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Mesquita RNO, Taylor JL, Heckman CJ, Trajano GS, Blazevich AJ. Persistent inward currents in human motoneurons: emerging evidence and future directions. J Neurophysiol 2024; 132:1278-1301. [PMID: 39196985 DOI: 10.1152/jn.00204.2024] [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: 06/02/2024] [Revised: 08/15/2024] [Accepted: 08/16/2024] [Indexed: 08/30/2024] Open
Abstract
The manner in which motoneurons respond to excitatory and inhibitory inputs depends strongly on how their intrinsic properties are influenced by the neuromodulators serotonin and noradrenaline. These neuromodulators enhance the activation of voltage-gated channels that generate persistent (long-lasting) inward sodium and calcium currents (PICs) into the motoneurons. PICs are crucial for initiating, accelerating, and maintaining motoneuron firing. A greater accessibility to state-of-the-art techniques that allows both the estimation and examination of PIC modulation in tens of motoneurons in vivo has rapidly evolved our knowledge of how motoneurons amplify and prolong the effects of synaptic input. We are now in a position to gain substantial mechanistic insight into the role of PICs in motor control at an unprecedented pace. The present review briefly describes the effects of PICs on motoneuron firing and the methods available for estimating them before presenting the emerging evidence of how PICs can be modulated in health and disease. Our rapidly developing knowledge of the potent effects of PICs on motoneuron firing has the potential to improve our understanding of how we move, and points to new approaches to improve motor control. Finally, gaps in our understanding are highlighted and methodological advancements are suggested to encourage readers to explore outstanding questions to further elucidate PIC physiology.
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Affiliation(s)
- Ricardo N O Mesquita
- Department of Electrical Engineering, Chalmers University of Technology, Gothenburg, Sweden
- Discipline of Exercise and Sports Science, School of Medical and Health Sciences, Edith Cowan University, Perth, Western Australia, Australia
- Neuroscience Research Australia, Sydney, New South Wales, Australia
| | - Janet L Taylor
- Discipline of Exercise and Sports Science, School of Medical and Health Sciences, Edith Cowan University, Perth, Western Australia, Australia
- Neuroscience Research Australia, Sydney, New South Wales, Australia
| | - C J Heckman
- Departments of Neuroscience, Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States of America
| | - Gabriel S Trajano
- School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology, Brisbane, Queensland, Australia
| | - Anthony J Blazevich
- Discipline of Exercise and Sports Science, School of Medical and Health Sciences, Edith Cowan University, Perth, Western Australia, Australia
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2
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Bonthron C, Burley S, Broadhead MJ, Metodieva V, Grant SGN, Chandran S, Miles GB. Excitatory to inhibitory synaptic ratios are unchanged at presymptomatic stages in multiple models of ALS. PLoS One 2024; 19:e0306423. [PMID: 39088455 PMCID: PMC11293752 DOI: 10.1371/journal.pone.0306423] [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: 02/22/2024] [Accepted: 06/17/2024] [Indexed: 08/03/2024] Open
Abstract
Hyperexcitability of motor neurons and spinal cord motor circuitry has been widely reported in the early stages of Amyotrophic Lateral Sclerosis (ALS). Changes in the relative amount of excitatory to inhibitory inputs onto a neuron (E:I synaptic ratio), possibly through a developmental shift in synapse formation in favour of excitatory transmission, could underlie pathological hyperexcitability. Given that astrocytes play a major role in early synaptogenesis and are implicated in ALS pathogenesis, their potential contribution to disease mechanisms involving synaptic imbalances and subsequent hyperexcitability is also of great interest. In order to assess E:I ratios in ALS, we utilised a novel primary spinal neuron / astrocyte co-culture system, derived from neonatal mice, in which synapses are formed in vitro. Using multiple ALS mouse models we found that no combination of astrocyte or neuron genotype produced alterations in E:I synaptic ratios assessed using pre- and post-synaptic anatomical markers. Similarly, we observed that ephrin-B1, a major contact-dependent astrocytic synaptogenic protein, was not differentially expressed by ALS primary astrocytes. Further to this, analysis of E:I ratios across the entire grey matter of the lumbar spinal cord in young (post-natal day 16-19) ALS mice revealed no differences versus controls. Finally, analysis in co-cultures of human iPSC-derived motor neurons and astrocytes harbouring the pathogenic C9orf72 hexanucleotide repeat expansion showed no evidence of a bias toward excitatory versus inhibitory synapse formation. We therefore conclude, utilising multiple ALS models, that we do not observe significant changes in the relative abundance of excitatory versus inhibitory synapses as would be expected if imbalances in synaptic inputs contribute to early hyperexcitability.
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Affiliation(s)
- Calum Bonthron
- School of Psychology and Neuroscience, University of St Andrews, St Andrews, United Kingdom
| | - Sarah Burley
- School of Psychology and Neuroscience, University of St Andrews, St Andrews, United Kingdom
- School of Biology, University of St Andrews, St Andrews, United Kingdom
| | - Matthew J. Broadhead
- School of Psychology and Neuroscience, University of St Andrews, St Andrews, United Kingdom
| | - Vanya Metodieva
- School of Biology, University of St Andrews, St Andrews, United Kingdom
- Centre of Biophotonics, University of St Andrews, St Andrews, United Kingdom
| | - Seth G. N. Grant
- Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom
- Simons Initiative for the Developing Brain (SIDB), Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Siddharthan Chandran
- Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom
- Simons Initiative for the Developing Brain (SIDB), Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom
- UK Dementia Research Institute, Edinburgh Medical School, University of Edinburgh, Edinburgh, United Kingdom
- Patrick Wild Centre, University of Edinburgh, Edinburgh, United Kingdom
| | - Gareth B. Miles
- School of Psychology and Neuroscience, University of St Andrews, St Andrews, United Kingdom
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Mohammadalinejad G, Afsharipour B, Yacyshyn A, Duchcherer J, Bashuk J, Bennett E, Pearcey GEP, Negro F, Quinlan KA, Bennett DJ, Gorassini MA. Intrinsic motoneuron properties in typical human development. J Physiol 2024; 602:2061-2087. [PMID: 38554126 PMCID: PMC11262706 DOI: 10.1113/jp285756] [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: 10/27/2023] [Accepted: 03/06/2024] [Indexed: 04/01/2024] Open
Abstract
Motoneuron properties and their firing patterns undergo significant changes throughout development and in response to neuromodulators such as serotonin. Here, we examined the age-related development of self-sustained firing and general excitability of tibialis anterior motoneurons in a young development (7-17 years), young adult (18-28 years) and adult (32-53 years) group, as well as in a separate group of participants taking selective serotonin reuptake inhibitors (SSRIs, aged 11-28 years). Self-sustained firing, as measured by ΔF, was larger in the young development (∼5.8 Hz, n = 20) compared to the young adult (∼4.9 Hz, n = 13) and adult (∼4.8 Hz, n = 8) groups, consistent with a developmental decrease in self-sustained firing mediated by persistent inward currents (PIC). ΔF was also larger in participants taking SSRIs (∼6.5 Hz, n = 9) compared to their age-matched controls (∼5.3 Hz, n = 26), consistent with increased levels of spinal serotonin facilitating the motoneuron PIC. Participants in the young development and SSRI groups also had higher firing rates and a steeper acceleration in initial firing rates (secondary ranges), consistent with the PIC producing a steeper acceleration in membrane depolarization at the onset of motoneuron firing. In summary, both the young development and SSRI groups exhibited increased intrinsic motoneuron excitability compared to the adults, which, in the young development group, was also associated with a larger unsteadiness in the dorsiflexion torque profiles. We propose several intrinsic and extrinsic factors that affect both motoneuron PICs and cell discharge which vary during development, with a time course similar to the changes in motoneuron firing behaviour observed in the present study. KEY POINTS: Neurons in the spinal cord that activate muscles in the limbs (motoneurons) undergo increases in excitability shortly after birth to help animals stand and walk. We examined whether the excitability of human ankle flexor motoneurons also continues to change from child to adulthood by recording the activity of the muscle fibres they innervate. Motoneurons in children and adolescents aged 7-17 years (young development group) had higher signatures of excitability that included faster firing rates and more self-sustained activity compared to adults aged ≥18 years. Participants aged 11-28 years of age taking serotonin reuptake inhibitors had the highest measures of motoneuron excitability compared to their age-matched controls. The young development group also had more unstable contractions, which might partly be related to the high excitability of the motoneurons.
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Affiliation(s)
- Ghazaleh Mohammadalinejad
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
- Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
| | - Babak Afsharipour
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
- Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
| | - Alex Yacyshyn
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
| | - Jennifer Duchcherer
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
| | - Jack Bashuk
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
| | - Erin Bennett
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
| | - Gregory E P Pearcey
- School of Human Kinetics and Recreation, Memorial University of Newfoundland, St John's Canada and Physical Therapy & Human Movement Sciences, Northwestern University, Chicago, IL, USA
| | - Francesco Negro
- Clinical and Experimental Sciences, Universita degli Studi di Brescia, Brescia, Italia
| | - Katharina A Quinlan
- George and Anne Ryan Institute for Neuroscience, Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
| | - David J Bennett
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
- Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, AB, Canada
| | - Monica A Gorassini
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
- Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
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Nascimento F, Özyurt MG, Halablab K, Bhumbra GS, Caron G, Bączyk M, Zytnicki D, Manuel M, Roselli F, Brownstone R, Beato M. Spinal microcircuits go through multiphasic homeostatic compensations in a mouse model of motoneuron degeneration. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.10.588918. [PMID: 38645210 PMCID: PMC11030447 DOI: 10.1101/2024.04.10.588918] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/23/2024]
Abstract
In neurological conditions affecting the brain, early-stage neural circuit adaption is key for long-term preservation of normal behaviour. We tested if motoneurons and respective microcircuits also adapt in the initial stages of disease progression in a mouse model of progressive motoneuron degeneration. Using a combination of in vitro and in vivo electrophysiology and super-resolution microscopy, we found that, preceding muscle denervation and motoneuron death, recurrent inhibition mediated by Renshaw cells is reduced in half due to impaired quantal size associated with decreased glycine receptor density. Additionally, higher probability of release from proprioceptive Ia terminals leads to increased monosynaptic excitation to motoneurons. Surprisingly, the initial impairment in recurrent inhibition is not a widespread feature of inhibitory spinal circuits, such as group I inhibitory afferents, and is compensated at later stages of disease progression. We reveal that in disease conditions, spinal microcircuits undergo specific multiphasic homeostatic compensations to preserve force output.
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Affiliation(s)
- Filipe Nascimento
- Department of Neuroscience Physiology and Pharmacology (NPP), Gower Street, University College London, WC1E 6BT, UK
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - M. Görkem Özyurt
- Department of Neuroscience Physiology and Pharmacology (NPP), Gower Street, University College London, WC1E 6BT, UK
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Kareen Halablab
- Department of Neurology, Ulm University, Ulm, Germany
- German Centre for Neurodegenerative Diseases-Ulm (DZNE-Ulm), Ulm, Germany
| | - Gardave Singh Bhumbra
- Department of Neuroscience Physiology and Pharmacology (NPP), Gower Street, University College London, WC1E 6BT, UK
| | - Guillaume Caron
- Saints-Pères Paris Institute for the Neurosciences (SPPIN), Université Paris Cité, Centre National de la Recherche Scientifique (CNRS), Paris, France
| | - Marcin Bączyk
- Department of Neurobiology, Poznań University of Physical Education, Poznań, Poland
| | - Daniel Zytnicki
- Saints-Pères Paris Institute for the Neurosciences (SPPIN), Université Paris Cité, Centre National de la Recherche Scientifique (CNRS), Paris, France
| | - Marin Manuel
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, USA
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
| | - Francesco Roselli
- Department of Neurology, Ulm University, Ulm, Germany
- German Centre for Neurodegenerative Diseases-Ulm (DZNE-Ulm), Ulm, Germany
| | - Rob 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), Gower Street, University College London, WC1E 6BT, UK
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5
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Harris-Warrick RM, Pecchi E, Drouillas B, Brocard F, Bos R. Effect of size on expression of bistability in mouse spinal motoneurons. J Neurophysiol 2024; 131:577-588. [PMID: 38380829 PMCID: PMC11305636 DOI: 10.1152/jn.00320.2023] [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: 08/24/2023] [Revised: 02/05/2024] [Accepted: 02/20/2024] [Indexed: 02/22/2024] Open
Abstract
Bistability in spinal motoneurons supports tonic spike activity in the absence of excitatory drive. Earlier work in adult preparations suggested that smaller motoneurons innervating slow antigravity muscle fibers are more likely to generate bistability for postural maintenance. However, whether large motoneurons innervating fast-fatigable muscle fibers display bistability is still controversial. To address this, we examined the relationship between soma size and bistability in lumbar (L4-L5) ventrolateral α-motoneurons of choline acetyltransferase (ChAT)-green fluorescent protein (GFP) and Hb9-GFP mice during the first 4 wk of life. We found that as neuron size increases, the prevalence of bistability rises. Smaller α-motoneurons lack bistability, whereas larger fast α-motoneurons [matrix metalloproteinase-9 (MMP-9)+/Hb9+] with a soma area ≥ 400 µm2 exhibit significantly higher bistability. Ionic currents associated with bistability, including the persistent Nav1.6 current, the thermosensitive Trpm5 Ca2+-activated Na+ current, and the slowly inactivating Kv1.2 current, also scale with cell size. Serotonin evokes full bistability in large motoneurons with partial bistable properties but not in small motoneurons. Our study provides important insights into the neural mechanisms underlying bistability and how motoneuron size correlates with bistability in mice.NEW & NOTEWORTHY Bistability is not a common feature of all mouse spinal motoneurons. It is absent in small, slow motoneurons but present in most large, fast motoneurons. This difference results from differential expression of ionic currents that enable bistability, which are highly expressed in large motoneurons but small or absent in small motoneurons. These results support a possible role for fast motoneurons in maintenance of tonic posture in addition to their known roles in fast movements.
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Affiliation(s)
- Ronald M Harris-Warrick
- Department of Neurobiology and Behavior, Cornell University, Ithaca, New York, United States
| | - Emilie Pecchi
- Aix Marseille Univ, CNRS, Institut de Neurosciences de la Timone (INT), UMR 7289, Marseille, France
| | - Benoît Drouillas
- Aix Marseille Univ, CNRS, Institut de Neurosciences de la Timone (INT), UMR 7289, Marseille, France
| | - Frédéric Brocard
- Aix Marseille Univ, CNRS, Institut de Neurosciences de la Timone (INT), UMR 7289, Marseille, France
| | - Rémi Bos
- Aix Marseille Univ, CNRS, Institut de Neurosciences de la Timone (INT), UMR 7289, Marseille, France
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Zhu H, Dalvi U, Cazenave W, Cattaert D, Branchereau P. Excitatory action of low frequency depolarizing GABA/glycine synaptic inputs is prevalent in prenatal spinal SOD1 G93A motoneurons. J Physiol 2024; 602:913-932. [PMID: 38345477 DOI: 10.1113/jp285105] [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: 06/01/2023] [Accepted: 01/24/2024] [Indexed: 03/09/2024] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a fatal adult-onset neurodegenerative disease characterized by progressive motor neuron degeneration and muscle paralysis. Recent evidence suggests the dysfunction of inhibitory signalling in ALS motor neurons. We have shown that embryonic day (E)17.5 spinal motoneurons (MNs) of the SOD1G93A mouse model of ALS exhibit an altered chloride homeostasis. At this prenatal stage, inhibition of spinal motoneurons (MNs) is mediated by depolarizing GABAergic/glycinergic postsynaptic potentials (dGPSPs). Here, using an ex vivo preparation and patch clamp recording from MNs with a chloride equilibrium set below spike threshold, we report that low input resistance (Rin ) E17.5 MNs from the SOD1G93A ALS mouse model do not correctly integrate dGPSPs evoked by electrical stimulations of GABA/glycine inputs at different frequencies. Indeed, firing activity of most wild-type (WT) MNs with low Rin was inhibited by incoming dGPSPs, whereas low Rin SOD1G93A MNs were excited or exhibited a dual response (excited by low frequency dGPSPs and inhibited by high frequency dGPSPs). Simulation highlighted the importance of the GABA/glycine input density and showed that pure excitation could be obtained in SOD-like MNs by moving GABA/glycine input away from the cell body to dendrites. This was in agreement with confocal imaging showing a lack of peri-somatic inhibitory terminals in SOD1G93A MNs compared to WT littermates. Putative fast ALS-vulnerable MNs with low Rin are therefore lacking functional inhibition at the near-term prenatal stage. KEY POINTS: We analysed the integration of GABAergic/glycinergic synaptic events by embryonic spinal motoneurons (MNs) in a mouse model of the amyotrophic lateral sclerosis (ALS) neurodegenerative disease. We found that GABAergic/glycinergic synaptic events do not properly inhibit ALS MNs with low input resistance, most probably corresponding to future vulnerable MNs. We used a neuron model to highlight the importance of the GABA/glycine terminal location and density in the integration of the GABAergic/glycinergic synaptic events. Confocal imaging showed a lack of GABA/glycine terminals on the cell body of ALS MNs. The present study suggests that putative ALS vulnerable MNs with low Rin lack functional inhibition at the near-term stage.
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Affiliation(s)
- Hongmei Zhu
- University Bordeaux, CNRS, INCIA, UMR 5287, Bordeaux, France
| | - Urvashi Dalvi
- University Bordeaux, CNRS, INCIA, UMR 5287, Bordeaux, France
| | | | - Daniel Cattaert
- University Bordeaux, CNRS, INCIA, UMR 5287, Bordeaux, France
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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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Sharples SA, Broadhead MJ, Gray JA, Miles GB. M-type potassium currents differentially affect activation of motoneuron subtypes and tune recruitment gain. J Physiol 2023; 601:5751-5775. [PMID: 37988235 DOI: 10.1113/jp285348] [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: 07/27/2023] [Accepted: 10/25/2023] [Indexed: 11/23/2023] Open
Abstract
The size principle is a key mechanism governing the orderly recruitment of motor units and is believed to be dependent on passive properties of the constituent motoneurons. However, motoneurons are endowed with voltage-sensitive ion channels that create non-linearities in their input-output functions. Here we describe a role for the M-type potassium current, conducted by KCNQ channels, in the control of motoneuron recruitment in mice. Motoneurons were studied with whole-cell patch clamp electrophysiology in transverse spinal slices and identified based on delayed (fast) and immediate (slow) onsets of repetitive firing. M-currents were larger in delayed compared to immediate firing motoneurons, which was not reflected by variations in the presence of Kv7.2 or Kv7.3 subunits. Instead, a more depolarized spike threshold in delayed-firing motoneurons afforded a greater proportion of the total M-current to become activated within the subthreshold voltage range, which translated to a greater influence on their recruitment with little influence on their firing rates. Pharmacological activation of M-currents also influenced motoneuron recruitment at the population level, producing a rightward shift in the recruitment curve of monosynaptic reflexes within isolated mouse spinal cords. These results demonstrate a prominent role for M-type potassium currents in regulating the function of motor units, which occurs primarily through the differential control of motoneuron subtype recruitment. More generally, these findings highlight the importance of active properties mediated by voltage-sensitive ion channels in the differential control of motoneuron recruitment, which is a key mechanism for the gradation of muscle force. KEY POINTS: M-currents exert an inhibitory influence on spinal motor output. This inhibitory influence is exerted by controlling the recruitment, but not the firing rate, of high-threshold fast-like motoneurons, with limited influence on low-threshold slow-like motoneurons. Preferential control of fast motoneurons may be linked to a larger M-current that is activated within the subthreshold voltage range compared to slow motoneurons. Larger M-currents in fast compared to slow motoneurons are not accounted for by differences in Kv7.2 or Kv7.3 channel composition. The orderly recruitment of motoneuron subtypes is shaped by differences in the contribution of voltage-gated ion channels, including KCNQ channels. KCNQ channels may provide a target to dynamically modulate the recruitment gain across the motor pool and readily adjust movement vigour.
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Affiliation(s)
- Simon A Sharples
- School of Psychology and Neuroscience, University of St Andrews, Fife, UK
| | | | - James A Gray
- School of Psychology and Neuroscience, University of St Andrews, Fife, UK
| | - Gareth B Miles
- School of Psychology and Neuroscience, University of St Andrews, Fife, UK
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9
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Harris-Warrick RM, Pecchi E, Drouillas B, Brocard F, Bos R. A size principle for bistability in mouse spinal motoneurons. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.29.559784. [PMID: 37808773 PMCID: PMC10557784 DOI: 10.1101/2023.09.29.559784] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/10/2023]
Abstract
Bistability in spinal motoneurons supports tonic spike activity in the absence of excitatory drive. Earlier work in adult preparations suggested that smaller motoneurons innervating slow antigravity muscle fibers are more likely to generate bistability for postural maintenance. However, whether large motoneurons innervating fast-fatigable muscle fibers display bistability related to postural tone is still controversial. To address this, we examined the relationship between soma size and bistability in lumbar ventrolateral α-motoneurons of ChAT-GFP and Hb9-GFP mice across different developmental stages: neonatal (P2-P7), young (P7-P14) and mature (P21-P25). We found that as neuron size increases, the prevalence of bistability rises. Smaller α-motoneurons lack bistability, while larger fast α-motoneurons (MMP-9 + /Hb9 + ) with a soma area ≥ 400µm 2 exhibit significantly higher bistability. Ionic currents associated with bistability, including the persistent Nav1.6 current, thermosensitive Trpm5 Ca 2+ -activated Na + current and the slowly inactivating Kv1.2 current, also scale with cell size. Serotonin evokes full bistability in large motoneurons with partial bistable properties, but not in small motoneurons. Our study provides important insights into the neural mechanisms underlying bistability and how motoneuron size dictates this process. New and Noteworthy Bistability is not a common feature of all mouse spinal motoneurons. It is absent in small, slow motoneurons but present in most large, fast motoneurons. This difference results from differential expression of ionic currents that enable bistability, which are highly expressed in large motoneurons but small or absent in small motoneurons. These results support a possible role for fast motoneurons in maintenance of tonic posture in addition to their known roles in fast movements.
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10
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Eleftheriadis PE, Pothakos K, Sharples SA, Apostolou PE, Mina M, Tetringa E, Tsape E, Miles GB, Zagoraiou L. Peptidergic modulation of motor neuron output via CART signaling at C bouton synapses. Proc Natl Acad Sci U S A 2023; 120:e2300348120. [PMID: 37733738 PMCID: PMC10523464 DOI: 10.1073/pnas.2300348120] [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: 01/17/2023] [Accepted: 07/17/2023] [Indexed: 09/23/2023] Open
Abstract
The intensity of muscle contraction, and therefore movement vigor, needs to be adaptable to enable complex motor behaviors. This can be achieved by adjusting the properties of motor neurons, which form the final common pathway for all motor output from the central nervous system. Here, we identify roles for a neuropeptide, cocaine- and amphetamine-regulated transcript (CART), in the control of movement vigor. We reveal distinct but parallel mechanisms by which CART and acetylcholine, both released at C bouton synapses on motor neurons, selectively amplify the output of subtypes of motor neurons that are recruited during intense movement. We find that mice with broad genetic deletion of CART or selective elimination of acetylcholine from C boutons exhibit deficits in behavioral tasks that require higher levels of motor output. Overall, these data uncover spinal modulatory mechanisms that control movement vigor to support movements that require a high degree of muscle force.
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Affiliation(s)
| | - Konstantinos Pothakos
- Center of Basic Research, Biomedical Research Foundation Academy of Athens, Athens11527, Greece
| | - Simon A. Sharples
- School of Psychology and Neuroscience, University of St. Andrews, St. AndrewsKY16 9JP, United Kingdom
| | - Panagiota E. Apostolou
- Center of Basic Research, Biomedical Research Foundation Academy of Athens, Athens11527, Greece
| | - Maria Mina
- Center of Basic Research, Biomedical Research Foundation Academy of Athens, Athens11527, Greece
| | - Efstathia Tetringa
- Center of Basic Research, Biomedical Research Foundation Academy of Athens, Athens11527, Greece
| | - Eirini Tsape
- Center of Basic Research, Biomedical Research Foundation Academy of Athens, Athens11527, Greece
| | - Gareth B. Miles
- School of Psychology and Neuroscience, University of St. Andrews, St. AndrewsKY16 9JP, United Kingdom
| | - Laskaro Zagoraiou
- Center of Basic Research, Biomedical Research Foundation Academy of Athens, Athens11527, Greece
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11
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Drouillas B, Brocard C, Zanella S, Bos R, Brocard F. Persistent Nav1.1 and Nav1.6 currents drive spinal locomotor functions through nonlinear dynamics. Cell Rep 2023; 42:113085. [PMID: 37665666 DOI: 10.1016/j.celrep.2023.113085] [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: 04/10/2023] [Revised: 06/29/2023] [Accepted: 08/16/2023] [Indexed: 09/06/2023] Open
Abstract
Persistent sodium current (INaP) in the spinal locomotor network promotes two distinct nonlinear firing patterns: a self-sustained spiking triggered by a brief excitation in bistable motoneurons and bursting oscillations in interneurons of the central pattern generator (CPG). Here, we identify the NaV channels responsible for INaP and their role in motor behaviors. We report the axonal Nav1.6 as the main molecular player for INaP in lumbar motoneurons. The inhibition of Nav1.6, but not of Nav1.1, in motoneurons impairs INaP, bistability, postural tone, and locomotor performance. In interneurons of the rhythmogenic CPG region, both Nav1.6 and Nav1.1 equally mediate INaP. Inhibition of both channels is required to abolish oscillatory bursting activities and the locomotor rhythm. Overall, Nav1.6 plays a significant role both in posture and locomotion by governing INaP-dependent bistability in motoneurons and working in tandem with Nav1.1 to provide INaP-dependent rhythmogenic properties of the CPG.
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Affiliation(s)
- Benoît Drouillas
- Institut de Neurosciences de la Timone, UMR 7289, Aix-Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France
| | - Cécile Brocard
- Institut de Neurosciences de la Timone, UMR 7289, Aix-Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France
| | - Sébastien Zanella
- Institut de Neurosciences de la Timone, UMR 7289, Aix-Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France
| | - Rémi Bos
- Institut de Neurosciences de la Timone, UMR 7289, Aix-Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France
| | - Frédéric Brocard
- Institut de Neurosciences de la Timone, UMR 7289, Aix-Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France.
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12
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Mechanisms Underlying the Recruitment of Inhibitory Interneurons in Fictive Swimming in Developing Xenopus laevis Tadpoles. J Neurosci 2023; 43:1387-1404. [PMID: 36693757 PMCID: PMC9987577 DOI: 10.1523/jneurosci.0520-22.2022] [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: 03/10/2022] [Revised: 10/27/2022] [Accepted: 12/02/2022] [Indexed: 01/26/2023] Open
Abstract
Developing spinal circuits generate patterned motor outputs while many neurons with high membrane resistances are still maturing. In the spinal cord of hatchling frog tadpoles of unknown sex, we found that the firing reliability in swimming of inhibitory interneurons with commissural and ipsilateral ascending axons was negatively correlated with their cellular membrane resistance. Further analyses showed that neurons with higher resistances had outward rectifying properties, low firing thresholds, and little delay in firing evoked by current injections. Input synaptic currents these neurons received during swimming, either compound, unitary current amplitudes, or unitary synaptic current numbers, were scaled with their membrane resistances, but their own synaptic outputs were correlated with membrane resistances of their postsynaptic partners. Analyses of neuronal dendritic and axonal lengths and their activities in swimming and cellular input resistances did not reveal a clear correlation pattern. Incorporating these electrical and synaptic properties into a computer swimming model produced robust swimming rhythms, whereas randomizing input synaptic strengths led to the breakdown of swimming rhythms, coupled with less synchronized spiking in the inhibitory interneurons. We conclude that the recruitment of these developing interneurons in swimming can be predicted by cellular input resistances, but the order is opposite to the motor-strength-based recruitment scheme depicted by Henneman's size principle. This form of recruitment/integration order in development before the emergence of refined motor control is progressive potentially with neuronal acquisition of mature electrical and synaptic properties, among which the scaling of input synaptic strengths with cellular input resistance plays a critical role.SIGNIFICANCE STATEMENT The mechanisms on how interneurons are recruited to participate in circuit function in developing neuronal systems are rarely investigated. In 2-d-old frog tadpole spinal cord, we found the recruitment of inhibitory interneurons in swimming is inversely correlated with cellular input resistances, opposite to the motor-strength-based recruitment order depicted by Henneman's size principle. Further analyses showed the amplitude of synaptic inputs that neurons received during swimming was inversely correlated with cellular input resistances. Randomizing/reversing the relation between input synaptic strengths and membrane resistances in modeling broke down swimming rhythms. Therefore, the recruitment or integration of these interneurons is conditional on the acquisition of several electrical and synaptic properties including the scaling of input synaptic strengths with cellular input resistances.
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13
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Petanjek Z, Banovac I, Sedmak D, Hladnik A. Dendritic Spines: Synaptogenesis and Synaptic Pruning for the Developmental Organization of Brain Circuits. ADVANCES IN NEUROBIOLOGY 2023; 34:143-221. [PMID: 37962796 DOI: 10.1007/978-3-031-36159-3_4] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
Synaptic overproduction and elimination is a regular developmental event in the mammalian brain. In the cerebral cortex, synaptic overproduction is almost exclusively correlated with glutamatergic synapses located on dendritic spines. Therefore, analysis of changes in spine density on different parts of the dendritic tree in identified classes of principal neurons could provide insight into developmental reorganization of specific microcircuits.The activity-dependent stabilization and selective elimination of the initially overproduced synapses is a major mechanism for generating diversity of neural connections beyond their genetic determination. The largest number of overproduced synapses was found in the monkey and human cerebral cortex. The highest (exceeding adult values by two- to threefold) and most protracted overproduction (up to third decade of life) was described for associative layer IIIC pyramidal neurons in the human dorsolateral prefrontal cortex.Therefore, the highest proportion and extraordinarily extended phase of synaptic spine overproduction is a hallmark of neural circuitry in human higher-order associative areas. This indicates that microcircuits processing the most complex human cognitive functions have the highest level of developmental plasticity. This finding is the backbone for understanding the effect of environmental impact on the development of the most complex, human-specific cognitive and emotional capacities, and on the late onset of human-specific neuropsychiatric disorders, such as autism and schizophrenia.
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Affiliation(s)
- Zdravko Petanjek
- Department of Anatomy and Clinical Anatomy, School of Medicine, University of Zagreb, Zagreb, Croatia.
- Department of Neuroscience, Croatian Institute for Brain Research, School of Medicine, University of Zagreb, Zagreb, Croatia.
- Center of Excellence for Basic, Clinical and Translational Neuroscience, School of Medicine, University of Zagreb, Zagreb, Croatia.
| | - Ivan Banovac
- Department of Anatomy and Clinical Anatomy, School of Medicine, University of Zagreb, Zagreb, Croatia
- Department of Neuroscience, Croatian Institute for Brain Research, School of Medicine, University of Zagreb, Zagreb, Croatia
- Center of Excellence for Basic, Clinical and Translational Neuroscience, School of Medicine, University of Zagreb, Zagreb, Croatia
| | - Dora Sedmak
- Department of Anatomy and Clinical Anatomy, School of Medicine, University of Zagreb, Zagreb, Croatia
- Department of Neuroscience, Croatian Institute for Brain Research, School of Medicine, University of Zagreb, Zagreb, Croatia
- Center of Excellence for Basic, Clinical and Translational Neuroscience, School of Medicine, University of Zagreb, Zagreb, Croatia
| | - Ana Hladnik
- Department of Anatomy and Clinical Anatomy, School of Medicine, University of Zagreb, Zagreb, Croatia
- Department of Neuroscience, Croatian Institute for Brain Research, School of Medicine, University of Zagreb, Zagreb, Croatia
- Center of Excellence for Basic, Clinical and Translational Neuroscience, School of Medicine, University of Zagreb, Zagreb, Croatia
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14
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Özyurt MG, Ojeda-Alonso J, Beato M, Nascimento F. In vitro longitudinal lumbar spinal cord preparations to study sensory and recurrent motor microcircuits of juvenile mice. J Neurophysiol 2022; 128:711-726. [PMID: 35946796 PMCID: PMC9485001 DOI: 10.1152/jn.00184.2022] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In vitro spinal cord preparations have been extensively used to study microcircuits involved in the control of movement. By allowing precise control of experimental conditions coupled with state-of-the-art genetics, imaging, and electrophysiological techniques, isolated spinal cords from mice have been an essential tool in detailing the identity, connectivity, and function of spinal networks. The majority of the research has arisen from in vitro spinal cords of neonatal mice, which are still undergoing important postnatal maturation. Studies from adults have been attempted in transverse slices, however, these have been quite challenging due to the poor motoneuron accessibility and viability, as well as the extensive damage to the motoneuron dendritic trees. In this work, we describe two types of coronal spinal cord preparations with either the ventral or the dorsal horn ablated, obtained from mice of different postnatal ages, spanning from preweaned to 1 mo old. These semi-intact preparations allow recordings of sensory-afferent and motor-efferent responses from lumbar motoneurons using whole cell patch-clamp electrophysiology. We provide details of the slicing procedure and discuss the feasibility of whole cell recordings. The in vitro dorsal and ventral horn-ablated spinal cord preparations described here are a useful tool to study spinal motor circuits in young mice that have reached the adult stages of locomotor development.NEW & NOTEWORTHY In the past 20 years, most of the research into the mammalian spinal circuitry has been limited to in vitro preparations from embryonic and neonatal mice. We describe two in vitro longitudinal lumbar spinal cord preparations from juvenile mice that allow the study of motoneuron properties and respective afferent or efferent spinal circuits through whole cell patch clamp. These preparations will be useful to those interested in the study of microcircuits at mature stages of motor development.
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Affiliation(s)
- Mustafa Görkem Özyurt
- 1Department of Neuroscience Physiology and Pharmacology (NPP), grid.83440.3bUniversity College London, London, United Kingdom,2Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom
| | - Julia Ojeda-Alonso
- 1Department of Neuroscience Physiology and Pharmacology (NPP), grid.83440.3bUniversity College London, London, United Kingdom
| | - Marco Beato
- 1Department of Neuroscience Physiology and Pharmacology (NPP), grid.83440.3bUniversity College London, London, United Kingdom
| | - Filipe Nascimento
- 1Department of Neuroscience Physiology and Pharmacology (NPP), grid.83440.3bUniversity College London, London, United Kingdom,2Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom
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15
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Charles J, Kissane R, Hoehfurtner T, Bates KT. From fibre to function: are we accurately representing muscle architecture and performance? Biol Rev Camb Philos Soc 2022; 97:1640-1676. [PMID: 35388613 PMCID: PMC9540431 DOI: 10.1111/brv.12856] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Revised: 03/22/2022] [Accepted: 03/25/2022] [Indexed: 12/11/2022]
Abstract
The size and arrangement of fibres play a determinate role in the kinetic and energetic performance of muscles. Extrapolations between fibre architecture and performance underpin our understanding of how muscles function and how they are adapted to power specific motions within and across species. Here we provide a synopsis of how this 'fibre to function' paradigm has been applied to understand muscle design, performance and adaptation in animals. Our review highlights the widespread application of the fibre to function paradigm across a diverse breadth of biological disciplines but also reveals a potential and highly prevalent limitation running through past studies. Specifically, we find that quantification of muscle architectural properties is almost universally based on an extremely small number of fibre measurements. Despite the volume of research into muscle properties, across a diverse breadth of research disciplines, the fundamental assumption that a small proportion of fibre measurements can accurately represent the architectural properties of a muscle has never been quantitatively tested. Subsequently, we use a combination of medical imaging, statistical analysis, and physics-based computer simulation to address this issue for the first time. By combining diffusion tensor imaging (DTI) and deterministic fibre tractography we generated a large number of fibre measurements (>3000) rapidly for individual human lower limb muscles. Through statistical subsampling simulations of these measurements, we demonstrate that analysing a small number of fibres (n < 25) typically used in previous studies may lead to extremely large errors in the characterisation of overall muscle architectural properties such as mean fibre length and physiological cross-sectional area. Through dynamic musculoskeletal simulations of human walking and jumping, we demonstrate that recovered errors in fibre architecture characterisation have significant implications for quantitative predictions of in-vivo dynamics and muscle fibre function within a species. Furthermore, by applying data-subsampling simulations to comparisons of muscle function in humans and chimpanzees, we demonstrate that error magnitudes significantly impact both qualitative and quantitative assessment of muscle specialisation, potentially generating highly erroneous conclusions about the absolute and relative adaption of muscles across species and evolutionary transitions. Our findings have profound implications for how a broad diversity of research fields quantify muscle architecture and interpret muscle function.
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Affiliation(s)
- James Charles
- Structure and Motion Lab, Comparative Biomedical SciencesRoyal Veterinary CollegeHawkshead LaneHatfieldHertfordshireAL9 7TAU.K.
- Department of Musculoskeletal & Ageing Science, Institute of Life Course & Medical SciencesUniversity of LiverpoolThe William Henry Duncan Building, 6 West Derby StreetLiverpoolL7 8TXU.K.
| | - Roger Kissane
- Department of Musculoskeletal & Ageing Science, Institute of Life Course & Medical SciencesUniversity of LiverpoolThe William Henry Duncan Building, 6 West Derby StreetLiverpoolL7 8TXU.K.
| | - Tatjana Hoehfurtner
- School of Life SciencesUniversity of Lincoln, Joseph Banks LaboratoriesGreen LaneLincolnLN6 7DLU.K.
| | - Karl T. Bates
- Department of Musculoskeletal & Ageing Science, Institute of Life Course & Medical SciencesUniversity of LiverpoolThe William Henry Duncan Building, 6 West Derby StreetLiverpoolL7 8TXU.K.
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16
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Differential effects of invasive anodal trans-spinal direct current stimulation on monosynaptic EPSPs, Ia afferents excitability, and motoneuron intrinsic properties between SOD1 G93A and WT mice. Neuroscience 2022; 498:125-143. [DOI: 10.1016/j.neuroscience.2022.06.035] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Revised: 05/27/2022] [Accepted: 06/25/2022] [Indexed: 01/06/2023]
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17
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Mesquita RNO, Taylor JL, Trajano GS, Škarabot J, Holobar A, Gonçalves BAM, Blazevich AJ. Effects of reciprocal inhibition and whole-body relaxation on persistent inward currents estimated by two different methods. J Physiol 2022; 600:2765-2787. [PMID: 35436349 PMCID: PMC9325475 DOI: 10.1113/jp282765] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Accepted: 04/13/2022] [Indexed: 11/08/2022] Open
Abstract
Abstract Persistent inward currents (PICs) are crucial for initiation, acceleration, and maintenance of motoneuron firing. As PICs are highly sensitive to synaptic inhibition and facilitated by serotonin and noradrenaline, we hypothesised that both reciprocal inhibition (RI) induced by antagonist nerve stimulation and whole‐body relaxation (WBR) would reduce PICs in humans. To test this, we estimated PICs using the well‐established paired motor unit (MU) technique. High‐density surface electromyograms were recorded from gastrocnemius medialis during voluntary, isometric 20‐s ramp, plantarflexor contractions and decomposed into MU discharges to calculate delta frequency (ΔF). Moreover, another technique (VibStim), which evokes involuntary contractions proposed to result from PIC activation, was used. Plantarflexion torque and soleus activity were recorded during 33‐s Achilles tendon vibration and simultaneous 20‐Hz bouts of neuromuscular electrical stimulation (NMES) of triceps surae. ΔF was decreased by RI (n = 15, 5 females) and WBR (n = 15, 7 females). In VibStim, torque during vibration at the end of NMES and sustained post‐vibration torque were reduced by WBR (n = 19, 10 females), while other variables remained unchanged. All VibStim variables remained unaltered in RI (n = 20, 10 females). Analysis of multiple human MUs in this study demonstrates the ability of local, focused inhibition to attenuate the effects of PICs on motoneuron output during voluntary motor control. Moreover, it shows the potential to reduce PICs through non‐pharmacological, neuromodulatory interventions such as WBR. The absence of a consistent effect in VibStim might be explained by a floor effect resulting from low‐magnitude involuntary torque combined with the negative effects of the interventions. Key points Spinal motoneurons transmit signals to skeletal muscles to regulate their contraction. Motoneuron firing partly depends on their intrinsic properties such as the strength of persistent (long‐lasting) inward currents (PICs) that make motoneurons more responsive to excitatory input. In this study, we demonstrate that both reciprocal inhibition onto motoneurons and whole‐body relaxation reduce the contribution of PICs to human motoneuron firing. This was observed through analysis of the firing of single motor units during voluntary contractions. However, an alternative technique that involves tendon vibration and neuromuscular electrical stimulation to evoke involuntary contractions showed less effect. Thus, it remains unclear whether this alternative technique can be used to estimate PICs under all physiological conditions. These results improve our understanding of the mechanisms of PIC depression in human motoneurons. Potentially, non‐pharmacological interventions such as electrical stimulation or relaxation could attenuate unwanted PIC‐induced muscle contractions in conditions characterised by motoneuron hyperexcitability.
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Affiliation(s)
- Ricardo N O Mesquita
- Centre for Human Performance, School of Medical and Health Sciences, Edith Cowan University, Perth, Australia.,Neuroscience Research Australia, Sydney, Australia
| | - Janet L Taylor
- Centre for Human Performance, School of Medical and Health Sciences, Edith Cowan University, Perth, Australia.,Neuroscience Research Australia, Sydney, Australia
| | - Gabriel S Trajano
- School of Exercise and Nutrition Sciences and Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia
| | - Jakob Škarabot
- School of Sport, Exercise and Health Sciences, Loughborough University, Leicestershire, UK
| | - Aleš Holobar
- Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, Slovenia
| | - Basílio A M Gonçalves
- Griffith Centre of Biomedical and Rehabilitation Engineering (GCORE), Menzies Health Institute Queensland, Griffith University, Brisbane, Australia
| | - Anthony J Blazevich
- Centre for Human Performance, School of Medical and Health Sciences, Edith Cowan University, Perth, Australia
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18
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Sharples SA, Parker J, Vargas A, Milla-Cruz JJ, Lognon AP, Cheng N, Young L, Shonak A, Cymbalyuk GS, Whelan PJ. Contributions of h- and Na+/K+ Pump Currents to the Generation of Episodic and Continuous Rhythmic Activities. Front Cell Neurosci 2022; 15:715427. [PMID: 35185470 PMCID: PMC8855656 DOI: 10.3389/fncel.2021.715427] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2021] [Accepted: 12/29/2021] [Indexed: 12/31/2022] Open
Abstract
Developing spinal motor networks produce a diverse array of outputs, including episodic and continuous patterns of rhythmic activity. Variation in excitability state and neuromodulatory tone can facilitate transitions between episodic and continuous rhythms; however, the intrinsic mechanisms that govern these rhythms and their transitions are poorly understood. Here, we tested the capacity of a single central pattern generator (CPG) circuit with tunable properties to generate multiple outputs. To address this, we deployed a computational model composed of an inhibitory half-center oscillator (HCO). Following predictions of our computational model, we tested the contributions of key properties to the generation of an episodic rhythm produced by isolated spinal cords of the newborn mouse. The model recapitulates the diverse state-dependent rhythms evoked by dopamine. In the model, episodic bursting depended predominantly on the endogenous oscillatory properties of neurons, with Na+/K+ ATPase pump (IPump) and hyperpolarization-activated currents (Ih) playing key roles. Modulation of either IPump or Ih produced transitions between episodic and continuous rhythms and silence. As maximal activity of IPump decreased, the interepisode interval and period increased along with a reduction in episode duration. Decreasing maximal conductance of Ih decreased episode duration and increased interepisode interval. Pharmacological manipulations of Ih with ivabradine, and IPump with ouabain or monensin in isolated spinal cords produced findings consistent with the model. Our modeling and experimental results highlight key roles of Ih and IPump in producing episodic rhythms and provide insight into mechanisms that permit a single CPG to produce multiple patterns of rhythmicity.
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Affiliation(s)
- Simon A. Sharples
- School of Psychology and Neuroscience, University of St Andrews, St Andrews, United Kingdom
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
- Department of Neuroscience, University of Calgary, Calgary, AB, Canada
| | - Jessica Parker
- Neuroscience Institute, Georgia State University, Atlanta, GA, United States
| | - Alex Vargas
- Neuroscience Institute, Georgia State University, Atlanta, GA, United States
| | - Jonathan J. Milla-Cruz
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
- Department of Comparative Biology and Experimental Medicine, University of Calgary, Calgary, AB, Canada
| | - Adam P. Lognon
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
- Department of Neuroscience, University of Calgary, Calgary, AB, Canada
| | - Ning Cheng
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
- Department of Comparative Biology and Experimental Medicine, University of Calgary, Calgary, AB, Canada
| | - Leanne Young
- Department of Comparative Biology and Experimental Medicine, University of Calgary, Calgary, AB, Canada
| | - Anchita Shonak
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
- Department of Neuroscience, University of Calgary, Calgary, AB, Canada
| | - Gennady S. Cymbalyuk
- Neuroscience Institute, Georgia State University, Atlanta, GA, United States
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA, United States
- Gennady S. Cymbalyuk,
| | - Patrick J. Whelan
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
- Department of Neuroscience, University of Calgary, Calgary, AB, Canada
- Department of Comparative Biology and Experimental Medicine, University of Calgary, Calgary, AB, Canada
- *Correspondence: Patrick J. Whelan,
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19
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Laliberte AM, Farah C, Steiner KR, Tariq O, Bui TV. Changes in Sensorimotor Connectivity to dI3 Interneurons in Relation to the Postnatal Maturation of Grasping. Front Neural Circuits 2022; 15:768235. [PMID: 35153680 PMCID: PMC8828486 DOI: 10.3389/fncir.2021.768235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Accepted: 12/31/2021] [Indexed: 11/23/2022] Open
Abstract
Primitive reflexes are evident shortly after birth. Many of these reflexes disappear during postnatal development as part of the maturation of motor control. This study investigates the changes of connectivity related to sensory integration by spinal dI3 interneurons during the time in which the palmar grasp reflex gradually disappears in postnatal mice pups. Our results reveal an increase in GAD65/67-labeled terminals to perisomatic Vglut1-labeled sensory inputs contacting cervical and lumbar dI3 interneurons between postnatal day 3 and day 25. In contrast, there were no changes in the number of perisomatic Vglut1-labeled sensory inputs to lumbar and cervical dI3 interneurons other than a decrease between postnatal day 15 and day 25. Changes in postsynaptic GAD65/67-labeled inputs to dI3 interneurons were inconsistent with a role in the sustained loss of the grasp reflex. These results suggest a possible link between the maturation of hand grasp during postnatal development and increased presynaptic inhibition of sensory inputs to dI3 interneurons.
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Affiliation(s)
- Alex M. Laliberte
- Brain and Mind Research Institute, Department of Biology, University of Ottawa, Ottawa, ON, Canada
| | - Carl Farah
- Brain and Mind Research Institute, Department of Biology, University of Ottawa, Ottawa, ON, Canada
| | - Kyra R. Steiner
- Brain and Mind Research Institute, Department of Biology, University of Ottawa, Ottawa, ON, Canada
| | - Omar Tariq
- School of Biomedical Engineering, University of British Columbia, Vancouver, BC, Canada
| | - Tuan V. Bui
- Brain and Mind Research Institute, Department of Biology, University of Ottawa, Ottawa, ON, Canada
- *Correspondence: Tuan V. Bui
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