51
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Perez-Sanchez J, Lorenzo LE, Lecker I, Zurek AA, Labrakakis C, Bridgwater EM, Orser BA, De Koninck Y, Bonin RP. α5GABAAReceptors Mediate Tonic Inhibition in the Spinal Cord Dorsal Horn and Contribute to the Resolution Of Hyperalgesia. J Neurosci Res 2016; 95:1307-1318. [DOI: 10.1002/jnr.23981] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Revised: 10/02/2016] [Accepted: 10/06/2016] [Indexed: 12/12/2022]
Affiliation(s)
| | | | - Irene Lecker
- Leslie Dan Faculty of Pharmacy; University of Toronto; Toronto Ontario Canada
| | | | - Charalampos Labrakakis
- Department of Biological Applications and Technology; University of Ioannina; Ioannina Greece
| | | | - Beverley A. Orser
- University of Toronto, Department of Physiology; Toronto Ontario Canada
- University of Toronto, Department of Anesthesia; Toronto Ontario Canada
- Department of Anesthesia; Sunnybrook Health Sciences Centre; Toronto Ontario Canada
| | - Yves De Koninck
- Institut Universitaire en Santé Mentale de Québec; Québec Canada
- Department of Psychiatry and Neuroscience; Université Laval; Québec Canada
| | - Robert P. Bonin
- Institut Universitaire en Santé Mentale de Québec; Québec Canada
- Leslie Dan Faculty of Pharmacy; University of Toronto; Toronto Ontario Canada
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52
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Townsend M, Whyment A, Walczak JS, Jeggo R, van den Top M, Flood DG, Leventhal L, Patzke H, Koenig G. α7-nAChR agonist enhances neural plasticity in the hippocampus via a GABAergic circuit. J Neurophysiol 2016; 116:2663-2675. [PMID: 27655963 DOI: 10.1152/jn.00243.2016] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 09/18/2016] [Indexed: 11/22/2022] Open
Abstract
Agonists of the α7-nicotinic acetylcholine receptor (α7-nAChR) have entered clinical trials as procognitive agents for treating schizophrenia and Alzheimer's disease. The most advanced compounds are orthosteric agonists, which occupy the ligand binding site. At the molecular level, agonist activation of α7-nAChR is reasonably well understood. However, the consequences of activating α7-nAChRs on neural circuits underlying cognition remain elusive. Here we report that an α7-nAChR agonist (FRM-17848) enhances long-term potentiation (LTP) in rat septo-hippocampal slices far below the cellular EC50 but at a concentration that coincides with multiple functional outcome measures as we reported in Stoiljkovic M, Leventhal L, Chen A, Chen T, Driscoll R, Flood D, Hodgdon H, Hurst R, Nagy D, Piser T, Tang C, Townsend M, Tu Z, Bertrand D, Koenig G, Hajós M. Biochem Pharmacol 97: 576-589, 2015. In this same concentration range, we observed a significant increase in spontaneous γ-aminobutyric acid (GABA) inhibitory postsynaptic currents and a moderate suppression of excitability in whole cell recordings from rat CA1 pyramidal neurons. This modulation of GABAergic activity is necessary for the LTP-enhancing effects of FRM-17848, since inhibiting GABAA α5-subunit-containing receptors fully reversed the effects of the α7-nAChR agonist. These data suggest that α7-nAChR agonists may increase synaptic plasticity in hippocampal slices, at least in part, through a circuit-level enhancement of a specific subtype of GABAergic receptor.
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Affiliation(s)
| | | | | | - Ross Jeggo
- Cerebrasol, Ltd., Montreal, Quebec City, Canada
| | | | | | - Liza Leventhal
- FORUM Pharmaceuticals, Inc., Waltham, Massachusetts; and
| | - Holger Patzke
- FORUM Pharmaceuticals, Inc., Waltham, Massachusetts; and
| | - Gerhard Koenig
- FORUM Pharmaceuticals, Inc., Waltham, Massachusetts; and
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53
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Deprez F, Vogt F, Floriou-Servou A, Lafourcade C, Rudolph U, Tyagarajan SK, Fritschy JM. Partial inactivation of GABAA receptors containing the α5 subunit affects the development of adult-born dentate gyrus granule cells. Eur J Neurosci 2016; 44:2258-71. [PMID: 27364953 DOI: 10.1111/ejn.13329] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2015] [Accepted: 06/28/2016] [Indexed: 01/13/2023]
Abstract
Alterations of neuronal activity due to changes in GABAA receptors (GABAA R) mediating tonic inhibition influence different hippocampal functions. Gabra5-null mice and α5 subunit((H105R)) knock-in mice exhibit signs of hippocampal dysfunction, but are capable of improved performance in several learning and memory tasks. Accordingly, alleviating abnormal GABAergic tonic inhibition in the hippocampal formation by selective α5-GABAA R modulators represents a possible therapeutic approach for several intellectual deficit disorders. Adult neurogenesis in the dentate gyrus is an important facet of hippocampal plasticity; it is regulated by tonic GABAergic transmission, as shown by deficits in proliferation, migration and dendritic development of adult-born neurons in Gabra4-null mice. Here, we investigated the contribution of α5-GABAA Rs to granule cell development, using retroviral vectors expressing eGFP for labeling precursor cells in the subgranular zone. Global α5-GABAA R knockout (α5-KO) mice showed no alterations in migration and morphological development of eGFP-positive granule cells. However, upregulation of α1 subunit-immunoreactivity was observed in the hippocampal formation and cerebral cortex. In contrast, partial gene inactivation in α5-heterozygous (α5-het) mice, as well as single-cell deletion of Gabra5 in newborn granule cells from α5-floxed mice, caused severe alterations of migration and dendrite development. In α5-het mice, retrovirally mediated overexpression of Cdk5 resulted in normal migration and dendritic branching, suggesting that Cdk5 cooperates with α5-GABAA Rs to regulate neuronal development. These results show that minor imbalance of α5-GABAA R-mediated transmission may have major consequences for neuronal plasticity; and call for caution upon chronic therapeutic use of negative allosteric modulators acting at these receptors.
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Affiliation(s)
- Francine Deprez
- Institute of Pharmacology and Toxicology, University of Zurich, 8057, Zurich, Switzerland.,Neuroscience Center Zurich, ETH and University of Zurich, Zurich, Switzerland
| | - Fabia Vogt
- Institute of Pharmacology and Toxicology, University of Zurich, 8057, Zurich, Switzerland
| | - Amalia Floriou-Servou
- Institute of Pharmacology and Toxicology, University of Zurich, 8057, Zurich, Switzerland
| | - Carlos Lafourcade
- Institute of Pharmacology and Toxicology, University of Zurich, 8057, Zurich, Switzerland
| | - Uwe Rudolph
- Laboratory of Genetic Neuropharmacology, McLean Hospital, Belmont, MA, USA.,Department of Psychiatry, Harvard Medical School, Boston, MA, USA
| | - Shiva K Tyagarajan
- Institute of Pharmacology and Toxicology, University of Zurich, 8057, Zurich, Switzerland.,Neuroscience Center Zurich, ETH and University of Zurich, Zurich, Switzerland
| | - Jean-Marc Fritschy
- Institute of Pharmacology and Toxicology, University of Zurich, 8057, Zurich, Switzerland.,Neuroscience Center Zurich, ETH and University of Zurich, Zurich, Switzerland
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54
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Low-frequency electrical stimulation enhances the effectiveness of phenobarbital on GABAergic currents in hippocampal slices of kindled rats. Neuroscience 2016; 330:26-38. [PMID: 27235746 DOI: 10.1016/j.neuroscience.2016.05.038] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Revised: 05/15/2016] [Accepted: 05/16/2016] [Indexed: 01/11/2023]
Abstract
Low frequency stimulation (LFS) has been proposed as a new approach in the treatment of epilepsy. The anticonvulsant mechanism of LFS may be through its effect on GABAA receptors, which are the main target of phenobarbital anticonvulsant action. We supposed that co-application of LFS and phenobarbital may increase the efficacy of phenobarbital. Therefore, the interaction of LFS and phenobarbital on GABAergic inhibitory post-synaptic currents (IPSCs) in kindled and control rats was investigated. Animals were kindled by electrical stimulation of basolateral amygdala in a semi rapid manner (12 stimulations/day). The effect of phenobarbital, LFS and phenobarbital+LFS was investigated on GABAA-mediated evoked and miniature IPSCs in the hippocampal brain slices in control and fully kindled animals. Phenobarbital and LFS had positive interaction on GABAergic currents. In vitro co-application of an ineffective pattern of LFS (100 pulses at afterdischarge threshold intensity) and a sub-threshold dose of phenobarbital (100μM) which had no significant effect on GABAergic currents alone, increased the amplitude and area under curve of GABAergic currents in CA1 pyramidal neurons of hippocampal slices significantly. Interestingly, the sub-threshold dose of phenobarbital potentiated the GABAergic currents when applied on the hippocampal slices of kindled animals which received LFS in vivo. Post-synaptic mechanisms may be involved in observed interactions. Obtained results implied a positive interaction between LFS and phenobarbital through GABAA currents. It may be suggested that a combined therapy of phenobarbital and LFS may be a useful manner for reinforcing the anticonvulsant action of phenobarbital.
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55
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Altered GABAA α5 subunit expression in the hypothalamic paraventricular nucleus of hypertensive and pregnant rats. Neurosci Lett 2016; 620:148-53. [DOI: 10.1016/j.neulet.2016.03.031] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Revised: 03/18/2016] [Accepted: 03/19/2016] [Indexed: 11/15/2022]
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56
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Abstract
In this issue of Neuron,Lin et al. (2015) report an optical method to precisely manipulate the activity of GABAA receptors by designing a mutant receptor that binds photosensitive compounds. This allows for studying GABAA receptors in situ and represents a valuable tool to investigate how inhibition affects brain physiology.
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Affiliation(s)
- Martin Mortensen
- Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, UK
| | - Trevor G Smart
- Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, UK.
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57
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Rapid Antidepressant Action and Restoration of Excitatory Synaptic Strength After Chronic Stress by Negative Modulators of Alpha5-Containing GABAA Receptors. Neuropsychopharmacology 2015; 40:2499-509. [PMID: 25900119 PMCID: PMC4569955 DOI: 10.1038/npp.2015.112] [Citation(s) in RCA: 88] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Revised: 04/08/2015] [Accepted: 04/08/2015] [Indexed: 01/30/2023]
Abstract
Selective serotonin reuptake inhibitors (SSRIs) are the primary pharmacological treatment for depression, but SSRIs are effective in only half of the patients and typically take several weeks to relieve symptoms. The NMDA receptor antagonist ketamine exerts a rapid antidepressant action, but has troubling side effects. We hypothesized that negative allosteric modulators of GABAA receptors would exert similar effects on brain activity as ketamine, but would not exert as many side effects if targeted only to GABAA receptors containing α5 subunits, which are enriched in the hippocampus and prefrontal cortex. Here, we show that the α5-selective negative modulator L-655,708 reversed the alterations in hedonic behavior in the sucrose preference and social interaction tests produced by two different chronic stress paradigms in rats within 24 h of systemic administration. Similar effects were observed with another α5-selective negative modulator, MRK-016. L-655,708 had no effect on hedonic or open-field behavior in unstressed animals. Within 24 h, L-655,708 injection also restored the strength of pathologically weakened excitatory synaptic transmission at the stress-sensitive temporoammonic-CA1 synapse, measured electrophysiologically, and increased levels of the GluA1 subunit of the AMPA receptor, measured with western blotting. We suggest that the ability of L-655,708 to restore excitatory synaptic strength rapidly may underlie its ability to restore stress-induced behavioral alterations rapidly, supporting evidence that dysfunction of multiple excitatory synapses in cortico-mesolimbic reward pathways contributes, in part, to the genesis of depression. Negative allosteric modulators of α5 subunit-containing GABAA receptors represent a promising novel class of fast-acting and clinically viable antidepressant compounds.
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58
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Schipper S, Aalbers MW, Rijkers K, Swijsen A, Rigo JM, Hoogland G, Vles JSH. Tonic GABAA Receptors as Potential Target for the Treatment of Temporal Lobe Epilepsy. Mol Neurobiol 2015; 53:5252-65. [PMID: 26409480 PMCID: PMC5012145 DOI: 10.1007/s12035-015-9423-8] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Accepted: 09/03/2015] [Indexed: 12/11/2022]
Abstract
Tonic GABAA receptors are a subpopulation of receptors that generate long-lasting inhibition and thereby control network excitability. In recent years, these receptors have been implicated in various neurological and psychiatric disorders, including Parkinson’s disease, schizophrenia, and epilepsy. Their distinct subunit composition and function, compared to phasic GABAA receptors, opens the possibility to specifically modulate network properties. In this review, the role of tonic GABAA receptors in epilepsy and as potential antiepileptic target will be discussed.
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Affiliation(s)
- S Schipper
- Department of Neurology, Maastricht University Medical Center, Maastricht, The Netherlands.
- Faculty of Health Medicine and Life Sciences, School of Mental Health and Neuroscience, Maastricht University Medical Center, Maastricht, The Netherlands.
| | - M W Aalbers
- Faculty of Health Medicine and Life Sciences, School of Mental Health and Neuroscience, Maastricht University Medical Center, Maastricht, The Netherlands
| | - K Rijkers
- Faculty of Health Medicine and Life Sciences, School of Mental Health and Neuroscience, Maastricht University Medical Center, Maastricht, The Netherlands
- Department of Neurosurgery and Orthopedic Surgery, Atrium Hospital Heerlen, Heerlen, The Netherlands
| | - A Swijsen
- BIOMED Research Institute, Hasselt University/Transnational University Limburg, Martelarenlaan 42, 3500, Hasselt, Belgium
| | - J M Rigo
- BIOMED Research Institute, Hasselt University/Transnational University Limburg, Martelarenlaan 42, 3500, Hasselt, Belgium
| | - G Hoogland
- Faculty of Health Medicine and Life Sciences, School of Mental Health and Neuroscience, Maastricht University Medical Center, Maastricht, The Netherlands
- Department of Neurosurgery, Maastricht University Medical Center, Maastricht, The Netherlands
| | - J S H Vles
- Department of Neurology, Maastricht University Medical Center, Maastricht, The Netherlands
- Faculty of Health Medicine and Life Sciences, School of Mental Health and Neuroscience, Maastricht University Medical Center, Maastricht, The Netherlands
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59
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Stamenić TT, Joksimović S, Biawat P, Stanković T, Marković B, Cook JM, Savić MM. Negative modulation of α₅ GABAA receptors in rats may partially prevent memory impairment induced by MK-801, but not amphetamine- or MK-801-elicited hyperlocomotion. J Psychopharmacol 2015; 29:1013-24. [PMID: 26105958 PMCID: PMC4861997 DOI: 10.1177/0269881115590601] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Reportedly, negative modulation of α5 GABAA receptors may improve cognition in normal and pharmacologically-impaired animals, and such modulation has been proposed as an avenue for treatment of cognitive symptoms in schizophrenia. This study assessed the actions of PWZ-029, administered at doses (2, 5, and 10 mg/kg) at which it reached micromolar concentrations in brain tissue with estimated free concentrations adequate for selective modulation of α5 GABAA receptors, in three cognitive tasks in male Wistar rats acutely treated with the noncompetitive N-methyl-d-aspartate receptor antagonist, MK-801 (0.1 mg/kg), as well in tests of locomotor activity potentiated by MK-801 (0.2 mg/kg) or amphetamine (0.5 mg/kg). In a hormetic-like manner, only 5 mg/kg PWZ-029 reversed MK-801-induced deficits in novel object recognition test (visual recognition memory), whereas in the Morris water maze, the 2 mg/kg dose of PWZ-029 exerted partial beneficial effects on spatial learning impairment. PWZ-029 did not affect recognition memory deficits in social novelty discrimination procedure. Motor hyperactivity induced with MK-801 or amphetamine was not preventable by PWZ-029. Our results show that certain MK-801-induced memory deficits can be ameliorated by negative modulation of α5 GABAA receptors, and point to the need for further elucidation of their translational relevance to cognitive deterioration in schizophrenia.
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Affiliation(s)
| | - Srdjan Joksimović
- Department of Pharmacology, University of Belgrade, Belgrade, Serbia
| | - Poonam Biawat
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, USA
| | - Tamara Stanković
- Department of Pharmacology, University of Belgrade, Belgrade, Serbia
| | - Bojan Marković
- Department of Pharmaceutical Chemistry, University of Belgrade, Belgrade, Serbia
| | - James M Cook
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, USA
| | - Miroslav M Savić
- Department of Pharmacology, University of Belgrade, Belgrade, Serbia
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60
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Gouzer G, Specht CG, Allain L, Shinoe T, Triller A. Benzodiazepine-dependent stabilization of GABA(A) receptors at synapses. Mol Cell Neurosci 2015; 63:101-13. [PMID: 25466558 DOI: 10.1016/j.mcn.2014.10.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2014] [Revised: 10/08/2014] [Accepted: 10/15/2014] [Indexed: 10/24/2022] Open
Abstract
GABA(A) receptors constitutively enter and exit synapses by lateral diffusion in the plane of the neuronal membrane. They are trapped at synapses through their interactions with gephyrin, the main scaffolding protein at inhibitory post-synaptic densities. Previous work has shown that the synaptic accumulation and diffusion dynamics of GABA(A)Rs are controlled via excitatory synaptic activity. However, it remains unknown whether GABA(A)R activity can itself impact the surface trafficking of the receptors. Here we report the effects of GABA(A)R agonists, antagonists and allosteric modulators on the receptor's surface dynamics. Using immunocytochemistry and single particle tracking experiments on mouse hippocampal neurons, we show that the agonist muscimol decreases GABA(A)R and gephyrin levels at synapses and accelerates the receptor's lateral diffusion within 30–120 min of treatment. In contrast, the GABA(A)R antagonist gabazine increased GABA(A)R amounts and slowed down GABA(A)R diffusion at synapses. The response to GABA(A)R activation or inhibition appears to be an adaptative regulation of GABAergic synapses. Surprisingly, the positive allosteric modulator diazepam abolished the regulation induced by muscimol, and this effect was observed on α1, α2, α5 and γ2 GABA(A)R subunits. Altogether these results indicate that diazepam stabilizes synaptic GABA(A)Rs and thus prevents the agonist-induced regulation of GABA(A)R levels at synapses. This occurred independently of neuronal activity and intracellular calcium and involved GABA(A)R–gephyrin interactions, suggesting that the changes in GABA(A)R diffusion depend on conformational changes of the receptor. Our study provides a new molecular mechanism involved in the adaptative response to changes in GABA(A)R activity and benzodiazepine treatments.
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61
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Jiang L, Kang D, Kang J. Potentiation of tonic GABAergic inhibition by activation of postsynaptic kainate receptors. Neuroscience 2015; 298:448-54. [PMID: 25934031 DOI: 10.1016/j.neuroscience.2015.04.043] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2014] [Revised: 04/02/2015] [Accepted: 04/21/2015] [Indexed: 10/23/2022]
Abstract
Presynaptic kainate-type glutamate ionotropic receptors (KARs) that mediate either the depression or the facilitation of GABA release have been intensively studied. Little attention has been given to the modulation of GABAA receptors (GABAARs) by postsynaptic KARs. Recent studies suggest that two GABAAR populations, synaptic (sGABAAR) and extrasynaptic (eGABAAR) GABAARs, mediate phasic and tonic forms of inhibition, respectively. Tonic inhibition plays an important role in the excitability of neuronal circuits and the occurrence of epileptic seizures. For this study, we are the first to report that the activation of postsynaptic KARs by the KAR agonist, Kainic acid (KA, 5 μM), enhanced tonic inhibition by potentiating eGABAARs. KA enhanced THIP-induced eGABAAR currents and prolonged the rise and decay time of muscimol-induced sGABAAR/eGABAAR currents, but also depressed the amplitude of evoked inhibitory postsynaptic currents (IPSCs), unitary IPSCs (uIPSCs), and muscimol-induced sGABAAR/eGABAAR currents. The PKC inhibitor, staurosporine (1 μM), in the patch pipette solution fully blocked the KA-induced potentiation of tonic inhibition, suggesting the involvement of an intracellular PKC pathway. Our study suggests that the activation of postsynaptic KARs potentiates eGABAARs but depresses sGABAARs. By activating postsynaptic KARs, synaptically released glutamate depresses phasic inhibition to facilitate neuronal plasticity, but potentiates tonic inhibition to protect neurons from over-excitation.
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Affiliation(s)
- L Jiang
- Department of Neurobiology and Behavior/Center for Nervous Systems Disorders Research, Stony Brook University, Stony Brook, New York 11794, USA
| | - D Kang
- Park Ridge High School, 2 Park Avenue, Park Ridge, NJ 07656, USA
| | - J Kang
- Department of Cell Biology and Anatomy, New York Medical College, 15 Dana Road, Valhalla, NY 10595, USA.
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62
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Radixin regulates synaptic GABAA receptor density and is essential for reversal learning and short-term memory. Nat Commun 2015; 6:6872. [PMID: 25891999 PMCID: PMC4411296 DOI: 10.1038/ncomms7872] [Citation(s) in RCA: 90] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Accepted: 03/06/2015] [Indexed: 12/24/2022] Open
Abstract
Neurotransmitter receptor density is a major variable in regulating synaptic strength. Receptors rapidly exchange between synapses and intracellular storage pools through endocytic recycling. In addition, lateral diffusion and confinement exchanges surface membrane receptors between synaptic and extrasynaptic sites. However, the signals that regulate this transition are currently unknown. GABAA receptors containing α5-subunits (GABAAR-α5) concentrate extrasynaptically through radixin (Rdx)-mediated anchorage at the actin cytoskeleton. Here we report a novel mechanism that regulates adjustable plasma membrane receptor pools in the control of synaptic receptor density. RhoA/ROCK signalling regulates an activity-dependent Rdx phosphorylation switch that uncouples GABAAR-α5 from its extrasynaptic anchor, thereby enriching synaptic receptor numbers. Thus, the unphosphorylated form of Rdx alters mIPSCs. Rdx gene knockout impairs reversal learning and short-term memory, and Rdx phosphorylation in wild-type mice exhibits experience-dependent changes when exposed to novel environments. Our data suggest an additional mode of synaptic plasticity, in which extrasynaptic receptor reservoirs supply synaptic GABAARs.
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63
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Brady ML, Jacob TC. Synaptic localization of α5 GABA (A) receptors via gephyrin interaction regulates dendritic outgrowth and spine maturation. Dev Neurobiol 2015; 75:1241-51. [PMID: 25663431 DOI: 10.1002/dneu.22280] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Revised: 02/04/2015] [Accepted: 02/04/2015] [Indexed: 11/08/2022]
Abstract
GABAA receptor subunit composition is a critical determinant of receptor localization and physiology, with synaptic receptors generating phasic inhibition and extrasynaptic receptors producing tonic inhibition. Extrasynaptically localized α5 GABAA receptors are largely responsible for tonic inhibition in hippocampal neurons. However, we show here that inhibitory synapses also contain a constant level of α5 GABAA receptors throughout neuronal development, as measured by its colocalization with gephyrin, the inhibitory postsynaptic scaffolding protein. Immunoprecipitation of the α5 subunit from both cultured neurons and adult rat brain coimmunoprecipitated gephyrin, confirming this interaction in vivo. Furthermore, the α5 subunit can interact with gephyrin independent of other synaptically localized alpha subunits, as shown by immunoprecipitation experiments in HEK cells. By replacing the α5 predicted gephyrin binding domain (Residues 370-385) with either the high affinity gephyrin binding domain of the α2 subunit or homologous residues from the extrasynaptic α4 subunit that does not interact with gephyrin, α5 GABAA receptor localization shifted into or out of the synapse, respectively. These shifts in the ratio of synaptic/extrasynaptic α5 localization disrupted dendritic outgrowth and spine maturation. In contrast to the predominant view of α5 GABAA receptors being extrasynaptic and modulating tonic inhibition, we identify an intimate association of the α5 subunit with gephyrin, resulting in constant synaptic levels of α5 GABAA R throughout circuit formation that regulates neuronal development.
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Affiliation(s)
- Megan L Brady
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, 15261
| | - Tija C Jacob
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, 15261
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64
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Balakrishnan S, Pearce RA. Spatiotemporal characteristics and pharmacological modulation of multiple gamma oscillations in the CA1 region of the hippocampus. Front Neural Circuits 2015; 8:150. [PMID: 25628540 PMCID: PMC4290596 DOI: 10.3389/fncir.2014.00150] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Accepted: 12/16/2014] [Indexed: 01/28/2023] Open
Abstract
Multiple components of "γ-oscillations" between 30-170 Hz in the CA1 region of the hippocampus have been described, based on their coherence with oscillations in other brain regions and on their cross-frequency coupling with local θ-oscillations. However, it remains unclear whether the different sub-bands are generated by a single broadband oscillator coupled to multiple external inputs, or by separate oscillators that incorporate distinct circuit elements. To distinguish between these possibilities, we used high-density linear array recording electrodes in awake behaving mice to examine the spatiotemporal characteristics of γ-oscillations and their responses to midazolam and atropine. We characterized oscillations using current source density (CSD) analysis, and measured θ-γ phase-amplitude coupling by cross frequency coupling (CFC) analysis. Prominent peaks were present in the CSD signal in the mid- and distal apical dendritic layers at all frequencies, and at stratum pyramidale for γ(slow) (30-45 Hz) and γ(mid) (50-90 Hz), but not γ(fast) (90-170 Hz) oscillations. Differences in the strength and timing of θ-γ(slow) and θ-γ(mid) cross frequency coupling, and a lack of coupling at the soma and mid-apical region for γ(fast) oscillations, indicated that separate circuit components generate the three sub-bands. Midazolam altered CSD amplitudes and cross-frequency coupling in a lamina- and frequency specific manner, providing further evidence for separate generator circuits. Atropine altered CSD amplitudes and θ-γ CFC uniformly at all locations. Simulations using a detailed compartmental model were consistent with γ(slow) and γ(mid) oscillations driven primarily by inputs at the mid-apical dendrites, and γ(fast) at the distal apical dendrite. Our results indicate that multiple distinct local circuits generate γ-oscillations in the CA1 region of the hippocampus, and provide detailed information about their spatiotemporal characteristics.
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Affiliation(s)
- Shilpashree Balakrishnan
- Neuroscience Training Program, University of Wisconsin-Madison Madison, WI, USA ; Department of Anesthesiology, University of Wisconsin-Madison Madison, WI, USA
| | - Robert A Pearce
- Department of Anesthesiology, University of Wisconsin-Madison Madison, WI, USA
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65
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Grienberger C, Chen X, Konnerth A. Dendritic function in vivo. Trends Neurosci 2014; 38:45-54. [PMID: 25432423 DOI: 10.1016/j.tins.2014.11.002] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Revised: 11/04/2014] [Accepted: 11/06/2014] [Indexed: 10/24/2022]
Abstract
Dendrites are the predominant entry site for excitatory synaptic potentials in most types of central neurons. There is increasing evidence that dendrites are not just passive transmitting devices but play active roles in synaptic integration through linear and non-linear mechanisms. Frequently, excitatory synapses are formed on dendritic spines. In addition to relaying incoming electrical signals, spines can play important roles in modifying these signals through complex biochemical processes and, thereby, determine learning and memory formation. Here, we review recent advances in our understanding of the function of spines and dendrites in central mammalian neurons in vivo by focusing particularly on insights obtained from Ca(2+) imaging studies.
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Affiliation(s)
- Christine Grienberger
- Institute of Neuroscience, Technical University Munich, Munich, Germany; Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Xiaowei Chen
- Institute of Neuroscience, Technical University Munich, Munich, Germany; Brain Research Center, Third Military Medical University, Chongqing, China
| | - Arthur Konnerth
- Institute of Neuroscience, Technical University Munich, Munich, Germany; Munich Cluster for Systems Neurology (SyNergy) and Center for Integrated Protein Sciences (CIPSM), Munich, Germany.
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Sengupta S, Weeraratne SD, Cho YJ, Pomeroy SL. Could α5-GABA-A receptor activation be used as a target for managing medulloblastomas? CNS Oncol 2014; 3:245-7. [PMID: 25286034 DOI: 10.2217/cns.14.27] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Affiliation(s)
- Soma Sengupta
- Department of Neurology, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA
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67
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Ding J, Huang C, Peng Z, Xie Y, Deng S, Nie YZ, Xu TL, Ge WH, Li WG, Li F. Electrophysiological characterization of methyleugenol: a novel agonist of GABA(A) receptors. ACS Chem Neurosci 2014; 5:803-11. [PMID: 24980777 DOI: 10.1021/cn500022e] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Methyleugenol (ME) is a natural constituent isolated from many plant essential oils having multiple biological effects including anticonvulsant and anesthetic activities, although the underlying mechanisms remain unclear. Here, we identify ME as a novel agonist of ionotropic γ-aminobutyric acid (GABA) receptors. At lower concentrations (∼30 μM), ME significantly sensitized GABA-induced, but not glutamate- or glycine-induced, currents in cultured hippocampal neurons, indicative of a preferentially modulatory role of this compound for A type GABA receptors (GABAARs). In addition, ME at higher concentrations (≥100 μM) induced a concentration-dependent, Cl(-)-permeable current in hippocampal neurons, which was inhibited by a GABAAR channel blocker, picrotoxin, and a competitive GABAAR antagonist, bicuculline, but not a specific glycine receptor inhibitor, strychnine. Moreover, ME activated a similar current mediated by recombinant α1-β2-γ2 or α5-β2-γ2 GABAARs in human embryonic kidney (HEK) cells. Consequently, ME produced a strong inhibition of synaptically driven neuronal excitation in hippocampal neurons. Together, these results suggest that ME represents a novel agonist of GABAARs, shedding additional light on future development of new therapeutics targeting GABAARs. The present study also adds GABAAR activation to the list of molecular targets of ME that probably account for its biological activities.
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Affiliation(s)
- Jing Ding
- Department
of Developmental and Behavioral Pediatrics, Shanghai Institute of
Pediatric Translational Medicine, Shanghai Children’s Medical
Center, Ministry of Education-Shanghai Key Laboratory of Children’s
Environmental Health, Shanghai Jiao Tong University School of Medicine, Shanghai 200129, China
- Department
of Chinese Materia Medica, College of Pharmaceutical Science, Zhejiang Chinese Medical University, Hangzhou 310053, China
- Neuroscience
Division, Departments of Anatomy, Histology and Embryology, Biochemistry,
and Molecular Cell Biology, Shanghai Key Laboratory for Tumor Microenvironment
and Inflammation, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Chen Huang
- Neuroscience
Division, Departments of Anatomy, Histology and Embryology, Biochemistry,
and Molecular Cell Biology, Shanghai Key Laboratory for Tumor Microenvironment
and Inflammation, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Zhong Peng
- Neuroscience
Division, Departments of Anatomy, Histology and Embryology, Biochemistry,
and Molecular Cell Biology, Shanghai Key Laboratory for Tumor Microenvironment
and Inflammation, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Yuxuan Xie
- Department
of Developmental and Behavioral Pediatrics, Shanghai Institute of
Pediatric Translational Medicine, Shanghai Children’s Medical
Center, Ministry of Education-Shanghai Key Laboratory of Children’s
Environmental Health, Shanghai Jiao Tong University School of Medicine, Shanghai 200129, China
| | - Shining Deng
- Department
of Developmental and Behavioral Pediatrics, Shanghai Institute of
Pediatric Translational Medicine, Shanghai Children’s Medical
Center, Ministry of Education-Shanghai Key Laboratory of Children’s
Environmental Health, Shanghai Jiao Tong University School of Medicine, Shanghai 200129, China
| | - Yan-Zhen Nie
- Department
of Developmental and Behavioral Pediatrics, Shanghai Institute of
Pediatric Translational Medicine, Shanghai Children’s Medical
Center, Ministry of Education-Shanghai Key Laboratory of Children’s
Environmental Health, Shanghai Jiao Tong University School of Medicine, Shanghai 200129, China
| | - Tian-Le Xu
- Neuroscience
Division, Departments of Anatomy, Histology and Embryology, Biochemistry,
and Molecular Cell Biology, Shanghai Key Laboratory for Tumor Microenvironment
and Inflammation, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Wei-Hong Ge
- Department
of Chinese Materia Medica, College of Pharmaceutical Science, Zhejiang Chinese Medical University, Hangzhou 310053, China
| | - Wei-Guang Li
- Department
of Developmental and Behavioral Pediatrics, Shanghai Institute of
Pediatric Translational Medicine, Shanghai Children’s Medical
Center, Ministry of Education-Shanghai Key Laboratory of Children’s
Environmental Health, Shanghai Jiao Tong University School of Medicine, Shanghai 200129, China
- Neuroscience
Division, Departments of Anatomy, Histology and Embryology, Biochemistry,
and Molecular Cell Biology, Shanghai Key Laboratory for Tumor Microenvironment
and Inflammation, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Fei Li
- Department
of Developmental and Behavioral Pediatrics, Shanghai Institute of
Pediatric Translational Medicine, Shanghai Children’s Medical
Center, Ministry of Education-Shanghai Key Laboratory of Children’s
Environmental Health, Shanghai Jiao Tong University School of Medicine, Shanghai 200129, China
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68
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Jin H, Chiou TT, Serwanski DR, Miralles CP, Pinal N, De Blas AL. Ring finger protein 34 (RNF34) interacts with and promotes γ-aminobutyric acid type-A receptor degradation via ubiquitination of the γ2 subunit. J Biol Chem 2014; 289:29420-36. [PMID: 25193658 DOI: 10.1074/jbc.m114.603068] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
We have found that the large intracellular loop of the γ2 GABAA receptor (R) subunit (γ2IL) interacts with RNF34 (an E3 ubiquitin ligase), as shown by yeast two-hybrid and in vitro pulldown assays. In brain extracts, RNF34 co-immunoprecipitates with assembled GABAARs. In co-transfected HEK293 cells, RNF34 reduces the expression of the γ2 GABAAR subunit by increasing the ratio of ubiquitinated/nonubiquitinated γ2. Mutating several lysines of the γ2IL into arginines makes the γ2 subunit resistant to RNF34-induced degradation. RNF34 also reduces the expression of the γ2 subunit when α1 and β3 subunits are co-assembled with γ2. This effect is partially reversed by leupeptin or MG132, indicating that both the lysosomal and proteasomal degradation pathways are involved. Immunofluorescence of cultured hippocampal neurons shows that RNF34 forms clusters and that a subset of these clusters is associated with GABAergic synapses. This association is also observed in the intact rat brain by electron microscopy immunocytochemistry. RNF34 is not expressed until the 2nd postnatal week of rat brain development, being highly expressed in some interneurons. Overexpression of RNF34 in hippocampal neurons decreases the density of γ2 GABAAR clusters and the number of GABAergic contacts that these neurons receive. Knocking down endogenous RNF34 with shRNA leads to increased γ2 GABAAR cluster density and GABAergic innervation. The results indicate that RNF34 regulates postsynaptic γ2-GABAAR clustering and GABAergic synaptic innervation by interacting with and ubiquitinating the γ2-GABAAR subunit promoting GABAAR degradation.
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Affiliation(s)
- Hongbing Jin
- From the Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269
| | - Tzu-Ting Chiou
- From the Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269
| | - David R Serwanski
- From the Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269
| | - Celia P Miralles
- From the Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269
| | - Noelia Pinal
- From the Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269
| | - Angel L De Blas
- From the Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269
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69
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Localized GABAergic inhibition of dendritic Ca(2+) signalling. Nat Rev Neurosci 2014; 15:567-72. [PMID: 25116141 DOI: 10.1038/nrn3803] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Neuronal circuits are defined by synaptic connections between their cellular constituents. In this article, I highlight several recent studies emphasizing the surprising level of precision exhibited by inhibitory GABAergic synapses within the neocortex and hippocampus. Specifically, GABAergic inputs to dendritic shafts and spines of pyramidal cells have a key role in the localized regulation of neuronal Ca(2+) signalling. These findings provide important new insights into the cellular mechanisms underlying the contributions of inhibitory transmission to both normal and abnormal brain activity.
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70
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Evidence for the participation of peripheral α5 subunit-containing GABAA receptors in GABAA agonists-induced nociception in rats. Eur J Pharmacol 2014; 734:91-7. [DOI: 10.1016/j.ejphar.2014.03.051] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Revised: 03/11/2014] [Accepted: 03/22/2014] [Indexed: 11/17/2022]
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71
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Postsynaptic activity reverses the sign of the acetylcholine-induced long-term plasticity of GABAA inhibition. Proc Natl Acad Sci U S A 2014; 111:E2741-50. [PMID: 24938789 DOI: 10.1073/pnas.1321777111] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Acetylcholine (ACh) regulates forms of plasticity that control cognitive functions but the underlying mechanisms remain largely unknown. ACh controls the intrinsic excitability, as well as the synaptic excitation and inhibition of CA1 hippocampal pyramidal cells (PCs), cells known to participate in circuits involved in cognition and spatial navigation. However, how ACh regulates inhibition in function of postsynaptic activity has not been well studied. Here we show that in rat PCs, a brief pulse of ACh or a brief stimulation of cholinergic septal fibers combined with repeated depolarization induces strong long-term enhancement of GABAA inhibition (GABAA-LTP). Indeed, this enhanced inhibition is due to the increased activation of α5βγ2 subunit-containing GABAA receptors by the GABA released. GABAA-LTP requires the activation of M1-muscarinic receptors and an increase in cytosolic Ca(2+). In the absence of PC depolarization ACh triggered a presynaptic depolarization-induced suppression of inhibition (DSI), revealing that postsynaptic activity gates the effects of ACh from presynaptic DSI to postsynaptic LTP. These results provide key insights into mechanisms potentially linked with cognitive functions, spatial navigation, and the homeostatic control of abnormal hyperexcitable states.
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72
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Sengupta S, Weeraratne SD, Sun H, Phallen J, Rallapalli SK, Teider N, Kosaras B, Amani V, Pierre-Francois J, Tang Y, Nguyen B, Yu F, Schubert S, Balansay B, Mathios D, Lechpammer M, Archer TC, Tran P, Reimer RJ, Cook JM, Lim M, Jensen FE, Pomeroy SL, Cho YJ. α5-GABAA receptors negatively regulate MYC-amplified medulloblastoma growth. Acta Neuropathol 2014; 127:593-603. [PMID: 24196163 DOI: 10.1007/s00401-013-1205-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Accepted: 10/28/2013] [Indexed: 11/25/2022]
Abstract
Neural tumors often express neurotransmitter receptors as markers of their developmental lineage. Although these receptors have been well characterized in electrophysiological, developmental and pharmacological settings, their importance in the maintenance and progression of brain tumors and, importantly, the effect of their targeting in brain cancers remains obscure. Here, we demonstrate high levels of GABRA5, which encodes the α5-subunit of the GABAA receptor complex, in aggressive MYC-driven, "Group 3" medulloblastomas. We hypothesized that modulation of α5-GABAA receptors alters medulloblastoma cell survival and monitored biological and electrophysiological responses of GABRA5-expressing medulloblastoma cells upon pharmacological targeting of the GABAA receptor. While antagonists, inverse agonists and non-specific positive allosteric modulators had limited effects on medulloblastoma cells, a highly specific and potent α5-GABAA receptor agonist, QHii066, resulted in marked membrane depolarization and a significant decrease in cell survival. This effect was GABRA5 dependent and mediated through the induction of apoptosis as well as accumulation of cells in S and G2 phases of the cell cycle. Chemical genomic profiling of QHii066-treated medulloblastoma cells confirmed inhibition of MYC-related transcriptional activity and revealed an enrichment of HOXA5 target gene expression. siRNA-mediated knockdown of HOXA5 markedly blunted the response of medulloblastoma cells to QHii066. Furthermore, QHii066 sensitized GABRA5 positive medulloblastoma cells to radiation and chemotherapy consistent with the role of HOXA5 in directly regulating p53 expression and inducing apoptosis. Thus, our results provide novel insights into the synthetic lethal nature of α5-GABAA receptor activation in MYC-driven/Group 3 medulloblastomas and propose its targeting as a novel strategy for the management of this highly aggressive tumor.
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Affiliation(s)
- Soma Sengupta
- Department of Neurology, Boston Children's Hospital, Boston, MA, USA
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73
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Stepanyuk AR, Borisyuk AL, Tsugorka TM, Belan PV. Different pools of postsynaptic GABAA receptors mediate inhibition evoked by low- and high-frequency presynaptic stimulation at hippocampal synapses. Synapse 2014; 68:344-54. [PMID: 24677449 DOI: 10.1002/syn.21742] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Revised: 03/16/2014] [Accepted: 03/21/2014] [Indexed: 11/12/2022]
Abstract
Patterns of short-term synaptic plasticity could considerably differ between synapses of the same axon. This may lead to separation of synaptic receptors transmitting either low- or high-frequency signals and, therefore, may have functional consequences for the information transfer in the brain. Here, we estimated a degree of such separation at hippocampal GABAergic synapses using a use-dependent GABAA receptor antagonist, picrotoxin, to selectively suppress a pool of GABAA receptors monosynaptically activated during the low-frequency stimulation. The relative changes in postsynaptic responses evoked by the high-frequency stimulation before and after such block were used to estimate the contribution of this GABAA receptor pool to synaptic transmission at high frequencies. Using this approach, we have shown that IPSCs evoked by low-frequency (0.2 Hz) stimulation and asynchronous currents evoked by high-frequency (20-40 Hz) stimulation are mediated by different pools of postsynaptic GABAA receptors. Thus, our findings suggest that inhibition produced by a single hippocampal interneuron may be selectively routed to different postsynaptic targets depending on the presynaptic discharge frequency.
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Affiliation(s)
- Andrey R Stepanyuk
- Department of General Physiology of the Nervous System, Bogomoletz Institute of Physiology, 4 Bogomoletz street, Kiev, 01024, Ukraine; State Key Laboratory of Molecular and Cellular Biology, Bogomoletz Institute of Physiology, 4 Bogomoletz street, Kiev, 01024, Ukraine
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74
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Fritschy JM, Panzanelli P. GABAAreceptors and plasticity of inhibitory neurotransmission in the central nervous system. Eur J Neurosci 2014; 39:1845-65. [DOI: 10.1111/ejn.12534] [Citation(s) in RCA: 144] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2014] [Revised: 01/29/2014] [Accepted: 01/29/2014] [Indexed: 12/11/2022]
Affiliation(s)
- Jean-Marc Fritschy
- Institute of Pharmacology and Toxicology; University of Zurich; Winterthurerstrasse 190 8057 Zurich Switzerland
- Neuroscience Center Zurich; University of Zurich and ETH; Zurich Switzerland
| | - Patrizia Panzanelli
- Department of Neuroscience Rita Levi Montalcini; University of Turin; Turin Italy
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75
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Ding J, Wang JJ, Huang C, Wang L, Deng S, Xu TL, Ge WH, Li WG, Li F. Curcumol from Rhizoma Curcumae suppresses epileptic seizure by facilitation of GABA(A) receptors. Neuropharmacology 2014; 81:244-55. [PMID: 24565642 DOI: 10.1016/j.neuropharm.2014.02.009] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Revised: 02/10/2014] [Accepted: 02/13/2014] [Indexed: 10/25/2022]
Abstract
Rhizoma Curcumae is a common Chinese dietary spice used in South Asia and China for thousands of years. As the main extract, Rhizoma Curcumae oil has attracted a great interest due to its newly raised therapeutic activities including its pharmacological effects upon central nervous system such as neuroprotection, cognitive enhancement, and anti-seizure efficacy; however the molecular mechanisms and the target identification remain to be established. Here we characterize an inhibitory effect of curcumol, a major bioactive component of Rhizoma Curcumae oil, on the excitability of hippocampal neurons in culture, the basal locomotor activity of freely moving animals, and the chemically induced seizure activity in vivo. Electrophysiological recording showed that acute application of curcumol significantly facilitated the γ-aminobutyric acid (GABA)-activated current in cultured mouse hippocampal neurons and in human embryonic kidney cells expressing α1- or α5-containing A type GABA (GABAA) receptors in a concentration-dependent manner. Measurement of tonic and miniature inhibitory postsynaptic GABAergic currents in hippocampal slices indicated that curcumol enhanced both forms of inhibition. In both pentylenetetrazole and kainate seizure models, curcumol suppressed epileptic activity in mice by prolonging the latency to clonic and tonic seizures and reducing the mortality as well as the susceptibility to seizure, presumably by facilitating the activation of GABAA receptors. Taken together, our results identified curcumol as a novel anti-seizure agent which inhibited neuronal excitability through enhancing GABAergic inhibition.
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Affiliation(s)
- Jing Ding
- Department of Chinese Materia Medica, College of Pharmaceutical Science, Zhejiang Chinese Medical University, Hangzhou 310053, China; Department of Developmental and Behavioral Pediatrics, Shanghai Institute of Pediatric Translational Medicine, Shanghai Children's Medical Center, Ministry of Education-Shanghai Key Laboratory of Children's Environmental Health, Shanghai Jiao Tong University School of Medicine, Shanghai 200129, China; Departments of Anatomy and Embryology, Biochemistry and Molecular Cell Biology, Shanghai Key Laboratory for Tumor Microenvironment and Inflammation, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Jing-Jing Wang
- Departments of Anatomy and Embryology, Biochemistry and Molecular Cell Biology, Shanghai Key Laboratory for Tumor Microenvironment and Inflammation, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Chen Huang
- Departments of Anatomy and Embryology, Biochemistry and Molecular Cell Biology, Shanghai Key Laboratory for Tumor Microenvironment and Inflammation, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Li Wang
- Departments of Anatomy and Embryology, Biochemistry and Molecular Cell Biology, Shanghai Key Laboratory for Tumor Microenvironment and Inflammation, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Shining Deng
- Department of Developmental and Behavioral Pediatrics, Shanghai Institute of Pediatric Translational Medicine, Shanghai Children's Medical Center, Ministry of Education-Shanghai Key Laboratory of Children's Environmental Health, Shanghai Jiao Tong University School of Medicine, Shanghai 200129, China
| | - Tian-Le Xu
- Departments of Anatomy and Embryology, Biochemistry and Molecular Cell Biology, Shanghai Key Laboratory for Tumor Microenvironment and Inflammation, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Wei-Hong Ge
- Department of Chinese Materia Medica, College of Pharmaceutical Science, Zhejiang Chinese Medical University, Hangzhou 310053, China
| | - Wei-Guang Li
- Department of Developmental and Behavioral Pediatrics, Shanghai Institute of Pediatric Translational Medicine, Shanghai Children's Medical Center, Ministry of Education-Shanghai Key Laboratory of Children's Environmental Health, Shanghai Jiao Tong University School of Medicine, Shanghai 200129, China; Departments of Anatomy and Embryology, Biochemistry and Molecular Cell Biology, Shanghai Key Laboratory for Tumor Microenvironment and Inflammation, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.
| | - Fei Li
- Department of Developmental and Behavioral Pediatrics, Shanghai Institute of Pediatric Translational Medicine, Shanghai Children's Medical Center, Ministry of Education-Shanghai Key Laboratory of Children's Environmental Health, Shanghai Jiao Tong University School of Medicine, Shanghai 200129, China.
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76
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Martínez-Cué C, Delatour B, Potier MC. Treating enhanced GABAergic inhibition in Down syndrome: use of GABA α5-selective inverse agonists. Neurosci Biobehav Rev 2014; 46 Pt 2:218-27. [PMID: 24412222 DOI: 10.1016/j.neubiorev.2013.12.008] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2013] [Revised: 11/27/2013] [Accepted: 12/16/2013] [Indexed: 11/27/2022]
Abstract
Excess inhibition in the brain of individuals carrying an extra copy of chromosome 21 could be responsible for cognitive deficits observed throughout their lives. A change in the excitatory/inhibitory balance in adulthood would alter synaptic plasticity, potentially triggering learning and memory deficits. γ-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mature central nervous system and binds to GABAA receptors, opens a chloride channel, and reduces neuronal excitability. In this review we discuss methods to alleviate neuronal inhibition in a mouse model of Down syndrome, the Ts65Dn mouse, using either an antagonist (pentylenetetrazol) or two different inverse agonists selective for the α5-subunit containing receptor. Both inverse agonists, which reduce inhibitory GABAergic transmission, could rescue learning and memory deficits in Ts65Dn mice. We also discuss safety issues since modulation of the excitatory-inhibitory balance to improve cognition without inducing seizures remains particularly difficult when using GABA antagonists.
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Affiliation(s)
- Carmen Martínez-Cué
- Department of Physiology and Pharmacology, Faculty of Medicine, University of Cantabria, Santander, Spain
| | - Benoît Delatour
- Institut du Cerveau et de Moelle Epinière, CNRS UMR7225, INSERM U1127, UPMC, IHUA-ICM, Hôpital Pitié-Salpêtrière, Paris, France
| | - Marie-Claude Potier
- Institut du Cerveau et de Moelle Epinière, CNRS UMR7225, INSERM U1127, UPMC, IHUA-ICM, Hôpital Pitié-Salpêtrière, Paris, France.
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77
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Gill KM, Grace AA. The role of α5 GABAA receptor agonists in the treatment of cognitive deficits in schizophrenia. Curr Pharm Des 2014; 20:5069-76. [PMID: 24345268 PMCID: PMC4074253 DOI: 10.2174/1381612819666131216114612] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2013] [Accepted: 12/10/2013] [Indexed: 11/22/2022]
Abstract
Currently available pharmacotherapies for the treatment of schizophrenia are ineffective in restoring the disrupted cognitive function associated with this disorder. As such, there is a continued search for more viable novel drug targets. Engaging in cognitive behaviors is associated with distinct coordinated oscillatory activity across brain regions, in particular the hippocampus and prefrontal cortex. In schizophrenia patients, pathological alterations in the functionality of GABAergic interneurons in the PFC and HPC responsible for generating network oscillations are thought to contribute to impaired cognition. Destabilized GABAergic interneuron activity in the HPC is further associated with aberrant increases in HPC output and enhanced dopamine neuron activity. Consequently, drugs directed at restoring HPC function could impact both oscillatory activity along with dopamine tone. There is compelling evidence from animal models of schizophrenia that allosteric modulation of the α5 subunit of the GABAA receptor is a viable means of resolving aberrant dopamine system activity through indirect alteration of HPC output. Consequently, these compounds are promising for their potential in also ameliorating cognitive deficits attributed to dysfunction in HPC network activity.
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Affiliation(s)
| | - Anthony A Grace
- University of Pittsburgh, Department of Neuroscience, A210 Langley Hall, Pittsburgh, PA 15260, USA.
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78
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Balia M, Vélez-Fort M, Passlick S, Schäfer C, Audinat E, Steinhäuser C, Seifert G, Angulo MC. Postnatal down-regulation of the GABAA receptor γ2 subunit in neocortical NG2 cells accompanies synaptic-to-extrasynaptic switch in the GABAergic transmission mode. ACTA ACUST UNITED AC 2013; 25:1114-23. [PMID: 24217990 DOI: 10.1093/cercor/bht309] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
NG2 cells, a main pool of glial progenitors, express γ-aminobutyric acid A (GABA(A)) receptors (GABA(A)Rs), the functional and molecular properties of which are largely unknown. We recently reported that transmission between GABAergic interneurons and NG2 cells drastically changes during development of the somatosensory cortex, switching from synaptic to extrasynaptic communication. Since synaptic and extrasynaptic GABA(A)Rs of neurons differ in their subunit composition, we hypothesize that GABA(A)Rs of NG2 cells undergo molecular changes during cortical development accompanying the switch of transmission modes. Single-cell RT-PCR and the effects of zolpidem and α5IA on evoked GABAergic currents reveal the predominance of functional α1- and α5-containing GABA(A)Rs at interneuron-NG2 cell synapses in the second postnatal week, while the α5 expression declines later in development when responses are exclusively extrasynaptic. Importantly, pharmacological and molecular analyses demonstrate that γ2, a subunit contributing to the clustering of GABA(A)Rs at postsynaptic sites in neurons, is down-regulated in NG2 cells in a cell type-specific manner in concomitance with the decline of synaptic activity and the switch of transmission mode. In keeping with the synaptic nature of γ2 in neurons, the down-regulation of this subunit is an important molecular hallmark of the change of transmission modes between interneurons and NG2 cells during development.
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Affiliation(s)
- Maddalena Balia
- INSERM U603, Paris, France CNRS UMR 8154, Paris, France Université Paris Descartes, Sorbonne Paris Cité, Paris, France and
| | - Mateo Vélez-Fort
- INSERM U603, Paris, France CNRS UMR 8154, Paris, France Université Paris Descartes, Sorbonne Paris Cité, Paris, France and Current address: Division of Neurophysiology, The National Institute for Medical Research, Mill Hill NW7 1AA, UK
| | - Stefan Passlick
- Institute of Cellular Neurosciences, University of Bonn, Bonn 53105, Germany
| | - Christoph Schäfer
- Institute of Cellular Neurosciences, University of Bonn, Bonn 53105, Germany Current address: Institute of Neurophysiology, University of Cologne, 50931 Cologne, Germany
| | - Etienne Audinat
- INSERM U603, Paris, France CNRS UMR 8154, Paris, France Université Paris Descartes, Sorbonne Paris Cité, Paris, France and
| | | | - Gerald Seifert
- Institute of Cellular Neurosciences, University of Bonn, Bonn 53105, Germany
| | - María Cecilia Angulo
- INSERM U603, Paris, France CNRS UMR 8154, Paris, France Université Paris Descartes, Sorbonne Paris Cité, Paris, France and
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79
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Sun Y, Wu Z, Kong S, Jiang D, Pitre A, Wang Y, Chen G. Regulation of epileptiform activity by two distinct subtypes of extrasynaptic GABAA receptors. Mol Brain 2013; 6:21. [PMID: 23634821 PMCID: PMC3652748 DOI: 10.1186/1756-6606-6-21] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Accepted: 04/20/2013] [Indexed: 11/13/2022] Open
Abstract
Background GABAergic deficit is one of the major mechanisms underlying epileptic seizures. Previous studies have mainly focused on alterations of synaptic GABAergic inhibition during epileptogenesis. Recent work suggested that tonic inhibition may also play a role in regulating epileptogenesis, but the underlying mechanism is not well understood. Results We employed molecular and pharmacological tools to investigate the role of tonic inhibition during epileptogenesis both in vitro and in vivo. We overexpressed two distinct subtypes of extrasynaptic GABAA receptors, α5β3γ2 and α6β3δ receptors, in cultured hippocampal neurons. We demonstrated that overexpression of both α5β3γ2 and α6β3δ receptors enhanced tonic inhibition and reduced epileptiform activity in vitro. We then showed that injection of THIP (5 μM), a selective agonist for extrasynaptic GABAA receptors at low concentration, into rat brain also suppressed epileptiform burst activity and behavioral seizures in vivo. Mechanistically, we discovered that low concentration of THIP had no effect on GABAergic synaptic transmission and did not affect the basal level of action potentials, but significantly inhibited high frequency neuronal activity induced by epileptogenic agents. Conclusions Our studies suggest that extrasynaptic GABAA receptors play an important role in controlling hyperexcitatory activity, such as that during epileptogenesis, but a less prominent role in modulating a low level of basal activity. We propose that tonic inhibition may play a greater role under pathological conditions than in physiological conditions in terms of modulating neural network activity.
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Affiliation(s)
- Yajie Sun
- Institutes of Brain Science and State Key Laboratory for Medical Neurobiology, Fudan University, Shanghai, 200032, China
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80
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Huang C, Li WG, Zhang XB, Wang L, Xu TL, Wu D, Li Y. Alpha-asarone from Acorus gramineus alleviates epilepsy by modulating A-Type GABA receptors. Neuropharmacology 2013; 65:1-11. [DOI: 10.1016/j.neuropharm.2012.09.001] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Revised: 08/08/2012] [Accepted: 09/02/2012] [Indexed: 11/25/2022]
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81
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Abstract
We have found that the γ2 subunit of the GABA(A) receptor (γ2-GABA(A)R) specifically interacts with protocadherin-γC5 (Pcdh-γC5) in the rat brain. The interaction occurs between the large intracellular loop of the γ2-GABA(A)R and the cytoplasmic domain of Pcdh-γC5. In brain extracts, Pcdh-γC5 coimmunoprecipitates with GABA(A)Rs. In cotransfected HEK293 cells, Pcdh-γC5 promotes the transfer of γ2-GABA(A)R to the cell surface. We have previously shown that, in cultured hippocampal neurons, endogenous Pcdh-γC5 forms clusters, some of which associate with GABAergic synapses. Overexpression of Pcdh-γC5 in hippocampal neurons increases the density of γ2-GABA(A)R clusters but has no significant effect on the number of GABAergic contacts that these neurons receive, indicating that Pcdh-γC5 is not synaptogenic. Deletion of the cytoplasmic domain of Pcdh-γC5 enhanced its surface expression but decreased the association with both γ2-GABA(A)R clusters and presynaptic GABAergic contacts. Cultured hippocampal neurons from the Pcdh-γ triple C-type isoform knock-out (TCKO) mouse (Pcdhg(tcko/tcko)) showed plenty of GABAergic synaptic contacts, although their density was reduced compared with sister cultures from wild-type and heterozygous mice. Knocking down Pcdh-γC5 expression with shRNA decreased γ2-GABA(A)R cluster density and GABAergic innervation. The results indicate that, although Pcdh-γC5 is not essential for GABAergic synapse formation or GABA(A)R clustering, (1) Pcdh-γC5 regulates the surface expression of GABA(A)Rs via cis-cytoplasmic interaction with γ2-GABA(A)R, and (2) Pcdh-γC5 plays a role in the stabilization and maintenance of some GABAergic synapses.
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82
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Abstract
The flux of neurotransmitter receptors in and out of synapses depends on receptor interaction with scaffolding molecules. However, the crowd of transmembrane proteins and the rich cytoskeletal environment may constitute obstacles to the diffusion of receptors within the synapse. To address this question, we studied the membrane diffusion of the γ-aminobutyric acid type A receptor (GABAAR) subunits clustered (γ2) or not (α5) at inhibitory synapses in rat hippocampal dissociated neurons. Relative to the extrasynaptic region, γ2 and α5 showed reduced diffusion and increased confinement at both inhibitory and excitatory synapses but they dwelled for a short time at excitatory synapses. In contrast, γ2 was ∼3-fold more confined and dwelled ∼3-fold longer in inhibitory synapses than α5, indicating faster synaptic escape of α5. Furthermore, using a gephyrin dominant-negative approach, we showed that the increased residency time of γ2 at inhibitory synapses was due to receptor-scaffold interactions. As shown for GABAAR, the excitatory glutamate receptor 2 subunit (GluA2) of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) had lower mobility in both excitatory and inhibitory synapses but a higher residency time at excitatory synapses. Therefore barriers impose significant diffusion constraints onto receptors at synapses where they accumulate or not. Our data further reveal that the confinement and the dwell time but not the diffusion coefficient report on the synapse specific sorting, trapping and accumulation of receptors.
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83
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Wu X, Wu Z, Ning G, Guo Y, Ali R, Macdonald RL, De Blas AL, Luscher B, Chen G. γ-Aminobutyric acid type A (GABAA) receptor α subunits play a direct role in synaptic versus extrasynaptic targeting. J Biol Chem 2012; 287:27417-30. [PMID: 22711532 DOI: 10.1074/jbc.m112.360461] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
GABA(A) receptors (GABA(A)-Rs) are localized at both synaptic and extrasynaptic sites, mediating phasic and tonic inhibition, respectively. Previous studies suggest an important role of γ2 and δ subunits in synaptic versus extrasynaptic targeting of GABA(A)-Rs. Here, we demonstrate differential function of α2 and α6 subunits in guiding the localization of GABA(A)-Rs. To study the targeting of specific subtypes of GABA(A)-Rs, we used a molecularly engineered GABAergic synapse model to precisely control the GABA(A)-R subunit composition. We found that in neuron-HEK cell heterosynapses, GABAergic events mediated by α2β3γ2 receptors were very fast (rise time ∼2 ms), whereas events mediated by α6β3δ receptors were very slow (rise time ∼20 ms). Such an order of magnitude difference in rise time could not be attributed to the minute differences in receptor kinetics. Interestingly, synaptic events mediated by α6β3 or α6β3γ2 receptors were significantly slower than those mediated by α2β3 or α2β3γ2 receptors, suggesting a differential role of α subunit in receptor targeting. This was confirmed by differential targeting of the same δ-γ2 chimeric subunits to synaptic or extrasynaptic sites, depending on whether it was co-assembled with the α2 or α6 subunit. In addition, insertion of a gephyrin-binding site into the intracellular domain of α6 and δ subunits brought α6β3δ receptors closer to synaptic sites. Therefore, the α subunits, together with the γ2 and δ subunits, play a critical role in governing synaptic versus extrasynaptic targeting of GABA(A)-Rs, possibly through differential interactions with gephyrin.
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Affiliation(s)
- Xia Wu
- Department of Biology, Huck Institutes of Life Sciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA
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84
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Neves G, Shah MM, Liodis P, Achimastou A, Denaxa M, Roalfe G, Sesay A, Walker MC, Pachnis V. The LIM homeodomain protein Lhx6 regulates maturation of interneurons and network excitability in the mammalian cortex. ACTA ACUST UNITED AC 2012; 23:1811-23. [PMID: 22710612 PMCID: PMC3698365 DOI: 10.1093/cercor/bhs159] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Deletion of LIM homeodomain transcription factor-encoding Lhx6 gene in mice results in defective tangential migration of cortical interneurons and failure of differentiation of the somatostatin (Sst)- and parvalbumin (Pva)-expressing subtypes. Here, we characterize a novel hypomorphic allele of Lhx6 and demonstrate that reduced activity of this locus leads to widespread differentiation defects in Sst(+) interneurons, but relatively minor and localized changes in Pva(+) interneurons. The reduction in the number of Sst-expressing cells was not associated with a loss of interneurons, because the migration and number of Lhx6-expressing interneurons and expression of characteristic molecular markers, such as calretinin or Neuropeptide Y, were not affected in Lhx6 hypomorphic mice. Consistent with a selective deficit in the differentiation of Sst(+) interneurons in the CA1 subfield of the hippocampus, we observed reduced expression of metabotropic Glutamate Receptor 1 in the stratum oriens and characteristic changes in dendritic inhibition, but normal inhibitory input onto the somatic compartment of CA1 pyramidal cells. Moreover, Lhx6 hypomorphs show behavioral, histological, and electroencephalographic signs of recurrent seizure activity, starting from early adulthood. These results demonstrate that Lhx6 plays an important role in the maturation of cortical interneurons and the formation of inhibitory circuits in the mammalian cortex.
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Affiliation(s)
- Guilherme Neves
- Division of Molecular Neurobiology, MRC National Institute for Medical Research, London, UK
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85
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Clément Y, Prut L, Saurini F, Mineur YS, Le Guisquet AM, Védrine S, Andres C, Vodjdani G, Belzung C. Gabra5-gene haplotype block associated with behavioral properties of the full agonist benzodiazepine chlordiazepoxide. Behav Brain Res 2012; 233:474-82. [PMID: 22677273 DOI: 10.1016/j.bbr.2012.05.041] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2012] [Revised: 05/21/2012] [Accepted: 05/25/2012] [Indexed: 01/09/2023]
Abstract
The gabra5 gene is associated with pharmacological properties (myorelaxant, amnesic, anxiolytic) of benzodiazepines. It is tightly located (0.5 cM) close to the pink-eyed dilution (p) locus which encodes for fur color on mouse chromosome 7. We tested the putative role of the gabra5 gene in pharmacological properties of the full non specific agonist chlordiazepoxide (CDP), using behavioral and molecular approaches in mutated p/p mice and wild type F2 from crosses between two multiple markers inbred strain ABP/Le and C57BL/6By strain. From our results, using rotarod, light-dark box, elevated maze and radial arm maze tests, we demonstrate that p/p mice are more sensitive than WT to the sensory motor, anxiolytic and amnesic effect of CDP. This is associated with the presence of a haplotypic block on the murine chromosome 7 and with an up regulation of gabra5 mRNAs in hippocampi of p/p F2 mice.
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Affiliation(s)
- Y Clément
- Centre de Recherche de l'Institut du Cerveau et de la Moelle Epinière, 75651 Paris Cedex, France.
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86
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Tretter V, Mukherjee J, Maric HM, Schindelin H, Sieghart W, Moss SJ. Gephyrin, the enigmatic organizer at GABAergic synapses. Front Cell Neurosci 2012; 6:23. [PMID: 22615685 PMCID: PMC3351755 DOI: 10.3389/fncel.2012.00023] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2011] [Accepted: 04/23/2012] [Indexed: 11/17/2022] Open
Abstract
GABAA receptors are clustered at synaptic sites to achieve a high density of postsynaptic receptors opposite the input axonal terminals. This allows for an efficient propagation of GABA mediated signals, which mostly result in neuronal inhibition. A key organizer for inhibitory synaptic receptors is the 93 kDa protein gephyrin that forms oligomeric superstructures beneath the synaptic area. Gephyrin has long been known to be directly associated with glycine receptor β subunits that mediate synaptic inhibition in the spinal cord. Recently, synaptic GABAA receptors have also been shown to directly interact with gephyrin and interaction sites have been identified and mapped within the intracellular loops of the GABAA receptor α1, α2, and α3 subunits. Gephyrin-binding to GABAA receptors seems to be at least one order of magnitude weaker than to glycine receptors (GlyRs) and most probably is regulated by phosphorylation. Gephyrin not only has a structural function at synaptic sites, but also plays a crucial role in synaptic dynamics and is a platform for multiple protein-protein interactions, bringing receptors, cytoskeletal proteins and downstream signaling proteins into close spatial proximity.
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Affiliation(s)
- Verena Tretter
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna Vienna, Austria
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87
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Harris KM, Weinberg RJ. Ultrastructure of synapses in the mammalian brain. Cold Spring Harb Perspect Biol 2012; 4:cshperspect.a005587. [PMID: 22357909 DOI: 10.1101/cshperspect.a005587] [Citation(s) in RCA: 275] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The morphology and molecular composition of synapses provide the structural basis for synaptic function. This article reviews the electron microscopy of excitatory synapses on dendritic spines, using data from rodent hippocampus, cerebral cortex, and cerebellar cortex. Excitatory synapses have a prominent postsynaptic density, in contrast with inhibitory synapses, which have less dense presynaptic or postsynaptic specializations and are usually found on the cell body or proximal dendritic shaft. Immunogold labeling shows that the presynaptic active zone provides a scaffold for key molecules involved in the release of neurotransmitter, whereas the postsynaptic density contains ligand-gated ionic channels, other receptors, and a complex network of signaling molecules. Delineating the structure and molecular organization of these axospinous synapses represents a crucial step toward understanding the mechanisms that underlie synaptic transmission and the dynamic modulation of neurotransmission associated with short- and long-term synaptic plasticity.
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Affiliation(s)
- Kristen M Harris
- Center for Learning and Memory, Neurobiology Section, University of Texas, Austin, 78712, USA.
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88
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Pavlov I, Walker MC. Tonic GABA(A) receptor-mediated signalling in temporal lobe epilepsy. Neuropharmacology 2012; 69:55-61. [PMID: 22538087 DOI: 10.1016/j.neuropharm.2012.04.003] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Revised: 03/27/2012] [Accepted: 04/02/2012] [Indexed: 11/25/2022]
Abstract
The tonic activation of extrasynaptic GABAA receptors by extracellular GABA provides a powerful means of regulating neuronal excitability. A consistent finding from studies that have used various models of temporal lobe epilepsy is that tonic GABAA receptor-mediated conductances are largely preserved in epileptic brain (in contrast to synaptic inhibition which is often reduced). Tonic inhibition is therefore an attractive target for antiepileptic drugs. However, the network consequences of a commonly used approach to augment tonic GABAA receptor-mediated conductances by global manipulation of extracellular GABA are difficult to predict without understanding how epileptogenesis alters the pharmacology and GABA sensitivity of tonic inhibition, and how manipulation of tonic conductances modulates the output of individual neurons. Here we review the current literature on epilepsy-associated changes in tonic GABAA receptor-mediated signalling, and speculate about possible effects they have at the network level. This article is part of the Special Issue entitled 'New Targets and Approaches to the Treatment of Epilepsy'.
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Affiliation(s)
- Ivan Pavlov
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London WC1N3BG, UK.
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89
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Mechanisms Underlying Tolerance after Long-Term Benzodiazepine Use: A Future for Subtype-Selective GABA(A) Receptor Modulators? Adv Pharmacol Sci 2012; 2012:416864. [PMID: 22536226 PMCID: PMC3321276 DOI: 10.1155/2012/416864] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2011] [Revised: 10/10/2011] [Accepted: 11/02/2011] [Indexed: 01/01/2023] Open
Abstract
Despite decades of basic and clinical research, our understanding of how benzodiazepines tend to lose their efficacy over time (tolerance) is at least incomplete. In appears that tolerance develops relatively quickly for the sedative and anticonvulsant actions of benzodiazepines, whereas tolerance to anxiolytic and amnesic effects probably does not develop at all. In light of this evidence, we review the current evidence for the neuroadaptive mechanisms underlying benzodiazepine tolerance, including changes of (i) the GABA(A) receptor (subunit expression and receptor coupling), (ii) intracellular changes stemming from transcriptional and neurotrophic factors, (iii) ionotropic glutamate receptors, (iv) other neurotransmitters (serotonin, dopamine, and acetylcholine systems), and (v) the neurosteroid system. From the large variance in the studies, it appears that either different (simultaneous) tolerance mechanisms occur depending on the benzodiazepine effect, or that the tolerance-inducing mechanism depends on the activated GABA(A) receptor subtypes. Importantly, there is no convincing evidence that tolerance occurs with α subunit subtype-selective compounds acting at the benzodiazepine site.
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90
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Mortensen M, Patel B, Smart TG. GABA Potency at GABA(A) Receptors Found in Synaptic and Extrasynaptic Zones. Front Cell Neurosci 2012; 6:1. [PMID: 22319471 PMCID: PMC3262152 DOI: 10.3389/fncel.2012.00001] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2011] [Accepted: 01/03/2012] [Indexed: 11/17/2022] Open
Abstract
The potency of GABA is vitally important for its primary role in activating GABAA receptors and acting as an inhibitory neurotransmitter. Although numerous laboratories have presented information, directly or indirectly, on GABA potency, it is often difficult to compare across such studies given the inevitable variations in the methods used, the cell types studied, whether native or recombinant receptors are examined, and their relevance to native synaptic and extrasynaptic GABAA receptors. In this review, we list the most relevant isoforms of synaptic and extrasynaptic GABAA receptors that are thought to assemble in surface membranes of neurons in the central nervous system. Using consistent methodology in one cell type, the potencies of the endogenous neurotransmitter GABA are compared across a spectrum of GABAA receptors. The highest potency for GABA is measured when activating extrasynaptic-type α6 subunit-containing receptors, whereas synaptic-type α2β3γ2 and α3β3γ2 receptors exhibited the lowest potency, and other GABAA receptor subtypes that are found both in synaptic and extrasynaptic compartments, showed intermediate sensitivities to GABA. The relatively simple potency relationship between GABA and its target receptors is important as it serves as one of the major determinants of GABAA receptor activation, with consequences for the development of inhibition, either by tonic or phasic mechanisms.
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Affiliation(s)
- Martin Mortensen
- Department of Neuroscience, Physiology and Pharmacology, University College London London, UK
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91
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Hines RM, Davies PA, Moss SJ, Maguire J. Functional regulation of GABAA receptors in nervous system pathologies. Curr Opin Neurobiol 2011; 22:552-8. [PMID: 22036769 DOI: 10.1016/j.conb.2011.10.007] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2011] [Revised: 10/05/2011] [Accepted: 10/06/2011] [Indexed: 01/01/2023]
Abstract
Inhibitory neurotransmission is primarily governed by γ-aminobutyric acid (GABA) type A receptors (GABAARs). GABAARs are heteropentameric ligand-gated channels formed by the combination of 19 possible subunits. GABAAR subunits are subject to multiple types of regulation, impacting the localization, properties, and function of assembled receptors. GABAARs mediate both phasic (synaptic) and tonic (extrasynaptic) inhibition. While the regulatory mechanisms governing synaptic receptors have begun to be defined, little is known about the regulation of extrasynaptic receptors. We examine the contributions of GABAARs to the pathogenesis of neurodevelopmental disorders, schizophrenia, depression, epilepsy, and stroke, with particular focus on extrasynaptic GABAARs. We suggest that extrasynaptic GABAARs are attractive targets for the treatment of these disorders, and that research should be focused on delineating the mechanisms that regulate extrasynaptic GABAARs, promoting new therapeutic approaches.
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Affiliation(s)
- Rochelle M Hines
- Department of Neuroscience, Tufts University School of Medicine, 136 Harrison Ave, Boston, MA 02111, USA
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92
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Vithlani M, Terunuma M, Moss SJ. The dynamic modulation of GABA(A) receptor trafficking and its role in regulating the plasticity of inhibitory synapses. Physiol Rev 2011; 91:1009-22. [PMID: 21742794 DOI: 10.1152/physrev.00015.2010] [Citation(s) in RCA: 148] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Inhibition in the adult mammalian central nervous system (CNS) is mediated by γ-aminobutyric acid (GABA). The fast inhibitory actions of GABA are mediated by GABA type A receptors (GABA(A)Rs); they mediate both phasic and tonic inhibition in the brain and are the principle sites of action for anticonvulsant, anxiolytic, and sedative-hypnotic agents that include benzodiazepines, barbiturates, neurosteroids, and some general anesthetics. GABA(A)Rs are heteropentameric ligand-gated ion channels that are found concentrated at inhibitory postsynaptic sites where they mediate phasic inhibition and at extrasynaptic sites where they mediate tonic inhibition. The efficacy of inhibition and thus neuronal excitability is critically dependent on the accumulation of specific GABA(A)R subtypes at inhibitory synapses. Here we evaluate how neurons control the number of GABA(A)Rs on the neuronal plasma membrane together with their selective stabilization at synaptic sites. We then go on to examine the impact that these processes have on the strength of synaptic inhibition and behavior.
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Affiliation(s)
- Mansi Vithlani
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts, USA
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93
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Panzanelli P, Gunn BG, Schlatter MC, Benke D, Tyagarajan SK, Scheiffele P, Belelli D, Lambert JJ, Rudolph U, Fritschy JM. Distinct mechanisms regulate GABAA receptor and gephyrin clustering at perisomatic and axo-axonic synapses on CA1 pyramidal cells. J Physiol 2011; 589:4959-80. [PMID: 21825022 DOI: 10.1113/jphysiol.2011.216028] [Citation(s) in RCA: 111] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Pyramidal cells express various GABA(A) receptor (GABA(A)R) subtypes, possibly to match inputs from functionally distinct interneurons targeting specific subcellular domains. Postsynaptic anchoring of GABA(A)Rs is ensured by a complex interplay between the scaffolding protein gephyrin, neuroligin-2 and collybistin. Direct interactions between these proteins and GABA(A)R subunits might contribute to synapse-specific distribution of GABA(A)R subtypes. In addition, the dystrophin-glycoprotein complex, mainly localized at perisomatic synapses, regulates GABA(A)R postsynaptic clustering at these sites. Here, we investigated how the functional and molecular organization of GABAergic synapses in CA1 pyramidal neurons is altered in mice lacking the GABA(A)R α2 subunit (α2-KO). We report a marked, layer-specific loss of postsynaptic gephyrin and neuroligin-2 clusters, without changes in GABAergic presynaptic terminals. Whole-cell voltage-clamp recordings in slices from α2-KO mice show a 40% decrease in GABAergic mIPSC frequency, with unchanged amplitude and kinetics. Applying low/high concentrations of zolpidem to discriminate between α1- and α2/α3-GABA(A)Rs demonstrates that residual mIPSCs in α2-KO mice are mediated by α1-GABA(A)Rs. Immunofluorescence analysis reveals maintenance of α1-GABA(A)R and neuroligin-2 clusters, but not gephyrin clusters, in perisomatic synapses of mutant mice, along with a complete loss of these three markers on the axon initial segment. This striking subcellular difference correlates with the preservation of dystrophin clusters, colocalized with neuroligin-2 and α1-GABA(A)Rs on pyramidal cell bodies of mutant mice. Dystrophin was not detected on the axon initial segment in either genotype. Collectively, these findings reveal synapse-specific anchoring of GABA(A)Rs at postsynaptic sites and suggest that the dystrophin-glycoprotein complex contributes to stabilize α1-GABA(A)R and neuroligin-2, but not gephyrin, in perisomatic postsynaptic densities.
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Affiliation(s)
- Patrizia Panzanelli
- Department of Anatomy, Pharmacology and Forensic Medicine and National Institute of Neuroscience-Italy, University of Turin, Italy
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94
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Salesse C, Mueller CL, Chamberland S, Topolnik L. Age-dependent remodelling of inhibitory synapses onto hippocampal CA1 oriens-lacunosum moleculare interneurons. J Physiol 2011; 589:4885-901. [PMID: 21825029 DOI: 10.1113/jphysiol.2011.215244] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Stratum oriens-lacunosum moleculare interneurons (O-LM INs) represent the major element of the hippocampal feedback inhibitory circuit, which provides inhibition to the distal dendritic sites of CA1 pyramidal neurons. Although the intrinsic conductance profile and the properties of glutamatergic transmission to O-LM INs have become a subject of intense investigation, far less is known about the properties of the inhibitory synapses formed onto these cells. Here, we used whole-cell patch-clamp recordings in acute mouse hippocampal slices to study the properties and plasticity of GABAergic inhibitory synapses onto O-LM INs. Surprisingly, we found that the kinetics of inhibitory postsynaptic currents (IPSCs) were slower in mature synapses (P26-40) due to the synaptic incorporation of the α5 subunit of the GABA(A) receptor (a5-GABA(A)R). Moreover, this age-dependent synaptic expression of a5-GABA(A)Rs was directly associated with the emergence of long-term potentiation at IN inhibitory synapses. Finally, the slower time course of IPSCs observed in O-LM INs of mature animals had a profound effect on IN excitability by significantly delaying its spike firing. Our data suggest that GABAergic synapses onto O-LM INs undergo significant modifications during postnatal maturation. The developmental switch in IPSC properties and plasticity is controlled by the synaptic incorporation of the a5-GABA(A)R subunit and may represent a potential mechanism for the age-dependent modifications in the inhibitory control of the hippocampal feedback inhibitory circuit.
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Affiliation(s)
- Charleen Salesse
- Axis of Cellular and Molecular Neuroscience, CRULRG, Department of Biochemistry, Microbiology and Bioinformatics, Université Laval, Québec, PQ, Canada
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95
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A novel α5GABA(A)R-positive allosteric modulator reverses hyperactivation of the dopamine system in the MAM model of schizophrenia. Neuropsychopharmacology 2011; 36:1903-11. [PMID: 21562483 PMCID: PMC3154109 DOI: 10.1038/npp.2011.76] [Citation(s) in RCA: 120] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
We have shown previously that aberrant hippocampal (HPC) output underlies the dopamine (DA) dysfunction observed in the methylazoxymethanol acetate (MAM) developmental model of schizophrenia in the rodent. This alteration of HPC activity was proposed to result from a reduction in parvalbumin (PV)-expressing GABAergic interneurons and consequent destabilization of the output of pyramidal neurons, as well as disrupted activation across a broad neural network. In vivo extracellular recordings were performed in the ventral tegmental area (VTA) and ventral HPC of saline- (SAL) and MAM-treated animals. A novel benzodiazepine-positive allosteric modulator (PAM), selective for the α5 subunit of the GABA(A) receptor, SH-053-2'F-R-CH3, was tested for its effects on the output of the HPC, leading to dopamine system hyperactivity in MAM-treated animals. In addition, the effect of SH-053-2'F-R-CH3 on the hyperactive locomotor response to amphetamine in MAM animals was examined. We demonstrate that treatment with the α5GABA(A)R PAM reduced the number of spontaneously active DA neurons in the VTA of MAM animals to levels observed in SAL rats, both when administered systemically and when directly infused into the ventral HPC. Moreover, HPC neurons in both SAL and MAM animals showed diminished cortical-evoked responses following α5GABA(A)R PAM treatment. In addition, the increased locomotor response to amphetamine observed in MAM rats was reduced following α5GABA(A)R treatment. This study supports a novel treatment of schizophrenia that targets abnormal HPC output, which in turn normalizes dopaminergic neuronal activity.
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96
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Luscher B, Fuchs T, Kilpatrick CL. GABAA receptor trafficking-mediated plasticity of inhibitory synapses. Neuron 2011; 70:385-409. [PMID: 21555068 DOI: 10.1016/j.neuron.2011.03.024] [Citation(s) in RCA: 316] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/30/2011] [Indexed: 12/22/2022]
Abstract
Proper developmental, neural cell-type-specific, and activity-dependent regulation of GABAergic transmission is essential for virtually all aspects of CNS function. The number of GABA(A) receptors in the postsynaptic membrane directly controls the efficacy of GABAergic synaptic transmission. Thus, regulated trafficking of GABA(A) receptors is essential for understanding brain function in both health and disease. Here we summarize recent progress in the understanding of mechanisms that allow dynamic adaptation of cell surface expression and postsynaptic accumulation and function of GABA(A) receptors. This includes activity-dependent and cell-type-specific changes in subunit gene expression, assembly of subunits into receptors, as well as exocytosis, endocytic recycling, diffusion dynamics, and degradation of GABA(A) receptors. In particular, we focus on the roles of receptor-interacting proteins, scaffold proteins, synaptic adhesion proteins, and enzymes that regulate the trafficking and function of receptors and associated proteins. In addition, we review neuropeptide signaling pathways that affect neural excitability through changes in GABA(A)R trafficking.
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Affiliation(s)
- Bernhard Luscher
- Department of Biology, Pennsylvania State University, University Park, PA 16802, USA.
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Rosas-Arellano A, Parodi J, Machuca-Parra AI, Sánchez-Gutiérrez A, Inestrosa NC, Miledi R, Martínez-Torres A. The GABA(A)ρ receptors in hippocampal spontaneous activity and their distribution in hippocampus, amygdala and visual cortex. Neurosci Lett 2011; 500:20-5. [PMID: 21683123 DOI: 10.1016/j.neulet.2011.05.235] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 05/13/2011] [Accepted: 05/31/2011] [Indexed: 10/18/2022]
Abstract
A bicuculline-resistant and TPMPA-sensitive GABAergic component was identified in hippocampal neurons in culture and in acute isolated brain slices. In both preparations, total GABAergic activity showed two inactivation kinetics: fast and slow. RT-PCR, in situ hybridization (ISH) and immunohistochemistry detected expression of GABAρ subunits. Immunogold and electron microscopy indicated that the receptors are mostly extrasynaptic. In addition, by RT-PCR and immunofluorescence we found GABAρ present in amygdala and visual cortex.
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Affiliation(s)
- Abraham Rosas-Arellano
- Departamento de Neurobiología Celular y Molecular, Laboratorio de Neurobiología Molecular y Celular, Instituto de Neurobiología, Campus UNAM-Juriquilla, Querétaro, QRO 76230, Mexico
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98
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Grace AA. Dopamine system dysregulation by the hippocampus: implications for the pathophysiology and treatment of schizophrenia. Neuropharmacology 2011; 62:1342-8. [PMID: 21621548 DOI: 10.1016/j.neuropharm.2011.05.011] [Citation(s) in RCA: 147] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2011] [Revised: 05/11/2011] [Accepted: 05/13/2011] [Indexed: 11/19/2022]
Abstract
For decades, the predominant hypothesis of schizophrenia centered on dysfunctions of the dopamine system. However, recent evidence now suggests that the dopamine system may be "normal" in its configuration, but instead is regulated abnormally by modulatory processes. Convergent studies in animals and in humans have now focused on the hippocampus as a central component in the generation of psychosis and possibly other symptom states in schizophrenia. Thus, activity in the ventral hippocampus has been shown to regulate dopamine neuron responsivity by controlling the number of dopamine neurons that can be phasically activated by stimuli. In this way, this structure determines the gain of the dopamine signal in response to stimuli. However, in schizophrenia, the hippocampus appears to be hyper-active, possibly due to attenuation of function of inhibitory interneurons. As a result, the dopamine system is driven into an overly responsive state. Current medications have focused on blockade of overstimulated dopamine receptors; however, this now appears to be several synapses downstream from the pathological antecedent. Therapeutic approaches that focus on normalizing hippocampal function may prove to be more effective treatment avenues for the schizophrenia patient.
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Affiliation(s)
- Anthony A Grace
- Departments of Neuroscience, Psychiatry and Psychology, University of Pittsburgh, 458 Crawford Hall, Pittsburgh, PA 15260, USA.
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99
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Chiou TT, Bonhomme B, Jin H, Miralles CP, Xiao H, Fu Z, Harvey RJ, Harvey K, Vicini S, De Blas AL. Differential regulation of the postsynaptic clustering of γ-aminobutyric acid type A (GABAA) receptors by collybistin isoforms. J Biol Chem 2011; 286:22456-68. [PMID: 21540179 DOI: 10.1074/jbc.m111.236190] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Collybistin promotes submembrane clustering of gephyrin and is essential for the postsynaptic localization of gephyrin and γ-aminobutyric acid type A (GABA(A)) receptors at GABAergic synapses in hippocampus and amygdala. Four collybistin isoforms are expressed in brain neurons; CB2 and CB3 differ in the C terminus and occur with and without the Src homology 3 (SH3) domain. We have found that in transfected hippocampal neurons, all collybistin isoforms (CB2(SH3+), CB2(SH3-), CB3(SH3+), and CB3(SH3-)) target to and concentrate at GABAergic postsynapses. Moreover, in non-transfected neurons, collybistin concentrates at GABAergic synapses. Hippocampal neurons co-transfected with CB2(SH3-) and gephyrin developed very large postsynaptic gephyrin and GABA(A) receptor clusters (superclusters). This effect was accompanied by a significant increase in the amplitude of miniature inhibitory postsynaptic currents. Co-transfection with CB2(SH3+) and gephyrin induced the formation of many (supernumerary) non-synaptic clusters. Transfection with gephyrin alone did not affect cluster number or size, but gephyrin potentiated the clustering effect of CB2(SH3-) or CB2(SH3+). Co-transfection with CB2(SH3-) or CB2(SH3+) and gephyrin did not affect the density of presynaptic GABAergic terminals contacting the transfected cells, indicating that collybistin is not synaptogenic. Nevertheless, the synaptic superclusters induced by CB2(SH3-) and gephyrin were accompanied by enlarged presynaptic GABAergic terminals. The enhanced clustering of gephyrin and GABA(A) receptors induced by collybistin isoforms was not accompanied by enhanced clustering of neuroligin 2. Moreover, during the development of GABAergic synapses, the clustering of gephyrin and GABA(A) receptors preceded the clustering of neuroligin 2. We propose a model in which the SH3- isoforms play a major role in the postsynaptic accumulation of GABA(A) receptors and in GABAergic synaptic strength.
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Affiliation(s)
- Tzu-Ting Chiou
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269, USA
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100
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Johnstone TB, Gu Z, Yoshimura RF, Villegier AS, Hogenkamp DJ, Whittemore ER, Huang JC, Tran MB, Belluzzi JD, Yakel JL, Gee KW. Allosteric modulation of related ligand-gated ion channels synergistically induces long-term potentiation in the hippocampus and enhances cognition. J Pharmacol Exp Ther 2010; 336:908-15. [PMID: 21159751 DOI: 10.1124/jpet.110.176255] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
α5 Subunit-containing GABA(A) receptors (GABA(A)Rs) and α7 neuronal nicotinic-acetylcholine receptors (nAChRs) are members of the Cys-loop family of ligand-gated ion channels (LGICs) that mediate cognitive and attentional processes in the hippocampus. α5 GABA(A)Rs alter network activity by tonic inhibition of CA1/CA3 pyramidal cells of the hippocampus. Postsynaptic α7 nAChRs in the hippocampus regulate inhibitory GABAergic interneuron activity required for synchronization of pyramidal neurons in the CA1, whereas presynaptic α7 nAChRs regulate glutamate release. Can simultaneous allosteric modulation of these LGICs produce synergistic effects on cognition? We show that combined transient application of two allosteric modulators that individually 1) inhibit α5 GABA(A)Rs and 2) enhance α7 nAChRs causes long-term potentiation (LTP) of mossy fiber stimulation-induced excitatory postsynaptic currents (EPSC) from CA1 pyramidal neurons of rat hippocampal slices. The LTP effect evoked by two compounds is replicated by 3-(2,5-difluorophenyl)-6-(N-ethylindol-5-yl)-1,2,4-triazolo[4,3-b]pyridazine (522-054), a compound we designed to simultaneously inhibit α5 GABA(A)Rs and enhance α7 nAChRs. Selective antagonists for either receptor block sustained EPSC potentiation produced by 522-054. In vivo, 522-054 enhances performance in the radial arm maze and facilitates attentional states in the five-choice serial reaction time trial with similar receptor antagonist sensitivity. These observations may translate into therapeutic utility of dual action compounds in diseases of hippocampal-based cognitive impairment.
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Affiliation(s)
- Timothy B Johnstone
- Department of Pharmacology, School of Medicine, University of California, Irvine, California, USA.
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