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Miles KD, Doll CA. Chloride imbalance in Fragile X syndrome. Front Neurosci 2022; 16:1008393. [PMID: 36312023 PMCID: PMC9596984 DOI: 10.3389/fnins.2022.1008393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2022] [Accepted: 09/20/2022] [Indexed: 11/26/2022] Open
Abstract
Developmental changes in ionic balance are associated with crucial hallmarks in neural circuit formation, including changes in excitation and inhibition, neurogenesis, and synaptogenesis. Neuronal excitability is largely mediated by ionic concentrations inside and outside of the cell, and chloride (Cl-) ions are highly influential in early neurodevelopmental events. For example, γ-aminobutyric acid (GABA) is the main inhibitory neurotransmitter of the mature central nervous system (CNS). However, during early development GABA can depolarize target neurons, and GABAergic depolarization is implicated in crucial neurodevelopmental processes. This developmental shift of GABAergic neurotransmission from depolarizing to hyperpolarizing output is induced by changes in Cl- gradients, which are generated by the relative expression of Cl- transporters Nkcc1 and Kcc2. Interestingly, the GABA polarity shift is delayed in Fragile X syndrome (FXS) models; FXS is one of the most common heritable neurodevelopmental disorders. The RNA binding protein FMRP, encoded by the gene Fragile X Messenger Ribonucleoprotein-1 (Fmr1) and absent in FXS, appears to regulate chloride transporter expression. This could dramatically influence FXS phenotypes, as the syndrome is hypothesized to be rooted in defects in neural circuit development and imbalanced excitatory/inhibitory (E/I) neurotransmission. In this perspective, we summarize canonical Cl- transporter expression and investigate altered gene and protein expression of Nkcc1 and Kcc2 in FXS models. We then discuss interactions between Cl- transporters and neurotransmission complexes, and how these links could cause imbalances in inhibitory neurotransmission that may alter mature circuits. Finally, we highlight current therapeutic strategies and promising new directions in targeting Cl- transporter expression in FXS patients.
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Affiliation(s)
| | - Caleb Andrew Doll
- Department of Pediatrics, Section of Developmental Biology, University of Colorado School of Medicine, Children’s Hospital Colorado, Aurora, CO, United States
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2
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Orexinergic Modulation of Spinal Motor Activity in the Neonatal Mouse Spinal Cord. eNeuro 2018; 5:eN-NWR-0226-18. [PMID: 30417080 PMCID: PMC6223113 DOI: 10.1523/eneuro.0226-18.2018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Revised: 10/15/2018] [Accepted: 10/20/2018] [Indexed: 11/21/2022] Open
Abstract
The role of orexin during development, and especially in terms of spinal cord function, is not well understood. It is for this reason that we focused on the network actions of orexin during the first week of development. We found that orexinergic fibers were present in the lumbar spinal cord of postnatal day 0 (P0) to P3 mice. The fibers were expressed mainly in the dorsal horn, but occasional fibers were observed in the ventral horn. Both orexin (OX) A and OXB increased the motoneurons (MNs) tonic neurogram discharge. However, only OXA was found to significantly increase spontaneous bursting activity and the frequency of fictive locomotor bursts. We show that OXA is able to act directly on MNs. To test the contribution of the recurrent MN collaterals, we blocked the nicotinic cholinergic drive and observed that OXA retained its ability to increase fictive locomotor activity. Additionally, we recorded neurograms from ventral lateral funiculi, where OXA had no effect on population discharge. These effects were also confirmed by recording from descending commissural interneurons via patch recordings. The loci of the effects of OXA were further investigated in a dorsal horn-removed preparation where OXA also shows an increase in the discharge from ventral root neurograms but no increase in the frequency of spontaneous or fictive locomotion burst activity. In summary, multiple lines of evidence from our work demonstrate the robust effects of orexins on spinal cord networks and MNs at the time of birth.
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Jean-Xavier C, Sharples SA, Mayr KA, Lognon AP, Whelan PJ. Retracing your footsteps: developmental insights to spinal network plasticity following injury. J Neurophysiol 2017; 119:521-536. [PMID: 29070632 DOI: 10.1152/jn.00575.2017] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
During development of the spinal cord, a precise interaction occurs between descending projections and sensory afferents, with spinal networks that lead to expression of coordinated motor output. In the rodent, during the last embryonic week, motor output first occurs as regular bursts of spontaneous activity, progressing to stochastic patterns of episodes that express bouts of coordinated rhythmic activity perinatally. Locomotor activity becomes functionally mature in the 2nd postnatal wk and is heralded by the onset of weight-bearing locomotion on the 8th and 9th postnatal day. Concomitantly, there is a maturation of intrinsic properties and key conductances mediating plateau potentials. In this review, we discuss spinal neuronal excitability, descending modulation, and afferent modulation in the developing rodent spinal cord. In the adult, plastic mechanisms are much more constrained but become more permissive following neurotrauma, such as spinal cord injury. We discuss parallel mechanisms that contribute to maturation of network function during development to mechanisms of pathological plasticity that contribute to aberrant motor patterns, such as spasticity and clonus, which emerge following central injury.
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Affiliation(s)
- C Jean-Xavier
- Hotchkiss Brain Institute, University of Calgary , Calgary, Alberta , Canada.,Department of Comparative Biology and Experimental Medicine, University of Calgary , Calgary, Alberta , Canada
| | - S A Sharples
- Hotchkiss Brain Institute, University of Calgary , Calgary, Alberta , Canada.,Department of Neuroscience, University of Calgary , Calgary, Alberta , Canada
| | - K A Mayr
- Hotchkiss Brain Institute, University of Calgary , Calgary, Alberta , Canada.,Department of Neuroscience, University of Calgary , Calgary, Alberta , Canada
| | - A P Lognon
- Department of Comparative Biology and Experimental Medicine, University of Calgary , Calgary, Alberta , Canada
| | - P J Whelan
- Hotchkiss Brain Institute, University of Calgary , Calgary, Alberta , Canada.,Department of Comparative Biology and Experimental Medicine, University of Calgary , Calgary, Alberta , Canada
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Benammi H, Erazi H, El Hiba O, Vinay L, Bras H, Viemari JC, Gamrani H. Disturbed sensorimotor and electrophysiological patterns in lead intoxicated rats during development are restored by curcumin I. PLoS One 2017; 12:e0172715. [PMID: 28267745 PMCID: PMC5340392 DOI: 10.1371/journal.pone.0172715] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2016] [Accepted: 02/08/2017] [Indexed: 01/01/2023] Open
Abstract
Lead poisoning is one of the most significant health problem of environmental origin. It is known to cause different damages in the central and peripheral nervous system which could be represented by several neurophysiological and behavioral symptoms. In this study we firstly investigated the effect of lead prenatal exposure in rats to (3g/L), from neonatal to young age, on the motor/sensory performances, excitability of the spinal cord and gaits during development. Then we evaluated neuroprotective effects of curcumin I (Cur I) against lead neurotoxicity, by means of grasping and cliff avoidance tests to reveal the impairment of the sensorimotor functions in neonatal rats exposed prenatally to lead. In addition, extracellular recordings of motor output in spinal cord revealed an hyper-excitability of spinal networks in lead treated rats. The frequency of induced fictive locomotion was also increased in treated rats. At the young age, rats exhibited an impaired locomotor gait. All those abnormalities were attenuated by Cur I treatment at a dose of 16g/kg. Based on our finding, Cur I has shown features of a potent chemical compound able to restore the neuronal and the relative locomotor behaviors disturbances induced by lead intoxication. Therefore, this chemical can be recommended as a new therapeutic trial against lead induced neurotoxicity.
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Affiliation(s)
- Hind Benammi
- Neuroscience, Pharmacology and Environment Team, faculty of Science Semlalia, Cadi Ayyad University, Marrakech, Morocco
| | - Hasna Erazi
- Neuroscience, Pharmacology and Environment Team, faculty of Science Semlalia, Cadi Ayyad University, Marrakech, Morocco
| | - Omar El Hiba
- Neuroscience, Pharmacology and Environment Team, faculty of Science Semlalia, Cadi Ayyad University, Marrakech, Morocco
- Department of Biology, faculty of Sciences, Chouaib Doukkali University, EL Jadida, Morocco
| | - Laurent Vinay
- Institut de Neurosciences de la Timone, Unité Mixte de Recherche 7289, CNRS, Université Aix-Marseille, Marseille, France
| | - Hélène Bras
- Institut de Neurosciences de la Timone, Unité Mixte de Recherche 7289, CNRS, Université Aix-Marseille, Marseille, France
| | - Jean-Charles Viemari
- Institut de Neurosciences de la Timone, Unité Mixte de Recherche 7289, CNRS, Université Aix-Marseille, Marseille, France
- * E-mail: (HG); (JCV)
| | - Halima Gamrani
- Neuroscience, Pharmacology and Environment Team, faculty of Science Semlalia, Cadi Ayyad University, Marrakech, Morocco
- * E-mail: (HG); (JCV)
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5
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Alterations in hypoglossal motor neurons due to GAD67 and VGAT deficiency in mice. Exp Neurol 2016; 289:117-127. [PMID: 27956032 DOI: 10.1016/j.expneurol.2016.12.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Revised: 11/25/2016] [Accepted: 12/08/2016] [Indexed: 02/03/2023]
Abstract
There is an emerging body of evidence that glycinergic and GABAergic synaptic inputs onto motor neurons (MNs) help regulate the final number of MNs and axonal muscle innervation patterns. Using mutant glutamate decarboxylase 67 (GAD67) and vesicular inhibitory amino acid transporter (VGAT) deficient mice, we describe the effect that deficiencies of presynaptic GABAergic and/or glycinergic release have on the post-synaptic somato-dendritic structure of motor neurons, and the development of excitatory and inhibitory synaptic inputs to MNs. We use whole-cell patch clamp recording of synaptic currents in E18.5 hypoglossal MNs from brainstem slices, combined with dye-filling of these recorded cells with Neurobiotin™, high-resolution confocal imaging and 3-dimensional reconstructions. Hypoglossal MNs from GAD67- and VGAT-deficient mice display decreased inhibitory neurotransmission and increased excitatory synaptic inputs. These changes are associated with increased dendritic arbor length, increased complexity of dendritic branching, and increased density of spiny processes. Our results show that presynaptic release of inhibitory amino acid neurotransmitters are potent regulators of hypoglossal MN morphology and key regulators of synaptic inputs during this critical developmental time point.
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O'Donovan MJ. Review : Robustness and Self-regulation in the Production of Neural Activity by Developing Networks. Neuroscientist 2016. [DOI: 10.1177/107385849900500106] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Spontaneous activity is an important regulator of network development throughout the nervous system. Activity produced in different parts of the developing nervous system shares many features, which suggests that it does not depend on the detailed architecture of developing networks but rather on their common properties. Insights into the mechanisms responsible for generating spontaneous activity have come from recent studies of the spinal cord. Developing spinal networks are hyperexcitable and their immature syn apses are subject to activity-dependent synaptic depression. The conjunction of these properties, which may be common throughout the developing nervous system, is responsible for the spontaneous, episodic activity expressed by spinal networks. These properties endow developing spinal networks with an extremely robust mechanism for generating spontaneous activity that is resistant to major pharmacological and surgical per turbations. NEUROSCIENTIST 5:41-47, 1999
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Affiliation(s)
- Michael J. O'Donovan
- Section on Developmental Neurobiology Laboratory of
Neural Control National Institute of Neurological Disorders and Stroke Bethesda,
Maryland
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Glycinergic Neurotransmission: A Potent Regulator of Embryonic Motor Neuron Dendritic Morphology and Synaptic Plasticity. J Neurosci 2016; 36:80-7. [PMID: 26740651 DOI: 10.1523/jneurosci.1576-15.2016] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Emerging evidence suggests that central synaptic inputs onto motor neurons (MNs) play an important role in developmental regulation of the final number of MNs and their muscle innervation for a particular motor pool. Here, we describe the effect of genetic deletion of glycinergic neurotransmission on single MN structure and on functional excitatory and inhibitory inputs to MNs. We measured synaptic currents in E18.5 hypoglossal MNs from brain slices using whole-cell patch-clamp recording, followed by dye-filling these same cells with Neurobiotin, to define their morphology by high-resolution confocal imaging and 3D reconstruction. We show that hypoglossal MNs of mice lacking gephyrin display increased dendritic arbor length and branching, increased spiny processes, decreased inhibitory neurotransmission, and increased excitatory neurotransmission. These findings suggest that central glycinergic synaptic activity plays a vital role in regulating MN morphology and glutamatergic central synaptic inputs during late embryonic development. SIGNIFICANCE STATEMENT MNs within the brainstem and spinal cord are responsible for integrating a diverse array of synaptic inputs into discrete contractions of skeletal muscle to achieve coordinated behaviors, such as breathing, vocalization, and locomotion. The last trimester in utero is critical in neuromotor development, as this is when central and peripheral synaptic connections are made onto and from MNs. At this time-point, using transgenic mice with negligible glycinergic postsynaptic responses, we show that this deficiency leads to abnormally high excitatory neurotransmission and alters the dendritic architecture responsible for coherently integrating these inputs. This study compliments the emerging concept that neurodevelopmental disorders (including autism, epilepsy, and amyotrophic lateral sclerosis) are underpinned by synaptic dysfunction and therefore will be useful to neuroscientists and neurologists alike.
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8
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Glycine plays a crucial role as a co-agonist of NMDA receptors in the neuronal circuit generating body movements in rat fetuses. Neurosci Res 2015; 97:13-9. [DOI: 10.1016/j.neures.2015.03.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Revised: 03/01/2015] [Accepted: 03/10/2015] [Indexed: 12/15/2022]
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9
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Shim Y, Husbands P. Incremental Embodied Chaotic Exploration of Self-Organized Motor Behaviors with Proprioceptor Adaptation. Front Robot AI 2015. [DOI: 10.3389/frobt.2015.00007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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10
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Khazipov R, Valeeva G, Khalilov I. Depolarizing GABA and developmental epilepsies. CNS Neurosci Ther 2014; 21:83-91. [PMID: 25438879 DOI: 10.1111/cns.12353] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2014] [Revised: 10/14/2014] [Accepted: 10/20/2014] [Indexed: 12/22/2022] Open
Abstract
Early in development, GABA, which is the main inhibitory neurotransmitter in adult brain, depolarizes immature neurons and exerts dual--excitatory and shunting/inhibitory--effects in the developing neuronal networks. The present review discusses some general questions, including the properties of excitation at depolarizing GABAergic synapse and shunting inhibition by depolarizing GABA; technical issues in exploration of depolarizing GABA using various techniques and preparations, including the developmental aspects of traumatic injury and what is known (or rather unknown) on the actions of GABA in vivo; complex roles of depolarizing GABA in developmental epilepsies, including a contribution of depolarizing GABA to enhanced excitability in the immature networks, caused by repetitive seizures accumulation of intracellular chloride concentration that increases excitatory GABA power and its synchronizing proconvulsive effects, and correction of chloride homeostasis as a potential strategy to treat neonatal seizures.
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Affiliation(s)
- Roustem Khazipov
- INMED-INSERM U901, Marseille, France; Aix-Marseille University, Marseille, France; Laboratory of Neurobiology, Kazan Federal University, Kazan, Russia
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11
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Genetic absence of the vesicular inhibitory amino acid transporter differentially regulates respiratory and locomotor motor neuron development. Brain Struct Funct 2013; 220:525-40. [PMID: 24276495 DOI: 10.1007/s00429-013-0673-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2013] [Accepted: 11/05/2013] [Indexed: 10/26/2022]
Abstract
During mid to late embryonic development (E13 to birth in mice), the neuromotor system is refined by reducing motor neuron (MN) numbers and establishing nascent synaptic connections onto and by MNs. Concurrently, the response to GABAergic and glycinergic synaptic activity switches from postsynaptic excitation to inhibition. Our previous studies on mutant mice lacking glycinergic transmission or deficient in GABA suggests that altered MN activity levels during this developmental period differentially regulates MN survival and muscle innervation for respiratory and non-respiratory motor pools. To determine if combined loss of GABAergic and glycinergic transmission plays a similar or exaggerated role, we quantified MN number and muscle innervation in two respiratory (hypoglossal and phrenic) and two locomotor (brachial and lumbar) motor pools, in mice lacking vesicular inhibitory amino acid transporter, which display absent or severely impaired GABAergic and glycinergic neurotransmission. For respiratory MNs, we observed significant decreases in MN number (-20 % hypoglossal and -36 % phrenic) and diaphragm axonal branching (-60 %). By contrast, for non-respiratory brachial and lumbar MNs, we observed increases in MN number (+62 % brachial and +84 % lumbar) and axonal branching for innervated muscles (+123 % latissimus dorsi for brachial and +61 % gluteal for lumbar). These results show that combined absence of GABAergic and glycinergic neurotransmission causes distinct regional changes in MN number and muscle innervation, which are dependent upon the motor function of the specific motor pool.
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12
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Abstract
Throughout development, the nervous system produces patterned spontaneous activity. Research over the past two decades has revealed a core group of mechanisms that mediate spontaneous activity in diverse circuits. Many circuits engage several of these mechanisms sequentially to accommodate developmental changes in connectivity. In addition to shared mechanisms, activity propagates through developing circuits and neuronal pathways (i.e., linked circuits in different brain areas) in stereotypic patterns. Increasing evidence suggests that spontaneous network activity shapes synaptic development in vivo Variations in activity-dependent plasticity may explain how similar mechanisms and patterns of activity can be employed to establish diverse circuits. Here, I will review common mechanisms and patterns of spontaneous activity in emerging neural networks and discuss recent insights into their contribution to synaptic development.
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Affiliation(s)
- Daniel Kerschensteiner
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Saint Louis, MO, USA Department of Anatomy and Neurobiology, Washington University School of Medicine, Saint Louis, MO, USA Hope Center for Neurological Disorders, Washington University School of Medicine, Saint Louis, MO, USA
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13
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GABAA receptor-mediated tonic depolarization in developing neural circuits. Mol Neurobiol 2013; 49:702-23. [PMID: 24022163 DOI: 10.1007/s12035-013-8548-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Accepted: 08/27/2013] [Indexed: 12/25/2022]
Abstract
The activation of GABAA receptors (the type A receptors for γ-aminobutyric acid) produces two distinct forms of responses, phasic (i.e., transient) and tonic (i.e., persistent), that are mediated by synaptic and extrasynaptic GABAA receptors, respectively. During development, the intracellular chloride levels are high so activation of these receptors causes a net outward flow of anions that leads to neuronal depolarization rather than hyperpolarization. Therefore, in developing neural circuits, tonic activation of GABAA receptors may provide persistent depolarization. Recently, it became evident that GABAA receptor-mediated tonic depolarization alters the structure of patterned spontaneous activity, a feature that is common in developing neural circuits and is important for neural circuit refinement. Thus, this persistent depolarization may lead to a long-lasting increase in intracellular calcium level that modulates network properties via calcium-dependent signaling cascades. This article highlights the features of GABAA receptor-mediated tonic depolarization, summarizes the principles for discovery, reviews the current findings in diverse developing circuits, examines the underlying molecular mechanisms and modulation systems, and discusses their functional specializations for each developing neural circuit.
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Momose-Sato Y, Sato K. Large-scale synchronized activity in the embryonic brainstem and spinal cord. Front Cell Neurosci 2013; 7:36. [PMID: 23596392 PMCID: PMC3625830 DOI: 10.3389/fncel.2013.00036] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2013] [Accepted: 03/20/2013] [Indexed: 01/09/2023] Open
Abstract
In the developing central nervous system, spontaneous activity appears well before the brain responds to external sensory inputs. One of the earliest activities is observed in the hindbrain and spinal cord, which is detected as rhythmic electrical discharges of cranial and spinal motoneurons or oscillations of Ca(2+)- and voltage-related optical signals. Shortly after the initial expression, the spontaneous activity appearing in the hindbrain and spinal cord exhibits a large-scale correlated wave that propagates over a wide region of the central nervous system, maximally extending to the lumbosacral cord and to the forebrain. In this review, we describe several aspects of this synchronized activity by focusing on the basic properties, development, origin, propagation pattern, pharmacological characteristics, and possible mechanisms underlying the generation of the activity. These profiles differ from those of the respiratory and locomotion pattern generators observed in the mature brainstem and spinal cord, suggesting that the wave is primordial activity that appears during a specific period of embryonic development and plays some important roles in the development of the central nervous system.
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Affiliation(s)
- Yoko Momose-Sato
- Department of Health and Nutrition, College of Human Environmental Studies, Kanto Gakuin UniversityYokohama, Japan
| | - Katsushige Sato
- Department of Health and Nutrition Sciences, Faculty of Human Health, Komazawa Women's UniversityTokyo, Japan
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15
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Valeeva G, Valiullina F, Khazipov R. Excitatory actions of GABA in the intact neonatal rodent hippocampus in vitro. Front Cell Neurosci 2013; 7:20. [PMID: 23467988 PMCID: PMC3587803 DOI: 10.3389/fncel.2013.00020] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Accepted: 02/14/2013] [Indexed: 11/27/2022] Open
Abstract
The excitatory action of gamma-aminobutyric acid (GABA) is considered to be a hallmark of the developing nervous system. However, in immature brain slices, excitatory GABA actions may be secondary to neuronal injury during slice preparation. Here, we explored GABA actions in the rodent intact hippocampal preparations and at different depths of hippocampal slices during the early post-natal period [post-natal days (P) 1–7]. We found that in the intact hippocampus at P1–3: (i) GABA exerts depolarizing action as seen in cell-attached single GABA(A) channel recordings; (ii) GABA(A) receptor (GABA(A)-R) agonist isoguvacine and synaptic activation of the GABA(A)-Rs increase the frequency of multiple unit activity and the frequency of the network-driven giant depolarizing potentials (GDPs); and that (iii) Na+–K+–2Cl- cotransporter (NKCC1) antagonist bumetanide suppresses GDPs and the excitatory actions of isoguvacine. In the hippocampal slices at P2–5, isoguvacine and synaptic activation of GABA(A)-Rs-evoked excitatory responses at all slice depths, including surface and core. Thus, GABA exerts excitatory actions in the intact hippocampus (P1–3) and at all depths of hippocampal slices (P2–5). Therefore, the excitatory actions of GABA in hippocampal slices during the first post-natal days are not due to neuronal injury during slice preparation, and the trauma-related excitatory GABA actions at the slice surface are a fundamentally different phenomenon observed during the second post-natal week.
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Affiliation(s)
- Guzel Valeeva
- Institut de Neurobiologie de la Méditerranée, INSERM U901 Marseille, France ; Aix-Marseille University Marseille, France ; Laboratory of Neurobiology, Kazan Federal University Kazan, Russia
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16
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Fogarty MJ, Smallcombe KL, Yanagawa Y, Obata K, Bellingham MC, Noakes PG. Genetic deficiency of GABA differentially regulates respiratory and non-respiratory motor neuron development. PLoS One 2013; 8:e56257. [PMID: 23457538 PMCID: PMC3574162 DOI: 10.1371/journal.pone.0056257] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Accepted: 01/07/2013] [Indexed: 11/25/2022] Open
Abstract
Central nervous system GABAergic and glycinergic synaptic activity switches from postsynaptic excitation to inhibition during the stage when motor neuron numbers are being reduced, and when synaptic connections are being established onto and by motor neurons. In mice this occurs between embryonic (E) day 13 and birth (postnatal day 0). Our previous work on mice lacking glycinergic transmission suggested that altered motor neuron activity levels correspondingly regulated motor neuron survival and muscle innervation for all respiratory and non respiratory motor neuron pools, during this period of development [1]. To determine if GABAergic transmission plays a similar role, we quantified motor neuron number and the extent of muscle innervation in four distinct regions of the brain stem and spinal cord; hypoglossal, phrenic, brachial and lumbar motor pools, in mice lacking the enzyme GAD67. These mice display a 90% drop in CNS GABA levels ( [2]; this study). For respiratory-based motor neurons (hypoglossal and phrenic motor pools), we have observed significant drops in motor neuron number (17% decline for hypoglossal and 23% decline for phrenic) and muscle innervations (55% decrease). By contrast for non-respiratory motor neurons of the brachial lateral motor column, we have observed an increase in motor neuron number (43% increase) and muscle innervations (99% increase); however for more caudally located motor neurons within the lumbar lateral motor column, we observed no change in either neuron number or muscle innervation. These results show in mice lacking physiological levels of GABA, there are distinct regional changes in motor neuron number and muscle innervation, which appear to be linked to their physiological function and to their rostral-caudal position within the developing spinal cord. Our results also suggest that for more caudal (lumbar) regions of the spinal cord, the effect of GABA is less influential on motor neuron development compared to that of glycine.
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Affiliation(s)
- Matthew J Fogarty
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia
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17
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Dehorter N, Vinay L, Hammond C, Ben-Ari Y. Timing of developmental sequences in different brain structures: physiological and pathological implications. Eur J Neurosci 2012; 35:1846-56. [PMID: 22708595 DOI: 10.1111/j.1460-9568.2012.08152.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The developing brain is not a small adult brain. Voltage- and transmitter-gated currents, like network-driven patterns, follow a developmental sequence. Studies initially performed in cortical structures and subsequently in subcortical structures have unravelled a developmental sequence of events in which intrinsic voltage-gated calcium currents are followed by nonsynaptic calcium plateaux and synapse-driven giant depolarising potentials, orchestrated by depolarizing actions of GABA and long-lasting NMDA receptor-mediated currents. The function of these early patterns is to enable heterogeneous neurons to fire and wire together rather than to code specific modalities. However, at some stage, behaviourally relevant activities must replace these immature patterns, implying the presence of programmed stop signals. Here, we show that the developing striatum follows a developmental sequence in which immature patterns are silenced precisely when the pup starts locomotion. This is mediated by a loss of the long-lasting NMDA-NR2C/D receptor-mediated current and the expression of a voltage-gated K(+) current. At the same time, the descending inputs to the spinal cord become fully functional, accompanying a GABA/glycine polarity shift and ending the expression of developmental patterns. Therefore, although the timetable of development differs in different brain structures, the g sequence is quite similar, relying first on nonsynaptic events and then on synaptic oscillations that entrain large neuronal populations. In keeping with the 'neuroarcheology' theory, genetic mutations or environmental insults that perturb these developmental sequences constitute early signatures of developmental disorders. Birth dating developmental disorders thus provides important indicators of the event that triggers the pathological cascade leading ultimately to disease.
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Affiliation(s)
- N Dehorter
- INMED, INSERM UMR901 and Aix-Marseille Université, Marseille, France
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18
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Boychuk CR, Woerman AL, Mendelowitz D. Modulation of bulbospinal rostral ventral lateral medulla neurons by hypoxia/hypercapnia but not medullary respiratory activity. Hypertension 2012; 60:1491-7. [PMID: 23108653 DOI: 10.1161/hypertensionaha.112.197954] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Although sympathetic vasomotor discharge has respiratory modulation, the site(s) responsible for this cardiorespiratory interaction is unknown. One likely source for this coupling is the rostral ventral lateral medulla (RVLM), where presympathetic neurons originate in close apposition to respiratory neurons. The current study tested the hypothesis that RVLM bulbospinal neurons are modulated by medullary respiratory network activity using whole-cell patch-clamp electrophysiological recordings of RVLM neurons while simultaneously recording fictive respiratory bursting activity from the hypoglossal rootlet. Additionally, we examined whether challenges to cardiorespiratory function, mainly hypoxia/hypercapnia, alter the activity of bulbospinal neurons and, secondarily, whether changes in synaptic input mediate these responses. Surprisingly, our results indicate that inspiratory-related activity did not modulate glutamatergic, γ-aminobutyric acid-ergic, or glycinergic synaptic events or spontaneous action potential firing in these RVLM neurons. However, hypoxia/hypercapnia reversibly decreased the frequency of γ-aminobutyric acid and glycine inhibitory postsynaptic currents. Glycinergic inhibitory postsynaptic current frequency was depressed from the fifth through the 10th minute, whereas the depression of γ-aminobutyric acid-ergic events became significant only at the 10th minute of hypoxia/hypercapnia. On the basis of spontaneous firing activity, there were 2 populations of RVLM bulbospinal neurons. The firing frequency of low-discharging RVLM neurons was facilitated by hypoxia/hypercapnia, and this increase depended on reduced inhibitory neurotransmission. The firing frequency in RVLM neurons with high-discharge rates was inhibited, independent of synaptic input, by hypoxia/hypercapnia. This article demonstrates that sympathetic-respiratory coupling is not active in the neonatal brain stem slice, and reductions in inhibitory neurotransmission to low spontaneously active bulbospinal RVLM neurons are responsible for hypoxia/hypercapnia-elicited increases in activity.
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Affiliation(s)
- Carie R Boychuk
- Department of Pharmacology and Physiology, George Washington University, Washington, DC 20037, USA
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Mire E, Mezzera C, Leyva-Díaz E, Paternain AV, Squarzoni P, Bluy L, Castillo-Paterna M, López MJ, Peregrín S, Tessier-Lavigne M, Garel S, Galcerán J, Lerma J, López-Bendito G. Spontaneous activity regulates Robo1 transcription to mediate a switch in thalamocortical axon growth. Nat Neurosci 2012; 15:1134-43. [PMID: 22772332 DOI: 10.1038/nn.3160] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Accepted: 06/08/2012] [Indexed: 01/27/2023]
Abstract
Developing axons must control their growth rate to follow the appropriate pathways and establish specific connections. However, the regulatory mechanisms involved remain elusive. By combining live imaging with transplantation studies in mice, we found that spontaneous calcium activity in the thalamocortical system and the growth rate of thalamocortical axons were developmentally and intrinsically regulated. Indeed, the spontaneous activity of thalamic neurons governed axon growth and extension through the cortex in vivo. This activity-dependent modulation of growth was mediated by transcriptional regulation of Robo1 through an NF-κB binding site. Disruption of either the Robo1 or Slit1 genes accelerated the progression of thalamocortical axons in vivo, and interfering with Robo1 signaling restored normal axon growth in electrically silent neurons. Thus, modifications to spontaneous calcium activity encode a switch in the axon outgrowth program that allows the establishment of specific neuronal connections through the transcriptional regulation of Slit1 and Robo1 signaling.
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Affiliation(s)
- Erik Mire
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-Consejo Superior de Investigaciones Científicas, San't Joan d'Alacant, Spain
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20
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Bos R, Vinay L. Glucose is an adequate energy substrate for the depolarizing action of GABA and glycine in the neonatal rat spinal cord in vitro. J Neurophysiol 2012; 107:3107-15. [PMID: 22457452 DOI: 10.1152/jn.00571.2011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
In vitro studies have repeatedly demonstrated that the neurotransmitters γ-aminobutyric acid (GABA) and glycine depolarize immature neurons in many areas of the CNS, including the spinal cord. This widely accepted phenomenon was recently challenged by experiments showing that the depolarizing action of GABA on neonatal hippocampus and neocortex in vitro was prevented by adding energy substrates (ES), such as the ketone body metabolite dl-β-hydroxybutyric acid (DL-BHB), lactate, or pyruvate to the artificial cerebrospinal fluid (ACSF). It was suggested that GABA-induced depolarizations in vitro might be an artifact due to inadequate energy supply when glucose is the sole energy source, consistent with the energy metabolism of neonatal rat brain being largely dependent on ESs other than glucose. Here we examined the effects of these ESs (DL-BHB, lactate, pyruvate) on inhibitory postsynaptic potentials (IPSPs) recorded from neonatal rat lumbar spinal cord motoneurons (MNs), in vitro. We report that supplementing the ACSF with physiologic concentrations of DL-BHB, lactate, or pyruvate does not alter the reversal potential of IPSPs (E(IPSP)). Only high concentrations of pyruvate hyperpolarized E(IPSP). In addition, the depolarizing action of GABA on primary afferent terminals was not affected by supplementing the ACSF with ES at physiologic concentrations. We conclude that depolarizing IPSPs in immature MNs and the primary afferent depolarizations are not caused by inadequate energy supply. Glucose at its standard concentration appears to be an adequate ES for the neonatal spinal cord in vitro.
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Affiliation(s)
- Rémi Bos
- Institut de Neurosciences de la Timone, Unité Mixte Recherche 7289, Centre National de la Recherche Scientifique, and Aix-Marseille Université, Marseille, France
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Artificial CSF motion ensures rhythmic activity in the developing CNS ex vivo: a mechanical source of rhythmogenesis? J Neurosci 2011; 31:8832-40. [PMID: 21677167 DOI: 10.1523/jneurosci.1354-11.2011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Spontaneous rhythmic activity is a ubiquitous feature of developing neural structures that has been shown to be essential for the establishment of functional CNS connectivity. However, the primordial origin of these rhythms remains unknown. Here, we describe two types of rhythmic activity in distinct parts of the developing CNS isolated ex vivo on microelectrode arrays, the expression of which was found to be strictly dependent upon the movement of the artificial CSF (aCSF) flowing over the inner wall of the ventricles or over the outer surface of the CNS. First, whole embryonic mouse hindbrain-spinal cord preparations (stages E12.5-E15.5) rhythmically expressed waves of activity originating in the hindbrain and propagating in the spinal cord. Interestingly enough, the frequency of this rhythm was completely determined by the speed of the aCSF flow. In particular, at all stages considered, hindbrain activity was abolished when the perfusion was stopped. Immature rhythmic activity was also recorded in the isolated newborn (P0-P8) mouse cortex under normal aCSF perfusion. Again, this rhythm was abolished when the perfusion flow was stopped. In both structures, this phenomenon was not due to changes in temperature, oxygen level, or pH of the bath, but to the movement itself of the aCSF. These observations challenge the so-called "spontaneous" nature of rhythmic activity in immature neural networks and suggest that the movement of CSF in the ventricles and around the brain in vivo may mechanically drive rhythmogenesis in the developing CNS.
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22
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Maturation of the GABAergic transmission in normal and pathologic motoneurons. Neural Plast 2011; 2011:905624. [PMID: 21785735 PMCID: PMC3140191 DOI: 10.1155/2011/905624] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2011] [Accepted: 04/17/2011] [Indexed: 12/14/2022] Open
Abstract
γ-aminobutyric acid (GABA) acting on Cl−-permeable ionotropic type A (GABAA) receptors (GABAAR) is the major inhibitory neurotransmitter in the adult central nervous system of vertebrates. In immature brain structures, GABA exerts depolarizing effects mostly contributing to the expression of spontaneous activities that are instructive for the construction of neural networks but GABA also acts as a potent trophic factor. In the present paper, we concentrate on brainstem and spinal motoneurons that are largely targeted by GABAergic interneurons, and we bring together data on the switch from excitatory to inhibitory effects of GABA, on the maturation of the GABAergic system and GABAAR subunits. We finally discuss the role of GABA and its GABAAR in immature hypoglossal motoneurons of the spastic (SPA) mouse, a model of human hyperekplexic syndrome.
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Viemari JC, Bos R, Boulenguez P, Brocard C, Brocard F, Bras H, Coulon P, Liabeuf S, Pearlstein E, Sadlaoud K, Stil A, Tazerart S, Vinay L. Chapter 1--importance of chloride homeostasis in the operation of rhythmic motor networks. PROGRESS IN BRAIN RESEARCH 2011; 188:3-14. [PMID: 21333799 DOI: 10.1016/b978-0-444-53825-3.00006-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/01/2023]
Abstract
GABA and glycine are classically called "inhibitory" amino acids, despite the fact that their action can rapidly switch from inhibition to excitation and vice versa. The postsynaptic action depends on the intracellular concentration of chloride ions ([Cl(-)](i)), which is regulated by proteins in the plasma membrane: the K(+)-Cl(-) cotransporter KCC2 and the Na(+)-K(+)-Cl(-) cotransporter NKCC1, which extrude and intrude Cl(-) ions, respectively. A high [Cl(-)](i) leads to a depolarizing (excitatory) action of GABA and glycine, as observed in mature dorsal root ganglion neurons and in motoneurons both early during development and in several pathological conditions, such as following spinal cord injury. Here, we review some recent data regarding chloride homeostasis in the spinal cord and its contribution to network operation involved in locomotion.
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Affiliation(s)
- Jean-Charles Viemari
- Laboratoire Plasticité et Physio-Pathologie de la Motricité (UMR6196), Centre National de la Recherche Scientifique CNRS) & Aix-Marseille Université, 31 Chemin Joseph Aiguier, Marseille Cedex 20, France
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24
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Stil A, Jean-Xavier C, Liabeuf S, Brocard C, Delpire E, Vinay L, Viemari JC. Contribution of the potassium-chloride co-transporter KCC2 to the modulation of lumbar spinal networks in mice. Eur J Neurosci 2011; 33:1212-22. [PMID: 21255132 DOI: 10.1111/j.1460-9568.2010.07592.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Spontaneous activity is observed in most developing neuronal circuits, such as the retina, hippocampus, brainstem and spinal cord. In the spinal cord, spontaneous activity is important for generating embryonic movements critical for the proper development of motor axons, muscles and synaptic connections. A spontaneous bursting activity can be recorded in vitro from ventral roots during perinatal development. The depolarizing action of the inhibitory amino acids γ-aminobutyric acid and glycine is widely proposed to contribute to spontaneous activity in several immature systems. During development, the intracellular chloride concentration decreases, leading to a shift of equilibrium potential for Cl(-) ions towards more negative values, and thereby to a change in glycine- and γ-aminobutyric acid-evoked potentials from depolarization/excitation to hyperpolarization/inhibition. The up-regulation of the outward-directed Cl(-) pump, the neuron-specific potassium-chloride co-transporter type 2 KCC2, has been shown to underlie this shift. Here, we investigated whether spontaneous and locomotor-like activities are altered in genetically modified mice that express only 8-20% of KCC2, compared with wild-type animals. We show that a reduced amount of KCC2 leads to a depolarized equilibrium potential for Cl(-) ions in lumbar motoneurons, an increased spontaneous activity and a faster locomotor-like activity. However, the left-right and flexor-extensor alternating pattern observed during fictive locomotion was not affected. We conclude that neuronal networks within the spinal cord are more excitable in KCC2 mutant mice, which suggests that KCC2 strongly modulates the excitability of spinal cord networks.
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Affiliation(s)
- Aurélie Stil
- Laboratoire Plasticité et Physio-Pathologie de la Motricité (UMR 6196), CNRS & Aix-Marseille Université, Marseille, France
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25
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Saito K, Kakizaki T, Hayashi R, Nishimaru H, Furukawa T, Nakazato Y, Takamori S, Ebihara S, Uematsu M, Mishina M, Miyazaki JI, Yokoyama M, Konishi S, Inoue K, Fukuda A, Fukumoto M, Nakamura K, Obata K, Yanagawa Y. The physiological roles of vesicular GABA transporter during embryonic development: a study using knockout mice. Mol Brain 2010; 3:40. [PMID: 21190592 PMCID: PMC3023674 DOI: 10.1186/1756-6606-3-40] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2010] [Accepted: 12/30/2010] [Indexed: 11/16/2022] Open
Abstract
Background The vesicular GABA transporter (VGAT) loads GABA and glycine from the neuronal cytoplasm into synaptic vesicles. To address functional importance of VGAT during embryonic development, we generated global VGAT knockout mice and analyzed them. Results VGAT knockouts at embryonic day (E) 18.5 exhibited substantial increases in overall GABA and glycine, but not glutamate, contents in the forebrain. Electrophysiological recordings from E17.5-18.5 spinal cord motoneurons demonstrated that VGAT knockouts presented no spontaneous inhibitory postsynaptic currents mediated by GABA and glycine. Histological examination of E18.5 knockout fetuses revealed reductions in the trapezius muscle, hepatic congestion and little alveolar spaces in the lung, indicating that the development of skeletal muscle, liver and lung in these mice was severely affected. Conclusion VGAT is fundamental for the GABA- and/or glycine-mediated transmission that supports embryonic development. VGAT knockout mice will be useful for further investigating the roles of VGAT in normal physiology and pathophysiologic processes.
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Affiliation(s)
- Kenzi Saito
- Department of Genetic and Behavioral Neuroscience, Gunma University Graduate School of Medicine, Maebashi, Japan
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26
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Characterization of rhythmic Ca2+ transients in early embryonic chick motoneurons: Ca2+ sources and effects of altered activation of transmitter receptors. J Neurosci 2009; 29:15232-44. [PMID: 19955376 DOI: 10.1523/jneurosci.3809-09.2009] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
In the nervous system, spontaneous Ca(2+) transients play important roles in many developmental processes. We previously found that altering the frequency of electrically recorded rhythmic spontaneous bursting episodes in embryonic chick spinal cords differentially perturbed the two main pathfinding decisions made by motoneurons, dorsal-ventral and pool-specific, depending on the sign of the frequency alteration. Here, we characterized the Ca(2+) transients associated with these bursts and showed that at early stages while motoneurons are still migrating and extending axons to the base of the limb bud, they display spontaneous, highly rhythmic, and synchronized Ca(2+) transients. Some precursor cells in the ependymal layer displayed similar transients. T-type Ca(2+) channels and a persistent Na(+) current were essential to initiate spontaneous bursts and associated transients. However, subsequent propagation of activity throughout the cord resulted from network-driven chemical transmission mediated presynaptically by Ca(2+) entry through N-type Ca(2+) channels and postsynaptically by acetylcholine acting on nicotinic receptors. The increased [Ca(2+)](i) during transients depended primarily on L-type and T-type channels with a modest contribution from TRP (transient receptor potential) channels and ryanodine-sensitive internal stores. Significantly, the drugs used previously to produce pathfinding errors altered transient frequency but not duration or amplitude. These observations imply that different transient frequencies may differentially modulate motoneuron pathfinding. However, the duration of the Ca(2+) transients differed significantly between pools, potentially enabling additional distinct pool-specific downstream signaling. Many early events in spinal motor circuit formation are thus potentially sensitive to the rhythmic Ca(2+) transients we have characterized and to any drugs that perturb them.
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Nishimaru H, Kakizaki M. The role of inhibitory neurotransmission in locomotor circuits of the developing mammalian spinal cord. Acta Physiol (Oxf) 2009; 197:83-97. [PMID: 19673737 DOI: 10.1111/j.1748-1716.2009.02020.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Neuronal circuits generating the basic coordinated limb movements during walking of terrestrial mammals are localized in the spinal cord. In these neuronal circuits, called central pattern generators (CPGs), inhibitory synaptic transmission plays a crucial part. Inhibitory synaptic transmission mediated by glycine and GABA is thought to be essential in coordinated activation of muscles during locomotion, in particular, controlling temporal and spatial activation patterns of muscles of each joint of each limb on the left and right side of the body. Inhibition is involved in other aspects of locomotion such as control of speed and stability of the rhythm. However, the precise roles of neurotransmitters and their receptors mediating inhibitory synaptic transmission in mammalian spinal CPGs remain unclear. Moreover, many of the inhibitory interneurones essential for output pattern of the CPG are yet to be identified. In this review, recent advances on these issues, mainly from studies in the developing rodent spinal cord utilizing electrophysiology, molecular and genetic approaches are discussed.
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Affiliation(s)
- H Nishimaru
- Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Japan.
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28
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Hong K, Nishiyama M. From Guidance Signals to Movement: Signaling Molecules Governing Growth Cone Turning. Neuroscientist 2009; 16:65-78. [DOI: 10.1177/1073858409340702] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Directed growth cone movements in response to external guidance signals are required for the establishment of functional neuronal connections during development, adult nerve regeneration, and adult neurogenesis. Growth cone intrinsic properties permit different growth cone responses (e.g., attraction or repulsion) to a guidance signal, and alterations to these intrinsic properties often result in opposite growth cone responses. This article reviews the current knowledge of growth cone signaling, emphasizing the dependency of Ca2+ signaling on membrane potential shifts, and cyclic nucleotide and phosphoinositide signaling pathways during growth cone turning in response to guidance signals. We also discuss how asymmetrical growth cone signaling is achieved for the fine-tuned growth cone movement.
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Affiliation(s)
- Kyonsoo Hong
- Department of Biochemistry, New York University School of Medicine, New York, New York,
| | - Makoto Nishiyama
- Department of Biochemistry, New York University School of Medicine, New York, New York
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Abstract
Neurobiologists have long sought to understand how circuits in the nervous system are organized to generate the precise neural outputs that underlie particular behaviours. The motor circuits in the spinal cord that control locomotion, commonly referred to as central pattern generator networks, provide an experimentally tractable model system for investigating how moderately complex ensembles of neurons generate select motor behaviours. The advent of novel molecular and genetic techniques coupled with recent advances in our knowledge of spinal cord development means that a comprehensive understanding of how the motor circuitry is organized and operates may be within our grasp.
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Affiliation(s)
- Martyn Goulding
- Molecular Neurobiology Laboratory, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, California 92037, USA.
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30
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Lavallée A, Pflieger JF. Developmental expression of spontaneous activity in the spinal cord of postnatal opossums, Monodelphis domestica: An anatomical study. Brain Res 2009; 1282:1-9. [DOI: 10.1016/j.brainres.2009.05.068] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2009] [Revised: 05/13/2009] [Accepted: 05/18/2009] [Indexed: 10/20/2022]
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Sibilla S, Ballerini L. GABAergic and glycinergic interneuron expression during spinal cord development: dynamic interplay between inhibition and excitation in the control of ventral network outputs. Prog Neurobiol 2009; 89:46-60. [PMID: 19539686 DOI: 10.1016/j.pneurobio.2009.06.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2008] [Revised: 04/10/2009] [Accepted: 06/09/2009] [Indexed: 11/28/2022]
Abstract
A key objective of neuroscience research is to understand the processes leading to mature neural circuitries in the central nervous system (CNS) that enable the control of different behaviours. During development, network-constitutive neurons undergo dramatic rearrangements, involving their intrinsic properties, such as the blend of ion channels governing their firing activity, and their synaptic interactions. The spinal cord is no exception to this rule; in fact, in the ventral horn the maturation of motor networks into functional circuits is a complex process where several mechanisms cooperate to achieve the development of motor control. Elucidating such a process is crucial in identifying neurons more vulnerable to degenerative or traumatic diseases or in developing new strategies aimed at rebuilding damaged tissue. The focus of this review is on recent advances in understanding the spatio-temporal expression of the glycinergic/GABAergic system and on the contribution of this system to early network function and to motor pattern transformation along with spinal maturation. During antenatal development, the operation of mammalian spinal networks strongly depends on the activity of glycinergic/GABAergic neurons, whose action is often excitatory until shortly before birth when locomotor networks acquire the ability to generate alternating motor commands between flexor and extensor motor neurons. At this late stage of prenatal development, GABA-mediated excitation is replaced by synaptic inhibition mediated by glycine and/or GABA. At this stage of spinal maturation, the large majority of GABAergic neurons are located in the dorsal horn. We propose that elucidating the role of inhibitory systems in development will improve our knowledge on the processes regulating spinal cord maturation.
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Affiliation(s)
- Sara Sibilla
- Life Science Department, Center for Neuroscience B.R.A.I.N., University of Trieste, via Fleming 22, 34127 Trieste, Italy
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Plasticity of spinal cord locomotor networks and contribution of cation–chloride cotransporters. ACTA ACUST UNITED AC 2008; 57:103-10. [DOI: 10.1016/j.brainresrev.2007.09.003] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2007] [Accepted: 09/08/2007] [Indexed: 11/18/2022]
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Sipilä ST, Kaila K. GABAergic control of CA3-driven network events in the developing hippocampus. Results Probl Cell Differ 2008; 44:99-121. [PMID: 17622497 DOI: 10.1007/400_2007_033] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Endogenous activity is a characteristic feature of developing neuronal networks. In the neonatal rat hippocampus, spontaneously occurring network events known as "Giant Depolarizing Potentials" (GDPs) are seen in vitro at a stage when GABAergic transmission is depolarizing. GDPs are triggered by the CA3 region and they are seen as brief recurrent events in field-potential recordings, paralleled by depolarization and spiking of pyramidal neurons. In the light of current data, GDPs are triggered by the glutamatergic pyramidal neurons which act as conditional pacemakers, while the depolarizing action of GABA plays a permissive role for the generation of these events in in vitro preparations. From an in vivo perspective, GDPs appear to be an immature form of hippocampal sharp waves.
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Affiliation(s)
- Sampsa T Sipilä
- Department of Biological and Environmental Sciences, University of Helsinki, P.O. Box 65, 00014 Helsinki, Finland
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34
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Ben-Ari Y, Gaiarsa JL, Tyzio R, Khazipov R. GABA: a pioneer transmitter that excites immature neurons and generates primitive oscillations. Physiol Rev 2007; 87:1215-84. [PMID: 17928584 DOI: 10.1152/physrev.00017.2006] [Citation(s) in RCA: 892] [Impact Index Per Article: 52.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Developing networks follow common rules to shift from silent cells to coactive networks that operate via thousands of synapses. This review deals with some of these rules and in particular those concerning the crucial role of the neurotransmitter gamma-aminobuytric acid (GABA), which operates primarily via chloride-permeable GABA(A) receptor channels. In all developing animal species and brain structures investigated, neurons have a higher intracellular chloride concentration at an early stage leading to an efflux of chloride and excitatory actions of GABA in immature neurons. This triggers sodium spikes, activates voltage-gated calcium channels, and acts in synergy with NMDA channels by removing the voltage-dependent magnesium block. GABA signaling is also established before glutamatergic transmission, suggesting that GABA is the principal excitatory transmitter during early development. In fact, even before synapse formation, GABA signaling can modulate the cell cycle and migration. The consequence of these rules is that developing networks generate primitive patterns of network activity, notably the giant depolarizing potentials (GDPs), largely through the excitatory actions of GABA and its synergistic interactions with glutamate signaling. These early types of network activity are likely required for neurons to fire together and thus to "wire together" so that functional units within cortical networks are formed. In addition, depolarizing GABA has a strong impact on synaptic plasticity and pathological insults, notably seizures of the immature brain. In conclusion, it is suggested that an evolutionary preserved role for excitatory GABA in immature cells provides an important mechanism in the formation of synapses and activity in neuronal networks.
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Affiliation(s)
- Yehezkel Ben-Ari
- Insititut de Neurobiologie de la Méditerranée, Institut National de la Santé et de la Recherche Médicale U. 29, Marseille, France.
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35
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Kiehn O, Quinlan KA, Restrepo CE, Lundfald L, Borgius L, Talpalar AE, Endo T. Excitatory components of the mammalian locomotor CPG. ACTA ACUST UNITED AC 2007; 57:56-63. [PMID: 17988744 DOI: 10.1016/j.brainresrev.2007.07.002] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2007] [Accepted: 07/01/2007] [Indexed: 12/01/2022]
Abstract
Locomotion in mammals is to a large degree controlled directly by intrinsic spinal networks, called central pattern generators (CPGs). The overall function of these networks is governed by interaction between inhibitory and excitatory neurons. In the present review, we will discuss recent findings addressing the role of excitatory synaptic transmission for network function including the role of specific excitatory neuronal populations in coordinating muscle activity and in generating rhythmic activity.
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Affiliation(s)
- Ole Kiehn
- Mammalian Locomotor Laboratory, Department of Neuroscience, Karolinska Institutet, Retzius väg 8, 171 77 Stockholm, Sweden.
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36
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Hanson MG, Milner LD, Landmesser LT. Spontaneous rhythmic activity in early chick spinal cord influences distinct motor axon pathfinding decisions. ACTA ACUST UNITED AC 2007; 57:77-85. [PMID: 17920131 DOI: 10.1016/j.brainresrev.2007.06.021] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2007] [Accepted: 06/26/2007] [Indexed: 10/23/2022]
Abstract
During embryonic development chick and mouse spinal cords are activated by highly rhythmic episodes of spontaneous bursting activity at very early stages, while motoneurons are still migrating and beginning to extend their axons to the base of the limb. While such spontaneous activity has been shown to be important in refining neural projections once axons have reached their targets, early pathfinding events have been thought to be activity independent. However, in-ovo pharmacological manipulation of the transmitter systems that drive such early activity has shown that early motor axon pathfinding events are highly dependent on the normal pattern of bursting activity. A modest decrease in episode frequency resulted in dorsal-ventral pathfinding errors by lumbar motoneurons, and in the downregulation of several molecules required to successfully execute this guidance decision. In contrast, increasing the episode frequency was without effect on dorsal-ventral pathfinding. However, it prevented the subsequent motoneuron pool specific fasciculation of axons and their targeting to appropriate muscles, resulting in marked segmental pathfinding errors. These observations emphasize the need to better evaluate how such early spontaneous electrical activity may influence the molecular and transcription factor pathways that have been shown to regulate the differentiation of motor and interneuron phenotypes and the formation of spinal cord circuits. The intracellular signaling pathways by which episode frequency affects motor axon pathfinding must now be elucidated and it will be important to more precisely characterize the patterns with which specific subsets of motor and inter-neurons are activated normally and under conditions that alter spinal circuit formation.
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Affiliation(s)
- M Gartz Hanson
- Department of Neurosciences, Case Western Reserve University, School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106, USA
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Jean-Xavier C, Mentis GZ, O'Donovan MJ, Cattaert D, Vinay L. Dual personality of GABA/glycine-mediated depolarizations in immature spinal cord. Proc Natl Acad Sci U S A 2007; 104:11477-82. [PMID: 17592145 PMCID: PMC2040923 DOI: 10.1073/pnas.0704832104] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The inhibitory action of glycine and GABA in adult neurons consists of both shunting incoming excitations and moving the membrane potential away from the action potential (AP) threshold. By contrast, in immature neurons, inhibitory postsynaptic potentials (IPSPs) are depolarizing; it is generally accepted that, despite their depolarizing action, these IPSPs are inhibitory because of the shunting action of the Cl(-) conductance increase. Here we investigated the integration of depolarizing IPSPs (dIPSPs) with excitatory inputs in the neonatal rodent spinal cord by means of both intracellular recordings from lumbar motoneurons and a simulation using the compartment model program "Neuron." We show that the ability of IPSPs to suppress suprathreshold excitatory events depends on E(Cl) and the location of inhibitory synapses. The depolarization outlasts the conductance changes and spreads electrotonically in the somatodendritic tree, whereas the shunting effect is restricted and local. As a consequence, dIPSPs facilitated AP generation by subthreshold excitatory events in the late phase of the response. The window of facilitation became wider as E(Cl) was more depolarized and started earlier as inhibitory synapses were moved away from the excitatory input. GAD65/67 immunohistochemistry demonstrated the existence of distal inhibitory synapses on motoneurons in the neonatal rodent spinal cord. This study demonstrates that small dIPSPs can either inhibit or facilitate excitatory inputs depending on timing and location. Our results raise the possibility that inhibitory synapses exert a facilitatory action on distant excitatory inputs and slight changes of E(Cl) may have important consequences for network processing.
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Affiliation(s)
- Céline Jean-Xavier
- *Laboratoire Plasticité et Physio-Pathologie de la Motricité, Centre National de la Recherche Scientifique, Aix-Marseille Université, 31 Chemin Joseph Aiguier, F-13402 Marseille Cedex 20, France
| | - George Z. Mentis
- Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
| | - Michael J. O'Donovan
- Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
| | - Daniel Cattaert
- Laboratoire de Neurobiologie des Réseaux, Centre National de la Recherche Scientifique, Université de Bordeaux, 1 Avenue des Facultés, 33405 Talence Cedex, France; and
| | - Laurent Vinay
- *Laboratoire Plasticité et Physio-Pathologie de la Motricité, Centre National de la Recherche Scientifique, Aix-Marseille Université, 31 Chemin Joseph Aiguier, F-13402 Marseille Cedex 20, France
- To whom correspondence should be addressed. E-mail:
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Momose-Sato Y, Sato K, Kinoshita M. Spontaneous depolarization waves of multiple origins in the embryonic rat CNS. Eur J Neurosci 2007; 25:929-44. [PMID: 17331191 DOI: 10.1111/j.1460-9568.2007.05352.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
During development, correlated neuronal activity plays an important role in the establishment of the central nervous system (CNS). We have previously reported that a widely propagating correlated neuronal activity, termed the depolarization wave, is evoked by various sensory inputs. A remarkable feature of the depolarization wave is that it spreads broadly through the brain and spinal cord. In the present study, we examined whether the depolarization wave occurs spontaneously in the embryonic rat CNS and, if so, where it originates. In E15-16 rat embryos, spontaneous optically-revealed signals appeared in association with the rhythmic discharges of cranial motoneurons and propagated widely with similar characteristics to the evoked depolarization wave. At E15, the spontaneous wave mostly originated in the cervical to upper lumbar cords. At E16, the wave was predominantly generated in the lumbosacral cord although a wave associated with the second oscillatory burst was initiated in the rostral cord. At E16, a few waves also originated in the rostral ventrolateral medulla and the dorsomedial pons. When the influence of the caudal cord was removed by transecting the spinal cord, the contribution of the medulla and pons became more significant. These results show that the depolarization wave can be triggered by the spontaneous activity of multiple neuronal populations which are distributed widely from the pons to the lumbosacral cord, although the spinal cord usually plays a predominant role. This network possibly works as a self-distributing system that maintains the incidence and complicated patterns of the correlated activity in the developing CNS.
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Affiliation(s)
- Yoko Momose-Sato
- Department of Physiology, Tokyo Medical and Dental University, Graduate School and Faculty of Medicine, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan.
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Furlan F, Taccola G, Grandolfo M, Guasti L, Arcangeli A, Nistri A, Ballerini L. ERG conductance expression modulates the excitability of ventral horn GABAergic interneurons that control rhythmic oscillations in the developing mouse spinal cord. J Neurosci 2007; 27:919-28. [PMID: 17251434 PMCID: PMC6672895 DOI: 10.1523/jneurosci.4035-06.2007] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
During antenatal development, the operation and maturation of mammalian spinal networks strongly depend on the activity of ventral horn GABAergic interneurons that mediate excitation first and inhibition later. Although the functional consequence of GABA actions may depend on maturational processes in target neurons, it is also likely that evolving changes in GABAergic transmission require fine-tuning in GABA release, probably via certain intrinsic mechanisms regulating GABAergic neuron excitability at different embryonic stages. Nevertheless, it has not been possible, to date, to identify certain ionic conductances upregulated or downregulated before birth in such cells. By using an experimental model with either mouse organotypic spinal cultures or isolated spinal cord preparations, the present study examined the role of the ERG current (I(K(ERG))), a potassium conductance expressed by developing, GABA-immunoreactive spinal neurons. In organotypic cultures, only ventral interneurons with fast adaptation and GABA immunoreactivity, and only after 1 week in culture, were transformed into high-frequency bursters by E4031, a selective inhibitor of I(K(ERG)) that also prolonged and made more regular spontaneous bursts. In the isolated spinal cord in which GABA immunoreactivity and m-erg mRNA were colocalized in interneurons, ventral root rhythms evoked by NMDA plus 5-hydroxytryptamine were stabilized and synchronized by E4031. All of these effects were lost after 2 weeks in culture or before birth in coincidence with decreased m-erg expression. These data suggest that, during an early stage of spinal cord development, the excitability of GABAergic ventral interneurons important for circuit maturation depended, at least in part, on the function of I(K(ERG)).
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Affiliation(s)
- Francesco Furlan
- Physiology and Pathology Department, Center for Neuroscience B.R.A.I.N., University of Trieste, 34127 Trieste, Italy
| | - Giuliano Taccola
- Neurobiology Sector, International School for Advanced Studies, 34014 Trieste, Italy, and SPINAL Project, Udine
| | - Micaela Grandolfo
- Neurobiology Sector, International School for Advanced Studies, 34014 Trieste, Italy, and SPINAL Project, Udine
| | - Leonardo Guasti
- Department of Experimental Pathology and Oncology, University of Firenze, 50134 Firenze, Italy
| | - Annarosa Arcangeli
- Department of Experimental Pathology and Oncology, University of Firenze, 50134 Firenze, Italy
| | - Andrea Nistri
- Neurobiology Sector, International School for Advanced Studies, 34014 Trieste, Italy, and SPINAL Project, Udine
| | - Laura Ballerini
- Physiology and Pathology Department, Center for Neuroscience B.R.A.I.N., University of Trieste, 34127 Trieste, Italy
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40
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Hanson MG, Landmesser LT. Increasing the frequency of spontaneous rhythmic activity disrupts pool-specific axon fasciculation and pathfinding of embryonic spinal motoneurons. J Neurosci 2006; 26:12769-80. [PMID: 17151280 PMCID: PMC6674837 DOI: 10.1523/jneurosci.4170-06.2006] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Rhythmic spontaneous bursting activity, which occurs in many developing neural circuits, has been considered to be important for the refinement of neural projections but not for early pathfinding decisions. However, the precise frequency of bursting activity differentially affects the two major pathfinding decisions made by chick lumbosacral motoneurons. Moderate slowing of burst frequency was shown previously to cause motoneurons to make dorsoventral (D-V) pathfinding errors and to alter the expression of molecules involved in that decision. Moderate speeding up of activity is shown here not to affect these molecules or D-V pathfinding but to strongly perturb the anteroposterior (A-P) pathfinding process by which motoneurons fasciculate into pool-specific fascicles at the limb base and then selectively grow to muscle targets. Resumption of normal frequency allowed axons to correct the A-P pathfinding errors by altering their trajectories distally, indicating the dynamic nature of this process and its continued sensitivity to patterned activity.
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Affiliation(s)
- M. Gartz Hanson
- Department of Neurosciences, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106-4975
| | - Lynn T. Landmesser
- Department of Neurosciences, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106-4975
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41
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Carrasco MA, Castro PA, Sepulveda FJ, Cuevas M, Tapia JC, Izaurieta P, van Zundert B, Aguayo LG. Anti-homeostatic synaptic plasticity of glycine receptor function after chronic strychnine in developing cultured mouse spinal neurons. J Neurochem 2006; 100:1143-54. [PMID: 17217420 DOI: 10.1111/j.1471-4159.2006.04306.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this study, we describe a novel form of anti-homeostatic plasticity produced after culturing spinal neurons with strychnine, but not bicuculline or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Strychnine caused a large increase in network excitability, detected as spontaneous synaptic currents and calcium transients. The calcium transients were associated with action potential firing and activation of gamma-aminobutyric acid (GABA(A)) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors as they were blocked by tetrodotoxin (TTX), bicuculline, and CNQX. After chronic blockade of glycine receptors (GlyRs), the frequency of synaptic transmission showed a significant enhancement demonstrating the phenomenon of anti-homeostatic plasticity. Spontaneous inhibitory glycinergic currents in treated cells showed a fourfold increase in frequency (from 0.55 to 2.4 Hz) and a 184% increase in average peak amplitude compared with control. Furthermore, the augmentation in excitability accelerated the decay time constant of miniature inhibitory post-synaptic currents. Strychnine caused an increase in GlyR current density, without changes in the apparent affinity. These findings support the idea of a post-synaptic action that partly explains the increase in synaptic transmission. This phenomenon of synaptic plasticity was blocked by TTX, an antibody against brain-derived neurotrophic factor (BDNF) and K252a suggesting the involvement of the neuronal activity-dependent BDNF-TrkB signaling pathway. These results show that the properties of GlyRs are regulated by the degree of neuronal activity in the developing network.
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Affiliation(s)
- M A Carrasco
- Laboratory of Neurophysiology, Department of Physiology, University of Concepción, Concepción, Chile
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42
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Allain AE, Baïri A, Meyrand P, Branchereau P. Expression of the glycinergic system during the course of embryonic development in the mouse spinal cord and its co-localization with GABA immunoreactivity. J Comp Neurol 2006; 496:832-46. [PMID: 16628621 DOI: 10.1002/cne.20967] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
To understand better the role of glycine and gamma-aminobutyric acid (GABA) in the mouse spinal cord during development, we previously described the ontogeny of GABA. Now, we present the ontogeny of glycine-immunoreactive (Gly-ir) somata and fibers, at brachial and lumbar levels, from embryonic day 11.5 (E11.5) to postnatal day 0 (P0). Spinal Gly-ir somata appeared at E12.5 in the ventral horn, with a higher density at the brachial level. They were intermingled with numerous Gly-ir fibers reaching the border of the marginal zone. By E13.5, at the brachial level, the number of Gly-ir perikarya sharply increased throughout the whole ventral horn, whereas the density of fibers declined in the marginal zone. In the dorsal horn, the first Gly-ir somata were then detected. From E13.5 to E16.5, at the brachial level, the density of Gly-ir cells remained stable in the ventral horn, and after E16.5 it decreased to reach a plateau. In the dorsal horn, the density of Gly-ir cells increased, and after E16.5 it remained stable. At the lumbar level, maximum expression was reached at E16.5 in both the ventral and dorsal horn. Finally, the co-localization of glycine and GABA was analyzed, in the ventral motor area, at E13.5, E15.5, and E17.5. The results showed that, regardless of developmental stage studied, one-third of the stained somata co-expressed GABA and glycine. Our data show that the glycinergic system matures 1 day later than the GABAergic system and follows a parallel spatiotemporal evolution, leading to a larger population of glycine cells in the ventral horn.
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Affiliation(s)
- Anne-Emilie Allain
- Laboratoire de Neurobiologie des Réseaux, Université Bordeaux 1 et Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5816, Talence, France
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43
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Liu Q, Wong-Riley MTT. Developmental changes in the expression of GABAA receptor subunits alpha1, alpha2, and alpha3 in brain stem nuclei of rats. Brain Res 2006; 1098:129-38. [PMID: 16750519 DOI: 10.1016/j.brainres.2006.05.001] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2006] [Revised: 04/21/2006] [Accepted: 05/01/2006] [Indexed: 12/29/2022]
Abstract
Gamma-aminobutyric acid (GABA)(A) receptor subunit switching is a suggested postnatal mechanism for changes in GABA transmission from depolarization to hyperpolarization. Previously, we found an apparent switch between GABA(A) alpha3 and alpha1 subunit expression in the rat pre-Bötzinger complex (PBC) on postnatal day (P) 12, a presumed peak critical period of respiratory nuclei development. The present study aimed at determining if GABA(A) subunit switching occurred in another respiratory nucleus, the ventrolateral subnucleus of the solitary tract nucleus (NTS(VL)), and in a non-respiratory cuneate nucleus (CN) of P0 to P21 rats. In both nuclei: (1) the expression of GABA(A) alpha1 subunit was relatively low at birth but increased with development; (2) that of GABA(A) alpha3 was relatively high at birth but declined with age; and (3) GABA(A) alpha2 remained relatively low and constant throughout development. However, the specific patterns differed between the two nuclei, but were similar between the NTS(VL) and the PBC. In the NTS(VL), GABA(A) alpha1 expression gradually increased from birth and peaked at P12, whereas that in the CN sharply rose from P7 and peaked at P10. GABA(A) alpha3 expression had a prominent decrease from P11 to P12 in the NTS(VL), whereas that in the CN only gradually declined from P10 to P12. The developmental trends of alpha1 and alpha3 in the NTS(VL) intersected close to P12, whereas those in the CN intersected at P10. Despite differences in timing, GABA(A) alpha subunit switching may be a common theme in the brain stem that may mediate different functional properties of GABA transmission.
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Affiliation(s)
- Qiuli Liu
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
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44
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Banks GB, Kanjhan R, Wiese S, Kneussel M, Wong LM, O'Sullivan G, Sendtner M, Bellingham MC, Betz H, Noakes PG. Glycinergic and GABAergic synaptic activity differentially regulate motoneuron survival and skeletal muscle innervation. J Neurosci 2005; 25:1249-59. [PMID: 15689563 PMCID: PMC6725962 DOI: 10.1523/jneurosci.1786-04.2005] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
GABAergic and glycinergic synaptic transmission is proposed to promote the maturation and refinement of the developing CNS. Here we provide morphological and functional evidence that glycinergic and GABAergic synapses control motoneuron development in a region-specific manner during programmed cell death. In gephyrin-deficient mice that lack all postsynaptic glycine receptor and some GABA(A) receptor clusters, there was increased spontaneous respiratory motor activity, reduced respiratory motoneuron survival, and decreased innervation of the diaphragm. In contrast, limb-innervating motoneurons showed decreased spontaneous activity, increased survival, and increased innervation of their target muscles. Both GABA and glycine increased limb-innervating motoneuron activity and decreased respiratory motoneuron activity in wild-type mice, but only glycine responses were abolished in gephyrin-deficient mice. Our results provide genetic evidence that the development of glycinergic and GABAergic synaptic inputs onto motoneurons plays an important role in the survival, axonal branching, and spontaneous activity of motoneurons in developing mammalian embryos.
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Affiliation(s)
- Glen B Banks
- School of Biomedical Sciences, University of Queensland, St. Lucia, 4072 Queensland, Australia
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45
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Ren J, Momose-Sato Y, Sato K, Greer JJ. Rhythmic neuronal discharge in the medulla and spinal cord of fetal rats in the absence of synaptic transmission. J Neurophysiol 2005; 95:527-34. [PMID: 16148265 DOI: 10.1152/jn.00735.2005] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Spontaneous rhythmic neuronal activity is generated in the developing vertebrate nervous system. The patterned activity spreads diffusely throughout the fetal neuraxis. Here we demonstrate the ability of the fetal rat spinal cord and medulla to generate and transmit robust rhythmic patterns in the absence of synaptic activity. Regular rhythmic discharges were produced by fetal tissue bathed in low or zero [Ca(2+)](o) solution. The activity persisted in the presence of antagonists to neurotransmitter receptors that are known to mediate synaptic-mediated events associated with fetal rhythms. A combination of ventral root recordings and optical imaging using voltage-sensitive dyes demonstrated the extensive spread of rhythmic discharge in spinal cord and medullary neuronal populations of in vitro preparations. Whole cell recordings from medullary slices were performed to examine the ionic conductances and revealed the importance of persistent sodium conductances for generation of rhythmic activity in hypoglossal (XII) motoneurons. Rhythmic bursting in XII motoneurons persisted in the presence of gap junction blockers, although the amplitude of synchronized motor discharge recorded from nerve roots was diminished. We propose that nonsynaptically mediated conductances, potentially by extracellular ionic flux and/or ephaptic and electrotonic interactions mechanisms, act in concert with neurochemical transmission and gap junctions to promote the diffuse spread of rhythmic motor patterns in the developing nervous system.
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Affiliation(s)
- Jun Ren
- Department of Physiology, Centre for Neuroscience, 513 HMRC, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
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46
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Myers CP, Lewcock JW, Hanson MG, Gosgnach S, Aimone JB, Gage FH, Lee KF, Landmesser LT, Pfaff SL. Cholinergic Input Is Required during Embryonic Development to Mediate Proper Assembly of Spinal Locomotor Circuits. Neuron 2005; 46:37-49. [PMID: 15820692 DOI: 10.1016/j.neuron.2005.02.022] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2004] [Revised: 01/10/2005] [Accepted: 02/18/2005] [Indexed: 11/28/2022]
Abstract
Rhythmic limb movements are controlled by pattern-generating neurons within the ventral spinal cord, but little is known about how these locomotor circuits are assembled during development. At early stages of embryogenesis, motor neurons are spontaneously active, releasing acetylcholine that triggers the depolarization of adjacent cells in the spinal cord. To investigate whether acetylcholine-driven activity is required for assembly of the central pattern-generating (CPG) circuit, we studied mice lacking the choline acetyltransferase (ChAT) enzyme. Our studies show that a rhythmically active spinal circuit forms in ChAT mutants, but the duration of each cycle period is elongated, and right-left and flexor-extensor coordination are abnormal. In contrast, blocking acetylcholine receptors after the locomotor network is wired does not affect right-left or flexor-extensor coordination. These findings suggest that the cholinergic neurotransmitter pathway is involved in configuring the CPG during a transient period of development.
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Affiliation(s)
- Christopher P Myers
- Gene Expression Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA
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47
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Tsunekawa N, Arata A, Obata K. Development of spontaneous mouth/tongue movement and related neural activity, and their repression in fetal mice lacking glutamate decarboxylase 67. Eur J Neurosci 2005; 21:173-8. [PMID: 15654854 DOI: 10.1111/j.1460-9568.2004.03860.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Spontaneous body movement starts at early fetal stage, at embryonic day (E) 12-15 in mice. In the present study, the movement of the head region was studied in E13-14 mice by in utero ultrasound imaging, together with the in vitro recording of underlying neural activities in the hypoglossal nerve and the ventral root of the upper cervical cord of an isolated brainstem-spinal cord preparation. The role of gamma-aminobutyric acid (GABA) in the generation of fetal movement was assessed using mice lacking GABA-synthesizing glutamate decarboxylase 67 (GAD67). At E14, mouth opening and tongue withdrawal were observed independently at frequency of 14/h each. This movement was rarely observed in the GAD67-deficient mouse. The intraventricular administration of picrotoxin or 3-mercaptopropionic acid abolished mouth opening in the wild-type mice. In a brainstem-spinal cord preparation, three types of neural discharge were recorded: mouth/tongue-moving burst, respiratory burst and irregular activity on the basis of their waveform, regularity in occurrence and concomitant muscle activity. In the GAD67-deficient mice, the occurrence of mouth/tongue-moving burst and irregular activity was inhibited to about 15 and 40% of those in the wild-type mice, respectively. Respiratory burst was slightly inhibited but the difference was not significant. Picrotoxin greatly reduced the frequency of mouth/tongue-moving burst. These results indicate that GABA is involved in rhythm generation in movement of the head region and support the hypothesis that cleft palate in the GAD67-deficient mouse is due to the impairment of mouth or tongue movement that assists palate formation.
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Affiliation(s)
- Naoko Tsunekawa
- Obata Research Unit, RIKEN Brain Science Institute, Hirosawa 2-1, Wako-shi, Saitama 351-0198, Japan
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48
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Onimaru H, Homma I. Developmental changes in the spatio-temporal pattern of respiratory neuron activity in the medulla of late fetal rat. Neuroscience 2005; 131:969-77. [PMID: 15749349 DOI: 10.1016/j.neuroscience.2004.11.041] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/26/2004] [Indexed: 12/01/2022]
Abstract
We investigated how the spatio-temporal pattern of respiratory neuron network activity in the ventral medulla changes during the late fetal period of rat. Brainstem-spinal cord preparations isolated from rat fetuses on embryonic days 17-21 (E17-E21) were stained with a voltage-sensitive dye for optical image analysis of neuronal activity of the ventral medulla. The spatio-temporal pattern of respiratory neuron activity in the preparation from E20 to E21 was basically identical to that of neonatal rat; pre-inspiratory activity in a limited region of the rostral ventrolateral medulla, the para-facial region, preceded by several hundred milliseconds the onset of inspiratory activity in the more caudal ventrolateral medulla, the pre-Bötzinger complex level. In contrast, in E17-E18 specimens, pre-inspiratory activity could not be detected in the rostral medulla at the level of the facial nucleus. Neuronal activity appeared to begin at the pre-Bötzinger complex level shortly before onset of the inspiratory burst. Strong activity then developed in the facial nucleus and peaked in the post-inspiratory phase. The transition of these patterns of respiratory activity occurred at E19. We conclude that the changes in the spatio-temporal pattern of neuronal activity reflect developmental changes in the cellular elements underlying rhythm generation in the fetal respiratory neuron network. We suggest that the pre-inspiratory neuron network of the para-facial region in the rostral ventrolateral medulla functions as the rhythm generator after E19/20.
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Affiliation(s)
- H Onimaru
- Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
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49
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Aguayo LG, van Zundert B, Tapia JC, Carrasco MA, Alvarez FJ. Changes on the properties of glycine receptors during neuronal development. ACTA ACUST UNITED AC 2004; 47:33-45. [PMID: 15572161 DOI: 10.1016/j.brainresrev.2004.06.007] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/11/2004] [Indexed: 11/29/2022]
Abstract
Glycine receptors (GlyRs) play a major role in the excitability of spinal cord and brain stem neurons. During development, several properties of these receptors undergo significant changes resulting in major modifications of their physiological functions. For example, the receptor structure switches from a monomeric alpha or heteromeric alpha 2 beta in immature neurons to an alpha 1 beta receptor type in mature neurons. Together with these changes in receptor subunits, the postsynaptic cluster size increases with development. Parallel to these modifications, the apparent receptor affinity to glycine and strychnine, as well as that of Zn(2+) and ethanol increases with time. The mature receptor is characterized by a slow desensitizing current and high sensitivity to modulation by protein kinase C. Also, the high level of glycinergic transmission in immature spinal neurons modulates neuronal excitability causing membrane depolarization and changes in intracellular calcium. Due to these properties, chronic inhibition of glycinergic transmission affects neurite outgrowth and produces changes in the level of synaptic transmission induced by GABA(A) and AMPA receptors. Finally, the high level of plasticity found in immature GlyRs is likely associated to changes in cytoskeleton dynamics.
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Affiliation(s)
- Luis G Aguayo
- Laboratory of Neurophysiology, Department of Physiology, University of Concepcion, P.O. Box 160-C, Concepcíon, Chile.
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50
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Rosato-Siri MD, Zoccolan D, Furlan F, Ballerini L. Interneurone bursts are spontaneously associated with muscle contractions only during early phases of mouse spinal network development: a study in organotypic cultures. Eur J Neurosci 2004; 20:2697-710. [PMID: 15548213 DOI: 10.1111/j.1460-9568.2004.03740.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
For a short time during development immature circuits in the spinal cord and other parts of the central nervous system spontaneously generate synchronous patterns of rhythmic activity. In the case of the spinal cord, it is still unclear how strongly synchronized bursts generated by interneurones are associated with motoneurone firing and whether the progressive decline in spontaneous bursting during circuit maturation proceeds in parallel for motoneurone and interneurone networks. We used organotypic cocultures of spinal cord and skeletal muscle in order to investigate the ontogenic evolution of endogenous spinal network activity associated with the generation of coordinate muscle fibre contractions. A combination of multiunit electrophysiological recordings, videomicroscopy and optical flow computation allowed us to measure the correlation between interneurone firing and motoneurone outputs after 1, 2 and 3 weeks of in vitro development. We found that, in spinal organotypic slices, there is a developmental switch of spontaneous activity from stable bursting to random patterns after the first week in culture. Conversely, bursting recorded in the presence of strychnine and bicuculline became increasingly regular with time in vitro. The time course of spontaneous activity maturation in organotypic slices is similar to that previously reported for the spinal cord developing in utero. We also demonstrated that spontaneous bursts of interneurone action potentials strongly correlate with muscular contractions only during the first week in vitro and that this is due to the activation of motoneurones via AMPA-type glutamate receptors. These results indicate the occurrence in vitro of motor network development regulating bursting inputs from interneurones to motoneurones.
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Affiliation(s)
- Marcelo D Rosato-Siri
- Neurobiology Sector and Istituto Nazionale di Fisica della Materia Unit, International School for Advanced Studies (SISSA), via Beirut 2-4, 34014 Trieste, Italy.
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