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Parato J, Bartolini F. The microtubule cytoskeleton at the synapse. Neurosci Lett 2021; 753:135850. [PMID: 33775740 DOI: 10.1016/j.neulet.2021.135850] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Revised: 03/19/2021] [Accepted: 03/22/2021] [Indexed: 12/13/2022]
Abstract
In neurons, microtubules (MTs) provide routes for transport throughout the cell and structural support for dendrites and axons. Both stable and dynamic MTs are necessary for normal neuronal functions. Research in the last two decades has demonstrated that MTs play additional roles in synaptic structure and function in both pre- and postsynaptic elements. Here, we review current knowledge of the functions that MTs perform in excitatory and inhibitory synapses, as well as in the neuromuscular junction and other specialized synapses, and discuss the implications that this knowledge may have in neurological disease.
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Affiliation(s)
- Julie Parato
- Columbia University Medical Center, Department of Pathology & Cell Biology, 630 West 168(th)Street, P&S 15-421, NY, NY, 10032, United States; SUNY Empire State College, Department of Natural Sciences, 177 Livingston Street, Brooklyn, NY, 11201, United States
| | - Francesca Bartolini
- Columbia University Medical Center, Department of Pathology & Cell Biology, 630 West 168(th)Street, P&S 15-421, NY, NY, 10032, United States.
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Muñoz-Montesino C, Burgos CF, Lara CO, Riquelme CR, Flaig D, San Martin VP, Aguayo LG, Fuentealba J, Castro PA, Guzmán L, Yévenes GE, Moraga-Cid G. Inhibition of the Glycine Receptor alpha 3 Function by Colchicine. Front Pharmacol 2020; 11:1143. [PMID: 32903667 PMCID: PMC7438739 DOI: 10.3389/fphar.2020.01143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2019] [Accepted: 07/13/2020] [Indexed: 11/22/2022] Open
Abstract
Colchicine is a plant alkaloid that is widely used as a therapeutic agent. It is widely accepted that colchicine reduces the production of inflammatory mediators mainly by altering cytoskeleton dynamics due to its microtubule polymerization inhibitory activity. However, other lines of evidence have shown that colchicine exerts direct actions on the function of ion channels, which are independent of cytoskeleton alterations. Colchicine is able to modify the function of several pentameric ligand-gated ion channels, including glycine receptors (GlyRs). Previous electrophysiological studies have shown that colchicine act as an antagonist of GlyRs composed by the α1 subunit. In addition, it was recently demonstrated that colchicine directly bind to the α3 subunit of GlyRs. Interestingly, other studies have shown a main role of α3GlyRs on chronic inflammatory pain. Nevertheless, the functional effects of colchicine on the α3GlyR function are still unknown. Here, by using electrophysiological techniques and bioinformatics, we show that colchicine inhibited the function of the α3GlyRs. Colchicine elicited concentration-dependent inhibitory effects on α3GlyRs at micromolar range and decreased the apparent affinity for glycine. Single-channel recordings show that the colchicine inhibition is associated with a decrease in the open probability of the ion channel. Molecular docking assays suggest that colchicine preferentially bind to the orthosteric site in the closed state of the ion channel. Altogether, our results suggest that colchicine is a competitive antagonist of the α3GlyRs.
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Alvarez FJ. Gephyrin and the regulation of synaptic strength and dynamics at glycinergic inhibitory synapses. Brain Res Bull 2016; 129:50-65. [PMID: 27612963 DOI: 10.1016/j.brainresbull.2016.09.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Revised: 08/23/2016] [Accepted: 09/05/2016] [Indexed: 01/23/2023]
Abstract
Glycinergic synapses predominate in brainstem and spinal cord where they modulate motor and sensory processing. Their postsynaptic mechanisms have been considered rather simple because they lack a large variety of glycine receptor isoforms and have relatively simple postsynaptic densities at the ultrastructural level. However, this simplicity is misleading being their postsynaptic regions regulated by a variety of complex mechanisms controlling the efficacy of synaptic inhibition. Early studies suggested that glycinergic inhibitory strength and dynamics depend largely on structural features rather than on molecular complexity. These include regulation of the number of postsynaptic glycine receptors, their localization and the amount of co-localized GABAA receptors and GABA-glycine co-transmission. These properties we now know are under the control of gephyrin. Gephyrin is the first postsynaptic scaffolding protein ever discovered and it was recently found to display a large degree of variation and regulation by splice variants, posttranslational modifications, intracellular trafficking and interactions with the underlying cytoskeleton. Many of these mechanisms are governed by converging excitatory activity and regulate gephyrin oligomerization and receptor binding, the architecture of the postsynaptic density (and by extension the whole synaptic complex), receptor retention and stability. These newly uncovered molecular mechanisms define the size and number of gephyrin postsynaptic regions and the numbers and proportions of glycine and GABAA receptors contained within. All together, they control the emergence of glycinergic synapses of different strength and temporal properties to best match the excitatory drive received by each individual neuron or local dendritic compartment.
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Affiliation(s)
- Francisco J Alvarez
- Department of Physiology, Emory University, Atlanta, GA 30322-3110, United States.
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4
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Abstract
The neurotransmitters GABA and glycine mediate fast synaptic inhibition by activating ligand-gated chloride channels--namely, type A GABA (GABA(A)) and glycine receptors. Both types of receptors are anchored postsynaptically by gephyrin, which self-assembles into a scaffold and interacts with the cytoskeleton. Current research indicates that postsynaptic gephyrin clusters are dynamic assemblies that are held together and regulated by multiple protein-protein interactions. Moreover, post-translational modifications of gephyrin regulate the formation and plasticity of GABAergic synapses by altering the clustering properties of postsynaptic scaffolds and thereby the availability and function of receptors and other signalling molecules. Here, we discuss the formation and regulation of the gephyrin scaffold, its role in GABAergic and glycinergic synaptic function and the implications for the pathophysiology of brain disorders caused by abnormal inhibitory neurotransmission.
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Marcette JD, Chen JJ, Nonet ML. The Caenorhabditis elegans microtubule minus-end binding homolog PTRN-1 stabilizes synapses and neurites. eLife 2014; 3:e01637. [PMID: 24569480 PMCID: PMC3930908 DOI: 10.7554/elife.01637] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2013] [Accepted: 01/17/2014] [Indexed: 12/17/2022] Open
Abstract
Microtubule dynamics facilitate neurite growth and establish morphology, but the role of minus-end binding proteins in these processes is largely unexplored. CAMSAP homologs associate with microtubule minus-ends, and are important for the stability of epithelial cell adhesions. In this study, we report morphological defects in neurons and neuromuscular defects in mutants of the C. elegans CAMSAP, ptrn-1. Mechanosensory neurons initially extend wild-type neurites, and subsequently remodel by overextending neurites and retracting synaptic branches and presynaptic varicosities. This neuronal remodeling can be activated by mutations known to alter microtubules, and depends on a functioning DLK-1 MAP kinase pathway. We found that PTRN-1 localizes to both neurites and synapses, and our results suggest that alterations of microtubule structures caused by loss of PTRN-1 function activates a remodeling program leading to changes in neurite morphology. We propose a model whereby minus-end microtubule stabilization mediated by a functional PTRN-1 is necessary for morphological maintenance of neurons. DOI: http://dx.doi.org/10.7554/eLife.01637.001.
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Affiliation(s)
- Jana Dorfman Marcette
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, United States
| | - Jessica Jie Chen
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, United States
| | - Michael L Nonet
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, United States
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Effects of two elongation factor 1A isoforms on the formation of gephyrin clusters at inhibitory synapses in hippocampal neurons. Histochem Cell Biol 2013; 140:603-9. [DOI: 10.1007/s00418-013-1122-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/15/2013] [Indexed: 10/26/2022]
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7
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San Martin L, Cerda F, Jimenez V, Fuentealba J, Muñoz B, Aguayo LG, Guzman L. Inhibition of the ethanol-induced potentiation of α1 glycine receptor by a small peptide that interferes with Gβγ binding. J Biol Chem 2012; 287:40713-21. [PMID: 23035114 DOI: 10.1074/jbc.m112.393603] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND Gβγ interaction with GlyR is an important determinant in ethanol potentiation of this channel. RESULTS A small peptide, RQH(C7), can inhibit ethanol potentiation of GlyR currents. CONCLUSION Results with RQH(C7) indicate that ethanol mediated potentiation of GlyR is in part by Gβγ activation. SIGNIFICANCE Molecular interaction between Gβγ and GlyR could be used as a target for pharmacological modification of ethanol effects. Previous studies indicate that ethanol can modulate glycine receptors (GlyR), in part, through Gβγ interaction with basic residues in the intracellular loop. In this study, we show that a seven-amino acid peptide (RQH(C7)), which has the primary structure of a motif in the large intracellular loop of GlyR (GlyR-IL), was able to inhibit the ethanol-elicited potentiation of this channel from 47 ± 2 to 16 ± 4%, without interfering with the effect of Gβγ on GIRK (G protein activated inwardly rectifying potassium channel) activation. RQH(C7) displayed a concentration-dependent effect on ethanol action in evoked and synaptic currents. A fragment of GlyR-IL without the basic amino acids did not interact with Gβγ or inhibit ethanol potentiation of GlyR. In silico analysis using docking and molecular dynamics allowed to identify a region of ~350Å(2) involving aspartic acids 186, 228, and 246 in Gβγ where we propose that RQH(C7) binds and exerts its blocking action on the effect of ethanol in GlyR.
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Affiliation(s)
- Loreto San Martin
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, 403901 Concepcion, Chile
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Gardiner J, Overall R, Marc J. The microtubule cytoskeleton acts as a key downstream effector of neurotransmitter signaling. Synapse 2011; 65:249-56. [PMID: 20687109 DOI: 10.1002/syn.20841] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Microtubules are well known to play a key role in the trafficking of neurotransmitters to the synapse. However, less attention has been paid to their role as downstream effectors of neurotransmitter signaling in the target neuron. Here, we show that neurotransmitter-based signaling to the microtubule cytoskeleton regulates downstream microtubule function through several mechanisms. These include tubulin posttranslational modification, binding of microtubule-associated proteins, release of microtubule-interacting second messenger molecules, and regulation of tubulin expression levels. We review the evidence for neurotransmitter regulation of the microtubule cytoskeleton, focusing on the neurotransmitters serotonin, melatonin, dopamine, glutamate, glycine, and acetylcholine. Some evidence suggests that microtubules may even play a more direct role in propagating action potentials through conductance of electric current. In turn, there is evidence for the regulation of neurotransmission by the microtubule cytoskeleton.
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Affiliation(s)
- John Gardiner
- The School of Biological Sciences, The University of Sydney 2006, New South Wales, Australia.
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Cantiello HF, Montalbetti N, Li Q, Chen XZ. The Cytoskeletal Connection to Ion Channels as a Potential Mechanosensory Mechanism: Lessons from Polycystin-2 (TRPP2). CURRENT TOPICS IN MEMBRANES 2007; 59:233-96. [PMID: 25168140 DOI: 10.1016/s1063-5823(06)59010-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Mechanosensitivity of ion channels, or the ability to transfer mechanical forces into a gating mechanism of channel regulation, is split into two main working (not mutually exclusive) hypotheses. One is that elastic and/or structural changes in membrane properties act as a transducing mechanism of channel regulation. The other hypothesis involves tertiary elements, such as the cytoskeleton which, itself by dynamic interactions with the ion channel, may convey conformational changes, including those ascribed to mechanical forces. This hypothesis is supported by numerous instances of regulatory changes in channel behavior by alterations in cytoskeletal structures/interactions. However, only recently, the molecular nature of these interactions has slowly emerged. Recently, a surge of evidence has emerged to indicate that transient receptor potential (TRP) channels are key elements in the transduction of a variety of environmental signals. This chapter describes the molecular linkage and regulatory elements of polycystin-2 (PC2), a TRP-type (TRPP2) nonselective cation channel whose mutations cause autosomal dominant polycystic kidney disease (ADPKD). The chapter focuses on the involvement of cytoskeletal structures in the regulation of PC2 and discusses how these connections are the transducing mechanism of environmental signals to its channel function.
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Affiliation(s)
- Horacio F Cantiello
- Renal Unit, Massachusetts General Hospital East, Charlestown, Massachusetts 02129; Department of Medicine, Harvard Medical School, Boston, Massachusetts 02115; Laboratorio de Canales Iónicos, Departamento de Fisicoquímica y Química Analítica, Facultad de Farmacia y Bioquímica, Buenos Aires 1113, Argentina
| | - Nicolás Montalbetti
- Laboratorio de Canales Iónicos, Departamento de Fisicoquímica y Química Analítica, Facultad de Farmacia y Bioquímica, Buenos Aires 1113, Argentina
| | - Qiang Li
- Department of Physiology, University of Alberta, Edmonton T6G 2H7, Canada
| | - Xing-Zhen Chen
- Department of Physiology, University of Alberta, Edmonton T6G 2H7, Canada
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Brown DPG, Gökmen-Polar Y, Jiang L, Tan J, Ringham H, Janecki DJ, Qi G, Witzmann FA, Sledge GW, Wang M. A comparative proteomic study to characterize the vinblastine resistance in human ovarian cancer cells. Proteomics Clin Appl 2007; 1:18-31. [DOI: 10.1002/prca.200600171] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2006] [Indexed: 11/10/2022]
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Hanus C, Ehrensperger MV, Triller A. Activity-dependent movements of postsynaptic scaffolds at inhibitory synapses. J Neurosci 2006; 26:4586-95. [PMID: 16641238 PMCID: PMC6674069 DOI: 10.1523/jneurosci.5123-05.2006] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Dendritic spines show an activity-dependent cytoskeleton-based remodeling coupled with variations in receptor number and the functional properties of excitatory synapses. In this study, we analyzed the dynamics of gephyrin containing inhibitory postsynaptic scaffolds imaging a Venus::gephyrin (VeGe) chimera in dissociated spinal cord neurons. We provide evidence that the postsynaptic scaffolds at mature synapses display a submicrometric rapid lateral motion and are continuously moving on the dendritic shaft. This dynamic behavior is calcium dependent and is controlled by the cytoskeleton. Minute rearrangement within the gephyrin scaffold as well as the scaffold lateral displacements are F-actin dependent. The lateral movements are counteracted by microtubules. Moreover, the action of the potassium channel blocker 4-aminopyridine and receptor antagonists indicate that the dynamics of postsynaptic gephyrin scaffolds are controlled by synaptic activity.
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Perán M, Hooper H, Boulaiz H, Marchal JA, Aránega A, Salas R. The M3/M4 cytoplasmic loop of the α1 subunit restricts GABAARs lateral mobility: A study using fluorescence recovery after photobleaching. ACTA ACUST UNITED AC 2006; 63:747-57. [PMID: 17029290 DOI: 10.1002/cm.20156] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A crucial problem in neurobiology is how neurons are able to maintain neurotransmitter receptors at specific membrane domains. The large structural heterogeneity of gamma aminobutyric acid receptors (GABAARs) led to the hypothesis that there could be a link between GABAAR gene diversity and the targeting properties of the receptor complex. Previous studies using Fluorescence Recovery After Photobleaching (FRAP) have shown a restricted mobility in GABAARs containing the alpha1 subunit. The M3/M4 cytoplasmic loop is the region of the alpha1 subunit with the lowest sequence homology to other subunits. Therefore, we asked whether the M3/M4 loop is involved in cytoskeletal anchoring and GABAAR clustering. A series of alpha1 chimeric subunits was constructed: alpha1CH (control subunit), alpha1CD (Cytoplasmic loop deleted), alpha1CD2, and alpha1CD3 (alpha1 with the M3/M4 loop from the alpha2 and alpha3 subunits, respectively). Our results using FRAP indicate an involvement of the M3/M4 cytoplasmic loop of the alpha1 subunit in controlling receptor lateral mobility. On the other hand, inmunocytochemical approaches showed that this domain is not involved in subunit targeting to the cell surface, subunit-subunit assembly, or receptor aggregation.
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Affiliation(s)
- Macarena Perán
- Department of Anatomy and Human Embryology, Faculty of Medicine, University of Granada, Granada, Spain.
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13
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van Zundert B, Castro P, Aguayo LG. Glycinergic and GABAergic synaptic transmission are differentially affected by gephyrin in spinal neurons. Brain Res 2005; 1050:40-7. [PMID: 15963957 DOI: 10.1016/j.brainres.2005.05.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2004] [Revised: 05/04/2005] [Accepted: 05/09/2005] [Indexed: 11/20/2022]
Abstract
In the present study, we have examined the physiological properties of synaptic currents mediated by GlyRs and GABAARs after culturing spinal neurons with a gephyrin antisense oligonucleotide. Application of gephyrin antisense, but not the sense, reduced the glycinergic mIPSC amplitude ( approximately 50%) and frequency ( approximately 85%), indicating the importance of gephyrin for GlyR anchoring at postsynaptic sites. On the other hand, the glycine-evoked current amplitude was unchanged indicating that functional GlyRs were still located in the extrasynaptic membrane. The analysis of the GABAergic transmission in the same neurons revealed approximately 70% reduction in the frequency of the GABAergic mIPSCs, without changes in the amplitude. Interestingly, the modulation of remaining GABAAR-mediated synaptic events by zinc and diazepam was significantly altered by the antisense. These results indicate that gephyrin is required for the membrane insertion/stabilization of the GABAAR gamma2 subunit as well as for its subsequent localization in the postsynaptic membrane.
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Affiliation(s)
- Brigitte van Zundert
- Department of Physiology, University of Concepción, Laboratory of Neurophysiology, P.O. Box 160-C, Concepción, Chile
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Cuevas ME, Carrasco MA, Fuentes Y, Castro P, Nualart F, Roa J, Aguayo LG. The presence of glia stimulates the appearance of glycinergic synaptic transmission in spinal cord neurons. Mol Cell Neurosci 2005; 28:770-8. [PMID: 15797723 DOI: 10.1016/j.mcn.2005.01.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2004] [Revised: 01/10/2005] [Accepted: 01/11/2005] [Indexed: 10/25/2022] Open
Abstract
Previous studies, using electrophysiological and fluorimetric analysis with a calcium sensitive dye, have shown that 5-7 DIV developing spinal cord neurons displayed high levels of glycinergic transmission. GABAergic and AMPAergic neurotransmission contributed much less to the overall transmission. Here, we show that culturing neurons in absence of a glia cell monolayer reduced the frequency of glycinergic spontaneous IPSCs (0.1 +/- 0.01 Hz), without altering the level of overall transmission (3 +/- 1.1 Hz). The predominant transmission was mediated by GABA(A) receptors (72% of total synaptic events). In addition, combination of bicuculline and CNQX blocked synaptically mediated calcium transients recorded with fluo-3. Furthermore, application of glycine revealed the presence of extrasynaptic receptors in these neurons (25 +/- 6 pA/pF). Culturing neurons on a glial cell monolayer increased the frequency of glycinergic currents (0.4 +/- 0.02 Hz), without changing the amplitude of the current (20 +/- 4 pA). The use of a glia-conditioned media reversed the effect of growing the neurons in a glia-deprived condition. These results indicate that the establishment of glycinergic transmission is dependent on the presence of a glia derived soluble factor. However, functional GlyRs were still able to insert in the neuronal membrane in a glia-independent manner.
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Affiliation(s)
- Magdalena E Cuevas
- Department of Physiology, University of Concepción, PO Box 160-C, Concepción, Chile
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15
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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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16
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Eggers ED, Berger AJ. Mechanisms for the modulation of native glycine receptor channels by ethanol. J Neurophysiol 2004; 91:2685-95. [PMID: 14762156 DOI: 10.1152/jn.00907.2003] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Previously, we showed that ethanol increases synaptic glycine currents, an effect that depends on ethanol concentration and developmental age of the preparation. Glycine receptor (GlyR) subunits undergo a shift from alpha2/beta to alpha1/beta from neonate to juvenile ages, with synaptic glycine currents from neonate hypoglossal motoneurons (HMs) being less sensitive to ethanol than those from juvenile HMs. Here we investigate whether these dose and developmental effects are also present in excised membrane patches containing GlyRs and if ethanol changes response kinetics. We excised outside-out patches from rat HM somata and applied glycine using either a picospritzer or piezo stack translator. Ethanol (100 mM) increased the response to glycine (200 microM) of patches from neonate and juvenile HMs. However, 30 mM ethanol increased the response from only juvenile HM patches. Using a lower concentration of glycine (30 microM) to observe single channel openings, we found that 100 mM ethanol increased the number of GlyRs that open in response to glycine and decreased first latency to channel opening. To investigate GlyR kinetic properties, we rapidly applied 1 mM glycine for 1 ms and found that glycine currents were increased by ethanol (100 mM) at both ages. For patches from juvenile HMs, ethanol consistently decreased response rise-time and increased response decay time. Using kinetic modeling, we determined that ethanol's potentiation of the glycine response arises from an increase in the glycine association (k(on)) and a decrease in the dissociation (k(off)) rate constants, resulting in increased glycine affinity of the GlyR.
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Affiliation(s)
- Erika D Eggers
- Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195, USA.
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17
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van Zundert B, Alvarez FJ, Tapia JC, Yeh HH, Diaz E, Aguayo LG. Developmental-dependent action of microtubule depolymerization on the function and structure of synaptic glycine receptor clusters in spinal neurons. J Neurophysiol 2004; 91:1036-49. [PMID: 12968009 DOI: 10.1152/jn.00364.2003] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Microtubules have been proposed to interact with gephyrin/glycine receptors (GlyRs) in synaptic aggregates. However, the consequence of microtubule disruption on the structure of postsynaptic GlyR/gephyrin clusters is controversial and possible alterations in function are largely unknown. In this study, we have examined the physiological and morphological properties of GlyR/gephyrin clusters after colchicine treatment in cultured spinal neurons during development. In immature neurons (5-7 DIV), disruption of microtubules resulted in a 33 +/- 4% decrease in the peak amplitude and a 72 +/- 15% reduction in the frequency of spontaneous glycinergic miniature postsynaptic currents (mIPSCs) recorded in whole cell mode. However, similar colchicine treatments resulted in smaller effects on 10-12 DIV neurons and no effect on mature neurons (15-17 DIV). The decrease in glycinergic mIPSC amplitude and frequency reflects postsynaptic actions of colchicine, since postsynaptic stabilization of microtubules with GTP prevented both actions and similar reductions in mIPSC frequency were obtained by modifying the Cl(-) driving force to obtain parallel reductions in mIPSC amplitude. Confocal microscopy revealed that colchicine reduced the average length and immunofluorescence intensity of synaptic gephyrin/GlyR clusters in immature (approximately 30%) and intermediate (approximately 15%) neurons, but not in mature clusters. Thus the structural and functional changes of postsynaptic gephyrin/GlyR clusters after colchicine treatment were tightly correlated. Finally, RT-PCR, kinetic analysis and picrotoxin blockade of glycinergic mIPSCs indicated a reorganization of the postsynaptic region from containing both alpha2beta and alpha1beta GlyRs in immature neurons to only alpha1beta GlyRs in mature neurons. Microtubule disruption preferentially affected postsynaptic sites containing alpha2beta-containing synaptic receptors.
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Affiliation(s)
- Brigitte van Zundert
- Laboratory of Neurophysiology, Department of Physiology, University of Concepción, Concepción, Chile
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18
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Mangin JM, Baloul M, Prado De Carvalho L, Rogister B, Rigo JM, Legendre P. Kinetic properties of the alpha2 homo-oligomeric glycine receptor impairs a proper synaptic functioning. J Physiol 2003; 553:369-86. [PMID: 12972628 PMCID: PMC2343566 DOI: 10.1113/jphysiol.2003.052142] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Ionotropic glycine receptors (GlyRs) are present in the central nervous system well before the establishment of synaptic contacts. Immature nerve cells are known, at least in the spinal cord, to express alpha2 homomeric GlyRs, the properties of which are relatively unknown compared to those of the adult synaptic form of the GlyR (mainly alpha1/beta heteromeres). Here, the kinetics properties of GlyRs at the single-channel level have been recorded in real-time by means of the patch-clamp technique in the outside-out configuration coupled with an ultra-fast flow application system (< 100 micros). Recordings were performed on chinese hamster ovary (CHO) cells stably transfected with the alpha2 GlyR subunit. We show that the onset, the relaxation and the desensitisation of alpha2 homomeric GlyR-mediated currents are slower by one or two orders of magnitude compared to synaptic mature GlyRs and to other ligand-gated ionotropic channels involved in fast synaptic transmission. First latency analysis performed on single GlyR channels revealed that their slow activation time course was due to delayed openings. When synaptic release of glycine was mimicked (1 mM glycine; 1 ms pulse duration), the opening probability of alpha2 homomeric GlyRs was low (P(o) approximately = 0.1) when compared to mature synaptic GlyRs (Po = 0.9). This low Po is likely to be a direct consequence of the relatively slow activation kinetics of alpha2 homomeric GlyRs when compared to the activation kinetics of mature alpha1/beta GlyRs. Such slow kinetics suggest that embryonic alpha2 homomeric GlyRs cannot be activated by fast neurotransmitter release at mature synapses but rather could be suited for a non-synaptic paracrine-like release of agonist, which is known to occur in the embryo.
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Affiliation(s)
- J M Mangin
- UMR CNRS 7102 Neurobiologie des Processus Adaptatifs, Université Pierre et Marie Curie, 9 quai St Bernard, 75252 Paris cedex 05, France.
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Yevenes GE, Peoples RW, Tapia JC, Parodi J, Soto X, Olate J, Aguayo LG. Modulation of glycine-activated ion channel function by G-protein betagamma subunits. Nat Neurosci 2003; 6:819-24. [PMID: 12858180 DOI: 10.1038/nn1095] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2003] [Accepted: 05/23/2003] [Indexed: 11/08/2022]
Abstract
Glycine receptors (GlyRs), together with GABA(A) and nicotinic acetylcholine (ACh) receptors, form part of the ligand-activated ion channel superfamily and regulate the excitability of the mammalian brain stem and spinal cord. Here we report that the ability of the neurotransmitter glycine to gate recombinant and native ionotropic GlyRs is modulated by the G protein betagamma dimer (Gbetagamma). We found that the amplitude of the glycine-activated Cl- current was enhanced after application of purified Gbetagamma or after activation of a G protein-coupled receptor. Overexpression of three distinct G protein alpha subunits (Galpha), as well as the Gbetagamma scavenger peptide ct-GRK2, significantly blunted the effect of G protein activation. Single-channel recordings from isolated membrane patches showed that Gbetagamma increased the GlyR open probability (nP(o)). Our results indicate that this interaction of Gbetagamma with GlyRs regulates both motor and sensory functions in the central nervous system.
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Affiliation(s)
- Gonzalo E Yevenes
- Laboratory of Neurophysiology, Department of Physiology, Box 160-C, University of Concepción, Chile
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Fritschy JM, Brünig I. Formation and plasticity of GABAergic synapses: physiological mechanisms and pathophysiological implications. Pharmacol Ther 2003; 98:299-323. [PMID: 12782242 DOI: 10.1016/s0163-7258(03)00037-8] [Citation(s) in RCA: 244] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
gamma-Aminobutyric acid(A) (GABA(A)) receptors mediate most of the fast inhibitory neurotransmission in the CNS. They represent a major site of action for clinically relevant drugs, such as benzodiazepines and ethanol, and endogenous modulators, including neuroactive steroids. Alterations in GABA(A) receptor expression and function are thought to contribute to prevalent neurological and psychiatric diseases. Molecular cloning and immunochemical characterization of GABA(A) receptor subunits revealed a multiplicity of receptor subtypes with specific functional and pharmacological properties. A major tenet of these studies is that GABA(A) receptor heterogeneity represents a key factor for fine-tuning of inhibitory transmission under physiological and pathophysiological conditions. The aim of this review is to highlight recent findings on the regulation of GABA(A) receptor expression and function, focusing on the mechanisms of sorting, targeting, and synaptic clustering of GABA(A) receptor subtypes and their associated proteins, on trafficking of cell-surface receptors as a means of regulating synaptic (and extrasynaptic) transmission on a short-time basis, on the role of endogenous neurosteroids for GABA(A) receptor plasticity, and on alterations of GABA(A) receptor expression and localization in major neurological disorders. Altogether, the findings presented in this review underscore the necessity of considering GABA(A) receptor-mediated neurotransmission as a dynamic and highly flexible process controlled by multiple mechanisms operating at the molecular, cellular, and systemic level. Furthermore, the selected topics highlight the relevance of concepts derived from experimental studies for understanding GABA(A) receptor alterations in disease states and for designing improved therapeutic strategies based on subtype-selective drugs.
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Affiliation(s)
- Jean-Marc Fritschy
- Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
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Petrini EM, Zacchi P, Barberis A, Mozrzymas JW, Cherubini E. Declusterization of GABAA receptors affects the kinetic properties of GABAergic currents in cultured hippocampal neurons. J Biol Chem 2003; 278:16271-9. [PMID: 12600990 DOI: 10.1074/jbc.m213081200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Speed and reliability of synaptic transmission are essential for information coding in neuronal networks and require the presence of clustered neurotransmitter receptors at the plasma membrane in precise apposition to presynaptic terminals. Receptor clusterization is the result of highly regulated processes involving functional and structural proteins. Among the structural elements, microtubules are known to play a crucial role in anchoring of gamma-aminobutyric acid, type A (GABA(A)) receptors. Here we show that microtubule depolymerization with nocodazole induces the declusterization of GABA(A) receptors and modifies the kinetic properties of GABAergic currents in cultured hippocampal neurons. In particular, this drug, applied either in the bath or via the patch pipette, induced the acceleration of the onset kinetics of miniature inhibitory postsynaptic currents (mIPSCs) without significantly affecting their frequency, thus suggesting a main postsynaptic site of action. After nocodazole treatment, current responses to ultrafast applications of GABA exhibited a faster rise time and an accelerated onset of desensitization. A quantitative analysis of GABA-evoked currents and model simulations suggest that declusterization affects the gating properties of GABA(A) receptors. In particular, a faster entry into the desensitized state of declustered GABA(A) receptors may account for the changes in the kinetic properties of mIPSCs after nocodazole treatment. Hence it appears that the clustered condition of GABA(A) receptors contributes in shaping GABAergic currents.
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Affiliation(s)
- Enrica Maria Petrini
- Neuroscience Programme and Istituto Nazionale Fisica della Materia Unit, International School for Advanced Studies, Via Beirut 2-4, Trieste 34014, Italy
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