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Douglass AM, Resch JM, Madara JC, Kucukdereli H, Yizhar O, Grama A, Yamagata M, Yang Z, Lowell BB. Neural basis for fasting activation of the hypothalamic-pituitary-adrenal axis. Nature 2023; 620:154-162. [PMID: 37495689 PMCID: PMC11168300 DOI: 10.1038/s41586-023-06358-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2022] [Accepted: 06/21/2023] [Indexed: 07/28/2023]
Abstract
Fasting initiates a multitude of adaptations to allow survival. Activation of the hypothalamic-pituitary-adrenal (HPA) axis and subsequent release of glucocorticoid hormones is a key response that mobilizes fuel stores to meet energy demands1-5. Despite the importance of the HPA axis response, the neural mechanisms that drive its activation during energy deficit are unknown. Here, we show that fasting-activated hypothalamic agouti-related peptide (AgRP)-expressing neurons trigger and are essential for fasting-induced HPA axis activation. AgRP neurons do so through projections to the paraventricular hypothalamus (PVH), where, in a mechanism not previously described for AgRP neurons, they presynaptically inhibit the terminals of tonically active GABAergic afferents from the bed nucleus of the stria terminalis (BNST) that otherwise restrain activity of corticotrophin-releasing hormone (CRH)-expressing neurons. This disinhibition of PVHCrh neurons requires γ-aminobutyric acid (GABA)/GABA-B receptor signalling and potently activates the HPA axis. Notably, stimulation of the HPA axis by AgRP neurons is independent of their induction of hunger, showing that these canonical 'hunger neurons' drive many distinctly different adaptations to the fasted state. Together, our findings identify the neural basis for fasting-induced HPA axis activation and uncover a unique means by which AgRP neurons activate downstream neurons: through presynaptic inhibition of GABAergic afferents. Given the potency of this disinhibition of tonically active BNST afferents, other activators of the HPA axis, such as psychological stress, may also work by reducing BNST inhibitory tone onto PVHCrh neurons.
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Affiliation(s)
- Amelia M Douglass
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
| | - Jon M Resch
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
- Department of Neuroscience and Pharmacology, University of Iowa Carver College of Medicine, Iowa City, IA, USA
| | - Joseph C Madara
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
| | - Hakan Kucukdereli
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
| | - Ofer Yizhar
- Departments of Brain Sciences and Molecular Neuroscience, Weizmann Institute of Science, Rehovot, Israel
| | - Abhinav Grama
- Center for Brain Science, Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA, USA
| | - Masahito Yamagata
- Center for Brain Science, Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA, USA
| | - Zongfang Yang
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
| | - Bradford B Lowell
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA.
- Program in Neuroscience, Harvard Medical School, Boston, MA, USA.
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Akk G, Germann AL, Sugasawa Y, Pierce SR, Evers AS, Steinbach JH. Enhancement of Muscimol Binding and Gating by Allosteric Modulators of the GABA A Receptor: Relating Occupancy to State Functions. Mol Pharmacol 2020; 98:303-313. [PMID: 32873746 PMCID: PMC7472144 DOI: 10.1124/molpharm.120.000066] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Accepted: 07/17/2020] [Indexed: 01/08/2023] Open
Abstract
Muscimol is a psychoactive isoxazole derived from the mushroom Amanita muscaria and a potent orthosteric agonist of the GABAA receptor. The binding of [3H]muscimol has been used to evaluate the distribution of GABAA receptors in the brain, and studies of modulation of [3H]muscimol binding by allosteric GABAergic modulators such as barbiturates and steroid anesthetics have provided insight into the modes of action of these drugs on the GABAA receptor. It has, however, not been feasible to directly apply interaction parameters derived from functional studies to describe the binding of muscimol to the receptor. Here, we employed the Monod-Wyman-Changeux concerted transition model to analyze muscimol binding isotherms. We show that the binding isotherms from recombinant α1β3 GABAA receptors can be qualitatively predicted using electrophysiological data pertaining to properties of receptor activation and desensitization in the presence of muscimol. The model predicts enhancement of [3H]muscimol binding in the presence of the steroids allopregnanolone and pregnenolone sulfate, although the steroids interact with distinct sites and either enhance (allopregnanolone) or reduce (pregnenolone sulfate) receptor function. We infer that the concerted transition model can be used to link radioligand binding and electrophysiological data. SIGNIFICANCE STATEMENT: The study employs a three-state resting-active-desensitized model to link radioligand binding and electrophysiological data. We show that the binding isotherms can be qualitatively predicted using parameters estimated in electrophysiological experiments and that the model accurately predicts the enhancement of [3H]muscimol binding in the presence of the potentiating steroid allopregnanolone and the inhibitory steroid pregnenolone sulfate.
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Affiliation(s)
- Gustav Akk
- Department of Anesthesiology (G.A., A.L.G., Y.S., S.R.P., A.S.E., J.H.S.) and the Taylor Family Institute for Innovative Psychiatric Research (G.A., A.S.E., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Allison L Germann
- Department of Anesthesiology (G.A., A.L.G., Y.S., S.R.P., A.S.E., J.H.S.) and the Taylor Family Institute for Innovative Psychiatric Research (G.A., A.S.E., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Yusuke Sugasawa
- Department of Anesthesiology (G.A., A.L.G., Y.S., S.R.P., A.S.E., J.H.S.) and the Taylor Family Institute for Innovative Psychiatric Research (G.A., A.S.E., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Spencer R Pierce
- Department of Anesthesiology (G.A., A.L.G., Y.S., S.R.P., A.S.E., J.H.S.) and the Taylor Family Institute for Innovative Psychiatric Research (G.A., A.S.E., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Alex S Evers
- Department of Anesthesiology (G.A., A.L.G., Y.S., S.R.P., A.S.E., J.H.S.) and the Taylor Family Institute for Innovative Psychiatric Research (G.A., A.S.E., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Joe Henry Steinbach
- Department of Anesthesiology (G.A., A.L.G., Y.S., S.R.P., A.S.E., J.H.S.) and the Taylor Family Institute for Innovative Psychiatric Research (G.A., A.S.E., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
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Serrano-Regal MP, Bayón-Cordero L, Ordaz RP, Garay E, Limon A, Arellano RO, Matute C, Sánchez-Gómez MV. Expression and Function of GABA Receptors in Myelinating Cells. Front Cell Neurosci 2020; 14:256. [PMID: 32973453 PMCID: PMC7472887 DOI: 10.3389/fncel.2020.00256] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2020] [Accepted: 07/24/2020] [Indexed: 01/14/2023] Open
Abstract
Myelin facilitates the fast transmission of nerve impulses and provides metabolic support to axons. Differentiation of oligodendrocyte progenitor cells (OPCs) and Schwann cell (SC) precursors is critical for myelination during development and myelin repair in demyelinating disorders. Myelination is tightly controlled by neuron-glia communication and requires the participation of a wide repertoire of signals, including neurotransmitters such as glutamate, ATP, adenosine, or γ-aminobutyric acid (GABA). GABA is the main inhibitory neurotransmitter in the central nervous system (CNS) and it is also present in the peripheral nervous system (PNS). The composition and function of GABA receptors (GABARs) are well studied in neurons, while their nature and role in glial cells are still incipient. Recent studies demonstrate that GABA-mediated signaling mechanisms play relevant roles in OPC and SC precursor development and function, and stand out the implication of GABARs in oligodendrocyte (OL) and SC maturation and myelination. In this review, we highlight the evidence supporting the novel role of GABA with an emphasis on the molecular identity of the receptors expressed in these glial cells and the possible signaling pathways involved in their actions. GABAergic signaling in myelinating cells may have potential implications for developing novel reparative therapies in demyelinating diseases.
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Affiliation(s)
- Mari Paz Serrano-Regal
- Laboratory of Neurobiology, Achucarro Basque Center for Neuroscience, Leioa, Spain
- Department of Neurosciences, University of the Basque Country (UPV/EHU), Leioa, Spain
- Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED), Leioa, Spain
| | - Laura Bayón-Cordero
- Laboratory of Neurobiology, Achucarro Basque Center for Neuroscience, Leioa, Spain
- Department of Neurosciences, University of the Basque Country (UPV/EHU), Leioa, Spain
- Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED), Leioa, Spain
| | - Rainald Pablo Ordaz
- Laboratorio de Neurofisiología Celular, Instituto de Neurobiología, Universidad Nacional Autónoma de México, Juriquilla, Mexico
| | - Edith Garay
- Laboratorio de Neurofisiología Celular, Instituto de Neurobiología, Universidad Nacional Autónoma de México, Juriquilla, Mexico
| | - Agenor Limon
- Department of Neurology, Mitchell Center for Neurodegenerative Diseases, University of Texas Medical Branch, Galveston, TX, United States
| | - Rogelio O. Arellano
- Laboratorio de Neurofisiología Celular, Instituto de Neurobiología, Universidad Nacional Autónoma de México, Juriquilla, Mexico
| | - Carlos Matute
- Laboratory of Neurobiology, Achucarro Basque Center for Neuroscience, Leioa, Spain
- Department of Neurosciences, University of the Basque Country (UPV/EHU), Leioa, Spain
- Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED), Leioa, Spain
| | - María Victoria Sánchez-Gómez
- Laboratory of Neurobiology, Achucarro Basque Center for Neuroscience, Leioa, Spain
- Department of Neurosciences, University of the Basque Country (UPV/EHU), Leioa, Spain
- Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED), Leioa, Spain
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4
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GABAergic mediation of hippocampal theta rhythm induced by stimulation of the vagal nerve. Brain Res Bull 2019; 147:110-123. [DOI: 10.1016/j.brainresbull.2019.02.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Accepted: 02/18/2019] [Indexed: 12/22/2022]
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Zhu S, Noviello CM, Teng J, Walsh RM, Kim JJ, Hibbs RE. Structure of a human synaptic GABA A receptor. Nature 2018; 559:67-72. [PMID: 29950725 PMCID: PMC6220708 DOI: 10.1038/s41586-018-0255-3] [Citation(s) in RCA: 325] [Impact Index Per Article: 54.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Accepted: 05/17/2018] [Indexed: 11/08/2022]
Abstract
Fast inhibitory neurotransmission in the brain is principally mediated by the neurotransmitter GABA (γ-aminobutyric acid) and its synaptic target, the type A GABA receptor (GABAA receptor). Dysfunction of this receptor results in neurological disorders and mental illnesses including epilepsy, anxiety and insomnia. The GABAA receptor is also a prolific target for therapeutic, illicit and recreational drugs, including benzodiazepines, barbiturates, anaesthetics and ethanol. Here we present high-resolution cryo-electron microscopy structures of the human α1β2γ2 GABAA receptor, the predominant isoform in the adult brain, in complex with GABA and the benzodiazepine site antagonist flumazenil, the first-line clinical treatment for benzodiazepine overdose. The receptor architecture reveals unique heteromeric interactions for this important class of inhibitory neurotransmitter receptor. This work provides a template for understanding receptor modulation by GABA and benzodiazepines, and will assist rational approaches to therapeutic targeting of this receptor for neurological disorders and mental illness.
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Affiliation(s)
- Shaotong Zhu
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Colleen M Noviello
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Jinfeng Teng
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Richard M Walsh
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Jeong Joo Kim
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Ryan E Hibbs
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
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6
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Zilles K, Palomero-Gallagher N. Multiple Transmitter Receptors in Regions and Layers of the Human Cerebral Cortex. Front Neuroanat 2017; 11:78. [PMID: 28970785 PMCID: PMC5609104 DOI: 10.3389/fnana.2017.00078] [Citation(s) in RCA: 85] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Accepted: 08/24/2017] [Indexed: 01/16/2023] Open
Abstract
We measured the densities (fmol/mg protein) of 15 different receptors of various transmitter systems in the supragranular, granular and infragranular strata of 44 areas of visual, somatosensory, auditory and multimodal association systems of the human cerebral cortex. Receptor densities were obtained after labeling of the receptors using quantitative in vitro receptor autoradiography in human postmortem brains. The mean density of each receptor type over all cortical layers and of each of the three major strata varies between cortical regions. In a single cortical area, the multi-receptor fingerprints of its strata (i.e., polar plots, each visualizing the densities of multiple different receptor types in supragranular, granular or infragranular layers of the same cortical area) differ in shape and size indicating regional and laminar specific balances between the receptors. Furthermore, the three strata are clearly segregated into well definable clusters by their receptor fingerprints. Fingerprints of different cortical areas systematically vary between functional networks, and with the hierarchical levels within sensory systems. Primary sensory areas are clearly separated from all other cortical areas particularly by their very high muscarinic M2 and nicotinic α4β2 receptor densities, and to a lesser degree also by noradrenergic α2 and serotonergic 5-HT2 receptors. Early visual areas of the dorsal and ventral streams are segregated by their multi-receptor fingerprints. The results are discussed on the background of functional segregation, cortical hierarchies, microstructural types, and the horizontal (layers) and vertical (columns) organization in the cerebral cortex. We conclude that a cortical column is composed of segments, which can be assigned to the cortical strata. The segments differ by their patterns of multi-receptor balances, indicating different layer-specific signal processing mechanisms. Additionally, the differences between the strata-and area-specific fingerprints of the 44 areas reflect the segregation of the cerebral cortex into functionally and topographically definable groups of cortical areas (visual, auditory, somatosensory, limbic, motor), and reveals their hierarchical position (primary and unimodal (early) sensory to higher sensory and finally to multimodal association areas). HighlightsDensities of transmitter receptors vary between areas of human cerebral cortex. Multi-receptor fingerprints segregate cortical layers. The densities of all examined receptor types together reach highest values in the supragranular stratum of all areas. The lowest values are found in the infragranular stratum. Multi-receptor fingerprints of entire areas and their layers segregate functional systems Cortical types (primary sensory, motor, multimodal association) differ in their receptor fingerprints.
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Affiliation(s)
- Karl Zilles
- Research Centre Jülich, Institute of Neuroscience and Medicine (INM-1)Jülich, Germany.,Department of Psychiatry, Psychotherapy, and Psychosomatics, Medical Faculty, RWTH Aachen, and JARA-Translational Brain MedicineAachen, Germany
| | - Nicola Palomero-Gallagher
- Research Centre Jülich, Institute of Neuroscience and Medicine (INM-1)Jülich, Germany.,Department of Psychiatry, Psychotherapy, and Psychosomatics, Medical Faculty, RWTH Aachen, and JARA-Translational Brain MedicineAachen, Germany
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7
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Novel Molecule Exhibiting Selective Affinity for GABA A Receptor Subtypes. Sci Rep 2017; 7:6230. [PMID: 28740086 PMCID: PMC5524711 DOI: 10.1038/s41598-017-05966-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 06/06/2017] [Indexed: 01/06/2023] Open
Abstract
Aminoquinoline derivatives were evaluated against a panel of receptors/channels/transporters in radioligand binding experiments. One of these derivatives (DCUK-OEt) displayed micromolar affinity for brain γ-aminobutyric acid type A (GABAA) receptors. DCUK-OEt was shown to be a positive allosteric modulator (PAM) of GABA currents with α1β2γ2, α1β3γ2, α5β3γ2 and α1β3δ GABAA receptors, while having no significant PAM effect on αβ receptors or α1β1γ2, α1β2γ1, α4β3γ2 or α4β3δ receptors. DCUK-OEt modulation of α1β2γ2 GABAA receptors was not blocked by flumazenil. The subunit requirements for DCUK-OEt actions distinguished DCUK-OEt from other currently known modulators of GABA function (e.g., anesthetics, neurosteroids or ethanol). Simulated docking of DCUK-OEt at the GABAA receptor suggested that its binding site may be at the α + β- subunit interface. In slices of the central amygdala, DCUK-OEt acted primarily on extrasynaptic GABAA receptors containing the α1 subunit and generated increases in extrasynaptic “tonic” current with no significant effect on phasic responses to GABA. DCUK-OEt is a novel chemical structure acting as a PAM at particular GABAA receptors. Given that neurons in the central amygdala responding to DCUK-OEt were recently identified as relevant for alcohol dependence, DCUK-OEt should be further evaluated for the treatment of alcoholism.
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Michałowski MA, Kraszewski S, Mozrzymas JW. Binding site opening by loop C shift and chloride ion-pore interaction in the GABAAreceptor model. Phys Chem Chem Phys 2017; 19:13664-13678. [DOI: 10.1039/c7cp00582b] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Molecular dynamics simulations of the shut α1β2γ2GABAAheteropentamer receptor homology model reveal significant differences between intersubunit interfaces (ligand binding G1, G2 and non-binding) compared to homomeric receptor assemblies and possible ion interaction sites in the top part of the transmembrane domain (TMD).
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Affiliation(s)
- M. A. Michałowski
- Laboratory of Neuroscience
- Department of Biophysics
- Wrocław Medical University
- ul. Chałubińskiego 3a
- 50-358 Wrocław
| | - S. Kraszewski
- Department of Biomedical Engineering
- Faculty of Fundamental Problems of Technology
- Wroclaw University of Science and Technology
- Wyb. Wyspiańskiego 27
- 50-370 Wrocław
| | - J. W. Mozrzymas
- Laboratory of Neuroscience
- Department of Biophysics
- Wrocław Medical University
- ul. Chałubińskiego 3a
- 50-358 Wrocław
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9
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Farb DH, Ratner MH. Targeting the modulation of neural circuitry for the treatment of anxiety disorders. Pharmacol Rev 2015; 66:1002-32. [PMID: 25237115 DOI: 10.1124/pr.114.009126] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Anxiety disorders are a major public health concern. Here, we examine the familiar area of anxiolysis in the context of a systems-level understanding that will hopefully lead to revealing an underlying pharmacological connectome. The introduction of benzodiazepines nearly half a century ago markedly improved the treatment of anxiety disorders. These agents reduce anxiety rapidly by allosterically enhancing the postsynaptic actions of GABA at inhibitory type A GABA receptors but side effects limit their use in chronic anxiety disorders. Selective serotonin reuptake inhibitors and serotonin/norepinephrine reuptake inhibitors have emerged as an effective first-line alternative treatment of such anxiety disorders. However, many individuals are not responsive and side effects can be limiting. Research into a relatively new class of agents known as neurosteroids has revealed novel modulatory sites and mechanisms of action that are providing insights into the pathophysiology of certain anxiety disorders, potentially bridging the gap between the GABAergic and serotonergic circuits underlying anxiety. However, translating the pharmacological activity of compounds targeted to specific receptor subtypes in rodent models of anxiety to effective therapeutics in human anxiety has not been entirely successful. Since modulating any one of several broad classes of receptor targets can produce anxiolysis, we posit that a systems-level discovery platform combined with an individualized medicine approach based on noninvasive brain imaging would substantially advance the development of more effective therapeutics.
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Affiliation(s)
- David H Farb
- Laboratory of Molecular Neurobiology, Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Boston, Massachusetts
| | - Marcia H Ratner
- Laboratory of Molecular Neurobiology, Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Boston, Massachusetts
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10
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Age- and sex-related characteristics of tonic GABA currents in the rat substantia nigra pars reticulata. Neurochem Res 2015; 40:747-57. [PMID: 25645446 DOI: 10.1007/s11064-015-1523-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2014] [Revised: 01/09/2015] [Accepted: 01/13/2015] [Indexed: 12/19/2022]
Abstract
Previous studies have shown that the pharmacologic effects of GABAergic drugs and the postsynaptic phasic GABAAergic inhibitory responses in the anterior part of the rat substantia nigra pars reticulata (SNRA) are age- and sex-specific. Here, we investigate whether there are age- and sex-related differences in the expression of the δ GABAA receptor (GABAAR) subunit and GABAAR mediated tonic currents. We have used δ-specific immunochemistry and whole cell patch clamp to study GABAAR mediated tonic currents in the SNRA of male and female postnatal day (PN) PN5-9, PN11-16, and PN25-32 rats. We observed age-related decline, but no sex-specific changes, in bicuculline (BIM) sensitive GABAAR tonic current density, which correlated with the decline in δ subunit in the SNRA between PN15 and 30. Furthermore, we show that the GABAAR tonic currents can be modified by muscimol (GABAAR agonist; partial GABACR agonist), THIP (4,5,6,7-tetrahydroisoxazolo (5,4-c)pyridin-3-ol: α4β3δ GABAARs agonist and GABACR antagonist), and zolpidem (α1-subunit selective GABAAR agonist) in age- and sex-dependent manner specific for each drug. We propose that the emergence of the GABAAR-sensitive anticonvulsant effects of the rat SNRA during development may depend upon the developmental decline in tonic GABAergic inhibition of the activity of rat SNRA neurons, although other sex-specific factors are also involved.
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11
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Johnston GAR. Muscimol as an ionotropic GABA receptor agonist. Neurochem Res 2014; 39:1942-7. [PMID: 24473816 DOI: 10.1007/s11064-014-1245-y] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2014] [Revised: 01/19/2014] [Accepted: 01/21/2014] [Indexed: 12/17/2022]
Abstract
Muscimol, a psychoactive isoxazole from Amanita muscaria and related mushrooms, has proved to be a remarkably selective agonist at ionotropic receptors for the inhibitory neurotransmitter GABA. This historic overview highlights the discovery and development of muscimol and related compounds as a GABA agonist by Danish and Australian neurochemists. Muscimol is widely used as a ligand to probe GABA receptors and was the lead compound in the development of a range of GABAergic agents including nipecotic acid, tiagabine, 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol, (Gaboxadol(®)) and 4-PIOL.
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Affiliation(s)
- Graham A R Johnston
- Adrien Albert Laboratory of Medicinal Chemistry, School of Medical Sciences (Pharmacology), The University of Sydney, Sydney, NSW, 2006, Australia,
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12
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Dostalova Z, Zhou X, Liu A, Zhang X, Zhang Y, Desai R, Forman SA, Miller KW. Human α1β3γ2L gamma-aminobutyric acid type A receptors: High-level production and purification in a functional state. Protein Sci 2013; 23:157-66. [PMID: 24288268 DOI: 10.1002/pro.2401] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Revised: 11/25/2013] [Accepted: 11/26/2013] [Indexed: 02/01/2023]
Abstract
Gamma-aminobutyric acid type A receptors (GABA(A)Rs) are the most important inhibitory chloride ion channels in the central nervous system and are major targets for a wide variety of drugs. The subunit compositions of GABA(A)Rs determine their function and pharmacological profile. GABAA Rs are heteropentamers of subunits, and (α1)2 (β3)2 (γ2L)1 is a common subtype. Biochemical and biophysical studies of GABA(A)Rs require larger quantities of receptors of defined subunit composition than are currently available. We previously reported high-level production of active human α1β3 GABA(A)R using tetracycline-inducible stable HEK293 cells. Here we extend the strategy to receptors containing three different subunits. We constructed a stable tetracycline-inducible HEK293-TetR cell line expressing human (N)-FLAG-α1β3γ2L-(C)-(GGS)3 GK-1D4 GABA(A)R. These cells achieved expression levels of 70-90 pmol [(3)H]muscimol binding sites/15-cm plate at a specific activity of 15-30 pmol/mg of membrane protein. Incorporation of the γ2 subunit was confirmed by the ratio of [(3)H]flunitrazepam to [(3)H]muscimol binding sites and sensitivity of GABA-induced currents to benzodiazepines and zinc. The α1β3γ2L GABA(A)Rs were solubilized in dodecyl-D-maltoside, purified by anti-FLAG affinity chromatography and reconstituted in CHAPS/asolectin at an overall yield of ∼ 30%. Typical purifications yielded 1.0-1.5 nmoles of [(3)H]muscimol binding sites/60 plates. Receptors with similar properties could be purified by 1D4 affinity chromatography with lower overall yield. The composition of the purified, reconstituted receptors was confirmed by ligand binding, Western blot, and proteomics. Allosteric interactions between etomidate and [(3)H]muscimol binding were maintained in the purified state.
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Affiliation(s)
- Zuzana Dostalova
- Department of Anesthesia and Critical Care, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, 02114; Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, 02115
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Prototypic GABA(A) receptor agonist muscimol acts preferentially through forebrain high-affinity binding sites. Neuropsychopharmacology 2010; 35:999-1007. [PMID: 20032968 PMCID: PMC2823376 DOI: 10.1038/npp.2009.203] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Muscimol has been regarded as a universal agonist for all gamma-aminobutyric acid type A receptor (GABA(A)-R) subtypes. However, brain regional distribution of muscimol's high-affinity binding sites greatly differs from those of other binding sites of the GABA(A)-R. To test whether behavioral effects of muscimol correlated with the density of high-affinity [(3)H]muscimol binding, we examined several GABA(A)-R subunit gene-modified mouse lines: alpha1, alpha4, or delta-knockouts (KO), alpha4+delta-double KO, and Thy1.2 promoter-driven alpha6 transgenic mice (Thy1alpha6). We determined the high-affinity [(3)H]muscimol binding in brain sections by quantitative autoradiography and sedative/ataxic effects induced in vivo by muscimol using a constant speed rotarod. alpha4-KO mice had reduced [(3)H]muscimol binding in the caudate-putamen, thalamus, and hippocampus, and were less sensitive to the behavioral impairment by muscimol. Similarly, delta-KO mice also had reduced binding to forebrain regions and a lower behavioral sensitivity to muscimol than their wild-type controls. In contrast, alpha1-KO mice had unaltered behavioral sensitivity to muscimol and unaltered [(3)H]muscimol binding, even though previous studies have demonstrated dramatically reduced binding to various other GABA(A)-R sites in these mice. Finally, Thy1alpha6 mice exhibited increased behavioral sensitivity to muscimol, and to another direct GABA-site agonist gaboxadol, and increased [(3)H]muscimol binding in the cerebral cortex and hippocampus. Thus, the differences in sedative and motor-impairing actions of muscimol in various mouse models correlated with the level of forebrain high-affinity [(3)H]muscimol binding. These data suggest that a small special population of GABA(A)-Rs, most likely extrasynaptic non-alpha1-containing receptors, strongly contributes to the in vivo pharmacological effects of muscimol.
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Abstract
GABA(A) receptors are sensitive to subtle changes in the environment in both early-life and adulthood. These neurochemical responses to stress in adulthood are sex-dependent. Acute stress induces rapid changes in GABA(A) receptors in experimental animals, with the direction of the changes varying according to the sex of the animals and the stress-paradigm studied. These rapid alterations are of particular interest as they provide an example of fast neurotransmitter system plasticity that may be mediated by stress-induced increases in neurosteroids, perhaps via effects on phosphorylation and/or receptor trafficking. Interestingly, some studies have also provided evidence for long-lasting changes in GABA(A) receptors as a result of exposure to stressors in early-life. The short- and long-term stress sensitivity of the GABAergic system implicates GABA(A) receptors in the non-genetic etiology of psychiatric illnesses such as depression and schizophrenia in which stress may be an important factor.
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Affiliation(s)
- Kelly J Skilbeck
- Department of Pharmacology, University of Sydney, Sydney, New South Wales, Australia
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Calabrese EJ. An Assessment of Anxiolytic Drug Screening Tests: Hormetic Dose Responses Predominate. Crit Rev Toxicol 2008; 38:489-542. [DOI: 10.1080/10408440802014238] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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Sex-differences and stress: Effects on regional high and low affinity [3H]GABA binding. Neurochem Int 2008; 52:1212-9. [DOI: 10.1016/j.neuint.2008.01.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2007] [Revised: 12/17/2007] [Accepted: 01/02/2008] [Indexed: 11/19/2022]
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Søgaard R, Werge TM, Bertelsen C, Lundbye C, Madsen KL, Nielsen CH, Lundbaek JA. GABAAReceptor Function is Regulated by Lipid Bilayer Elasticity†. Biochemistry 2006; 45:13118-29. [PMID: 17059229 DOI: 10.1021/bi060734+] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Docosahexaenoic acid (DHA) and other polyunsaturated fatty acids (PUFAs) promote GABA(A) receptor [(3)H]-muscimol binding, and DHA increases the rate of GABA(A) receptor desensitization. Triton X-100, a structurally unrelated amphiphile, similarly promotes [(3)H]-muscimol binding. The mechanism(s) underlying these effects are poorly understood. DHA and Triton X-100, at concentrations that affect GABA(A) receptor function, increase the elasticity of lipid bilayers measured as decreased bilayer stiffness using gramicidin channels as molecular force transducers. We have previously shown that membrane protein function can be regulated by amphiphile-induced changes in bilayer elasticity and hypothesized that GABA(A) receptors could be similarly regulated. We therefore studied the effects of four structurally unrelated amphiphiles that decrease bilayer stiffness (Triton X-100, octyl-beta-glucoside, capsaicin, and DHA) on GABA(A) receptor function in mammalian cells. All the compounds promoted GABA(A) receptor [(3)H]-muscimol binding by increasing the binding capacity of high-affinity binding without affecting the associated equilibrium binding constant. A semiquantitative analysis found a similar quantitative relation between the effects on bilayer stiffness and [(3)H]-muscimol binding. Membrane cholesterol depletion, which also decreases bilayer stiffness, similarly promoted [(3)H]-muscimol binding. In whole-cell voltage-clamp experiments, Triton X-100, octyl-beta-glucoside, capsaicin, and DHA all reduced the peak amplitude of the GABA-induced currents and increased the rate of receptor desensitization. The effects of the amphiphiles did not correlate with the expected changes in monolayer spontaneous curvature. We conclude that GABA(A) receptor function is regulated by lipid bilayer elasticity. PUFAs may generally regulate membrane protein function by affecting the elasticity of the host lipid bilayer.
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Affiliation(s)
- Rikke Søgaard
- Research Institute of Biological Psychiatry, Sct. Hans Hospital, Boserupvej 2, DK-4000 Roskilde, Denmark
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Velísek L, Velísková J, Giorgi FS, Moshé SL. Sex-specific control of flurothyl-induced tonic-clonic seizures by the substantia nigra pars reticulata during development. Exp Neurol 2006; 201:203-11. [PMID: 16730708 DOI: 10.1016/j.expneurol.2006.04.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2006] [Revised: 03/14/2006] [Accepted: 04/01/2006] [Indexed: 01/13/2023]
Abstract
The substantia nigra pars reticulata (SNR) plays an important age- and sex-specific role in control of clonic seizures. Its involvement in control of tonic-clonic seizures is contradictory. We investigated the role of the SNR in the tonic-clonic seizures induced in male, female and neonatally castrated male rats using flurothyl. In adult female rats, vaginal impedance determined the changes in progesterone/estrogen ratio. Rats at various postnatal ages received infusions of muscimol or vehicle in the SNRanterior or SNRposterior. Furthermore, in 15-day-old (P15) and adult male rats, ZAPA (a GABA(A) receptor agonist) or AP7 (an NMDA receptor antagonist) was infused. The developmental profile of tonic-clonic seizure threshold differed between male and female rats possibly due to early postnatal testosterone surge in male rats. On the other hand, changing estrogen/progesterone ratio in cycling adult female rats had no effect on seizure threshold. Intranigral muscimol had proconvulsant effects on tonic-clonic seizures only in immature rats, and this effect was dependent on the perinatal testosterone surge. ZAPA had anticonvulsant effects in P15 rats but was not effective in adult rats. Only AP7 had anticonvulsant effects in both adult and P15 rats. Results indicate that thresholds for flurothyl-induced tonic-clonic seizures develop under the control of postnatal testosterone. Although GABAergic inhibition in the SNR affects tonic-clonic seizures in developing rats, only the NMDA antagonist had consistent anticonvulsant effects throughout development.
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Affiliation(s)
- Libor Velísek
- Department of Neurology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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Sotiriou E, Papatheodoropoulos C, Angelatou F. Differential expression of gamma-aminobutyric acid--a receptor subunits in rat dorsal and ventral hippocampus. J Neurosci Res 2006; 82:690-700. [PMID: 16273537 DOI: 10.1002/jnr.20670] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Recent data demonstrate weaker gamma-aminobutyric acid (GABA)-ergic inhibition in ventral (VH) compared with dorsal (DH) hippocampus. Therefore, we examined possible differences regarding the GABAA receptors between VH and DH as follows: 1) the expression of the GABAA receptor subunits (alpha1/2/4/5, beta1/2/3, gamma2, delta) mRNA and protein and 2) the quantitative distribution and kinetic parameters of [3H] muscimol (GABAA receptor agonist) binding. VH compared with DH showed: 1) lower levels for alpha1, beta2, gamma2 but higher levels for alpha2 and beta1 subunits in CA1, CA2, and CA3, the differences being more pronounced in CA1 region; in the CA1 region, the mRNA levels of alpha5 were higher, whereas those of alpha4 subunit were slightly lower; in dentate gyrus, the mRNA levels of alpha4, beta3, and delta subunits were significantly lower, presumably suggesting a lower expression of the alpha4/beta3/delta receptor subtype; and 2) lower levels of [3H]muscimol binding, with the lowest value observed in CA1, apparently resulting from weaker binding affinity, insofar as the KD values were higher in VH, whereas the Bmax values were similar between DH and VH. The differences in the subunit expression and the lower affinity of GABAA receptor binding observed predominantly in the CA1 region of VH suggest that the alpha1/beta2/gamma2 GABAA receptor subtype dominates in DH, and the alpha2/beta1/gamma2 subtype prevails in VH. This could underlie the lower GABAA-mediated inhibition observed in VH and, to some extent, explain 1) the higher liability of VH for epileptic activity and 2) the differential involvement of DH and VH in cognitive and emotional processes.
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Affiliation(s)
- Evangelos Sotiriou
- Physiology Department, Medical School, University of Patras, Patras, Greece
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Machu TK, Dillon GH, Huang R, Lovinger DM, Leidenheimer NJ. Temperature: an important experimental variable in studying PKC modulation of ligand-gated ion channels. Brain Res 2006; 1086:1-8. [PMID: 16626662 DOI: 10.1016/j.brainres.2006.01.091] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2005] [Revised: 12/14/2005] [Accepted: 01/20/2006] [Indexed: 10/24/2022]
Abstract
Amphibian oocyte and mammalian heterologous expression systems are often used to investigate the function of recombinant ion channels using electrophysiological techniques. Although both systems have yielded important information, the results obtained in these systems are sometimes conflicting. Oocytes and mammalian cells differ in their physiological temperature requirements. While room temperature is within the physiological temperature range for oocytes, this temperature is far below that required by mammalian cells. Since electrophysiological studies are often performed in both oocytes and mammalian cells at room temperature, we sought to determine if recording temperature could be a factor in some disparate results obtained in these cell types. For these studies, we examined phorbol ester modulation of GABA(A) and glycine receptors. Consistent with the literature, at room temperature, PMA (phorbol 12-myristate 13-acetate) produced a large reproducible decrease in the peak amplitude of GABA and glycine-gated currents in Xenopus oocytes. In contrast, PMA was ineffective in modulating these heterologously expressed receptors at room temperature in human embryonic kidney (HEK) 293 cells. However, when electrophysiological experiments were performed at 35 degrees C in HEK 293 cells, PMA decreased the function of these receptors. Our results indicate that the temperature at which electrophysiological studies are conducted is an important experimental variable. To determine the extent to which electrophysiological recordings are performed at physiological temperatures in HEK 293 cells, a PubMed search was conducted using the search terms "patch clamp" and "HEK" for the years 2003-2004. This search revealed that only 15% of the patch clamp studies were reported to have been conducted in the temperature range of 32-37 degrees C. The results of our study indicate that temperature is an important experimental variable that requires rational consideration in the design of electrophysiological experiments.
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Affiliation(s)
- Tina K Machu
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Forth Worth, 76203-1067, USA
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Deng C, Huang XF. Increased density of GABAA receptors in the superior temporal gyrus in schizophrenia. Exp Brain Res 2005; 168:587-90. [PMID: 16362364 DOI: 10.1007/s00221-005-0290-9] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2005] [Accepted: 11/05/2005] [Indexed: 01/18/2023]
Abstract
The superior temporal gyrus (STG) is strongly implicated in the pathophysiology of schizophrenia, particularly with regards to auditory hallucinations. In a previous study we reported a decrease in the density of M1 and M2/M4 muscarinic receptors in the STG in schizophrenia. In this study, we investigated the density of GABA(A) receptors in the left STG of schizophrenia patients compared to control subjects. We used quantitative autoradiography to investigate the binding of the agonist [(3)H] muscimol to GABA(A )receptors in the STG. A significantly higher density of [(3)H] muscimol binding was observed in the upper three quarters of the STG grey matter (corresponding to layers I-IV) than in the lower one-quarter (layers V-VI) in both groups. A significant increase (about 30%, P<0.05) in binding of [(3)H] muscimol was clearly observed in schizophrenia patients compared to control subjects. There were no significant correlations between [(3)H] muscimol binding density and age, post-mortem interval, brain pH or final recorded antipsychotic drug use. These results suggest an increase of GABA(A) receptor densities in the STG of schizophrenia patients.
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Affiliation(s)
- Chao Deng
- Department of Biomedical Science, University of Wollongong, 2522 Wollongong, NSW, Australia.
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García DA, Bujons J, Vale C, Suñol C. Allosteric positive interaction of thymol with the GABAA receptor in primary cultures of mouse cortical neurons. Neuropharmacology 2005; 50:25-35. [PMID: 16185724 DOI: 10.1016/j.neuropharm.2005.07.009] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2005] [Revised: 06/27/2005] [Accepted: 07/20/2005] [Indexed: 02/06/2023]
Abstract
Thymol is a naturally occurring phenolic monoterpene known for its anti-microbial and anti-oxidant properties. It is used in dental practice and in anaesthetic halothane preparations. Recent studies have reported enhanced GABA(A) receptor-operated chloride channel activity and increased binding affinity of [(3)H]flunitrazepam in the presence of thymol. In the present work, we more closely examined the pharmacological action of thymol on the native GABA(A) receptor by using primary cultures of cortical neurons. Thymol enhanced GABA-induced (5 microM) chloride influx at concentrations lower than those exhibiting direct activity in the absence of GABA (EC(50) = 12 microM and 135 microM, respectively). This direct effect was inhibited by competitive and non-competitive GABA(A) receptor antagonists. Thymol increased [(3)H]flunitrazepam binding (EC(50) = 131 microM) and showed a tendency to increase [(3)H]muscimol binding. These results confirm that thymol is a positive allosteric modulator of the GABA(A) receptor. The thymol structural analogues menthol and cymene, which lack an aromatic ring or a hydroxyl group, did not affect [(3)H]flunitrazepam binding. Using a pharmacophoric model that includes a hydrogen bond donor group as well as an aromatic ring with two aliphatic substituents, we propose to demonstrate the molecular essential features of these compounds to interact with GABA(A) receptors. Thymol (0-1 mM) did not affect cellular viability.
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Affiliation(s)
- Daniel A García
- Department of Neurochemistry, Institut d'Investigacions Biomèdiques de Barcelona, CSIC-IDIBAPS, Rosselló 161, Spain
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Böhme I, Rabe H, Lüddens H. Four amino acids in the alpha subunits determine the gamma-aminobutyric acid sensitivities of GABAA receptor subtypes. J Biol Chem 2004; 279:35193-200. [PMID: 15199051 DOI: 10.1074/jbc.m405653200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
GABA(A) receptors, mediators of fast inhibitory neurotransmission, are heteropentameric assemblies from a large array of subunits. Differences in the sensitivity of receptor subtypes to endogenous GABA may permit subunit-dependent finely tuned responsiveness to the same GABAergic inputs. Using both radioligand binding and electrophysiology combined with mutagenesis, we identified a domain of four amino acids within the alpha subunits that mediates the distinct sensitivities to GABA allowing their selective switch between alphabeta3gamma2 combinations. Replacing this domain in alpha3 by the corresponding segments of alpha1-alpha5 resulted in mutant receptors displaying the GABA EC(50) values of the respective wild-type receptors. Vice versa, the alpha3 motif forced the low sensitivity to GABA of alpha3 upon alpha1beta3gamma2, alpha4beta3gamma2, and alpha5beta3gamma2. Binding of the GABA agonist [(3)H]muscimol was not affected by the exchange of the motif between alpha1 and alpha3 subunits. Thus, the equilibrium binding pocket is maintained upon replacement of the four amino acids. Taken together our data suggest that the identified motifs contribute to a structure involved in the transduction of the binding signal rather than to the binding itself.
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Affiliation(s)
- Ingo Böhme
- Laboratory of Molecular Biology, Department of Psychiatry, University of Mainz, Untere Zahlbacher Strasse 8, 55131 Mainz, Germany
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