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Grau JW, Hudson KE, Johnston DT, Partipilo SR. Updating perspectives on spinal cord function: motor coordination, timing, relational processing, and memory below the brain. Front Syst Neurosci 2024; 18:1184597. [PMID: 38444825 PMCID: PMC10912355 DOI: 10.3389/fnsys.2024.1184597] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2023] [Accepted: 01/29/2024] [Indexed: 03/07/2024] Open
Abstract
Those studying neural systems within the brain have historically assumed that lower-level processes in the spinal cord act in a mechanical manner, to relay afferent signals and execute motor commands. From this view, abstracting temporal and environmental relations is the province of the brain. Here we review work conducted over the last 50 years that challenges this perspective, demonstrating that mechanisms within the spinal cord can organize coordinated behavior (stepping), induce a lasting change in how pain (nociceptive) signals are processed, abstract stimulus-stimulus (Pavlovian) and response-outcome (instrumental) relations, and infer whether stimuli occur in a random or regular manner. The mechanisms that underlie these processes depend upon signal pathways (e.g., NMDA receptor mediated plasticity) analogous to those implicated in brain-dependent learning and memory. New data show that spinal cord injury (SCI) can enable plasticity within the spinal cord by reducing the inhibitory effect of GABA. It is suggested that the signals relayed to the brain may contain information about environmental relations and that spinal cord systems can coordinate action in response to descending signals from the brain. We further suggest that the study of stimulus processing, learning, memory, and cognitive-like processing in the spinal cord can inform our views of brain function, providing an attractive model system. Most importantly, the work has revealed new avenues of treatment for those that have suffered a SCI.
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Affiliation(s)
- James W. Grau
- Lab of Dr. James Grau, Department of Psychological and Brain Sciences, Cellular and Behavioral Neuroscience, Texas A&M University, College Station, TX, United States
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2
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Davis LA, Fogarty MJ, Brown A, Sieck GC. Structure and Function of the Mammalian Neuromuscular Junction. Compr Physiol 2022; 12:3731-3766. [PMID: 35950651 PMCID: PMC10461538 DOI: 10.1002/cphy.c210022] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The mammalian neuromuscular junction (NMJ) comprises a presynaptic terminal, a postsynaptic receptor region on the muscle fiber (endplate), and the perisynaptic (terminal) Schwann cell. As with any synapse, the purpose of the NMJ is to transmit signals from the nervous system to muscle fibers. This neural control of muscle fibers is organized as motor units, which display distinct structural and functional phenotypes including differences in pre- and postsynaptic elements of NMJs. Motor units vary considerably in the frequency of their activation (both motor neuron discharge rate and duration/duty cycle), force generation, and susceptibility to fatigue. For earlier and more frequently recruited motor units, the structure and function of the activated NMJs must have high fidelity to ensure consistent activation and continued contractile response to sustain vital motor behaviors (e.g., breathing and postural balance). Similarly, for higher force less frequent behaviors (e.g., coughing and jumping), the structure and function of recruited NMJs must ensure short-term reliable activation but not activation sustained for a prolonged period in which fatigue may occur. The NMJ is highly plastic, changing structurally and functionally throughout the life span from embryonic development to old age. The NMJ also changes under pathological conditions including acute and chronic disease. Such neuroplasticity often varies across motor unit types. © 2022 American Physiological Society. Compr Physiol 12:1-36, 2022.
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Affiliation(s)
- Leah A. Davis
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Matthew J. Fogarty
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Alyssa Brown
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Gary C. Sieck
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
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3
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The emerging role of the sympathetic nervous system in skeletal muscle motor innervation and sarcopenia. Ageing Res Rev 2021; 67:101305. [PMID: 33610815 DOI: 10.1016/j.arr.2021.101305] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Revised: 01/06/2021] [Accepted: 02/15/2021] [Indexed: 12/30/2022]
Abstract
Examining neural etiologic factors'role in the decline of neuromuscular function with aging is essential to our understanding of the mechanisms underlying sarcopenia, the age-dependent decline in muscle mass, force and power. Innervation of the skeletal muscle by both motor and sympathetic axons has been established, igniting interest in determining how the sympathetic nervous system (SNS) affect skeletal muscle composition and function throughout the lifetime. Selective expression of the heart and neural crest derivative 2 gene in peripheral SNs increases muscle mass and force regulating skeletal muscle sympathetic and motor innervation; improving acetylcholine receptor stability and NMJ transmission; preventing inflammation and myofibrillar protein degradation; increasing autophagy; and probably enhancing protein synthesis. Elucidating the role of central SNs will help to define the coordinated response of the visceral and neuromuscular system to physiological and pathological challenges across ages. This review discusses the following questions: (1) Does the SNS regulate skeletal muscle motor innervation? (2) Does the SNS regulate presynaptic and postsynaptic neuromuscular junction (NMJ) structure and function? (3) Does sympathetic neuron (SN) regulation of NMJ transmission decline with aging? (4) Does maintenance of SNs attenuate aging sarcopenia? and (5) Do central SN group relays influence sympathetic and motor muscle innervation?
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4
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Fu XQ, Peng J, Wang AH, Luo ZG. Tumor necrosis factor alpha mediates neuromuscular synapse elimination. Cell Discov 2020; 6:9. [PMID: 32140252 PMCID: PMC7051980 DOI: 10.1038/s41421-020-0143-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2019] [Accepted: 01/03/2020] [Indexed: 12/17/2022] Open
Abstract
During the development of mammalian neuromuscular junction (NMJ), the original supernumerary axon inputs are gradually eliminated, finally leaving each muscle fiber innervated by a single axon terminal. However, the molecular cues that mediate the elimination of redundant axon inputs remain unclear. Here we show that tumor necrosis factor-α (TNFα) expressed in postsynaptic muscle cells plays an important role in presynaptic axonal elimination at the NMJ. We found that intramuscular injection of TNFα into the levator auris longus (LAL) muscles caused disassociation of presynaptic nerve terminals from the postsynaptic acetylcholine receptor (AChR) clusters. By contrast, genetic ablation of TNFα globally or specifically in skeletal muscle cells, but not in motoneurons or Schwann cells, delayed the synaptic elimination. Moreover, ablation of TNFα in muscle cells attenuated the tendency of activity-dependent competition in a motoneuron-muscle coculture system. These results suggest a role of postsynaptic TNFα in the elimination of redundant synaptic inputs.
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Affiliation(s)
- Xiu-Qing Fu
- School of Life Science and Technology, ShanghaiTech University, Shanghai, 201210 China
| | - Jian Peng
- School of Life Science and Technology, ShanghaiTech University, Shanghai, 201210 China
- State Key Laboratory of Neuroscience, Center for Excellence in Brain Science and Intelligence Technology, Institute of Neuroscience, Chinese Academy of Sciences, Shanghai, 200031 China
- University of Chinese Academy of Sciences, Beijing, 100049 China
| | - Ai-Hua Wang
- School of Life Science and Technology, ShanghaiTech University, Shanghai, 201210 China
| | - Zhen-Ge Luo
- School of Life Science and Technology, ShanghaiTech University, Shanghai, 201210 China
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5
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Fogarty MJ, Sieck GC. Evolution and Functional Differentiation of the Diaphragm Muscle of Mammals. Compr Physiol 2019; 9:715-766. [PMID: 30873594 PMCID: PMC7082849 DOI: 10.1002/cphy.c180012] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Symmorphosis is a concept of economy of biological design, whereby structural properties are matched to functional demands. According to symmorphosis, biological structures are never over designed to exceed functional demands. Based on this concept, the evolution of the diaphragm muscle (DIAm) in mammals is a tale of two structures, a membrane that separates and partitions the primitive coelomic cavity into separate abdominal and thoracic cavities and a muscle that serves as a pump to generate intra-abdominal (Pab ) and intrathoracic (Pth ) pressures. The DIAm partition evolved in reptiles from folds of the pleural and peritoneal membranes that was driven by the biological advantage of separating organs in the larger coelomic cavity into separate thoracic and abdominal cavities, especially with the evolution of aspiration breathing. The DIAm pump evolved from the advantage afforded by more effective generation of both a negative Pth for ventilation of the lungs and a positive Pab for venous return of blood to the heart and expulsive behaviors such as airway clearance, defecation, micturition, and child birth. © 2019 American Physiological Society. Compr Physiol 9:715-766, 2019.
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Affiliation(s)
- Matthew J Fogarty
- Mayo Clinic, Department of Physiology & Biomedical Engineering, Rochester, Minnesota, USA
| | - Gary C Sieck
- Mayo Clinic, Department of Physiology & Biomedical Engineering, Rochester, Minnesota, USA
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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: 82] [Impact Index Per Article: 16.4] [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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Lanuza MA, Tomàs J, Garcia N, Cilleros-Mañé V, Just-Borràs L, Tomàs M. Axonal competition and synapse elimination during neuromuscular junction development. CURRENT OPINION IN PHYSIOLOGY 2018. [DOI: 10.1016/j.cophys.2018.04.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Zolnik TA, Connors BW. Electrical synapses and the development of inhibitory circuits in the thalamus. J Physiol 2016; 594:2579-92. [PMID: 26864476 PMCID: PMC4865577 DOI: 10.1113/jp271880] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Accepted: 02/05/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The thalamus is a structure critical for information processing and transfer to the cortex. Thalamic reticular neurons are inhibitory cells interconnected by electrical synapses, most of which require the gap junction protein connexin36 (Cx36). We investigated whether electrical synapses play a role in the maturation of thalamic networks by studying neurons in mice with and without Cx36. When Cx36 was deleted, inhibitory synapses were more numerous, although both divergent inhibitory connectivity and dendritic complexity were reduced. Surprisingly, we observed non-Cx36-dependent electrical synapses with unusual biophysical properties interconnecting some reticular neurons in mice lacking Cx36. The results of the present study suggest an important role for Cx36-dependent electrical synapses in the development of thalamic circuits. ABSTRACT Neurons within the mature thalamic reticular nucleus (TRN) powerfully inhibit ventrobasal (VB) thalamic relay neurons via GABAergic synapses. TRN neurons are also coupled to one another by electrical synapses that depend strongly on the gap junction protein connexin36 (Cx36). Electrical synapses in the TRN precede the postnatal development of TRN-to-VB inhibition. We investigated how the deletion of Cx36 affects the maturation of TRN and VB neurons, electrical coupling and GABAergic synapses by studying wild-type (WT) and Cx36 knockout (KO) mice. The incidence and strength of electrical coupling in TRN was sharply reduced, but not abolished, in KO mice. Surprisingly, electrical synapses between Cx36-KO neurons had faster voltage-dependent decay kinetics and conductance asymmetry (rectification) than did electrical synapses between WT neurons. The properties of TRN-mediated inhibition in VB also depended on the Cx36 genotype. Deletion of Cx36 increased the frequency and shifted the amplitude distributions of miniature IPSCs, whereas the paired-pulse ratio of evoked IPSCs was unaffected, suggesting that the absence of Cx36 led to an increase in GABAergic synaptic contacts. VB neurons from Cx36-KO mice also tended to have simpler dendritic trees and fewer divergent inputs from the TRN compared to WT cells. The findings obtained in the present study suggest that proper development of thalamic inhibitory circuitry, neuronal morphology, TRN cell function and electrical coupling requires Cx36. In the absence of Cx36, some TRN neurons express asymmetric electrical coupling mediated by other unidentified connexin subtypes.
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Affiliation(s)
- Timothy A Zolnik
- Department of Neuroscience, Division of Biology & Medicine, Brown University, Providence, RI, USA
- Charité Universitätsmedizin Berlin, Berlin, Germany
| | - Barry W Connors
- Department of Neuroscience, Division of Biology & Medicine, Brown University, Providence, RI, USA
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Bautista W, McCrea DA, Nagy JI. Connexin36 identified at morphologically mixed chemical/electrical synapses on trigeminal motoneurons and at primary afferent terminals on spinal cord neurons in adult mouse and rat. Neuroscience 2014; 263:159-80. [PMID: 24406437 PMCID: PMC3951135 DOI: 10.1016/j.neuroscience.2013.12.057] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Revised: 12/20/2013] [Accepted: 12/24/2013] [Indexed: 10/25/2022]
Abstract
Morphologically mixed chemical/electrical synapses at axon terminals, with the electrical component formed by gap junctions, is common in the CNS of lower vertebrates. In mammalian CNS, evidence for morphologically mixed synapses has been obtained in only a few locations. Here, we used immunofluorescence approaches to examine the localization of the neuronally expressed gap junction forming protein connexin36 (Cx36) in relation to the axon terminal marker vesicular glutamate transporter-1 (vglut1) in the spinal cord and the trigeminal motor nucleus (Mo5) of rat and mouse. In adult rodents, immunolabeling for Cx36 appeared exclusively as Cx36-puncta, and was widely distributed at all rostro-caudal levels in most spinal cord laminae and in the Mo5. A high proportion of Cx36-puncta was co-localized with vglut1, forming morphologically mixed synapses on motoneurons, in intermediate spinal cord lamina, and in regions of medial lamina VII, where vglut1-containing terminals associated with Cx36 converged on neurons adjacent to the central canal. Unilateral transection of lumbar dorsal roots reduced immunolabeling of both vglut1 and Cx36 in intermediate laminae and lamina IX. Further, vglut1-terminals displaying Cx36-puncta were contacted by terminals labeled for glutamic acid decarboxylase65, which is known to be contained in presynaptic terminals on large-diameter primary afferents. Developmentally, mixed synapses begin to emerge in the spinal cord only after the second to third postnatal week and thereafter increase to adult levels. Our findings demonstrate that axon terminals of primary afferent origin form morphologically mixed synapses containing Cx36 in broadly distributed areas of adult rodent spinal cord and Mo5.
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Affiliation(s)
- W Bautista
- Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada
| | - D A McCrea
- Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada
| | - J I Nagy
- Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
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10
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Sukal-Moulton T, Krosschell KJ, Gaebler-Spira DJ, Dewald JP. Motor impairment factors related to brain injury timing in early hemiparesis. Part I: expression of upper-extremity weakness. Neurorehabil Neural Repair 2014; 28:13-23. [PMID: 24009182 PMCID: PMC3974904 DOI: 10.1177/1545968313500564] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
BACKGROUND Extensive neuromotor development occurs early in human life, but the time that a brain injury occurs during development has not been rigorously studied when quantifying motor impairments. OBJECTIVE This study investigated the impact of timing of brain injury on the magnitude and distribution of weakness in the paretic arm of individuals with childhood-onset hemiparesis. METHODS A total of 24 individuals with hemiparesis were divided into time periods of injury before birth (PRE-natal, n = 8), around the time of birth (PERI-natal, n = 8), or after 6 months of age (POST-natal, n = 8). They, along with 8 typically developing peers, participated in maximal isometric shoulder, elbow, wrist, and finger torque generation tasks using a multiple-degree-of-freedom load cell to quantify torques in 10 directions. A mixed-model ANOVA was used to determine the effect of group and task on a calculated relative weakness ratio between arms. RESULTS There was a significant effect of both time of injury group (P < .001) and joint torque direction (P < .001) on the relative weakness of the paretic arm. Distal joints were more affected compared with proximal joints, especially in the POST-natal group. CONCLUSIONS The distribution of weakness provides evidence for the relative preservation of ipsilateral corticospinal motor pathways to the paretic limb in those individuals injured earlier, whereas those who sustained later injury may rely more on indirect ipsilateral corticobulbospinal projections during the generation of torques with the paretic arm.
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Affiliation(s)
- Theresa Sukal-Moulton
- Department of Biomedical Engineering, Northwestern University
- Department of Physical Therapy and Human Movement Sciences, Northwestern University
| | | | - Deborah J. Gaebler-Spira
- Department of Physical Medicine and Rehabilitation, Northwestern University
- The Rehabilitation Institute of Chicago
| | - Julius P.A. Dewald
- Department of Biomedical Engineering, Northwestern University
- Department of Physical Therapy and Human Movement Sciences, Northwestern University
- Department of Physical Medicine and Rehabilitation, Northwestern University
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11
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Bautista W, Rash JE, Vanderpool KG, Yasumura T, Nagy JI. Re-evaluation of connexins associated with motoneurons in rodent spinal cord, sexually dimorphic motor nuclei and trigeminal motor nucleus. Eur J Neurosci 2013; 39:757-70. [PMID: 24313680 DOI: 10.1111/ejn.12450] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2013] [Revised: 11/06/2013] [Accepted: 11/09/2013] [Indexed: 11/30/2022]
Abstract
Electrical synapses formed by neuronal gap junctions composed of connexin36 (Cx36) are a common feature in mammalian brain circuitry, but less is known about their deployment in spinal cord. It has been reported based on connexin mRNA and/or protein detection that developing and/or mature motoneurons express a variety of connexins, including Cx26, Cx32, Cx36 and Cx43 in trigeminal motoneurons, Cx36, Cx37, Cx40, Cx43 and Cx45 in spinal motoneurons, and Cx32 in sexually dimorphic motoneurons. We re-examined the localization of these connexins during postnatal development and in adult rat and mouse using immunofluorescence labeling for each connexin. We found Cx26 in association only with leptomeninges in the trigeminal motor nucleus (Mo5), Cx32 only with oligodendrocytes and myelinated fibers among motoneurons in this nucleus and in the spinal cord, and Cx37, Cx40 and Cx45 only with blood vessels in the ventral horn of spinal cord, including those among motoneurons. By freeze-fracture replica immunolabeling, > 100 astrocyte gap junctions but no neuronal gap junctions were found based on immunogold labeling for Cx43, whereas 16 neuronal gap junctions at postnatal day (P)4, P7 and P18 were detected based on Cx36 labeling. Punctate labeling for Cx36 was localized to the somatic and dendritic surfaces of peripherin-positive motoneurons in the Mo5, motoneurons throughout the spinal cord, and sexually dimorphic motoneurons at lower lumbar levels. In studies of electrical synapses and electrical transmission between developing and between adult motoneurons, our results serve to focus attention on mediation of this transmission by gap junctions composed of Cx36.
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Affiliation(s)
- W Bautista
- Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, MB, Canada
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12
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A MusD retrotransposon insertion in the mouse Slc6a5 gene causes alterations in neuromuscular junction maturation and behavioral phenotypes. PLoS One 2012; 7:e30217. [PMID: 22272310 PMCID: PMC3260239 DOI: 10.1371/journal.pone.0030217] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2011] [Accepted: 12/15/2011] [Indexed: 11/20/2022] Open
Abstract
Glycine is the major inhibitory neurotransmitter in the spinal cord and some brain regions. The presynaptic glycine transporter, GlyT2, is required for sustained glycinergic transmission through presynaptic reuptake and recycling of glycine. Mutations in SLC6A5, encoding GlyT2, cause hereditary hyperekplexia in humans, and similar phenotypes in knock-out mice, and variants are associated with schizophrenia. We identified a spontaneous mutation in mouse Slc6a5, caused by a MusD retrotransposon insertion. The GlyT2 protein is undetectable in homozygous mutants, indicating a null allele. Homozygous mutant mice are normal at birth, but develop handling-induced spasms at five days of age, and only survive for two weeks, but allow the study of early activity-regulated developmental processes. At the neuromuscular junction, synapse elimination and the switch from embryonic to adult acetylcholine receptor subunits are hastened, consistent with a presumed increase in motor neuron activity, and transcription of acetylcholine receptors is elevated. Heterozygous mice, which show no reduction in lifespan but nonetheless have reduced levels of GlyT2, have a normal thermal sensitivity with the hot-plate test, but differences in repetitive grooming and decreased sleep time with home-cage monitoring. Open-field and elevated plus-maze tests did not detect anxiety-like behaviors; however, the latter showed a hyperactivity phenotype. Importantly, grooming and hyperactivity are observed in mouse schizophrenia models. Thus, mutations in Slc6a5 show changes in neuromuscular junction development as homozygotes, and behavioral phenotypes as heterozygotes, indicating their usefulness for studies related to glycinergic dysfunction.
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Fregosi RF. Respiratory related control of hypoglossal motoneurons--knowing what we do not know. Respir Physiol Neurobiol 2011; 179:43-7. [PMID: 21741499 DOI: 10.1016/j.resp.2011.06.023] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Revised: 06/24/2011] [Accepted: 06/26/2011] [Indexed: 10/18/2022]
Abstract
Because tongue position and stiffness help insure that the pharyngeal airspace is sufficiently open during breathing, the respiration-related behavior of the tongue muscles has been studied in detail, particularly during the last two decades. Although eight different muscles act upon the mammal tongue, we know very little about the respiration-related control of the majority of these, and almost nothing about how they work together as a complex electro-mechanical system. Other significant gaps include how hypoglossal motoneuron axons find their appropriate muscle target during development, whether the biophysical properties of hypoglossal motoneurons driving different muscles are the same, and how afferent information from cardiorespiratory reflex systems is transmitted from major brainstem integrating centers to the hypoglossal motoneuron pool. This brief review outlines some of these issues, with the hope that this will spur research in the field, ultimately leading to an improved understanding of the respiration-related control of the mammalian tongue musculature.
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Affiliation(s)
- Ralph F Fregosi
- Department of Physiology, College of Medicine and Department of Neuroscience, College of Science, The University of Arizona, Tucson, AZ 85721-0093, United States.
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Chen YH, Huang FL, Cheng YC, Wu CJ, Yang CN, Tsay HJ. Knockdown of zebrafish Nav1.6 sodium channel impairs embryonic locomotor activities. J Biomed Sci 2007; 15:69-78. [PMID: 17687633 DOI: 10.1007/s11373-007-9200-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2007] [Accepted: 07/21/2007] [Indexed: 10/23/2022] Open
Abstract
Although multiple subtypes of sodium channels are expressed in most neurons, the specific contributions of the individual sodium channels remain to be studied. The role of zebrafish Na(v)1.6 sodium channels in the embryonic locomotor movements has been investigated by the antisense morpholino (MO) knockdown. MO1 and MO2 are targeted at the regions surrounding the translation start site of zebrafish Na(v)1.6 mRNA. MO3 is targeted at the RNA splicing donor site of exon 2. The correctly spliced Na(v)1.6 mRNA of MO3 morphants is 6% relative to that of the wild-type embryos. Na(v)1.6-targeted MO1, MO2 and MO3 attenuate the spontaneous contraction, tactile sensitivity, and swimming in comparison with a scrambled morpholino and mutated MO3 morpholino. No significant defect is observed in the development of slow muscles, the axonal projection of primary motoneurons, and neuromuscular junctions. The movement impairments caused by MO1, MO2, and MO3 suggest that the function of Na(v)1.6 sodium channels is essential on the normal early embryonic locomotor activities.
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Affiliation(s)
- Yau-Hung Chen
- Graduate Institute of Life Sciences, Tamkang University, Taipei, Taiwan
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15
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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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16
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Abstract
The selective elimination of axons, dendrites, axon and dendrite branches, and synapses, without loss of the parent neurons, occurs during normal development of the nervous system as well as in response to injury or disease in the adult. The widespread developmental phenomena of exuberant axonal projections and synaptic connections require both small-scale and large-scale axon pruning to generate precise adult connectivity, and they provide a mechanism for neural plasticity in the developing and adult nervous system, as well as a mechanism to evolve differences between species in a projection system. Such pruning is also required to remove axonal connections damaged in the adult, to stabilize the affected neural circuits, and to initiate their repair. Pruning occurs through either retraction or degeneration. Here we review examples of these phenomena and consider potential cellular and molecular mechanisms that underlie axon retraction and degeneration and how they might relate to each other in development and disease.
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Affiliation(s)
- Liqun Luo
- Department of Biological Sciences, Neurosciences Program, Stanford University, Stanford, CA 94305, USA.
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17
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De Stefano ME, Leone L, Lombardi L, Paggi P. Lack of dystrophin leads to the selective loss of superior cervical ganglion neurons projecting to muscular targets in genetically dystrophic mdx mice. Neurobiol Dis 2005; 20:929-42. [PMID: 16023353 DOI: 10.1016/j.nbd.2005.06.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2005] [Revised: 05/26/2005] [Accepted: 06/03/2005] [Indexed: 12/31/2022] Open
Abstract
Autonomic imbalance is a pathological aspect of Duchenne muscular dystrophy. Here, we show that the sympathetic superior cervical ganglion (SCG) of mdx mice, which lack dystrophin (Dp427), has 36% fewer neurons than that of wild-type animals. Cell loss occurs around P10 and affects those neurons innervating muscular targets (heart and iris), which, differently from the submandibular gland (non-muscular target), are precociously damaged by the lack of Dp427. In addition, although we reveal altered axonal defasciculation in the submandibular gland and reduced terminal sprouting in all SCG target organs, poor adrenergic innervation is observed only in the heart and iris. These alterations, detected as early as P5, when neuronal loss has not yet occurred, suggest that in mdx mice the absence of Dp427 directly impairs the axonal growth and terminal sprouting of sympathetic neurons. However, when these intrinsic alterations combine with structural and/or functional damages of muscular targets, neuronal death occurs.
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MESH Headings
- Animals
- Autonomic Nervous System Diseases/genetics
- Autonomic Nervous System Diseases/metabolism
- Autonomic Nervous System Diseases/physiopathology
- Cell Death/genetics
- Disease Models, Animal
- Dystrophin/deficiency
- Growth Cones/metabolism
- Growth Cones/ultrastructure
- Heart/growth & development
- Heart/innervation
- Iris/growth & development
- Iris/innervation
- Iris/ultrastructure
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Inbred mdx
- Microscopy, Electron, Transmission
- Muscle, Smooth/innervation
- Muscle, Smooth/physiopathology
- Muscles/innervation
- Muscles/ultrastructure
- Muscular Dystrophy, Duchenne/metabolism
- Muscular Dystrophy, Duchenne/pathology
- Muscular Dystrophy, Duchenne/physiopathology
- Myocardium/ultrastructure
- Nerve Degeneration/genetics
- Nerve Degeneration/metabolism
- Nerve Degeneration/physiopathology
- Neuronal Plasticity/genetics
- Neurons/metabolism
- Neurons/pathology
- Superior Cervical Ganglion/metabolism
- Superior Cervical Ganglion/pathology
- Superior Cervical Ganglion/physiopathology
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Affiliation(s)
- M Egle De Stefano
- Dipartimento di Biologia Cellulare e dello Sviluppo, Università La Sapienza, Piazzale Aldo Moro 5, 00185 Roma, Italy.
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18
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Hormuzdi SG, Filippov MA, Mitropoulou G, Monyer H, Bruzzone R. Electrical synapses: a dynamic signaling system that shapes the activity of neuronal networks. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2004; 1662:113-37. [PMID: 15033583 DOI: 10.1016/j.bbamem.2003.10.023] [Citation(s) in RCA: 154] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2003] [Revised: 10/14/2003] [Accepted: 10/14/2003] [Indexed: 01/25/2023]
Abstract
Gap junctions consist of intercellular channels dedicated to providing a direct pathway for ionic and biochemical communication between contacting cells. After an initial burst of publications describing electrical coupling in the brain, gap junctions progressively became less fashionable among neurobiologists, as the consensus was that this form of synaptic transmission would play a minimal role in shaping neuronal activity in higher vertebrates. Several new findings over the last decade (e.g. the implication of connexins in genetic diseases of the nervous system, in processing sensory information and in synchronizing the activity of neuronal networks) have brought gap junctions back into the spotlight. The appearance of gap junctional coupling in the nervous system is developmentally regulated, restricted to distinct cell types and persists after the establishment of chemical synapses, thus suggesting that this form of cell-cell signaling may be functionally interrelated with, rather than alternative to chemical transmission. This review focuses on gap junctions between neurons and summarizes the available data, derived from molecular, biological, electrophysiological, and genetic approaches, that are contributing to a new appreciation of their role in brain function.
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Affiliation(s)
- Sheriar G Hormuzdi
- Department of Clinical Neurobiology, Interdisciplinary Center for Neurosciences, University of Heidelberg, 69120 Heidelberg, Germany
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19
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Prieto-Lloret J, Caceres AI, Obeso A, Rocher A, Rigual R, Agapito MT, Bustamante R, Castañeda J, Perez-Garcia MT, Lopez-Lopez JR, Gonzalez C. Ventilatory responses and carotid body function in adult rats perinatally exposed to hyperoxia. J Physiol 2004; 554:126-44. [PMID: 14678497 PMCID: PMC1664733 DOI: 10.1113/jphysiol.2003.049445] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Hypoxia increases the release of neurotransmitters from chemoreceptor cells of the carotid body (CB) and the activity in the carotid sinus nerve (CSN) sensory fibers, elevating ventilatory drive. According to previous reports, perinatal hyperoxia causes CSN hypotrophy and varied diminishment of CB function and the hypoxic ventilatory response. The present study aimed to characterize the presumptive hyperoxic damage. Hyperoxic rats were born and reared for 28 days in 55%-60% O2; subsequent growth (to 3.5-4.5 months) was in a normal atmosphere. Hyperoxic and control rats (born and reared in a normal atmosphere) responded with a similar increase in ventilatory frequency to hypoxia and hypercapnia. In comparison with the controls, hyperoxic CBs showed (1) half the size, but comparable percentage area positive to tyrosine hydroxylase (chemoreceptor cells) in histological sections; (2) a twofold increase in dopamine (DA) concentration, but a 50% reduction in DA synthesis rate; (3) a 75% reduction in hypoxia-evoked DA release, but normal high [K+]0-evoked release; (4) a 75% reduction in the number of hypoxia-sensitive CSN fibers (although responding units displayed a nearly normal hypoxic response); and (5) a smaller percentage of chemoreceptor cells that increased [Ca2+]1 in hypoxia, although responses were within the normal range. We conclude that perinatal hyperoxia causes atrophy of the CB-CSN complex, resulting in a smaller number of chemoreceptor cells and fibers. Additionally, hyperoxia damages O2-sensing, but not exocytotic, machinery in most surviving chemoreceptor cells. Although hyperoxic CBs contain substantially smaller numbers of chemoreceptor cells/sensory fibers responsive to hypoxia they appear sufficient to evoke normal increases in ventilatory frequency.
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Affiliation(s)
- J Prieto-Lloret
- Departamento de Bioquimica y Biología Molecular y Fisiología/Instituto de Biología y Genética Molecular, Universidad de Valladolid/Consejo Superior de Investigaciones Científicas, Facultad de Medicina, 47005 Valladolid, Spain
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20
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Abstract
The notion that astrocytes have a profound influence on the function of synapses between CNS neurons implies that the development of synaptic connections and their glial neighbors are controlled by reciprocally acting signals. Currently, however, synaptogenesis is considered a purely neuronal affair. This article summarizes recent experimental evidence suggesting that this may not be the case. Astrocytes may indeed regulate the formation, maturation and maintenance of synapses. The recent advances caution that synapses cannot develop correctly without astrocytes. Further progress on this issue requires new experimental models to identify signaling pathways and to scrutinize the relevance of glia-synapse interactions in vivo.
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Affiliation(s)
- Michal Slezak
- Max-Planck/CNRS Group, UPR 2356, Centre de Neurochimie, 5 rue Blaise Pascal, F-67084 Strasbourg, France.
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21
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Bradley NS, Jahng DY. Selective effects of light exposure on distribution of motility in the chick embryo at E18. J Neurophysiol 2003; 90:1408-17. [PMID: 12761280 DOI: 10.1152/jn.00393.2003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
It is well established that orderly patterns of motor neuron activity, muscle recruitment, and limb movement are generated in chicks during motility by embryonic day (E)9, the midpoint in embryonic development. However, our recent work suggests that some attributes of motility, such as the rhythm of repetitive limb movements and distribution of activity, become less orderly after E9. In this study, we extend these observations by performing continuous force recordings over a 24-h period in ovo at E18 with augmented sampling of synchronized video and electromyogram (EMG) recordings. We report the distribution of three repetitive behaviors, rapid limb movement, respiratory-like movement, and beak clapping, identified in force recordings, and the general distribution of motility. We also test a model recently proposed to account for age-related changes in motility parameters. In the model, we proposed that circadian networks contribute to the age-related changes in distribution of motility. As a first test of this hypothesis, we examine whether light exposure contributes to the variable distribution of motility by comparing motility parameters at E18 for embryos incubated and tested under either a 12-h light/dark cycle or continuous light. Results suggest that exposure to light increases the total amount of activity and hastens the onset of extended respiratory-like movement sequences but does not impact expression of repetitive limb movement or beak clapping at E18. The possible influence of circadian mechanisms on embryonic behavior and insensitivity of repetitive limb movements to light exposure are discussed.
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Affiliation(s)
- Nina S Bradley
- Department of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, California 90033, USA.
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22
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Kasthuri N, Lichtman JW. The role of neuronal identity in synaptic competition. Nature 2003; 424:426-30. [PMID: 12879070 DOI: 10.1038/nature01836] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2003] [Accepted: 06/02/2003] [Indexed: 11/08/2022]
Abstract
In developing mammalian muscle, axon branches of several motor neurons co-innervate the same muscle fibre. Competition among them results in the strengthening of one and the withdrawal of the rest. It is not known why one particular axon branch survives or why some competitions resolve sooner than others. Here we show that the fate of axonal branches is strictly related to the identity of the axons with which they compete. When two neurons co-innervate multiple target cells, the losing axon branches in each contest belong to the same neuron and are at nearly the same stage of withdrawal. The axonal arbor of one neuron engages in multiple sets of competitions simultaneously. Each set proceeds at a different rate and heads towards a common outcome based on the identity of the competitor. Competitive vigour at each of these sets of local competitions depends on a globally distributed resource: neurons with larger arborizations are at a competitive disadvantage when confronting neurons with smaller arborizations. An accompanying paper tests the idea that the amount of neurotransmitter released is this global resource.
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Affiliation(s)
- Narayanan Kasthuri
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St Louis, Missouri 63110, USA
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23
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Abstract
Functional and structural decline in the neuromuscular system with aging has been recognized as a cause of impairment in physical performance and loss of independence in the elderly. Alterations in spinal cord motor neurones and at the neuromuscular junction have been identified as evidence of denervation in skeletal muscles from aging mammals, including humans. However, the reciprocal influences of neurones on gene expression in muscle and of muscle on age-related neurodegeneration are poorly understood, and, as a result, interventions aimed at delaying or preventing degeneration of the neural component in aging muscle have been largely unsuccessful. The present article discusses the evidence for neural influence on age-related impairments of skeletal muscle, including a role in excitation-contraction uncoupling. The role of nerves in regulating the trophic actions of insulin-like growth factor-1 (IGF-1) and other neurotrophic factors is considered as a novel influence on the effects of aging on the neuromuscular junction. A better understanding of nerve-muscle interactions will allow for more rational interventions in the aging neuromuscular system.
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Affiliation(s)
- Osvaldo Delbono
- Department of Physiology and Pharmacology, Neuroscience Program, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA.
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24
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Abstract
Recent studies suggest that glial cells regulate certain aspects of synapse development. Neurons can form synapses without glia, but may require glia-derived cholesterol to form numerous and efficient synapses. During synapse maturation, soluble and contact-dependent factors from glia may influence the composition of the postsynaptic density. Finally, synaptic connections appear to require glia to support their structural stability. Given the new evidence, it may be time now to acknowledge glia as a source for synaptogenesis-promoting signals. Scrutinizing the molecular mechanisms underlying this new function of glia and testing its relevance in vivo may help to understand how synapses develop and why they degenerate under pathological conditions.
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Affiliation(s)
- Frank W Pfrieger
- Max-Planck/CNRS Group, UPR 2356, Centre de Neurochimie, 5 rue Blaise Pascal, Strasbourg, France.
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25
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Corner MA, van Pelt J, Wolters PS, Baker RE, Nuytinck RH. Physiological effects of sustained blockade of excitatory synaptic transmission on spontaneously active developing neuronal networks--an inquiry into the reciprocal linkage between intrinsic biorhythms and neuroplasticity in early ontogeny. Neurosci Biobehav Rev 2002; 26:127-85. [PMID: 11856557 DOI: 10.1016/s0149-7634(01)00062-8] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Spontaneous bioelectric activity (SBA) taking the form of extracellularly recorded spike trains (SBA) has been quantitatively analyzed in organotypic neonatal rat visual cortex explants at different ages in vitro, and the effects investigated of both short- and long-term pharmacological suppression of glutamatergic synaptic transmission. In the presence of APV, a selective NMDA receptor blocker, 1-2- (but not 3-)week-old cultures recovered their previous SBA levels in a matter of hours, although in imitation of the acute effect of the GABAergic inhibitor picrotoxin (PTX), bursts of action potentials were abnormally short and intense. Cultures treated either overnight or chronically for 1-3 weeks with APV, the AMPA/kainate receptor blocker DNQX, or a combination of the two were found to display very different abnormalities in their firing patterns. NMDA receptor blockade for 3 weeks produced the most severe deviations from control SBA, consisting of greatly prolonged and intensified burst firing with a strong tendency to be broken up into trains of shorter spike clusters. This pattern was most closely approximated by acute GABAergic disinhibition in cultures of the same age, but this latter treatment also differed in several respects from the chronic-APV effect. In 2-week-old explants, in contrast, it was the APV+DNQX treated group which showed the most exaggerated spike bursts. Functional maturation of neocortical networks, therefore, may specifically require NMDA receptor activation (not merely a high level of neuronal firing) which initially is driven by endogenous rather than afferent evoked bioelectric activity. Putative cellular mechanisms are discussed in the context of a thorough review of the extensive but scattered literature relating activity-dependent brain development to spontaneous neuronal firing patterns.
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Affiliation(s)
- M A Corner
- Academic Medical Centre, Meibergdreef 33, Netherlands Institute for Brain Research, 1105 AZ Amsterdam, The Netherlands.
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26
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Personius K, Chang Q, Bittman K, Panzer J, Balice-Gordon R. Gap junctional communication among motor and other neurons shapes patterns of neural activity and synaptic connectivity during development. CELL COMMUNICATION & ADHESION 2001; 8:329-33. [PMID: 12064613 DOI: 10.3109/15419060109080748] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
We are studying the functional roles of neuronal gap junctional coupling during development, using motor neurons and their synapses with muscle fibers as a model system. At neuromuscular synapses, several studies have shown that the relative pattern of activity among motor inputs competing for innervation of the same target muscle fiber determines how patterns of innervation are sculpted during the first weeks after birth. We asked whether gap junctional coupling among motor neurons modulates the relative timing of motor neuron activity in awake, behaving neonatal mice. We found that the activity of motor neurons innervating the same muscle is temporally correlated perinatally, during the same period that gap junction-mediated electrical and dye coupling are present. In vivo blockade of gap junctions abolished temporal correlations in motor neuron activity, without changing overall motor behavior, motor neuron activity patterns or firing frequency. Together with preliminary studies in mice lacking gap junction protein Cx40, our data suggest that developmentally regulated gap junctional coupling among motor and other neurons affects the activity in nascent neural circuits and thus in turn affects synaptic connectivity. Dynamic monitoring of dye coupling can be used to explore this possibility in normal mice and in mice lacking gap junction proteins during embryonic and neonatal development.
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Affiliation(s)
- K Personius
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia 19104-6074, USA
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27
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Abstract
The development of the neural control circuitry underlying different patterns of behavior is rapidly expanding area of interest in neuroscience. New important insights have been gained over the last few years at different molecular, cellular, network, and behavioral levels. Based primarily on the issues presented in the review articles in this issue, I have added some reflections as to what I find most challenging and important.
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Affiliation(s)
- S Grillner
- Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden.
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