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Thorstensen JR, Henderson TT, Kavanagh JJ. Serotonergic and noradrenergic contributions to motor cortical and spinal motoneuronal excitability in humans. Neuropharmacology 2024; 242:109761. [PMID: 37838337 DOI: 10.1016/j.neuropharm.2023.109761] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2023] [Revised: 10/05/2023] [Accepted: 10/11/2023] [Indexed: 10/16/2023]
Abstract
Animal models indicate that motor behaviour is shaped by monoamine neuromodulators released diffusely throughout the brain and spinal cord. As an alternative to conducting a single study to explore the effects of neuromodulators on the human motor system, we have identified and collated human experiments investigating motor effects of well-characterised drugs that act on serotonergic and noradrenergic networks. In doing so, we present strong neuropharmacology evidence that human motor pathways are affected by neuromodulators across both healthy and clinical populations, insight that cannot be determined from a single reductionist experiment. We have focused our review on the effects that monoaminergic drugs have on muscle responses to non-invasive stimulation of the motor cortex and peripheral nerves, and other closely related tests of motoneuron excitability, and discuss how these measurement techniques elucidate the effects of neuromodulators at motor cortical and spinal motoneuronal levels. Although there is some heterogeneity in study methods, we find drugs acting to enhance extracellular concentrations of serotonin tend to reduce the excitability of the human motor cortex, and enhanced extracellular concentrations of noradrenaline increases motor cortical excitability by enhancing intracortical facilitation and reducing inhibition. Both monoamines tend to enhance the excitability of spinal motoneurons. Overall, this review details the importance of neuromodulators for the output of human motor pathways and suggests that commonly prescribed monoaminergic drugs target the motor system in addition to their typical psychiatric/neurological indications.
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Affiliation(s)
- Jacob R Thorstensen
- School of Biomedical Sciences, The University of Queensland, Brisbane, Australia.
| | - Tyler T Henderson
- Menzies Health Institute Queensland, Griffith University, Gold Coast, Australia
| | - Justin J Kavanagh
- Menzies Health Institute Queensland, Griffith University, Gold Coast, Australia
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2
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Khairuddin S, Lim WL, Aquili L, Tsui KC, Tse ACK, Jayalath S, Varma R, Sharp T, Benazzouz A, Steinbusch H, Blokland A, Temel Y, Lim LW. Prelimbic Cortical Stimulation Induces Antidepressant-like Responses through Dopaminergic-Dependent and -Independent Mechanisms. Cells 2023; 12:1449. [PMID: 37296570 PMCID: PMC10253143 DOI: 10.3390/cells12111449] [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: 04/05/2023] [Revised: 05/16/2023] [Accepted: 05/18/2023] [Indexed: 06/12/2023] Open
Abstract
High-frequency stimulation (HFS) is a promising therapy for patients with depression. However, the mechanisms underlying the HFS-induced antidepressant-like effects on susceptibility and resilience to depressive-like behaviors remain obscure. Given that dopaminergic neurotransmission has been found to be disrupted in depression, we investigated the dopamine(DA)-dependent mechanism of the antidepressant-like effects of HFS of the prelimbic cortex (HFS PrL). We performed HFS PrL in a rat model of mild chronic unpredictable stress (CUS) together with 6-hydroxydopamine lesioning in the dorsal raphe nucleus (DRN) and ventral tegmental area (VTA). Animals were assessed for anxiety, anhedonia, and behavioral despair. We also examined levels of corticosterone, hippocampal neurotransmitters, neuroplasticity-related proteins, and morphological changes in dopaminergic neurons. We found 54.3% of CUS animals exhibited decreased sucrose consumption and were designated as CUS-susceptible, while the others were designated CUS-resilient. HFS PrL in both the CUS-susceptible and CUS-resilient animals significantly increased hedonia, reduced anxiety, decreased forced swim immobility, enhanced hippocampal DA and serotonin levels, and reduced corticosterone levels when compared with the respective sham groups. The hedonic-like effects were abolished in both DRN- and VTA-lesioned groups, suggesting the effects of HFS PrL are DA-dependent. Interestingly, VTA-lesioned sham animals had increased anxiety and forced swim immobility, which was reversed by HFS PrL. The VTA-lesioned HFS PrL animals also had elevated DA levels, and reduced p-p38 MAPK and NF-κB levels when compared to VTA-lesioned sham animals. These findings suggest that HFS PrL in stressed animals leads to profound antidepressant-like responses possibly through both DA-dependent and -independent mechanisms.
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Affiliation(s)
- Sharafuddin Khairuddin
- Neuromodulation Laboratory, School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
| | - Wei Ling Lim
- Neuromodulation Laboratory, School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
- Department of Biological Sciences, Sunway University, Bandar Sunway, Petaling Jaya 47500, Malaysia
| | - Luca Aquili
- Neuromodulation Laboratory, School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
- Discipline of Psychology, College of Health and Education, Murdoch University, Perth 6150, Australia
| | - Ka Chun Tsui
- Neuromodulation Laboratory, School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
| | - Anna Chung-Kwan Tse
- Neuromodulation Laboratory, School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
| | - Shehani Jayalath
- Neuromodulation Laboratory, School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
| | - Ruhani Varma
- Neuromodulation Laboratory, School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
| | - Trevor Sharp
- Department of Pharmacology, University of Oxford, Oxford OX1 3QT, UK
| | - Abdelhamid Benazzouz
- CNRS UMR5293, Institute of Neurodegenerative Diseases, University de Bordeaux, 33000 Bordeaux, France
| | - Harry Steinbusch
- Department of Neuroscience, Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Arjan Blokland
- Department of Neuropsychology and Psychopharmacology, Faculty of Psychology and Neuroscience, Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Yasin Temel
- Department of Neuroscience, Maastricht University, 6229 ER Maastricht, The Netherlands
- Department of Neurosurgery, Maastricht University, 6229 HX Maastricht, The Netherlands
| | - Lee Wei Lim
- Neuromodulation Laboratory, School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
- Department of Biological Sciences, Sunway University, Bandar Sunway, Petaling Jaya 47500, Malaysia
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3
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Kavanagh JJ, Taylor JL. Voluntary activation of muscle in humans: does serotonergic neuromodulation matter? J Physiol 2022; 600:3657-3670. [PMID: 35864781 PMCID: PMC9541597 DOI: 10.1113/jp282565] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Accepted: 07/12/2022] [Indexed: 11/08/2022] Open
Abstract
Ionotropic inputs to motoneurones have the capacity to depolarise and hyperpolarise the motoneurone, whereas neuromodulatory inputs control the state of excitability of the motoneurone. Intracellular recordings of motoneurones from in vitro and in situ animal preparations have provided extraordinary insight into the mechanisms that underpin how neuromodulators regulate neuronal excitability. However, far fewer studies have attempted to translate the findings from cellular and molecular studies into a human model. In this review, we focus on the role that serotonin plays in muscle activation in humans. Serotonin (5-HT) is a potent regulator of neuronal firing rates which can influence the force that can be generated by muscles during voluntary contractions. We firstly outline structural and functional characteristics of the serotonergic system, and then describe how motoneurone discharge can be facilitated and suppressed depending on the 5-HT receptor subtype that is activated. We then provide a narrative on how 5-HT effects can influence voluntary activation during muscle contractions in humans, and detail how 5-HT may be a mediator of exercise-induced fatigue that arises from the central nervous system. Abstract figure legend Inputs to neuromodulatory receptors on motoneurones, such as those involved in the serotonergic system, modify the motoneuroneâ¿¿s responsiveness to ionotropic input. The release of serotonin (5-HT) into the spinal cord is linked to the level of motor activity being performed, where 5-HT can increase the discharge rate of motoneurones via excitatory 5-HT receptors on the soma and dendrites. This in turn can lead to increased voluntary muscle activation (VA) and maximal force generation. However, intense release of 5-HT onto motoneurones may lead to a spill over of 5-HT into extracellular compartments to activate inhibitory 5-HT receptors on the axon initial segment. This can cause a reduction in motoneurone discharge rate, thus decreasing VA and maximal force generation. To gain insight into the serotonergic contributions to muscle activation in humans, pharmacological interventions have been employed to enhance the concentration of 5-HT in the central nervous system or activate selective 5-HT receptors. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Justin J Kavanagh
- Menzies Health Institute Queensland, Griffith University, Gold Coast, Australia
| | - Janet L Taylor
- School of Medical and Health Sciences, Edith Cowan University, Perth, Australia.,Neuroscience Research Australia, Sydney, Australia
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Tseng CT, Gaulding SJ, Dancel CLE, Thorn CA. Local activation of α2 adrenergic receptors is required for vagus nerve stimulation induced motor cortical plasticity. Sci Rep 2021; 11:21645. [PMID: 34737352 PMCID: PMC8568982 DOI: 10.1038/s41598-021-00976-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Accepted: 10/20/2021] [Indexed: 11/09/2022] Open
Abstract
Vagus nerve stimulation (VNS) paired with rehabilitation training is emerging as a potential treatment for improving recovery of motor function following stroke. In rats, VNS paired with skilled forelimb training results in significant reorganization of the somatotopic cortical motor map; however, the mechanisms underlying this form of VNS-dependent plasticity remain unclear. Recent studies have shown that VNS-driven cortical plasticity is dependent on noradrenergic innervation of the neocortex. In the central nervous system, noradrenergic α2 receptors (α2-ARs) are widely expressed in the motor cortex and have been critically implicated in synaptic communication and plasticity. In current study, we examined whether activation of cortical α2-ARs is necessary for VNS-driven motor cortical reorganization to occur. Consistent with previous studies, we found that VNS paired with motor training enlarges the map representation of task-relevant musculature in the motor cortex. Infusion of α2-AR antagonists into M1 blocked VNS-driven motor map reorganization from occurring. Our results suggest that local α2-AR activation is required for VNS-induced cortical reorganization to occur, providing insight into the mechanisms that may underlie the neuroplastic effects of VNS therapy.
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Affiliation(s)
- Ching-Tzu Tseng
- School of Behavioral and Brain Sciences, University of Texas at Dallas, 800 W. Campbell Rd, Richardson, TX, 75080, USA
| | - Solomon J Gaulding
- School of Behavioral and Brain Sciences, University of Texas at Dallas, 800 W. Campbell Rd, Richardson, TX, 75080, USA
| | - Canice Lei E Dancel
- School of Behavioral and Brain Sciences, University of Texas at Dallas, 800 W. Campbell Rd, Richardson, TX, 75080, USA
| | - Catherine A Thorn
- School of Behavioral and Brain Sciences, University of Texas at Dallas, 800 W. Campbell Rd, Richardson, TX, 75080, USA.
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Melo L, Mosayebi-Samani M, Ghanavati E, Nitsche MA, Kuo MF. Dosage-Dependent Impact of Acute Serotonin Enhancement on Transcranial Direct Current Stimulation Effects. Int J Neuropsychopharmacol 2021; 24:787-797. [PMID: 34106250 PMCID: PMC8538892 DOI: 10.1093/ijnp/pyab035] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/14/2021] [Revised: 05/27/2021] [Accepted: 06/07/2021] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND The serotonergic system has an important impact on basic physiological and higher brain functions. Acute and chronic enhancement of serotonin levels via selective serotonin reuptake inhibitor administration impacts neuroplasticity in humans, as shown by its effects on cortical excitability alterations induced by non-invasive brain stimulation, including transcranial direct current stimulation (tDCS). Nevertheless, the interaction between serotonin activation and neuroplasticity is not fully understood, particularly considering dose-dependent effects. Our goal was to explore dosage-dependent effects of acute serotonin enhancement on stimulation-induced plasticity in healthy individuals. METHODS Twelve healthy adults participated in 7 sessions conducted in a crossover, partially double-blinded, randomized, and sham-controlled study design. Anodal and cathodal tDCS was applied to the motor cortex under selective serotonin reuptake inhibitor (20 mg/40 mg citalopram) or placebo medication. Motor cortex excitability was monitored by single-pulse transcranial magnetic stimulation. RESULTS Under placebo medication, anodal tDCS enhanced, and cathodal tDCS reduced, excitability for approximately 60-120 minutes after the intervention. Citalopram enhanced and prolonged the facilitation induced by anodal tDCS regardless of the dosage while turning cathodal tDCS-induced excitability diminution into facilitation. For the latter, prolonged effects were observed when 40 mg was administrated. CONCLUSIONS Acute serotonin enhancement modulates tDCS after-effects and has largely similar modulatory effects on motor cortex neuroplasticity regardless of the specific dosage. A minor dosage-dependent effect was observed only for cathodal tDCS. The present findings support the concept of boosting the neuroplastic effects of anodal tDCS by serotonergic enhancement, a potential clinical approach for the treatment of neurological and psychiatric disorders.
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Affiliation(s)
- Lorena Melo
- Department of Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors (IfADo), Dortmund, Germany,International Graduate School of Neuroscience (IGSN), Ruhr-University Bochum, Germany
| | - Mohsen Mosayebi-Samani
- Department of Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors (IfADo), Dortmund, Germany
| | - Elham Ghanavati
- Department of Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors (IfADo), Dortmund, Germany
| | - Michael A Nitsche
- Department of Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors (IfADo), Dortmund, Germany,Department of Neurology, University Medical Hospital Bergmannsheil, Bochum, Germany
| | - Min-Fang Kuo
- Department of Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors (IfADo), Dortmund, Germany,Correspondence: Min-Fang Kuo, MD, PhD, Department of Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors (IfADo), Ardeystraße 67, 44139 Dortmund, Germany ()
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Jin B, Alam M, Tierno A, Zhong H, Roy RR, Gerasimenko Y, Lu DC, Edgerton VR. Serotonergic Facilitation of Forelimb Functional Recovery in Rats with Cervical Spinal Cord Injury. Neurotherapeutics 2021; 18:1226-1243. [PMID: 33420588 PMCID: PMC8423890 DOI: 10.1007/s13311-020-00974-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/14/2020] [Indexed: 10/22/2022] Open
Abstract
Serotonergic agents can improve the recovery of motor ability after a spinal cord injury. Herein, we compare the effects of buspirone, a 5-HT1A receptor partial agonist, to fluoxetine, a selective serotonin reuptake inhibitor, on forelimb motor function recovery after a C4 bilateral dorsal funiculi crush in adult female rats. After injury, single pellet reaching performance and forelimb muscle activity decreased in all rats. From 1 to 6 weeks after injury, rats were tested on these tasks with and without buspirone (1-2 mg/kg) or fluoxetine (1-5 mg/kg). Reaching and grasping success rates of buspirone-treated rats improved rapidly within 2 weeks after injury and plateaued over the next 4 weeks of testing. Electromyography (EMG) from selected muscles in the dominant forelimb showed that buspirone-treated animals used new reaching strategies to achieve success after the injury. However, forelimb performance dramatically decreased within 2 weeks of buspirone withdrawal. In contrast, fluoxetine treatment resulted in a more progressive rate of improvement in forelimb performance over 8 weeks after injury. Neither buspirone nor fluoxetine significantly improved quadrupedal locomotion on the horizontal ladder test. The improved accuracy of reaching and grasping, patterns of muscle activity, and increased excitability of spinal motor-evoked potentials after buspirone administration reflect extensive reorganization of connectivity within and between supraspinal and spinal sensory-motor netxcopy works. Thus, both serotonergic drugs, buspirone and fluoxetine, neuromodulated these networks to physiological states that enabled markedly improved forelimb function after cervical spinal cord injury.
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Affiliation(s)
- Benita Jin
- Department of Integrative Biology and Physiology, University of California, Los Angeles, 610 Charles E. Young Drive, Los Angeles, CA, 90095-1527, USA
| | - Monzurul Alam
- Department of Integrative Biology and Physiology, University of California, Los Angeles, 610 Charles E. Young Drive, Los Angeles, CA, 90095-1527, USA
| | - Alexa Tierno
- Department of Integrative Biology and Physiology, University of California, Los Angeles, 610 Charles E. Young Drive, Los Angeles, CA, 90095-1527, USA
| | - Hui Zhong
- Department of Integrative Biology and Physiology, University of California, Los Angeles, 610 Charles E. Young Drive, Los Angeles, CA, 90095-1527, USA
| | - Roland R Roy
- Department of Integrative Biology and Physiology, University of California, Los Angeles, 610 Charles E. Young Drive, Los Angeles, CA, 90095-1527, USA
- Brain Research Institute, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Yury Gerasimenko
- Department of Integrative Biology and Physiology, University of California, Los Angeles, 610 Charles E. Young Drive, Los Angeles, CA, 90095-1527, USA
- Pavlov Institute of Physiology, St. Petersburg, 199034, Russia
- Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, 420006, Russia
| | - Daniel C Lu
- Department of Neurosurgery, University of California, Los Angeles, CA, 90095, USA
| | - V Reggie Edgerton
- Department of Integrative Biology and Physiology, University of California, Los Angeles, 610 Charles E. Young Drive, Los Angeles, CA, 90095-1527, USA.
- Brain Research Institute, University of California, Los Angeles, Los Angeles, CA, 90095, USA.
- Department of Neurosurgery, University of California, Los Angeles, CA, 90095, USA.
- Department of Neurobiology, University of California, Los Angeles, CA, 90095, USA.
- Faculty of Science, The Centre for Neuroscience and Regenerative Medicine, University of Technology Sydney, Ultimo, NSW, Australia.
- Institut Guttmann, Hospital de Neurorehabilitació, Institut Universitari adscript a la Universitat Autònoma de Barcelona, 08916, Badalona, Spain.
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Brunet A, Stuart-Lopez G, Burg T, Scekic-Zahirovic J, Rouaux C. Cortical Circuit Dysfunction as a Potential Driver of Amyotrophic Lateral Sclerosis. Front Neurosci 2020; 14:363. [PMID: 32410944 PMCID: PMC7201269 DOI: 10.3389/fnins.2020.00363] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2019] [Accepted: 03/25/2020] [Indexed: 12/11/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that affects selected cortical and spinal neuronal populations, leading to progressive paralysis and death. A growing body of evidences suggests that the disease may originate in the cerebral cortex and propagate in a corticofugal manner. In particular, transcranial magnetic stimulation studies revealed that ALS patients present with early cortical hyperexcitability arising from a combination of increased excitability and decreased inhibition. Here, we discuss the possibility that initial cortical circuit dysfunction might act as the main driver of ALS onset and progression, and review recent functional, imaging and transcriptomic studies conducted on ALS patients, along with electrophysiological, pathological and transcriptomic studies on animal and cellular models of the disease, in order to evaluate the potential cellular and molecular origins of cortical hyperexcitability in ALS.
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Affiliation(s)
| | | | | | | | - Caroline Rouaux
- INSERM UMR_S 1118, Mécanismes Centraux et Périphériques de la Neurodégénérescence, Faculté de Médecine, Université de Strasbourg, Strasbourg, France
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Balbinot G, Schuch CP. Compensatory Relearning Following Stroke: Cellular and Plasticity Mechanisms in Rodents. Front Neurosci 2019; 12:1023. [PMID: 30766468 PMCID: PMC6365459 DOI: 10.3389/fnins.2018.01023] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Accepted: 12/18/2018] [Indexed: 11/13/2022] Open
Abstract
von Monakow’s theory of diaschisis states the functional ‘standstill’ of intact brain regions that are remote from a damaged area, often implied in recovery of function. Accordingly, neural plasticity and activity patterns related to recovery are also occurring at the same regions. Recovery relies on plasticity in the periinfarct and homotopic contralesional regions and involves relearning to perform movements. Seeking evidence for a relearning mechanism following stroke, we found that rodents display many features that resemble classical learning and memory mechanisms. Compensatory relearning is likely to be accompanied by gradual shaping of these regions and pathways, with participating neurons progressively adapting cortico-striato-thalamic activity and synaptic strengths at different cortico-thalamic loops – adapting function relayed by the striatum. Motor cortex functional maps are progressively reinforced and shaped by these loops as the striatum searches for different functional actions. Several cortical and striatal cellular mechanisms that influence motor learning may also influence post-stroke compensatory relearning. Future research should focus on how different neuromodulatory systems could act before, during or after rehabilitation to improve stroke recovery.
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Affiliation(s)
- Gustavo Balbinot
- Brain Institute, Universidade Federal do Rio Grande do Norte, Natal, Brazil
| | - Clarissa Pedrini Schuch
- Graduate Program in Rehabilitation Sciences, Universidade Federal de Ciências da Saúde de Porto Alegre (UFCSPA), Porto Alegre, Brazil
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Holschbach MA, Vitale EM, Lonstein JS. Serotonin-specific lesions of the dorsal raphe disrupt maternal aggression and caregiving in postpartum rats. Behav Brain Res 2018; 348:53-64. [PMID: 29653128 DOI: 10.1016/j.bbr.2018.04.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Revised: 03/28/2018] [Accepted: 04/06/2018] [Indexed: 11/29/2022]
Abstract
The behavioral modifications associated with early motherhood, which include high aggression, caring for the young, and low anxiety, are all affected by acute pharmacological manipulation of serotonin signaling. However, the effects on all these behaviors of permanently disrupting serotonin signaling from one of its primary sources, the dorsal raphe nucleus (DR), have not been examined in detail. To address this, serotonin-specific lesions centered on the dorsomedial DR (DRdm; DR subregion strongly implicated in emotional behaviors) were induced at mid-pregnancy (day 15) or early postpartum (day 2) in rats using a saporin-conjugated neurotoxin targeting the serotonin transporter (Anti-SERT-SAP). Prepartum or postpartum Anti-SERT-SAP reduced DRdm serotonin immunoreactivity by ∼40-65%, and postpartum Anti-SERT-SAP also reduced it in the ventromedial and lateral wings of the DR, as well as in the median raphe. Serotonin-immunoreactive fibers were significantly reduced in the anterior hypothalamus, but not medial preoptic area, of lesioned dams. Pre- or postpartum lesions both greatly reduced maternal aggression, but while prepartum lesions did not affect later undisturbed maternal caregiving, the larger postpartum lesions prevented the postpartum decline in kyphotic nursing and reduced pup licking. Serotonin lesions did not affect pup retrieval, but the prepartum lesions temporarily increased maternal hovering over and licking the pups observed immediately after the disruptive retrieval tests. Dams' anxiety-like behaviors and litter weight gains were unaffected by the lesions. These findings suggest that DRdm serotonin projecting to the AH is particularly critical for maternal aggression, but that more widespread disruption of midbrain raphe serotonin is necessary to greatly impair maternal caregiving. Postpartum anxiety may rely more on other neurochemical systems or different midbrain serotonergic cell populations.
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Affiliation(s)
- M Allie Holschbach
- Neuroscience Program, 108 Giltner Hall, Michigan State University, East Lansing, MI, 48824, USA
| | - Erika M Vitale
- Department of Psychology, 108 Giltner Hall, Michigan State University, East Lansing, MI, 48824, USA
| | - Joseph S Lonstein
- Neuroscience Program, 108 Giltner Hall, Michigan State University, East Lansing, MI, 48824, USA; Department of Psychology, 108 Giltner Hall, Michigan State University, East Lansing, MI, 48824, USA.
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Vitrac C, Benoit-Marand M. Monoaminergic Modulation of Motor Cortex Function. Front Neural Circuits 2017; 11:72. [PMID: 29062274 PMCID: PMC5640772 DOI: 10.3389/fncir.2017.00072] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2017] [Accepted: 09/19/2017] [Indexed: 01/09/2023] Open
Abstract
Elaboration of appropriate responses to behavioral situations rests on the ability of selecting appropriate motor outcomes in accordance to specific environmental inputs. To this end, the primary motor cortex (M1) is a key structure for the control of voluntary movements and motor skills learning. Subcortical loops regulate the activity of the motor cortex and thus contribute to the selection of appropriate motor plans. Monoamines are key mediators of arousal, attention and motivation. Their firing pattern enables a direct encoding of different states thus promoting or repressing the selection of actions adapted to the behavioral context. Monoaminergic modulation of motor systems has been extensively studied in subcortical circuits. Despite evidence of converging projections of multiple neurotransmitters systems in the motor cortex pointing to a direct modulation of local circuits, their contribution to the execution and learning of motor skills is still poorly understood. Monoaminergic dysregulation leads to impaired plasticity and motor function in several neurological and psychiatric conditions, thus it is critical to better understand how monoamines modulate neural activity in the motor cortex. This review aims to provide an update of our current understanding on the monoaminergic modulation of the motor cortex with an emphasis on motor skill learning and execution under physiological conditions.
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Affiliation(s)
- Clément Vitrac
- Laboratoire de Neurosciences Expérimentales et Cliniques, INSERM U1084, Poitiers, France.,Laboratoire de Neurosciences Expérimentales et Cliniques, Université de Poitiers, Poitiers, France
| | - Marianne Benoit-Marand
- Laboratoire de Neurosciences Expérimentales et Cliniques, INSERM U1084, Poitiers, France.,Laboratoire de Neurosciences Expérimentales et Cliniques, Université de Poitiers, Poitiers, France
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El Oussini H, Scekic-Zahirovic J, Vercruysse P, Marques C, Dirrig-Grosch S, Dieterlé S, Picchiarelli G, Sinniger J, Rouaux C, Dupuis L. Degeneration of serotonin neurons triggers spasticity in amyotrophic lateral sclerosis. Ann Neurol 2017; 82:444-456. [PMID: 28856708 DOI: 10.1002/ana.25030] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Revised: 08/22/2017] [Accepted: 08/24/2017] [Indexed: 12/11/2022]
Abstract
OBJECTIVE Spasticity occurs in a wide range of neurological diseases, including neurodegenerative diseases, after trauma, and after stroke, and is characterized by increased reflexes leading to muscle hypertonia. Spasticity is a painful symptom and can severely restrict everyday life, but might also participate in maintaining a low level of motor function in severely impaired patients. Constitutive activity of the serotonin receptors 5-HT2B/C is required for the development of spasticity after spinal cord injury and during amyotrophic lateral sclerosis (ALS). We sought here to provide direct evidence for a role of brainstem serotonin neurons in spasticity. METHODS SOD1(G37R) mice expressing a conditional allele of an ALS-linked SOD1 mutation were crossed with Tph2-Cre mice expressing Cre in serotonergic neurons. Measurement of long-lasting reflex using electromyography, behavioral follow-up, and histological techniques was used to characterize spasticity and motor phenotype. RESULTS Deleting mutant SOD1 expression selectively in brainstem serotonin neurons was sufficient to rescue loss of TPH2 immunoreactivity and largely preserve serotonin innervation of motor neurons in the spinal cord. Furthermore, this abrogated constitutive activity of 5-HT2B/C receptors and abolished spasticity in end-stage mice. Consistent with spasticity mitigating motor symptoms, selective deletion worsened motor function and accelerated the onset of paralysis. INTERPRETATION Degeneration of serotonin neurons is necessary to trigger spasticity through the 5-HT2B/C receptor. The wide range of drugs targeting the serotonergic system could be useful to treat spasticity in neurological diseases. Ann Neurol 2017;82:444-456.
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Affiliation(s)
- Hajer El Oussini
- Faculty of medicine, Inserm UMR-S1118, France.,Fédération de médecine translationnelle, Université de Strasbourg, France
| | - Jelena Scekic-Zahirovic
- Faculty of medicine, Inserm UMR-S1118, France.,Fédération de médecine translationnelle, Université de Strasbourg, France
| | - Pauline Vercruysse
- Faculty of medicine, Inserm UMR-S1118, France.,Fédération de médecine translationnelle, Université de Strasbourg, France.,Department of Neurology, University of Ulm, Ulm, Germany
| | - Christine Marques
- Faculty of medicine, Inserm UMR-S1118, France.,Fédération de médecine translationnelle, Université de Strasbourg, France
| | - Sylvie Dirrig-Grosch
- Faculty of medicine, Inserm UMR-S1118, France.,Fédération de médecine translationnelle, Université de Strasbourg, France
| | - Stéphane Dieterlé
- Faculty of medicine, Inserm UMR-S1118, France.,Fédération de médecine translationnelle, Université de Strasbourg, France
| | - Gina Picchiarelli
- Faculty of medicine, Inserm UMR-S1118, France.,Fédération de médecine translationnelle, Université de Strasbourg, France
| | - Jérôme Sinniger
- Faculty of medicine, Inserm UMR-S1118, France.,Fédération de médecine translationnelle, Université de Strasbourg, France
| | - Caroline Rouaux
- Faculty of medicine, Inserm UMR-S1118, France.,Fédération de médecine translationnelle, Université de Strasbourg, France
| | - Luc Dupuis
- Faculty of medicine, Inserm UMR-S1118, France.,Fédération de médecine translationnelle, Université de Strasbourg, France
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12
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Boychuk JA, Farrell JS, Palmer LA, Singleton AC, Pittman QJ, Teskey GC. HCN channels segregate stimulation-evoked movement responses in neocortex and allow for coordinated forelimb movements in rodents. J Physiol 2016; 595:247-263. [PMID: 27568501 DOI: 10.1113/jp273068] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2016] [Accepted: 08/17/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The present study tested whether HCN channels contribute to the organization of motor cortex and to skilled motor behaviour during a forelimb reaching task. Experimental reductions in HCN channel signalling increase the representation of complex multiple forelimb movements in motor cortex as assessed by intracortical microstimulation. Global HCN1KO mice exhibit reduced reaching accuracy and atypical movements during a single-pellet reaching task relative to wild-type controls. Acute pharmacological inhibition of HCN channels in forelimb motor cortex decreases reaching accuracy and increases atypical movements during forelimb reaching. ABSTRACT The mechanisms by which distinct movements of a forelimb are generated from the same area of motor cortex have remained elusive. Here we examined a role for HCN channels, given their ability to alter synaptic integration, in the expression of forelimb movement responses during intracortical microstimulation (ICMS) and movements of the forelimb on a skilled reaching task. We used short-duration high-resolution ICMS to evoke forelimb movements following pharmacological (ZD7288), experimental (electrically induced cortical seizures) or genetic approaches that we confirmed with whole-cell patch clamp to substantially reduce Ih current. We observed significant increases in the number of multiple movement responses evoked at single sites in motor maps to all three experimental manipulations in rats or mice. Global HCN1 knockout mice were less successful and exhibited atypical movements on a skilled-motor learning task relative to wild-type controls. Furthermore, in reaching-proficient rats, reaching accuracy was reduced and forelimb movements were altered during infusion of ZD7288 within motor cortex. Thus, HCN channels play a critical role in the separation of overlapping movement responses and allow for successful reaching behaviours. These data provide a novel mechanism for the encoding of multiple movement responses within shared networks of motor cortex. This mechanism supports a viewpoint of primary motor cortex as a site of dynamic integration for behavioural output.
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Affiliation(s)
- Jeffery A Boychuk
- Department of Physiology, University of Kentucky, Lexington, Kentucky, USA.,Epilepsy Center, University of Kentucky, Lexington, Kentucky, USA.,Department of Cell Biology and Anatomy, University of Calgary, Calgary, Alberta, Canada.,Department of Neuroscience, University of Calgary, Calgary, Alberta, Canada.,Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada
| | - Jordan S Farrell
- Department of Cell Biology and Anatomy, University of Calgary, Calgary, Alberta, Canada.,Department of Neuroscience, University of Calgary, Calgary, Alberta, Canada
| | - Laura A Palmer
- Department of Cell Biology and Anatomy, University of Calgary, Calgary, Alberta, Canada.,Department of Neuroscience, University of Calgary, Calgary, Alberta, Canada
| | - Anna C Singleton
- Department of Neuroscience, University of Calgary, Calgary, Alberta, Canada
| | - Quentin J Pittman
- Department of Neuroscience, University of Calgary, Calgary, Alberta, Canada.,Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada.,Hotchkiss Brain Institute, Calgary, Alberta, Canada
| | - G Campbell Teskey
- Department of Cell Biology and Anatomy, University of Calgary, Calgary, Alberta, Canada.,Department of Neuroscience, University of Calgary, Calgary, Alberta, Canada.,Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada.,Hotchkiss Brain Institute, Calgary, Alberta, Canada
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13
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Scullion K, Guy AR, Singleton A, Spanswick SC, Hill MN, Teskey GC. Delta-9-tetrahydrocannabinol (THC) affects forelimb motor map expression but has little effect on skilled and unskilled behavior. Neuroscience 2016; 319:134-45. [PMID: 26826333 DOI: 10.1016/j.neuroscience.2016.01.050] [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: 11/02/2015] [Revised: 01/22/2016] [Accepted: 01/22/2016] [Indexed: 01/13/2023]
Abstract
It has previously been shown in rats that acute administration of delta-9-tetrahydrocannabinol (THC) exerts a dose-dependent effect on simple locomotor activity, with low doses of THC causing hyper-locomotion and high doses causing hypo-locomotion. However the effect of acute THC administration on cortical movement representations (motor maps) and skilled learned movements is completely unknown. It is important to determine the effects of THC on motor maps and skilled learned behaviors because behaviors like driving place people at a heightened risk. Three doses of THC were used in the current study: 0.2mg/kg, 1.0mg/kg and 2.5mg/kg representing the approximate range of the low to high levels of available THC one would consume from recreational use of cannabis. Acute peripheral administration of THC to drug naïve rats resulted in dose-dependent alterations in motor map expression using high resolution short duration intracortical microstimulation (SD-ICMS). THC at 0.2mg/kg decreased movement thresholds and increased motor map size, while 1.0mg/kg had the opposite effect, and 2.5mg/kg had an even more dramatic effect. Deriving complex movement maps using long duration (LD)-ICMS at 1.0mg/kg resulted in fewer complex movements. Dosages of 1.0mg/kg and 2.5mg/kg THC reduced the number of reach attempts but did not affect percentage of success or the kinetics of reaching on the single pellet skilled reaching task. Rats that received 2.5mg/kg THC did show an increase in latency of forelimb removal on the bar task, while dose-dependent effects of THC on unskilled locomotor activity using the rotorod and horizontal ladder tasks were not observed. Rats may be employing compensatory strategies after receiving THC, which may account for the robust changes in motor map expression but moderate effects on behavior.
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Affiliation(s)
- K Scullion
- Department of Neuroscience, Cumming School of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada; Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada
| | - A R Guy
- Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada
| | - A Singleton
- Department of Neuroscience, Cumming School of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada; Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada
| | - S C Spanswick
- Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada
| | - M N Hill
- Department of Cell Biology and Anatomy, Cumming School of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada; Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada
| | - G C Teskey
- Department of Cell Biology and Anatomy, Cumming School of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada; Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada.
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14
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Smith J, Rho JM, Teskey GC. Ketogenic diet restores aberrant cortical motor maps and excitation-to-inhibition imbalance in the BTBR mouse model of autism spectrum disorder. Behav Brain Res 2016; 304:67-70. [PMID: 26876011 DOI: 10.1016/j.bbr.2016.02.015] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Revised: 01/28/2016] [Accepted: 02/09/2016] [Indexed: 11/25/2022]
Abstract
Autism spectrum disorder (ASD) is an increasingly prevalent neurodevelopmental disorder characterized by deficits in sociability and communication, and restricted and/or repetitive motor behaviors. Amongst the diverse hypotheses regarding the pathophysiology of ASD, one possibility is that there is increased neuronal excitation, leading to alterations in sensory processing, functional integration and behavior. Meanwhile, the high-fat, low-carbohydrate ketogenic diet (KD), traditionally used in the treatment of medically intractable epilepsy, has already been shown to reduce autistic behaviors in both humans and in rodent models of ASD. While the mechanisms underlying these effects remain unclear, we hypothesized that this dietary approach might shift the balance of excitation and inhibition towards more normal levels of inhibition. Using high-resolution intracortical microstimulation, we investigated basal sensorimotor excitation/inhibition in the BTBR T+Itpr(tf)/J (BTBR) mouse model of ASD and tested whether the KD restores the balance of excitation/inhibition. We found that BTBR mice had lower movement thresholds and larger motor maps indicative of higher excitation/inhibition compared to C57BL/6J (B6) controls, and that the KD reversed both these abnormalities. Collectively, our results afford a greater understanding of cortical excitation/inhibition balance in ASD and may help expedite the development of therapeutic approaches aimed at improving functional outcomes in this disorder.
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Affiliation(s)
- Jacklyn Smith
- Departments of Pediatrics, Clinical Neurosciences, Physiology & Pharmacology, Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Jong M Rho
- Departments of Pediatrics, Clinical Neurosciences, Physiology & Pharmacology, Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - G Campbell Teskey
- Department of Cell Biology and Anatomy, Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Alberta, Canada.
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15
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Ganzer PD, Manohar A, Shumsky JS, Moxon KA. Therapy induces widespread reorganization of motor cortex after complete spinal transection that supports motor recovery. Exp Neurol 2016; 279:1-12. [PMID: 26826448 DOI: 10.1016/j.expneurol.2016.01.022] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2015] [Revised: 12/28/2015] [Accepted: 01/26/2016] [Indexed: 01/07/2023]
Abstract
Reorganization of the somatosensory system and its relationship to functional recovery after spinal cord injury (SCI) has been well studied. However, little is known about the impact of SCI on organization of the motor system. Recent studies suggest that step-training paradigms in combination with spinal stimulation, either electrically or through pharmacology, are more effective than step training alone at inducing recovery and that reorganization of descending corticospinal circuits is necessary. However, simpler, passive exercise combined with pharmacotherapy has also shown functional improvement after SCI and reorganization of, at least, the sensory cortex. In this study we assessed the effect of passive exercise and serotonergic (5-HT) pharmacological therapies on behavioral recovery and organization of the motor cortex. We compared the effects of passive hindlimb bike exercise to bike exercise combined with daily injections of 5-HT agonists in a rat model of complete mid-thoracic transection. 5-HT pharmacotherapy combined with bike exercise allowed the animals to achieve unassisted weight support in the open field. This combination of therapies also produced extensive expansion of the axial trunk motor cortex into the deafferented hindlimb motor cortex and, surprisingly, reorganization within the caudal and even the rostral forelimb motor cortex areas. The extent of the axial trunk expansion was correlated to improvement in behavioral recovery of hindlimbs during open field locomotion, including weight support. From a translational perspective, these data suggest a rationale for developing and optimizing cost-effective, non-invasive, pharmacological and passive exercise regimes to promote plasticity that supports restoration of movement after spinal cord injury.
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Affiliation(s)
- Patrick D Ganzer
- School of Biomedical Engineering, Science and Health Systems, Drexel University, 3141 Chestnut St., Philadelphia, PA 19104, United States
| | - Anitha Manohar
- School of Biomedical Engineering, Science and Health Systems, Drexel University, 3141 Chestnut St., Philadelphia, PA 19104, United States
| | - Jed S Shumsky
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, 2900 Queen Lane, Philadelphia, PA 19129, United States
| | - Karen A Moxon
- School of Biomedical Engineering, Science and Health Systems, Drexel University, 3141 Chestnut St., Philadelphia, PA 19104, United States; Department of Neurobiology and Anatomy, Drexel University College of Medicine, 2900 Queen Lane, Philadelphia, PA 19129, United States.
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16
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Hussin AT, Boychuk JA, Brown AR, Pittman QJ, Teskey GC. Intracortical Microstimulation (ICMS) Activates Motor Cortex Layer 5 Pyramidal Neurons Mainly Transsynaptically. Brain Stimul 2015; 8:742-50. [PMID: 25892002 DOI: 10.1016/j.brs.2015.03.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Revised: 02/08/2015] [Accepted: 03/19/2015] [Indexed: 11/15/2022] Open
Abstract
BACKGROUND Intracortical microstimulation (ICMS) is a technique used for a number of purposes including the derivation of cortical movement representations (motor maps). Its application can activate the output layer 5 of motor cortex and can result in the elicitation of body movements depending upon the stimulus parameters used. OBJECTIVE The extent to which pyramidal tract projection neurons of the motor cortex are activated transsynaptically or directly by ICMS remains an open question. Given this uncertainty in the mode of activation, we used a preparation that combined patch clamp whole-cell recordings from single layer 5 pyramidal neurons and extracellular ICMS in slices of motor cortex as well as a standard in vivo mapping technique to ask how ICMS activated motor cortex pyramidal neurons. METHODS We measured changes in synaptic spike threshold and spiking rate to ICMS in vitro and movement threshold in vivo in the presence or absence of specific pharmacological blockers of glutamatergic (AMPA, NMDA and Kainate) receptors and GABAA receptors. RESULTS With major excitatory and inhibitory synaptic transmission blocked (with DNQX, APV and bicuculline methiodide), we observed a significant increase in the ICMS current intensity required to elicit a movement in vivo as well as to the first spike and an 85% reduction in spiking responses in vitro. Subsets of neurons were still responsive after the synaptic block, especially at higher current intensities, suggesting a modest direct activation. CONCLUSION Taken together our data indicate a mainly synaptic mode of activation to ICMS in layer 5 of rat motor cortex.
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Affiliation(s)
- Ahmed T Hussin
- Hotchkiss Brain Institute, University of Calgary, Alberta, Canada T2N 4N1; Department of Neuroscience, University of Calgary, Alberta, Canada T2N 4N1
| | - Jeffery A Boychuk
- Hotchkiss Brain Institute, University of Calgary, Alberta, Canada T2N 4N1; Department of Neuroscience, University of Calgary, Alberta, Canada T2N 4N1; Department of Physiology and Pharmacology, University of Calgary, Alberta, Canada T2N 4N1; Department of Cell Biology and Anatomy, University of Calgary, Alberta, Canada T2N 4N1
| | - Andrew R Brown
- Hotchkiss Brain Institute, University of Calgary, Alberta, Canada T2N 4N1; Department of Neuroscience, University of Calgary, Alberta, Canada T2N 4N1
| | - Quentin J Pittman
- Hotchkiss Brain Institute, University of Calgary, Alberta, Canada T2N 4N1; Department of Neuroscience, University of Calgary, Alberta, Canada T2N 4N1; Department of Physiology and Pharmacology, University of Calgary, Alberta, Canada T2N 4N1
| | - G Campbell Teskey
- Hotchkiss Brain Institute, University of Calgary, Alberta, Canada T2N 4N1; Department of Neuroscience, University of Calgary, Alberta, Canada T2N 4N1; Department of Physiology and Pharmacology, University of Calgary, Alberta, Canada T2N 4N1; Department of Cell Biology and Anatomy, University of Calgary, Alberta, Canada T2N 4N1.
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17
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Ghosh M, Pearse DD. The role of the serotonergic system in locomotor recovery after spinal cord injury. Front Neural Circuits 2015; 8:151. [PMID: 25709569 PMCID: PMC4321350 DOI: 10.3389/fncir.2014.00151] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2014] [Accepted: 12/28/2014] [Indexed: 11/30/2022] Open
Abstract
Serotonin (5-HT), a monoamine neurotransmitter synthesized in various populations of brainstem neurons, plays an important role in modulating the activity of spinal networks involved in vertebrate locomotion. Following spinal cord injury (SCI) there is a disruption of descending serotonergic projections to spinal motor areas, which results in a subsequent depletion in 5-HT, the dysregulation of 5-HT transporters as well as the elevated expression, super-sensitivity and/or constitutive auto-activation of specific 5-HT receptors. These changes in the serotonergic system can produce varying degrees of locomotor dysfunction through to paralysis. To date, various approaches targeting the different components of the serotonergic system have been employed to restore limb coordination and improve locomotor function in experimental models of SCI. These strategies have included pharmacological modulation of serotonergic receptors, through the administration of specific 5-HT receptor agonists, or by elevating the 5-HT precursor 5-hydroxytryptophan, which produces a global activation of all classes of 5-HT receptors. Stimulation of these receptors leads to the activation of the locomotor central pattern generator (CPG) below the site of injury to facilitate or improve the quality and frequency of movements, particularly when used in concert with the activation of other monoaminergic systems or coupled with electrical stimulation. Another approach has been to employ cell therapeutics to replace the loss of descending serotonergic input to the CPG, either through transplanted fetal brainstem 5-HT neurons at the site of injury that can supply 5-HT to below the level of the lesion or by other cell types to provide a substrate at the injury site for encouraging serotonergic axon regrowth across the lesion to the caudal spinal cord for restoring locomotion.
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Affiliation(s)
- Mousumi Ghosh
- The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine Miami, FL, USA ; Department of Neurological Surgery, University of Miami Miller School of Medicine Miami, FL, USA
| | - Damien D Pearse
- The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine Miami, FL, USA ; Department of Neurological Surgery, University of Miami Miller School of Medicine Miami, FL, USA ; The Neuroscience Program, University of Miami Miller School of Medicine Miami, FL, USA ; The Interdisciplinary Stem Cell Institute, University of Miami Miller School of Medicine Miami, FL, USA
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