1
|
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.
Collapse
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
| |
Collapse
|
2
|
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.
Collapse
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
| |
Collapse
|
3
|
Vargova I, Kriska J, Kwok JCF, Fawcett JW, Jendelova P. Long-Term Cultures of Spinal Cord Interneurons. Front Cell Neurosci 2022; 16:827628. [PMID: 35197829 PMCID: PMC8859857 DOI: 10.3389/fncel.2022.827628] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Accepted: 01/12/2022] [Indexed: 11/25/2022] Open
Abstract
Spinal cord interneurons (SpINs) are highly diverse population of neurons that play a significant role in circuit reorganization and spontaneous recovery after spinal cord injury. Regeneration of SpIN axons across rodent spinal injuries has been demonstrated after modification of the environment and neurotrophin treatment, but development of methods to enhance the intrinsic regenerative ability of SpINs is needed. There is a lack of described in vitro models of spinal cord neurons in which to develop new regeneration treatments. For this reason, we developed a new model of mouse primary spinal cord neuronal culture in which to analyze maturation, morphology, physiology, connectivity and regeneration of identified interneurons. Isolated from E14 mice, the neurons mature over 15 days in vitro, demonstrated by expression of maturity markers, electrophysiological patch-clamp recordings, and formation of synapses. The neurons express markers of SpINs, including Tlx3, Lmx1b, Lbx1, Chx10, and Pax2. The neurons demonstrate distinct morphologies and some form perineuronal nets in long-term cultivation. Live neurons in various maturation stages were axotomized, using a 900 nm multiphoton laser and their fate was observed overnight. The percentage of axons that regenerated declined with neuronal maturity. This model of SpINs will be a valuable tool in future regenerative, developmental, and functional studies alongside existing models using cortical or hippocampal neurons.
Collapse
Affiliation(s)
- Ingrid Vargova
- Department of Neuroregeneration, Institute of Experimental Medicine, Czech Academy of Sciences, Prague, Czechia
- Second Faculty of Medicine, Charles University, Prague, Czechia
| | - Jan Kriska
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Czech Academy of Sciences, Prague, Czechia
| | - Jessica C. F. Kwok
- The Center for Reconstructive Neuroscience, Institute of Experimental Medicine, Czech Academy of Sciences, Prague, Czechia
- Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - James W. Fawcett
- The Center for Reconstructive Neuroscience, Institute of Experimental Medicine, Czech Academy of Sciences, Prague, Czechia
- John van Geest Centre for Brain Repair, Department of Clinical Neurosciences, University of Cambridge, Cambridge, United Kingdom
| | - Pavla Jendelova
- Department of Neuroregeneration, Institute of Experimental Medicine, Czech Academy of Sciences, Prague, Czechia
- Second Faculty of Medicine, Charles University, Prague, Czechia
| |
Collapse
|
4
|
Bos R, Rihan K, Quintana P, El-Bazzal L, Bernard-Marissal N, Da Silva N, Jabbour R, Mégarbané A, Bartoli M, Brocard F, Delague V. Altered action potential waveform and shorter axonal initial segment in hiPSC-derived motor neurons with mutations in VRK1. Neurobiol Dis 2022; 164:105609. [PMID: 34990802 DOI: 10.1016/j.nbd.2021.105609] [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: 04/20/2021] [Revised: 10/24/2021] [Accepted: 12/30/2021] [Indexed: 11/25/2022] Open
Abstract
We recently described new pathogenic variants in VRK1, in patients affected with distal Hereditary Motor Neuropathy associated with upper motor neurons signs. Specifically, we provided evidences that hiPSC-derived Motor Neurons (hiPSC-MN) from these patients display Cajal Bodies (CBs) disassembly and defects in neurite outgrowth and branching. We here focused on the Axonal Initial Segment (AIS) and the related firing properties of hiPSC-MNs from these patients. We found that the patient's Action Potential (AP) was smaller in amplitude, larger in duration, and displayed a more depolarized threshold while the firing patterns were not altered. These alterations were accompanied by a decrease in the AIS length measured in patients' hiPSC-MNs. These data indicate that mutations in VRK1 impact the AP waveform and the AIS organization in MNs and may ultimately lead to the related motor neuron disease.
Collapse
Affiliation(s)
- Rémi Bos
- Aix Marseille Univ, CNRS, Institut de Neurosciences de la Timone (INT), UMR 7289, Marseille, France.
| | - Khalil Rihan
- Aix Marseille Univ, Inserm, MMG, U 1251, Institut Marseille Maladies Rares (MarMaRa), Marseille, France
| | - Patrice Quintana
- Aix Marseille Univ, Inserm, MMG, U 1251, Institut Marseille Maladies Rares (MarMaRa), Marseille, France
| | - Lara El-Bazzal
- Aix Marseille Univ, Inserm, MMG, U 1251, Institut Marseille Maladies Rares (MarMaRa), Marseille, France
| | - Nathalie Bernard-Marissal
- Aix Marseille Univ, Inserm, MMG, U 1251, Institut Marseille Maladies Rares (MarMaRa), Marseille, France
| | - Nathalie Da Silva
- Aix Marseille Univ, Inserm, MMG, U 1251, Institut Marseille Maladies Rares (MarMaRa), Marseille, France
| | - Rosette Jabbour
- Neurology Division, Department of Internal Medicine, St George Hospital University Medical Center, University of Balamand, Beirut, Lebanon
| | - André Mégarbané
- Department of Human Genetics, Gilbert and RoseMary Chagoury Hospital, Lebanese American University, Byblos, Lebanon
| | - Marc Bartoli
- Aix Marseille Univ, Inserm, MMG, U 1251, Institut Marseille Maladies Rares (MarMaRa), Marseille, France
| | - Frédéric Brocard
- Aix Marseille Univ, CNRS, Institut de Neurosciences de la Timone (INT), UMR 7289, Marseille, France
| | - Valérie Delague
- Aix Marseille Univ, Inserm, MMG, U 1251, Institut Marseille Maladies Rares (MarMaRa), Marseille, France.
| |
Collapse
|
5
|
Durand J, Filipchuk A. Electrical and Morphological Properties of Developing Motoneurons in Postnatal Mice and Early Abnormalities in SOD1 Transgenic Mice. ADVANCES IN NEUROBIOLOGY 2022; 28:353-373. [PMID: 36066832 DOI: 10.1007/978-3-031-07167-6_14] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
In this chapter, we review electrical and morphological properties of lumbar motoneurons during postnatal development in wild-type (WT) and transgenic superoxide dismutase 1 (SOD1) mice, models of amyotrophic lateral sclerosis. First we showed that sensorimotor reflexes do not develop normally in transgenic SOD1G85R pups. Fictive locomotor activity recorded in in vitro whole brainstem/spinal cord preparations was not induced in these transgenic SOD1G85R mice using NMDA and 5HT in contrast to WT mice. Further, abnormal electrical properties were detected as early as the second postnatal week in lumbar motoneurons of SOD1 mice while they develop clinical symptoms several months after birth. We compared two different strains of mice (G85R and G93A) at the same postnatal period using intracellular recordings and patch clamp recordings of WT and SOD1 motoneurons. We defined three types of motoneurons according to their discharge firing pattern (transient, sustained and delayed onset firing) when motor units are not yet mature. The delayed-onset firing motoneurons had the higher rheobase compared to the transient and sustained firing groups in the WT mice. We demonstrated hypoexcitability in the delayed onset-firing motoneurons of SOD1 mice. Intracellular staining of motoneurons revealed dendritic overbranching in SOD1 lumbar motoneurons that was more pronounced in the sustained firing motoneurons. We suggested that motoneuronal hypoexcitability is an early pathological sign affecting a subset of lumbar motoneurons in the spinal cord of SOD1 mice.
Collapse
Affiliation(s)
- Jacques Durand
- Institut de Neurosciences de la Timone (INT) P3M team, Aix Marseille Université, Marseille, cedex 05, France.
| | - Anton Filipchuk
- Department for Integrative and Computational Neuroscience (ICN), Paris-Saclay Institute of Neuroscience (NeuroPSI), Gif-sur-Yvette, France
| |
Collapse
|
6
|
Sharples SA, Miles GB. Maturation of persistent and hyperpolarization-activated inward currents shapes the differential activation of motoneuron subtypes during postnatal development. eLife 2021; 10:e71385. [PMID: 34783651 PMCID: PMC8641952 DOI: 10.7554/elife.71385] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2021] [Accepted: 11/15/2021] [Indexed: 12/15/2022] Open
Abstract
The size principle underlies the orderly recruitment of motor units; however, motoneuron size is a poor predictor of recruitment amongst functionally defined motoneuron subtypes. Whilst intrinsic properties are key regulators of motoneuron recruitment, the underlying currents involved are not well defined. Whole-cell patch-clamp electrophysiology was deployed to study intrinsic properties, and the underlying currents, that contribute to the differential activation of delayed and immediate firing motoneuron subtypes. Motoneurons were studied during the first three postnatal weeks in mice to identify key properties that contribute to rheobase and may be important to establish orderly recruitment. We find that delayed and immediate firing motoneurons are functionally homogeneous during the first postnatal week and are activated based on size, irrespective of subtype. The rheobase of motoneuron subtypes becomes staggered during the second postnatal week, which coincides with the differential maturation of passive and active properties, particularly persistent inward currents. Rheobase of delayed firing motoneurons increases further in the third postnatal week due to the development of a prominent resting hyperpolarization-activated inward current. Our results suggest that motoneuron recruitment is multifactorial, with recruitment order established during postnatal development through the differential maturation of passive properties and sequential integration of persistent and hyperpolarization-activated inward currents.
Collapse
Affiliation(s)
- Simon A Sharples
- School of Psychology and Neuroscience, University of St AndrewsSt AndrewsUnited Kingdom
| | - Gareth B Miles
- School of Psychology and Neuroscience, University of St AndrewsSt AndrewsUnited Kingdom
| |
Collapse
|
7
|
Durand J, Filipchuk A, Pambo-Pambo A, Gaudel F, Liabeuf S, Brocard C, Guéritaud JP. Hypoexcitability of Motoneurons: An Early Pathological Sign in ALS. Neuroscience 2021; 465:233-234. [PMID: 34053506 DOI: 10.1016/j.neuroscience.2021.03.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Accepted: 03/15/2021] [Indexed: 10/21/2022]
Affiliation(s)
- J Durand
- Institut de Neurosciences de la Timone, Equipe P3M, UMR 7289 CNRS-AMU, Aix Marseille Université, 27 Bd Jean Moulin, 13585 Marseille Cedex 20, France
| | - A Filipchuk
- Institut de Neurosciences de la Timone, Equipe P3M, UMR 7289 CNRS-AMU, Aix Marseille Université, 27 Bd Jean Moulin, 13585 Marseille Cedex 20, France; Paris-Saclay Institute of Neuroscience (NeuroPSI), Department of Integrative and Computational Neuroscience (ICN), Centre National de la Recherche Scientifique (CNRS), 91198 Gif-sur-Yvette, France
| | - A Pambo-Pambo
- Institut de Neurosciences de la Timone, Equipe P3M, UMR 7289 CNRS-AMU, Aix Marseille Université, 27 Bd Jean Moulin, 13585 Marseille Cedex 20, France
| | - F Gaudel
- Institut de Neurosciences de la Timone, Equipe P3M, UMR 7289 CNRS-AMU, Aix Marseille Université, 27 Bd Jean Moulin, 13585 Marseille Cedex 20, France
| | - S Liabeuf
- Institut de Neurosciences de la Timone, Equipe P3M, UMR 7289 CNRS-AMU, Aix Marseille Université, 27 Bd Jean Moulin, 13585 Marseille Cedex 20, France
| | - C Brocard
- Institut de Neurosciences de la Timone, Equipe P3M, UMR 7289 CNRS-AMU, Aix Marseille Université, 27 Bd Jean Moulin, 13585 Marseille Cedex 20, France
| | - J P Guéritaud
- Institut de Neurosciences de la Timone, Equipe P3M, UMR 7289 CNRS-AMU, Aix Marseille Université, 27 Bd Jean Moulin, 13585 Marseille Cedex 20, France
| |
Collapse
|
8
|
Fogarty MJ. Neuronal Hypoexcitability and Dendritic Overbranching - The Case for Failed Compensatory Mechanisms in ALS Aetiology. Neuroscience 2021; 465:231-232. [PMID: 34053505 DOI: 10.1016/j.neuroscience.2021.02.034] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Accepted: 02/28/2021] [Indexed: 12/15/2022]
Affiliation(s)
- Matthew J Fogarty
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, USA; School of Biomedical Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia
| |
Collapse
|
9
|
Boeri J, Meunier C, Le Corronc H, Branchereau P, Timofeeva Y, Lejeune FX, Mouffle C, Arulkandarajah H, Mangin JM, Legendre P, Czarnecki A. Two opposite voltage-dependent currents control the unusual early development pattern of embryonic Renshaw cell electrical activity. eLife 2021; 10:62639. [PMID: 33899737 PMCID: PMC8139835 DOI: 10.7554/elife.62639] [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: 08/31/2020] [Accepted: 04/24/2021] [Indexed: 11/25/2022] Open
Abstract
Renshaw cells (V1R) are excitable as soon as they reach their final location next to the spinal motoneurons and are functionally heterogeneous. Using multiple experimental approaches, in combination with biophysical modeling and dynamical systems theory, we analyzed, for the first time, the mechanisms underlying the electrophysiological properties of V1R during early embryonic development of the mouse spinal cord locomotor networks (E11.5–E16.5). We found that these interneurons are subdivided into several functional clusters from E11.5 and then display an unexpected transitory involution process during which they lose their ability to sustain tonic firing. We demonstrated that the essential factor controlling the diversity of the discharge pattern of embryonic V1R is the ratio of a persistent sodium conductance to a delayed rectifier potassium conductance. Taken together, our results reveal how a simple mechanism, based on the synergy of two voltage-dependent conductances that are ubiquitous in neurons, can produce functional diversity in embryonic V1R and control their early developmental trajectory.
Collapse
Affiliation(s)
- Juliette Boeri
- INSERM, UMR_S 1130, CNRS, UMR 8246, Neuroscience Paris Seine, Institute of Biology Paris Seine, Sorbonne Univ, Paris, France
| | - Claude Meunier
- Centre de Neurosciences Intégratives et Cognition, CNRS UMR 8002, Institut Neurosciences et Cognition, Université de Paris, Paris, France
| | - Hervé Le Corronc
- INSERM, UMR_S 1130, CNRS, UMR 8246, Neuroscience Paris Seine, Institute of Biology Paris Seine, Sorbonne Univ, Paris, France.,Univ Angers, Angers, France
| | | | - Yulia Timofeeva
- Department of Computer Science and Centre for Complexity Science, University of Warwick, Coventry, United Kingdom.,Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom
| | - François-Xavier Lejeune
- Institut du Cerveau et de la Moelle Epinière, Centre de Recherche CHU Pitié-Salpétrière, INSERM, U975, CNRS, UMR 7225, Sorbonne Univ, Paris, France
| | - Christine Mouffle
- INSERM, UMR_S 1130, CNRS, UMR 8246, Neuroscience Paris Seine, Institute of Biology Paris Seine, Sorbonne Univ, Paris, France
| | - Hervé Arulkandarajah
- INSERM, UMR_S 1130, CNRS, UMR 8246, Neuroscience Paris Seine, Institute of Biology Paris Seine, Sorbonne Univ, Paris, France
| | - Jean Marie Mangin
- INSERM, UMR_S 1130, CNRS, UMR 8246, Neuroscience Paris Seine, Institute of Biology Paris Seine, Sorbonne Univ, Paris, France
| | - Pascal Legendre
- INSERM, UMR_S 1130, CNRS, UMR 8246, Neuroscience Paris Seine, Institute of Biology Paris Seine, Sorbonne Univ, Paris, France
| | - Antonny Czarnecki
- INSERM, UMR_S 1130, CNRS, UMR 8246, Neuroscience Paris Seine, Institute of Biology Paris Seine, Sorbonne Univ, Paris, France.,Univ. Bordeaux, CNRS, EPHE, INCIA, Bordeaux, France
| |
Collapse
|
10
|
Early Hypoexcitability in a Subgroup of Spinal Motoneurons in Superoxide Dismutase 1 Transgenic Mice, a Model of Amyotrophic Lateral Sclerosis. Neuroscience 2021; 463:337-353. [PMID: 33556455 DOI: 10.1016/j.neuroscience.2021.01.039] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2020] [Revised: 01/22/2021] [Accepted: 01/31/2021] [Indexed: 11/24/2022]
Abstract
In amyotrophic lateral sclerosis (ALS), large motoneurons degenerate first, causing muscle weakness. Transgenic mouse models with a mutation in the gene encoding the enzyme superoxide dismutase 1 (SOD1) revealed that motoneurons innervating the fast-fatigable muscular fibres disconnect very early. The cause of this peripheric disconnection has not yet been established. Early pathological signs were described in motoneurons during the postnatal period of SOD1 transgenic mice. Here, we investigated whether the early changes of electrical and morphological properties previously reported in the SOD1G85R strain also occur in the SOD1G93A-low expressor line with particular attention to the different subsets of motoneurons defined by their discharge firing pattern (transient, sustained, or delayed-onset firing). Intracellular staining and recording were performed in lumbar motoneurons from entire brainstem-spinal cord preparations of SOD1G93A-low transgenic mice and their WT littermates during the second postnatal week. Our results show that SOD1G93A-low motoneurons exhibit a dendritic overbranching similar to that described previously in the SOD1G85R strain at the same age. Further we found an hypoexcitability in the delayed-onset firing SOD1G93A-low motoneurons (lower gain and higher voltage threshold). We conclude that dendritic overbranching and early hypoexcitability are common features of both low expressor SOD1 mutants (G85R and G93A-low). In the high-expressor SOD1G93A line, we found hyperexcitability in the sustained firing motoneurons at the same period, suggesting a delay in compensatory mechanisms. Overall, our results suggest that the hypoexcitability indicate an early dysfunction of the delayed-onset motoneurons and could account as early pathological signs of the disease.
Collapse
|
11
|
A dynamic role for dopamine receptors in the control of mammalian spinal networks. Sci Rep 2020; 10:16429. [PMID: 33009442 PMCID: PMC7532218 DOI: 10.1038/s41598-020-73230-w] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Accepted: 09/11/2020] [Indexed: 12/21/2022] Open
Abstract
Dopamine is well known to regulate movement through the differential control of direct and indirect pathways in the striatum that express D1 and D2 receptors respectively. The spinal cord also expresses all dopamine receptors; however, how the specific receptors regulate spinal network output in mammals is poorly understood. We explore the receptor-specific mechanisms that underlie dopaminergic control of spinal network output of neonatal mice during changes in spinal network excitability. During spontaneous activity, which is a characteristic of developing spinal networks operating in a low excitability state, we found that dopamine is primarily inhibitory. We uncover an excitatory D1-mediated effect of dopamine on motoneurons and network output that also involves co-activation with D2 receptors. Critically, these excitatory actions require higher concentrations of dopamine; however, analysis of dopamine concentrations of neonates indicates that endogenous levels of spinal dopamine are low. Because endogenous levels of spinal dopamine are low, this excitatory dopaminergic pathway is likely physiologically-silent at this stage in development. In contrast, the inhibitory effect of dopamine, at low physiological concentrations is mediated by parallel activation of D2, D3, D4 and α2 receptors which is reproduced when endogenous dopamine levels are increased by blocking dopamine reuptake and metabolism. We provide evidence in support of dedicated spinal network components that are controlled by excitatory D1 and inhibitory D2 receptors that is reminiscent of the classic dopaminergic indirect and direct pathway within the striatum. These results indicate that network state is an important factor that dictates receptor-specific and therefore dose-dependent control of neuromodulators on spinal network output and advances our understanding of how neuromodulators regulate neural networks under dynamically changing excitability.
Collapse
|
12
|
|
13
|
Manuel M, Zytnicki D. Molecular and electrophysiological properties of mouse motoneuron and motor unit subtypes. CURRENT OPINION IN PHYSIOLOGY 2018; 8:23-29. [PMID: 32551406 DOI: 10.1016/j.cophys.2018.11.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The field of motoneuron and motor unit physiology in mammals has deeply evolved the last decade thanks to the parallel development of mouse genetics and transcriptomic analysis and of in vivo mouse preparations that allow intracellular electrophysiological recordings of motoneurons. We review the efforts made to investigate the electrophysiological properties of the different functional subtypes of mouse motoneurons, to decipher the mosaic of molecular markers specifically expressed in each subtype, and to elucidate which of those factors drive the identity of motoneurons.
Collapse
Affiliation(s)
- Marin Manuel
- Center for Neurophysics, Physiology and Pathology, Paris Descartes University, CNRS UMR 8119, Paris, France
| | - Daniel Zytnicki
- Center for Neurophysics, Physiology and Pathology, Paris Descartes University, CNRS UMR 8119, Paris, France
| |
Collapse
|
14
|
Bos R, Harris-Warrick RM, Brocard C, Demianenko LE, Manuel M, Zytnicki D, Korogod SM, Brocard F. Kv1.2 Channels Promote Nonlinear Spiking Motoneurons for Powering Up Locomotion. Cell Rep 2018; 22:3315-3327. [PMID: 29562186 PMCID: PMC5907934 DOI: 10.1016/j.celrep.2018.02.093] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Revised: 02/02/2018] [Accepted: 02/23/2018] [Indexed: 01/15/2023] Open
Abstract
Spinal motoneurons are endowed with nonlinear spiking behaviors manifested by a spike acceleration whose functional significance remains uncertain. Here, we show in rodent lumbar motoneurons that these nonlinear spiking properties do not rely only on activation of dendritic nifedipine-sensitive L-type Ca2+ channels, as assumed for decades, but also on the slow inactivation of a nifedipine-sensitive K+ current mediated by Kv1.2 channels that are highly expressed in axon initial segments. Specifically, the pharmacological and computational inhibition of Kv1.2 channels occluded the spike acceleration of rhythmically active motoneurons and the correlated slow buildup of rhythmic motor output recorded at the onset of locomotor-like activity. This study demonstrates that slow inactivation of Kv1.2 channels provides a potent gain control mechanism in mammalian spinal motoneurons and has a behavioral role in enhancing locomotor drive during the transition from immobility to steady-state locomotion.
Collapse
Affiliation(s)
- Rémi Bos
- Institut de Neurosciences de la Timone (UMR7289), Aix-Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France
| | | | - Cécile Brocard
- Institut de Neurosciences de la Timone (UMR7289), Aix-Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France
| | - Liliia E Demianenko
- Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kiev, Ukraine
| | - Marin Manuel
- Centre de Neurophysique, Physiologie et Pathologie, UMR 8119, CNRS/Université Paris Descartes, 45 rue des Saints-Pères, 75270 Paris Cedex 06, France
| | - Daniel Zytnicki
- Centre de Neurophysique, Physiologie et Pathologie, UMR 8119, CNRS/Université Paris Descartes, 45 rue des Saints-Pères, 75270 Paris Cedex 06, France
| | - Sergiy M Korogod
- Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kiev, Ukraine
| | - Frédéric Brocard
- Institut de Neurosciences de la Timone (UMR7289), Aix-Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France.
| |
Collapse
|
15
|
Lombardo J, Harrington MA. Nonreciprocal mechanisms in up- and downregulation of spinal motoneuron excitability by modulators of KCNQ/Kv7 channels. J Neurophysiol 2016; 116:2114-2124. [PMID: 27512022 DOI: 10.1152/jn.00446.2016] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Accepted: 08/05/2016] [Indexed: 12/11/2022] Open
Abstract
KCNQ/Kv7 channels form a slow noninactivating K+ current, also known as the M current. They activate in the subthreshold range of membrane potentials and regulate different aspects of excitability in neurons of the central nervous system. In spinal motoneurons (MNs), KCNQ/Kv7 channels have been identified in the somata, axonal initial segment, and nodes of Ranvier, where they generate a slow, noninactivating, K+ current sensitive to both muscarinic receptor-mediated inhibition and KCNQ/Kv7 channel blockers. In this study, we thoroughly reevaluated the function of up- and downregulation of KCNQ/Kv7 channels in mouse immature spinal MNs. Using electrophysiological techniques together with specific pharmacological modulators of the activity of KCNQ/Kv7 channels, we show that enhancement of the activity of these channels decreases the excitability of spinal MNs in mouse neonates. This action on MNs results from a combination of hyperpolarization of the resting membrane potential, a decrease in the input resistance, and depolarization of the voltage threshold. On the other hand, the effect of inhibition of KCNQ/Kv7 channels suggested that these channels play a limited role in regulating basal excitability. Computer simulations confirmed that pharmacological enhancement of KCNQ/Kv7 channel activity decreases excitability and also suggested that the effects of inhibition of KCNQ/Kv7 channels on the excitability of spinal MNs do not depend on a direct effect in these neurons but likely on spinal cord synaptic partners. These results indicate that KCNQ/Kv7 channels have a fundamental role in the modulation of the excitability of spinal MNs acting both in these neurons and in their local presynaptic partners.
Collapse
Affiliation(s)
- Joseph Lombardo
- Department of Biological Sciences, Delaware State University, Dover, Delaware
| | | |
Collapse
|
16
|
Wakefield HE, Fregosi RF, Fuglevand AJ. Current injection and receptor-mediated excitation produce similar maximal firing rates in hypoglossal motoneurons. J Neurophysiol 2016; 115:1307-13. [PMID: 26745245 PMCID: PMC4808106 DOI: 10.1152/jn.00848.2015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 12/21/2015] [Indexed: 11/22/2022] Open
Abstract
The maximum firing rates of motoneurons (MNs), activated in response to synaptic drive, appear to be much lower than that elicited by current injection. It could be that the decrease in input resistance associated with increased synaptic activity (but not current injection) might blunt overall changes in membrane depolarization and thereby limit spike-frequency output. To test this idea, we recorded, in the same cells, maximal firing responses to current injection and to synaptic activation. We prepared 300 μm medullary slices in neonatal rats that contained hypoglossal MNs and used whole-cell patch-clamp electrophysiology to record their maximum firing rates in response to triangular-ramp current injections and to glutamate receptor-mediated excitation. Brief pressure pulses of high-concentration glutamate led to significant depolarization, high firing rates, and temporary cessation of spiking due to spike inactivation. In the same cells, we applied current clamp protocols that approximated the time course of membrane potential change associated with glutamate application and with peak current levels large enough to cause spike inactivation. Means (SD) of maximum firing rates obtained in response to glutamate application were nearly identical to those obtained in response to ramp current injection [glutamate 47.1 ± 12.0 impulses (imp)/s, current injection 47.5 ± 11.2 imp/s], even though input resistance was 40% less during glutamate application compared with current injection. Therefore, these data suggest that the reduction in input resistance associated with receptor-mediated excitation does not, by itself, limit the maximal firing rate responses in MNs.
Collapse
Affiliation(s)
- Hilary E Wakefield
- Department of Physiology, College of Medicine, Arizona Health Sciences Center, University of Arizona, Tucson, Arizona; and
| | - Ralph F Fregosi
- Department of Physiology, College of Medicine, Arizona Health Sciences Center, University of Arizona, Tucson, Arizona; and Department of Neuroscience, University of Arizona, Tucson, Arizona
| | - Andrew J Fuglevand
- Department of Physiology, College of Medicine, Arizona Health Sciences Center, University of Arizona, Tucson, Arizona; and Department of Neuroscience, University of Arizona, Tucson, Arizona
| |
Collapse
|