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Özyurt MG, Nascimento F, Brownstone RM, Beato M. On the origin of F-wave: involvement of central synaptic mechanisms. Brain 2024; 147:406-413. [PMID: 37796028 PMCID: PMC10834253 DOI: 10.1093/brain/awad342] [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: 06/16/2023] [Revised: 09/21/2023] [Accepted: 09/27/2023] [Indexed: 10/06/2023] Open
Abstract
Neurophysiological methods are used widely to gain information about motor neuron excitability and axon conduction in neurodegenerative diseases. The F-wave is a common biomarker used to test motor neuron properties in the diagnosis of neurological diseases. Although the origin of the F-wave is a subject of debate, the most widely accepted mechanism posits that the F-wave is generated by the backfiring of motor neurons stimulated antidromically from the periphery. In this study, we developed an ex vivo mouse sciatic nerve-attached spinal cord preparation with sensory axons severed. In this preparation, stimulation of the whole sciatic nerve or its tibial branch evoked responses with the electrophysiological signatures of F-waves. Manipulations of synaptic transmission by either removal of extracellular calcium or block of post-synaptic glutamate receptors abolished these responses. These results suggest that F-waves are mediated by spinal microcircuits activated by recurrent motor axon collaterals via glutamatergic synapses.
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Affiliation(s)
- M Görkem Özyurt
- Department of Neuroscience Physiology and Pharmacology (NPP), University College London, London WC1E 6BT, UK
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Filipe Nascimento
- Department of Neuroscience Physiology and Pharmacology (NPP), University College London, London WC1E 6BT, UK
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Robert M Brownstone
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Marco Beato
- Department of Neuroscience Physiology and Pharmacology (NPP), University College London, London WC1E 6BT, UK
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2
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Schmid L, Klotz T, Röhrle O, Powers RK, Negro F, Yavuz UŞ. Postinhibitory excitation in motoneurons can be facilitated by hyperpolarization-activated inward currents: A simulation study. PLoS Comput Biol 2024; 20:e1011487. [PMID: 38241412 PMCID: PMC10843122 DOI: 10.1371/journal.pcbi.1011487] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 02/05/2024] [Accepted: 01/09/2024] [Indexed: 01/21/2024] Open
Abstract
Postinhibitory excitation is a transient overshoot of a neuron's baseline firing rate following an inhibitory stimulus and can be observed in vivo in human motoneurons. However, the biophysical origin of this phenomenon is still unknown and both reflex pathways and intrinsic motoneuron properties have been proposed. We hypothesized that postinhibitory excitation in motoneurons can be facilitated by hyperpolarization-activated inward currents (h-currents). Using an electrical circuit model, we investigated how h-currents can modulate the postinhibitory response of motoneurons. Further, we analyzed the spike trains of human motor units from the tibialis anterior muscle during reciprocal inhibition. The simulations revealed that the activation of h-currents by an inhibitory postsynaptic potential can cause a short-term increase in a motoneuron's firing probability. This result suggests that the neuron can be excited by an inhibitory stimulus. In detail, the modulation of the firing probability depends on the time delay between the inhibitory stimulus and the previous action potential. Further, the postinhibitory excitation's strength correlates with the inhibitory stimulus's amplitude and is negatively correlated with the baseline firing rate as well as the level of input noise. Hallmarks of h-current activity, as identified from the modeling study, were found in 50% of the human motor units that showed postinhibitory excitation. This study suggests that h-currents can facilitate postinhibitory excitation and act as a modulatory system to increase motoneuron excitability after a strong inhibition.
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Affiliation(s)
- Laura Schmid
- Institute for Modelling and Simulation of Biomechanical Systems, University of Stuttgart, Stuttgart, Germany
| | - Thomas Klotz
- Institute for Modelling and Simulation of Biomechanical Systems, University of Stuttgart, Stuttgart, Germany
| | - Oliver Röhrle
- Institute for Modelling and Simulation of Biomechanical Systems, University of Stuttgart, Stuttgart, Germany
- Stuttgart Center for Simulation Sciences (SC SimTech), University of Stuttgart, Stuttgart, Germany
| | - Randall K. Powers
- Department of Physiology and Biophysics, University of Washington, Seattle, Washington, United States of America
| | - Francesco Negro
- Department of Clinical and Experimental Sciences, Università degli Studi di Brescia, Brescia, Italy
| | - Utku Ş. Yavuz
- Department of Biomedical Signals and Systems, Faculty of Electrical Engineering, Mathematics and Computer Sciences, University of Twente, Enschede, Netherlands
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3
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Arslan BT, Görkem Özyurt M, İşak B, Cecen S, Türker KS. Single motor unit estimation of the cutaneous silent period in ALS. Clin Neurophysiol 2024; 157:110-119. [PMID: 38096766 DOI: 10.1016/j.clinph.2023.11.013] [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: 07/10/2023] [Revised: 11/08/2023] [Accepted: 11/16/2023] [Indexed: 01/13/2024]
Abstract
OBJECTIVE Recent evidence indicated that amyotrophic lateral sclerosis (ALS) also impairs spinal circuits, including those mediating cutaneous silent period (CSP). However, most studies utilised surface electromyography (sEMG), which needs more resolution to pinpoint changes at the single motoneuron level. We aimed to investigate CSP properties using single motor unit discharges in ALS. METHODS In mild and severe ALS patients and controls, CSP was recorded in the first dorsal interosseus and analysed using the discharge rate method, which accurately shows the inhibitory postsynaptic potentials (IPSPs) profile. RESULTS Our findings confirmed that the CSP latency was prolonged only in severe ALS patients. Moreover, the CSP duration was similar in each group, but late-stage ALS patients tend to have a longer CSP duration. The discharge rate method revealed a significantly longer duration (up to 150 ms) than the duration detected using sEMG. Strikingly, the motoneuron discharge rate - IPSP duration inverse relationship is lost in ALS patients, indicating a possible impairment in the motoneuron integrative properties. CONCLUSIONS Our data support previous findings of prolonged latency, presented input-output modifications of motoneurons, and revealed the entire course of the CSP, representing a much stronger inhibitory event than previously thought. SIGNIFICANCE Motoneuron integrative property modification assessed by CSP could be a new biomarker for ALS.
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Affiliation(s)
| | - M Görkem Özyurt
- Department of Neuromuscular Diseases, Queen Square Institute of Neurology, University College London, London, United Kingdom
| | - Barış İşak
- Marmara University Pendik Training and Research Hospital, Istanbul, Turkey
| | - Serpil Cecen
- Health Science University, Hamidiye Medical Faculty, Istanbul, Turkey
| | - Kemal S Türker
- Istanbul Gelisim University, Faculty of Dentistry, Physiology, Istanbul, Turkey.
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4
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Orssatto LBR, Blazevich AJ, Trajano GS. Ageing reduces persistent inward current contribution to motor neurone firing: Potential mechanisms and the role of exercise. J Physiol 2023; 601:3705-3716. [PMID: 37488952 DOI: 10.1113/jp284603] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2023] [Accepted: 06/26/2023] [Indexed: 07/26/2023] Open
Abstract
Nervous system deterioration is a primary driver of age-related motor impairment. The motor neurones, which act as the interface between the central nervous system and the muscles, play a crucial role in amplifying excitatory synaptic input to produce the desired motor neuronal firing output. For this, they utilise their ability to generate persistent (long-lasting) depolarising currents that increase cell excitability, and both amplify and prolong the output activity of motor neurones for a given synaptic input. Modulation of these persistent inward currents (PICs) contributes to the motor neurones' capacities to attain the required firing frequencies and rapidly modulate them to competently complete most tasks. Thus, PICs are crucial for adequate movement generation. Impairments in intrinsic motor neurone properties can impact motor unit firing capacity, with convincing evidence indicating that the PIC contribution to motor neurone firing is reduced in older adults. Indeed, this could be an important mechanism underpinning the age-related reductions in strength and physical function. Furthermore, resistance training has emerged as a promising intervention to counteract age-associated PIC impairments, with changes in PICs being correlated with improvements in muscular strength and physical function after training. In this review, we present the current knowledge of the PIC magnitude decline during ageing and discuss whether reduced serotonergic and noradrenergic input onto the motor neurones, voltage-gated calcium channel dysfunction or inhibitory input impairments are candidates that: (i) explain age-related reductions in the PIC contribution to motor neurone firing and (ii) underpin the enhanced PIC contribution to motor neurone firing following resistance training in older adults.
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Affiliation(s)
- Lucas B R Orssatto
- Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences, Faculty of Health, Deakin University, Geelong, VIC, Australia
| | - Anthony J Blazevich
- School of Medical and Health Sciences, Centre for Human Performance, Edith Cowan University, Joondalup, WA, Australia
| | - Gabriel S Trajano
- School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology (QUT), Brisbane, QLD, Australia
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5
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Tan S, Faull RLM, Curtis MA. The tracts, cytoarchitecture, and neurochemistry of the spinal cord. Anat Rec (Hoboken) 2023; 306:777-819. [PMID: 36099279 DOI: 10.1002/ar.25079] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 08/01/2022] [Accepted: 09/11/2022] [Indexed: 11/06/2022]
Abstract
The human spinal cord can be described using a range of nomenclatures with each providing insight into its structure and function. Here we have comprehensively reviewed the key literature detailing the general structure, configuration of tracts, the cytoarchitecture of Rexed's laminae, and the neurochemistry at the spinal segmental level. The purpose of this review is to detail current anatomical understanding of how the spinal cord is structured and to aid researchers in identifying gaps in the literature that need to be studied to improve our knowledge of the spinal cord which in turn will improve the potential of therapeutic intervention for disorders of the spinal cord.
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Affiliation(s)
- Sheryl Tan
- Centre for Brain Research and Department of Anatomy and Medical Imaging, University of Auckland, Auckland, New Zealand
| | - Richard L M Faull
- Centre for Brain Research and Department of Anatomy and Medical Imaging, University of Auckland, Auckland, New Zealand
| | - Maurice A Curtis
- Centre for Brain Research and Department of Anatomy and Medical Imaging, University of Auckland, Auckland, New Zealand
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6
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Muceli S, Poppendieck W, Holobar A, Gandevia S, Liebetanz D, Farina D. Blind identification of the spinal cord output in humans with high-density electrode arrays implanted in muscles. SCIENCE ADVANCES 2022; 8:eabo5040. [PMID: 36383647 PMCID: PMC9668292 DOI: 10.1126/sciadv.abo5040] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Accepted: 10/20/2022] [Indexed: 06/16/2023]
Abstract
Invasive electromyography opened a new window to explore motoneuron behavior in vivo. However, the technique is limited by the small fraction of active motoneurons that can be concurrently detected, precluding a population analysis in natural tasks. Here, we developed a high-density intramuscular electrode for in vivo human recordings along with a fully automatic methodology that could detect the discharges of action potentials of up to 67 concurrently active motoneurons with 99% accuracy. These data revealed that motoneurons of the same pool receive common synaptic input at frequencies up to 75 Hz and that late-recruited motoneurons inhibit the discharges of those recruited earlier. These results constitute an important step in the population coding analysis of the human motor system in vivo.
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Affiliation(s)
- Silvia Muceli
- Department of Electrical Engineering, Chalmers University of Technology, Gothenburg, Sweden
| | | | - Aleš Holobar
- Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, Slovenia
| | - Simon Gandevia
- Neuroscience Research Australia and University of New South Wales, Randwick, Sydney, New South Wales, Australia
| | - David Liebetanz
- Department of Neurology, University Medical Center Göttingen, Georg-August University, Göttingen, Germany
| | - Dario Farina
- Department of Bioengineering, Imperial College London, London, UK
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7
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Lyle MA, Cuadra C, Wolf SL. Quadriceps muscle stimulation evokes heteronymous inhibition onto soleus with limited Ia activation compared to femoral nerve stimulation. Exp Brain Res 2022; 240:2375-2388. [PMID: 35881156 PMCID: PMC10314715 DOI: 10.1007/s00221-022-06422-7] [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: 03/22/2022] [Accepted: 07/12/2022] [Indexed: 11/30/2022]
Abstract
Heteronymous excitatory feedback from muscle spindles and inhibitory feedback from Golgi tendon organs and recurrent inhibitory circuits can influence motor coordination. The functional role of inhibitory feedback is difficult to determine, because nerve stimulation, the primary method used in humans, cannot evoke inhibition without first activating the largest diameter muscle spindle axons. Here, we tested the hypothesis that quadriceps muscle stimulation could be used to examine heteronymous inhibition more selectively when compared to femoral nerve stimulation by comparing the effects of nerve and muscle stimulation onto ongoing soleus EMG held at 20% of maximal effort. Motor threshold and two higher femoral nerve and quadriceps stimulus intensities matched by twitch evoked torque magnitudes were examined. We found that significantly fewer participants exhibited excitation during quadriceps muscle stimulation when compared to nerve stimulation (14-29% vs. 64-71% of participants across stimulation intensities) and the magnitude of heteronymous excitation from muscle stimulation, when present, was much reduced compared to nerve stimulation. Muscle and nerve stimulation resulted in heteronymous inhibition that significantly increased with increasing stimulation evoked torque magnitudes. This study provides novel evidence that muscle stimulation may be used to more selectively examine inhibitory heteronymous feedback between muscles in the human lower limb when compared to nerve stimulation.
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Affiliation(s)
- Mark A Lyle
- Division of Physical Therapy, Department of Rehabilitation Medicine, Emory University School of Medicine, 1441 Clifton Road, N.E. Room 236D, Atlanta, GA, 30322, USA.
| | - Cristian Cuadra
- Division of Physical Therapy, Department of Rehabilitation Medicine, Emory University School of Medicine, 1441 Clifton Road, N.E. Room 236D, Atlanta, GA, 30322, USA
- Exercise and Rehabilitation Sciences Laboratory, School of Physical Therapy, Faculty of Rehabilitation Sciences, Universidad Andres Bello, 7591538, Santiago, Chile
| | - Steven L Wolf
- Division of Physical Therapy, Department of Rehabilitation Medicine, Emory University School of Medicine, 1441 Clifton Road, N.E. Room 236D, Atlanta, GA, 30322, USA
- Senior Research Scientist, Center for Visual and Neurocognitive Rehabilitation, Atlanta VA Health Care System, Atlanta, GA, USA
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8
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Sangari S, Peyre I, Lackmy‐Vallée A, Bayen E, Pradat P, Marchand‐Pauvert V. Transient increase in recurrent inhibition in amyotrophic lateral sclerosis as a putative protection from neurodegeneration. Acta Physiol (Oxf) 2022; 234:e13758. [PMID: 34981890 DOI: 10.1111/apha.13758] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2021] [Revised: 12/15/2021] [Accepted: 01/01/2022] [Indexed: 11/28/2022]
Abstract
AIM Adaptive mechanisms in spinal circuits are likely involved in homeostatic responses to maintain motor output in amyotrophic lateral sclerosis. Given the role of Renshaw cells in regulating the motoneuron input/output gain, we investigated the modulation of heteronymous recurrent inhibition. METHODS Electrical stimulations were used to activate recurrent collaterals resulting in the Hoffmann reflex depression. Inhibitions from soleus motor axons to quadriceps motoneurons, and vice versa, were tested in 38 patients and matched group of 42 controls. RESULTS Compared with controls, the mean depression of quadriceps reflex was larger in patients, while that of soleus was smaller, suggesting that heteronymous recurrent inhibition was enhanced in quadriceps but reduced in soleus. The modulation of recurrent inhibition was linked to the size of maximal direct motor response and lower limb dysfunctions, suggesting a significant relationship with the integrity of the target motoneuron pool and functional abilities. No significant link was found between the integrity of motor axons activating Renshaw cells and the level of inhibition. Enhanced inhibition was particularly observed in patients within the first year after symptom onset and with slow progression of lower limb dysfunctions. Normal or reduced inhibitions were mainly observed in patients with motor weakness first in lower limbs and greater dysfunctions in lower limbs. CONCLUSION We provide the first evidence for enhanced recurrent inhibition and speculate that Renshaw cells might have transient protective role on motoneuron by counteracting hyperexcitability at early stages. Several mechanisms likely participate including cortical influence on Renshaw cell and reinnervation by slow motoneurons.
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Affiliation(s)
- Sina Sangari
- Laboratoire d’Imagerie Biomédicale Sorbonne Université INSERM CNRS Paris France
- Shirley Ryan AbilityLab Chicago Illinois USA
- Department of Physical Medicine and Rehabilitation Northwestern University Chicago Illinois USA
| | - Iseline Peyre
- Laboratoire d’Imagerie Biomédicale Sorbonne Université INSERM CNRS Paris France
| | | | - Eléonore Bayen
- Laboratoire d’Imagerie Biomédicale Sorbonne Université INSERM CNRS Paris France
- Pôle MSN, Hôpital Pitié‐Salpêtrière AP‐HP Paris France
| | - Pierre‐François Pradat
- Laboratoire d’Imagerie Biomédicale Sorbonne Université INSERM CNRS Paris France
- Pôle MSN, Hôpital Pitié‐Salpêtrière AP‐HP Paris France
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9
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Abstract
Although several methods have been used to estimate exercise-induced changes in human neuronal networks, there are growing doubts about the methodologies used. This review describes a single motor unit-based method that minimizes the errors inherent in classical methods. With this method, it is now possible to identify human neuronal networks' changes due to exercise.
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Affiliation(s)
- Kemal S Türker
- Istanbul Gelisim University, Faculty of Dentistry, Istanbul, Turkey
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10
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Spatial and Temporal Arrangement of Recurrent Inhibition in the Primate Upper Limb. J Neurosci 2021; 41:1443-1454. [PMID: 33334866 PMCID: PMC7896010 DOI: 10.1523/jneurosci.1589-20.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 10/19/2020] [Accepted: 11/11/2020] [Indexed: 11/21/2022] Open
Abstract
Renshaw cells mediate recurrent inhibition between motoneurons within the spinal cord. The function of this circuit is not clear; we previously suggested based on computational modeling that it may cancel oscillations in muscle activity around 10 Hz, thereby reducing physiological tremor. Such tremor is especially problematic for dexterous hand movements, yet knowledge of recurrent inhibitory function is sparse for the control of the primate upper limb, where no direct measurements have been made to date. In this study, we made intracellular penetrations into 89 motoneurons in the cervical enlargement of four terminally anesthetized female macaque monkeys, and recorded recurrent IPSPs in response to antidromic stimulation of motor axons. Recurrent inhibition was strongest to motoneurons innervating shoulder muscles and elbow extensors, weak to wrist and digit extensors, and almost absent to the intrinsic muscles of the hand. Recurrent inhibitory connections often spanned joints, for example from motoneurons innervating wrist and digit muscles to those controlling the shoulder and elbow. Wrist and digit flexor motoneurons sometimes inhibited the corresponding extensors, and vice versa. This complex connectivity presumably reflects the flexible usage of the primate upper limb. Using trains of stimuli to motor nerves timed as a Poisson process and coherence analysis, we also examined the temporal properties of recurrent inhibition. The recurrent feedback loop effectively carried frequencies up to 100 Hz, with a coherence peak around 20 Hz. The coherence phase validated predictions from our previous computational model, supporting the idea that recurrent inhibition may function to reduce tremor. SIGNIFICANCE STATEMENT We present the first direct measurements of recurrent inhibition in primate upper limb motoneurons, revealing that it is more flexibly organized than previous observations in cat. Recurrent inhibitory connections were relatively common between motoneurons controlling muscles that act at different joints, and between flexors and extensors. As in the cat, connections were minimal for motoneurons innervating the most distal intrinsic hand muscles. Empirical data are consistent with previous modeling: temporal properties of the recurrent inhibitory feedback loop are compatible with a role in reducing physiological tremor by suppressing oscillations around 10 Hz.
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11
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Amyotrophic lateral sclerosis weakens spinal recurrent inhibition and post-activation depression. Clin Neurophysiol 2020; 131:2875-2886. [DOI: 10.1016/j.clinph.2020.09.021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2020] [Revised: 08/15/2020] [Accepted: 09/07/2020] [Indexed: 01/07/2023]
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12
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Göztepe MB, Özyurt MG, Türker KS, Uysal H. Comparison of the temporal properties of medium latency responses induced by cortical and peripheral stimulation. J Electromyogr Kinesiol 2020; 55:102477. [PMID: 33074130 DOI: 10.1016/j.jelekin.2020.102477] [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: 08/23/2020] [Revised: 09/26/2020] [Accepted: 09/29/2020] [Indexed: 11/19/2022] Open
Abstract
Sudden foot dorsiflexion lengthens soleus muscle and activates stretch-based spinal reflexes. Dorsiflexion can be triggered by activating tibialis anterior (TA) muscle through peroneal nerve stimulation or transcranial magnetic stimulation (TMS) which evokes a response in the soleus muscle referred to as Medium Latency Reflex (MLR) or motor-evoked potential-80 (Soleus MEP80), respectively. This study aimed to examine the relationship between these responses in humans. Therefore, latency characteristics and correlation of responses between soleus MEP80 and MLR were investigated. We have also calculated the latencies from the onset of tibialis activity, i.e., subtracting of TA-MEP from MEP80 and TA direct motor response from MLR. We referred to these calculations as Stretch Loop Latency Central (SLLc) for MEP80 and Stretch Loop Latency Peripheral (SLLp) for MLR. The latency of SLLc was found to be 61.4 ± 5.6 ms which was significantly shorter (P = 0.0259) than SLLp (64.0 ± 4.2 ms) and these latencies were correlated (P = 0.0045, r = 0.689). The latency of both responses was also found to be inversely related to the response amplitude (P = 0.0121, r = 0.451) probably due to the activation of large motor units. When amplitude differences were corrected, i.e. investigating the responses with similar amplitudes, SLLp, and SLLc latencies found to be similar (P = 0.1317). Due to the identical features of the soleus MEP80 and MLR, we propose that they may both have spinal origins.
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Affiliation(s)
| | - Mustafa Görkem Özyurt
- School of Medicine, Koç University, Istanbul, Turkey; Department of Neuroscience, Physiology & Pharmacology, University College London, London, United Kingdom
| | | | - Hilmi Uysal
- Neurology Department, Faculty of Medicine, Akdeniz University, Antalya, Turkey.
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13
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Özyurt MG, Topkara B, Şenocak BS, Budan AS, Yüce MN, Türker KS. Post-activation depression of primary afferents reevaluated in humans. J Electromyogr Kinesiol 2020; 54:102460. [PMID: 32905963 DOI: 10.1016/j.jelekin.2020.102460] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2020] [Revised: 08/05/2020] [Accepted: 08/19/2020] [Indexed: 11/26/2022] Open
Abstract
Amplitude variation of Hoffmann Reflex (H-reflex) was used as a tool to investigate many neuronal networks. However, H-reflex itself is a subject to intrinsic changes including post-activation depression (P-AD). We aimed to investigate P-AD and its implication on motor control in humans. Upon tibial nerve stimulation in 23 healthy participants, peak-to-peak amplitude change of H-reflex was investigated using surface electromyography (SEMG) of soleus muscle. Variety of stimulus intensities, interstimulus intervals (ISIs), voluntary contraction levels/types and force recording were used to investigate the nature of P-AD. We have shown that P-AD was significantly stronger in the shorter ISIs. The only exception was the ISI of 200 msecs which had a weaker P-AD than some of the longer ISIs. Sudden muscle relaxation, on the other hand, further increased the effectiveness of the ongoing P-AD. Moreover, P-AD displayed its full effect with the first stimulus when there was no muscle contraction and was efficient to reduce the muscle force output by about 30%. These findings provide insight about the variations and mechanism of P-AD and could lead to improvements in diagnostic tools in neurological diseases.
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Affiliation(s)
| | - Betilay Topkara
- Koç University, School of Medicine, 34450 Sariyer, Istanbul, Turkey
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14
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Zavvarian MM, Hong J, Fehlings MG. The Functional Role of Spinal Interneurons Following Traumatic Spinal Cord Injury. Front Cell Neurosci 2020; 14:127. [PMID: 32528250 PMCID: PMC7247430 DOI: 10.3389/fncel.2020.00127] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Accepted: 04/17/2020] [Indexed: 12/17/2022] Open
Abstract
Traumatic spinal cord injury (SCI) impedes signal transmission by disrupting both the local neurons and their surrounding synaptic connections. Although the majority of SCI patients retain spared neural tissue at the injury site, they predominantly suffer from complete autonomic and sensorimotor dysfunction. While there have been significant advances in the characterization of the spared neural tissue following SCI, the functional role of injury-induced interneuronal plasticity remains elusive. In healthy individuals, spinal interneurons are responsible for relaying signals to coordinate both sympathetic and parasympathetic functions. However, the spontaneous synaptic loss following injury alters these intricate interneuronal networks in the spinal cord. Here, we propose the synaptopathy hypothesis of SCI based on recent findings regarding the maladaptive role of synaptic changes amongst the interneurons. These maladaptive consequences include circuit inactivation, neuropathic pain, spasticity, and autonomic dysreflexia. Recent preclinical advances have uncovered the therapeutic potential of spinal interneurons in activating the dormant relay circuits to restore sensorimotor function. This review will survey the diverse role of spinal interneurons in SCI pathogenesis as well as treatment strategies to target spinal interneurons.
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Affiliation(s)
- Mohammad-Masoud Zavvarian
- Division of Genetics and Development, Krembil Research Institute, University Health Network, Toronto, ON, Canada.,Institute of Medical Science, University of Toronto, Toronto, ON, Canada
| | - James Hong
- Division of Genetics and Development, Krembil Research Institute, University Health Network, Toronto, ON, Canada.,Institute of Medical Science, University of Toronto, Toronto, ON, Canada
| | - Michael G Fehlings
- Division of Genetics and Development, Krembil Research Institute, University Health Network, Toronto, ON, Canada.,Institute of Medical Science, University of Toronto, Toronto, ON, Canada.,Faculty of Medicine, University of Toronto, Toronto, ON, Canada.,Division of Neurosurgery, University of Toronto, Toronto, ON, Canada
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15
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Özyurt MG, Haavik H, Nedergaard RW, Topkara B, Şenocak BS, Göztepe MB, Niazi IK, Türker KS. Transcranial magnetic stimulation induced early silent period and rebound activity re-examined. PLoS One 2019; 14:e0225535. [PMID: 31800618 PMCID: PMC6892484 DOI: 10.1371/journal.pone.0225535] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Accepted: 11/06/2019] [Indexed: 12/17/2022] Open
Abstract
Despite being widely studied, the underlying mechanisms of transcranial magnetic brain stimulation (TMS) induced motor evoked potential (MEP), early cortical silent period (CSP) and rebound activity are not fully understood. Our aim is to better characterize these phenomena by combining various analysis tools on firing motor units. Responses of 29 tibialis anterior (TA) and 8 abductor pollicis brevis (APB) motor units to TMS pulses were studied using discharge rate and probability-based tools to illustrate the profile of the synaptic potentials as they develop on motoneurons in 24 healthy volunteers. According to probability-based methods, TMS pulse produces a short-latency MEP which is immediately followed by CSP that terminates at rebound activity. Discharge rate analysis, however, revealed not three, but just two events with distinct time courses; a long-lasting excitatory period (71.2 ± 9.0 ms for TA and 42.1 ± 11.2 ms for APB) and a long-latency inhibitory period with duration of 57.9 ± 9.5 ms for TA and 67.3 ± 13.8 ms for APB. We propose that part of the CSP may relate to the falling phase of net excitatory postsynaptic potential induced by TMS. Rebound activity, on the other hand, may represent tendon organ inhibition induced by MEP activated soleus contraction and/or long-latency intracortical inhibition. Due to generation of field potentials when high intensity TMS is used, this study is limited to investigate the events evoked by low intensity TMS only and does not provide information about later parts of much longer CSPs induced by high intensity TMS. Adding discharge rate analysis contributes to obtain a more accurate picture about the characteristics of TMS-induced events. These results have implications for interpreting motor responses following TMS for diagnosis and overseeing recovery from various neurological conditions.
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Affiliation(s)
| | - Heidi Haavik
- Centre for Chiropractic Research, New Zealand College of Chiropractic, Auckland, New Zealand
| | | | | | - Beatrice Selen Şenocak
- Frank H. Netter MD School of Medicine, Quinnipiac University, North Haven, CT, United States of America
| | | | - Imran Khan Niazi
- Centre for Chiropractic Research, New Zealand College of Chiropractic, Auckland, New Zealand
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Medium latency excitatory reflex of soleus re-examined. Exp Brain Res 2019; 237:1717-1725. [PMID: 31016349 DOI: 10.1007/s00221-019-05544-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Accepted: 04/19/2019] [Indexed: 12/19/2022]
Abstract
We aimed to study the receptor origin and postsynaptic potential profile of the medium latency reflex (MLR) response that develops in the soleus muscle when common peroneal nerve of antagonist tibialis anterior (TA) muscle is electrically stimulated. To achieve this aim, we electrically stimulated common peroneal nerve and recorded surface electromyography (SEMG) responses of soleus and TA muscles of informed volunteers. Additionally, we recorded intramuscular EMG from the soleus muscle. Stimulation of common peroneal nerve induced a direct motor response (M-response) in the TA and MLR in SEMG of the soleus. Using voluntarily-activated single motor units (SMUs) from the soleus muscle we noted that there were two distinct responses following the stimulus. The first response was a reciprocal inhibitory reflex probably originating from the antagonist muscle spindle primary (Ia) afferents. This was followed by an indirect reflex response activated by the contraction of the TA muscle during the M-response. This contraction generated a rapid acceleration in the direction of dorsiflexion hence inducing a stretch stimulus on soleus muscle. The response of soleus to this stimulus was a stretch reflex. We suggest that this stretch reflex is the main contributor to the so-called soleus MLR in the literature. This study illustrated the importance of using SMUs and also using discharge-rate based analysis for closely examining previously 'established' reflexes.
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Alvarez FJ. A motor physiology recurrent topic: simplify assumptions to gain extra insight. J Physiol 2019; 597:2117-2118. [PMID: 30779129 DOI: 10.1113/jp277715] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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