1
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Ohno T, Fukuda S, Murabe N, Niido M, Sakurai M. Temporal Course of Transient Direct Corticomotoneuronal Connections during Development in Rodents. Neuroscience 2021; 478:89-99. [PMID: 34534634 DOI: 10.1016/j.neuroscience.2021.09.006] [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: 01/18/2021] [Revised: 09/03/2021] [Accepted: 09/06/2021] [Indexed: 11/28/2022]
Abstract
We previously observed in rodents that during the 2nd postnatal week corticospinal axons make monosynaptic connections with motoneurons. Prior to that finding, it had been believed that such contacts only occur in higher primates. Although an in vitro electrophysiological study is prerequisite for studying the developmental time course of synaptic connections, the technical difficulty of reliably recording synaptic responses from spinal motoneurons in animals over 2 weeks old hampered the study. Instead, we used retrograde transsynaptic labeling with a genetically modified rabies virus to confirm the presence of direct corticomotoneuronal connections at an early developmental stage and to show that these connections were subsequently eliminated. However, determination of an accurate elimination time course and quantitative evaluation of synaptic connectivity cannot be achieved through viral-tracing experiments. For the present study, we improved the slice preparation procedure and maintenance of slice viability, which enabled us to record postsynaptic responses using the whole cell patch-clamp technique from retrogradely labeled forearm motoneurons up until postnatal week 7. We examined the extent of corticomotoneuronal monosynaptic connections and studied the time course of their accumulation and loss. Positive ratios of monosynaptic corticomotoneuronal EPSCs increased from P6 to P8 and then plateaued (P8-P13: 65%). Thereafter, the monosynaptic connections declined until P21, at which time they were no longer detected. The time course of the falling phase and elimination was confirmed by experiments using optogenetic stimulation. The timing of the elimination fell within the same range (P18-22) estimated in our earlier study using retrograde transsynaptic labeling.
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Affiliation(s)
- Takae Ohno
- Department of Physiology, Teikyo University School of Medicine, Kaga 2-11-1, Itabashi-ku, Tokyo 173-8605, Japan.
| | - Satoshi Fukuda
- Department of Physiology, Teikyo University School of Medicine, Kaga 2-11-1, Itabashi-ku, Tokyo 173-8605, Japan.
| | - Naoyuki Murabe
- Department of Physiology, Teikyo University School of Medicine, Kaga 2-11-1, Itabashi-ku, Tokyo 173-8605, Japan.
| | - Mizuho Niido
- Department of Physiology, Teikyo University School of Medicine, Kaga 2-11-1, Itabashi-ku, Tokyo 173-8605, Japan.
| | - Masaki Sakurai
- Department of Physiology, Teikyo University School of Medicine, Kaga 2-11-1, Itabashi-ku, Tokyo 173-8605, Japan.
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2
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Henstridge CM, Tzioras M, Paolicelli RC. Glial Contribution to Excitatory and Inhibitory Synapse Loss in Neurodegeneration. Front Cell Neurosci 2019; 13:63. [PMID: 30863284 PMCID: PMC6399113 DOI: 10.3389/fncel.2019.00063] [Citation(s) in RCA: 74] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2018] [Accepted: 02/08/2019] [Indexed: 12/12/2022] Open
Abstract
Synapse loss is an early feature shared by many neurodegenerative diseases, and it represents the major correlate of cognitive impairment. Recent studies reveal that microglia and astrocytes play a major role in synapse elimination, contributing to network dysfunction associated with neurodegeneration. Excitatory and inhibitory activity can be affected by glia-mediated synapse loss, resulting in imbalanced synaptic transmission and subsequent synaptic dysfunction. Here, we review the recent literature on the contribution of glia to excitatory/inhibitory imbalance, in the context of the most common neurodegenerative disorders. A better understanding of the mechanisms underlying pathological synapse loss will be instrumental to design targeted therapeutic interventions, taking in account the emerging roles of microglia and astrocytes in synapse remodeling.
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Affiliation(s)
- Christopher M Henstridge
- Centre for Discovery Brain Sciences, The University of Edinburgh, Edinburgh, United Kingdom.,Dementia Research Institute UK, The University of Edinburgh, Edinburgh, United Kingdom
| | - Makis Tzioras
- Centre for Discovery Brain Sciences, The University of Edinburgh, Edinburgh, United Kingdom.,Dementia Research Institute UK, The University of Edinburgh, Edinburgh, United Kingdom
| | - Rosa C Paolicelli
- Department of Physiology, University of Lausanne, Lausanne, Switzerland
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3
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Isoo N, Ohno T, Isowaki M, Fukuda S, Murabe N, Mizukami H, Ozawa K, Mishina M, Sakurai M. The decline in synaptic GluN2B and rise in inhibitory neurotransmission determine the end of a critical period. Sci Rep 2016; 6:34196. [PMID: 27677249 PMCID: PMC5039748 DOI: 10.1038/srep34196] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Accepted: 09/09/2016] [Indexed: 12/20/2022] Open
Abstract
Neuronal plasticity is especially active in the young, during short windows of time termed critical periods, and loss of a critical period leads to functional limitations in the adults. The mechanism that governs the length of critical periods remains unknown. Here we show that levels of the NMDA receptor GluN2B subunit, which functions as a Ca2+ channel, declines in spinal cord synapses toward the end of the critical period for activity-dependent corticospinal synapse elimination. This period could be prolonged by blocking the decline of GluN2B, and after its termination the critical period could be reopened through upregulation of GluN2B. It is known that inhibitory neural activity increases with development in the CNS including the spinal cord. Suppression of the increasing inhibitory activity using low-dose strychnine also prolonged this critical period. During the strychnine-widened time window, Ca2+ influx through GluN2B channels returned to a level comparable to that seen during the critical period, though the level of GluN2B was slightly reduced. These findings indicate that loss of GluN2B subunits and the associated reduction in Ca2+ influx determines the end of the critical period in our in vitro CS system.
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Affiliation(s)
- Noriko Isoo
- Department of Physiology, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi-ku, Tokyo 173-8605, Japan
| | - Takae Ohno
- Department of Physiology, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi-ku, Tokyo 173-8605, Japan
| | - Mutsumi Isowaki
- Department of Physiology, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi-ku, Tokyo 173-8605, Japan
| | - Satoshi Fukuda
- Department of Physiology, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi-ku, Tokyo 173-8605, Japan
| | - Naoyuki Murabe
- Department of Physiology, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi-ku, Tokyo 173-8605, Japan
| | - Hiroaki Mizukami
- Division of Genetic Therapeutics, Center for Molecular Medicine, Jichi Medical University, 3311-1 Yakushiji, Shimono, Tochigi 329-0498, Japan
| | - Keiya Ozawa
- Division of Genetic Therapeutics, Center for Molecular Medicine, Jichi Medical University, 3311-1 Yakushiji, Shimono, Tochigi 329-0498, Japan.,Division of Genetic Therapeutics, the Institute of Medical Science, the University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
| | - Masayoshi Mishina
- Department of Molecular Neurobiology &Pharmacology, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan.,Brain Science Laboratory, The Research Organization of Science and Technology, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan
| | - Masaki Sakurai
- Department of Physiology, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi-ku, Tokyo 173-8605, Japan
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Maeda H, Fukuda S, Kameda H, Murabe N, Isoo N, Mizukami H, Ozawa K, Sakurai M. Corticospinal axons make direct synaptic connections with spinal motoneurons innervating forearm muscles early during postnatal development in the rat. J Physiol 2015; 594:189-205. [PMID: 26503304 DOI: 10.1113/jp270885] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2015] [Accepted: 10/21/2015] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Direct connections between corticospinal (CS) axons and motoneurons (MNs) appear to be present only in higher primates, where they are essential for discrete movement of the digits. Their presence in adult rodents was once claimed but is now questioned. We report that MNs innervating forearm muscles in infant rats receive monosynaptic input from CS axons, but MNs innervating proximal muscles do not, which is a pattern similar to that in primates. Our experiments were carefully designed to show monosynaptic connections. This entailed selective electrical and optogenetic stimulation of CS axons and recording from MNs identified by retrograde labelling from innervated muscles. Morphological evidence was also obtained for rigorous identification of CS axons and MNs. These connections would be transient and would regress later during development. These results shed light on the development and evolution of direct CS-MN connections, which serve as the basis for dexterity in humans. Recent evidence suggests there is no direct connection between corticospinal (CS) axons and spinal motoneurons (MNs) in adult rodents. We previously showed that CS synapses are present throughout the spinal cord for a time, but are eliminated from the ventral horn during development in rodents. This raises the possibility that CS axons transiently make direct connections with MNs located in the ventral horn of the spinal cord. This was tested in the present study. Using cervical cord slices prepared from rats on postnatal days (P) 7-9, CS axons were stimulated and whole cell recordings were made from MNs retrogradely labelled with fluorescent cholera toxin B subunit (CTB) injected into selected groups of muscles. To selectively activate CS axons, electrical stimulation was carefully limited to the CS tract. In addition we employed optogenetic stimulation after injecting an adeno-associated virus vector encoding channelrhodopsin-2 (ChR2) into the sensorimotor cortex on P0. We were then able to record monosynaptic excitatory postsynaptic currents from MNs innervating forearm muscles, but not from those innervating proximal muscles. We also showed close contacts between CTB-labelled MNs and CS axons labelled through introduction of fluorescent protein-conjugated synaptophysin or the ChR2 expression system. We confirmed that some of these contacts colocalized with postsynaptic density protein 95 in their partner dendrites. It is intriguing from both phylogenetic and ontogenetic viewpoints that direct and putatively transient CS-MN connections were found only on MNs innervating the forearm muscles in infant rats, as this is analogous to the connection pattern seen in adult primates.
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Affiliation(s)
- Hitoshi Maeda
- Department of Physiology, Teikyo University School of Medicine, Tokyo, 173-8605, Japan
| | - Satoshi Fukuda
- Department of Physiology, Teikyo University School of Medicine, Tokyo, 173-8605, Japan
| | - Hiroshi Kameda
- Department of Physiology, Teikyo University School of Medicine, Tokyo, 173-8605, Japan
| | - Naoyuki Murabe
- Department of Physiology, Teikyo University School of Medicine, Tokyo, 173-8605, Japan
| | - Noriko Isoo
- Department of Physiology, Teikyo University School of Medicine, Tokyo, 173-8605, Japan
| | - Hiroaki Mizukami
- Division of Genetic Therapeutics, Jichi Medical University, Tochigi, 329-0498, Japan
| | - Keiya Ozawa
- Division of Genetic Therapeutics, Jichi Medical University, Tochigi, 329-0498, Japan.,Research Hospital, Institute of Medical Science, Tokyo University, Tokyo, 108-8639, Japan
| | - Masaki Sakurai
- Department of Physiology, Teikyo University School of Medicine, Tokyo, 173-8605, Japan
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5
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Meng L, Mulcahy B, Cook SJ, Neubauer M, Wan A, Jin Y, Yan D. The Cell Death Pathway Regulates Synapse Elimination through Cleavage of Gelsolin in Caenorhabditis elegans Neurons. Cell Rep 2015; 11:1737-48. [PMID: 26074078 DOI: 10.1016/j.celrep.2015.05.031] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2014] [Revised: 05/01/2015] [Accepted: 05/15/2015] [Indexed: 11/17/2022] Open
Abstract
Synapse elimination occurs in development, plasticity, and disease. Although the importance of synapse elimination has been documented in many studies, the molecular mechanisms underlying this process are unclear. Here, using the development of C. elegans RME neurons as a model, we have uncovered a function for the apoptosis pathway in synapse elimination. We find that the conserved apoptotic cell death (CED) pathway and axonal mitochondria are required for the elimination of transiently formed clusters of presynaptic components in RME neurons. This function of the CED pathway involves the activation of the actin-filament-severing protein, GSNL-1. Furthermore, we show that caspase CED-3 cleaves GSNL-1 at a conserved C-terminal region and that the cleaved active form of GSNL-1 promotes its actin-severing ability. Our data suggest that activation of the CED pathway contributes to selective elimination of synapses through disassembly of the actin filament network.
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Affiliation(s)
- Lingfeng Meng
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Research Drive, Durham, NC 27710, USA
| | - Ben Mulcahy
- Lunenfeld-Tanenbaum Research Institute, Toronto, ON M5G 1X5, Canada
| | - Steven J Cook
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Marianna Neubauer
- Department of Physics and Center for Brain Science, Harvard University, Cambridge, MA 02138, USA
| | - Airong Wan
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Research Drive, Durham, NC 27710, USA
| | - Yishi Jin
- Neurobiology Section, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA; Department of Cellular and Molecular Medicine, School of Medicine, University of California, San Diego, La Jolla, CA 92093, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA
| | - Dong Yan
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Research Drive, Durham, NC 27710, USA; Department of Neurobiology and Duke Institute for Brain Sciences, Duke University Medical Center, Research Drive, Durham, NC 27710, USA.
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6
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Corticospinal tract development and spinal cord innervation differ between cervical and lumbar targets. J Neurosci 2015; 35:1181-91. [PMID: 25609632 DOI: 10.1523/jneurosci.2842-13.2015] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The corticospinal (CS) tract is essential for voluntary movement, but what we know about the organization and development of the CS tract remains limited. To determine the total cortical area innervating the seventh cervical spinal cord segment (C7), which controls forelimb movement, we injected a retrograde tracer (fluorescent microspheres) into C7 such that it would spread widely within the unilateral gray matter (to >80%), but not to the CS tract. Subsequent detection of the tracer showed that, in both juvenile and adult mice, neurons distributed over an unexpectedly broad portion of the rostral two-thirds of the cerebral cortex converge to C7. This even included cortical areas controlling the hindlimbs (the fourth lumbar segment, L4). With aging, cell densities greatly declined, mainly due to axon branch elimination. Whole-cell recordings from spinal cord cells upon selective optogenetic stimulation of CS axons, and labeling of axons (DsRed) and presynaptic structures (synaptophysin) through cotransfection using exo utero electroporation, showed that overgrowing CS axons make synaptic connections with spinal cells in juveniles. This suggests that neuronal circuits involved in the CS tract to C7 are largely reorganized during development. By contrast, the cortical areas innervating L4 are limited to the conventional hindlimb area, and the cell distribution and density do not change during development. These findings call for an update of the traditional notion of somatotopic CS projection and imply that there are substantial developmental differences in the cortical control of forelimb and hindlimb movements, at least in rodents.
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7
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Biane JS, Scanziani M, Tuszynski MH, Conner JM. Motor cortex maturation is associated with reductions in recurrent connectivity among functional subpopulations and increases in intrinsic excitability. J Neurosci 2015; 35:4719-28. [PMID: 25788688 PMCID: PMC4363396 DOI: 10.1523/jneurosci.2792-14.2015] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Revised: 01/26/2015] [Accepted: 02/06/2015] [Indexed: 11/21/2022] Open
Abstract
Behavior is derived from the configuration of synaptic connectivity among functionally diverse neurons. Fine motor behavior is absent at birth in most mammals but gradually emerges during subsequent postnatal corticospinal system maturation; the nature of circuit development and reorganization during this period has been largely unexplored. We investigated connectivity and synaptic signaling among functionally distinct corticospinal populations in Fischer 344 rats from postnatal day 18 through 75 using retrograde tracer injections into specific spinal cord segments associated with distinct aspects of forelimb function. Primary motor cortex slices were prepared enabling simultaneous patch-clamp recordings of up to four labeled corticospinal neurons and testing of 3489 potential synaptic connections. We find that, in immature animals, local connectivity is biased toward corticospinal neurons projecting to the same spinal cord segment; this within-population connectivity significantly decreases through maturation until connection frequency is similar between neurons projecting to the same (within-population) or different (across-population) spinal segments. Concomitantly, postnatal maturation is associated with a significant reduction in synaptic efficacy over time and an increase in intrinsic neuronal excitability, altering how excitation is effectively transmitted across recurrent corticospinal networks. Collectively, the postnatal emergence of fine motor control is associated with a relative broadening of connectivity between functionally diverse cortical motor neurons and changes in synaptic properties that could enable the emergence of smaller independent networks, enabling fine motor movement. These changes in synaptic patterning and physiological function provide a basis for the increased capabilities of the mature versus developing brain.
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Affiliation(s)
| | - Massimo Scanziani
- Departments of Neurosciences and Neurobiology, University of California San Diego, La Jolla, California 92093, Howard Hughes Medical Institute, San Diego, California 92093, and
| | - Mark H Tuszynski
- Departments of Neurosciences and Veterans Administration Medical Center, San Diego, California 92161
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8
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Yoshikawa A, Nakamachi T, Shibato J, Rakwal R, Shioda S. Comprehensive analysis of neonatal versus adult unilateral decortication in a mouse model using behavioral, neuroanatomical, and DNA microarray approaches. Int J Mol Sci 2014; 15:22492-517. [PMID: 25490135 PMCID: PMC4284721 DOI: 10.3390/ijms151222492] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2014] [Revised: 11/17/2014] [Accepted: 11/20/2014] [Indexed: 01/29/2023] Open
Abstract
Previously, studying the development, especially of corticospinal neurons, it was concluded that the main compensatory mechanism after unilateral brain injury in rat at the neonatal stage was due in part to non-lesioned ipsilateral corticospinal neurons that escaped selection by axonal elimination or neuronal apoptosis. However, previous results suggesting compensatory mechanism in neonate brain were not correlated with high functional recovery. Therefore, what is the difference among neonate and adult in the context of functional recovery and potential mechanism(s) therein? Here, we utilized a brain unilateral decortication mouse model and compared motor functional recovery mechanism post-neonatal brain hemisuction (NBH) with adult brain hemisuction (ABH). Three analyses were performed: (1) Quantitative behavioral analysis of forelimb movements using ladder walking test; (2) neuroanatomical retrograde tracing analysis of unlesioned side corticospinal neurons; and (3) differential global gene expressions profiling in unlesioned-side neocortex (rostral from bregma) in NBH and ABH on a 8 × 60 K mouse whole genome Agilent DNA chip. Behavioral data confirmed higher recovery ability in NBH over ABH is related to non-lesional frontal neocortex including rostral caudal forelimb area. A first inventory of differentially expressed genes genome-wide in the NBH and ABH mouse model is provided as a resource for the scientific community.
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Affiliation(s)
- Akira Yoshikawa
- Department of Anatomy, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa, Tokyo 142-8555, Japan.
| | - Tomoya Nakamachi
- Department of Anatomy, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa, Tokyo 142-8555, Japan.
| | - Junko Shibato
- Department of Anatomy, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa, Tokyo 142-8555, Japan.
| | - Randeep Rakwal
- Department of Anatomy, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa, Tokyo 142-8555, Japan.
| | - Seiji Shioda
- Department of Anatomy, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa, Tokyo 142-8555, Japan.
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9
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Lack of adenylate cyclase 1 (AC1): Consequences on corticospinal tract development and on locomotor recovery after spinal cord injury. Brain Res 2014; 1549:1-10. [DOI: 10.1016/j.brainres.2014.01.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2013] [Revised: 12/07/2013] [Accepted: 01/03/2014] [Indexed: 01/14/2023]
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10
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Wang S, Corson J, Hill D, Erisir A. Postnatal development of chorda tympani axons in the rat nucleus of the solitary tract. J Comp Neurol 2013; 520:3217-35. [PMID: 22430892 DOI: 10.1002/cne.23093] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The chorda tympani nerve (CT), one of three nerves that convey gustatory information to the nucleus of the solitary tract (NTS), displays terminal field reorganization after postnatal day 15 in the rat. Aiming to gain insight into mechanisms of this phenomenon, CT axon projection field and terminal morphology in NTS subdivisions were examined using tract tracing, light microscopy, and immunoelectron microscopy at four postnatal ages: P15, P25, P35, and adult. The CT axons that innervated NTS rostrolateral subdivision both in the adult and in P15 rats were morphologically distinct from those that innervated the rostrocentral, gustatory subdivision. In both subdivisions, CT terminals reached morphological maturity before P15. Rostrolateral, but not rostrocentral axons, went through substantial axonal branch elimination after P15. Rostrocentral CT synapses, however, redistribute onto postsynaptic targets in the following weeks. CT terminal preference for GABAergic postsynaptic targets was drastically reduced after P15. Furthermore, CT synapses became a smaller component of the total synaptic input to the rostrocentral NTS after P35. The results underlined that CT axons in rostrocentral and rostrolateral subdivisions represent two distinct populations of CT input, displaying different morphological properties and structural reorganization mechanisms during postnatal development.
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Affiliation(s)
- Siting Wang
- University of Virginia, Charlottesville, Virginia 22904, USA
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11
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Yoshikawa A, Atobe Y, Takeda A, Kamiya Y, Takiguchi M, Funakoshi K. A Retrograde Tracing Study of Compensatory Corticospinal Projections in Rats with Neonatal Hemidecortication. Dev Neurosci 2011; 33:539-47. [DOI: 10.1159/000335526] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2011] [Accepted: 11/29/2011] [Indexed: 11/19/2022] Open
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12
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Specific involvement of postsynaptic GluN2B-containing NMDA receptors in the developmental elimination of corticospinal synapses. Proc Natl Acad Sci U S A 2010; 107:15252-7. [PMID: 20696923 DOI: 10.1073/pnas.0906551107] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The GluN2B (GluRepsilon2/NR2B) and GluN2A (GluRepsilon1/NR2A) NMDA receptor (NMDAR) subtypes have been differentially implicated in activity-dependent synaptic plasticity. However, little is known about the respective contributions made by these two subtypes to developmental plasticity, in part because studies of GluN2B KO [Grin2b(-/-) (2b(-/-))] mice are hampered by early neonatal mortality. We previously used in vitro slice cocultures of rodent cerebral cortex (Cx) and spinal cord (SpC) to show that corticospinal (CS) synapses, once present throughout the SpC, are eliminated from the ventral side during development in an NMDAR-dependent manner. To study subtype specificity of NMDAR in this developmental plasticity, we cocultured Cx and SpC slices derived from postnatal day 0 (P0) animals with different genotypes [2b(-/-), Grin2a(-/-) (2a(-/-)), or WT mice]. The distribution of CS synapses was studied electrophysiologically and with a voltage-sensitive dye. Synapse elimination on the ventral side was blocked in WT(Cx)-2b(-/-)(SpC) pairs but not in WT(Cx)-2a(-/-)(SpC) or 2b(-/-)(Cx)-WT(SpC) pairs. CS axonal regression was also observed through live imaging of CS axons labeled with enhanced yellow fluorescent protein (EYFP) through exo utero electroporation. These findings suggest that postsynaptic GluN2B is selectively involved in CS synapse elimination. In addition, the elimination was not blocked in 2a(-/-) SpC slices, where Ca(2+) entry through GluN2B-mediated CS synaptic currents was reduced to the same level as in 2b(-/-) slices, suggesting that the differential effect of GluN2B and GluN2A in CS synapse elimination might not be explained based solely on greater Ca(2+) entry through GluN2B-containing channels.
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13
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Abstract
AbstractA CST-YFP transgenic mouse has been developed for the study of the corticospinal tract in which yellow fluorescent protein is expressed under the control of thy1 and emx1 promoters in order to restrict expression to forebrain neurones. We explored plasticity of the developing corticospinal tract of these mice following a unilateral lesion to the sensorimotor cortex at postnatal day 7. The extent of innervation of the cervical spinal cord at time points post-lesion was assessed by measuring density of immunoperoxidase reactivity for yellow fluorescent protein in the dorsal funiculi and a defined region of each dorsal horn, and by counting immunoreactive axonal varicosities in the ventral horns. Two/three days post-lesion, the density of immunoreactivity in the dorsal horn contralateral to the lesion was reduced proportional to the decrease in positive fibres in the dorsal funiculus, however density of immunoreactive varicosities in the ventral horn was more resistant to loss. Over a three week period, immunoreactive axonal processes in the grey matter increased on the contralateral side, particularly in the ventral horn, but without an increase in immunopositive fibres in the contralateral dorsal funiculus, demonstrating sprouting of surviving immunoreactive fibres to replace lesioned corticospinal axons. However, the origin of sprouting fibres could not be identified with confidence as parallel observations revealed strongly immunoreactive neuronal cell bodies in the spinal cord, medulla and red nucleus. We have demonstrated plasticity in response to a developmental lesion but discovered a drawback to using these mice if visualisation of individual axons is enhanced by immunohistochemistry.
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14
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Richter MW, Roskams AJ. Corticospinal neurons respond differentially to neurotrophins and myelin-associated glycoprotein in vitro. J Neurosci Res 2009; 87:2222-36. [PMID: 19301432 DOI: 10.1002/jnr.22053] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Elucidating the mechanisms that regulate the survival and outgrowth of corticospinal tract (CST) neurons and other CNS tracts will be a key component in developing novel approaches for the treatment of central nervous system (CNS) disorders, including stroke, spinal cord injury (SCI), and motor neuron disease (MND). However, the in vivo complexities of these diseases make a systematic evaluation of potential therapeutics that directly affect corticospinal regeneration or survival very challenging. Here, we use Thy1.2 transgenic mice expressing yellow fluorescent protein (YFP) in postnatal day 8 (P8) corticospinal neurons, as a source of CST neurons that have already established synapses in the spinal cord, to assess factors that influence neurite outgrowth and survival of axotomized CST neurons. After culture, YFP-positive corticospinal neurons represent an enriched neuronal population over other glia and interneurons, survive, and extend processes over time. YFP-positive CST neurons also continue to express the corticospinal markers CTIP2 and Otx1. CST neurons display different degrees of axon extension, dendritic branch length and elaboration, and neurite elongation in response to neurotrophin-3 and ciliary neurotrophic factor, and an inhibitory outgrowth response when cultured on myelin-associated glycoprotein. Some CST neurons are lost with extended culture, which provides a baseline from which we can also assess factors that enhance CST neuron survival. This assay thus allows us to assess independent aspects of CST axonal and dendritic outgrowth kinetics, which allows for the rapid and sensitive investigation of new therapies to address corticospinal neuron outgrowth in the context of CNS injury and neurodegenerative disorders.
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Affiliation(s)
- Miranda W Richter
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
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15
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Yoshioka N, Murabe N, Sakurai M. Regressive events in rat corticospinal axons during development in in vitro slice cocultures: retraction, amputation, and degeneration. J Comp Neurol 2009; 513:164-72. [PMID: 19127522 DOI: 10.1002/cne.21950] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Axonal regression is utilized to refine neuronal circuits during development, but the dynamic properties of such regression remain largely unknown. We used confocal time-lapse imaging to examine the regression of single enhanced yellow fluorescent protein-labeled axons in corticospinal slice cocultures. By acquiring images at long (1 day) and short (30-60 min) intervals on days 5-13 in vitro, we detected three types of regressive events: 1) retractions, 2) amputations (referred to as autoaxotomy), and 3) degeneration. Retractions proceeded at some constant rate for up to 3 hours and then paused or switched to another constant rate, apparently shifting stepwise among three retraction rates (6, 12, 17 microm/hours). Autoaxotomy was a previously unreported strategy for regression. It occurred spontaneously, either at a proximal branch neck or at a distal end. Axons also underwent a form of degeneration that had several novel characteristics. Degenerating axons showed bright bead-like spots arranged at 3-9-microm intervals. The gaps were much larger than the spot size, and there was no prior sign of damage (e.g., swelling). Each spot's fluorescence intensity often waxed and waned, with its position unchanged. Degeneration progressed without clear proximal-to-distal directionality and was complete within 3-4 hours. Quantitative analysis of daily branch regression showed that branches almost always regressed up to their branch point or stopped before it, thereby keeping the branch point stable. This branch-point stability was retained for all three regression strategies observed, suggesting that the fate of each branch is determined relatively independently during the development of axonal arborization.
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Affiliation(s)
- Noboru Yoshioka
- Department of Physiology, Teikyo University School of Medicine, Tokyo 173-8605, Japan
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Canty A, Murphy M. Molecular mechanisms of axon guidance in the developing corticospinal tract. Prog Neurobiol 2008; 85:214-35. [DOI: 10.1016/j.pneurobio.2008.02.001] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2007] [Revised: 12/11/2007] [Accepted: 02/08/2008] [Indexed: 02/04/2023]
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Maeda H, Ohno T, Sakurai M. Optical and electrophysiological recordings of corticospinal synaptic activity and its developmental change in in vitro rat slice co-cultures. Neuroscience 2007; 150:829-40. [PMID: 18022322 DOI: 10.1016/j.neuroscience.2007.10.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2007] [Revised: 10/05/2007] [Accepted: 10/17/2007] [Indexed: 10/22/2022]
Abstract
Electrophysiological recordings and optical imaging with a fast voltage-sensitive dye (di-4-ANNEPS) were used to directly examine the spatiotemporal properties of in vitro corticospinal synapses formed in co-cultures of cerebral cortex and spinal cord slices. Whole cell recordings from spinal cord cells showed both monosynaptic and polysynaptic excitatory postsynaptic currents (EPSCs) in response to stimulation of corticospinal axons. Monosynaptic EPSCs and excitatory postsynaptic potentials (EPSPs) were isolated in artificial cerebrospinal fluid containing high concentrations of divalent cations. Optical imaging and extracellular recordings were done simultaneously. Both EPSPs and optically recorded excitatory postsynaptic potentials (optEPSPs) lasted 300-500 ms and were almost always positive. The major component of these long-lasting potentials was blocked by ifenprodil, a specific antagonist of the NR2B subunit-containing N-methyl-d-aspartate receptor (NMDAR). The spatial distribution of corticospinal optEPSPs paralleled that of the corticospinal field excitatory postsynaptic potentials (fEPSPs), suggesting that positive fEPSP amplitude is a reliable indicator of the distribution of corticospinal synapses. Corticospinal optEPSPs spread into the ventrolateral region by 6-7 days in vitro (DIV), but were restricted to the dorsomedial area by 11-13 DIV, suggesting synapses were eliminated from the ventrolateral side of the spinal cord. After the recordings were complete, corticospinal fibers were often anterogradely labeled with biocytin to assess the relation between presynaptic fiber distribution and the optical signals (optically-recorded presynaptic fiber volley (opt-prevolley) and optEPSP). The distributions of the opt-prevolleys and optEPSPs correlated well with the distribution of presynaptic fibers, suggesting the opt-prevolley reflects corticospinal fiber activity and that the fibers made synapses relatively evenly along their axons. The NR2B-mediated component of the corticospinal synaptic response declined during the interval between 6 and 7 DIV and 11-13 DIV, suggesting that a shift in the NMDAR subtype from NR2B to something else (perhaps NR2A) may be involved in regulating developmental plasticity in the rat spinal cord and the process of corticospinal synapse elimination.
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Affiliation(s)
- H Maeda
- Department of Physiology, Teikyo University School of Medicine, Kaga 2-11-1, Itabashi-ku, Tokyo 173-8605, Japan
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Martin JH, Friel KM, Salimi I, Chakrabarty S. Activity- and use-dependent plasticity of the developing corticospinal system. Neurosci Biobehav Rev 2007; 31:1125-35. [PMID: 17599407 PMCID: PMC2769920 DOI: 10.1016/j.neubiorev.2007.04.017] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2007] [Accepted: 04/26/2007] [Indexed: 01/15/2023]
Abstract
The corticospinal (CS) system, critical for controlling skilled movements, develops during the late prenatal and early postnatal periods in all species examined. In the cat, there is a sequence of development of the mature pattern of terminations of CS tract axons in the spinal gray matter, followed by motor map development of the primary motor cortex. Skilled limb movements begin to be expressed as the map develops. Development of the proper connections between CS axons and spinal neurons in cats depends on CS neural activity and motor behavioral experience during a critical postnatal period. Reversible CS inactivation or preventing limb use produces an aberrant distribution of CS axon terminations and impairs visually guided movements. This altered pattern of CS connections after inactivation in cats resembles the aberrant pattern of motor responses evoked by transcranial magnetic stimulation in hemiplegic cerebral palsy patients. Left untreated in the cat, these impairments do not resolve. We have found that activity-dependent processes can be harnessed in cats to reestablish normal CS connections and function. This finding suggests that aspects of normal CS connectivity and function might some day be restored in hemiplegic cerebral palsy.
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Affiliation(s)
- John H Martin
- Center for Neurobiology and Behavior, Columbia University, N.Y.S. Psychiatric Institute, New York, NY 10032, USA.
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Clowry GJ. The dependence of spinal cord development on corticospinal input and its significance in understanding and treating spastic cerebral palsy. Neurosci Biobehav Rev 2007; 31:1114-24. [PMID: 17544509 DOI: 10.1016/j.neubiorev.2007.04.007] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2007] [Accepted: 04/24/2007] [Indexed: 11/18/2022]
Abstract
The final phase of spinal cord development follows the arrival of descending pathways which brings about a reorganisation that allows mature motor behaviours to emerge under the control of higher brain centres. Observations made during typical human development have shown that low threshold stretch reflexes, including excitatory reflexes between agonist and antagonist muscle pairs are a feature of the newborn. However, perinatal lesions of the corticospinal tract can lead to abnormal development of spinal reflexes that includes retention and reinforcement of developmental features that do not emerge in adult stroke victims, even though they also suffer from spasticity. This review describes investigations in animal models into how corticospinal input may drive segmental maturation. It compares their findings with observations made in humans and discusses how therapeutic interventions in cerebral palsy might aim to correct imbalances between descending and segmental inputs, bearing in mind that descending activity may play the crucial role in development.
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Affiliation(s)
- Gavin J Clowry
- Neural Development, Plasticity and Repair, School of Clinical Medical Sciences and Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK.
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Martin JH. Chapter 3 Development of the corticospinal system and spinal motor circuits. HANDBOOK OF CLINICAL NEUROLOGY 2007; 82:39-56. [PMID: 18808888 DOI: 10.1016/s0072-9752(07)80006-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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