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Huang YH, Lee MT, Hsueh HY, Knutson DE, Cook J, Mihovilovic MD, Sieghart W, Chiou LC. Cerebellar α6GABA A Receptors as a Therapeutic Target for Essential Tremor: Proof-of-Concept Study with Ethanol and Pyrazoloquinolinones. Neurotherapeutics 2023; 20:399-418. [PMID: 36696034 PMCID: PMC10121996 DOI: 10.1007/s13311-023-01342-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/29/2022] [Indexed: 01/26/2023] Open
Abstract
Ethanol has been shown to suppress essential tremor (ET) in patients at low-to-moderate doses, but its mechanism(s) of action remain unknown. One of the ET hypotheses attributes the ET tremorgenesis to the over-activated firing of inferior olivary neurons, causing synchronic rhythmic firings of cerebellar Purkinje cells. Purkinje cells, however, also receive excitatory inputs from granule cells where the α6 subunit-containing GABAA receptors (α6GABAARs) are abundantly expressed. Since ethanol is a positive allosteric modulator (PAM) of α6GABAARs, such action may mediate its anti-tremor effect. Employing the harmaline-induced ET model in male ICR mice, we evaluated the possible anti-tremor effects of ethanol and α6GABAAR-selective pyrazoloquinolinone PAMs. The burrowing activity, an indicator of well-being in rodents, was measured concurrently. Ethanol significantly and dose-dependently attenuated action tremor at non-sedative doses (0.4-2.4 g/kg, i.p.). Propranolol and α6GABAAR-selective pyrazoloquinolinones also significantly suppressed tremor activity. Neither ethanol nor propranolol, but only pyrazoloquinolinones, restored burrowing activity in harmaline-treated mice. Importantly, intra-cerebellar micro-injection of furosemide (an α6GABAAR antagonist) had a trend of blocking the effect of pyrazoloquinolinone Compound 6 or ethanol on harmaline-induced tremor. In addition, the anti-tremor effects of Compound 6 and ethanol were synergistic. These results suggest that low doses of ethanol and α6GABAAR-selective PAMs can attenuate action tremor, at least partially by modulating cerebellar α6GABAARs. Thus, α6GABAARs are potential therapeutic targets for ET, and α6GABAAR-selective PAMs may be a potential mono- or add-on therapy.
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Affiliation(s)
- Ya-Hsien Huang
- Department and Graduate Institute of Pharmacology, College of Medicine, National Taiwan University, No. 1, Jen-Ai Rd., Section 1, Taipei, 10051, Taiwan
| | - Ming Tatt Lee
- Department and Graduate Institute of Pharmacology, College of Medicine, National Taiwan University, No. 1, Jen-Ai Rd., Section 1, Taipei, 10051, Taiwan
- Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, 56000, Malaysia
| | - Han-Yun Hsueh
- Department and Graduate Institute of Pharmacology, College of Medicine, National Taiwan University, No. 1, Jen-Ai Rd., Section 1, Taipei, 10051, Taiwan
| | - Daniel E Knutson
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, USA
| | - James Cook
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, USA
| | | | - Werner Sieghart
- Center for Brain Research, Department of Molecular Neurosciences, Medical University Vienna, Vienna, 1090, Austria
| | - Lih-Chu Chiou
- Department and Graduate Institute of Pharmacology, College of Medicine, National Taiwan University, No. 1, Jen-Ai Rd., Section 1, Taipei, 10051, Taiwan.
- Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, 10051, Taiwan.
- Graduate Institute of Acupuncture Science, China Medical University, Taichung, 40402, Taiwan.
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Simeone X, Ernst M, Seidel T, Heider J, Enz D, Monticelli S, Vogel FD, Koniuszewski F, Langer T, Scholze P, Pace V, Miele M. Novel alpha6 preferring GABA-A receptor ligands based on loreclezole. Eur J Med Chem 2022; 244:114780. [DOI: 10.1016/j.ejmech.2022.114780] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2022] [Revised: 09/12/2022] [Accepted: 09/14/2022] [Indexed: 11/04/2022]
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Sieghart W, Chiou LC, Ernst M, Fabjan J, M Savić M, Lee MT. α6-Containing GABA A Receptors: Functional Roles and Therapeutic Potentials. Pharmacol Rev 2022; 74:238-270. [PMID: 35017178 DOI: 10.1124/pharmrev.121.000293] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Accepted: 09/08/2021] [Indexed: 12/11/2022] Open
Abstract
GABAA receptors containing the α6 subunit are highly expressed in cerebellar granule cells and less abundantly in many other neuronal and peripheral tissues. Here, we for the first time summarize their importance for the functions of the cerebellum and the nervous system. The cerebellum is not only involved in motor control but also in cognitive, emotional, and social behaviors. α6βγ2 GABAA receptors located at cerebellar Golgi cell/granule cell synapses enhance the precision of inputs required for cerebellar timing of motor activity and are thus involved in cognitive processing and adequate responses to our environment. Extrasynaptic α6βδ GABAA receptors regulate the amount of information entering the cerebellum by their tonic inhibition of granule cells, and their optimal functioning enhances input filtering or contrast. The complex roles of the cerebellum in multiple brain functions can be compromised by genetic or neurodevelopmental causes that lead to a hypofunction of cerebellar α6-containing GABAA receptors. Animal models mimicking neuropsychiatric phenotypes suggest that compounds selectively activating or positively modulating cerebellar α6-containing GABAA receptors can alleviate essential tremor and motor disturbances in Angelman and Down syndrome as well as impaired prepulse inhibition in neuropsychiatric disorders and reduce migraine and trigeminal-related pain via α6-containing GABAA receptors in trigeminal ganglia. Genetic studies in humans suggest an association of the human GABAA receptor α6 subunit gene with stress-associated disorders. Animal studies support this conclusion. Neuroimaging and post-mortem studies in humans further support an involvement of α6-containing GABAA receptors in various neuropsychiatric disorders, pointing to a broad therapeutic potential of drugs modulating α6-containing GABAA receptors. SIGNIFICANCE STATEMENT: α6-Containing GABAA receptors are abundantly expressed in cerebellar granule cells, but their pathophysiological roles are widely unknown, and they are thus out of the mainstream of GABAA receptor research. Anatomical and electrophysiological evidence indicates that these receptors have a crucial function in neuronal circuits of the cerebellum and the nervous system, and experimental, genetic, post-mortem, and pharmacological studies indicate that selective modulation of these receptors offers therapeutic prospects for a variety of neuropsychiatric disorders and for stress and its consequences.
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Affiliation(s)
- Werner Sieghart
- Center for Brain Research, Department of Molecular Neurosciences (W.S.), and Center for Brain Research, Department of Pathobiology of the Nervous System (M.E., J.F.), Medical University Vienna, Vienna, Austria; Graduate Institute of Pharmacology (L.-C.C., M.T.L.), and Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan (L.-C.C., M.T.L.); Faculty of Pharmacy, Department of Pharmacology, University of Belgrade, Belgrade, Serbia (M.M.S.); Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, Malaysia (M.T.L.); and Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan (L.-C.C.)
| | - Lih-Chu Chiou
- Center for Brain Research, Department of Molecular Neurosciences (W.S.), and Center for Brain Research, Department of Pathobiology of the Nervous System (M.E., J.F.), Medical University Vienna, Vienna, Austria; Graduate Institute of Pharmacology (L.-C.C., M.T.L.), and Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan (L.-C.C., M.T.L.); Faculty of Pharmacy, Department of Pharmacology, University of Belgrade, Belgrade, Serbia (M.M.S.); Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, Malaysia (M.T.L.); and Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan (L.-C.C.)
| | - Margot Ernst
- Center for Brain Research, Department of Molecular Neurosciences (W.S.), and Center for Brain Research, Department of Pathobiology of the Nervous System (M.E., J.F.), Medical University Vienna, Vienna, Austria; Graduate Institute of Pharmacology (L.-C.C., M.T.L.), and Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan (L.-C.C., M.T.L.); Faculty of Pharmacy, Department of Pharmacology, University of Belgrade, Belgrade, Serbia (M.M.S.); Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, Malaysia (M.T.L.); and Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan (L.-C.C.)
| | - Jure Fabjan
- Center for Brain Research, Department of Molecular Neurosciences (W.S.), and Center for Brain Research, Department of Pathobiology of the Nervous System (M.E., J.F.), Medical University Vienna, Vienna, Austria; Graduate Institute of Pharmacology (L.-C.C., M.T.L.), and Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan (L.-C.C., M.T.L.); Faculty of Pharmacy, Department of Pharmacology, University of Belgrade, Belgrade, Serbia (M.M.S.); Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, Malaysia (M.T.L.); and Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan (L.-C.C.)
| | - Miroslav M Savić
- Center for Brain Research, Department of Molecular Neurosciences (W.S.), and Center for Brain Research, Department of Pathobiology of the Nervous System (M.E., J.F.), Medical University Vienna, Vienna, Austria; Graduate Institute of Pharmacology (L.-C.C., M.T.L.), and Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan (L.-C.C., M.T.L.); Faculty of Pharmacy, Department of Pharmacology, University of Belgrade, Belgrade, Serbia (M.M.S.); Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, Malaysia (M.T.L.); and Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan (L.-C.C.)
| | - Ming Tatt Lee
- Center for Brain Research, Department of Molecular Neurosciences (W.S.), and Center for Brain Research, Department of Pathobiology of the Nervous System (M.E., J.F.), Medical University Vienna, Vienna, Austria; Graduate Institute of Pharmacology (L.-C.C., M.T.L.), and Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan (L.-C.C., M.T.L.); Faculty of Pharmacy, Department of Pharmacology, University of Belgrade, Belgrade, Serbia (M.M.S.); Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, Malaysia (M.T.L.); and Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan (L.-C.C.)
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4
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Grotell M, Abdurakhmanova S, Elsilä LV, Korpi ER. Mice Lacking GABA A Receptor δ Subunit Have Altered Pharmaco-EEG Responses to Multiple Drugs. Front Pharmacol 2021; 12:706894. [PMID: 34234684 PMCID: PMC8255781 DOI: 10.3389/fphar.2021.706894] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2021] [Accepted: 06/11/2021] [Indexed: 11/13/2022] Open
Abstract
In the brain, extrasynaptically expressed ionotropic, δ subunit-containing γ-aminobutyric acid A-type receptors (δ-GABAARs) have been implicated in drug effects at both neuronal and behavioral levels. These alterations are supposed to be caused via drug-induced modulation of receptor ionophores affecting chloride ion-mediated inhibitory tonic currents. Often, a transgenic mouse model genetically lacking the δ-GABAARs (δ-KO) has been used to study the roles of δ-GABAARs in brain functions, because a specific antagonist of the δ-GABAARs is still lacking. We have previously observed with these δ-KO mice that activation of δ-GABAARs is needed for morphine-induced conditioning of place preference, and others have suggested that δ-GABAARs act as targets selectively for low doses of ethanol. Furthermore, activation of these receptors via drug-mediated agonism induces a robust increase in the slow-wave frequency bands of electroencephalography (EEG). Here, we tested δ-KO mice (compared to littermate wild-type controls) for the pharmaco-EEG responses of a broad spectrum of pharmacologically different drug classes, including alcohol, opioids, stimulants, and psychedelics. Gaboxadol (THIP), a known superagonist of δ-GABAARs, was included as the positive control, and as expected, δ-KO mice produced a blunted pharmaco-EEG response to 6 mg/kg THIP. Pharmaco-EEGs showed notable differences between treatments but also differences between δ-KO mice and their wild-type littermates. Interestingly mephedrone (4-MMC, 5 mg/kg), an amphetamine-like stimulant, had reduced effects in the δ-KO mice. The responses to ethanol (1 g/kg), LSD (0.2 mg/kg), and morphine (20 mg/kg) were similar in δ-KO and wild-type mice. Since stimulants are not known to act on δ-GABAARs, our findings on pharmaco-EEG effects of 4-MMC suggest that δ-GABAARs are involved in the secondary indirect regulation of the brain rhythms after 4-MMC.
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Affiliation(s)
- Milo Grotell
- Department of Pharmacology, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | | | - Lauri V Elsilä
- Department of Pharmacology, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Esa R Korpi
- Department of Pharmacology, Faculty of Medicine, University of Helsinki, Helsinki, Finland
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5
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Luo Y, Kusay AS, Jiang T, Chebib M, Balle T. Delta-containing GABA A receptors in pain management: Promising targets for novel analgesics. Neuropharmacology 2021; 195:108675. [PMID: 34153311 DOI: 10.1016/j.neuropharm.2021.108675] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2020] [Revised: 06/01/2021] [Accepted: 06/11/2021] [Indexed: 12/26/2022]
Abstract
Communication between nerve cells depends on the balance between excitatory and inhibitory circuits. GABA, the major inhibitory neurotransmitter, regulates this balance and insufficient GABAergic activity is associated with numerous neuropathological disorders including pain. Of the various GABAA receptor subtypes, the δ-containing receptors are particularly interesting drug targets in management of chronic pain. These receptors are pentameric ligand-gated ion channels composed of α, β and δ subunits and can be activated by ambient levels of GABA to generate tonic conductance. However, only a few ligands preferentially targeting δ-containing GABAA receptors have so far been identified, limiting both pharmacological understanding and drug-discovery efforts, and more importantly, understanding of how they affect pain pathways. Here, we systemically review and discuss the known drugs and ligands with analgesic potential targeting δ-containing GABAA receptors and further integrate the biochemical nature of the receptors with clinical perspectives in pain that might generate interest among researchers and clinical physicians to encourage analgesic discovery efforts leading to more efficient therapies.
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Affiliation(s)
- Yujia Luo
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia; Brain and Mind Centre, The University of Sydney, Camperdown, NSW, 2050, Australia
| | - Ali Saad Kusay
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia; Brain and Mind Centre, The University of Sydney, Camperdown, NSW, 2050, Australia
| | - Tian Jiang
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia; Brain and Mind Centre, The University of Sydney, Camperdown, NSW, 2050, Australia
| | - Mary Chebib
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia; Brain and Mind Centre, The University of Sydney, Camperdown, NSW, 2050, Australia
| | - Thomas Balle
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia; Brain and Mind Centre, The University of Sydney, Camperdown, NSW, 2050, Australia.
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6
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Falk-Petersen CB, Rostrup F, Löffler R, Buchleithner S, Harpsøe K, Gloriam DE, Frølund B, Wellendorph P. Molecular Determinants Underlying Delta Selective Compound 2 Activity at δ-Containing GABA A Receptors. Mol Pharmacol 2021; 100:46-56. [PMID: 33990405 DOI: 10.1124/molpharm.121.000266] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Accepted: 04/22/2021] [Indexed: 11/22/2022] Open
Abstract
Delta selective compound 2 (DS2; 4-chloro-N-[2-(2-thienyl)imidazo[1,2-a]pyridin-3-yl]benzamide) is one of the most widely used tools to study selective actions mediated by δ-subunit-containing GABAA receptors. DS2 was discovered over 10 years ago, but despite great efforts, the precise molecular site of action has remained elusive. Using a combination of computational modeling, site-directed mutagenesis, and cell-based pharmacological assays, we probed three potential binding sites for DS2 and analogs at α 4 β 1 δ receptors: an α 4 (+) δ (-) interface site in the extracellular domain (ECD), equivalent to the diazepam binding site in αβγ 2 receptors, and two sites in the transmembrane domain (TMD) - one in the α 4 (+) β 1 (-) and one in the α 4 (-) β 1 (+) interface, with the α 4 (-) β 1 (+) site corresponding to the binding site for etomidate and a recently disclosed low-affinity binding site for diazepam. We show that mutations in the ECD site did not abrogate DS2 modulation. However, mutations in the TMD α 4 (+) β 1 (-) interface, either α 4(S303L) of the α 4 (+) side or β 1(I289Q) of the β 1 (-) side, convincingly disrupted the positive allosteric modulation by DS2. This was consistently demonstrated both in an assay measuring membrane potential changes and by whole-cell patch-clamp electrophysiology and rationalized by docking studies. Importantly, general sensitivity to modulators was not compromised in the mutated receptors. This study sheds important light on the long-sought molecular recognition site for DS2, refutes the misconception that the selectivity of DS2 for δ-containing receptors is caused by a direct interaction with the δ-subunit, and instead points toward a functional selectivity of DS2 and its analogs via a surprisingly well conserved binding pocket in the TMD. SIGNIFICANCE STATEMENT: δ-Containing GABAA receptors represent potential drug targets for the treatment of several neurological conditions with aberrant tonic inhibition, yet no drugs are currently in clinical use. With the identification of the molecular determinants responsible for positive modulation by the known compound delta selective compound 2, the ground is laid for design of ligands that selectively target δ-containing GABAA receptor subtypes, for better understanding of tonic inhibition, and ultimately, for rational development of novel drugs.
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Affiliation(s)
- Christina B Falk-Petersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Frederik Rostrup
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Rebekka Löffler
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Stine Buchleithner
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Kasper Harpsøe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - David E Gloriam
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Bente Frølund
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Petrine Wellendorph
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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Rostrup F, Falk-Petersen CB, Harpso E K, Buchleithner S, Conforti I, Jung S, Gloriam DE, Schirmeister T, Wellendorph P, Fro Lund B. Structural Determinants for the Mode of Action of Imidazopyridine DS2 at δ-Containing γ-Aminobutyric Acid Type A Receptors. J Med Chem 2021; 64:4730-4743. [PMID: 33847501 DOI: 10.1021/acs.jmedchem.0c02163] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Despite the therapeutic relevance of δ-containing γ-aminobutyric acid type A receptors (GABAARs) and the need for δ-selective compounds, the structural determinants for the mode and molecular site of action of δ-selective positive allosteric modulator imidazo[1,2-a]pyridine DS2 remain elusive. To guide the quest for insight, we synthesized a series of DS2 analogues guided by a structural receptor model. Using a fluorescence-based fluorometric imaging plate reader membrane potential assay, we found that the δ-selectivity and the pharmacological profile are severely affected by substituents in the 5-position of the imidazopyridine core scaffold. Interestingly, the 5-methyl, 5-bromo, and 5-chloro DS2 analogues, 30, 35, and 36, were shown to be superior to DS2 at α4β1δ as mid-high nanomolar potency δ-selective allosteric modulators, displaying 6-16 times higher potency than DS2. Of these, 30 also displayed at least 60-fold selectivity for α4β1δ over α4β1γ2 receptor subtypes representing a potential tool for the selective characterization of δ-containing GABAARs in general.
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Affiliation(s)
- Frederik Rostrup
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen DK-2100, Denmark
| | - Christina B Falk-Petersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen DK-2100, Denmark
| | - Kasper Harpso E
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen DK-2100, Denmark
| | - Stine Buchleithner
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen DK-2100, Denmark
| | - Irene Conforti
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen DK-2100, Denmark
| | - Sascha Jung
- Institute of Pharmaceutical and Biomedical Sciences, Johannes Gutenberg University Mainz, Mainz D-55128, Germany
| | - David E Gloriam
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen DK-2100, Denmark
| | - Tanja Schirmeister
- Institute of Pharmaceutical and Biomedical Sciences, Johannes Gutenberg University Mainz, Mainz D-55128, Germany
| | - Petrine Wellendorph
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen DK-2100, Denmark
| | - Bente Fro Lund
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen DK-2100, Denmark
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GABAergic Mechanisms Can Redress the Tilted Balance between Excitation and Inhibition in Damaged Spinal Networks. Mol Neurobiol 2021; 58:3769-3786. [PMID: 33826070 PMCID: PMC8279998 DOI: 10.1007/s12035-021-02370-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2020] [Accepted: 03/22/2021] [Indexed: 12/19/2022]
Abstract
Correct operation of neuronal networks depends on the interplay between synaptic excitation and inhibition processes leading to a dynamic state termed balanced network. In the spinal cord, balanced network activity is fundamental for the expression of locomotor patterns necessary for rhythmic activation of limb extensor and flexor muscles. After spinal cord lesion, paralysis ensues often followed by spasticity. These conditions imply that, below the damaged site, the state of balanced networks has been disrupted and that restoration might be attempted by modulating the excitability of sublesional spinal neurons. Because of the widespread expression of inhibitory GABAergic neurons in the spinal cord, their role in the early and late phases of spinal cord injury deserves full attention. Thus, an early surge in extracellular GABA might be involved in the onset of spinal shock while a relative deficit of GABAergic mechanisms may be a contributor to spasticity. We discuss the role of GABA A receptors at synaptic and extrasynaptic level to modulate network excitability and to offer a pharmacological target for symptom control. In particular, it is proposed that activation of GABA A receptors with synthetic GABA agonists may downregulate motoneuron hyperexcitability (due to enhanced persistent ionic currents) and, therefore, diminish spasticity. This approach might constitute a complementary strategy to regulate network excitability after injury so that reconstruction of damaged spinal networks with new materials or cell transplants might proceed more successfully.
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Benkherouf AY, Eerola K, Soini SL, Uusi-Oukari M. Humulone Modulation of GABA A Receptors and Its Role in Hops Sleep-Promoting Activity. Front Neurosci 2020; 14:594708. [PMID: 33177986 PMCID: PMC7591795 DOI: 10.3389/fnins.2020.594708] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Accepted: 09/24/2020] [Indexed: 12/12/2022] Open
Abstract
Humulus lupulus L. (hops) is a major constituent of beer. It exhibits neuroactive properties that make it useful as a sleeping aid. These effects are hypothesized to be mediated by an increase in GABAA receptor function. In the quest to uncover the constituents responsible for the sedative and hypnotic properties of hops, recent evidence revealed that humulone, a prenylated phloroglucinol derivative comprising 35-70% of hops alpha acids, may act as a positive modulator of GABAA receptors at low micromolar concentrations. This raises the question whether humulone plays a key role in hops pharmacological activity and potentially interacts with other modulators such as ethanol, bringing further enhancement in GABAA receptor-mediated effects of beer. Here we assessed electrophysiologically the positive modulatory activity of humulone on recombinant GABAA receptors expressed in HEK293 cells. We then examined humulone interactions with other active hops compounds and ethanol on GABA-induced displacement of [3H]EBOB binding to native GABAA receptors in rat brain membranes. Using BALB/c mice, we assessed humulone's hypnotic behavior with pentobarbital- and ethanol-induced sleep as well as sedation in spontaneous locomotion with open field test. We demonstrated for the first time that humulone potentiates GABA-induced currents in α1β3γ2 receptors. In radioligand binding to native GABAA receptors, the inclusion of ethanol enhanced humulone modulation of GABA-induced displacement of [3H]EBOB binding in rat forebrain and cerebellum as it produced a leftward shift in [3H]EBOB displacement curves. Moreover, the additive modulatory effects between humulone, isoxanthohumol and 6-prenylnaringenin were evident and corresponded to the sum of [3H]EBOB displacement by each compound individually. In behavioral tests, humulone shortened sleep onset and increased the duration of sleep induced by pentobarbital and decreased the spontaneous locomotion in open field at 20 mg/kg (i.p.). Despite the absence of humulone effects on ethanol-induced sleep onset, sleep duration was increased dose-dependently down to 10 mg/kg (i.p.). Our findings confirmed humulone's positive allosteric modulation of GABAA receptor function and displayed its sedative and hypnotic behavior. Humulone modulation can be potentially enhanced by ethanol and hops modulators suggesting a probable enhancement in the intoxicating effects of ethanol in hops-enriched beer.
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Affiliation(s)
| | | | | | - Mikko Uusi-Oukari
- Integrative Physiology and Pharmacology, Institute of Biomedicine, University of Turku, Turku, Finland
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de Oliveira TM, van Beek L, Shilliday F, Debreczeni JÉ, Phillips C. Cryo-EM: The Resolution Revolution and Drug Discovery. SLAS DISCOVERY 2020; 26:17-31. [PMID: 33016175 DOI: 10.1177/2472555220960401] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Single-particle cryogenic electron microscopy (cryo-EM) has been elevated to the mainstream of structural biology propelled by technological advancements in numerous fronts, including imaging analysis and the development of direct electron detectors. The drug discovery field has watched with (initial) skepticism and wonder at the progression of the technique and how it revolutionized the molecular understanding of previously intractable targets. This article critically assesses how cryo-EM has impacted drug discovery in diverse therapeutic areas. Targets that have been brought into the realm of structure-based drug design by cryo-EM and are thus reviewed here include membrane proteins like the GABAA receptor, several TRP channels, and G protein-coupled receptors, and multiprotein complexes like the ribosomes, the proteasome, and eIF2B. We will describe these studies highlighting the achievements, challenges, and caveats.
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Affiliation(s)
| | - Lotte van Beek
- Structure, Biophysics and FBLG, Discovery Sciences, AstraZeneca R&D, Cambridge, UK
| | - Fiona Shilliday
- Structure, Biophysics and FBLG, Discovery Sciences, AstraZeneca R&D, Cambridge, UK
| | - Judit É Debreczeni
- Structure, Biophysics and FBLG, Discovery Sciences, AstraZeneca R&D, Cambridge, UK
| | - Chris Phillips
- Structure, Biophysics and FBLG, Discovery Sciences, AstraZeneca R&D, Cambridge, UK
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11
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Agoglia AE, Zhu M, Ying R, Sidhu H, Natividad LA, Wolfe SA, Buczynski MW, Contet C, Parsons LH, Roberto M, Herman MA. Corticotropin-Releasing Factor Receptor-1 Neurons in the Lateral Amygdala Display Selective Sensitivity to Acute and Chronic Ethanol Exposure. eNeuro 2020; 7:ENEURO.0420-19.2020. [PMID: 32041742 PMCID: PMC7059189 DOI: 10.1523/eneuro.0420-19.2020] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Revised: 01/15/2020] [Accepted: 01/28/2020] [Indexed: 12/19/2022] Open
Abstract
The lateral amygdala (LA) serves as the point of entry for sensory information within the amygdala complex, a structure that plays a critical role in emotional processes and has been implicated in alcohol use disorders. Within the amygdala, the corticotropin-releasing factor (CRF) system has been shown to mediate some of the effects of both stress and ethanol, but the effects of ethanol on specific CRF1 receptor circuits in the amygdala have not been fully established. We used male CRF1:GFP reporter mice to characterize CRF1-expressing (CRF1+) and nonexpressing (CRF1-) LA neurons and investigate the effects of acute and chronic ethanol exposure on these populations. The CRF1+ population was found to be composed predominantly of glutamatergic projection neurons with a minority subpopulation of interneurons. CRF1+ neurons exhibited a tonic conductance that was insensitive to acute ethanol. CRF1- neurons did not display a basal tonic conductance, but the application of acute ethanol induced a δ GABAA receptor subunit-dependent tonic conductance and enhanced phasic GABA release onto these cells. Chronic ethanol increased CRF1+ neuronal excitability but did not significantly alter phasic or tonic GABA signaling in either CRF1+ or CRF1- cells. Chronic ethanol and withdrawal also did not alter basal extracellular GABA or glutamate transmitter levels in the LA/BLA and did not alter the sensitivity of GABA or glutamate to acute ethanol-induced increases in transmitter release. Together, these results provide the first characterization of the CRF1+ population of LA neurons and suggest mechanisms for differential acute ethanol sensitivity within this region.
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Affiliation(s)
- Abigail E Agoglia
- Department of Pharmacology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
- Bowles Center for Alcohol Studies, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - ManHua Zhu
- Neuroscience Curriculum, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Rose Ying
- Department of Pharmacology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
- Bowles Center for Alcohol Studies, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Harpreet Sidhu
- Department of Neuroscience, The Scripps Research Institute, La Jolla, California 92037
| | - Luis A Natividad
- University of Texas at Austin, College of Pharmacy - Division of Pharmacology and Toxicology, Austin, TX 78712
| | - Sarah A Wolfe
- Department of Neuroscience, The Scripps Research Institute, La Jolla, California 92037
| | - Matthew W Buczynski
- School of Neuroscience, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
| | - Candice Contet
- Department of Neuroscience, The Scripps Research Institute, La Jolla, California 92037
| | - Loren H Parsons
- Department of Neuroscience, The Scripps Research Institute, La Jolla, California 92037
| | - Marisa Roberto
- Department of Neuroscience, The Scripps Research Institute, La Jolla, California 92037
| | - Melissa A Herman
- Department of Pharmacology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
- Bowles Center for Alcohol Studies, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
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12
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Simeone X, Iorio M, Siebert D, Rehman S, Schnürch M, Mihovilovic M, Ernst M. Defined concatenated α6α1β3γ2 GABAA receptor constructs reveal dual action of pyrazoloquinolinone allosteric modulators. Bioorg Med Chem 2019; 27:3167-3178. [DOI: 10.1016/j.bmc.2019.06.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 05/08/2019] [Accepted: 06/03/2019] [Indexed: 12/20/2022]
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13
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Mazzone GL, Nistri A. Modulation of extrasynaptic GABAergic receptor activity influences glutamate release and neuronal survival following excitotoxic damage to mouse spinal cord neurons. Neurochem Int 2019; 128:175-185. [PMID: 31051211 DOI: 10.1016/j.neuint.2019.04.018] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Revised: 04/08/2019] [Accepted: 04/30/2019] [Indexed: 12/14/2022]
Abstract
Excitotoxic levels of released glutamate trigger a cascade of deleterious cellular events leading to delayed neuronal death. This phenomenon implies extensive dysregulation in the balance between network excitation and inhibition. Our hypothesis was that enhancing network inhibition should prevent excitotoxicity and provide neuroprotection. To test this notion, we used mouse organotypic spinal slice cultures and explored if excitotoxicity caused by the potent glutamate analogue kainate was blocked by pharmacological increase in GABAA receptor activity. To this end we monitored (with a biosensor) real-time glutamate release following 1 h kainate application and quantified neuronal survival 24 h later. Glutamate release evoked by kainate was strongly decreased by the allosteric GABAA modulator midazolam (10 nM) or the GABA agonist THIP (10 μM), leading to neuroprotection. On the contrary, much higher glutamate release was induced by the GABA antagonist bicuculline (20 μM) that inhibits synaptic and extrasynaptic GABAA receptors. Gabazine (20 μM), an antagonist of synaptic GABAA receptors, had no effect on glutamate release or neuroprotection. No effect was observed with the glycine antagonist strychnine or the glycine agonist L-alanine. These findings indicate that enhancement of GABA receptor activity was an effective tool to counteract excitotoxic death in spinal networks. In view of the potent activity by THIP, preferentially acting on extrasynaptic GABAA receptors, the present data imply a significant role for extrasynaptic GABAA receptors in sparing spinal cord neurons from injury.
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Affiliation(s)
- Graciela L Mazzone
- Instituto de Investigaciones en Medicina Traslacional (IIMT), CONICET-Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina.
| | - Andrea Nistri
- Neuroscience Dept., International School for Advanced Studies (SISSA), Trieste, Italy
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14
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Liao VWY, Chua HC, Kowal NM, Chebib M, Balle T, Ahring PK. Concatenated γ-aminobutyric acid type A receptors revisited: Finding order in chaos. J Gen Physiol 2019; 151:798-819. [PMID: 30988061 PMCID: PMC6572006 DOI: 10.1085/jgp.201812133] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2018] [Accepted: 03/20/2019] [Indexed: 12/19/2022] Open
Abstract
Subunit concatenation is a powerful technique used to control the assembly of structurally diverse heteromeric receptors such as GABAARs. Liao et al. find that existing GABAAR concatemers do not assemble as expected and describe refinements that allow expression of uniform receptor populations. γ-aminobutyric acid type A receptors (GABAARs), the major inhibitory neurotransmitter receptors in the mammalian central nervous system, are arguably the most challenging member of the pentameric Cys-loop receptors to study due to their heteromeric structure. When two or more subunits are expressed together in heterologous systems, receptors of variable subunit type, ratio, and orientation can form, precluding accurate interpretation of data from functional studies. Subunit concatenation is a technique that involves the linking of individual subunits and in theory allows the precise control of the uniformity of expressed receptors. In reality, the resulting concatemers from widely used constructs are flexible in their orientation and may therefore assemble with themselves or free GABAAR subunits in unexpected ways. In this study, we examine functional responses of receptors from existing concatenated constructs and describe refinements necessary to allow expression of uniform receptor populations. We find that dimers from two commonly used concatenated constructs, β-23-α and α-10-β, assemble readily in both the clockwise and the counterclockwise orientations when coexpressed with free subunits. Furthermore, we show that concatemers formed from new tetrameric α-10-β-α-β and α-10-β-α-γ constructs also assemble in both orientations with free subunits to give canonical αβγ receptors. To restrict linker flexibility, we systematically shorten linker lengths of dimeric and pentameric constructs and find optimized constructs that direct the assembly of GABAARs only in one orientation, thus eliminating the ambiguity associated with previously described concatemers. Based on our data, we revisit some noncanonical GABAAR configurations proposed in recent years and explain how the use of some concatenated constructs may have led to wrong conclusions. Our results help clarify current contradictions in the literature regarding GABAAR subunit stoichiometry and arrangement. The lessons learned from this study may guide future efforts in understanding other related heteromeric receptors.
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Affiliation(s)
- Vivian Wan Yu Liao
- The University of Sydney, Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Camperdown, New South Wales, Australia
| | - Han Chow Chua
- The University of Sydney, Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Camperdown, New South Wales, Australia
| | - Natalia Magdalena Kowal
- The University of Sydney, Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Camperdown, New South Wales, Australia.,Faculty of Pharmaceutical Sciences, School of Health Sciences, University of Iceland, Reykjavik, Iceland
| | - Mary Chebib
- The University of Sydney, Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Camperdown, New South Wales, Australia
| | - Thomas Balle
- The University of Sydney, Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Camperdown, New South Wales, Australia
| | - Philip Kiær Ahring
- The University of Sydney, Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Camperdown, New South Wales, Australia
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15
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Leggio GM, Di Marco R, Gulisano W, D'Ascenzo M, Torrisi SA, Geraci F, Lavanco G, Dahl K, Giurdanella G, Castorina A, Aitta-Aho T, Aceto G, Bucolo C, Puzzo D, Grassi C, Korpi ER, Drago F, Salomone S. Dopaminergic-GABAergic interplay and alcohol binge drinking. Pharmacol Res 2019; 141:384-391. [PMID: 30648615 DOI: 10.1016/j.phrs.2019.01.022] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Revised: 01/10/2019] [Accepted: 01/11/2019] [Indexed: 12/23/2022]
Abstract
The dopamine D3 receptor (D3R), in the nucleus accumbens (NAc), plays an important role in alcohol reward mechanisms. The major neuronal type within the NAc is the GABAergic medium spiny neuron (MSN), whose activity is regulated by dopaminergic inputs. We previously reported that genetic deletion or pharmacological blockade of D3R increases GABAA α6 subunit in the ventral striatum. Here we tested the hypothesis that D3R-dependent changes in GABAA α6 subunit in the NAc affect voluntary alcohol intake, by influencing the inhibitory transmission of MSNs. We performed in vivo and ex vivo experiments in D3R knockout (D3R -/-) mice and wild type littermates (D3R +/+). Ro 15-4513, a high affinity α6-GABAA ligand was used to study α6 activity. At baseline, NAc α6 expression was negligible in D3R+/+, whereas it was robust in D3R-/-; other relevant GABAA subunits were not changed. In situ hybridization and qPCR confirmed α6 subunit mRNA expression especially in the NAc. In the drinking-in-the-dark paradigm, systemic administration of Ro 15-4513 inhibited alcohol intake in D3R+/+, but increased it in D3R-/-; this was confirmed by intra-NAc administration of Ro 15-4513 and furosemide, a selective α6-GABAA antagonist. Whole-cell patch-clamp showed peak amplitudes of miniature inhibitory postsynaptic currents in NAc medium spiny neurons higher in D3R-/- compared to D3R+/+; Ro 15-4513 reduced the peak amplitude in the NAc of D3R-/-, but not in D3R+/+. We conclude that D3R-dependent enhanced expression of α6 GABAA subunit inhibits voluntary alcohol intake by increasing GABA inhibition in the NAc.
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Affiliation(s)
- Gian Marco Leggio
- Department of Biomedical and Biotechnological Sciences, School of Medicine, University of Catania, Catania, Italy
| | - Roberta Di Marco
- Department of Biomedical and Biotechnological Sciences, School of Medicine, University of Catania, Catania, Italy
| | - Walter Gulisano
- Department of Biomedical and Biotechnological Sciences, School of Medicine, University of Catania, Catania, Italy
| | - Marcello D'Ascenzo
- Institute of Human Physiology, Medical School, Università Cattolica, Rome, Italy; Fondazione Policlinico Universitario A. Gemelli IRCCS, Roma, Italia
| | - Sebastiano Alfio Torrisi
- Department of Biomedical and Biotechnological Sciences, School of Medicine, University of Catania, Catania, Italy
| | - Federica Geraci
- Department of Biomedical and Biotechnological Sciences, School of Medicine, University of Catania, Catania, Italy
| | - Gianluca Lavanco
- Department of Biomedical and Biotechnological Sciences, School of Medicine, University of Catania, Catania, Italy
| | - Kristiina Dahl
- Department of Pharmacology, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Giovanni Giurdanella
- Department of Biomedical and Biotechnological Sciences, School of Medicine, University of Catania, Catania, Italy
| | - Alessandro Castorina
- Department of Biomedical and Biotechnological Sciences, School of Medicine, University of Catania, Catania, Italy
| | - Teemu Aitta-Aho
- Department of Pharmacology, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Giuseppe Aceto
- Institute of Human Physiology, Medical School, Università Cattolica, Rome, Italy
| | - Claudio Bucolo
- Department of Biomedical and Biotechnological Sciences, School of Medicine, University of Catania, Catania, Italy
| | - Daniela Puzzo
- Department of Biomedical and Biotechnological Sciences, School of Medicine, University of Catania, Catania, Italy
| | - Claudio Grassi
- Institute of Human Physiology, Medical School, Università Cattolica, Rome, Italy; Fondazione Policlinico Universitario A. Gemelli IRCCS, Roma, Italia
| | - Esa R Korpi
- Department of Pharmacology, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Filippo Drago
- Department of Biomedical and Biotechnological Sciences, School of Medicine, University of Catania, Catania, Italy
| | - Salvatore Salomone
- Department of Biomedical and Biotechnological Sciences, School of Medicine, University of Catania, Catania, Italy.
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16
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Liao Y, Liu X, Jounaidi Y, Forman SA, Feng HJ. Etomidate Effects on Desensitization and Deactivation of α4 β3 δ GABA A Receptors Inducibly Expressed in HEK293 TetR Cells. J Pharmacol Exp Ther 2019; 368:100-105. [PMID: 30389723 PMCID: PMC6304376 DOI: 10.1124/jpet.118.252403] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2018] [Accepted: 10/31/2018] [Indexed: 02/01/2023] Open
Abstract
Central α4βδ receptors are the most abundant isoform of δ subunit-containing extrasynaptic GABAA receptors that mediate tonic inhibition. Although the amplitude of GABA-activated currents through α4βδ receptors is modulated by multiple general anesthetics, the effects of general anesthetics on desensitization and deactivation of α4βδ receptors remain unknown. In the current study, we investigated the effect of etomidate, a potent general anesthetic, on the kinetics and the pseudo steady-state current amplitude of α4β3δ receptors inducibly expressed in human embryonic kidney 293 TetR cells. Etomidate directly activates α4β3δ receptors in a concentration-dependent manner. Etomidate at a clinically relevant concentration (3.2 μM) enhances maximal response without altering the EC50 of GABA concentration response. Etomidate also increases the extent of desensitization and prolongs the deactivation of α4β3δ receptors in the presence of maximally activating concentrations of GABA (1 mM). To mimic the modulatory effect of etomidate on tonic currents, long pulses (30-60 seconds) of a low GABA concentration (1 μM) were applied to activate α4β3δ receptors in the absence and presence of etomidate. Although etomidate increases the desensitization of α4β3δ receptors, the pseudo steady-state current amplitude at 1 μM GABA is augmented by etomidate. Our data demonstrate that etomidate enhances the pseudo steady-state current of α4β3δ receptors evoked by a GABA concentration comparable to an ambient GABA level, suggesting that α4β3δ receptors may mediate etomidate's anesthetic effect in the brain.
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Affiliation(s)
- Yiwei Liao
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts (Y.L., X.L., Y.J., S.A.F., H.-J.F.); Department of Neurosurgery, Xiangya Hospital, Central South University, Changsha, China (Y.L.); and Department of Anesthesia, The Sixth Affiliated Hospital, Sun Yat-Sen University, Guangzhou, China (X.L.)
| | - Xiang Liu
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts (Y.L., X.L., Y.J., S.A.F., H.-J.F.); Department of Neurosurgery, Xiangya Hospital, Central South University, Changsha, China (Y.L.); and Department of Anesthesia, The Sixth Affiliated Hospital, Sun Yat-Sen University, Guangzhou, China (X.L.)
| | - Youssef Jounaidi
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts (Y.L., X.L., Y.J., S.A.F., H.-J.F.); Department of Neurosurgery, Xiangya Hospital, Central South University, Changsha, China (Y.L.); and Department of Anesthesia, The Sixth Affiliated Hospital, Sun Yat-Sen University, Guangzhou, China (X.L.)
| | - Stuart A Forman
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts (Y.L., X.L., Y.J., S.A.F., H.-J.F.); Department of Neurosurgery, Xiangya Hospital, Central South University, Changsha, China (Y.L.); and Department of Anesthesia, The Sixth Affiliated Hospital, Sun Yat-Sen University, Guangzhou, China (X.L.)
| | - Hua-Jun Feng
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts (Y.L., X.L., Y.J., S.A.F., H.-J.F.); Department of Neurosurgery, Xiangya Hospital, Central South University, Changsha, China (Y.L.); and Department of Anesthesia, The Sixth Affiliated Hospital, Sun Yat-Sen University, Guangzhou, China (X.L.)
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17
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Agoglia AE, Herman MA. The center of the emotional universe: Alcohol, stress, and CRF1 amygdala circuitry. Alcohol 2018; 72:61-73. [PMID: 30220589 PMCID: PMC6165695 DOI: 10.1016/j.alcohol.2018.03.009] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Revised: 03/15/2018] [Accepted: 03/27/2018] [Indexed: 12/15/2022]
Abstract
The commonalities between different phases of stress and alcohol use as well as the high comorbidity between alcohol use disorders (AUDs) and anxiety disorders suggest common underlying cellular mechanisms governing the rewarding and aversive aspects of these related conditions. As an integrative center that assigns emotional salience to a wide variety of internal and external stimuli, the amygdala complex plays a major role in how alcohol and stress influence cellular physiology to produce disordered behavior. Previous work has illustrated the broad role of the amygdala in alcohol, stress, and anxiety. However, the challenge of current and future studies is to identify the specific dysregulations that occur within distinct amygdala circuits and subpopulations and the commonalities between these alterations in each disorder, with the long-term goal of identifying potential targets for therapeutic intervention. Specific intra-amygdala circuits and cell type-specific subpopulations are emerging as critical targets for stress- and alcohol-induced plasticity, chief among them the corticotropin releasing factor (CRF) and CRF receptor 1 (CRF1) system. CRF and CRF1 have been implicated in the effects of alcohol in several amygdala nuclei, including the basolateral (BLA) and central amygdala (CeA); however, the precise circuitry involved in these effects and the role of these circuits in stress and anxiety are only beginning to be understood.
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Affiliation(s)
- Abigail E Agoglia
- Bowles Center for Alcohol Studies, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, United States
| | - Melissa A Herman
- Bowles Center for Alcohol Studies, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, United States.
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18
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Delineation of the functional properties and the mechanism of action of AA29504, an allosteric agonist and positive allosteric modulator of GABA A receptors. Biochem Pharmacol 2018; 150:305-319. [DOI: 10.1016/j.bcp.2018.02.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Accepted: 02/13/2018] [Indexed: 11/22/2022]
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19
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Yakoub K, Jung S, Sattler C, Damerow H, Weber J, Kretzschmann A, Cankaya AS, Piel M, Rösch F, Haugaard AS, Frølund B, Schirmeister T, Lüddens H. Structure–Function Evaluation of Imidazopyridine Derivatives Selective for δ-Subunit-Containing γ-Aminobutyric Acid Type A (GABAA) Receptors. J Med Chem 2018; 61:1951-1968. [DOI: 10.1021/acs.jmedchem.7b01484] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Kirsten Yakoub
- Department of Psychiatry and Psychotherapy, Faculty of Health and Medical Sciences, University Medical Center Mainz, D-55131 Mainz, Germany
| | | | - Christian Sattler
- Department of Psychiatry and Psychotherapy, Faculty of Health and Medical Sciences, University Medical Center Mainz, D-55131 Mainz, Germany
| | | | | | | | | | | | | | - Anne S. Haugaard
- Department of Drug Design and Pharmacology, University of Copenhagen, DK-2100 Copenhagen, Denmark
| | - Bente Frølund
- Department of Drug Design and Pharmacology, University of Copenhagen, DK-2100 Copenhagen, Denmark
| | | | - Hartmut Lüddens
- Department of Psychiatry and Psychotherapy, Faculty of Health and Medical Sciences, University Medical Center Mainz, D-55131 Mainz, Germany
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20
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Functional properties and mechanism of action of PPTQ, an allosteric agonist and low nanomolar positive allosteric modulator at GABAA receptors. Biochem Pharmacol 2018; 147:153-169. [DOI: 10.1016/j.bcp.2017.11.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2017] [Accepted: 11/13/2017] [Indexed: 11/23/2022]
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21
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Baur R, Sigel E. Low Expression in Xenopus Oocytes and Unusual Functional Properties of α1β2γ2 GABAA Receptors with Non-Conventional Subunit Arrangement. PLoS One 2017; 12:e0170572. [PMID: 28114407 PMCID: PMC5256883 DOI: 10.1371/journal.pone.0170572] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Accepted: 01/07/2017] [Indexed: 11/25/2022] Open
Abstract
The major subunit isoform of GABAA receptors is α1β2γ2. The subunits are thought to surround an ion pore with the counterclockwise arrangement α1γ2β2α1β2 as seen from the outside of the neuron. These receptors have two agonist sites and one high affinity drug binding site specific for benzodiazepines. Recently, this receptor was postulated to assume alternative subunit stoichiometries and arrangements resulting in only one agonist site and one or even two sites for benzodiazepines. In order to force a defined subunit arrangement we expressed a combination of triple and dual concatenated subunits. Here we report that these unconventional receptors express only small current amplitudes in Xenopus oocytes. We determined agonist properties and modulation by diazepam of two of these receptors that resulted in currents large enough for a characterization, that is, β2-α1-γ2/α1-γ2 and β2-α1-γ2/β2-γ2. The first pentamer predicted to have two benzodiazepine binding sites shows similar response to diazepam as the standard receptor. As expected for both receptors with a single predicted agonist site the concentration response curves for GABA were characterized by a Hill coefficient < 1. β2-α1-γ2/β2-γ2 displayed a mM apparent GABA affinity for channel opening instead of the expected μM affinity. Based on their subunit and binding site stoichiometry, that contradicts all previous observations, their unusual functional properties and their very low expression levels in oocytes, we consider it unlikely that these unconventional receptors are expressed in neurons to an appreciable extent.
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Affiliation(s)
- Roland Baur
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
| | - Erwin Sigel
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
- * E-mail:
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22
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Chua HC, Chebib M. GABA A Receptors and the Diversity in their Structure and Pharmacology. ADVANCES IN PHARMACOLOGY 2017; 79:1-34. [DOI: 10.1016/bs.apha.2017.03.003] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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23
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A pharmacological characterization of GABA, THIP and DS2 at binary α4β3 and β3δ receptors: GABA activates β3δ receptors via the β3(+)δ(−) interface. Brain Res 2016; 1644:222-30. [DOI: 10.1016/j.brainres.2016.05.019] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Revised: 04/21/2016] [Accepted: 05/09/2016] [Indexed: 11/24/2022]
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24
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Wongsamitkul N, Baur R, Sigel E. Toward Understanding Functional Properties and Subunit Arrangement of α4β2δ γ-Aminobutyric Acid, Type A (GABAA) Receptors. J Biol Chem 2016; 291:18474-83. [PMID: 27382064 DOI: 10.1074/jbc.m116.738906] [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: 05/18/2016] [Indexed: 11/06/2022] Open
Abstract
GABAA receptors are pentameric ligand-gated channels mediating inhibitory neurotransmission in the CNS. α4βxδ GABAA receptors are extrasynaptic receptors important for tonic inhibition. The functional properties and subunit arrangement of these receptors are controversial. We predefined subunit arrangement by using subunit concatenation. α4, β2, and δ subunits were concatenated to dimeric, trimeric, and, in some cases, pentameric subunits. We constructed in total nine different receptor pentamers in at least two different ways and expressed them in Xenopus oocytes. The δ subunit was substituted in any of the five positions in the α1β2 receptor. In addition, we investigated all receptors with the 2:2:1 subunit stoichiometry for α4, β2, and δ. Several functional receptors were obtained. Interestingly, all of these receptors had very similar EC50 values for GABA in the presence of the neurosteroid 3α, 21-dihydroxy-5α-pregnan-20-one (THDOC). All functional receptors containing δ subunits were sensitive to 4-chloro-N-[2-(2-thienyl)imidazo[1,2-a]pyridin-3-yl]benzamide (DS2). Moreover, none of the receptors was affected by ethanol up to 30 mm These properties recapitulate those of non-concatenated receptors expressed from a cRNA ratio of 1:1:5 coding for α4, β2, and δ subunits. We conclude that the subunit arrangement of α4β2δ GABAA receptors is not strongly predefined but is mostly satisfying the 2:2:1 subunit stoichiometry for α4, β2, and δ subunits and that several subunit arrangements result in receptors with similar functional properties tuned to physiological conditions.
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Affiliation(s)
- Nisa Wongsamitkul
- From the Institute of Biochemistry and Molecular Medicine, University of Bern, 3012 Bern, Switzerland
| | - Roland Baur
- From the Institute of Biochemistry and Molecular Medicine, University of Bern, 3012 Bern, Switzerland
| | - Erwin Sigel
- From the Institute of Biochemistry and Molecular Medicine, University of Bern, 3012 Bern, Switzerland
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Förstera B, Castro PA, Moraga-Cid G, Aguayo LG. Potentiation of Gamma Aminobutyric Acid Receptors (GABAAR) by Ethanol: How Are Inhibitory Receptors Affected? Front Cell Neurosci 2016; 10:114. [PMID: 27199667 PMCID: PMC4858537 DOI: 10.3389/fncel.2016.00114] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Accepted: 04/20/2016] [Indexed: 01/10/2023] Open
Abstract
In recent years there has been an increase in the understanding of ethanol actions on the type A γ-aminobutyric acid chloride channel (GABAAR), a member of the pentameric ligand gated ion channels (pLGICs). However, the mechanism by which ethanol potentiates the complex is still not fully understood and a number of publications have shown contradictory results. Thus many questions still remain unresolved requiring further studies for a better comprehension of this effect. The present review concentrates on the involvement of GABAAR in the acute actions of ethanol and specifically focuses on the immediate, direct or indirect, synaptic and extra-synaptic modulatory effects. To elaborate on the immediate, direct modulation of GABAAR by acute ethanol exposure, electrophysiological studies investigating the importance of different subunits, and data from receptor mutants will be examined. We will also discuss the nature of the putative binding sites for ethanol based on structural data obtained from other members of the pLGICs family. Finally, we will briefly highlight the glycine gated chloride channel (GlyR), another member of the pLGIC family, as a suitable target for the development of new pharmacological tools.
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Affiliation(s)
- Benjamin Förstera
- Laboratory of Neurophysiology, Department of Physiology, University of Concepcion Concepcion, Chile
| | - Patricio A Castro
- Laboratory of Environmental Neurotoxicology, Department of Biomedical Sciences, Faculty of Medicine, Universidad Católica del Norte Coquimbo, Chile
| | - Gustavo Moraga-Cid
- Hindbrain Integrative Neurobiology Laboratory, Institut de Neurobiologie Alfred Fessard Gif-Sur-Yvette, France
| | - Luis G Aguayo
- Laboratory of Neurophysiology, Department of Physiology, University of Concepcion Concepcion, Chile
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Valenzuela CF, Jotty K. Mini-Review: Effects of Ethanol on GABAA Receptor-Mediated Neurotransmission in the Cerebellar Cortex--Recent Advances. THE CEREBELLUM 2016; 14:438-46. [PMID: 25575727 DOI: 10.1007/s12311-014-0639-3] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Studies from several laboratories have shown that ethanol impairs cerebellar function, in part, by altering GABAergic transmission. Here, we discuss recent advances in our understanding of the acute effects of ethanol on GABA(A) receptor-mediated neurotransmission at cerebellar cortical circuits, mainly focusing on electrophysiological studies with slices from laboratory animals. These studies have shown that acute ethanol exposure increases GABA release at molecular layer interneuron-to-Purkinje cell synapses and also at reciprocal synapses between molecular layer interneurons. In granule cells, studies with rat cerebellar slices have consistently shown that acute ethanol exposure both potentiates tonic currents mediated by extrasynaptic GABA(A) receptors and also increases the frequency of spontaneous inhibitory postsynaptic currents mediated by synaptic GABA(A) receptors. These effects have been also documented in some granule cells from mice and nonhuman primates. Currently, there are two distinct models on how ethanol produces these effects. In one model, ethanol primarily acts by directly potentiating extrasynaptic GABA(A) receptors, including a population that excites granule cell axons and stimulates glutamate release onto Golgi cells. In the other model, ethanol acts indirectly by increasing spontaneous Golgi cell firing via inhibition of the Na(+)/K(+) ATPase, a quinidine-sensitive K(+) channel, and neuronal nitric oxide synthase. It was also demonstrated that a direct inhibitory effect of ethanol on tonic currents can be unmasked under conditions of low protein kinase C activity. In the last section, we briefly discuss studies on the chronic effect of ethanol on cerebellar GABA(A) receptor-mediated transmission and highlight potential areas where future research is needed.
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Affiliation(s)
- C Fernando Valenzuela
- Department of Neurosciences, School of Medicine, University of New Mexico Health Sciences Center, Albuquerque, NM, 87131, USA,
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Herman MA, Roberto M. Cell-type-specific tonic GABA signaling in the rat central amygdala is selectively altered by acute and chronic ethanol. Addict Biol 2016; 21:72-86. [PMID: 25170988 DOI: 10.1111/adb.12181] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The central nucleus of the amygdala (CeA) is an important site for the reinforcing effects of ethanol and has been implicated in the development of alcohol dependence. The CeA GABAA receptor system is particularly vulnerable to the effects of acute and chronic ethanol exposure. Previous work in the CeA focused on ethanol and phasic GABAA receptor signaling, but tonic GABAA receptor signaling in the rat CeA remains understudied. In the present study, we found that the CeA contains two types of tonic conductance that are expressed in a cell-type-specific manner. Low threshold bursting (LTB) and some regular spiking (RS) neurons have an ongoing tonic conductance that is mediated by the α1-GABAA receptor subunit and is insensitive to acute ethanol exposure. Late spiking (LS) and a separate population of RS neurons do not display a persistent tonic conductance but have the potential for tonic signaling that is mediated by the δ-GABAA receptor subunit and can be activated by increasing the ambient GABA concentration or by acute ethanol exposure. Acute ethanol exposure differentially alters the firing discharge of different CeA cell types. Chronic ethanol exposure produces a switch in tonic signaling such that the tonic conductance in LTB and some RS neurons is lost and an ongoing tonic conductance is present in LS and a separate population of RS neurons. Collectively, these data demonstrate cell-type-specific tonic signaling in the CeA and provide new insight into how acute and chronic ethanol exposure differentially alter specific aspects of inhibitory circuitry in the CeA.
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Affiliation(s)
- Melissa Ann Herman
- Committee on the Neurobiology of Addictive Disorders; The Scripps Research Institute; La Jolla CA USA
| | - Marisa Roberto
- Committee on the Neurobiology of Addictive Disorders; The Scripps Research Institute; La Jolla CA USA
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Kuver A, Smith SS. Flumazenil decreases surface expression of α4β2δ GABAA receptors by increasing the rate of receptor internalization. Brain Res Bull 2015; 120:131-43. [PMID: 26592470 DOI: 10.1016/j.brainresbull.2015.11.015] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2015] [Revised: 11/15/2015] [Accepted: 11/18/2015] [Indexed: 11/25/2022]
Abstract
Increases in expression of α4βδ GABAA receptors (GABARs), triggered by fluctuations in the neurosteroid THP (3α-OH-5α[β]-pregnan-20-one), are associated with changes in mood and cognition. We tested whether α4βδ trafficking and surface expression would be altered by in vitro exposure to flumazenil, a benzodiazepine ligand which reduces α4βδ expression in vivo. We first determined that flumazenil (100 nM-100 μM, IC50=∼1 μM) acted as a negative modulator, reducing GABA (10 μM)-gated current in the presence of 100 nM THP (to increase receptor efficacy), assessed with whole cell patch clamp recordings of recombinant α4β2δ expressed in HEK-293 cells. Surface expression of recombinant α4β2δ receptors was detected using a 3XFLAG reporter at the C-terminus of α4 (α4F) using confocal immunocytochemical techniques following 48 h exposure of cells to GABA (10 μM)+THP (100 nM). Flumazenil (10 μM) decreased surface expression of α4F by ∼60%, while increasing its intracellular accumulation, after 48 h. Reduced surface expression of α4β2δ after flumazenil treatment was confirmed by decreases in the current responses to 100 nM of the GABA agonist gaboxadol. Flumazenil-induced decreases in surface expression of α4β2δ were prevented by the dynamin blocker, dynasore, and by leupeptin, which blocks lysosomal enzymes, suggesting that flumazenil is acting to increase endocytosis and lysosomal degradation of the receptor. Flumazenil increased the rate of receptor removal from the cell surface by 2-fold, assessed using botulinum toxin B to block insertion of new receptors. These findings may suggest new therapeutic strategies for regulation of α4β2δ expression using flumazenil.
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Affiliation(s)
- Aarti Kuver
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave, Brooklyn, NY 11203, USA
| | - Sheryl S Smith
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave, Brooklyn, NY 11203, USA.
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29
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Villumsen IS, Wellendorph P, Smart TG. Pharmacological characterisation of murine α4β1δ GABAA receptors expressed in Xenopus oocytes. BMC Neurosci 2015; 16:8. [PMID: 25887256 PMCID: PMC4359537 DOI: 10.1186/s12868-015-0148-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Accepted: 02/20/2015] [Indexed: 11/15/2022] Open
Abstract
Background GABAA receptor subunit composition has a profound effect on the receptor’s physiological and pharmacological properties. The receptor β subunit is widely recognised for its importance in receptor assembly, trafficking and post-translational modifications, but its influence on extrasynaptic GABAA receptor function is less well understood. Here, we examine the pharmacological properties of a potentially native extrasynaptic GABAA receptor that incorporates the β1 subunit, specifically composed of α4β1δ and α4β1 subunits. Results GABA activated concentration-dependent responses at α4β1δ and α4β1 receptors with EC50 values in the nanomolar to micromolar range, respectively. The divalent cations Zn2+ and Cu2+, and the β1-selective inhibitor salicylidine salicylhydrazide (SCS), inhibited GABA-activated currents at α4β1δ receptors. Surprisingly the α4β1 receptor demonstrated biphasic sensitivity to Zn2+ inhibition that may reflect variable subunit stoichiometries with differing sensitivity to Zn2+. The neurosteroid tetrahydro-deoxycorticosterone (THDOC) significantly increased GABA-initiated responses in concentrations above 30 nM for α4β1δ receptors. Conclusions With this study we report the first pharmacological characterisation of various GABAA receptor ligands acting at murine α4β1δ GABAA receptors, thereby improving our understanding of the molecular pharmacology of this receptor isoform. This study highlights some notable differences in the pharmacology of murine and human α4β1δ receptors. We consider the likelihood that the α4β1δ receptor may play a role as an extrasynaptic GABAA receptor in the nervous system.
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Affiliation(s)
- Inge S Villumsen
- Department of Neuroscience, Physiology & Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK. .,Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Fruebjergvej 3, 2100, Copenhagen, Denmark.
| | - Petrine Wellendorph
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Fruebjergvej 3, 2100, Copenhagen, Denmark.
| | - Trevor G Smart
- Department of Neuroscience, Physiology & Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK.
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Probing α4βδ GABAA receptor heterogeneity: differential regional effects of a functionally selective α4β1δ/α4β3δ receptor agonist on tonic and phasic inhibition in rat brain. J Neurosci 2015; 34:16256-72. [PMID: 25471566 DOI: 10.1523/jneurosci.1495-14.2014] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
In the present study, the orthosteric GABAA receptor (GABAAR) ligand 4,5,6,7-tetrahydroisothiazolo[5,4-c]pyridin-3-ol (Thio-THIP) was found to possess a highly interesting functional profile at recombinant human GABAARs and native rat GABAARs. Whereas Thio-THIP displayed weak antagonist activity at α1,2,5β2,3γ2S and ρ1 GABAARs and partial agonism at α6β2,3δ GABAARs expressed in Xenopus oocytes, the pronounced agonism exhibited by the compound at α4β1δ and α4β3δ GABAARs was contrasted by its negligible activity at the α4β2δ subtype. To elucidate to which extent this in vitro profile translated into functionality at native GABAARs, we assessed the effects of 100 μm Thio-THIP at synaptic and extrasynaptic receptors in principal cells of four different brain regions by slice electrophysiology. In concordance with its α6β2,3δ agonism, Thio-THIP evoked robust currents through extrasynaptic GABAARs in cerebellar granule cells. In contrast, the compound did not elicit significant currents in dentate gyrus granule cells or in striatal medium spiny neurons (MSNs), indicating predominant expression of extrasynaptic α4β2δ receptors in these cells. Interestingly, Thio-THIP evoked differential degrees of currents in ventrobasal thalamus neurons, a diversity that could arise from differential expression of extrasynaptic α4βδ subtypes in the cells. Finally, whereas 100 μm Thio-THIP did not affect the synaptic currents in ventrobasal thalamus neurons or striatal MSNs, it reduced the current amplitudes recorded from dentate gyrus granule cells, most likely by targeting perisynaptic α4βδ receptors expressed at distal dendrites of these cells. Being the first published ligand capable of discriminating between β2- and β3-containing receptor subtypes, Thio-THIP could be a valuable tool in explorations of native α4βδ GABAARs.
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31
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Krall J, Balle T, Krogsgaard-Larsen N, Sørensen TE, Krogsgaard-Larsen P, Kristiansen U, Frølund B. GABAA Receptor Partial Agonists and Antagonists: Structure, Binding Mode, and Pharmacology. DIVERSITY AND FUNCTIONS OF GABA RECEPTORS: A TRIBUTE TO HANNS MÖHLER, PART A 2015; 72:201-27. [DOI: 10.1016/bs.apha.2014.10.003] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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32
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Bhandage AK, Jin Z, Bazov I, Kononenko O, Bakalkin G, Korpi ER, Birnir B. GABA-A and NMDA receptor subunit mRNA expression is altered in the caudate but not the putamen of the postmortem brains of alcoholics. Front Cell Neurosci 2014; 8:415. [PMID: 25538565 PMCID: PMC4257153 DOI: 10.3389/fncel.2014.00415] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2014] [Accepted: 11/15/2014] [Indexed: 01/16/2023] Open
Abstract
Chronic consumption of alcohol by humans has been shown to lead to impairment of executive and cognitive functions. Here, we have studied the mRNA expression of ion channel receptors for glutamate and GABA in the dorsal striatum of post-mortem brains from alcoholics (n = 29) and normal controls (n = 29), with the focus on the caudate nucleus that is associated with the frontal cortex executive functions and automatic thinking and on the putamen area that is linked to motor cortices and automatic movements. The results obtained by qPCR assay revealed significant changes in the expression of specific excitatory ionotropic glutamate and inhibitory GABA-A receptor subunit genes in the caudate but not the putamen. Thus, in the caudate we found reduced levels of mRNAs encoding the GluN2A glutamate receptor and the δ, ε, and ρ2 GABA-A receptor subunits, and increased levels of the mRNAs encoding GluD1, GluD2, and GABA-A γ1 subunits in the alcoholics as compared to controls. Interestingly in the controls, 11 glutamate and 5 GABA-A receptor genes were more prominently expressed in the caudate than the putamen (fold-increase varied from 1.24 to 2.91). Differences in gene expression patterns between the striatal regions may underlie differences in associated behavioral outputs. Our results suggest an altered balance between caudate-mediated voluntarily controlled and automatic behaviors in alcoholics, including diminished executive control on goal-directed alcohol-seeking behavior.
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Affiliation(s)
- Amol K Bhandage
- Molecular Physiology and Neuroscience, Biomedical Center, Uppsala University Uppsala, Sweden
| | - Zhe Jin
- Molecular Physiology and Neuroscience, Biomedical Center, Uppsala University Uppsala, Sweden
| | - Igor Bazov
- Pharmacology, Institute of Biomedicine, University of Helsinki Helsinki, Finland
| | - Olga Kononenko
- Pharmacology, Institute of Biomedicine, University of Helsinki Helsinki, Finland
| | - Georgy Bakalkin
- Pharmacology, Institute of Biomedicine, University of Helsinki Helsinki, Finland
| | - Esa R Korpi
- Department of Pharmaceutical Bioscience (Biological Research on Drug Dependence), Biomedical Center, Uppsala University Uppsala, Sweden
| | - Bryndis Birnir
- Molecular Physiology and Neuroscience, Biomedical Center, Uppsala University Uppsala, Sweden
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33
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Mutations in the Gabrb1 gene promote alcohol consumption through increased tonic inhibition. Nat Commun 2014; 4:2816. [PMID: 24281383 PMCID: PMC3843143 DOI: 10.1038/ncomms3816] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2013] [Accepted: 10/24/2013] [Indexed: 01/06/2023] Open
Abstract
Alcohol-dependence is a common, complex and debilitating disorder with genetic and environmental influences. Here we show that alcohol consumption increases following mutations to the γ-aminobutyric acidA receptor (GABAAR) β1 subunit gene (Gabrb1). Using N-ethyl-N-nitrosourea mutagenesis on an alcohol-averse background (F1 BALB/cAnN × C3H/HeH), we develop a mouse model exhibiting strong heritable preference for ethanol resulting from a dominant mutation (L285R) in Gabrb1. The mutation causes spontaneous GABA ion channel opening and increases GABA sensitivity of recombinant GABAARs, coupled to increased tonic currents in the nucleus accumbens, a region long-associated with alcohol reward. Mutant mice work harder to obtain ethanol, and are more sensitive to alcohol intoxication. Another spontaneous mutation (P228H) in Gabrb1 also causes high ethanol consumption accompanied by spontaneous GABA ion channel opening and increased accumbal tonic current. Our results provide a new and important link between GABAAR function and increased alcohol consumption that could underlie some forms of alcohol abuse.
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34
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Patel B, Mortensen M, Smart TG. Stoichiometry of δ subunit containing GABA(A) receptors. Br J Pharmacol 2014; 171:985-94. [PMID: 24206220 PMCID: PMC3925037 DOI: 10.1111/bph.12514] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Revised: 10/02/2013] [Accepted: 10/24/2013] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND AND PURPOSE Although the stoichiometry of the major synaptic αβγ subunit-containing GABAA receptors has consensus support for 2α:2β:1γ, a clear view of the stoichiometry of extrasynaptic receptors containing δ subunits has remained elusive. Here we examine the subunit stoichiometry of recombinant α4β3δ receptors using a reporter mutation and a functional electrophysiological approach. EXPERIMENTAL APPROACH Using site-directed mutagenesis, we inserted a highly characterized 9' serine to leucine mutation into the second transmembrane (M2) region of α4, β3 and δ subunits that increases receptor sensitivity to GABA. Whole-cell, GABA-activated currents were recorded from HEK-293 cells co-expressing different combinations of wild-type (WT) and/or mutant α4(L297S), β3(L284S) and δ(L288S) subunits. KEY RESULTS Recombinant receptors containing one or more mutant subunits showed increased GABA sensitivity relative to WT receptors by approximately fourfold, independent of the subunit class (α, β or δ) carrying the mutation. GABA dose-response curves of cells co-expressing WT subunits with their respective L9'S mutants exhibited multiple components, with the number of discernible components enabling a subunit stoichiometry of 2α, 2β and 1δ to be deduced for α4β3δ receptors. Varying the cDNA transfection ratio by 10-fold had no significant effect on the number of incorporated δ subunits. CONCLUSIONS AND IMPLICATIONS Subunit stoichiometry is an important determinant of GABAA receptor function and pharmacology, and δ subunit-containing receptors are important mediators of tonic inhibition in several brain regions. Here we demonstrate a preferred subunit stoichiometry for α4β3δ receptors of 2α, 2β and 1δ.
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Affiliation(s)
- B Patel
- Department of Neuroscience, Physiology and Pharmacology, University College LondonLondon, UK
| | - M Mortensen
- Department of Neuroscience, Physiology and Pharmacology, University College LondonLondon, UK
| | - T G Smart
- Department of Neuroscience, Physiology and Pharmacology, University College LondonLondon, UK
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35
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Diaz MR, Morton RA. Ethanol untangles the amygdala-anxiety circuit through tonic GABA inhibition. Alcohol Clin Exp Res 2013; 38:619-23. [PMID: 24224844 DOI: 10.1111/acer.12298] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2013] [Accepted: 09/18/2013] [Indexed: 11/30/2022]
Abstract
The central amygdala (CeA) has a unique role in integrating stress and the rewarding effects of ethanol (EtOH) and plays a major role in the development of EtOH dependence via signaling of corticotropin-releasing factor (CRF). A recent report by Herman and colleagues (2013) entitled "Novel Subunit-Specific Tonic GABA Currents and Differential Effects of Ethanol in the Central Amygdala of CRF Receptor-1 Reporter Mice" is the first study to investigate inhibitory tonic currents in relation to CRF signaling in the CeA. The findings of that study significantly enhance our understanding of inhibitory tonic currents in the CeA and give insight into how EtOH may differentially affect CRF signaling within the CeA, leading to the development of EtOH dependence. This commentary will focus on the recent findings of Herman and colleagues and will discuss the effects of EtOH on the entire anxiety/emotion circuitry.
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Affiliation(s)
- Marvin R Diaz
- Department of Neurosciences, University of New Mexico Health Sciences Center, Albuquerque, New Mexico
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36
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Smith SS. α4βδ GABAA receptors and tonic inhibitory current during adolescence: effects on mood and synaptic plasticity. Front Neural Circuits 2013; 7:135. [PMID: 24027497 PMCID: PMC3759753 DOI: 10.3389/fncir.2013.00135] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Accepted: 07/28/2013] [Indexed: 11/13/2022] Open
Abstract
The onset of puberty is associated with alterations in mood as well as changes in cognitive function, which can be more pronounced in females. Puberty onset in female mice is associated with increased expression of α4βδ γ-amino-butyric acid-A (GABAA) receptors (GABARs) in CA1 hippocampus. These receptors, which normally have low expression in this central nervous system (CNS) site, emerge along the apical dendrites as well as on the dendritic spines of pyramidal neurons, adjacent to excitatory synapses where they underlie a tonic inhibition that shunts excitatory current and impairs activation of N-methyl-D-aspartate (NMDA) receptors, the trigger for synaptic plasticity. As would be expected, α4βδ expression at puberty also prevents long-term potentiation (LTP), an in vitro model of learning which is a function of network activity, induced by theta burst stimulation of the Schaffer collaterals to the CA1 hippocampus. The expression of these receptors also impairs spatial learning in a hippocampal-dependent task. These impairments are not seen in δ knock-out (-/-) mice, implicating α4βδ GABARs. α4βδ GABARs are also a sensitive target for steroids such as THP ([allo]pregnanolone or 3α-OH-5α[β]-pregnan-20-one), which are dependent upon the polarity of GABAergic current. It is well-known that THP can increase depolarizing current gated by α4βδ GABARs, but more recent data suggest that THP can reduce hyperpolarizing current by accelerating receptor desensitization. At puberty, THP reduces the hyperpolarizing GABAergic current, which removes the shunting inhibition that impairs synaptic plasticity and learning at this time. However, THP, a stress steroid, also increases anxiety, via its action at α4βδ GABARs because it is not seen in δ(-/-) mice. These findings will be discussed as well as their relevance to changes in mood and cognition at puberty, which can be a critical period for certain types of learning and when anxiety disorders and mood swings can emerge.
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Affiliation(s)
- Sheryl S Smith
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center Brooklyn, NY 11203, USA.
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37
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Novel subunit-specific tonic GABA currents and differential effects of ethanol in the central amygdala of CRF receptor-1 reporter mice. J Neurosci 2013; 33:3284-98. [PMID: 23426657 DOI: 10.1523/jneurosci.2490-12.2013] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The central nucleus of the amygdala (CeA) is an important integrative site for the reinforcing effects of drugs of abuse, such as ethanol. Activation of corticotropin-releasing factor type 1 (CRF1) receptors in the CeA plays a critical role in the development of ethanol dependence, but these neurons remain uncharacterized. Using CRF1:GFP reporter mice and a combined electrophysiological/immunohistochemical approach, we found that CRF1 neurons exhibit an α1 GABA(A) receptor subunit-mediated tonic conductance that is driven by action potential-dependent GABA release. In contrast, unlabeled CeA neurons displayed a δ subunit-mediated tonic conductance that is enhanced by ethanol. Ethanol increased the firing discharge of CRF1 neurons and decreased the firing discharge of unlabeled CeA neurons. Retrograde tracing studies indicate that CeA CRF1 neurons project into the bed nucleus of the stria terminalis. Together, these data demonstrate subunit-specific tonic signaling and provide mechanistic insight into the specific effects of ethanol on CeA microcircuitry.
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Abstract
The GABA(A) receptors are the major inhibitory neurotransmitter receptors in mammalian brain. Each isoform consists of five homologous or identical subunits surrounding a central chloride ion-selective channel gated by GABA. How many isoforms of the receptor exist is far from clear. GABA(A) receptors located in the postsynaptic membrane mediate neuronal inhibition that occurs in the millisecond time range; those located in the extrasynaptic membrane respond to ambient GABA and confer long-term inhibition. GABA(A) receptors are responsive to a wide variety of drugs, e.g. benzodiazepines, which are often used for their sedative/hypnotic and anxiolytic effects.
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Affiliation(s)
- Erwin Sigel
- Institute of Biochemistry and Molecular Medicine, University of Bern, CH-3012 Bern, Switzerland.
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39
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Karim N, Wellendorph P, Absalom N, Bang LH, Jensen ML, Hansen MM, Lee HJ, Johnston GA, Hanrahan JR, Chebib M. Low nanomolar GABA effects at extrasynaptic α4β1/β3δ GABAA receptor subtypes indicate a different binding mode for GABA at these receptors. Biochem Pharmacol 2012; 84:549-57. [DOI: 10.1016/j.bcp.2012.05.017] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2012] [Revised: 05/18/2012] [Accepted: 05/21/2012] [Indexed: 10/28/2022]
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40
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Brickley SG, Mody I. Extrasynaptic GABA(A) receptors: their function in the CNS and implications for disease. Neuron 2012; 73:23-34. [PMID: 22243744 DOI: 10.1016/j.neuron.2011.12.012] [Citation(s) in RCA: 494] [Impact Index Per Article: 41.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/18/2011] [Indexed: 12/30/2022]
Abstract
Over the past two decades, research has identified extrasynaptic GABA(A) receptor populations that enable neurons to sense the low ambient GABA concentrations present in the extracellular space in order to generate a form of tonic inhibition not previously considered in studies of neuronal excitability. The importance of this tonic inhibition in regulating states of consciousness is highlighted by the fact that extrasynaptic GABA(A) receptors (GABA(A)Rs) are believed to be key targets for anesthetics, sleep-promoting drugs, neurosteroids, and alcohol. The neurosteroid sensitivity of these extrasynaptic GABA(A)Rs may explain their importance in stress-, ovarian cycle-, and pregnancy-related mood disorders. Moreover, disruptions in network dynamics associated with schizophrenia, epilepsy, and Parkinson's disease may well involve alterations in the tonic GABA(A)R-mediated conductance. Extrasynaptic GABA(A)Rs may therefore present a therapeutic target for treatment of these diseases, with the potential to enhance cognition and aid poststroke functional recovery.
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Affiliation(s)
- Stephen G Brickley
- Division of Cell & Molecular Biology, South Kensington Campus, Imperial College, London SW7 2AZ, UK.
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41
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Jin Z, Bazov I, Kononenko O, Korpi ER, Bakalkin G, Birnir B. Selective Changes of GABA(A) Channel Subunit mRNAs in the Hippocampus and Orbitofrontal Cortex but not in Prefrontal Cortex of Human Alcoholics. Front Cell Neurosci 2012; 5:30. [PMID: 22319468 PMCID: PMC3249692 DOI: 10.3389/fncel.2011.00030] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Accepted: 12/14/2011] [Indexed: 11/13/2022] Open
Abstract
Alcohol dependence is a common chronic relapsing disorder. The development of alcohol dependence has been associated with changes in brain GABA(A) channel-mediated neurotransmission and plasticity. We have examined mRNA expression of the GABA(A) channel subunit genes in three brain regions in individuals with or without alcohol dependence using quantitative real-time PCR assay. The levels of selective GABA(A) channel subunit mRNAs were altered in specific brain regions in alcoholic subjects. Significant increase in the α1, α4, α5, β1, and γ1 subunit mRNAs in the hippocampal dentate gyrus region, and decrease in the β2 and δ subunit mRNAs in the orbitofrontal cortex were identified whereas no changes in the dorsolateral prefrontal cortex were detected. The data increase our understanding of the role of GABA(A) channels in the development of alcohol dependence.
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Affiliation(s)
- Zhe Jin
- The Division of Molecular Physiology and Neuroscience, Department of Neuroscience, Uppsala University Uppsala, Sweden
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Meera P, Wallner M, Otis TS. Molecular basis for the high THIP/gaboxadol sensitivity of extrasynaptic GABA(A) receptors. J Neurophysiol 2011; 106:2057-64. [PMID: 21795619 DOI: 10.1152/jn.00450.2011] [Citation(s) in RCA: 140] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Extrasynaptic GABA(A) receptors (eGABARs) allow ambient GABA to tonically regulate neuronal excitability and are implicated as targets for ethanol and anesthetics. These receptors are thought to be heteropentameric proteins made up of two α subunits-either α4 or α6-two β2 or β3 subunits, and one δ subunit. The GABA analog 4,5,6,7-tetrahydroisoxazolo (5,4-c)pyridin-3(-ol) (THIP) has been proposed as a selective ligand for eGABARs. Behavioral and in vitro studies suggest that eGABARs have nanomolar affinity for THIP; however, all published studies on recombinant versions of eGABARs report micromolar affinities. Here, we examine THIP sensitivity of native eGABARs on cerebellar neurons and on reconstituted GABARs in heterologous systems. Concentration-response data for THIP, obtained from cerebellar granule cells and molecular layer interneurons in wild-type and δ subunit knockout slices, confirm that submicromolar THIP sensitivity requires δ subunits. In recombinant experiments, we find that δ subunit coexpression leads to receptors activated by nanomolar THIP concentrations (EC(50) of 30-50 nM for α4β3δ and α6β3δ), a sensitivity almost 1,000-fold higher than receptors formed by α4/6 and β3 subunits. In contrast, γ2 subunit expression significantly reduces THIP sensitivity. Even when δ subunit cDNA or cRNA was supplied in excess, high- and low-sensitivity THIP responses were often apparent, indicative of variable mixtures of low-affinity αβ and high-affinity αβδ receptors. We conclude that δ subunit incorporation into GABARs leads to a dramatic increase in THIP sensitivity, a defining feature that accounts for the unique behavioral and neurophysiological properties of THIP.
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Affiliation(s)
- Pratap Meera
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, USA
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Howard RJ, Slesinger PA, Davies DL, Das J, Trudell JR, Harris RA. Alcohol-binding sites in distinct brain proteins: the quest for atomic level resolution. Alcohol Clin Exp Res 2011; 35:1561-73. [PMID: 21676006 DOI: 10.1111/j.1530-0277.2011.01502.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Defining the sites of action of ethanol on brain proteins is a major prerequisite to understanding the molecular pharmacology of this drug. The main barrier to reaching an atomic-level understanding of alcohol action is the low potency of alcohols, ethanol in particular, which is a reflection of transient, low-affinity interactions with their targets. These mechanisms are difficult or impossible to study with traditional techniques such as radioligand binding or spectroscopy. However, there has been considerable recent progress in combining X-ray crystallography, structural modeling, and site-directed mutagenesis to define the sites and mechanisms of action of ethanol and related alcohols on key brain proteins. We review such insights for several diverse classes of proteins including inwardly rectifying potassium, transient receptor potential, and neurotransmitter-gated ion channels, as well as protein kinase C epsilon. Some common themes are beginning to emerge from these proteins, including hydrogen bonding of the hydroxyl group and van der Waals interactions of the methylene groups of ethanol with specific amino acid residues. The resulting binding energy is proposed to facilitate or stabilize low-energy state transitions in the bound proteins, allowing ethanol to act as a "molecular lubricant" for protein function. We discuss evidence for characteristic, discrete alcohol-binding sites on protein targets, as well as evidence that binding to some proteins is better characterized by an interaction region that can accommodate multiple molecules of ethanol.
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Affiliation(s)
- Rebecca J Howard
- Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Texas 77812, USA.
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Abstract
GABAA receptors mediate the majority of the fast inhibition in the mature brain and play an important role in the pathogenesis of many neurological and psychiatric disorders. The αβδ GABAA receptor localizes extra- or perisynaptically and mediates GABAergic tonic inhibition. Compared with synaptically localized αβγ receptors, αβδ receptors are more sensitive to GABA, display relatively slower desensitization and exhibit lower efficacy to GABA agonism. Interestingly, αβδ receptors can be positively modulated by a variety of structurally different compounds, even at saturating GABA concentrations. This review focuses on allosteric modulation of recombinant αβδ receptor currents and αβδ receptor-mediated tonic currents by anesthetics and ethanol. The possible mechanisms for the positive modulation of αβδ receptors by these compounds will also be discussed.
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Meera P, Olsen RW, Otis TS, Wallner M. Alcohol- and alcohol antagonist-sensitive human GABAA receptors: tracking δ subunit incorporation into functional receptors. Mol Pharmacol 2010; 78:918-24. [PMID: 20699325 DOI: 10.1124/mol.109.062687] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
GABA(A) receptors (GABA(A)Rs) have long been a focus as targets for alcohol actions. Recent work suggests that tonic GABAergic inhibition mediated by extrasynaptic δ subunit-containing GABA(A)Rs is uniquely sensitive to ethanol and enhanced at concentrations relevant for human alcohol consumption. Ethanol enhancement of recombinant α4β3δ receptors is blocked by the behavioral alcohol antagonist 8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid ethyl ester (Ro15-4513), suggesting that EtOH/Ro15-4513-sensitive receptors mediate important behavioral alcohol actions. Here we confirm alcohol/alcohol antagonist sensitivity of α4β3δ receptors using human clones expressed in a human cell line and test the hypothesis that discrepant findings concerning the high alcohol sensitivity of these receptors are due to difficulties incorporating δ subunits into functional receptors. To track δ subunit incorporation, we used a functional tag, a single amino acid change (H68A) in a benzodiazepine binding residue in which a histidine in the δ subunit is replaced by an alanine residue found at the homologous position in γ subunits. We demonstrate that the δH68A substitution confers diazepam sensitivity to otherwise diazepam-insensitive α4β3δ receptors. The extent of enhancement of α4β3δH68A receptors by 1 μM diazepam, 30 mM EtOH, and 1 μM β-carboline-3-carboxy ethyl ester (but not 1 μM Zn(2+) block) is correlated in individual recordings, suggesting that δ subunit incorporation into recombinant GABA(A)Rs varies from cell to cell and that this variation accounts for the variable pharmacological profile. These data are consistent with the notion that δ subunit-incorporation is often incomplete in recombinant systems yet is necessary for high ethanol sensitivity, one of the features of native δ subunit-containing GABA(A)Rs.
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Affiliation(s)
- Pratap Meera
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095-1735, USA
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Baur R, Kaur KH, Sigel E. Diversity of structure and function of alpha1alpha6beta3delta GABAA receptors: comparison with alpha1beta3delta and alpha6beta3delta receptors. J Biol Chem 2010; 285:17398-405. [PMID: 20382738 DOI: 10.1074/jbc.m110.108670] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
delta subunit-containing gamma-aminobutyric acid, type A (GABA(A))receptors are expressed extrasynaptically and mediate tonic inhibition. In cerebellar granule cells, they often form receptors together with alpha(1) and/or alpha(6) subunits. We were interested in determining the architecture of receptors containing both subunits. We predefined the subunit arrangement of several different GABA(A) receptor pentamers by concatenation. These receptors composed of alpha(1), alpha(6), beta(3), and delta subunits were expressed in Xenopus oocytes. Currents elicited in response to GABA were determined in the presence and absence of 3alpha,21-dihydroxy-5alpha-pregnan-20-one (THDOC) or ethanol, or currents were elicited by 4,5,6,7-tetrahydroisoxazolo[5,4-c]-pyridin-3-ol (THIP). Several subunit configurations formed active channels. We therefore conclude that delta can assume multiple positions in a receptor pentamer made up of alpha(1), alpha(6), beta(3), and delta subunits. The different receptors differ in their functional properties. Functional expression of one receptor type was only evident in the combined presence of the neurosteroid THDOC with the channel agonist GABA. Most, but not all, receptors active with GABA/THDOC responded to THIP. None of the receptors was modulated by ethanol concentrations up to 30 mm. Several observations point to a preferred position of delta subunits between two alpha subunits in alpha(1)alpha(6)beta(3)delta receptors. This property is shared by alpha(1)beta(3)delta and alpha(6)beta(3)delta receptors, but there are differences in the additionally expressed isoforms.
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Affiliation(s)
- Roland Baur
- Institute of Biochemistry and Molecular Medicine, University of Bern, CH-3012 Bern, Switzerland
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Wagoner KR, Czajkowski C. Stoichiometry of expressed alpha(4)beta(2)delta gamma-aminobutyric acid type A receptors depends on the ratio of subunit cDNA transfected. J Biol Chem 2010; 285:14187-94. [PMID: 20233712 DOI: 10.1074/jbc.m110.104257] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The gamma-aminobutyric acid type A receptor (GABA(A)R) is the target of many depressants, including benzodiazepines, anesthetics, and alcohol. Although the highly prevalent alphabetagamma GABA(A)R subtype mediates the majority of fast synaptic inhibition in the brain, receptors containing delta subunits also play a key role, mediating tonic inhibition and the actions of endogenous neurosteroids and alcohol. However, the fundamental properties of delta-containing GABA(A)Rs, such as subunit stoichiometry, are not well established. To determine subunit stoichiometry of expressed delta-containing GABA(A)Rs, we inserted the alpha-bungarotoxin binding site tag in the alpha(4), beta(2), and delta subunit N termini. An enhanced green fluorescent protein tag was also inserted into the beta(2) subunit to shift its molecular weight, allowing us to separate subunits using SDS-PAGE. Tagged alpha(4)beta(2)delta GABA(A)Rs were expressed in HEK293T cells using various ratios of subunit cDNA, and receptor subunit stoichiometry was determined by quantitating fluorescent alpha-bungarotoxin bound to each subunit on Western blots of surface immunopurified tagged GABA(A)Rs. The results demonstrate that the subunit stoichiometry of alpha(4)beta(2)delta GABA(A)Rs is regulated by the ratio of subunit cDNAs transfected. Increasing the ratio of delta subunit cDNA transfected increased delta subunit incorporation into surface receptors with a concomitant decrease in beta(2) subunit incorporation. Because receptor subunit stoichiometry can directly influence GABA(A)R pharmacological and functional properties, considering how the transfection protocols used affect subunit stoichiometry is essential when studying heterologously expressed alpha(4)beta(2)delta GABA(A)Rs. Successful bungarotoxin binding site tagging of GABA(A)R subunits is a novel tool with which to accurately quantitate subunit stoichiometry and will be useful for monitoring GABA(A)R trafficking in live cells.
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Affiliation(s)
- Kelly R Wagoner
- Molecular and Cellular Pharmacology Graduate Program, University of Wisconsin at Madison, Madison, Wisconsin 53711, USA
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Use of concatamers to study GABAA receptor architecture and function: application to delta-subunit-containing receptors and possible pitfalls. Biochem Soc Trans 2010; 37:1338-42. [PMID: 19909272 DOI: 10.1042/bst0371338] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Many membrane proteins, including the GABA(A) [GABA (gamma-aminobutyric acid) type A] receptors, are oligomers often built from different subunits. As an example, the major adult isoform of the GABA(A) receptor is a pentamer built from three different subunits. Theoretically, co-expression of three subunits may result in many different receptor pentamers. Subunit concatenation allows us to pre-define the relative arrangement of the subunits. This method may thus be used to study receptor architecture, but also the nature of binding sites. Indeed, it made possible the discovery of a novel benzodiazepine site. We use here subunit concatenation to study delta-subunit-containing GABA(A) receptors. We provide evidence for the formation of different functional subunit arrangements in recombinant alpha(1)beta(3)delta and alpha(6)beta(3)delta receptors. As with all valuable techniques, subunit concatenation has also some pitfalls. Most of these can be avoided by carefully titrating and minimizing the length of the linker sequences joining the two linked subunits and avoiding inclusion of the signal sequence of all but the N-terminal subunit of a multi-subunit construct. Maybe the most common error found in the literature is that low expression can be overcome by simply overloading the expression system with genetic information. As some concatenated constructs result by themselves in a low level of expression, this erroneous assembly leading to receptor function may be promoted by overloading the expression system and leads to wrong conclusions.
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