. Findings are reviewed on the intracellularly recorded electrophysiology of spinal MNs as studied in vivo and in vitro using animal preparations, and the extracellularly recorded discharge of MUs as studied in conscious humans. The latter "top-down" approach, combined with kinetic measurements, has provided most of what is currently known about the neurobiology of muscle fatigue, including its task and context dependencies. It is argued that although the question addressed is still open, it should now be possible to design new "bottom-up" research paradigms using animal preparations that take advantage of what has been learned with the use of relatively noninvasive quantitative procedures in conscious humans.
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Affiliation(s)
- Michael A Nordstrom
- Discipline of Physiology, School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia, Australia
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27
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Kerman IA, Shabrang C, Taylor L, Akil H, Watson SJ. Relationship of presympathetic-premotor neurons to the serotonergic transmitter system in the rat brainstem. J Comp Neurol 2007; 499:882-96. [PMID: 17072838 DOI: 10.1002/cne.21129] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Numerous physiological conditions and emotionally motivated behaviors require concomitant activation of somatomotor and sympathetic efferents. Using a virally mediated retrograde transsynaptic tract-tracing approach, we have previously determined locations of presympathetic-premotor neurons (PSPMNs) in the rat brainstem. These putative dual-function neurons send projections to somatomotor and sympathetic targets and likely participate in sympatho-somatomotor integration. A significant portion of these neurons is found within brainstem areas known to contain serotonergic neurons. Thus, we hypothesized that some of the PSPMNs utilize serotonin as their neurotransmitter. To test this hypothesis we first produced an antibody against TPH2, a brain-specific isoform of tryptophan hydroxylase (serotonin synthetic enzyme). We identified PSPMNs by using recombinant strains of the pseudorabies virus (PRV) for transsynaptic tract-tracing. PRV-152, a strain that expresses enhanced green fluorescent protein, was injected into sympathectomized gastrocnemius muscle, while PRV-BaBlu, which expresses beta-galactosidase, was injected into the adrenal gland in the same animals. Using immunofluorescent methods we determined whether coinfected neurons expressed TPH2. Our findings demonstrate that TPH2-positive PSPMNs are present at different rostrocaudal levels of the brainstem. Just over half of them are found at the pontomedullary junction within raphe obscurus, raphe magnus, and gigantocellular nucleus pars alpha. These cells may play a role in mediating responses to acute pain stimuli and/or participate in the central control of exercise. Overactivity of these serotonergic sympatho-somatomotor circuits may also play a role in the pathophysiology of serotonin syndrome.
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Affiliation(s)
- Ilan A Kerman
- Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, Michigan 48109, USA.
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