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Cha DS, Kleine N, Teopiz KM, Di Vincenzo JD, Ho R, Galibert SL, Samra A, Zilm SPM, Cha RH, d'Andrea G, Gill H, Ceban F, Meshkat S, Wong S, Le GH, Kwan ATH, Rosenblat JD, Rhee TG, Mansur RB, McIntyre RS. The efficacy of zuranolone in postpartum depression and major depressive disorder: a review & number needed to treat (NNT) analysis. Expert Opin Pharmacother 2024; 25:5-14. [PMID: 38164653 DOI: 10.1080/14656566.2023.2298340] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Accepted: 12/19/2023] [Indexed: 01/03/2024]
Abstract
INTRODUCTION Major depressive disorder (MDD) is a common and debilitating mental illness. Postpartum depression (PPD) impacts women globally and is one of the most common complications of childbirth that is underdiagnosed and undertreated, adversely impacting the mental health of women, children, and partners.Available antidepressant medications require weeks to months before showing effect. In this setting, zuranolone, an oral neuroactive steroid and a positive allosteric modulator of GABAA receptors, is an attractive alternative as a rapid-acting antidepressant treatment. AREAS COVERED This article reviews zuranolone (SAGE217), focusing on available clinical studies in individuals with PPD and MDD. This paper adds to the extant literature by presenting the efficacy data as Number Needed to Treat (NNT) to facilitate indirect comparisons with other antidepressants. EXPERT OPINION Zuranolone is a novel rapid-acting (i.e. two week course) oral antidepressant for the treatment of adults with PPD with ongoing clinical trials evaluating its efficacy in adults with MDD. Zuranolone is well tolerated with no significant safety concerns in any clinical trials completed to date. Zuranolone will be scheduled by the Drug Enforcement Agency (DEA).
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Affiliation(s)
- Danielle S Cha
- Royal Brisbane & Women's Hospital, Mental Health Services, Brisbane, Queensland, Australia
- School of Clinical Medicine - Royal Brisbane Clinical Unit, University of Queensland, Brisbane, Queensland, Australia
- Brain and Cognition Foundation, Toronto, ON, Canada
- Mood Disorders Psychopharmacology Department, Toronto Western Hospital, University Health Network, Toronto, ON, Canada
- Royal Brisbane & Women's Hospital, Metro North Hospital and Health Service, Brisbane, Queensland, Australia
| | - Nicholas Kleine
- Mood Disorders Psychopharmacology Department, Toronto Western Hospital, University Health Network, Toronto, ON, Canada
- Department of Pharmacology, University of Toronto, Toronto, Canada
| | - Kayla M Teopiz
- Mood Disorders Psychopharmacology Department, Toronto Western Hospital, University Health Network, Toronto, ON, Canada
- Department of Pharmacology, University of Toronto, Toronto, Canada
| | - Joshua D Di Vincenzo
- Brain and Cognition Foundation, Toronto, ON, Canada
- Mood Disorders Psychopharmacology Department, Toronto Western Hospital, University Health Network, Toronto, ON, Canada
| | - Roger Ho
- Institute for Health Innovation and Technology (iHealthtech), National University of Singapore, Singapore, Singapore
- Department of Neuroscience, Imaging and Clinical Sciences, University "G. d'Annunzio", Chieti, Italy
| | - Stephanie L Galibert
- Department of Obstetrics and Gynaecology, Logan Hospital, Logan, Queensland, Australia
| | - Amrita Samra
- Royal Brisbane & Women's Hospital, Metro North Hospital and Health Service, Brisbane, Queensland, Australia
| | - Samuel P M Zilm
- Royal Brisbane & Women's Hospital, Metro North Hospital and Health Service, Brisbane, Queensland, Australia
| | - Rebekah H Cha
- Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Giacomo d'Andrea
- Department of Neuroscience, Imaging and Clinical Sciences, University "G. D'Annunzio", Chieti, Italy
| | - Hartej Gill
- Brain and Cognition Foundation, Toronto, ON, Canada
- Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada
| | - Felicia Ceban
- Brain and Cognition Foundation, Toronto, ON, Canada
- Mood Disorders Psychopharmacology Department, Toronto Western Hospital, University Health Network, Toronto, ON, Canada
- Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada
| | | | - Sabrina Wong
- Brain and Cognition Foundation, Toronto, ON, Canada
- Mood Disorders Psychopharmacology Department, Toronto Western Hospital, University Health Network, Toronto, ON, Canada
| | - Gia Han Le
- Brain and Cognition Foundation, Toronto, ON, Canada
- Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada
| | - Angela T H Kwan
- Brain and Cognition Foundation, Toronto, ON, Canada
- Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada
| | - Joshua D Rosenblat
- Brain and Cognition Foundation, Toronto, ON, Canada
- Mood Disorders Psychopharmacology Department, Toronto Western Hospital, University Health Network, Toronto, ON, Canada
- Department of Psychiatry, University of Toronto
| | - Taeho Greg Rhee
- Department of Psychiatry, Yale School of Medicine, New Haven, CT, USA
- Department of Public Health Sciences, University of Connecticut School of Medicine, Farmington, CT, USA
| | - Rodrigo B Mansur
- Brain and Cognition Foundation, Toronto, ON, Canada
- Mood Disorders Psychopharmacology Department, Toronto Western Hospital, University Health Network, Toronto, ON, Canada
| | - Roger S McIntyre
- Department of Psychiatry and Pharmacology, University of Toronto, Toronto, Canada
- Brain and Cognition Discovery Foundation (BCDF), Toronto, ON, Canada
- Board Chair, Depression and Bipolar Support Alliance (DBSA) Board of Directors, Chicago, IL, USA
- Guangzhou Medical University, Guangzhou, GD, China
- College of Medicine, Korea University, Seoul, Republic of Korea
- College of Medicine, University of the Philippines, Manila, Philippines
- State University of New York (SUNY) Upstate Medical University, Syracuse, NY, USA
- Department of Psychiatry and Neurosciences, University of California School of Medicine, Riverside, CA, USA
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Li Z, Wu Q, Peng P, Wu M, Liu S, Liu T. Efficacy and safety of zuranolone for the treatment of depression: A systematic review and meta-analysis. Psychiatry Res 2024; 331:115640. [PMID: 38029628 DOI: 10.1016/j.psychres.2023.115640] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2023] [Revised: 11/19/2023] [Accepted: 11/25/2023] [Indexed: 12/01/2023]
Abstract
Major depressive disorder (MDD) and postpartum depression (PPD) are common and burdensome conditions. This study aims to evaluate the efficacy and safety of zuranolone, a neuroactive steroid γ-aminobutyric acid type A receptors-positive allosteric modulator, in treating MDD and PPD. A comprehensive literature search was conducted until September 2023, identifying seven randomized controlled trials (RCTs). The results demonstrated that zuranolone significantly decreased Hamilton Rating Scale for Depression (HAM-D) scores in patients with PPD or MDD at day 15 (concluding the 14-day course) and day 42-45 (4 weeks after treatment cessation) compared with the placebo, albeit exhibiting a diminishing trend. Moreover, a higher percentage of patients with PPD or MDD achieved HAM-D response and remission with zuranolone treatment compared with placebo at day 15. However, zuranolone did not significantly increase the proportion of MDD patients achieving HAM-D remission at 42/43 days. Adverse events (AEs) such as somnolence, dizziness, and sedation were linked to zuranolone, with a higher but not statistically significant rate of discontinuation due to AEs in the zuranolone group. Overall, our findings support the rapid antidepressant effects of zuranolone in MDD and PPD, along with a relatively favorable safety and tolerability. Large-scale longitudinal RCTs are needed to evaluate the long-term efficacy of zuranolone.
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Affiliation(s)
- Zejun Li
- Department of Psychiatry, National Clinical Research Center for Mental Disorders, and National Center for Mental Disorders, The Second Xiangya Hospital of Central South University, 139 Middle Renmin Road, Changsha, Hunan 410011, China
| | - Qiuxia Wu
- Department of Psychiatry, National Clinical Research Center for Mental Disorders, and National Center for Mental Disorders, The Second Xiangya Hospital of Central South University, 139 Middle Renmin Road, Changsha, Hunan 410011, China
| | - Pu Peng
- Department of Psychiatry, National Clinical Research Center for Mental Disorders, and National Center for Mental Disorders, The Second Xiangya Hospital of Central South University, 139 Middle Renmin Road, Changsha, Hunan 410011, China
| | - Min Wu
- Department of Psychiatry, National Clinical Research Center for Mental Disorders, and National Center for Mental Disorders, The Second Xiangya Hospital of Central South University, 139 Middle Renmin Road, Changsha, Hunan 410011, China
| | - Shouhuan Liu
- Department of Psychiatry, First Affiliated Hospital of Kunming Medical University, 295 Xichang Road, Kunming, Yunnan 650032, China.
| | - Tieqiao Liu
- Department of Psychiatry, National Clinical Research Center for Mental Disorders, and National Center for Mental Disorders, The Second Xiangya Hospital of Central South University, 139 Middle Renmin Road, Changsha, Hunan 410011, China.
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Clayton AH, Lasser R, Parikh SV, Iosifescu DV, Jung J, Kotecha M, Forrestal F, Jonas J, Kanes SJ, Doherty J. Zuranolone for the Treatment of Adults With Major Depressive Disorder: A Randomized, Placebo-Controlled Phase 3 Trial. Am J Psychiatry 2023; 180:676-684. [PMID: 37132201 DOI: 10.1176/appi.ajp.20220459] [Citation(s) in RCA: 17] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
OBJECTIVE This study assessed the efficacy and safety of a 14-day treatment course of once-daily zuranolone 50 mg, an investigational oral positive allosteric modulator of the γ-aminobutyric acid type A (GABAA) receptor, for the treatment of major depressive disorder. METHODS Patients 18-64 years of age with severe major depressive disorder were enrolled in this randomized, double-blind, placebo-controlled trial. Patients self-administered zuranolone 50 mg or placebo once daily for 14 days. The primary endpoint was change from baseline in total score on the 17-item Hamilton Depression Rating Scale (HAM-D) at day 15. Safety and tolerability were assessed by incidence of adverse events. RESULTS Of 543 randomized patients, 534 (266 in the zuranolone group, 268 in the placebo group) constituted the full analysis set. Compared with patients in the placebo group, patients in the zuranolone group demonstrated a statistically significant improvement in depressive symptoms at day 15 (least squares mean change from baseline HAM-D score, -14.1 vs. -12.3). Numerically greater improvements in depressive symptoms for zuranolone versus placebo were observed by day 3 (least squares mean change from baseline HAM-D score, -9.8 vs. -6.8), which were sustained at all visits throughout the treatment and follow-up periods of the study (through day 42, with the difference remaining nominally significant through day 12). Two patients in each group experienced a serious adverse event; nine patients in the zuranolone group and four in the placebo group discontinued treatment due to adverse events. CONCLUSIONS Zuranolone at 50 mg/day elicited a significantly greater improvement in depressive symptoms at day 15, with a rapid time to effect (day 3). Zuranolone was generally well tolerated, with no new safety findings compared with previously studied lower dosages. These findings support the potential of zuranolone in treating adults with major depressive disorder.
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Affiliation(s)
- Anita H Clayton
- Department of Psychiatry and Neurobehavioral Sciences, University of Virginia School of Medicine, Charlottesville (Clayton); Sage Therapeutics, Cambridge, Mass. (Lasser, Jung, Jonas, Kanes, Doherty); Department of Psychiatry, University of Michigan, Ann Arbor (Parikh); Nathan Kline Institute for Psychiatric Research and Department of Psychiatry, New York University School of Medicine, New York (Iosifescu); Biogen, Cambridge, Mass. (Kotecha, Forrestal)
| | - Robert Lasser
- Department of Psychiatry and Neurobehavioral Sciences, University of Virginia School of Medicine, Charlottesville (Clayton); Sage Therapeutics, Cambridge, Mass. (Lasser, Jung, Jonas, Kanes, Doherty); Department of Psychiatry, University of Michigan, Ann Arbor (Parikh); Nathan Kline Institute for Psychiatric Research and Department of Psychiatry, New York University School of Medicine, New York (Iosifescu); Biogen, Cambridge, Mass. (Kotecha, Forrestal)
| | - Sagar V Parikh
- Department of Psychiatry and Neurobehavioral Sciences, University of Virginia School of Medicine, Charlottesville (Clayton); Sage Therapeutics, Cambridge, Mass. (Lasser, Jung, Jonas, Kanes, Doherty); Department of Psychiatry, University of Michigan, Ann Arbor (Parikh); Nathan Kline Institute for Psychiatric Research and Department of Psychiatry, New York University School of Medicine, New York (Iosifescu); Biogen, Cambridge, Mass. (Kotecha, Forrestal)
| | - Dan V Iosifescu
- Department of Psychiatry and Neurobehavioral Sciences, University of Virginia School of Medicine, Charlottesville (Clayton); Sage Therapeutics, Cambridge, Mass. (Lasser, Jung, Jonas, Kanes, Doherty); Department of Psychiatry, University of Michigan, Ann Arbor (Parikh); Nathan Kline Institute for Psychiatric Research and Department of Psychiatry, New York University School of Medicine, New York (Iosifescu); Biogen, Cambridge, Mass. (Kotecha, Forrestal)
| | - JungAh Jung
- Department of Psychiatry and Neurobehavioral Sciences, University of Virginia School of Medicine, Charlottesville (Clayton); Sage Therapeutics, Cambridge, Mass. (Lasser, Jung, Jonas, Kanes, Doherty); Department of Psychiatry, University of Michigan, Ann Arbor (Parikh); Nathan Kline Institute for Psychiatric Research and Department of Psychiatry, New York University School of Medicine, New York (Iosifescu); Biogen, Cambridge, Mass. (Kotecha, Forrestal)
| | - Mona Kotecha
- Department of Psychiatry and Neurobehavioral Sciences, University of Virginia School of Medicine, Charlottesville (Clayton); Sage Therapeutics, Cambridge, Mass. (Lasser, Jung, Jonas, Kanes, Doherty); Department of Psychiatry, University of Michigan, Ann Arbor (Parikh); Nathan Kline Institute for Psychiatric Research and Department of Psychiatry, New York University School of Medicine, New York (Iosifescu); Biogen, Cambridge, Mass. (Kotecha, Forrestal)
| | - Fiona Forrestal
- Department of Psychiatry and Neurobehavioral Sciences, University of Virginia School of Medicine, Charlottesville (Clayton); Sage Therapeutics, Cambridge, Mass. (Lasser, Jung, Jonas, Kanes, Doherty); Department of Psychiatry, University of Michigan, Ann Arbor (Parikh); Nathan Kline Institute for Psychiatric Research and Department of Psychiatry, New York University School of Medicine, New York (Iosifescu); Biogen, Cambridge, Mass. (Kotecha, Forrestal)
| | - Jeffrey Jonas
- Department of Psychiatry and Neurobehavioral Sciences, University of Virginia School of Medicine, Charlottesville (Clayton); Sage Therapeutics, Cambridge, Mass. (Lasser, Jung, Jonas, Kanes, Doherty); Department of Psychiatry, University of Michigan, Ann Arbor (Parikh); Nathan Kline Institute for Psychiatric Research and Department of Psychiatry, New York University School of Medicine, New York (Iosifescu); Biogen, Cambridge, Mass. (Kotecha, Forrestal)
| | - Stephen J Kanes
- Department of Psychiatry and Neurobehavioral Sciences, University of Virginia School of Medicine, Charlottesville (Clayton); Sage Therapeutics, Cambridge, Mass. (Lasser, Jung, Jonas, Kanes, Doherty); Department of Psychiatry, University of Michigan, Ann Arbor (Parikh); Nathan Kline Institute for Psychiatric Research and Department of Psychiatry, New York University School of Medicine, New York (Iosifescu); Biogen, Cambridge, Mass. (Kotecha, Forrestal)
| | - James Doherty
- Department of Psychiatry and Neurobehavioral Sciences, University of Virginia School of Medicine, Charlottesville (Clayton); Sage Therapeutics, Cambridge, Mass. (Lasser, Jung, Jonas, Kanes, Doherty); Department of Psychiatry, University of Michigan, Ann Arbor (Parikh); Nathan Kline Institute for Psychiatric Research and Department of Psychiatry, New York University School of Medicine, New York (Iosifescu); Biogen, Cambridge, Mass. (Kotecha, Forrestal)
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Huang TH, Lin YS, Hsiao CW, Wang LY, Ajibola MI, Abdulmajeed WI, Lin YL, Li YJ, Chen CY, Lien CC, Chiu CD, Cheng IHJ. Differential expression of GABA A receptor subunits δ and α6 mediates tonic inhibition in parvalbumin and somatostatin interneurons in the mouse hippocampus. Front Cell Neurosci 2023; 17:1146278. [PMID: 37545878 PMCID: PMC10397515 DOI: 10.3389/fncel.2023.1146278] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Accepted: 06/14/2023] [Indexed: 08/08/2023] Open
Abstract
Inhibitory γ-aminobutyric acid (GABA)-ergic interneurons mediate inhibition in neuronal circuitry and support normal brain function. Consequently, dysregulation of inhibition is implicated in various brain disorders. Parvalbumin (PV) and somatostatin (SST) interneurons, the two major types of GABAergic inhibitory interneurons in the hippocampus, exhibit distinct morpho-physiological properties and coordinate information processing and memory formation. However, the molecular mechanisms underlying the specialized properties of PV and SST interneurons remain unclear. This study aimed to compare the transcriptomic differences between these two classes of interneurons in the hippocampus using the ribosome tagging approach. The results revealed distinct expressions of genes such as voltage-gated ion channels and GABAA receptor subunits between PV and SST interneurons. Gabrd and Gabra6 were identified as contributors to the contrasting tonic GABAergic inhibition observed in PV and SST interneurons. Moreover, some of the differentially expressed genes were associated with schizophrenia and epilepsy. In conclusion, our results provide molecular insights into the distinct roles of PV and SST interneurons in health and disease.
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Affiliation(s)
- Tzu-Hsuan Huang
- Institute of Brain Science, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Yi-Sian Lin
- Institute of Biomedical Informatics, National Yang Ming Chiao Tung University, Taipei, Taiwan
- Program in Genetics and Genomics, Baylor College of Medicine, Houston, TX, United States
| | - Chiao-Wan Hsiao
- Institute of Brain Science, National Yang Ming Chiao Tung University, Taipei, Taiwan
- Program in Molecular Medicine, National Yang Ming Chiao Tung University and Academia Sinica, Taipei, Taiwan
| | - Liang-Yun Wang
- Institute of Biomedical Informatics, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Musa Iyiola Ajibola
- Institute of Neuroscience, National Yang Ming Chiao Tung University, Taipei, Taiwan
- Taiwan International Graduate Program in Interdisciplinary Neuroscience, College of Life Sciences, National Yang Ming Chiao Tung University and Academia Sinica, Taipei, Taiwan
| | - Wahab Imam Abdulmajeed
- Institute of Neuroscience, National Yang Ming Chiao Tung University, Taipei, Taiwan
- Taiwan International Graduate Program in Interdisciplinary Neuroscience, College of Life Sciences, National Yang Ming Chiao Tung University and Academia Sinica, Taipei, Taiwan
- Department of Physiology, Faculty of Basic Medical Sciences, College of Health Sciences, University of Ilorin, Ilorin, Nigeria
| | - Yu-Ling Lin
- Institute of Neuroscience, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Yu-Jui Li
- Institute of Neuroscience, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Cho-Yi Chen
- Institute of Biomedical Informatics, National Yang Ming Chiao Tung University, Taipei, Taiwan
- Brain Research Center, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Cheng-Chang Lien
- Program in Molecular Medicine, National Yang Ming Chiao Tung University and Academia Sinica, Taipei, Taiwan
- Institute of Neuroscience, National Yang Ming Chiao Tung University, Taipei, Taiwan
- Taiwan International Graduate Program in Interdisciplinary Neuroscience, College of Life Sciences, National Yang Ming Chiao Tung University and Academia Sinica, Taipei, Taiwan
- Brain Research Center, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Cheng-Di Chiu
- Department of Neurosurgery, China Medical University Hospital, Taichung, Taiwan
- Spine Center, China Medical University Hospital, Taichung, Taiwan
- Graduate Institute of Biomedical Science, China Medical University, Taichung, Taiwan
- School of Medicine, China Medical University, Taichung, Taiwan
| | - Irene Han-Juo Cheng
- Institute of Brain Science, National Yang Ming Chiao Tung University, Taipei, Taiwan
- Program in Molecular Medicine, National Yang Ming Chiao Tung University and Academia Sinica, Taipei, Taiwan
- Brain Research Center, National Yang Ming Chiao Tung University, Taipei, Taiwan
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Gruol DL, Calderon D, French K, Melkonian C, Huitron-Resendiz S, Cates-Gatto C, Roberts AJ. Neuroimmune interactions with binge alcohol drinking in the cerebellum of IL-6 transgenic mice. Neuropharmacology 2023; 228:109455. [PMID: 36775097 PMCID: PMC10029700 DOI: 10.1016/j.neuropharm.2023.109455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 01/20/2023] [Accepted: 02/03/2023] [Indexed: 02/12/2023]
Abstract
The neuroimmune system of the brain, which is comprised primarily of astrocytes and microglia, regulates a variety of homeostatic mechanisms that underlie normal brain function. Numerous conditions, including alcohol consumption, can disrupt this regulatory process by altering brain levels of neuroimmune factors. Alcohol and neuroimmune factors, such as proinflammatory cytokines IL-6 and TNF-alpha, act at similar targets in the brain, including excitatory and inhibitory synaptic transmission. Thus, alcohol-induced production of IL-6 and/or TNF-alpha could be important contributing factors to the effects of alcohol on the brain. Recent studies indicate that IL-6 plays a role in alcohol drinking and the effects of alcohol on the brain activity following the cessation of alcohol consumption (post-alcohol period), however information on these topics is limited. Here we used homozygous and heterozygous female and male transgenic mice with increased astrocyte expression of IL-6 to examined further the interactions between alcohol and IL-6 with respect to voluntary alcohol drinking, brain activity during the post-alcohol period, IL-6 signal transduction, and expression of synaptic proteins. Wildtype littermates (WT) served as controls. The transgenic mice model brain neuroimmune status with respect to IL-6 in subjects with a history of persistent alcohol use. Results showed a genotype dependent reduction in voluntary alcohol consumption in the Drinking in the Dark protocol and in frequency-dependent relationships between brain activity in EEG recordings during the post-alcohol period and alcohol consumption. IL-6, TNF-alpha, IL-6 signal transduction partners pSTAT3 and c/EBP beta, and synaptic proteins were shown to play a role in these genotypic effects.
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Affiliation(s)
- Donna L Gruol
- Neuroscience Department, The Scripps Research Institute, La Jolla, CA, 92037, USA.
| | - Delilah Calderon
- Neuroscience Department, The Scripps Research Institute, La Jolla, CA, 92037, USA
| | - Katharine French
- Neuroscience Department, The Scripps Research Institute, La Jolla, CA, 92037, USA
| | - Claudia Melkonian
- Neuroscience Department, The Scripps Research Institute, La Jolla, CA, 92037, USA
| | | | - Chelsea Cates-Gatto
- Animal Models Core Facility, The Scripps Research Institute, La Jolla, CA, 92037, USA
| | - Amanda J Roberts
- Animal Models Core Facility, The Scripps Research Institute, La Jolla, CA, 92037, USA
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Klett NJ, Cravetchi O, Allen CN. Long-Term Imaging Reveals a Circadian Rhythm of Intracellular Chloride in Neurons of the Suprachiasmatic Nucleus. J Biol Rhythms 2022; 37:110-123. [PMID: 34994231 DOI: 10.1177/07487304211059770] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Both inhibitory and excitatory GABA transmission exist in the mature suprachiasmatic nucleus (SCN), the master pacemaker of circadian physiology. Whether GABA is inhibitory or excitatory depends on the intracellular chloride concentration ([Cl-]i). Here, using the genetically encoded ratiometric probe Cl-Sensor, we investigated [Cl-]i in AVP and VIP-expressing SCN neurons for several days in culture. The chloride ratio (RCl) demonstrated circadian rhythmicity in AVP + neurons and VIP + neurons, but was not detected in GFAP + astrocytes. RCl peaked between ZT 7 and ZT 8 in both AVP + and VIP + neurons. RCl rhythmicity was not dependent on the activity of several transmembrane chloride carriers, action potential generation, or the L-type voltage-gated calcium channels, but was sensitive to GABA antagonists. We conclude that [Cl-]i is under circadian regulation in both AVP + and VIP + neurons.
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Affiliation(s)
- Nathan J Klett
- Neuroscience Graduate Program, Oregon Health & Science University, Portland, Oregon, USA.,Oregon Institute for Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon, USA.,Neurophysiology, Department of Cell and Chemical Biology, Leiden University Medical Center, Leiden, The Netherlands
| | - Olga Cravetchi
- Oregon Institute for Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon, USA
| | - Charles N Allen
- Oregon Institute for Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon, USA.,Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon, USA
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Milla BM. Loss of MeCP2 increases GABA uptake by astrocytes to suppress tonic inhibition of CA1 pyramidal neurons. J Neurophysiol 2021; 126:1310-1313. [PMID: 34495776 DOI: 10.1152/jn.00222.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Rett syndrome (RTT) is a neurodevelopmental disorder characterized a spectrum of phenotypes affecting neuronal and glial populations. Recent work by Dong et al. (Dong Q, Kim J, Nguyen L, Bu Q, Chang Q. J Neurosci 40: 6250-6261, 2020) suggests that augmented GABA uptake by astrocytes diminishes tonic inhibition in the hippocampus and contributes to increased seizure propensity in RTT. Here, I will review evidence supporting this possibility and critically evaluate how increased expression of a GABA transporter might contribute to this mechanism.
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Affiliation(s)
- Brenda M Milla
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut
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8
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Xiong B, Karim F, Eloy DJ, Ye JH. Gabra6100Q allele Sprague-Dawley rats have a higher sensitivity to hypnosis induced by isoflurane and ethanol than the wild type rats. Neurosci Lett 2021; 762:136142. [PMID: 34332026 DOI: 10.1016/j.neulet.2021.136142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Revised: 07/24/2021] [Accepted: 07/26/2021] [Indexed: 10/20/2022]
Abstract
BACKGROUND The neurobiological mechanisms underlying how general anesthetics render a patient's unconsciousness (hypnosis) remains elusive. The role of the cerebellum in hypnosis induced by general anesthetics is unknown. Gabra6100Q allele Sprague-Dawley (SD) rats have a naturally occurring single nucleotide polymorphism in the GABAA receptor α6 subunit gene that is expressed exclusively in cerebellum granule cells. METHODS We examined the loss of righting reflex (LORR) induced by isoflurane, and ethanol in Gabra6100Q rats compared with those in wild type (WT) SD rats. We also examined the change of c-Fos expression induced by isoflurane exposure in cerebellum granule cells of both mutant and WT rats. RESULTS Gabra6100Q rats are more sensitive than WT rats to the LORR induced by isoflurane and ethanol. Moreover, isoflurane exposure induced a greater reduction in c-Fos expression in cerebellum granule cells of Gabra6100Q rats than WT rats. CONCLUSIONS Based on these data, we speculate that cerebellum may be involved in the hypnosis induced by some general anesthetics and thus may represent a novel target of general anesthetics.
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Affiliation(s)
- Bo Xiong
- Department of Anesthesiology, Pharmacology and Physiology, Rutgers-New Jersey Medical School, Newark, NJ, USA; Department of Anesthesiology, Shanghai Cancer Center, Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China
| | - Farabi Karim
- Department of Anesthesiology, Pharmacology and Physiology, Rutgers-New Jersey Medical School, Newark, NJ, USA
| | - Daniel J Eloy
- Department of Anesthesiology, Pharmacology and Physiology, Rutgers-New Jersey Medical School, Newark, NJ, USA
| | - Jiang-Hong Ye
- Department of Anesthesiology, Pharmacology and Physiology, Rutgers-New Jersey Medical School, Newark, NJ, USA.
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9
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Moldavan M, Cravetchi O, Allen CN. Diurnal properties of tonic and synaptic GABA A receptor-mediated currents in suprachiasmatic nucleus neurons. J Neurophysiol 2021; 126:637-652. [PMID: 34259044 DOI: 10.1152/jn.00556.2020] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Synaptic and extrasynaptic GABAA receptor (GABAAR)-mediated neurotransmission is a critical component of the suprachiasmatic nucleus (SCN) neuronal network. However, the properties of the GABAA tonic current (Itonic) and its origin remain unexplored. Spontaneous GABAA postsynaptic currents (sGPSCs) and Itonic were recorded from SCN neurons with the whole cell voltage-clamp technique at different times of the day. GABAAR antagonists (bicuculline, gabazine, and picrotoxin) inhibited sGPSC and induced an outward shift of the holding current, which defined the Itonic amplitude. The sGPSC frequency, synaptic charge transfer, and Itonic amplitude all demonstrated significant diurnal rhythms, with peaks in the middle of the day [zeitgeber time (ZT)7-8] and nadirs at night (ZT19-20). The Itonic amplitude increased proportionally with the sGPSC frequency and synaptic charge transfer during the day and required action potential-mediated GABA release, which was confirmed by TTX application. The activation of presynaptic GABAB receptors by baclofen did not significantly alter the Itonic of neurons with low-frequency sGPSC. The equilibrium potential (Eq) for Itonic was similar to the Eq for chloride and GABAA receptor-activated currents. Itonic showed outward rectification at membrane potentials over the range of -70 to -10 mV and then was linear at voltages greater than -10 mV. GABAAR containing α4-, α5-, and δ-subunits were expressed in SCN, and their contribution to Itonic was confirmed by application of the GABAAR agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) and the GABAAR inverse agonist 11,12,13,13a-tetrahydro-7-methoxy-9-oxo-9H-imidazo[1,5-a]pyrrolo[2,1-c][1,4]benzodiazepine-1-carboxylic acid ethyl ester (L655,708). Thus, the Itonic was mediated by extrasynaptic GABAARs activated predominantly by GABA diffusing out of GABAergic synapses.NEW & NOTEWORTHY A tonic current (Itonic) mediated by GABAA receptors (GABAARs) containing α4-, α5- and δ-subunits was observed in the suprachiasmatic nucleus. The Itonic amplitude strongly depended on the action potential-mediated synaptic release of GABA. The equilibrium potential for Itonic corresponds to that for GABAA currents. The frequency of GABAA postsynaptic currents and Itonic amplitude increased during the day, with peak in the middle of the day, and then gradually declined with a nadir at night, thus showing a diurnal rhythm.
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Affiliation(s)
- Michael Moldavan
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon
| | - Olga Cravetchi
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon
| | - Charles N Allen
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon.,Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon
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10
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Traumatic Brain Injury Broadly Affects GABAergic Signaling in Dentate Gyrus Granule Cells. eNeuro 2021; 8:ENEURO.0055-20.2021. [PMID: 33514602 PMCID: PMC8116114 DOI: 10.1523/eneuro.0055-20.2021] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Revised: 01/08/2021] [Accepted: 01/12/2021] [Indexed: 02/02/2023] Open
Abstract
Traumatic brain injury (TBI) causes cellular and molecular alterations that contribute to neuropsychiatric disease and epilepsy. GABAergic dysfunction figures prominently in the pathophysiology of TBI, yet the effects of TBI on tonic inhibition in hippocampus remain uncertain. We used a mouse model of severe TBI [controlled cortical impact (CCI)] to investigate GABAergic signaling in dentate gyrus granule cells (DGGCs). Basal tonic GABA currents were not affected by CCI. However, tonic currents induced by the δ subunit-selective GABAA receptor agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP; 10 μm) were reduced by 44% in DGGCs ipsilateral to CCI (CCI-ipsi), but not in contralateral DGGCs. Reduced THIP currents were apparent one week after injury and persisted up to 15 weeks. The frequency of spontaneous IPSCs (sIPSCs) was reduced in CCI-ipsi cells, but the amplitude and kinetics of sIPSCs were unaffected. Immunohistochemical analysis showed reduced expression of GABAA receptor δ subunits and GABAB receptor B2 subunits after CCI, by 43% and 40%, respectively. Activation of postsynaptic GABAB receptors caused a twofold increase in tonic currents, and this effect was markedly attenuated in CCI-ipsi cells (92% reduction). GABAB receptor-activated K+ currents in DGGCs were also significantly reduced in CCI-ipsi cells, confirming a functional deficit of GABAB receptors after CCI. Results indicate broad disruption of GABAergic signaling in DGGCs after CCI, with deficits in both phasic and tonic inhibition and GABAB receptor function. These changes are predicted to disrupt operation of hippocampal networks and contribute to sequelae of severe TBI, including epilepsy.
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11
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Sadamitsu K, Shigemitsu L, Suzuki M, Ito D, Kashima M, Hirata H. Characterization of zebrafish GABA A receptor subunits. Sci Rep 2021; 11:6242. [PMID: 33737538 PMCID: PMC7973766 DOI: 10.1038/s41598-021-84646-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Accepted: 02/18/2021] [Indexed: 11/23/2022] Open
Abstract
γ-Aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system, exerts its effect through the activation of GABA receptors. GABAA receptors are ligand-gated chloride channels composed of five subunit proteins. Mammals have 19 different GABAA receptor subunits (α1–6, β1–3, γ1–3, δ, ε, π, θ, and ρ1–3), the physiological properties of which have been assayed by electrophysiology. However, the evolutionary conservation of the physiological characteristics of diverged GABAA receptor subunits remains unclear. Zebrafish have 23 subunits (α1, α2a, α2b, α3–5, α6a, α6b, β1–4, γ1–3, δ, π, ζ, ρ1, ρ2a, ρ2b, ρ3a, and ρ3b), but the electrophysiological properties of these subunits have not been explored. In this study, we cloned the coding sequences for zebrafish GABAA receptor subunits and investigated their expression patterns in larval zebrafish by whole-mount in situ hybridization. We also performed electrophysiological recordings of GABA-evoked currents from Xenopus oocytes injected with one or multiple zebrafish GABAA receptor subunit cRNAs and calculated the half-maximal effective concentrations (EC50s) for each. Our results revealed the spatial expressions and electrophysiological GABA sensitivities of zebrafish GABAA receptors, suggesting that the properties of GABAA receptor subunits are conserved among vertebrates.
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Affiliation(s)
- Kenichiro Sadamitsu
- Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, Sagamihara, 252-5258, Japan
| | - Leona Shigemitsu
- Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, Sagamihara, 252-5258, Japan
| | - Marina Suzuki
- Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, Sagamihara, 252-5258, Japan
| | - Daishi Ito
- Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, Sagamihara, 252-5258, Japan
| | - Makoto Kashima
- Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, Sagamihara, 252-5258, Japan
| | - Hiromi Hirata
- Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, Sagamihara, 252-5258, Japan.
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12
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Gruol DL, Melkonian C, Ly K, Sisouvanthong J, Tan Y, Roberts AJ. Alcohol and IL-6 Alter Expression of Synaptic Proteins in Cerebellum of Transgenic Mice with Increased Astrocyte Expression of IL-6. Neuroscience 2020; 442:124-137. [PMID: 32634532 DOI: 10.1016/j.neuroscience.2020.06.043] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Revised: 06/03/2020] [Accepted: 06/29/2020] [Indexed: 12/15/2022]
Abstract
Recent studies indicate that neuroimmune factors, including the cytokine interleukin-6 (IL-6), play a role in the CNS actions of alcohol. The cerebellum is a sensitive target of alcohol, but few studies have examined a potential role for neuroimmune factors in the actions of alcohol on this brain region. A number of studies have shown that synaptic transmission, and in particular inhibitory synaptic transmission, is an important cerebellar target of alcohol. IL-6 also alters synaptic transmission, although it is unknown if IL-6 targets are also targets of alcohol. This is an important issue because alcohol induces glial production of IL-6, which could then covertly influence the actions of alcohol. The persistent cerebellar effects of both IL-6 and alcohol typically involve chronic exposure and, presumably, altered gene and protein expression. Thus, in the current studies we tested the possibility that proteins involved in inhibitory and excitatory synaptic transmission in the cerebellum are common targets of alcohol and IL-6. We used transgenic mice that express elevated levels of astrocyte produced IL-6 to model persistently elevated expression of IL-6, as would occur in alcohol use disorders, and a chronic intermittent alcohol exposure/withdrawal paradigm (CIE/withdrawal) that is known to produce alcohol dependence. Multiple cerebellar synaptic proteins were assessed by Western blot. Results show that IL-6 and CIE/withdrawal have both unique and common actions that affect synaptic protein expression. These common targets could provide sites for IL-6/alcohol exposure/withdrawal interactions and play an important role in cerebellar symptoms of alcohol use such as ataxia.
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Affiliation(s)
- Donna L Gruol
- Neuroscience Department, The Scripps Research Institute, La Jolla, CA 92037, USA.
| | - Claudia Melkonian
- Neuroscience Department, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Kristine Ly
- Neuroscience Department, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Jasmin Sisouvanthong
- Neuroscience Department, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Yvette Tan
- Neuroscience Department, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Amanda J Roberts
- Animal Models Core Facility, The Scripps Research Institute, La Jolla, CA 92037, USA
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13
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An Astrocytic Influence on Impaired Tonic Inhibition in Hippocampal CA1 Pyramidal Neurons in a Mouse Model of Rett Syndrome. J Neurosci 2020; 40:6250-6261. [PMID: 32616668 DOI: 10.1523/jneurosci.3042-19.2020] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2019] [Revised: 05/13/2020] [Accepted: 06/10/2020] [Indexed: 01/28/2023] Open
Abstract
Rett syndrome (RTT) is a severe neurodevelopmental disease caused by mutations in the methyl-CpG binding protein 2 (MECP2) gene. Although altered interneuron development and function are clearly demonstrated in RTT mice, a particular mode of inhibition, tonic inhibition, has not been carefully examined. We report here that tonic inhibition is significantly reduced in pyramidal neurons in the CA1 region of the hippocampus in mice where Mecp2 is deleted either in all cells or specifically in astrocytes. Since no change is detected in the level of GABA receptors, such a reduction in tonic inhibition is likely a result of decreased ambient GABA level in the extracellular space. Consistent with this explanation, we observed increased expression of a GABA transporter, GABA transporter 3 (GAT3), in the hippocampus of the Mecp2 KO mice, as well as a corresponding increase of GAT3 current in hippocampal astrocytes. These phenotypes are relevant to RTT because pharmacological blockage of GAT3 can normalize tonic inhibition and intrinsic excitability in CA1 pyramidal neurons, and rescue the phenotype of increased network excitability in acute hippocampal slices from the Mecp2 KO mice. Finally, chronic administration of a GAT3 antagonist improved a composite symptom score and extended lifespan in the Mecp2 KO mice. Only male mice were used in this study. These results not only advance our understanding of RTT etiology by defining a new neuronal phenotype and revealing how it can be influenced by astrocytic alterations, but also reveal potential targets for intervention.SIGNIFICANCE STATEMENT Our study reports a novel phenotype of reduced tonic inhibition in hippocampal CA1 pyramidal neurons in the Rett syndrome mice, reveal a potential mechanism of increased GABA transporter expression/activity in the neighboring astrocytes, describe a disease-relevant consequence in hyperexcitability, and provide preliminary evidence that targeting this phenotype may slow down disease progression in Rett syndrome mice. These results help our understanding of the disease etiology and identify a new therapeutic target for treating Rett syndrome.
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14
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Abbott GW. KCNQs: Ligand- and Voltage-Gated Potassium Channels. Front Physiol 2020; 11:583. [PMID: 32655402 PMCID: PMC7324551 DOI: 10.3389/fphys.2020.00583] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Accepted: 05/11/2020] [Indexed: 12/26/2022] Open
Abstract
Voltage-gated potassium (Kv) channels in the KCNQ (Kv7) family are essential features of a broad range of excitable and non-excitable cell types and are found in organisms ranging from Hydra vulgaris to Homo sapiens. Although they are firmly in the superfamily of S4 domain-bearing voltage-sensing ion channels, KCNQ channels are highly sensitive to a range of endogenous and exogenous small molecules that act directly on the pore, the voltage-sensing domain, or the interface between the two. The focus of this review is regulation of KCNQs by direct binding of neurotransmitters and metabolites from both animals and plants and the role of the latter in the effects of plants consumed for food and as traditional folk medicines. The conceptual question arises: Are KCNQs voltage-gated channels that are also sensitive to ligands or ligand-gated channels that are also sensitive to voltage?
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Affiliation(s)
- Geoffrey W Abbott
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, Irvine, CA, United States
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15
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Pandit S, Neupane C, Woo J, Sharma R, Nam MH, Lee GS, Yi MH, Shin N, Kim DW, Cho H, Jeon BH, Kim HW, Lee CJ, Park JB. Bestrophin1-mediated tonic GABA release from reactive astrocytes prevents the development of seizure-prone network in kainate-injected hippocampi. Glia 2019; 68:1065-1080. [PMID: 31833596 DOI: 10.1002/glia.23762] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2019] [Revised: 11/25/2019] [Accepted: 11/28/2019] [Indexed: 12/22/2022]
Abstract
Tonic extrasynaptic GABAA receptor (GABAA R) activation is under the tight control of tonic GABA release from astrocytes to maintain the brain's excitation/inhibition (E/I) balance; any slight E/I balance disturbance can cause serious pathological conditions including epileptic seizures. However, the pathophysiological role of tonic GABA release from astrocytes has not been tested in epileptic seizures. Here, we report that pharmacological or genetic intervention of the GABA-permeable Bestrophin-1 (Best1) channel prevented the generation of tonic GABA inhibition, disinhibiting CA1 pyramidal neuronal firing and augmenting seizure susceptibility in kainic acid (KA)-induced epileptic mice. Astrocyte-specific Best1 over-expression in KA-injected Best1 knockout mice fully restored the generation of tonic GABA inhibition and effectively suppressed seizure susceptibility. We demonstrate for the first time that tonic GABA from reactive astrocytes strongly contributes to the compensatory shift of E/I balance in epileptic hippocampi, serving as a good therapeutic target against altered E/I balance in epileptic seizures.
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Affiliation(s)
- Sudip Pandit
- Department of Medical Science, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea.,Department of Physiology, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea
| | - Chiranjivi Neupane
- Department of Medical Science, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea.,Department of Physiology, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea
| | - Junsung Woo
- Center for Glia-Neuron Interaction and Neuroscience, Korea Institute of Science and Technology (KIST), Seoul, Republic of Korea
| | - Ramesh Sharma
- Department of Medical Science, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea.,Department of Physiology, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea
| | - Min-Ho Nam
- Center for Glia-Neuron Interaction and Neuroscience, Korea Institute of Science and Technology (KIST), Seoul, Republic of Korea
| | - Gyu-Seung Lee
- Department of Physiology, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea
| | - Min-Hee Yi
- Department of Anatomy, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea
| | - Nara Shin
- Department of Medical Science, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea.,Department of Anatomy, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea
| | - Dong Woon Kim
- Department of Medical Science, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea.,Department of Anatomy, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea
| | - Hyunsill Cho
- Department of Physiology, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea
| | - Byeong Hwa Jeon
- Department of Medical Science, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea.,Department of Physiology, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea
| | - Hyun-Woo Kim
- Department of Medical Science, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea.,Department of Physiology, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea
| | - C Justin Lee
- Center for Glia-Neuron Interaction and Neuroscience, Korea Institute of Science and Technology (KIST), Seoul, Republic of Korea.,Center for Cognition and Sociality, Institute for Basic Science, Daejeon, Republic of Korea
| | - Jin Bong Park
- Department of Medical Science, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea.,Department of Physiology, College of Medicine and Brain Research Institute, Chungnam National University, Daejeon, Republic of Korea
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16
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Manville RW, Papanikolaou M, Abbott GW. M-Channel Activation Contributes to the Anticonvulsant Action of the Ketone Body β-Hydroxybutyrate. J Pharmacol Exp Ther 2019; 372:148-156. [PMID: 31757819 DOI: 10.1124/jpet.119.263350] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2019] [Accepted: 11/20/2019] [Indexed: 12/26/2022] Open
Abstract
Ketogenic diets are effective therapies for refractory epilepsy, yet the underlying mechanisms are incompletely understood. The anticonvulsant efficacy of ketogenic diets correlates positively to the serum concentration of β-hydroxybutyrate (BHB), the primary ketone body generated by ketosis. Voltage-gated potassium channels generated by KCNQ2-5 subunits, especially KCNQ2/3 heteromers, generate the M-current, a therapeutic target for synthetic anticonvulsants. Here, we report that BHB directly activates KCNQ2/3 channels (EC50 = 0.7 µM), via a highly conserved S5 tryptophan (W265) on KCNQ3. BHB was also acutely effective as an anticonvulsant in the pentylene tetrazole (PTZ) seizure assay in mice. Strikingly, coadministration of γ-amino-β-hydroxybutyric acid, a high-affinity KCNQ2/3 partial agonist that also acts via KCNQ3-W265, similarly reduced the efficacy of BHB in KCNQ2/3 channel activation in vitro and in the PTZ seizure assay in vivo. Our results uncover a novel, unexpected molecular basis for anticonvulsant effects of the major ketone body induced by ketosis. SIGNIFICANCE STATEMENT: Ketogenic diets are used to treat refractory epilepsy but the therapeutic mechanism is not fully understood. Here, we show that clinically relevant concentrations of β-hydroxybutyrate, the primary ketone body generated during ketogenesis, activates KCNQ2/3 potassium channels by binding to a specific site on KCNQ3, an effect known to reduce neuronal excitability. We provide evidence using a mouse chemoconvulsant model that KCNQ2/3 activation contributes to the antiepileptic action of β-hydroxybutyrate.
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Affiliation(s)
- Rían W Manville
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California
| | - Maria Papanikolaou
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California
| | - Geoffrey W Abbott
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California
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17
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Mechanisms of GABA B receptor enhancement of extrasynaptic GABA A receptor currents in cerebellar granule cells. Sci Rep 2019; 9:16683. [PMID: 31723152 PMCID: PMC6853962 DOI: 10.1038/s41598-019-53087-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Accepted: 10/26/2019] [Indexed: 12/31/2022] Open
Abstract
Many neurons, including cerebellar granule cells, exhibit a tonic GABA current mediated by extrasynaptic GABAA receptors. This current is a critical regulator of firing and the target of many clinically relevant compounds. Using a combination of patch clamp electrophysiology and photolytic uncaging of RuBi-GABA we show that GABAB receptors are tonically active and enhance extrasynaptic GABAA receptor currents in cerebellar granule cells. This enhancement is not associated with meaningful changes in GABAA receptor potency, mean channel open-time, open probability, or single-channel current. However, there was a significant (~40%) decrease in the number of channels participating in the GABA uncaging current and an increase in receptor desensitization. Furthermore, we find that adenylate cyclase, PKA, CaMKII, and release of Ca2+ from intracellular stores are necessary for modulation of GABAA receptors. Overall, this work reveals crosstalk between postsynaptic GABAA and GABAB receptors and identifies the signaling pathways and mechanisms involved.
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18
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Khatri SN, Wu WC, Yang Y, Pugh JR. Direction of action of presynaptic GABA A receptors is highly dependent on the level of receptor activation. J Neurophysiol 2019; 121:1896-1905. [PMID: 30892973 DOI: 10.1152/jn.00779.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Many synapses, including parallel fiber synapses in the cerebellum, express presynaptic GABAA receptors. However, reports of the functional consequences of presynaptic GABAA receptor activation are variable across synapses, from inhibition to enhancement of transmitter release. We find that presynaptic GABAA receptor function is bidirectional at parallel fiber synapses depending on GABA concentration and modulation of GABAA receptors in mice. Activation of GABAA receptors by low GABA concentrations enhances glutamate release, whereas activation of receptors by higher GABA concentrations inhibits release. Furthermore, blocking GABAB receptors reduces GABAA receptor currents and shifts presynaptic responses toward greater enhancement of release across a wide range of GABA concentrations. Conversely, enhancing GABAA receptor currents with ethanol or neurosteroids shifts responses toward greater inhibition of release. The ability of presynaptic GABAA receptors to enhance or inhibit transmitter release at the same synapse depending on activity level provides a new mechanism for fine control of synaptic transmission by GABA and may explain conflicting reports of presynaptic GABAA receptor function across synapses. NEW & NOTEWORTHY GABAA receptors are widely expressed at presynaptic terminals in the central nervous system. However, previous reports have produced conflicting results on the function of these receptors at different synapses. We show that presynaptic GABAA receptor function is strongly dependent on the level of receptor activation. Low levels of receptor activation enhance transmitter release, whereas higher levels of activation inhibit release at the same synapses. This provides a novel mechanism by which presynaptic GABAA receptors fine-tune synaptic transmission.
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Affiliation(s)
- Shailesh N Khatri
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio , San Antonio, Texas
| | - Wan-Chen Wu
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio , San Antonio, Texas
| | - Ying Yang
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio , San Antonio, Texas.,Xiangya School of Medicine, Central South University , Changsha, Hunan , China
| | - Jason R Pugh
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio , San Antonio, Texas.,Center for Biomedical Neuroscience, University of Texas Health Science Center at San Antonio , San Antonio, Texas
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19
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Direct neurotransmitter activation of voltage-gated potassium channels. Nat Commun 2018; 9:1847. [PMID: 29748663 PMCID: PMC5945843 DOI: 10.1038/s41467-018-04266-w] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Accepted: 04/16/2018] [Indexed: 11/25/2022] Open
Abstract
Voltage-gated potassium channels KCNQ2–5 generate the M-current, which controls neuronal excitability. KCNQ2–5 subunits each harbor a high-affinity anticonvulsant drug-binding pocket containing an essential tryptophan (W265 in human KCNQ3) conserved for >500 million years, yet lacking a known physiological function. Here, phylogenetic analysis, electrostatic potential mapping, in silico docking, electrophysiology, and radioligand binding assays reveal that the anticonvulsant binding pocket evolved to accommodate endogenous neurotransmitters including γ-aminobutyric acid (GABA), which directly activates KCNQ5 and KCNQ3 via W265. GABA, and endogenous metabolites β-hydroxybutyric acid (BHB) and γ-amino-β-hydroxybutyric acid (GABOB), competitively and differentially shift the voltage dependence of KCNQ3 activation. Our results uncover a novel paradigm: direct neurotransmitter activation of voltage-gated ion channels, enabling chemosensing of the neurotransmitter/metabolite landscape to regulate channel activity and cellular excitability. M-current is conveyed by voltage-sensitive KCNQ channels, which are enriched in GABAergic neurons and are activated by anticonvulsants such as retigabine. Here the authors show that GABA directly activates KCNQ3, at the residue required for its anticonvulsant activity.
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20
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Optogenetic Visualization of Presynaptic Tonic Inhibition of Cerebellar Parallel Fibers. J Neurosci 2017; 36:5709-23. [PMID: 27225762 DOI: 10.1523/jneurosci.4366-15.2016] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2015] [Accepted: 03/31/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Tonic inhibition was imaged in cerebellar granule cells of transgenic mice expressing the optogenetic chloride indicator, Clomeleon. Blockade of GABAA receptors substantially reduced chloride concentration in granule cells due to block of tonic inhibition. This indicates that tonic inhibition is a significant contributor to the resting chloride concentration of these cells. Tonic inhibition was observed not only in granule cell bodies, but also in their axons, the parallel fibers (PFs). This presynaptic tonic inhibition could be observed in slices both at room and physiological temperatures, as well as in vivo, and has many of the same properties as tonic inhibition measured in granule cell bodies. GABA application revealed that PFs possess at least two types of GABAA receptor: one high-affinity receptor that is activated by ambient GABA and causes a chloride influx that mediates tonic inhibition, and a second with a low affinity for GABA that causes a chloride efflux that excites PFs. Presynaptic tonic inhibition regulates glutamate release from PFs because GABAA receptor blockade enhanced both the frequency of spontaneous EPSCs and the amplitude of evoked EPSCs at the PF-Purkinje cell synapse. We conclude that tonic inhibition of PFs could play an important role in regulating information flow though cerebellar synaptic circuits. Such cross talk between phasic and tonic signaling could be a general mechanism for fine tuning of synaptic circuits. SIGNIFICANCE STATEMENT This paper demonstrates that an unconventional form of signaling, known as tonic inhibition, is found in presynaptic terminals and affects conventional synaptic communication. Our results establish the basic characteristics and mechanisms of presynaptic tonic inhibition and show that it occurs in vivo as well as in isolated brain tissue.
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21
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Albers HE, Walton JC, Gamble KL, McNeill JK, Hummer DL. The dynamics of GABA signaling: Revelations from the circadian pacemaker in the suprachiasmatic nucleus. Front Neuroendocrinol 2017; 44:35-82. [PMID: 27894927 PMCID: PMC5225159 DOI: 10.1016/j.yfrne.2016.11.003] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2016] [Revised: 10/16/2016] [Accepted: 11/22/2016] [Indexed: 12/31/2022]
Abstract
Virtually every neuron within the suprachiasmatic nucleus (SCN) communicates via GABAergic signaling. The extracellular levels of GABA within the SCN are determined by a complex interaction of synthesis and transport, as well as synaptic and non-synaptic release. The response to GABA is mediated by GABAA receptors that respond to both phasic and tonic GABA release and that can produce excitatory as well as inhibitory cellular responses. GABA also influences circadian control through the exclusively inhibitory effects of GABAB receptors. Both GABA and neuropeptide signaling occur within the SCN, although the functional consequences of the interactions of these signals are not well understood. This review considers the role of GABA in the circadian pacemaker, in the mechanisms responsible for the generation of circadian rhythms, in the ability of non-photic stimuli to reset the phase of the pacemaker, and in the ability of the day-night cycle to entrain the pacemaker.
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Affiliation(s)
- H Elliott Albers
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Neuroscience Institute, Georgia State University, Atlanta, GA 30302, United States.
| | - James C Walton
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Neuroscience Institute, Georgia State University, Atlanta, GA 30302, United States
| | - Karen L Gamble
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35294, United States
| | - John K McNeill
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Neuroscience Institute, Georgia State University, Atlanta, GA 30302, United States
| | - Daniel L Hummer
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Department of Psychology, Morehouse College, Atlanta, GA 30314, United States
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Domínguez S, Fernández de Sevilla D, Buño W. Muscarinic Long-Term Enhancement of Tonic and Phasic GABA A Inhibition in Rat CA1 Pyramidal Neurons. Front Cell Neurosci 2016; 10:244. [PMID: 27833531 PMCID: PMC5080370 DOI: 10.3389/fncel.2016.00244] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Accepted: 10/06/2016] [Indexed: 01/23/2023] Open
Abstract
Acetylcholine (ACh) regulates network operation in the hippocampus by controlling excitation and inhibition in rat CA1 pyramidal neurons (PCs), the latter through gamma-aminobutyric acid type-A receptors (GABAARs). Although, the enhancing effects of ACh on GABAARs have been reported (Dominguez et al., 2014, 2015), its role in regulating tonic GABAA inhibition has not been explored in depth. Therefore, we aimed at determining the effects of the activation of ACh receptors on responses mediated by synaptic and extrasynaptic GABAARs. Here, we show that under blockade of ionotropic glutamate receptors ACh, acting through muscarinic type 1 receptors, paired with post-synaptic depolarization induced a long-term enhancement of tonic GABAA currents (tGABAA) and puff-evoked GABAA currents (pGABAA). ACh combined with depolarization also potentiated IPSCs (i.e., phasic inhibition) in the same PCs, without signs of interactions of synaptic responses with pGABAA and tGABAA, suggesting the contribution of two different GABAA receptor pools. The long-term enhancement of GABAA currents and IPSCs reduced the excitability of PCs, possibly regulating plasticity and learning in behaving animals.
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Affiliation(s)
- Soledad Domínguez
- Instituto Cajal - Consejo Superior de Investigaciones CientificasMadrid, Spain; Centre National de la Recherche Scientifique, Paris Descartes University, UMR 8118, ParisFrance
| | - David Fernández de Sevilla
- Instituto Cajal - Consejo Superior de Investigaciones CientificasMadrid, Spain; Departamento de Anatomía, Histología y Neurociencia, Facultad de Medicina, Universidad Autonoma de MadridMadrid, Spain
| | - Washington Buño
- Instituto Cajal - Consejo Superior de Investigaciones Cientificas Madrid, Spain
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23
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Yang L, Xu T, Zhang K, Wei Z, Li X, Huang M, Rose GM, Cai X. The essential role of hippocampal alpha6 subunit-containing GABAA receptors in maternal separation stress-induced adolescent depressive behaviors. Behav Brain Res 2016; 313:135-143. [DOI: 10.1016/j.bbr.2016.07.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Revised: 06/29/2016] [Accepted: 07/02/2016] [Indexed: 12/14/2022]
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Howell RD, Pugh JR. Biphasic modulation of parallel fibre synaptic transmission by co-activation of presynaptic GABAA and GABAB receptors in mice. J Physiol 2016; 594:3651-66. [PMID: 27061582 DOI: 10.1113/jp272124] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Accepted: 03/30/2016] [Indexed: 01/23/2023] Open
Abstract
KEY POINTS Many excitatory synapses co-express presynaptic GABAA and GABAB receptors, despite their opposing actions on synaptic transmission. It is still unclear how co-activation of these receptors modulates synapse function. We measured presynaptic GABA receptor function at parallel fibre synapses onto stellate cells in the cerebellum using whole-cell patch-clamp recording and photolytic uncaging of RuBi-GABA. Activation of presynaptic GABA receptors results in a transient (∼100 ms) enhancement of synaptic transmission (mediated by GABAA receptors) followed by a long lasting (>500 ms) inhibition of transmission (mediated by GABAB receptors). When activated just prior to high-frequency trains of stimulation, presynaptic GABAA and GABAB receptors work together to reduce short-term facilitation/enhance depression, altering the filtering properties of synaptic transmission. Inhibition of synaptic transmission by GABAB receptors is more sensitive to GABA than enhancement by GABAA receptors, suggesting GABAB receptors may be activated by ambient GABA or release from greater distances. ABSTRACT GABAA and GABAB receptors are co-expressed at many presynaptic terminals in the central nervous system. Previous studies have shown that GABAA receptors typically enhance vesicle release while GABAB receptors inhibit release. However, it is not clear how the competing actions of these receptors modulate synaptic transmission when co-activated, as is likely in vivo. We investigated this question at parallel fibre synapses in the cerebellum, which co-express presynaptic GABAA and GABAB receptors. In acute slices from C57BL/6 mice, we find that co-activation of presynaptic GABA receptors by photolytic uncaging of RuBi-GABA has a biphasic effect on EPSC amplitudes recorded from stellate cells. Synchronous and asynchronous EPSCs evoked within ∼100 ms of GABA uncaging were increased, while EPSCs evoked ∼300-600 ms after GABA uncaging were reduced compared to interleaved control sweeps. We confirmed these effects are presynaptic by measuring the paired-pulse ratio, variance of EPSC amplitudes, and response probability. During trains of high-frequency stimulation GABAA and GABAB receptors work together (rather than oppose one another) to reduce short-term facilitation when GABA is uncaged just prior to the onset of stimulation. We also find that GABAB receptor-mediated inhibition can be elicited by lower GABA concentrations than GABAA receptor-mediated enhancement of EPSCs, suggesting GABAB receptors may be selectively activated by ambient GABA or release from more distance synapses. These data suggest that GABA, acting through both presynaptic GABAA and GABAB receptors, modulate the amplitude and short-term plasticity of excitatory synapses, a result not possible from activation of either receptor type alone.
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Affiliation(s)
- Rebecca D Howell
- University of Texas Health Science Center at San Antonio, Department of Physiology, San Antonio, TX 78229, USA
| | - Jason R Pugh
- University of Texas Health Science Center at San Antonio, Department of Physiology, San Antonio, TX 78229, USA
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25
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Xiao F, Hrabe J, Hrabetova S. Anomalous extracellular diffusion in rat cerebellum. Biophys J 2016; 108:2384-95. [PMID: 25954895 DOI: 10.1016/j.bpj.2015.02.034] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Revised: 02/05/2015] [Accepted: 02/25/2015] [Indexed: 12/31/2022] Open
Abstract
Extracellular space (ECS) is a major channel transporting biologically active molecules and drugs in the brain. Diffusion-mediated transport of these substances is hindered by the ECS structure but the microscopic basis of this hindrance is not fully understood. One hypothesis proposes that the hindrance originates in large part from the presence of dead-space (DS) microdomains that can transiently retain diffusing molecules. Because previous theoretical and modeling work reported an initial period of anomalous diffusion in similar environments, we expected that brain regions densely populated by DS microdomains would exhibit anomalous extracellular diffusion. Specifically, we targeted granular layers (GL) of rat and turtle cerebella that are populated with large and geometrically complex glomeruli. The integrative optical imaging (IOI) method was employed to evaluate diffusion of fluorophore-labeled dextran (MW 3000) in GL, and the IOI data analysis was adapted to quantify the anomalous diffusion exponent dw from the IOI records. Diffusion was significantly anomalous in rat GL, where dw reached 4.8. In the geometrically simpler turtle GL, dw was elevated but not robustly anomalous (dw = 2.6). The experimental work was complemented by numerical Monte Carlo simulations of anomalous ECS diffusion in several three-dimensional tissue models containing glomeruli-like structures. It demonstrated that both the duration of transiently anomalous diffusion and the anomalous exponent depend on the size of model glomeruli and the degree of their wrapping. In conclusion, we have found anomalous extracellular diffusion in the GL of rat cerebellum. This finding lends support to the DS microdomain hypothesis. Transiently anomalous diffusion also has a profound effect on the spatiotemporal distribution of molecules released into the ECS, especially at diffusion distances on the order of a few cell diameters, speeding up short-range diffusion-mediated signals in less permeable structures.
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Affiliation(s)
- Fanrong Xiao
- Department of Cell Biology, State University of New York, Downstate Medical Center, Brooklyn, New York
| | - Jan Hrabe
- Department of Cell Biology, State University of New York, Downstate Medical Center, Brooklyn, New York; Medical Physics Laboratory, Nathan S. Kline Institute, Orangeburg, New York
| | - Sabina Hrabetova
- Department of Cell Biology, State University of New York, Downstate Medical Center, Brooklyn, New York; The Robert F. Furchgott Center for Neural and Behavioral Science, State University of New York Downstate Medical Center, Brooklyn, New York.
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26
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Carver CM, Reddy DS. Neurosteroid Structure-Activity Relationships for Functional Activation of Extrasynaptic δGABA(A) Receptors. J Pharmacol Exp Ther 2016; 357:188-204. [PMID: 26857959 DOI: 10.1124/jpet.115.229302] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2015] [Accepted: 02/05/2016] [Indexed: 01/18/2023] Open
Abstract
Synaptic GABAA receptors are primary mediators of rapid inhibition in the brain and play a key role in the pathophysiology of epilepsy and other neurologic disorders. The δ-subunit GABAA receptors are expressed extrasynaptically in the dentate gyrus and contribute to tonic inhibition, promoting network shunting as well as reducing seizure susceptibility. However, the neurosteroid structure-function relationship at δGABA(A) receptors within the native hippocampus neurons remains unclear. Here we report a structure-activity relationship for neurosteroid modulation of extrasynaptic GABAA receptor-mediated tonic inhibition in the murine dentate gyrus granule cells. We recorded neurosteroid allosteric potentiation of GABA as well as direct activation of tonic currents using a wide array of natural and synthetic neurosteroids. Our results shows that, for all neurosteroids, the C3α-OH group remains obligatory for extrasynaptic receptor functional activity, as C3β-OH epimers were inactive in activating tonic currents. Allopregnanolone and related pregnane analogs exhibited the highest potency and maximal efficacy in promoting tonic currents. Alterations at the C17 or C20 region of the neurosteroid molecule drastically altered the transduction kinetics of tonic current activation. The androstane analogs had the weakest modulatory response among the analogs tested. Neurosteroid potentiation of tonic currents was completely (approximately 95%) diminished in granule cells from δ-knockout mice, suggesting that δ-subunit receptors are essential for neurosteroid activity. The neurosteroid sensitivity of δGABA(A) receptors was confirmed at the systems level using a 6-Hz seizure test. A consensus neurosteroid pharmacophore model at extrasynaptic δGABA(A) receptors is proposed based on a structure-activity relationship for activation of tonic current and seizure protection.
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Affiliation(s)
- Chase Matthew Carver
- Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M University Health Science Center, Bryan, Texas
| | - Doodipala Samba Reddy
- Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M University Health Science Center, Bryan, Texas
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27
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Werner DF, Porcu P, Boyd KN, O'Buckley TK, Carter JM, Kumar S, Morrow AL. Ethanol-induced GABAA receptor alpha4 subunit plasticity involves phosphorylation and neuroactive steroids. Mol Cell Neurosci 2016; 72:1-8. [PMID: 26805653 DOI: 10.1016/j.mcn.2016.01.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2015] [Revised: 12/11/2015] [Accepted: 01/09/2016] [Indexed: 10/22/2022] Open
Abstract
GABAA receptors containing α4 subunits are widely implicated in acute ethanol sensitivity, and their spatial and temporal regulation prominently contributes to ethanol-induced neuroplasticity in hippocampus and cortex. However, it is unknown if α4-containing GABAA receptors in the thalamus, an area of high α4 expression, display similar regulatory patterns following ethanol administration, and if so, by which molecular mechanisms. In the current study, thalamic GABAA receptor α4 subunit levels were increased following a 6-week-, but not a 2-week chronic ethanol diet. Following acute high-dose ethanol administration, thalamic GABAA receptor α4 subunit levels were regulated in a temporal fashion, as a decrease was observed at 2h followed by a delayed transient increase. PKCγ and PKCδ levels paralleled α4 temporal expression patterns following ethanol exposure. Initial decreases in α4 subunit expression were associated with reduced serine phosphorylation. Delayed increases in expression were not associated with a change in phosphorylation state, but were prevented by inhibiting neuroactive steroid production with the 5α-reductase inhibitor finasteride. Overall, these studies indicate that thalamic GABAA receptor α4 subunit expression following acute and chronic ethanol administration exhibits similar regulatory patterns as other regions and that transient expression patterns following acute exposure in vivo are likely dependent on both subunit phosphorylation state and neuroactive steroids.
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Affiliation(s)
- David F Werner
- Bowles Center for Alcohol Studies, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7178, USA; Department of Psychology, Center for Development and Behavioral Neuroscience, Binghamton University - State University of New York, Binghamton, NY 13902, USA.
| | - Patrizia Porcu
- Bowles Center for Alcohol Studies, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7178, USA; Department of Psychiatry, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7178, USA; Neuroscience Institute, National Research Council of Italy (CNR), Cagliari, Italy
| | - Kevin N Boyd
- Bowles Center for Alcohol Studies, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7178, USA
| | - Todd K O'Buckley
- Bowles Center for Alcohol Studies, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7178, USA
| | - Jenna M Carter
- Department of Psychology, Center for Development and Behavioral Neuroscience, Binghamton University - State University of New York, Binghamton, NY 13902, USA
| | - Sandeep Kumar
- Bowles Center for Alcohol Studies, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7178, USA; Department of Psychiatry, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7178, USA
| | - A Leslie Morrow
- Bowles Center for Alcohol Studies, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7178, USA; Department of Psychiatry, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7178, USA; Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7178, USA
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28
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Tong X, Peng Z, Zhang N, Cetina Y, Huang CS, Wallner M, Otis TS, Houser CR. Ectopic Expression of α6 and δ GABAA Receptor Subunits in Hilar Somatostatin Neurons Increases Tonic Inhibition and Alters Network Activity in the Dentate Gyrus. J Neurosci 2015; 35:16142-58. [PMID: 26658866 PMCID: PMC4682781 DOI: 10.1523/jneurosci.2853-15.2015] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Revised: 10/23/2015] [Accepted: 11/01/2015] [Indexed: 11/21/2022] Open
Abstract
The role of GABAA receptor (GABAAR)-mediated tonic inhibition in interneurons remains unclear and may vary among subgroups. Somatostatin (SOM) interneurons in the hilus of the dentate gyrus show negligible expression of nonsynaptic GABAAR subunits and very low tonic inhibition. To determine the effects of ectopic expression of tonic GABAAR subtypes in these neurons, Cre-dependent viral vectors were used to express GFP-tagged GABAAR subunits (α6 and δ) selectively in hilar SOM neurons in SOM-Cre mice. In single-transfected animals, immunohistochemistry demonstrated strong expression of either the α6 or δ subunit; in cotransfected animals, both subunits were consistently expressed in the same neurons. Electrophysiology revealed a robust increase of tonic current, with progressively larger increases following transfection of δ, α6, and α6/δ subunits, respectively, indicating formation of functional receptors in all conditions and likely coassembly of the subunits in the same receptor following cotransfection. An in vitro model of repetitive bursting was used to determine the effects of increased tonic inhibition in hilar SOM interneurons on circuit activity in the dentate gyrus. Upon cotransfection, the frequency of GABAAR-mediated bursting in granule cells was reduced, consistent with a reduction in synchronous firing among hilar SOM interneurons. Moreover, in vivo studies of Fos expression demonstrated reduced activation of α6/δ-cotransfected neurons following acute seizure induction by pentylenetetrazole. The findings demonstrate that increasing tonic inhibition in hilar SOM interneurons can alter dentate gyrus circuit activity during strong stimulation and suggest that tonic inhibition of interneurons could play a role in regulating excessive synchrony within the network. SIGNIFICANCE STATEMENT In contrast to many hippocampal interneurons, somatostatin (SOM) neurons in the hilus of the dentate gyrus have very low levels of nonsynaptic GABAARs and exhibit very little tonic inhibition. In an effort to increase tonic inhibition selectively in these interneurons, we used Cre-dependent viral vectors in SOM-Cre mice to achieve interneuron-specific expression of the nonsynaptic GABAAR subunits (α6 and δ) in vivo. We show, for the first time, that such recombinant GFP-tagged GABAAR subunits are expressed robustly, assemble to form functional receptors, substantially increase tonic inhibition in SOM interneurons, and alter circuit activity within the dentate gyrus.
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Affiliation(s)
- Xiaoping Tong
- Departments of Neurobiology and Department of Anatomy, Histology and Embryology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China, and
| | | | | | | | | | - Martin Wallner
- Molecular and Medical Pharmacology and Brain Research Institute, David Geffen School of Medicine at the University of California, Los Angeles, Los Angeles, California 90095
| | - Thomas S Otis
- Departments of Neurobiology and Brain Research Institute, David Geffen School of Medicine at the University of California, Los Angeles, Los Angeles, California 90095, Roche Pharmaceutical Research and Early Development, Neuroscience, Ophthalmology, and Rare Diseases Translational Area, Roche Innovation Center Basel, CH-4070, Basel, Switzerland
| | - Carolyn R Houser
- Departments of Neurobiology and Brain Research Institute, David Geffen School of Medicine at the University of California, Los Angeles, Los Angeles, California 90095,
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29
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Synaptic GABA release prevents GABA transporter type-1 reversal during excessive network activity. Nat Commun 2015; 6:6597. [PMID: 25798861 PMCID: PMC4374149 DOI: 10.1038/ncomms7597] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Accepted: 02/10/2015] [Indexed: 12/15/2022] Open
Abstract
GABA transporters control extracellular GABA, which regulates the key aspects of neuronal and network behaviour. A prevailing view is that modest neuronal depolarization results in GABA transporter type-1 (GAT-1) reversal causing non-vesicular GABA release into the extracellular space during intense network activity. This has important implications for GABA uptake-targeting therapies. Here we combined a realistic kinetic model of GAT-1 with experimental measurements of tonic GABAA receptor currents in ex vivo hippocampal slices to examine GAT-1 operation under varying network conditions. Our simulations predict that synaptic GABA release during network activity robustly prevents GAT-1 reversal. We test this in the 0 Mg2+ model of epileptiform discharges using slices from healthy and chronically epileptic rats and find that epileptiform activity is associated with increased synaptic GABA release and is not accompanied by GAT-1 reversal. We conclude that sustained efflux of GABA through GAT-1 is unlikely to occur during physiological or pathological network activity. Membrane depolarization during increased neuronal activity as seen during epilepsy has been suggested to easily reverse neuronal GABA transporters. Here the authors use modelling and experimental data and challenge this view by showing that synaptic GABA release during excessive neuronal firing averts reversal of GABA uptake.
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30
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Abstract
Gamma-amino butyric acid (GABA) is the major inhibitory neurotransmitter that is known to be synthesized and released from GABAergic neurons in the brain. However, recent studies have shown that not only neurons but also astrocytes contain a considerable amount of GABA that can be released and activate GABA receptors in neighboring neurons. These exciting new findings for glial GABA raise further interesting questions about the source of GABA, its mechanism of release and regulation and the functional role of glial GABA. In this review, we highlight recent studies that identify the presence and release of GABA in glial cells, we show several proposed potential pathways for accumulation and modulation of glial intracellular and extracellular GABA content, and finally we discuss functional roles for glial GABA in the brain.
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Affiliation(s)
- Bo-Eun Yoon
- Department of Nanobiomedical Science, Dankook University Chungnam, South Korea
| | - C Justin Lee
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST) Seoul, South Korea ; Center for Neural Science and Center for Functional Connectomics, Korea Institute of Science and Technology (KIST) Seoul, South Korea
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31
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Yoon BE, Woo J, Chun YE, Chun H, Jo S, Bae JY, An H, Min JO, Oh SJ, Han KS, Kim HY, Kim T, Kim YS, Bae YC, Lee CJ. Glial GABA, synthesized by monoamine oxidase B, mediates tonic inhibition. J Physiol 2014; 592:4951-68. [PMID: 25239459 DOI: 10.1113/jphysiol.2014.278754] [Citation(s) in RCA: 111] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
GABA is the major inhibitory transmitter in the brain and is released not only from a subset of neurons but also from glia. Although neuronal GABA is well known to be synthesized by glutamic acid decarboxylase (GAD), the source of glial GABA is unknown. After estimating the concentration of GABA in Bergmann glia to be around 5-10 mM by immunogold electron microscopy, we demonstrate that GABA production in glia requires MAOB, a key enzyme in the putrescine degradation pathway. In cultured cerebellar glia, both Ca(2+)-induced and tonic GABA release are significantly reduced by both gene silencing of MAOB and the MAOB inhibitor selegiline. In the cerebellum and striatum of adult mice, general gene silencing, knock out of MAOB or selegiline treatment resulted in elimination of tonic GABA currents recorded from granule neurons and medium spiny neurons. Glial-specific rescue of MAOB resulted in complete rescue of tonic GABA currents. Our results identify MAOB as a key synthesizing enzyme of glial GABA, which is released via bestrophin 1 (Best1) channel to mediate tonic inhibition in the brain.
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Affiliation(s)
- Bo-Eun Yoon
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Center for Neural Science, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Neuroscience Program, University of Science and Technology (UST), Daejeon, 305-350, Korea Department of Nanobiomedical Science, Dankook University, Chungnam, 330-714, Korea
| | - Junsung Woo
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Center for Neural Science, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Neuroscience Program, University of Science and Technology (UST), Daejeon, 305-350, Korea
| | - Ye-Eun Chun
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Center for Neural Science, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Neuroscience Program, University of Science and Technology (UST), Daejeon, 305-350, Korea
| | - Heejung Chun
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Center for Neural Science, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea
| | - Seonmi Jo
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 305-701, Korea
| | - Jin Young Bae
- Department of Oral Anatomy and Neurobiology, BK21, School of Dentistry, Kyungpook National University, Daegu, 700-412, Republic of Korea
| | - Heeyoung An
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Center for Neural Science, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea KU-KIST School of Converging Science and Technology, Korea University, Seoul, 136-701, Korea
| | - Joo Ok Min
- Department of Nanobiomedical Science, Dankook University, Chungnam, 330-714, Korea
| | - Soo-Jin Oh
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Center for Neural Science, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea
| | - Kyung-Seok Han
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Center for Neural Science, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Neuroscience Program, University of Science and Technology (UST), Daejeon, 305-350, Korea
| | - Hye Yun Kim
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea
| | - Taekeun Kim
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea
| | - Young Soo Kim
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea
| | - Yong Chul Bae
- Department of Oral Anatomy and Neurobiology, BK21, School of Dentistry, Kyungpook National University, Daegu, 700-412, Republic of Korea
| | - C Justin Lee
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Center for Neural Science, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Korea Neuroscience Program, University of Science and Technology (UST), Daejeon, 305-350, Korea
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32
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Liang J, Olsen RW. Alcohol use disorders and current pharmacological therapies: the role of GABA(A) receptors. Acta Pharmacol Sin 2014; 35:981-93. [PMID: 25066321 PMCID: PMC4125717 DOI: 10.1038/aps.2014.50] [Citation(s) in RCA: 86] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Accepted: 05/16/2014] [Indexed: 12/18/2022] Open
Abstract
Alcohol use disorders (AUD) are defined as alcohol abuse and alcohol dependence, which create large problems both for society and for the drinkers themselves. To date, no therapeutic can effectively solve these problems. Understanding the underlying mechanisms leading to AUD is critically important for developing effective and safe pharmacological therapies. Benzodiazepines (BZs) are used to reduce the symptoms of alcohol withdrawal syndrome. However, frequent use of BZs causes cross-tolerance, dependence, and cross-addiction to alcohol. The FDA-approved naltrexone and acamprosate have shown mixed results in clinical trials. Naltrexone is effective to treat alcohol dependence (decreased length and frequency of drinking bouts), but its severe side effects, including withdrawal symptoms, are difficult to overcome. Acamprosate showed efficacy for treating alcohol dependence in European trials, but two large US trials have failed to confirm the efficacy. Another FDA-approved medication, disulfiram, does not diminish craving, and it causes a peripheral neuropathy. Kudzu is the only natural medication mentioned by the National Institute on Alcohol Abuse and Alcoholism, but its mechanisms of action are not yet established. It has been recently shown that dihydromyricetin, a flavonoid purified from Hovenia, has unique effects on GABAA receptors and blocks ethanol intoxication and withdrawal in alcoholic animal models. In this article, we review the role of GABAA receptors in the treatment of AUD and currently available and potentially novel pharmacological agents.
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Affiliation(s)
- Jing Liang
- Department of Molecular & Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Richard W Olsen
- Department of Molecular & Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
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Xia Y, Zhao Y, Yang M, Zeng S, Shu Y. Regulation of action potential waveforms by axonal GABAA receptors in cortical pyramidal neurons. PLoS One 2014; 9:e100968. [PMID: 24971996 PMCID: PMC4074163 DOI: 10.1371/journal.pone.0100968] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2014] [Accepted: 05/30/2014] [Indexed: 01/11/2023] Open
Abstract
GABAA receptors distributed in somatodendritic compartments play critical roles in regulating neuronal activities, including spike timing and firing pattern; however, the properties and functions of GABAA receptors at the axon are still poorly understood. By recording from the cut end (bleb) of the main axon trunk of layer -5 pyramidal neurons in prefrontal cortical slices, we found that currents evoked by GABA iontophoresis could be blocked by picrotoxin, indicating the expression of GABAA receptors in axons. Stationary noise analysis revealed that single-channel properties of axonal GABAA receptors were similar to those of somatic receptors. Perforated patch recording with gramicidin revealed that the reversal potential of the GABA response was more negative than the resting membrane potential at the axon trunk, suggesting that GABA may hyperpolarize the axonal membrane potential. Further experiments demonstrated that the activation of axonal GABAA receptors regulated the amplitude and duration of action potentials (APs) and decreased the AP-induced Ca2+ transients at the axon. Together, our results indicate that the waveform of axonal APs and the downstream Ca2+ signals are modulated by axonal GABAA receptors.
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Affiliation(s)
- Yang Xia
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, P. R. China
| | - Yuan Zhao
- Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics-Huazhong University of Science and Technology, Wuhan, P. R. China
| | - Mingpo Yang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, P. R. China
| | - Shaoqun Zeng
- Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics-Huazhong University of Science and Technology, Wuhan, P. R. China
- * E-mail: (YS); (SZ)
| | - Yousheng Shu
- State Key Laboratory of Cognitive Neuroscience and Learning & IDG/McGovern Institute for Brain Research, Center for Collaboration and Innovation in Brain and Learning Sciences, Beijing Normal University, Beijing, P. R. China
- * E-mail: (YS); (SZ)
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Scimemi A. Structure, function, and plasticity of GABA transporters. Front Cell Neurosci 2014; 8:161. [PMID: 24987330 PMCID: PMC4060055 DOI: 10.3389/fncel.2014.00161] [Citation(s) in RCA: 155] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Accepted: 05/27/2014] [Indexed: 11/13/2022] Open
Abstract
GABA transporters belong to a large family of neurotransmitter:sodium symporters. They are widely expressed throughout the brain, with different levels of expression in different brain regions. GABA transporters are present in neurons and in astrocytes and their activity is crucial to regulate the extracellular concentration of GABA under basal conditions and during ongoing synaptic events. Numerous efforts have been devoted to determine the structural and functional properties of GABA transporters. There is also evidence that the expression of GABA transporters on the cell membrane and their lateral mobility can be modulated by different intracellular signaling cascades. The strength of individual synaptic contacts and the activity of entire neuronal networks may be finely tuned by altering the density, distribution and diffusion rate of GABA transporters within the cell membrane. These findings are intriguing because they suggest the existence of complex regulatory systems that control the plasticity of GABAergic transmission in the brain. Here we review the current knowledge on the structural and functional properties of GABA transporters and highlight the molecular mechanisms that alter the expression and mobility of GABA transporters at central synapses.
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Scimemi A. Plasticity of GABA transporters: an unconventional route to shape inhibitory synaptic transmission. Front Cell Neurosci 2014; 8:128. [PMID: 24860430 PMCID: PMC4026733 DOI: 10.3389/fncel.2014.00128] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Accepted: 04/22/2014] [Indexed: 11/13/2022] Open
Abstract
The brain relies on GABAergic neurons to control the ongoing activity of neuronal networks. GABAergic neurons control the firing pattern of excitatory cells, the temporal structure of membrane potential oscillations and the time window for integration of synaptic inputs. These actions require a fine control of the timing of GABA receptor activation which, in turn, depends on the precise timing of GABA release from pre-synaptic terminals and GABA clearance from the extracellular space. Extracellular GABA is not subject to enzymatic breakdown, and its clearance relies entirely on diffusion and uptake by specific transporters. In contrast to glutamate transporters, GABA transporters are abundantly expressed in neuronal pre-synaptic terminals. GABA transporters move laterally within the plasma membrane and are continuously trafficked to/from intracellular compartments. It is hypothesized that due to their proximity to GABA release sites, changes in the concentration and lateral mobility of GABA transporters may have a significant effect on the time course of the GABA concentration profile in and out of the synaptic cleft. To date, this hypothesis remains to be tested. Here we use 3D Monte Carlo reaction-diffusion simulations to analyze how changes in the density of expression and lateral mobility of GABA transporters in the cell membrane affect the extracellular GABA concentration profile and the activation of GABA receptors. Our results indicate that these manipulations mainly alter the GABA concentration profile away from the synaptic cleft. These findings provide novel insights into how the ability of GABA transporters to undergo plastic changes may alter the strength of GABAergic signals and the activity of neuronal networks in the brain.
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Mapelli L, Solinas S, D'Angelo E. Integration and regulation of glomerular inhibition in the cerebellar granular layer circuit. Front Cell Neurosci 2014; 8:55. [PMID: 24616663 PMCID: PMC3933946 DOI: 10.3389/fncel.2014.00055] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2013] [Accepted: 02/06/2014] [Indexed: 11/26/2022] Open
Abstract
Inhibitory synapses can be organized in different ways and be regulated by a multitude of mechanisms. One of the best known examples is provided by the inhibitory synapses formed by Golgi cells onto granule cells in the cerebellar glomeruli. These synapses are GABAergic and inhibit granule cells through two main mechanisms, phasic and tonic. The former is based on vesicular neurotransmitter release, the latter on the establishment of tonic γ-aminobutyric acid (GABA) levels determined by spillover and regulation of GABA uptake. The mechanisms of post-synaptic integration have been clarified to a considerable extent and have been shown to differentially involve α1 and α6 subunit-containing GABA-A receptors. Here, after reviewing the basic mechanisms of GABAergic transmission in the cerebellar glomeruli, we examine how inhibition controls signal transfer at the mossy fiber-granule cell relay. First of all, we consider how vesicular release impacts on signal timing and how tonic GABA levels control neurotransmission gain. Then, we analyze the integration of these inhibitory mechanisms within the granular layer network. Interestingly, it turns out that glomerular inhibition is just one element in a large integrated signaling system controlled at various levels by metabotropic receptors. GABA-B receptor activation by ambient GABA regulates glutamate release from mossy fibers through a pre-synaptic cross-talk mechanisms, GABA release through pre-synaptic auto-receptors, and granule cell input resistance through post-synaptic receptor activation and inhibition of a K inward-rectifier current. Metabotropic glutamate receptors (mGluRs) control GABA release from Golgi cell terminals and Golgi cell input resistance and autorhythmic firing. This complex set of mechanisms implements both homeostatic and winner-take-all processes, providing the basis for fine-tuning inhibitory neurotransmission and for optimizing signal transfer through the cerebellar cortex.
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Affiliation(s)
- Lisa Mapelli
- Department of Brain and Behavioral Sciences, University of PaviaPavia, Italy
- Brain Connectivity Center, C. Mondino National Neurological InstitutePavia, Italy
| | - Sergio Solinas
- Department of Brain and Behavioral Sciences, University of PaviaPavia, Italy
- Brain Connectivity Center, C. Mondino National Neurological InstitutePavia, Italy
| | - Egidio D'Angelo
- Department of Brain and Behavioral Sciences, University of PaviaPavia, Italy
- Brain Connectivity Center, C. Mondino National Neurological InstitutePavia, Italy
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Proddutur A, Yu J, Elgammal FS, Santhakumar V. Seizure-induced alterations in fast-spiking basket cell GABA currents modulate frequency and coherence of gamma oscillation in network simulations. CHAOS (WOODBURY, N.Y.) 2013; 23:046109. [PMID: 24387588 PMCID: PMC3855147 DOI: 10.1063/1.4830138] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Accepted: 10/30/2013] [Indexed: 05/21/2023]
Abstract
Gamma frequency oscillations have been proposed to contribute to memory formation and retrieval. Fast-spiking basket cells (FS-BCs) are known to underlie development of gamma oscillations. Fast, high amplitude GABA synapses and gap junctions have been suggested to contribute to gamma oscillations in FS-BC networks. Recently, we identified that, apart from GABAergic synapses, FS-BCs in the hippocampal dentate gyrus have GABAergic currents mediated by extrasynaptic receptors. Our experimental studies demonstrated two specific changes in FS-BC GABA currents following experimental seizures [Yu et al., J. Neurophysiol. 109, 1746 (2013)]: increase in the magnitude of extrasynaptic (tonic) GABA currents and a depolarizing shift in GABA reversal potential (E(GABA)). Here, we use homogeneous networks of a biophysically based model of FS-BCs to examine how the presence of extrasynaptic GABA conductance (g(GABA-extra)) and experimentally identified, seizure-induced changes in g(GABA-extra) and E(GABA) influence network activity. Networks of FS-BCs interconnected by fast GABAergic synapses developed synchronous firing in the dentate gamma frequency range (40-100 Hz). Systematic investigation revealed that the biologically realistic range of 30 to 40 connections between FS-BCs resulted in greater coherence in the gamma frequency range when networks were activated by Poisson-distributed dendritic synaptic inputs rather than by homogeneous somatic current injections, which were balanced for FS-BC firing frequency in unconnected networks. Distance-dependent conduction delay enhanced coherence in networks with 30-40 FS-BC interconnections while inclusion of gap junctional conductance had a modest effect on coherence. In networks activated by somatic current injections resulting in heterogeneous FS-BC firing, increasing g(GABA-extra) reduced the frequency and coherence of FS-BC firing when E(GABA) was shunting (-74 mV), but failed to alter average FS-BC frequency when E(GABA) was depolarizing (-54 mV). When FS-BCs were activated by biologically based dendritic synaptic inputs, enhancing g(GABA-extra) reduced the frequency and coherence of FS-BC firing when E(GABA) was shunting and increased average FS-BC firing when E(GABA) was depolarizing. Shifting E(GABA) from shunting to depolarizing potentials consistently increased network frequency to and above high gamma frequencies (>80 Hz). Since gamma oscillations may contribute to learning and memory processing [Fell et al., Nat. Neurosci. 4, 1259 (2001); Jutras et al., J. Neurosci. 29, 12521 (2009); Wang, Physiol. Rev. 90, 1195 (2010)], our demonstration that network oscillations are modulated by extrasynaptic inhibition in FS-BCs suggests that neuroactive compounds that act on extrasynaptic GABA receptors could impact memory formation by modulating hippocampal gamma oscillations. The simulation results indicate that the depolarized FS-BC GABA reversal, observed after experimental seizures, together with enhanced spillover extrasynaptic GABA currents are likely to promote generation of focal high frequency activity associated with epileptic networks.
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Affiliation(s)
- Archana Proddutur
- Department of Neurology and Neurosciences, New Jersey Medical School, Rutgers, Newark, New Jersey 07103, USA
| | - Jiandong Yu
- Department of Neurology and Neurosciences, New Jersey Medical School, Rutgers, Newark, New Jersey 07103, USA
| | - Fatima S Elgammal
- Department of Neurology and Neurosciences, New Jersey Medical School, Rutgers, Newark, New Jersey 07103, USA
| | - Vijayalakshmi Santhakumar
- Department of Neurology and Neurosciences, New Jersey Medical School, Rutgers, Newark, New Jersey 07103, USA
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A reorganized GABAergic circuit in a model of epilepsy: evidence from optogenetic labeling and stimulation of somatostatin interneurons. J Neurosci 2013; 33:14392-405. [PMID: 24005292 DOI: 10.1523/jneurosci.2045-13.2013] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Axonal sprouting of excitatory neurons is frequently observed in temporal lobe epilepsy, but the extent to which inhibitory interneurons undergo similar axonal reorganization remains unclear. The goal of this study was to determine whether somatostatin (SOM)-expressing neurons in stratum (s.) oriens of the hippocampus exhibit axonal sprouting beyond their normal territory and innervate granule cells of the dentate gyrus in a pilocarpine model of epilepsy. To obtain selective labeling of SOM-expressing neurons in s. oriens, a Cre recombinase-dependent construct for channelrhodopsin2 fused to enhanced yellow fluorescent protein (ChR2-eYFP) was virally delivered to this region in SOM-Cre mice. In control mice, labeled axons were restricted primarily to s. lacunosum-moleculare. However, in pilocarpine-treated animals, a rich plexus of ChR2-eYFP-labeled fibers and boutons extended into the dentate molecular layer. Electron microscopy with immunogold labeling demonstrated labeled axon terminals that formed symmetric synapses on dendritic profiles in this region, consistent with innervation of granule cells. Patterned illumination of ChR2-labeled fibers in s. lacunosum-moleculare of CA1 and the dentate molecular layer elicited GABAergic inhibitory responses in dentate granule cells in pilocarpine-treated mice but not in controls. Similar optical stimulation in the dentate hilus evoked no significant responses in granule cells of either group of mice. These findings indicate that under pathological conditions, SOM/GABAergic neurons can undergo substantial axonal reorganization beyond their normal territory and establish aberrant synaptic connections. Such reorganized circuitry could contribute to functional deficits in inhibition in epilepsy, despite the presence of numerous GABAergic terminals in the region.
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Carver CM, Reddy DS. Neurosteroid interactions with synaptic and extrasynaptic GABA(A) receptors: regulation of subunit plasticity, phasic and tonic inhibition, and neuronal network excitability. Psychopharmacology (Berl) 2013; 230:151-88. [PMID: 24071826 PMCID: PMC3832254 DOI: 10.1007/s00213-013-3276-5] [Citation(s) in RCA: 171] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Accepted: 08/29/2013] [Indexed: 12/25/2022]
Abstract
RATIONALE Neurosteroids are steroids synthesized within the brain with rapid effects on neuronal excitability. Allopregnanolone, allotetrahydrodeoxycorticosterone, and androstanediol are three widely explored prototype endogenous neurosteroids. They have very different targets and functions compared to conventional steroid hormones. Neuronal γ-aminobutyric acid (GABA) type A (GABA(A)) receptors are one of the prime molecular targets of neurosteroids. OBJECTIVE This review provides a critical appraisal of recent advances in the pharmacology of endogenous neurosteroids that interact with GABA(A) receptors in the brain. Neurosteroids possess distinct, characteristic effects on the membrane potential and current conductance of the neuron, mainly via potentiation of GABA(A) receptors at low concentrations and direct activation of receptor chloride channel at higher concentrations. The GABA(A) receptor mediates two types of inhibition, now characterized as synaptic (phasic) and extrasynaptic (tonic) inhibition. Synaptic release of GABA results in the activation of low-affinity γ2-containing synaptic receptors, while high-affinity δ-containing extrasynaptic receptors are persistently activated by the ambient GABA present in the extracellular fluid. Neurosteroids are potent positive allosteric modulators of synaptic and extrasynaptic GABA(A) receptors and therefore enhance both phasic and tonic inhibition. Tonic inhibition is specifically more sensitive to neurosteroids. The resulting tonic conductance generates a form of shunting inhibition that controls neuronal network excitability, seizure susceptibility, and behavior. CONCLUSION The growing understanding of the mechanisms of neurosteroid regulation of the structure and function of the synaptic and extrasynaptic GABA(A) receptors provides many opportunities to create improved therapies for sleep, anxiety, stress, epilepsy, and other neuropsychiatric conditions.
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Affiliation(s)
- Chase Matthew Carver
- Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M University Health Science Center, 2008 Medical Research and Education Building, 8447 State Highway 47, Bryan, TX, 77807-3260, USA
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Egawa K, Fukuda A. Pathophysiological power of improper tonic GABA(A) conductances in mature and immature models. Front Neural Circuits 2013; 7:170. [PMID: 24167475 PMCID: PMC3807051 DOI: 10.3389/fncir.2013.00170] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2013] [Accepted: 09/28/2013] [Indexed: 11/25/2022] Open
Abstract
High-affinity extrasynaptic gamma-aminobutyric acid A (GABAA) receptors are tonically activated by low and consistent levels of ambient GABA, mediating chronic inhibition against neuronal excitability (tonic inhibition) and the modulation of neural development. Synaptic (phasic) inhibition is spatially and temporally precise compared with tonic inhibition, which provides blunt yet strong integral inhibitory force by shunting electrical signaling. Although effects of acute modification of tonic inhibition are known, its pathophysiological significance remains unclear because homeostatic regulation of neuronal excitability can compensate for long-term deficit of extrasynaptic GABAA receptor activation. Nevertheless, tonic inhibition is of great interest for its pathophysiological involvement in central nervous system (CNS) diseases and thus as a therapeutic target. Together with the development of experimental models for various pathological states, recent evidence demonstrates such pathological involvements of tonic inhibition in neuronal dysfunction. This review focuses on the recent progress of tonic activation of GABAA conductance on the development and pathology of the CNS. Findings indicate that neuronal function in various brain regions are exacerbated with a gain or loss of function of tonic inhibition by GABA spillover. Disturbance of tonic GABAA conductance mediated by non-synaptic ambient GABA may result in brain mal-development. Therefore, various pathological states (epilepsy, motor dysfunctions, psychiatric disorders, and neurodevelopmental disorders) may be partly attributable to abnormal tonic GABAA conductances. Thus, the tone of tonic conductance and level of ambient GABA may be precisely tuned to maintain the regular function and development of the CNS. Therefore, receptor expression and factors for regulating the ambient GABA concentration are highlighted to gain a deeper understanding of pathology and therapeutic strategy for CNS diseases.
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Affiliation(s)
- Kiyoshi Egawa
- Department of Neurology, Massachusetts General Hospital Charlestown, MA, USA ; Department of Pediatrics, Hokkaido University Graduate School of Medicine Sapporo, Japan
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Santhakumar V, Meera P, Karakossian MH, Otis TS. A reinforcing circuit action of extrasynaptic GABAA receptor modulators on cerebellar granule cell inhibition. PLoS One 2013; 8:e72976. [PMID: 23977374 PMCID: PMC3747091 DOI: 10.1371/journal.pone.0072976] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Accepted: 07/23/2013] [Indexed: 01/04/2023] Open
Abstract
GABAA receptors (GABARs) are the targets of a wide variety of modulatory drugs which enhance chloride flux through GABAR ion channels. Certain GABAR modulators appear to acutely enhance the function of δ subunit-containing GABAR subtypes responsible for tonic forms of inhibition. Here we identify a reinforcing circuit mechanism by which these drugs, in addition to directly enhancing GABAR function, also increase GABA release. Electrophysiological recordings in cerebellar slices from rats homozygous for the ethanol-hypersensitive (α6100Q) allele show that modulators and agonists selective for δ-containing GABARs such as THDOC, ethanol and THIP (gaboxadol) increased the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) in granule cells. Ethanol fails to augment granule cell sIPSC frequency in the presence of glutamate receptor antagonists, indicating that circuit mechanisms involving granule cell output contribute to ethanol-enhancement of synaptic inhibition. Additionally, GABAR antagonists decrease ethanol-induced enhancement of Golgi cell firing. Consistent with a role for glutamatergic inputs, THIP-induced increases in Golgi cell firing are abolished by glutamate receptor antagonists. Moreover, THIP enhances the frequency of spontaneous excitatory postsynaptic currents in Golgi cells. Analyses of knockout mice indicate that δ subunit-containing GABARs are required for enhancing GABA release in the presence of ethanol and THIP. The limited expression of the GABAR δ subunit protein within the cerebellar cortex suggests that an indirect, circuit mechanism is responsible for stimulating Golgi cell GABA release by drugs selective for extrasynaptic isoforms of GABARs. Such circuit effects reinforce direct actions of these positive modulators on tonic GABAergic inhibition and are likely to contribute to the potent effect of these compounds as nervous system depressants.
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Affiliation(s)
- Vijayalakshmi Santhakumar
- Department of Neurobiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America.
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Szemes M, Davies RL, Garden CLP, Usowicz MM. Weaker control of the electrical properties of cerebellar granule cells by tonically active GABAA receptors in the Ts65Dn mouse model of Down's syndrome. Mol Brain 2013; 6:33. [PMID: 23870245 PMCID: PMC3723448 DOI: 10.1186/1756-6606-6-33] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2013] [Accepted: 07/14/2013] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND Down's syndrome (DS) is caused by triplication of all or part of human chromosome 21 and is characterized by a decrease in the overall size of the brain. One of the brain regions most affected is the cerebellum, in which the number of granule cells (GCs) is markedly decreased. GCs process sensory information entering the cerebellum via mossy fibres and pass it on to Purkinje cells and inhibitory interneurons. How GCs transform incoming signals depends on their input-output relationship, which is adjusted by tonically active GABA(A) receptor channels. RESULTS We report that in the Ts65Dn mouse model of DS, in which cerebellar volume and GC number are decreased as in DS, the tonic GABA(A) receptor current in GCs is smaller than in wild-type mice and is less effective in moderating input resistance and raising the minimum current required for action potential firing. We also find that tonically active GABA(A) receptors curb the height and broaden the width of action potentials in wild-type GCs but not in Ts65Dn GCs. Single-cell real-time quantitative PCR reveals that these electrical differences are accompanied by decreased expression of the gene encoding the GABA(A) receptor β3 subunit but not genes coding for some of the other GABA(A) receptor subunits expressed in GCs (α1, α6, β2 and δ). CONCLUSIONS Weaker moderation of excitability and action potential waveform in GCs of the Ts65Dn mouse by tonically active GABA(A) receptors is likely to contribute to atypical transfer of information through the cerebellum. Similar changes may occur in DS.
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Affiliation(s)
- Marianna Szemes
- Present address: School of Cellular and Molecular Medicine, University of Bristol, University Walk, Bristol BS8 1TD, UK
| | - Rachel L Davies
- Present address: Research & Enterprise Development, University of Bristol, Senate House, Tyndall Avenue, Bristol BS8 1TH, UK
| | - Claire LP Garden
- Present address: School of Life, Sport and Social Sciences, Edinburgh Napier University, Sighthill Court, Edinburgh EH11 4BN, UK
| | - Maria M Usowicz
- School of Physiology & Pharmacology, University of Bristol, University Walk, Bristol BS8 1TD, UK
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Egawa K, Kitagawa K, Inoue K, Takayama M, Takayama C, Saitoh S, Kishino T, Kitagawa M, Fukuda A. Decreased tonic inhibition in cerebellar granule cells causes motor dysfunction in a mouse model of Angelman syndrome. Sci Transl Med 2013; 4:163ra157. [PMID: 23220633 DOI: 10.1126/scitranslmed.3004655] [Citation(s) in RCA: 92] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Angelman syndrome is a neurodevelopmental disorder caused by loss of function of the UBE3A gene encoding a ubiquitin E3 ligase. Motor dysfunction is a characteristic feature of Angelman syndrome, but neither the mechanisms of action nor effective therapeutic strategies have yet been elucidated. We report that tonic inhibition is specifically decreased in cerebellar granule cells of Ube3a-deficient mice, a model of Angelman syndrome. As a mechanism underlying this decrease in tonic inhibition, we show that Ube3a controls degradation of γ-aminobutyric acid (GABA) transporter 1 (GAT1) and that deficiency of Ube3a induces a surplus of GAT1 that results in a decrease in GABA concentrations in the extrasynaptic space. Administering low doses of 4,5,6,7-tetrahydroisothiazolo-[5,4-c]pyridin-3-ol (THIP), a selective extrasynaptic GABA(A) receptor agonist, improves the abnormal firing properties of a population of Purkinje cells in cerebellar brain slices and reduces cerebellar ataxia in Ube3a-deficient mice in vivo. These results suggest that pharmacologically increasing tonic inhibition may be a useful strategy for alleviating motor dysfunction in Angelman syndrome.
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Affiliation(s)
- Kiyoshi Egawa
- Department of Neurophysiology, Hamamatsu University School of Medicine, Hamamatsu 431-3192, Japan.
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Robust photoregulation of GABA(A) receptors by allosteric modulation with a propofol analogue. Nat Commun 2013; 3:1095. [PMID: 23033071 PMCID: PMC4023869 DOI: 10.1038/ncomms2094] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Accepted: 08/29/2012] [Indexed: 01/09/2023] Open
Abstract
Photochemical switches represent a powerful method for improving pharmacological therapies and controlling cellular physiology. Here we report the photo-regulation of GABAA receptors (GABAARs) by a derivative of propofol (2,6-diisopropylphenol), a GABAAR allosteric modulator, that we have modified to contain photo-isomerizable azobenzene. Using α1β2γ2 GABAARs expressed in Xenopus laevis oocytes and native GABAARs of isolated retinal ganglion cells, we show that the trans-azobenzene isomer of the new compound (trans-MPC088), generated by visible light (wavelengths ~440 nm), potentiates the GABA-elicited response and at higher concentrations directly activates the receptors. cis-MPC088, generated from trans-MPC088 by UV light (~365 nm), produces little if any receptor potentiation/activation. In cerebellar slices, MPC088 co-applied with GABA affords bidirectional photo-modulation of Purkinje cell membrane current and spike-firing rate. The findings demonstrate photo-control of GABAARs by an allosteric ligand and open new avenues for fundamental and clinically oriented research on GABAARs, a major class of neurotransmitter receptors in the central nervous system.
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Yu J, Proddutur A, Elgammal FS, Ito T, Santhakumar V. Status epilepticus enhances tonic GABA currents and depolarizes GABA reversal potential in dentate fast-spiking basket cells. J Neurophysiol 2013; 109:1746-63. [PMID: 23324316 DOI: 10.1152/jn.00891.2012] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Temporal lobe epilepsy is associated with loss of interneurons and inhibitory dysfunction in the dentate gyrus. While status epilepticus (SE) leads to changes in granule cell inhibition, whether dentate basket cells critical for regulating granule cell feedforward and feedback inhibition express tonic GABA currents (I(GABA)) and undergo changes in inhibition after SE is not known. We find that interneurons immunoreactive for parvalbumin in the hilar-subgranular region express GABAA receptor (GABA(A)R) δ-subunits, which are known to underlie tonic I(GABA). Dentate fast-spiking basket cells (FS-BCs) demonstrate baseline tonic I(GABA) blocked by GABA(A)R antagonists. In morphologically and physiologically identified FS-BCs, tonic I(GABA) is enhanced 1 wk after pilocarpine-induced SE, despite simultaneous reduction in spontaneous inhibitory postsynaptic current (sIPSC) frequency. Amplitude of tonic I(GABA) in control and post-SE FS-BCs is enhanced by 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP), demonstrating the contribution of GABA(A)R δ-subunits. Whereas FS-BC resting membrane potential is unchanged after SE, perforated-patch recordings from FS-BCs show that the reversal potential for GABA currents (E(GABA)) is depolarized after SE. In model FS-BCs, increasing tonic GABA conductance decreased excitability when E(GABA) was shunting and increased excitability when E(GABA) was depolarizing. Although simulated focal afferent activation evoked seizurelike activity in model dentate networks with FS-BC tonic GABA conductance and shunting E(GABA), excitability of identical networks with depolarizing FS-BC E(GABA) showed lower activity levels. Thus, together, post-SE changes in tonic I(GABA) and E(GABA) maintain homeostasis of FS-BC activity and limit increases in dentate excitability. These findings have implications for normal FS-BC function and can inform studies examining comorbidities and therapeutics following SE.
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Affiliation(s)
- Jiandong Yu
- Department of Neurology and Neurosciences, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ, USA
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Abstract
TRP channels were first identified as membrane proteins mediating phototransduction in fruit flies. Astrocytes were initially referred to as the silent elements of the nervous system. At the time these discoveries were made, few would have suspected TRP channels and astrocytes could contribute significantly to our understanding of brain signalling. Recent findings, however, put TRP channels and astrocytes in the spotlight, describe their ability to modulate the activity of specific sets of synapses, and raise some interesting questions. What makes astrocytes capable of exerting cell-specific effects on interneuronal signals? How do different synapses respond to changes in astrocytic function and in the local micro-structure of the neuropil? Can astrocytes be considered good candidate targets for therapeutic intervention to treat neurological diseases? Here I discuss the recent developments on TRP channels and astrocytes that have made us aware of the many structural and functional features of synapses that still need to be discovered and that could lead a new avant-garde in decoding the cellular and molecular basis of brain (dys)function.
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Affiliation(s)
- Annalisa Scimemi
- Synaptic Physiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive 3C316, Bethesda, MD 20892-3701, USA.
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47
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Kirischuk S, Parpura V, Verkhratsky A. Sodium dynamics: another key to astroglial excitability? Trends Neurosci 2012; 35:497-506. [PMID: 22633141 DOI: 10.1016/j.tins.2012.04.003] [Citation(s) in RCA: 172] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Revised: 04/06/2012] [Accepted: 04/10/2012] [Indexed: 11/19/2022]
Abstract
Astroglial excitability is largely mediated by fluctuations in intracellular ion concentrations. In addition to generally acknowledged Ca²⁺ excitability of astroglia, recent studies have demonstrated that neuronal activity triggers transient increases in the cytosolic Na⁺ concentration ([Na⁺](i)) in perisynaptic astrocytes. These [Na⁺](i) transients are controlled by multiple Na⁺-permeable channels and Na⁺-dependent transporters; spatiotemporally organized [Na⁺](i) dynamics in turn regulate diverse astroglial homeostatic responses such as metabolic/signaling utilization of lactate and glutamate, transmembrane transport of neurotransmitters and K⁺ buffering. In particular, near-membrane [Na⁺](i) transients determine the rate and the direction of the transmembrane transport of GABA and Ca²⁺. We discuss here the role of Na⁺ in the regulation of various systems that mediate fast bidirectional communication between neurones and glia at the single synapse level.
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Affiliation(s)
- Sergei Kirischuk
- Institute of Physiology and Pathophysiology, Universal Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
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48
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Vardya I, Hoestgaard-Jensen K, Nieto-Gonzalez JL, Dósa Z, Boddum K, Holm MM, Wolinsky TD, Jones KA, Dalby NO, Ebert B, Jensen K. Positive modulation of δ-subunit containing GABA(A) receptors in mouse neurons. Neuropharmacology 2012; 63:469-79. [PMID: 22579928 DOI: 10.1016/j.neuropharm.2012.04.023] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2010] [Revised: 04/20/2012] [Accepted: 04/23/2012] [Indexed: 12/23/2022]
Abstract
δ-subunit containing extrasynaptic GABA(A) receptors are potential targets for modifying neuronal activity in a range of brain disorders. With the aim of gaining more insight in synaptic and extrasynaptic inhibition, we used a new positive modulator, AA29504, of δ-subunit containing GABA(A) receptors in mouse neurons in vitro and in vivo. Whole-cell patch-clamp recordings were carried out in the dentate gyrus in mouse brain slices. In granule cells, AA29504 (1 μM) caused a 4.2-fold potentiation of a tonic current induced by THIP (1 μM), while interneurons showed a potentiation of 2.6-fold. Moreover, AA29504 (1 μM) increased the amplitude and prolonged the decay of miniature inhibitory postsynaptic currents (mIPSCs) in granule cells, and this effect was abolished by Zn²⁺ (15 μM). AA29504 (1 μM) also induced a small tonic current (12.7 ± 3.2 pA) per se, and when evaluated in a nominally GABA-free environment using Ca²⁺ imaging in cultured neurons, AA29504 showed GABA(A) receptor agonism in the absence of agonist. Finally, AA29504 exerted dose-dependent stress-reducing and anxiolytic effects in mice in vivo. We propose that AA29504 potentiates δ-containing GABA(A) receptors to enhance tonic inhibition, and possibly recruits perisynaptic δ-containing receptors to participate in synaptic phasic inhibition in dentate gyrus.
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Affiliation(s)
- Irina Vardya
- Synaptic Physiology Laboratory, Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark
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49
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Decrease in tonic inhibition contributes to increase in dentate semilunar granule cell excitability after brain injury. J Neurosci 2012; 32:2523-37. [PMID: 22396425 DOI: 10.1523/jneurosci.4141-11.2012] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Brain injury is an etiological factor for temporal lobe epilepsy and can lead to memory and cognitive impairments. A recently characterized excitatory neuronal class in the dentate molecular layer, semilunar granule cell (SGC), has been proposed to regulate dentate network activity patterns and working memory formation. Although SGCs, like granule cells, project to CA3, their typical sustained firing and associational axon collaterals suggest that they are functionally distinct from granule cells. We find that brain injury results in an enhancement of SGC excitability associated with an increase in input resistance 1 week after trauma. In addition to prolonging miniature and spontaneous IPSC interevent intervals, brain injury significantly reduces the amplitude of tonic GABA currents in SGCs. The postinjury decrease in SGC tonic GABA currents is in direct contrast to the increase observed in granule cells after trauma. Although our observation that SGCs express Prox1 indicates a shared lineage with granule cells, data from control rats show that SGC tonic GABA currents are larger and sIPSC interevent intervals shorter than in granule cells, demonstrating inherent differences in inhibition between these cell types. GABA(A) receptor antagonists selectively augmented SGC input resistance in controls but not in head-injured rats. Moreover, post-traumatic differences in SGC firing were abolished in GABA(A) receptor blockers. Our data show that cell-type-specific post-traumatic decreases in tonic GABA currents boost SGC excitability after brain injury. Hyperexcitable SGCs could augment dentate throughput to CA3 and contribute substantively to the enhanced risk for epilepsy and memory dysfunction after traumatic brain injury.
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50
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Verkhratsky A, Rodríguez JJ, Parpura V. Neurotransmitters and integration in neuronal-astroglial networks. Neurochem Res 2012; 37:2326-38. [PMID: 22476701 DOI: 10.1007/s11064-012-0765-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2012] [Revised: 03/18/2012] [Accepted: 03/22/2012] [Indexed: 10/28/2022]
Abstract
Two major neural cell types, glia, astrocytes in particular, and neurones can release chemical transmitters that act as soluble signalling compounds for intercellular communication. Exocytosis, a process which depends on an increase in cytosolic Ca(2+) levels, represents a common denominator for release of neurotransmitters, stored in secretory vesicles, from these neural cells. While neurones rely predominately on the immediate entry of Ca(2+) from the extracellular space to the cytosol in this process, astrocytes support their cytosolic Ca(2+) increases by appropriating this ion from the intracellular endoplasmic reticulum store and extracellular space. Additionally, astrocytes can release neurotransmitters using a variety of non-vesicular pathways which are mediated by an assortment of plasmalemmal channels and transporters. Once a neuronal and/or astrocytic neurotransmitter is released into the extracellular space, it can activate plasma membrane neurotransmitter receptors on neural cells, causing autocrine and/or paracrine signalling. Moreover, chemical transmission is essential not only for homocellular, but also for heterocellular bi-directional communication in the brain. Further detailed understanding of chemical transmission will aid our comprehension of the brain (dys)function in heath and disease.
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Affiliation(s)
- Alexei Verkhratsky
- Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK.
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