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O'Connor EC, Kambara K, Bertrand D. Advancements in the use of xenopus oocytes for modelling neurological disease for novel drug discovery. Expert Opin Drug Discov 2024; 19:173-187. [PMID: 37850233 DOI: 10.1080/17460441.2023.2270902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Accepted: 10/11/2023] [Indexed: 10/19/2023]
Abstract
INTRODUCTION Introduced about 50 years ago, the model of Xenopus oocytes for the expression of recombinant proteins has gained a broad spectrum of applications. The authors herein review the benefits brought from using this model system, with a focus on modeling neurological disease mechanisms and application to drug discovery. AREAS COVERED Using multiple examples spanning from ligand gated ion channels to transporters, this review presents, in the light of the latest publications, the benefits offered from using Xenopus oocytes. Studies range from the characterization of gene mutations to the discovery of novel treatments for disorders of the central nervous system (CNS). EXPERT OPINION Development of new drugs targeting CNS disorders has been marked by failures in the translation from preclinical to clinical studies. As progress in genetics and molecular biology highlights large functional differences arising from a single to a few amino acid exchanges, the need for drug screening and functional testing against human proteins is increasing. The use of Xenopus oocytes to enable precise modeling and characterization of clinically relevant genetic variants constitutes a powerful model system that can be used to inform various aspects of CNS drug discovery and development.
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Affiliation(s)
- Eoin C O'Connor
- Roche Pharma Research and Early Development, Neuroscience & Rare Diseases, Roche Innovation Center Basel, Basel, Switzerland
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2
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Becchetti A, Grandi LC, Cerina M, Amadeo A. Nicotinic acetylcholine receptors and epilepsy. Pharmacol Res 2023; 189:106698. [PMID: 36796465 DOI: 10.1016/j.phrs.2023.106698] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 02/04/2023] [Accepted: 02/13/2023] [Indexed: 02/16/2023]
Abstract
Despite recent advances in understanding the causes of epilepsy, especially the genetic, comprehending the biological mechanisms that lead to the epileptic phenotype remains difficult. A paradigmatic case is constituted by the epilepsies caused by altered neuronal nicotinic acetylcholine receptors (nAChRs), which exert complex physiological functions in mature as well as developing brain. The ascending cholinergic projections exert potent control of forebrain excitability, and wide evidence implicates nAChR dysregulation as both cause and effect of epileptiform activity. First, tonic-clonic seizures are triggered by administration of high doses of nicotinic agonists, whereas non-convulsive doses have kindling effects. Second, sleep-related epilepsy can be caused by mutations on genes encoding nAChR subunits widely expressed in the forebrain (CHRNA4, CHRNB2, CHRNA2). Third, in animal models of acquired epilepsy, complex time-dependent alterations in cholinergic innervation are observed following repeated seizures. Heteromeric nAChRs are central players in epileptogenesis. Evidence is wide for autosomal dominant sleep-related hypermotor epilepsy (ADSHE). Studies of ADSHE-linked nAChR subunits in expression systems suggest that the epileptogenic process is promoted by overactive receptors. Investigation in animal models of ADSHE indicates that expression of mutant nAChRs can lead to lifelong hyperexcitability by altering i) the function of GABAergic populations in the mature neocortex and thalamus, ii) synaptic architecture during synaptogenesis. Understanding the balance of the epileptogenic effects in adult and developing networks is essential to plan rational therapy at different ages. Combining this knowledge with a deeper understanding of the functional and pharmacological properties of individual mutations will advance precision and personalized medicine in nAChR-dependent epilepsy.
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Affiliation(s)
- Andrea Becchetti
- Department of Biotechnology and Biosciences, and NeuroMI (Milan Center of Neuroscience), University of Milano-Bicocca, Piazza della Scienza 2, Milano 20126, Italy.
| | - Laura Clara Grandi
- Department of Biotechnology and Biosciences, and NeuroMI (Milan Center of Neuroscience), University of Milano-Bicocca, Piazza della Scienza 2, Milano 20126, Italy.
| | - Marta Cerina
- Department of Biotechnology and Biosciences, and NeuroMI (Milan Center of Neuroscience), University of Milano-Bicocca, Piazza della Scienza 2, Milano 20126, Italy.
| | - Alida Amadeo
- Department of Biosciences, University of Milano, Via Celoria 26, Milano 20133, Italy.
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Mazzaferro S, Strikwerda JR, Sine SM. Stoichiometry-selective modulation of α4β2 nicotinic ACh receptors by divalent cations. Br J Pharmacol 2022; 179:1353-1370. [PMID: 34768309 DOI: 10.1111/bph.15723] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 10/11/2021] [Accepted: 10/18/2021] [Indexed: 02/03/2023] Open
Abstract
BACKGROUND AND PURPOSE α4β2 nicotinic ACh receptors (nAChRs) comprise the most abundant class of nAChRs in the nervous system. They assemble in two stoichiometric forms, each exhibiting distinct functional and pharmacological signatures. However, whether one or both forms are modulated by calcium or magnesium has not been established. EXPERIMENTAL APPROACH To assess the functional consequences of calcium and magnesium, each stoichiometric form was expressed in clonal mammalian fibroblasts and single-channel currents were recorded in the presence of a range of ACh concentrations. KEY RESULTS In the absence of divalent cations, each stoichiometric form exhibits high unitary conductance and simple gating kinetics composed of solitary channel openings or short bursts of openings. However, in the presence of calcium and magnesium, the conductance and gating kinetics change in a stoichiometry-dependent manner. Calcium and magnesium reduce the conductance of both stoichiometric forms, with each cation producing an equivalent reduction, but the reduction is greater for the (α4)2 (β2)3 form. Moreover, divalent cations promote efficient channel opening of the (α4)3 (β2)2 stoichiometry, while minimally affecting the (α4)2 (β2)3 stoichiometry. For the (α4)3 (β2)2 stoichiometry, at high but not low ACh concentrations, calcium in synergy with magnesium promote clustering of channel openings into episodes of many openings in quick succession. CONCLUSION AND IMPLICATIONS Modulation of the α4β2 nAChR by divalent cations depends on the ACh concentration, the type of cation and the subunit stoichiometry. The functional consequences of modulation are expected to depend on the regional distributions of the stoichiometric forms and synaptic versus extrasynaptic locations of the receptors.
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Affiliation(s)
- Simone Mazzaferro
- Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
| | - John R Strikwerda
- Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
| | - Steven M Sine
- Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota, USA.,Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic College of Medicine, Rochester, Minnesota, USA.,Department of Neurology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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A single historical substitution drives an increase in acetylcholine receptor complexity. Proc Natl Acad Sci U S A 2021; 118:2018731118. [PMID: 33579823 DOI: 10.1073/pnas.2018731118] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Human adult muscle-type acetylcholine receptors are heteropentameric ion channels formed from four different, but evolutionarily related, subunits. These subunits assemble with a precise stoichiometry and arrangement such that two chemically distinct agonist-binding sites are formed between specific subunit pairs. How this subunit complexity evolved and became entrenched is unclear. Here we show that a single historical amino acid substitution is able to constrain the subunit stoichiometry of functional acetylcholine receptors. Using a combination of ancestral sequence reconstruction, single-channel electrophysiology, and concatenated subunits, we reveal that an ancestral β-subunit can not only replace the extant β-subunit but can also supplant the neighboring δ-subunit. By forward evolving the ancestral β-subunit with a single amino acid substitution, we restore the requirement for a δ-subunit for functional channels. These findings reveal that a single historical substitution necessitates an increase in acetylcholine receptor complexity and, more generally, that simple stepwise mutations can drive subunit entrenchment in this model heteromeric protein.
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Okada M. Can rodent models elucidate the pathomechanisms of genetic epilepsy? Br J Pharmacol 2021; 179:1620-1639. [PMID: 33689168 PMCID: PMC9291625 DOI: 10.1111/bph.15443] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Revised: 02/03/2021] [Accepted: 03/04/2021] [Indexed: 12/31/2022] Open
Abstract
Autosomal dominant sleep-related hypermotor epilepsy (ADSHE; previously autosomal dominant nocturnal frontal lobe epilepsy, ADNFLE), originally reported in 1994, was the first distinct genetic epilepsy shown to be caused by CHNRA4 mutation. In the past two decades, we have identified several functional abnormalities of mutant ion channels and their associated transmissions using several experiments involving single-cell and genetic animal (rodent) models. Currently, epileptologists understand that functional abnormalities underlying epileptogenesis/ictogenesis in humans and rodents are more complicated than previously believed and that the function of mutant molecules alone cannot contribute to the development of epileptogenesis/ictogenesis but play important roles in the development of epileptogenesis/ictogenesis through formation of abnormalities in various other transmission systems before epilepsy onset. Based on our recent findings using genetic rat ADSHE models, harbouring Chrna4 mutant, corresponding to human S284L-mutant CRHNA4, this review proposes a hypothesis associated with tripartite synaptic transmission in ADSHE pathomechanisms induced by mutant ACh receptors.
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Affiliation(s)
- Motohiro Okada
- Department of Neuropsychiatry, Division of Neuroscience, Graduate School of Medicine, Mie University, Tsu, Japan
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Phillips MB, Nigam A, Johnson JW. Interplay between Gating and Block of Ligand-Gated Ion Channels. Brain Sci 2020; 10:brainsci10120928. [PMID: 33271923 PMCID: PMC7760600 DOI: 10.3390/brainsci10120928] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 11/21/2020] [Accepted: 11/26/2020] [Indexed: 02/03/2023] Open
Abstract
Drugs that inhibit ion channel function by binding in the channel and preventing current flow, known as channel blockers, can be used as powerful tools for analysis of channel properties. Channel blockers are used to probe both the sophisticated structure and basic biophysical properties of ion channels. Gating, the mechanism that controls the opening and closing of ion channels, can be profoundly influenced by channel blocking drugs. Channel block and gating are reciprocally connected; gating controls access of channel blockers to their binding sites, and channel-blocking drugs can have profound and diverse effects on the rates of gating transitions and on the stability of channel open and closed states. This review synthesizes knowledge of the inherent intertwining of block and gating of excitatory ligand-gated ion channels, with a focus on the utility of channel blockers as analytic probes of ionotropic glutamate receptor channel function.
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Affiliation(s)
- Matthew B. Phillips
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA; (M.B.P.); (A.N.)
- Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Aparna Nigam
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA; (M.B.P.); (A.N.)
| | - Jon W. Johnson
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA; (M.B.P.); (A.N.)
- Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
- Correspondence: ; Tel.: +1-(412)-624-4295
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Hernandez CC, Zhang Y, Hu N, Shen D, Shen W, Liu X, Kong W, Jiang Y, Macdonald RL. GABA A Receptor Coupling Junction and Pore GABRB3 Mutations are Linked to Early-Onset Epileptic Encephalopathy. Sci Rep 2017; 7:15903. [PMID: 29162865 PMCID: PMC5698489 DOI: 10.1038/s41598-017-16010-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Accepted: 10/11/2017] [Indexed: 12/17/2022] Open
Abstract
GABAA receptors are brain inhibitory chloride ion channels. Here we show functional analyses and structural simulations for three de novo missense mutations in the GABAA receptor β3 subunit gene (GABRB3) identified in patients with early-onset epileptic encephalopathy (EOEE) and profound developmental delay. We sought to obtain insights into the molecular mechanisms that might link defects in GABAA receptor biophysics and biogenesis to patients with EOEE. The mutant residues are part of conserved structural domains such as the Cys-loop (L170R) and M2-M3 loop (A305V) that form the GABA binding/channel gating coupling junction and the channel pore (T288N), which are functionally coupled during receptor activation. The mutant coupling junction residues caused rearrangements and formation of new hydrogen bonds in the open state, while the mutant pore residue reshaped the pore cavity. Whereas mutant coupling junction residues uncoupled during activation and caused gain of function, the mutant pore residue favoured low conductance receptors and differential sensitivity to diazepam and loss of function. These data reveal novel molecular mechanisms by which EOEE-linked mutations affect GABAA receptor function.
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Affiliation(s)
- Ciria C Hernandez
- Department of Neurology, Vanderbilt University, Nashville, TN., 37240-7915., USA. .,University of Michigan, Life Sciences Institute, 210 Washtenaw Ave., Room 6115, Ann Arbor, MI, 48109-2216, USA.
| | - Yujia Zhang
- Department of Pediatrics, Peking University First Hospital, Beijing, 100034, China
| | - Ningning Hu
- Department of Neurology, Vanderbilt University, Nashville, TN., 37240-7915., USA
| | - Dingding Shen
- The Graduate Program of Neuroscience, Vanderbilt University, Nashville, 37240-7915., TN, USA
| | - Wangzhen Shen
- Department of Neurology, Vanderbilt University, Nashville, TN., 37240-7915., USA
| | - Xiaoyan Liu
- Department of Pediatrics, Peking University First Hospital, Beijing, 100034, China
| | - Weijing Kong
- Department of Pediatrics, Peking University First Hospital, Beijing, 100034, China
| | - Yuwu Jiang
- Department of Pediatrics, Peking University First Hospital, Beijing, 100034, China.
| | - Robert L Macdonald
- Department of Neurology, Vanderbilt University, Nashville, TN., 37240-7915., USA.
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Boillot M, Baulac S. Genetic models of focal epilepsies. J Neurosci Methods 2016; 260:132-43. [DOI: 10.1016/j.jneumeth.2015.06.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2015] [Revised: 06/03/2015] [Accepted: 06/04/2015] [Indexed: 01/06/2023]
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9
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Eggert M, Winterer G, Wanischeck M, Hoda JC, Bertrand D, Steinlein O. The nicotinic acetylcholine receptor alpha 4 subunit contains a functionally relevant SNP Haplotype. BMC Genet 2015; 16:46. [PMID: 25934188 PMCID: PMC4417232 DOI: 10.1186/s12863-015-0204-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Accepted: 04/22/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Non-coding single nucleotide polymorphisms within the nicotinic acetylcholine receptor alpha 4 subunit gene (CHRNA4) are robustly associated with various neurological and behavioral phenotypes including schizophrenia, cognition and smoking. The most commonly associated polymorphisms are located in exon 5 and segregate as part of a haplotype. So far it is unknown if this haplotype is indeed functional, or if the observed associations are an indirect effect caused by linkage disequilibrium with not yet identified adjacent functional variants. We therefore analyzed the functional relevance of the exon 5 haplotype alleles. RESULTS Using voltage clamp experiments we were able to show that the CHRNA4 haplotype alleles differ with respect to their functional effects on receptor sensitivity including reversal of receptor sensitivity between low and high acetylcholine concentrations. The results indicate that underlying mechanisms might include differences in codon usage bias and changes in mRNA stability. CONCLUSIONS Our data demonstrate that the complementary alleles of the CHRNA4 exon 5 haplotype are functionally relevant, and might therefore be causative for the above mentioned associations.
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Affiliation(s)
- Marlene Eggert
- Marlene Eggert, Institute of Human Genetics, Ludwig-Maximilians-University Hospital, 80336, Munich, Germany.
| | - Georg Winterer
- Georg Winterer, Experimental and Clinical Research Center (ECRC), Charité - University Medicine Berlin, Berlin, Germany.
| | - Mario Wanischeck
- Mario Wanischeck, Institute of Human Genetics, Ludwig-Maximilians-University Hospital, 80336, Munich, Germany.
| | - Jean-Charles Hoda
- Jean-Charles Hoda, SwissCheckUp SA, 1400, Yverdon-Les-Bains, Switzerland.
| | - Daniel Bertrand
- Daniel Bertrand, HiQScreen, 1222, Vésenaz, Geneva, Switzerland.
| | - Ortrud Steinlein
- Ortrud K Steinlein, Institute of Human Genetics, Ludwig-Maximilians-University Hospital, 80336, Munich, Germany.
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Conti V, Aracri P, Chiti L, Brusco S, Mari F, Marini C, Albanese M, Marchi A, Liguori C, Placidi F, Romigi A, Becchetti A, Guerrini R. Nocturnal frontal lobe epilepsy with paroxysmal arousals due to CHRNA2 loss of function. Neurology 2015; 84:1520-8. [PMID: 25770198 DOI: 10.1212/wnl.0000000000001471] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Accepted: 12/29/2014] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE We assessed the mutation frequency in nicotinic acetylcholine receptor (nAChR) subunits CHRNA4, CHRNB2, and CHRNA2 in a cohort including autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) and sporadic nocturnal frontal lobe epilepsy (NFLE). Upon finding a novel mutation in CHRNA2 in a large family, we tested in vitro its functional effects. METHODS We sequenced all the coding exons and their flanking intronic regions in 150 probands (73 NFLE, 77 ADNFLE), in most of whom diagnosis had been validated by EEG recording of seizures. Upon finding a missense mutation in CHRNA2, we measured whole-cell currents in human embryonic kidney cells in both wild-type and mutant α2β4 and α2β2 nAChR subtypes stimulated with nicotine. RESULTS We found a c.889A>T (p.Ile297Phe) mutation in the proband (≈0.6% of the whole cohort) of a large ADNFLE family (1.2% of familial cases) and confirmed its segregation in all 6 living affected individuals. Video-EEG studies demonstrated sleep-related paroxysmal epileptic arousals in all mutation carriers. Oxcarbazepine treatment was effective in all. Whole-cell current density was reduced to about 40% in heterozygosity and to 0% in homozygosity, with minor effects on channel permeability and sensitivity to nicotine. CONCLUSION ADNFLE had previously been associated with CHRNA2 dysfunction in one family, in which a gain of function mutation was demonstrated. We confirm the causative role of CHRNA2 mutations in ADNFLE and demonstrate that also loss of function of α2 nAChRs may have pathogenic effects. CHRNA2 mutations are a rare cause of ADNFLE but this gene should be included in mutation screening.
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Affiliation(s)
- Valerio Conti
- From the Pediatric Neurology and Neurogenetics Unit and Laboratories (V.C., L.C., F.M., C.M., R.G.), A. Meyer Children's Hospital-University of Florence; Department of Biotechnology and Biosciences and Center of Neuroscience (P.A., S.B., A.B.), Università di Milano-Bicocca, Milan; Neurophysiopathology Unit (M.A., A.M., C.L., F.P., A.R.), Sleep and Epilepsy Center, Department of Systems Medicine, University of Rome Tor Vergata General Hospital, Rome; IRCCS Neuromed (A.R.), Pozzilli, Isernia; and IRCCS Stella Maris Foundation (R.G.), Calambrone, Pisa, Italy
| | - Patrizia Aracri
- From the Pediatric Neurology and Neurogenetics Unit and Laboratories (V.C., L.C., F.M., C.M., R.G.), A. Meyer Children's Hospital-University of Florence; Department of Biotechnology and Biosciences and Center of Neuroscience (P.A., S.B., A.B.), Università di Milano-Bicocca, Milan; Neurophysiopathology Unit (M.A., A.M., C.L., F.P., A.R.), Sleep and Epilepsy Center, Department of Systems Medicine, University of Rome Tor Vergata General Hospital, Rome; IRCCS Neuromed (A.R.), Pozzilli, Isernia; and IRCCS Stella Maris Foundation (R.G.), Calambrone, Pisa, Italy
| | - Laura Chiti
- From the Pediatric Neurology and Neurogenetics Unit and Laboratories (V.C., L.C., F.M., C.M., R.G.), A. Meyer Children's Hospital-University of Florence; Department of Biotechnology and Biosciences and Center of Neuroscience (P.A., S.B., A.B.), Università di Milano-Bicocca, Milan; Neurophysiopathology Unit (M.A., A.M., C.L., F.P., A.R.), Sleep and Epilepsy Center, Department of Systems Medicine, University of Rome Tor Vergata General Hospital, Rome; IRCCS Neuromed (A.R.), Pozzilli, Isernia; and IRCCS Stella Maris Foundation (R.G.), Calambrone, Pisa, Italy
| | - Simone Brusco
- From the Pediatric Neurology and Neurogenetics Unit and Laboratories (V.C., L.C., F.M., C.M., R.G.), A. Meyer Children's Hospital-University of Florence; Department of Biotechnology and Biosciences and Center of Neuroscience (P.A., S.B., A.B.), Università di Milano-Bicocca, Milan; Neurophysiopathology Unit (M.A., A.M., C.L., F.P., A.R.), Sleep and Epilepsy Center, Department of Systems Medicine, University of Rome Tor Vergata General Hospital, Rome; IRCCS Neuromed (A.R.), Pozzilli, Isernia; and IRCCS Stella Maris Foundation (R.G.), Calambrone, Pisa, Italy
| | - Francesco Mari
- From the Pediatric Neurology and Neurogenetics Unit and Laboratories (V.C., L.C., F.M., C.M., R.G.), A. Meyer Children's Hospital-University of Florence; Department of Biotechnology and Biosciences and Center of Neuroscience (P.A., S.B., A.B.), Università di Milano-Bicocca, Milan; Neurophysiopathology Unit (M.A., A.M., C.L., F.P., A.R.), Sleep and Epilepsy Center, Department of Systems Medicine, University of Rome Tor Vergata General Hospital, Rome; IRCCS Neuromed (A.R.), Pozzilli, Isernia; and IRCCS Stella Maris Foundation (R.G.), Calambrone, Pisa, Italy
| | - Carla Marini
- From the Pediatric Neurology and Neurogenetics Unit and Laboratories (V.C., L.C., F.M., C.M., R.G.), A. Meyer Children's Hospital-University of Florence; Department of Biotechnology and Biosciences and Center of Neuroscience (P.A., S.B., A.B.), Università di Milano-Bicocca, Milan; Neurophysiopathology Unit (M.A., A.M., C.L., F.P., A.R.), Sleep and Epilepsy Center, Department of Systems Medicine, University of Rome Tor Vergata General Hospital, Rome; IRCCS Neuromed (A.R.), Pozzilli, Isernia; and IRCCS Stella Maris Foundation (R.G.), Calambrone, Pisa, Italy
| | - Maria Albanese
- From the Pediatric Neurology and Neurogenetics Unit and Laboratories (V.C., L.C., F.M., C.M., R.G.), A. Meyer Children's Hospital-University of Florence; Department of Biotechnology and Biosciences and Center of Neuroscience (P.A., S.B., A.B.), Università di Milano-Bicocca, Milan; Neurophysiopathology Unit (M.A., A.M., C.L., F.P., A.R.), Sleep and Epilepsy Center, Department of Systems Medicine, University of Rome Tor Vergata General Hospital, Rome; IRCCS Neuromed (A.R.), Pozzilli, Isernia; and IRCCS Stella Maris Foundation (R.G.), Calambrone, Pisa, Italy
| | - Angela Marchi
- From the Pediatric Neurology and Neurogenetics Unit and Laboratories (V.C., L.C., F.M., C.M., R.G.), A. Meyer Children's Hospital-University of Florence; Department of Biotechnology and Biosciences and Center of Neuroscience (P.A., S.B., A.B.), Università di Milano-Bicocca, Milan; Neurophysiopathology Unit (M.A., A.M., C.L., F.P., A.R.), Sleep and Epilepsy Center, Department of Systems Medicine, University of Rome Tor Vergata General Hospital, Rome; IRCCS Neuromed (A.R.), Pozzilli, Isernia; and IRCCS Stella Maris Foundation (R.G.), Calambrone, Pisa, Italy
| | - Claudio Liguori
- From the Pediatric Neurology and Neurogenetics Unit and Laboratories (V.C., L.C., F.M., C.M., R.G.), A. Meyer Children's Hospital-University of Florence; Department of Biotechnology and Biosciences and Center of Neuroscience (P.A., S.B., A.B.), Università di Milano-Bicocca, Milan; Neurophysiopathology Unit (M.A., A.M., C.L., F.P., A.R.), Sleep and Epilepsy Center, Department of Systems Medicine, University of Rome Tor Vergata General Hospital, Rome; IRCCS Neuromed (A.R.), Pozzilli, Isernia; and IRCCS Stella Maris Foundation (R.G.), Calambrone, Pisa, Italy
| | - Fabio Placidi
- From the Pediatric Neurology and Neurogenetics Unit and Laboratories (V.C., L.C., F.M., C.M., R.G.), A. Meyer Children's Hospital-University of Florence; Department of Biotechnology and Biosciences and Center of Neuroscience (P.A., S.B., A.B.), Università di Milano-Bicocca, Milan; Neurophysiopathology Unit (M.A., A.M., C.L., F.P., A.R.), Sleep and Epilepsy Center, Department of Systems Medicine, University of Rome Tor Vergata General Hospital, Rome; IRCCS Neuromed (A.R.), Pozzilli, Isernia; and IRCCS Stella Maris Foundation (R.G.), Calambrone, Pisa, Italy
| | - Andrea Romigi
- From the Pediatric Neurology and Neurogenetics Unit and Laboratories (V.C., L.C., F.M., C.M., R.G.), A. Meyer Children's Hospital-University of Florence; Department of Biotechnology and Biosciences and Center of Neuroscience (P.A., S.B., A.B.), Università di Milano-Bicocca, Milan; Neurophysiopathology Unit (M.A., A.M., C.L., F.P., A.R.), Sleep and Epilepsy Center, Department of Systems Medicine, University of Rome Tor Vergata General Hospital, Rome; IRCCS Neuromed (A.R.), Pozzilli, Isernia; and IRCCS Stella Maris Foundation (R.G.), Calambrone, Pisa, Italy
| | - Andrea Becchetti
- From the Pediatric Neurology and Neurogenetics Unit and Laboratories (V.C., L.C., F.M., C.M., R.G.), A. Meyer Children's Hospital-University of Florence; Department of Biotechnology and Biosciences and Center of Neuroscience (P.A., S.B., A.B.), Università di Milano-Bicocca, Milan; Neurophysiopathology Unit (M.A., A.M., C.L., F.P., A.R.), Sleep and Epilepsy Center, Department of Systems Medicine, University of Rome Tor Vergata General Hospital, Rome; IRCCS Neuromed (A.R.), Pozzilli, Isernia; and IRCCS Stella Maris Foundation (R.G.), Calambrone, Pisa, Italy
| | - Renzo Guerrini
- From the Pediatric Neurology and Neurogenetics Unit and Laboratories (V.C., L.C., F.M., C.M., R.G.), A. Meyer Children's Hospital-University of Florence; Department of Biotechnology and Biosciences and Center of Neuroscience (P.A., S.B., A.B.), Università di Milano-Bicocca, Milan; Neurophysiopathology Unit (M.A., A.M., C.L., F.P., A.R.), Sleep and Epilepsy Center, Department of Systems Medicine, University of Rome Tor Vergata General Hospital, Rome; IRCCS Neuromed (A.R.), Pozzilli, Isernia; and IRCCS Stella Maris Foundation (R.G.), Calambrone, Pisa, Italy.
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Benallegue N, Mazzaferro S, Alcaino C, Bermudez I. The additional ACh binding site at the α4(+)/α4(-) interface of the (α4β2)2α4 nicotinic ACh receptor contributes to desensitization. Br J Pharmacol 2014; 170:304-16. [PMID: 23742319 DOI: 10.1111/bph.12268] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Revised: 05/16/2013] [Accepted: 05/23/2013] [Indexed: 12/01/2022] Open
Abstract
BACKGROUND AND PURPOSE Nicotinic ACh (α4β2)2α4 receptors are highly prone to desensitization by prolonged exposure to low concentrations of agonist. Here, we report on the sensitivity of the three agonist sites of the (α4β2)2α4 to desensitization induced by prolonged exposure to ACh. We present electrophysiological data that show that the agonist sites of the (α4β2)2α4 receptor have different sensitivity to desensitization and that full receptor occupation decreases sensitivity to desensitization. EXPERIMENTAL APPROACH Two-electrode voltage-clamp electrophysiology was used to study the desensitization of concatenated (α4β2)2α4 receptors expressed heterologously in Xenopus oocytes. Desensitization was assessed by measuring the degree of functional inhibition caused by prolonged exposure to ACh, as measured under equilibrium conditions. We used the single-point mutation α4W182A to measure the contribution of individual agonist sites to desensitization. KEY RESULTS (α4β2)2α4 receptors are less sensitive to activation and desensitization by ACh than (α4β2)2β2 receptors. Incorporation of α4W182A into any of the agonist sites of concatenated (α4β2)2α4 receptors decreased sensitivity to activation and desensitization but the effects were more pronounced when the mutation was introduced into the α4(+)/α4(-) interface. CONCLUSIONS AND IMPLICATIONS The findings suggest that the agonist sites in (α4β2)2α4 receptors are not functionally equivalent. The agonist site at the α4(+)/α4(-) interface defines the sensitivity of (α4β2)2α4 receptors to agonist-induced activation and desensitization. Functional differences between (α4β2)2α4 and (α4β2)2β2 receptors might shape the physiological and behavioural responses to nicotinic ligands when the receptors are exposed to nicotinic ligands for prolonged periods of times.
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Affiliation(s)
- N Benallegue
- Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, UK
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12
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Abstract
Epilepsy affects almost 1% of the population, and yet the pathophysiology of this disorder is unknown in the majority of the cases. Recently, a number of mutations in different genes were identified, mostly in cases of familial epilepsy with a Mendelian mode of inheritance. The majority of these genes code for voltage- or ligand-gated ion channels. Interestingly, not only generalized epilepsies, but also focal epilepsies were shown to be caused by mutated genes, which in some cases are expressed ubiquitously in the brain. This review will focus on the monogenic familial epilepsies and the clinical and molecular aspects of these diseases.
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Affiliation(s)
- Danielle M Andrade
- University of Toronto, Division of Neurology, Krembil Neuroscience Centre, Toronto Western Hospital, Toronto, Canada.
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13
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Chang WP, Shyu BC. Anterior Cingulate epilepsy: mechanisms and modulation. Front Integr Neurosci 2014; 7:104. [PMID: 24427123 PMCID: PMC3879463 DOI: 10.3389/fnint.2013.00104] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2013] [Accepted: 12/16/2013] [Indexed: 11/13/2022] Open
Abstract
Epilepsy is a common neurological disorder, about 1% population worldwide suffered from this disease. In 1989, the International League Against Epilepsy (ILAE) classified anterior cingulate epilepsy as a form of frontal lobe epilepsy (FLE). FLE is the second most common type of epilepsy. Previous clinical studies showed that FLE account an important cause in refractory epilepsy, therefore to find alternative approach to modulate FLE is very important. Basic research using animal models and brain slice have revealed some insights on the epileptogenesis and modulation of seizure in anterior cingulate cortex (ACC). Interneurons play an important role in the synchronization of cingulate epilepsy. Research has shown that the epileptogenesis of seizure originated from mesial frontal lobe might be caused by a selective increase in nicotine-evoked γ-aminobutyric acid (GABA) inhibition, because the application of the GABAA receptor antagonist picrotoxin inhibited epileptic discharges. Gap junctions are also involved in the regulation of cingulate epilepsy. Previous studies have shown that the application of gap junction blockers could attenuate ACC seizures, while gap junction opener could enhance them in an in vitro preparation. μ-Opioid receptors have been shown to be involved in the epileptic synchronization mechanism in ACC seizures in a brain slice preparation. Application of the μ-opioid agonist DAMGO significantly abolished the ictal discharges in a 4-aminopyridine induced electrographic seizure model in ACC. Basic research has also found that thalamic modulation has an inhibitory effect on ACC seizures. Studies have shown that the medial thalamus may be a target for deep brain stimulation to cure ACC seizures.
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Affiliation(s)
- Wei-Pang Chang
- Graduate Institute of Life Science, National Defense Medical Center Taipei, Taiwan ; Institute of Biomedical Science, Academia Sinica Taipei, Taiwan
| | - Bai-Chuang Shyu
- Graduate Institute of Life Science, National Defense Medical Center Taipei, Taiwan ; Institute of Biomedical Science, Academia Sinica Taipei, Taiwan
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14
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Functional Distribution and Regulation of Neuronal Nicotinic ACh Receptors in the Mammalian Brain. NICOTINIC RECEPTORS 2014. [DOI: 10.1007/978-1-4939-1167-7_5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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15
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Yakel JL. Cholinergic receptors: functional role of nicotinic ACh receptors in brain circuits and disease. Pflugers Arch 2013; 465:441-50. [PMID: 23307081 PMCID: PMC3633680 DOI: 10.1007/s00424-012-1200-1] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2012] [Revised: 12/03/2012] [Accepted: 12/03/2012] [Indexed: 12/13/2022]
Abstract
The neurotransmitter acetylcholine (ACh) can regulate neuronal excitability throughout the nervous system by acting on both the cys-loop ligand-gated nicotinic ACh receptor channels (nAChRs) and the G protein-coupled muscarinic ACh receptors (mAChRs). The hippocampus is an important area in the brain for learning and memory, where both nAChRs and mAChRs are expressed. The primary cholinergic input to the hippocampus arises from the medial septum and diagonal band of Broca, the activation of which can activate both nAChRs and mAChRs in the hippocampus and regulate synaptic communication and induce oscillations that are thought to be important for cognitive function. Dysfunction in the hippocampal cholinergic system has been linked with cognitive deficits and a variety of neurological disorders and diseases, including Alzheimer's disease and schizophrenia. My lab has focused on the role of the nAChRs in regulating hippocampal function, from understanding the expression and functional properties of the various subtypes of nAChRs, and what role these receptors may be playing in regulating synaptic plasticity. Here, I will briefly review this work, and where we are going in our attempts to further understand the role of these receptors in learning and memory, as well as in disease and neuroprotection.
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Affiliation(s)
- Jerrel L Yakel
- Laboratory of Neurobiology, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, P.O. Box 12233, Mail Drop F2-08, Research Triangle Park, NC 27709, USA.
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16
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Miwa JM, Lester HA, Walz A. Optimizing cholinergic tone through lynx modulators of nicotinic receptors: implications for plasticity and nicotine addiction. Physiology (Bethesda) 2012; 27:187-99. [PMID: 22875450 DOI: 10.1152/physiol.00002.2012] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The cholinergic system underlies both adaptive (learning and memory) and nonadaptive (addiction and dependency) behavioral changes through its ability to shape and regulate plasticity. Protein modulators such as lynx family members can fine tune the activity of the cholinergic system and contribute to the graded response of the cholinergic system, stabilizing neural circuitry through direct interaction with nicotinic receptors. Release of this molecular brake can unmask cholinergic-dependent mechanisms in the brain. Lynx proteins have the potential to provide top-down control over plasticity mechanisms, including addictive propensity. If this is indeed the case, then, what regulates the regulator? Transcriptional changes of lynx genes in response to pharmacological, physiological, and pathological alterations are explored in this review.
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Affiliation(s)
- Julie M Miwa
- California Institute of Technology, Pasadena, California, USA.
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Becchetti A. Neuronal nicotinic receptors in sleep-related epilepsy: studies in integrative biology. ISRN BIOCHEMISTRY 2012; 2012:262941. [PMID: 25969754 PMCID: PMC4392997 DOI: 10.5402/2012/262941] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/25/2012] [Accepted: 10/21/2012] [Indexed: 11/23/2022]
Abstract
Although Mendelian diseases are rare, when considered one by one, overall they constitute a significant social burden. Besides the medical aspects, they propose us one of the most general biological problems. Given the simplest physiological perturbation of an organism, that is, a single gene mutation, how do its effects percolate through the hierarchical biological levels to determine the pathogenesis? And how robust is the physiological system to this perturbation? To solve these problems, the study of genetic epilepsies caused by mutant ion channels presents special advantages, as it can exploit the full range of modern experimental methods. These allow to extend the functional analysis from single channels to whole brains. An instructive example is autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE), which can be caused by mutations in neuronal nicotinic acetylcholine receptors. In vitro, such mutations often produce hyperfunctional receptors, at least in heterozygous condition. However, understanding how this leads to sleep-related frontal epilepsy is all but straightforward. Several available animal models are helping us to determine the effects of ADNFLE mutations on the mammalian brain. Because of the complexity of the cholinergic regulation in both developing and mature brains, several pathogenic mechanisms are possible, which also present different therapeutic implications.
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Affiliation(s)
- Andrea Becchetti
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy
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18
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Mefford HC, Cook J, Gospe SM. Epilepsy due to 20q13.33 subtelomere deletion masquerading as pyridoxine-dependent epilepsy. Am J Med Genet A 2012; 158A:3190-5. [DOI: 10.1002/ajmg.a.35633] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Accepted: 07/30/2012] [Indexed: 02/03/2023]
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19
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Velisetty P, Chalamalasetti SV, Chakrapani S. Conformational transitions underlying pore opening and desensitization in membrane-embedded Gloeobacter violaceus ligand-gated ion channel (GLIC). J Biol Chem 2012; 287:36864-72. [PMID: 22977232 DOI: 10.1074/jbc.m112.401067] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Direct structural insight into the mechanisms underlying activation and desensitization remain unavailable for the pentameric ligand-gated channel family. Here, we report the structural rearrangements underlying gating transitions in membrane-embedded GLIC, a prokaryotic homologue, using site-directed spin labeling and electron paramagnetic resonance (EPR) spectroscopy. We particularly probed the conformation of pore-lining second transmembrane segment (M2) under conditions that favor the closed and the ligand-bound desensitized states. The spin label mobility, intersubunit spin-spin proximity, and the solvent-accessibility parameters in the two states clearly delineate the underlying protein motions within M2. Our results show that during activation the extracellular hydrophobic region undergoes major changes involving an outward translational movement, away from the pore axis, leading to an increase in the pore diameter, whereas the lower end of M2 remains relatively immobile. Most notably, during desensitization, the intervening polar residues in the middle of M2 move closer to form a solvent-occluded barrier and thereby reveal the location of a distinct desensitization gate. In comparison with the crystal structure of GLIC, the structural dynamics of the channel in a membrane environment suggest a more loosely packed conformation with water-accessible intrasubunit vestibules penetrating from the extracellular end all the way to the middle of M2 in the closed state. These regions have been implicated to play a major role in alcohol and drug modulation. Overall, these findings represent a key step toward understanding the fundamentals of gating mechanisms in this class of channels.
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Affiliation(s)
- Phanindra Velisetty
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA
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20
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Gourfinkel-An I, Baulac S, Brice A, Leguern E, Baulac M. Genetics of inherited human epilepsies. DIALOGUES IN CLINICAL NEUROSCIENCE 2012. [PMID: 22034131 PMCID: PMC3181638 DOI: 10.31887/dcns.2001.3.1/igourfinkelan] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Major advances have recently been made in our understanding of the genetic basis of monogenic inherited epilepsies. Progress has been particularly spectacular with respect to idiopathic epilepsies, with the discovery that mutations in ion channel subunits are implicated. However, important advances have also been made in many inherited symptomatic epilepsies, for which direct molecular diagnosis is now possible, simplifying previously complex investigations, it is expected that identification of the genes implicated in familial forms of epilepsies will lead to a better understanding of the underlying pathophysiological mechanisms of these disorders and to the development of experimental models and new therapeutic strategies, in this article, we review the clinical and genetic data concerning most of the inherited human epilepsies.
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Affiliation(s)
- I Gourfinkel-An
- Unité d'Epileptologie, Hôpital Pitié-Salpêtrière, Paris, France; Service d'Electrophysiologie, Hôpital Pitié-Salpêtrière, Paris, France
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21
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Velisetty P, Chakrapani S. Desensitization mechanism in prokaryotic ligand-gated ion channel. J Biol Chem 2012; 287:18467-77. [PMID: 22474322 DOI: 10.1074/jbc.m112.348045] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Crystal structures of Gloeobacter violaceus ligand-gated ion channel (GLIC), a proton-gated prokaryotic homologue of pentameric ligand-gated ion channel (LGIC) from G. violaceus, have provided high-resolution models of the channel architecture and its role in selective ion conduction and drug binding. However, it is still unclear which functional states of the LGIC gating scheme these crystal structures represent. Much of this uncertainty arises from a lack of thorough understanding of the functional properties of these prokaryotic channels. To elucidate the molecular events that constitute gating, we have carried out an extensive characterization of GLIC function and dynamics in reconstituted proteoliposomes by patch clamp measurements and EPR spectroscopy. We find that GLIC channels show rapid activation upon jumps to acidic pH followed by a time-dependent loss of conductance because of desensitization. GLIC desensitization is strongly coupled to activation and is modulated by voltage, permeant ions, pore-blocking drugs, and membrane cholesterol. Many of these properties are parallel to functions observed in members of eukaryotic LGIC. Conformational changes in loop C, measured by site-directed spin labeling and EPR spectroscopy, reveal immobilization during desensitization analogous to changes in LGIC and acetylcholine binding protein. Together, our studies suggest conservation of mechanistic aspects of desensitization among LGICs of prokaryotic and eukaryotic origin.
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Affiliation(s)
- Phanindra Velisetty
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA
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22
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Yakel JL. Nicotinic ACh receptors in the hippocampus: role in excitability and plasticity. Nicotine Tob Res 2012; 14:1249-57. [PMID: 22472168 DOI: 10.1093/ntr/nts091] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
INTRODUCTION The nicotinic ACh receptors (nAChRs) are in the cys-loop family of ligand-gated ion channels. They are widely expressed throughout the brain, including in the hippocampus where they are thought to be involved in regulating excitability, plasticity, and cognitive function. In addition, dysfunction in hippocampal nAChRs has been linked to a variety of neurological disorders and diseases, including Alzheimer's disease, schizophrenia, and epilepsy. In order to understand how to treat nAChR-related disorders and diseases, it is critical to understand how these receptors participate in normal brain function; this entails not only understanding the biophysical properties of ion channel function and their pattern of expression but also how these receptors are regulating excitability and circuit behavior. DISCUSSION The primary cholinergic input to the hippocampus comes from the medial septum and diagonal band of Broca; however, the mechanistic details are unknown of how activation of cholinergic receptors, either through exogenous nAChR ligands or the activation of endogenous acetylcholine release, regulates hippocampal network activity. This entails direct study of the excitatory and inhibitory neuronal networks, as well as the role of nonneuronal cells, in regulating hippocampal function. CONCLUSIONS Here, I will review the latest work from my laboratory in which we have attempted to do just that, with the overall goal of learning more about the role of the hippocampal nAChR in synaptic plasticity.
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Affiliation(s)
- Jerrel L Yakel
- Laboratory of Neurobiology, National Institute of Environmental Health Sciences, P.O. Box 12233, Mail Drop F2-08, Research Triangle Park, NC 27709, USA.
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23
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Tammimäki A, Horton WJ, Stitzel JA. Recent advances in gene manipulation and nicotinic acetylcholine receptor biology. Biochem Pharmacol 2011; 82:808-19. [PMID: 21704022 DOI: 10.1016/j.bcp.2011.06.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2011] [Revised: 06/07/2011] [Accepted: 06/08/2011] [Indexed: 11/26/2022]
Abstract
Pharmacological and immunological methods have been valuable for both identifying some native nicotinic acetylcholine receptor (nAChR) subtypes that exist in vivo and determining the neurobiological and behavioral role of certain nAChR subtypes. However, these approaches suffer from shortage of subtype specific ligands and reliable immunological reagents. Consequently, genetic approaches have been developed to complement earlier approaches to identify native nAChR subtypes and to assess the contribution of nAChRs to brain function and behavior. In this review we describe how assembly partners, knock-in mice and targeted lentiviral re-expression of genes have been utilized to improve our understanding of nAChR neurobiology. In addition, we summarize emerging genetic tools in nAChR research.
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Affiliation(s)
- Anne Tammimäki
- Institute for Behavioral Genetics, University of Colorado at Boulder, UCB 447, Boulder, CO 80309, United States.
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24
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Steinlein OK. Gene polymorphisms and their role in epilepsy treatment and prognosis. Naunyn Schmiedebergs Arch Pharmacol 2010; 382:109-18. [PMID: 20556360 DOI: 10.1007/s00210-010-0531-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2010] [Accepted: 05/27/2010] [Indexed: 12/16/2022]
Abstract
The human genome carries an enormous number of genetic variants, many of them of functional consequence. In epilepsy, they are likely to be involved in drug-specific treatment efficacy, unwanted or even toxic drug reactions, teratogenic risks in pregnancy as well as in the long-term prognosis of patients with epilepsy. As in many other disorders with a complex genetic background, the associated genetic variants that could be verified successfully in replication studies are still only a few. However, new techniques and improved research strategies are likely to increase their number in the foreseeable future, although at a much slower pace as initially expected.
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Affiliation(s)
- Ortrud K Steinlein
- Institute of Human Genetics, University Hospital, Ludwig-Maximilians-University of Munich, Goethestr. 29, 80336, Munich, Germany.
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25
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Bacher I, Wu B, Shytle DR, George TP. Mecamylamine - a nicotinic acetylcholine receptor antagonist with potential for the treatment of neuropsychiatric disorders. Expert Opin Pharmacother 2010; 10:2709-21. [PMID: 19874251 DOI: 10.1517/14656560903329102] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Mecamylamine (Inversine), the first orally available antihypertensive agent launched in the 1950s, is rarely used today for hypertension because of its widespread ganglionic side effects at antihypertensive doses (25 - 90 mg/day). However, more recent clinical studies suggest that mecamylamine is effective at much lower doses for blocking the central and peripheral effects of nicotine. Pharmacologically, mecamylamine has been well characterized as a nonselective and noncompetitive antagonist of nicotinic acetylcholine receptors (nAChRs). Because mecamylamine easily crosses the blood - brain barrier at relatively low doses (2.5 - 10 mg), it has been used by several research groups over the past two decades investigating the role of central nAChRs in the etiology and treatment of various neuropsychiatric disorders, including addiction disorders, Tourette's syndrome, schizophrenia and various cognitive and mood disorders. Two independent Phase II clinical trials recently confirmed mecamylamine's hypothesized antidepressant activity and suggest that it may be effective as an augmentation pharmacotherapy for SSRI treatment resistant major depression. These areas of investigation for mecamylamine are reviewed and recommendations for future research directions are proposed.
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Affiliation(s)
- Ingrid Bacher
- University of Toronto, Department of Psychiatry, Faculty of Medicine, Toronto, Canada.
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26
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27
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Steinlein OK, Bertrand D. Nicotinic receptor channelopathies and epilepsy. Pflugers Arch 2009; 460:495-503. [DOI: 10.1007/s00424-009-0766-8] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2009] [Revised: 11/23/2009] [Accepted: 11/24/2009] [Indexed: 02/05/2023]
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Genetic basis in epilepsies caused by malformations of cortical development and in those with structurally normal brain. Hum Genet 2009; 126:173-93. [PMID: 19536565 DOI: 10.1007/s00439-009-0702-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2009] [Accepted: 06/02/2009] [Indexed: 01/10/2023]
Abstract
Epilepsy is the most common neurological disorder affecting young people. The etiologies are multiple and most cases are sporadic. However, some rare families with Mendelian inheritance have provided evidence of genes' important role in epilepsy. Two important but apparently different groups of disorders have been extensively studied: epilepsies associated with malformations of cortical development (MCDs) and epilepsies associated with a structurally normal brain (or with minimal abnormalities only). This review is focused on clinical and molecular aspects of focal cortical dysplasia, polymicrogyria, periventricular nodular heterotopia, subcortical band heterotopia, lissencephaly and schizencephaly as examples of MCDs. Juvenile myoclonic epilepsy, childhood absence epilepsy, some familial forms of focal epilepsy and epilepsies associated with febrile seizures are discussed as examples of epileptic conditions in (apparently) structurally normal brains.
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29
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Cortical hyperexcitability and epileptogenesis: Understanding the mechanisms of epilepsy – Part 1. J Clin Neurosci 2009; 16:355-65. [DOI: 10.1016/j.jocn.2008.08.026] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2008] [Accepted: 08/12/2008] [Indexed: 11/22/2022]
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Sharma G, Vijayaraghavan S. Nicotinic Receptors: Role in Addiction and Other Disorders of the Brain. Subst Abuse 2008; 2008:81. [PMID: 20148179 PMCID: PMC2817963] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Nicotine, the addictive component of cigarette smoke has profound effects on the brain. Activation of its receptors by nicotine has complex consequences for network activity throughout the brain, potentially contributing to the addictive property of the drug. Nicotinic receptors have been implicated in psychiatric illnesses like schizophrenia and are also neuroprotective, potentially beneficial for neurodegenerative diseases. These effects of nicotine serve to emphasize the multifarious roles the drug, acting through multiple nicotinic acetylcholine receptor subtypes. The findings also remind us of the complexity of signaling mechanisms and stress the risks of unintended consequences of drugs designed to combat nicotine addiction.
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Affiliation(s)
| | - Sukumar Vijayaraghavan
- Correspondence: Sukumar Vijayaraghavan, Department of Physiology and Biophysics University of Colorado, Denver, School of Medicine, MS 8307, PO Box 6511, 12800 E. 19th Avenue, Aurora CO 80045. Tel: 303-724-4531;
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31
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Affiliation(s)
- Samuel F. Berkovic
- Epilepsy Research Institute, The University of Melbourne, Austin and Repatriation Medical Centre,
West Heidelberg, Victoria, Australia
| | - Ingrid E. Scheffer
- Epilepsy Research Institute, The University of Melbourne, Austin and Repatriation Medical Centre,
West Heidelberg, Victoria, Australia
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32
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Lipovsek M, Plazas P, Savino J, Klaassen A, Boulter J, Elgoyhen AB, Katz E. Properties of mutated murine α4β2 nicotinic receptors linked to partial epilepsy. Neurosci Lett 2008; 434:165-9. [DOI: 10.1016/j.neulet.2007.12.061] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2007] [Revised: 12/13/2007] [Accepted: 12/24/2007] [Indexed: 10/22/2022]
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Sharma G, Vijayaraghavan S. Nicotinic Receptors: Role in Addiction and Other Disorders of the Brain. SUBSTANCE ABUSE: RESEARCH AND TREATMENT 2008. [DOI: 10.1177/117822180800100005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/08/2023]
Abstract
Nicotine, the addictive component of cigarette smoke has profound effects on the brain. Activation of its receptors by nicotine has complex consequences for network activity throughout the brain, potentially contributing to the addictive property of the drug. Nicotinic receptors have been implicated in psychiatric illnesses like schizophrenia and are also neuroprotective, potentially beneficial for neurodegenerative diseases. These effects of nicotine serve to emphasize the multifarious roles the drug, acting through multiple nicotinic acetylcholine receptor subtypes. The findings also remind us of the complexity of signaling mechanisms and stress the risks of unintended consequences of drugs designed to combat nicotine addiction.
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Affiliation(s)
- Geeta Sharma
- Department of Physiology and Biophysics and the Neuroscience Program, University of Colorado, Denver, School of Medicine Aurora CO 80045
| | - Sukumar Vijayaraghavan
- Department of Physiology and Biophysics and the Neuroscience Program, University of Colorado, Denver, School of Medicine Aurora CO 80045
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Stoichiometric analysis of the TM2 6' phenylalanine mutation on desensitization in alpha1beta2 and alpha1beta2gamma2 GABA A receptors. Neurosci Lett 2007; 431:184-9. [PMID: 18162311 DOI: 10.1016/j.neulet.2007.11.039] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2007] [Revised: 10/28/2007] [Accepted: 11/29/2007] [Indexed: 11/22/2022]
Abstract
The presence of phenylalanine (F) at the 6' position of transmembrane domain 2 (TM2) in the alpha4 subunit of alpha4beta2 nicotinic receptors enhances desensitization. As the GABA A receptor affords the ability to study the influence of as few as one and as many as five Fs at this position, we have used it to investigate potential subunit- and stoichiometry-dependent effects of the TM2 6'F mutation on desensitization. Whereas the presence of one F at this position decreased extent of desensitization, desensitization was increased in all configurations that included two or more Fs at the TM2 6' position; desensitization was particularly rapid with 3 or 4 F residues present. Our results demonstrate the ability of F residues at the TM2 6' position to modulate desensitization is likely conserved in the cys-loop family of ligand-gated ion channels. Moreover, our findings demonstrate both stoichiometric- and subunit-dependent effects of the ability of this mutation to regulate desensitization in GABA A receptors.
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Teper Y, Whyte D, Cahir E, Lester HA, Grady SR, Marks MJ, Cohen BN, Fonck C, McClure-Begley T, McIntosh JM, Labarca C, Lawrence A, Chen F, Gantois I, Davies PJ, Petrou S, Murphy M, Waddington J, Horne MK, Berkovic SF, Drago J. Nicotine-induced dystonic arousal complex in a mouse line harboring a human autosomal-dominant nocturnal frontal lobe epilepsy mutation. J Neurosci 2007; 27:10128-42. [PMID: 17881519 PMCID: PMC6672658 DOI: 10.1523/jneurosci.3042-07.2007] [Citation(s) in RCA: 65] [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
We generated a mouse line harboring an autosomal-dominant nocturnal frontal lobe epilepsy (ADNFLE) mutation: the alpha4 nicotinic receptor S248F knock-in strain. In this mouse, modest nicotine doses (1-2 mg/kg) elicit a novel behavior termed the dystonic arousal complex (DAC). The DAC includes stereotypical head movements, body jerking, and forelimb dystonia; these behaviors resemble some core features of ADNFLE. A marked Straub tail is an additional component of the DAC. Similar to attacks in ADNFLE, the DAC can be partially suppressed by the sodium channel blocker carbamazepine or by pre-exposure to a very low dose of nicotine (0.1 mg/kg). The DAC is centrally mediated, genetically highly penetrant, and, surprisingly, not associated with overt ictal electrical activity as assessed by (1) epidural or frontal lobe depth-electrode electroencephalography or (2) hippocampal c-fos-regulated gene expression. Heterozygous knock-in mice are partially protected from nicotine-induced seizures. The noncompetitive antagonist mecamylamine does not suppress the DAC, although it suppresses high-dose nicotine-induced wild-type-like seizures. Experiments on agonist-induced 86Rb+ and neurotransmitter efflux from synaptosomes and on alpha4S248Fbeta2 receptors expressed in oocytes confirm that the S248F mutation confers resistance to mecamylamine blockade. Genetic background, gender, and mutant gene expression levels modulate expression of the DAC phenotype in mice. The S248F mouse thus appears to provide a model for the paroxysmal dystonic element of ADNFLE semiology. Our model complements what is seen in other ADNFLE animal models. Together, these mice cover the spectrum of behavioral and electrographic events seen in the human condition.
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Affiliation(s)
| | | | | | - Henry A. Lester
- Division of Biology, California Institute of Technology, Pasadena, California 91125
| | - Sharon R. Grady
- Institute of Behavioral Genetics, University of Colorado, Boulder, Colorado 80309
| | - Michael J. Marks
- Institute of Behavioral Genetics, University of Colorado, Boulder, Colorado 80309
| | - Bruce N. Cohen
- Division of Biology, California Institute of Technology, Pasadena, California 91125
| | - Carlos Fonck
- Division of Biology, California Institute of Technology, Pasadena, California 91125
| | | | - J. Michael McIntosh
- Departments of Biology and Psychiatry, University of Utah, Salt Lake City, Utah 84112-0840
| | - Cesar Labarca
- Division of Biology, California Institute of Technology, Pasadena, California 91125
| | | | | | | | | | | | - Mark Murphy
- Department of Anatomy and Cell Biology, The University of Melbourne, Victoria 3010, Australia
| | - John Waddington
- Royal College of Surgeons in Ireland, Dublin 2, Ireland, and
| | | | - Samuel F. Berkovic
- Department of Medicine and Epilepsy Research Centre, University of Melbourne, Austin Health, Heidelberg West, Victoria 3081, Australia
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Marini C, Guerrini R. The role of the nicotinic acetylcholine receptors in sleep-related epilepsy. Biochem Pharmacol 2007; 74:1308-14. [PMID: 17662253 DOI: 10.1016/j.bcp.2007.06.030] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2007] [Revised: 06/18/2007] [Accepted: 06/19/2007] [Indexed: 12/01/2022]
Abstract
The role of neuronal acetylcholine receptors (nAChRs) in epilepsy has been clearly established by the finding of mutations in a subset of genes coding for subunits of the nAChRs in a form of sleep-related epilepsy with familial occurrence in about 30% of probands and dominant inheritance, named autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE). Sporadic and familial forms have similar clinical and EEG features. Seizures begin in middle childhood as clusters of sleep-related attacks with prominent motor activity, and sustained dystonic posturing. In addition to nocturnal seizures, psychosis or schizophrenia, behavioral disorders, memory deficits and mental retardation were described in some individuals. Although over hundred families are on record, only a minority of them have been linked to mutations in the genes coding for the alpha4, alpha2 and beta2 (CHRNA4, CHRNA2, and CHRNB2) subunits of the nAChRs, indicating that ADNFLE is genetically heterogeneous despite a relatively homogeneous clinical picture. Functional characterization of some mutations suggests that gain of the receptor function might be the basis for epileptogenesis. In vitro and in vivo studies have shown high density of nAChRs in the thalamus, over activated brainstem ascending cholinergic pathway and enhanced GABAergic function, reinforcing the hypothesis that cortico-subcortical networks, regulating arousal from sleep, play a central role in seizure precipitation in ADNFLE.
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Affiliation(s)
- Carla Marini
- Epilepsy, Neurophysiology and Neurogenetics Unit, Department of Child Neurology and Psychiatry, IRCCS Stella Maris Foundation, Pisa, Italy.
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37
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Klaassen A, Glykys J, Maguire J, Labarca C, Mody I, Boulter J. Seizures and enhanced cortical GABAergic inhibition in two mouse models of human autosomal dominant nocturnal frontal lobe epilepsy. Proc Natl Acad Sci U S A 2006; 103:19152-7. [PMID: 17146052 PMCID: PMC1681351 DOI: 10.1073/pnas.0608215103] [Citation(s) in RCA: 169] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Selected mutations in the human alpha4 or beta2 neuronal nicotinic acetylcholine receptor subunit genes cosegregate with a partial epilepsy syndrome known as autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE). To examine possible mechanisms underlying this inherited epilepsy, we engineered two ADNFLE mutations (Chrna4(S252F) and Chrna4(+L264)) in mice. Heterozygous ADNFLE mutant mice show persistent, abnormal cortical electroencephalograms with prominent delta and theta frequencies, exhibit frequent spontaneous seizures, and show an increased sensitivity to the proconvulsant action of nicotine. Relative to WT, electrophysiological recordings from ADNFLE mouse layer II/III cortical pyramidal cells reveal a >20-fold increase in nicotine-evoked inhibitory postsynaptic currents with no effect on excitatory postsynaptic currents. i.p. injection of a subthreshold dose of picrotoxin, a use-dependent gamma-aminobutyric acid receptor antagonist, reduces cortical electroencephalogram delta power and transiently inhibits spontaneous seizure activity in ADNFLE mutant mice. Our studies suggest that the mechanism underlying ADNFLE seizures may involve inhibitory synchronization of cortical networks via activation of mutant alpha4-containing nicotinic acetylcholine receptors located on the presynaptic terminals and somatodendritic compartments of cortical GABAergic interneurons.
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Affiliation(s)
- Alwin Klaassen
- *Graduate Interdepartmental Program in Neuroscience, 675 Charles Young Drive South, University of California, Los Angeles, CA 90095
| | - Joseph Glykys
- *Graduate Interdepartmental Program in Neuroscience, 675 Charles Young Drive South, University of California, Los Angeles, CA 90095
| | - Jamie Maguire
- Department of Neurology, 655 Charles Young Drive South, University of California, Los Angeles, CA 90095; and
| | - Cesar Labarca
- Division of Biology, California Institute of Technology, Pasadena, CA 91125
| | - Istvan Mody
- Department of Neurology, 655 Charles Young Drive South, University of California, Los Angeles, CA 90095; and
| | - Jim Boulter
- Department of Psychiatry and Biobehavioral Sciences, Hatos Research Center for Neuropharmacology, Brain Research and Molecular Biology Institutes, and
- To whom correspondence should be addressed. E-mail:
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DeLorenzo RJ, Sun DA, Deshpande LS. Erratum to "Cellular mechanisms underlying acquired epilepsy: the calcium hypothesis of the induction and maintenance of epilepsy." [Pharmacol. Ther. 105(3) (2005) 229-266]. Pharmacol Ther 2006; 111:288-325. [PMID: 16832874 DOI: 10.1016/j.pharmthera.2004.10.015] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Epilepsy is one of the most common neurological disorders. Although epilepsy can be idiopathic, it is estimated that up to 50% of all epilepsy cases are initiated by neurological insults and are called acquired epilepsy (AE). AE develops in 3 phases: (1) the injury [central nervous system (CNS) insult]. (2) epileptogenesis (latency), and (3) the chronic epileptic (spontaneous recurrent seizure) phases. Status epilepticus (SE), stroke, and traumatic brain injury (TBI) are 3 major examples of common brain injuries that can lead to the development of AE. It is especially important to understand the molecular mechanisms that cause AE because it may lead to innovative strategies to prevent or cure this common condition. Recent studies have offered new insights into the cause of AE and indicate that injury-induced alterations in intracellular calcium concentration levels ([Ca(2+)](i)) and calcium homeostatic mechanisms play a role in the development and maintenance of AE. The injuries that cause AE are different, but the share a common molecular mechanism for producing brain damage--an increase in extracellular glutamate and are exposed to increased [Ca(2+)](i) are the cellular substrates to develop epilepsy because dead cells do not seize. The neurons that survive injury sustain permanent long-term plasticity changes in [Ca(2+)](i) and calcium homeostatic mechanisms that are permanent and are a prominent feature of the epileptic phenotype. In the last several years, evidence has accumulated indicating that the prolonged alteration in neuronal calcium dynamics plays an important role in the induction and maintenance of the prolonged neuroplasticity changes underlying the epileptic phenotype. Understanding the role of calcium as a second messenger in the induction and maintenance of epilepsy may provide novel insights into therapeutic advances that will prevent and even cure AE.
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Affiliation(s)
- Robert J DeLorenzo
- Department of Neurology, Virginia Commonwealth University, School of Medicine, Richmond, 23298-0599, USA.
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Miwa JM, Stevens TR, King SL, Caldarone BJ, Ibanez-Tallon I, Xiao C, Fitzsimonds RM, Pavlides C, Lester HA, Picciotto MR, Heintz N. The Prototoxin lynx1 Acts on Nicotinic Acetylcholine Receptors to Balance Neuronal Activity and Survival In Vivo. Neuron 2006; 51:587-600. [PMID: 16950157 DOI: 10.1016/j.neuron.2006.07.025] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2004] [Revised: 10/21/2005] [Accepted: 07/19/2006] [Indexed: 10/24/2022]
Abstract
Nicotinic acetylcholine receptors (nAChRs) affect a wide array of biological processes, including learning and memory, attention, and addiction. lynx1, the founding member of a family of mammalian prototoxins, modulates nAChR function in vitro by altering agonist sensitivity and desensitization kinetics. Here we demonstrate, through the generation of lynx1 null mutant mice, that lynx1 modulates nAChR signaling in vivo. Its loss decreases the EC(50) for nicotine by approximately 10-fold, decreases receptor desensitization, elevates intracellular calcium levels in response to nicotine, and enhances synaptic efficacy. lynx1 null mutant mice exhibit enhanced performance in specific tests of learning and memory. Consistent with reports that mutations resulting in hyperactivation of nAChRs can lead to neurodegeneration, aging lynx1 null mutant mice exhibit a vacuolating degeneration that is exacerbated by nicotine and ameliorated by null mutations in nAChRs. We conclude that lynx1 functions as an allosteric modulator of nAChR function in vivo, balancing neuronal activity and survival in the CNS.
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Affiliation(s)
- Julie M Miwa
- The Laboratory of Molecular Biology, Howard Hughes Medical Institute, The Rockefeller University, New York, NY 10021, USA
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Zayas R, Lasalde-Dominicci J, Gomez CM. Macroscopic properties of spontaneous mutations in slow-channel syndrome: correlation by domain and disease severity. Synapse 2006; 60:441-9. [PMID: 16881075 DOI: 10.1002/syn.20317] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The slow-channel syndrome (SCS) is a neuromuscular disorder characterized by fatigability, progressive weakness, and degeneration of the neuromuscular junction. The SCS is caused by missense mutations in the four subunits of the skeletal muscle acetylcholine receptor (AChR), which leads to altered channel gating, prolonged neuromuscular postsynaptic currents, and impaired neuromuscular transmission. Although a diverse set of mutations in different functional domains of the AChR appear to be associated with symptoms of widely ranging severity, there is as yet no mutant channel property or combination that explains the variations in disease severity. By observing the recovery time of AChR from desensitization, the authors determined that this process is significantly enhanced in SCS channels. In addition, as expected, the authors found that SCS macroscopic decay currents in transfected HEK293 cells are slower than wild type currents. While slight differences in relative Ca(2+) permeability between some SCS mutations were identified, they did not correlate with apparent disease severity. These results suggest that of the different AChR kinetic features studied, only recovery from desensitization and slow postsynaptic currents correlate with the severity observed in the different mutations of this syndrome.
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Affiliation(s)
- Roberto Zayas
- Department of Neuroscience and Neurology, University of Minnesota, Minneapolis, 55455, USA
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41
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Hirose S. A new paradigm of channelopathy in epilepsy syndromes: Intracellular trafficking abnormality of channel molecules. Epilepsy Res 2006; 70 Suppl 1:S206-17. [PMID: 16860540 DOI: 10.1016/j.eplepsyres.2005.12.007] [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: 11/08/2005] [Revised: 12/01/2005] [Accepted: 12/01/2005] [Indexed: 10/24/2022]
Abstract
Mutations in genes encoding ion channels in brain neurons have been identified in various epilepsy syndromes. In neuronal networks, "gain-of-function" of channels in excitatory neurotransmission could lead to hyper-excitation while "loss-of-function" in inhibitory transmission impairs neuronal inhibitory system, both of which can result in epilepsy. A working hypothesis to view epilepsy as a disorder of channel or "channelopathy" seems rational to explore the pathogenesis of epilepsy. However, the imbalance resulting from channel dysfunction is not sufficient to delineate the pathogenesis of all epilepsy syndromes of which the underlying channel abnormalities have been verified. Mutations identified in epilepsy, mainly in genes encoding subunits of GABA(A) receptors, undermine intracellular trafficking, thus leading to retention of channel molecules in the endoplasmic reticulum (ER). This process may cause ER stress followed by apoptosis, which is a known pathomechanism of certain neurodegenerative disorders. Thus, the pathomechanism of "channel trafficking abnormality" may provide a new paradigm to channelopathy to unsolved questions underlying epilepsy, such as differences between generalized epilepsy with febrile seizures plus and severe myoclonic epilepsy in infancy, which share the causative genetic abnormalities in the same genes and hence are so far considered to be within the spectrum of one disease entity or allelic variants.
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Affiliation(s)
- Shinichi Hirose
- Department of Pediatrics, Fukuoka University, 45-1,7-chome Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan.
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42
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Reid CA, Coleman HA, Finkelstein DI, Horne MK, Drago J. Null mutation of the alpha4 nicotinic receptor subunit increases the propensity of muscarinic-mediated neuronal bursting in mouse hippocampal slices. Neuropharmacology 2006; 51:587-96. [PMID: 16806302 DOI: 10.1016/j.neuropharm.2006.05.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2005] [Revised: 04/11/2006] [Accepted: 05/03/2006] [Indexed: 11/21/2022]
Abstract
Alpha4 subunit nicotinic cholinergic receptor (nAChR) knock out mice (KO) have a greater susceptibility to proconvulsant-induced seizures than do wild type (WT). The underlying mechanisms remain obscure. We tested whether such seizure-like activity was reflected in bursting activity of hippocampal neurons by recording with intracellular microelectrodes from CA1 pyramidal neurons in slices from WT and KO mice. Intriguingly, while carbachol-induced bursting activity occurred in only 21% of WT slices, qualitatively identical patterns of bursting occurred in 72% of KO slices. Extracellular recordings from CA1 and CA3 regions suggest that carbachol-mediated population activity was regionalized in our preparations. The relative weighting of excitatory to inhibitory synaptic potentials was similar between WT and alpha4 KO mice. However, burst-firing cells had a smaller input time constant than non-bursters. Low-concentration DHbetaE (selective alpha4beta2 nAChR antagonist) did not increase the propensity of WT slices to burst-fire, indicating that absence of alpha4 subunits per se, cannot explain the differences in activity between slices from WT and KO mice. These observations suggest that alpha4 nAChRs are unlikely to be involved in modulating the pattern of bursting neural activity, but their absence could induce subtle developmental changes in the sensitivity of hippocampal circuits to develop this behaviour.
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Affiliation(s)
- Christopher A Reid
- Department of Medicine, Monash Medical Centre, Monash University, Melbourne, Vic. 3800, Australia
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Fonck C, Cohen BN, Nashmi R, Whiteaker P, Wagenaar DA, Rodrigues-Pinguet N, Deshpande P, McKinney S, Kwoh S, Munoz J, Labarca C, Collins AC, Marks MJ, Lester HA. Novel seizure phenotype and sleep disruptions in knock-in mice with hypersensitive alpha 4* nicotinic receptors. J Neurosci 2006; 25:11396-411. [PMID: 16339034 PMCID: PMC6725918 DOI: 10.1523/jneurosci.3597-05.2005] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A leucine to alanine substitution (L9'A) was introduced in the M2 region of the mouse alpha4 neuronal nicotinic acetylcholine receptor (nAChR) subunit. Expressed in Xenopus oocytes, alpha4(L9'A)beta2 nAChRs were > or =30-fold more sensitive than wild type (WT) to both ACh and nicotine. We generated knock-in mice with the L9'A mutation and studied their cellular responses, seizure phenotype, and sleep-wake cycle. Seizure studies on alpha4-mutated animals are relevant to epilepsy research because all known mutations linked to autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) occur in the M2 region of alpha4or beta2 subunits. Thalamic cultures and synaptosomes from L9'A mice were hypersensitive to nicotine-induced ion flux. L9'A mice were approximately 15-fold more sensitive to seizures elicited by nicotine injection than their WT littermates. Seizures in L9'A mice differed qualitatively from those in WT: L9'A seizures started earlier, were prevented by nicotine pretreatment, lacked EEG spike-wave discharges, and consisted of fast repetitive movements. Nicotine-induced seizures in L9'A mice were partial, whereas WT seizures were generalized. When L9'A homozygous mice received a 10 mg/kg nicotine injection, there was temporal and phenomenological separation of mutant and WT-like seizures: an initial seizure approximately 20 s after injection was clonic and showed no EEG changes. A second seizure began 3-4 min after injection, was tonic-clonic, and had EEG spike-wave activity. No spontaneous seizures were detected in L9'A mice during chronic video/EEG recordings, but their sleep-wake cycle was altered. Our findings show that hypersensitive alpha4* nicotinic receptors in mice mediate changes in the sleep-wake cycle and nicotine-induced seizures resembling ADNFLE.
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Affiliation(s)
- Carlos Fonck
- Division of Biology, California Institute of Technology, Pasadena, California 91125, USA
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Andermann F, Kobayashi E, Andermann E. Genetic Focal Epilepsies: State of the Art and Paths to the Future. Epilepsia 2005; 46 Suppl 10:61-7. [PMID: 16359475 DOI: 10.1111/j.1528-1167.2005.00361.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The concept of genetic focal epilepsies is relatively new as compared to awareness of the importance of genetic factors in the generalized epilepsies. However, in the past decade, there has been increasing recognition of families with dominantly inherited partial epilepsies. Better definition of the phenotypes allows identification of distinct syndromes. The main familial focal epilepsies are autosomal-dominant nocturnal frontal lobe epilepsy (ADNFLE), familial mesial TLE (FMTLE), familial lateral TLE (FLTLE), and familial partial epilepsy with variable foci (FPEVF). The only genes identified so far are those for ADNFLE and FLTLE. In these disorders, functional studies are the next step and could provide advances leading to clarification of the pathophysiology as well as to new therapeutic strategies. At present, we can provide genetic counseling and a more accurate prognosis for most of the familial focal epilepsies. Greater awareness of the genetic basis in this group of disorders by the treating physicians is essential for identification of new families. This will allow further linkage studies, candidate gene screening, and identification of new genes, which will hopefully result in genetically based prevention and treatment.
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Affiliation(s)
- Frederick Andermann
- Montreal Neurological Institute and Hospital McGill University, Montreal, Canada.
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45
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Abstract
Desensitization is an intriguing characteristic of ligand-gated channels, whereby a decrease or loss of biological response occurs following prolonged or repetitive stimulation. Nicotinic acetylcholine receptors (nAChRs), as a member of transmitter gated ion channels family, also can be desensitized by continuous or repeated exposure to agonist. Desensitization of nicotinic receptors can occur as a result of extended nicotine exposure during smoking or prolonged acetylcholine when treatment of Alzheimer's disease (AD) with cholinesterase inhibitors, or anticholinesterase agent poisoning. Studies from our lab have shown that nAChRs desensitization is not a nonfunctional state and we proposed that desensitized nAChRs could increase sensitivity of brain muscarinic receptor to its agonists. Here, we will review the regulation of nicotinic receptor desensitization and discuss the important biological function of desensitized nicotinic receptors in light of our previous studies. These studies provide the critical information for understanding the importance of nicotinic receptors desensitization in both normal physiological processing and in various disease states.
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Affiliation(s)
- Hai Wang
- Beijing Institute of Pharmacology and Toxicology, Beijing 100850, P.R. China.
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46
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Rodrigues-Pinguet NO, Pinguet TJ, Figl A, Lester HA, Cohen BN. Mutations Linked to Autosomal Dominant Nocturnal Frontal Lobe Epilepsy Affect Allosteric Ca2+ Activation of the α4β2 Nicotinic Acetylcholine Receptor. Mol Pharmacol 2005; 68:487-501. [DOI: 10.1124/mol.105.011155] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Silva-Barrat C, Velluti J, Szente M, Batini C, Champagnat J. Exaggeration of epileptic-like patterns by nicotine receptor activation during the GABA withdrawal syndrome. Brain Res 2005; 1042:133-43. [PMID: 15854585 DOI: 10.1016/j.brainres.2005.02.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2004] [Revised: 02/02/2005] [Accepted: 02/04/2005] [Indexed: 10/25/2022]
Abstract
To understand how nicotinic cholinergic receptors may participate in epileptic seizures, we tested the effects of nicotine and of the competitive nicotinic antagonists dihydro-beta-erythroidine and alpha-bungarotoxin on synaptic paroxysmal depolarization shifts (PDSs) and intrinsic bursts of action potentials recorded in slices from rats presenting a cortical status epilepticus. This model named GABA-withdrawal syndrome (GWS) appears consecutive to the interruption of a prolonged intracortical GABA infusion. Effects of both nicotinic antagonists suggest a distinct involvement of alpha4-beta2 and alpha7 subunits in shaping individual PDSs and patterning repetitive bursts. On one hand, in GWS rats, an increase of PDS latency and prolongation of PDS and bursts were induced by nicotine and reduced by dihydro-beta-erythroidine, but not by alpha-bungarotoxin. The K+ blocker tetraethylammonium also increased duration without changing latency. Thus, dihydro-beta-erythroidine-sensitive receptors exert distinct controls on the presynaptic generation of PDS and on the process which terminates PDSs and bursts. On the other hand, alpha-bungarotoxin depolarized neurons and generated rhythmic discharges of clustered bursts. Clustered bursts were also observed in slices obtained from GWS rats treated with the acetylcholinesterase inhibitor eserine. We suggest that both dihydro-beta-erythroidine and alpha-bungarotoxin-sensitive sites control paroxysmic activities in GWS and could be involved in some human and animal epilepsies presenting mutations of nicotinic cholinergic receptors.
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Affiliation(s)
- Carmen Silva-Barrat
- Laboratoire de Génétique Moléculaire de la Neurotransmission et des Processus Neurodégénératifs, UMR 7091, CNRS, 75634 Paris, France.
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Delorenzo RJ, Sun DA, Deshpande LS. Cellular mechanisms underlying acquired epilepsy: the calcium hypothesis of the induction and maintainance of epilepsy. Pharmacol Ther 2005; 105:229-66. [PMID: 15737406 PMCID: PMC2819430 DOI: 10.1016/j.pharmthera.2004.10.004] [Citation(s) in RCA: 202] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2004] [Accepted: 10/12/2004] [Indexed: 01/22/2023]
Abstract
Epilepsy is one of the most common neurological disorders. Although epilepsy can be idiopathic, it is estimated that up to 50% of all epilepsy cases are initiated by neurological insults and are called acquired epilepsy (AE). AE develops in 3 phases: (1) the injury (central nervous system [CNS] insult), (2) epileptogenesis (latency), and (3) the chronic epileptic (spontaneous recurrent seizure) phases. Status epilepticus (SE), stroke, and traumatic brain injury (TBI) are 3 major examples of common brain injuries that can lead to the development of AE. It is especially important to understand the molecular mechanisms that cause AE because it may lead to innovative strategies to prevent or cure this common condition. Recent studies have offered new insights into the cause of AE and indicate that injury-induced alterations in intracellular calcium concentration levels [Ca(2+)](i) and calcium homeostatic mechanisms play a role in the development and maintenance of AE. The injuries that cause AE are different, but they share a common molecular mechanism for producing brain damage-an increase in extracellular glutamate concentration that causes increased intracellular neuronal calcium, leading to neuronal injury and/or death. Neurons that survive the injury induced by glutamate and are exposed to increased [Ca(2+)](i) are the cellular substrates to develop epilepsy because dead cells do not seize. The neurons that survive injury sustain permanent long-term plasticity changes in [Ca(2+)](i) and calcium homeostatic mechanisms that are permanent and are a prominent feature of the epileptic phenotype. In the last several years, evidence has accumulated indicating that the prolonged alteration in neuronal calcium dynamics plays an important role in the induction and maintenance of the prolonged neuroplasticity changes underlying the epileptic phenotype. Understanding the role of calcium as a second messenger in the induction and maintenance of epilepsy may provide novel insights into therapeutic advances that will prevent and even cure AE.
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Affiliation(s)
- Robert J Delorenzo
- Department of Neurology, Virginia Commonwealth University, School of Medicine, Richmond, VA 23298-0599, USA.
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Callenbach PMC, van den Maagdenberg AMJM, Frants RR, Brouwer OF. Clinical and genetic aspects of idiopathic epilepsies in childhood. Eur J Paediatr Neurol 2005; 9:91-103. [PMID: 15843076 DOI: 10.1016/j.ejpn.2004.12.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2004] [Revised: 12/11/2004] [Accepted: 12/14/2004] [Indexed: 11/27/2022]
Abstract
The identification of the first genes associated with idiopathic epilepsy has been an important breakthrough in the field of epilepsy research. In almost all cases these genes were found to encode components of voltage- or ligand-gated ion channels or functionally related structures. For many other idiopathic syndromes, there is linkage evidence to one or more chromosomes, but the genes have not yet been identified. Identification of the responsible genes and their gene products will further increase the knowledge of the pathogenic mechanisms involved in epilepsy, and will hopefully facilitate the development of drug targets for the effective treatment of epilepsy. This review gives an overview of the clinical characteristics and an update of genetic research of those idiopathic childhood epilepsies for which genes have been identified and the monogenic idiopathic childhood epilepsies for which mapping data are available.
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Affiliation(s)
- Petra M C Callenbach
- Department of Neurology, University Medical Centre Groningen, Hanzeplein 1/P.O. Box 30001, 9700 RB Groningen, The Netherlands
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Liang Y, Salas R, Marubio L, Bercovich D, De Biasi M, Beaudet AL, Dani JA. Functional polymorphisms in the human beta4 subunit of nicotinic acetylcholine receptors. Neurogenetics 2004; 6:37-44. [PMID: 15742216 DOI: 10.1007/s10048-004-0199-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2004] [Accepted: 10/15/2004] [Indexed: 10/26/2022]
Abstract
Human nicotinic acetylcholine receptor (nAChR) polymorphisms occur in different ethnic populations and may result in differences in nAChR ion channel properties. We have identified four nAChR beta 4 subunit (beta4) nucleotide variants: 392C-->T, 526C-->T, 538A-->G, and 1519A-->G. Their corresponding amino acid substitutions are: Thr to Ile at codon 91 (T91I), Arg to Trp at codon 136 (R136W), Ser to Gly at codon 140 (S140G), and Met to Val at codon 467 (M467V), respectively. The nAChR ion channel properties of these variants were studied and compared with the more-common (wild-type) allele as wild-types. The nAChRs (alpha4beta4 channels) were expressed heterologously in Xenopus oocytes and studied using the two-electrode voltage clamp technique to reveal functional differences between the wild-type and the variants. The receptors containing the R136W and M467V mutations (or variants) had a higher sensitivity to acetylcholine and lower EC50 than the wild-type. The T91I mutation had lower sensitivity to acetylcholine and the EC50 was larger than in wild-type nAChRs. The S140G mutation had a dose-response relationship that was similar to the wild-type. The T91I, R136W, and M467V mutations (or variants) also showed a slightly greater degree of steady-state desensitization than the wild-type in response to a 30-min exposure to one tenth of their EC50. The present results demonstrate that human beta4 nAChR DNA polymorphisms result in functional changes, and suggest that certain individuals with those variants may be more or less sensitive to cholinergic drugs or to dysfunctions associated with nicotinic cholinergic systems.
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Affiliation(s)
- Yong Liang
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, USA
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