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Murray BP, Kiernan EA. Physiologic Effects of Substance Use. Emerg Med Clin North Am 2024; 42:69-91. [PMID: 37977754 DOI: 10.1016/j.emc.2023.06.022] [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] [Indexed: 11/19/2023]
Abstract
Physiologic and psychological effects of substance use are common occurrences. They may be the proximate purpose of the exposure or related to an unintended complication. Acute short-term exposure effects may not be the same as long-term effects. These effects are mediated by different receptors they act on and the homeostatic changes that occur due to repeat exposure. We review in this article the physiologic and psychological effects from exposure to commonly encountered drugs, ethanol, sedative hypnotics, cocaine, amphetamines, marijuana, opioids, nicotine, hydrocarbons (halogenated and non-halogenated), and nitrous oxide.
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Affiliation(s)
- Brian Patrick Murray
- Department of Emergency Medicine, Wright State Boonshoft School of Medicine, 2555 University Boulevard, Suite 110, Dayton, OH 45324, USA.
| | - Emily Anne Kiernan
- Department of Emergency Medicine, Emory University School of Medicine, 50 Hurtz Plaza Southeast, Suite 600, Atlanta, GA, USA; Georgia Poison Center, 50 Hurtz Plaza Southeast, Suite 600, Atlanta, GA, USA
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2
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Bappi MH, Prottay AAS, Kamli H, Sonia FA, Mia MN, Akbor MS, Hossen MM, Awadallah S, Mubarak MS, Islam MT. Quercetin Antagonizes the Sedative Effects of Linalool, Possibly through the GABAergic Interaction Pathway. Molecules 2023; 28:5616. [PMID: 37513487 PMCID: PMC10384931 DOI: 10.3390/molecules28145616] [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: 06/09/2023] [Revised: 07/15/2023] [Accepted: 07/20/2023] [Indexed: 07/30/2023] Open
Abstract
Sedatives promote calmness or sleepiness during surgery or severely stressful events. In addition, depression is a mental health issue that negatively affects emotional well-being. A group of drugs called anti-depressants is used to treat major depressive illnesses. The aim of the present work was to evaluate the effects of quercetin (QUR) and linalool (LIN) on thiopental sodium (TS)-induced sleeping mice and to investigate the combined effects of these compounds using a conventional co-treatment strategy and in silico studies. For this, the TS-induced sleeping mice were monitored to compare the occurrence, latency, and duration of the sleep-in response to QUR (10, 25, 50 mg/kg), LIN (10, 25, 50 mg/kg), and diazepam (DZP, 3 mg/kg, i.p.). Moreover, an in silico investigation was undertaken to assess this study's putative modulatory sedation mechanism. For this, we observed the ability of test and standard medications to interact with various gamma-aminobutyric acid A receptor (GABAA) subunits. Results revealed that QUR and LIN cause dose-dependent antidepressant-like and sedative-like effects in animals, respectively. In addition, QUR-50 mg/kg and LIN-50 mg/kg and/or DZP-3 mg/kg combined were associated with an increased latency period and reduced sleeping times in animals. Results of the in silico studies demonstrated that QUR has better binding interaction with GABAA α3, β1, and γ2 subunits when compared with DZP, whereas LIN showed moderate affinity with the GABAA receptor. Taken together, the sleep duration of LIN and DZP is opposed by QUR in TS-induced sleeping mice, suggesting that QUR may be responsible for providing sedation-antagonizing effects through the GABAergic interaction pathway.
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Affiliation(s)
- Mehedi Hasan Bappi
- Department of Pharmacy, Bangabandhu Sheikh Mujibur Rahman Science and Technology University, Gopalganj 8100, Bangladesh
| | - Abdullah Al Shamsh Prottay
- Department of Pharmacy, Bangabandhu Sheikh Mujibur Rahman Science and Technology University, Gopalganj 8100, Bangladesh
| | - Hossam Kamli
- Department of Clinical Laboratory Sciences, College of Applied Medical Sciences, King Khalid University, Abha 61421, Saudi Arabia
| | - Fatema Akter Sonia
- Department of Pharmacy, Bangabandhu Sheikh Mujibur Rahman Science and Technology University, Gopalganj 8100, Bangladesh
| | - Md Nayem Mia
- Department of Pharmacy, Bangabandhu Sheikh Mujibur Rahman Science and Technology University, Gopalganj 8100, Bangladesh
| | - Md Showkoth Akbor
- Department of Pharmacy, Bangabandhu Sheikh Mujibur Rahman Science and Technology University, Gopalganj 8100, Bangladesh
| | - Md Munnaf Hossen
- School of Health and Biomedical Sciences, RMIT University, Bundoora, VIC 3083, Australia
| | - Samir Awadallah
- Department of Medical Lab Sciences, Faculty of Allied Medical Sciences, Zarqa University, Zarqa 13110, Jordan
| | | | - Muhammad Torequl Islam
- Department of Pharmacy, Bangabandhu Sheikh Mujibur Rahman Science and Technology University, Gopalganj 8100, Bangladesh
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Investigation of [3H]diazepam derivatives as allosteric modulators of GABAA receptor α1β2γ2 subtypes: combination of molecular docking/dynamic simulations, pharmacokinetics/drug-likeness prediction, and QSAR analysis. Struct Chem 2022; 34:791-823. [PMID: 35971551 PMCID: PMC9365687 DOI: 10.1007/s11224-022-02029-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Accepted: 08/02/2022] [Indexed: 11/30/2022]
Abstract
In this paper, a data set of [3H] diazepam derivatives was analyzed using various computational methods: molecular docking/dynamic simulations, and QSAR analysis. The main aims of these studies are to understand the binding mechanisms by which benzodiazepines allosterically modulate GABAA receptor α1β2γ2 subtypes, from inducing neuronal inhibition at lower doses to the anesthetic effect at higher doses, and also, to define the structural requirements that contribute to improving the response of GABAA/α1β2γ2 receptor to benzodiazepine drugs. The results of the molecular docking study allowed selecting Ro12-6377 and proflazepam as the best modulators for the four binding sites simultaneously. Subsequently, the stability of the selected complexes was investigated by performing molecular dynamics simulation. The latter confirmed the features of both modulators to exert direct effects on the chloride-channel lining residues. Pharmacokinetics and drug-likeness profile were assessed through in silico tool. Furthermore, a QSAR analysis was conducted using an improved vemolecular dynamics simulations proposed byrsion of PLS regression. The goodness of fit and the predictive power of the resulting PLS model were estimated according to internal and external validation parameters: R2 = 0.632, R2adj = 0.584, F = 12.806; p-value = 6.2050e − 07, Q2loo = 0.639, and Q2F3 = 0.813. Clearly, the obtained results ensure the predictive ability of the developed QSAR model for the design of new high-potency benzodiazepine drugs.
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Rapid effects of neurosteroids on neuronal plasticity and their physiological and pathological implications. Neurosci Lett 2021; 750:135771. [PMID: 33636284 DOI: 10.1016/j.neulet.2021.135771] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Revised: 02/15/2021] [Accepted: 02/20/2021] [Indexed: 11/22/2022]
Abstract
Current neuroscience research on neurosteroids and their synthetic analogues - neuroactive steroids - clearly demonstrate their drug likeness in a variety of neurological and psychiatric conditions. Moreover, research on neurosteroids continues to provide novel mechanistic insights into receptor activation or inhibition of various receptors. This mini-review will provide a high-level overview of the research area and discuss the various classes of potential physiological and pathological implications discovered so far.
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Simeone X, Koniuszewski F, Müllegger M, Smetka A, Steudle F, Puthenkalam R, Ernst M, Scholze P. A Benzodiazepine Ligand with Improved GABA A Receptor α5-Subunit Selectivity Driven by Interactions with Loop C. Mol Pharmacol 2020; 99:39-48. [PMID: 33268553 DOI: 10.1124/molpharm.120.000067] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Accepted: 10/20/2020] [Indexed: 01/30/2023] Open
Abstract
The family of GABAA receptors is an important drug target group in the treatment of sleep disorders, anxiety, epileptic seizures, and many others. The most frequent GABAA receptor subtype is composed of two α-, two β-, and one γ2-subunit, whereas the nature of the α-subunit critically determines the properties of the benzodiazepine binding site of those receptors. Nearly all of the clinically relevant drugs target all GABAA receptor subtypes equally. In the past years, however, drug development research has focused on studying α5-containing GABAA receptors. Beyond the central nervous system, α5-containing GABAA receptors in airway smooth muscles are considered as an emerging target for bronchial asthma. Here, we investigated a novel compound derived from the previously described imidazobenzodiazepine SH-053-2'F-R-CH3 (SH53d-ester). Although SH53d-ester is only moderately selective for α5-subunit-containing GABAA receptors, the derivative SH53d-acid shows superior (>40-fold) affinity selectivity and is a positive modulator. Using two-electrode voltage clamp electrophysiology in Xenopus laevis oocytes and radioligand displacement assays with human embryonic kidney 293 cells, we demonstrated that an acid group as substituent on the imidazobenzodiazepine scaffold leads to large improvements of functional and binding selectivity for α5β3γ2 over other αxβ3γ2 GABAA receptors. Atom level structural studies provide hypotheses for the improved affinity to this receptor subtype. Mutational analysis confirmed the hypotheses, indicating that loop C of the GABAA receptor α-subunit is the dominant molecular determinant of drug selectivity. Thus, we characterize a promising novel α5-subunit-selective drug candidate. SIGNIFICANCE STATEMENT: In the current study we present the detailed pharmacological characterization of a novel compound derived from the previously described imidazobenzodiazepine SH-053-2'F-R-CH3. We describe its superior (>40-fold) affinity selectivity for α5-containing GABAA receptors and show atom-level structure predictions to provide hypotheses for the improved affinity to this receptor subtype. Mutational analysis confirmed the hypotheses, indicating that loop C of the GABAA receptor α-subunit is the dominant molecular determinant of drug selectivity.
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Affiliation(s)
- Xenia Simeone
- Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Filip Koniuszewski
- Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Markus Müllegger
- Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Andreas Smetka
- Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Friederike Steudle
- Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Roshan Puthenkalam
- Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Margot Ernst
- Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Petra Scholze
- Center for Brain Research, Medical University of Vienna, Vienna, Austria
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Farquharson S, Brouillette C, Smith W, Shende C. A Surface-Enhanced Raman Spectral Library of Important Drugs Associated With Point-of-Care and Field Applications. Front Chem 2019; 7:706. [PMID: 31709234 PMCID: PMC6823623 DOI: 10.3389/fchem.2019.00706] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Accepted: 10/08/2019] [Indexed: 12/03/2022] Open
Abstract
During the past decade, the ability of surface-enhanced Raman spectroscopy (SERS) to measure extremely low concentrations, such as mg/L and below, and the availability of hand-held Raman spectrometers, has led to a significant growth in the number and variety of applications of SERS to real-world problems. Most of these applications involve the measurement of drugs, such as quantifying medication in patients, identifying illicit drugs in impaired drivers, and more recently, identifying drugs used as weapons. Similar to Raman spectroscopy, most of the point-of-care and field applications involve the identification of the drug to determine the course of action. However, unlike Raman spectroscopy, spectral libraries are not readily available to perform the necessary identification. In a large part, this is due to the uniqueness of the commercially available SERS substrates, each of which can produce different spectra for the same drug. In an effort to overcome this limitation, we have measured numerous drugs using the most common, and readily available SERS material and hand-held Raman analyzers, specifically gold colloids and analyzers using 785 nm laser excitation. Here we present the spectra of some 39 drugs of current interest, such as buprenorphine, delta-9 tetrahydrocannabinol, and fentanyl, which we hope will aid in the development of current and future SERS drug analysis applications.
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Moody OA, Jenkins A. The role of loops B and C in determining the potentiation of GABA A receptors by midazolam. Pharmacol Res Perspect 2018; 6:e00433. [PMID: 30459951 PMCID: PMC6234229 DOI: 10.1002/prp2.433] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Revised: 07/19/2018] [Accepted: 07/21/2018] [Indexed: 12/31/2022] Open
Abstract
Many benzodiazepines are positive allosteric modulators (PAMs) of GABAA receptors that cause sedation, hypnosis, and anxiolysis. Benzodiazepines bind GABAA receptors at the extracellular interface of the α and γ subunits. Within the α subunit, the benzodiazepine binding site is defined by three highly conserved structural loops, loops A-C. Although previous mutagenesis studies have identified His102 in Loop A as important for benzodiazepine modulation of GABAA receptors, the functional roles of many of the other conserved residues in loops A-C remain incompletely understood. In this study, we made single mutations in loops A-C of the benzodiazepine binding-site across all six α subunits. We used whole-cell patch clamp recording to measure the functional effects of these mutations on midazolam potentiation. The results showed that mutating the threonine in loop B and serine in loop C (Thr163 and S206 in human α1) did not abolish the receptors' responsiveness to midazolam, as the α1(H102R) mutation did. The loop C mutations exhibited a novel array of α-isoform specific effects on midazolam potentiation. The α3(S230I) and α5(S209I) mutations had the largest effect on midazolam potentiation, increasing the efficacy of midazolam. Novel benzodiazepines targeting loop C may represent a future direction for designing new drugs that specifically alter the activity of α3- and α5-containing GABAA receptors.
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Affiliation(s)
- Olivia A. Moody
- Neuroscience ProgramGraduate Division of Biological and Biomedical SciencesLaney Graduate SchoolEmory UniversityAtlantaGeorgia
| | - Andrew Jenkins
- Departments of Anesthesiology & PharmacologyEmory UniversityAtlantaGeorgia
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Chiou LC, Lee HJ, Ernst M, Huang WJ, Chou JF, Chen HL, Mouri A, Chen LC, Treven M, Mamiya T, Fan PC, Knutson DE, Witzigmann C, Cook J, Sieghart W, Nabeshima T. Cerebellar α 6 -subunit-containing GABA A receptors: a novel therapeutic target for disrupted prepulse inhibition in neuropsychiatric disorders. Br J Pharmacol 2018. [PMID: 29518821 DOI: 10.1111/bph.14198] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE The pathophysiological role of α6 -subunit-containing GABAA receptors, which are mainly expressed in cerebellar granule cells, remains unclear. Recently, we demonstrated that hispidulin, a flavonoid isolated from a local herb that remitted a patient's intractable motor tics, attenuated methamphetamine-induced hyperlocomotion in mice as a positive allosteric modulator (PAM) of cerebellar α6 GABAA receptors. Here, using hispidulin and a selective α6 GABAA receptor PAM, the pyrazoloquinolinone Compound 6, we revealed an unprecedented role of cerebellar α6 GABAA receptors in disrupted prepulse inhibition of the startle response (PPI), which reflects sensorimotor gating deficits manifested in several neuropsychiatric disorders. EXPERIMENTAL APPROACH PPI disruptions were induced by methamphetamine and NMDA receptor antagonists in mice. Effects of the tested compounds were measured in Xenopus oocytes expressing recombinant α6 β3 γ2S GABAA receptors. KEY RESULTS Hispidulin given i.p. or by bilateral intracerebellar (i.cb.) injection rescued PPI disruptions induced by methamphetamine, ketamine, MK-801 and phencyclidine. Intracerebellar effects of hispidulin were mimicked by Ro15-4513 and loreclezole (two α6 GABAA receptor PAMs), but not by diazepam (an α6 GABAA receptor-inactive benzodiazepine) and were antagonized by furosemide (i.cb.), an α6 GABAA receptor antagonist. Importantly, Compound 6 (i.p.) also rescued methamphetamine-induced PPI disruption, an effect prevented by furosemide (i.cb.). Both hispidulin and Compound 6 potentiated α6 β3 γ2S GABAA receptor-mediated GABA currents. CONCLUSIONS AND IMPLICATIONS Positive allosteric modulation of cerebellar α6 GABAA receptors rescued disrupted PPI by attenuating granule cell activity. α6 GABAA receptor-selective PAMs are potential medicines for treating sensorimotor gating deficits in neuropsychiatric disorders. A mechanistic hypothesis is based on evidence for cerebellar contributions to cognitive functioning including sensorimotor gating.
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Affiliation(s)
- Lih-Chu Chiou
- Graduate Institute of Pharmacology, National Taiwan University, Taipei, Taiwan,Graduate Institute of Brain and Mind Sciences, National TaiwanUniversity, Taipei, Taiwan,Graduate Institute of Acupuncture Science, Taichung, Taiwan
| | - Hsin-Jung Lee
- Graduate Institute of Pharmacology, National Taiwan University, Taipei, Taiwan
| | - Margot Ernst
- Center for Brain Research, Department of Molecular Neurosciences, Medical University Vienna, Vienna, Austria
| | - Wei-Jan Huang
- Graduate Institute of Pharmacognosy, Taipei Medical University, Taipei, Taiwan
| | - Jui-Feng Chou
- Graduate Institute of Pharmacology, National Taiwan University, Taipei, Taiwan
| | - Hon-Lie Chen
- Graduate Institute of Pharmacology, National Taiwan University, Taipei, Taiwan
| | - Akihiro Mouri
- Department of Chemical Pharmacology, Faculty of Pharmacy, Meijo University, Nagoya, Japan,Advanced Diagnostic System Research Laboratory, Graduate School of Health Sciences, Fujita Health University, Toyoake, Japan
| | - Liang-Chieh Chen
- Graduate Institute of Pharmacognosy, Taipei Medical University, Taipei, Taiwan
| | - Marco Treven
- Center for Brain Research, Department of Molecular Neurosciences, Medical University Vienna, Vienna, Austria
| | - Takayoshi Mamiya
- Department of Chemical Pharmacology, Faculty of Pharmacy, Meijo University, Nagoya, Japan
| | - Pi-Chuan Fan
- Department of Pediatrics, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Daniel E Knutson
- Department of Chemistry and Biochemistry, University of Wisconsin – Milwaukee, Milwaukee, WI, USA
| | - Chris Witzigmann
- Department of Chemistry and Biochemistry, University of Wisconsin – Milwaukee, Milwaukee, WI, USA
| | - James Cook
- Department of Chemistry and Biochemistry, University of Wisconsin – Milwaukee, Milwaukee, WI, USA
| | - Werner Sieghart
- Center for Brain Research, Department of Molecular Neurosciences, Medical University Vienna, Vienna, Austria
| | - Toshitaka Nabeshima
- Department of Chemical Pharmacology, Faculty of Pharmacy, Meijo University, Nagoya, Japan,Advanced Diagnostic System Research Laboratory, Graduate School of Health Sciences, Fujita Health University, Toyoake, Japan,Aino University, Ibaraki, Japan
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Snell HD, Gonzales EB. 5-(N, N-Hexamethylene) amiloride is a GABA-A ρ1 receptor positive allosteric modulator. Channels (Austin) 2016; 10:498-506. [PMID: 27367557 PMCID: PMC5034777 DOI: 10.1080/19336950.2016.1207021] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Revised: 06/19/2016] [Accepted: 06/20/2016] [Indexed: 10/21/2022] Open
Abstract
Guanidine compounds act as ion channel modulators. In the case of Cys-loop receptors, the guanidine compound amiloride antagonized the heteromeric GABA-A, glycine, and nicotinic acetylcholine receptors. However, amiloride exhibits characteristics consistent with a positive allosteric modulator for the human GABA-A (hGABA-A) ρ1 receptor. Site-directed mutagenesis revealed that the positive allosteric modulation was influenced by the GABA-A ρ1 second transmembrane domain 15' position, a site implicated in ligand allosteric modulation of Cys-loop receptors. There are a variety of amiloride derivatives that provide opportunities to assess the significance of amiloride functional groups (e.g., the guanidine group, the pyrazine ring, etc.) in the modulation of the GABA-A ρ1 receptor activity. We utilized 3 amiloride derivatives (benzamil, phenamil, and 5-(N, N-Hexamethylene) amiloride) to assess the contribution of these groups toward the potentiation of the GABA-A ρ1 receptor. Benzamil and phenamil failed to potentiate on the wild type GABA-A ρ1 GABA-mediated current while HMA demonstrated efficacy only at the highest concentration studied. The hGABA-A ρ1 (I15'N) mutant receptor activity was potentiated by lower HMA concentrations compared to the wild type receptor. Our findings suggest that an exposed guanidine group on amiloride and amiloride derivatives is critical for modulating the GABA-A ρ1 receptor. The present study provides a conceptual framework for predicting which amiloride derivatives will demonstrate positive allosteric modulation of the GABA-A ρ1 receptor.
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Affiliation(s)
- Heather D. Snell
- Center for Neuroscience Discovery, Institute for Healthy Aging, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Eric B. Gonzales
- Center for Neuroscience Discovery, Institute for Healthy Aging, University of North Texas Health Science Center, Fort Worth, TX, USA
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Hodolic M, Topakian R, Pichler R. (18)F-fluorodeoxyglucose and (18)F-flumazenil positron emission tomography in patients with refractory epilepsy. Radiol Oncol 2016; 50:247-53. [PMID: 27679539 PMCID: PMC5024661 DOI: 10.1515/raon-2016-0032] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Accepted: 04/29/2016] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Epilepsy is a neurological disorder characterized by epileptic seizures as a result of excessive neuronal activity in the brain. Approximately 65 million people worldwide suffer from epilepsy; 20-40% of them are refractory to medication therapy. Early detection of disease is crucial in the management of patients with epilepsy. Correct localization of the ictal onset zone is associated with a better surgical outcome. The modern non-invasive techniques used for structural-functional localization of the seizure focus includes electroencephalography (EEG) monitoring, magnetic resonance imaging (MRI), single photon emission tomography/computed tomography (SPECT/CT) and positron emission tomography/computed tomography (PET/CT). PET/CT can predict surgical outcome in patients with refractory epilepsy. The aim of the article is to review the current role of routinely used tracer 2-deoxy-2-[(18)F]fluoro-D-glucose ((18)F-FDG) as well as non routinely used (18)F-Flumazenil ((18)F-FMZ) tracers PET/CT in patients with refractory epilepsy. CONCLUSIONS Functional information delivered by PET and the morphologic information delivered by CT or MRI are essential in presurgical evaluation of epilepsy. Nowadays (18)F-FDG PET/CT is a routinely performed imaging modality in localization of the ictal onset zone in patients with refractory epilepsy who are unresponsive to medication therapy. Unfortunately, (18)F-FDG is not an ideal PET tracer regarding the management of patients with epilepsy: areas of glucose hypometabolism do not correlate precisely with the proven degree of change within hippocampal sclerosis, as observed by histopathology or MRI. Benzodiazepine-receptor imaging is a promising alternative in nuclear medicine imaging of epileptogenic focus. The use of (11)C-FMZ in clinical practice has been limited by its short half-life and necessitating an on-site cyclotron for production. Therefore, (18)F-FMZ might be established as one of the tracers of choice for patients with refractory epilepsy because of better sensitivity and anatomical resolution.
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Affiliation(s)
- Marina Hodolic
- Nuclear Medicine Research Department, Iason, Graz, Austria
- Department of Nuclear Medicine, Palacký University Olomouc, Czech Republic
| | - Raffi Topakian
- Department of Neurology, Klinikum Wels-Grieskirchen, Wels, Austria
| | - Robert Pichler
- Institute of Nuclear Medicine, Kepler Universitätsklinikum, Neuromed Campus, Linz, Austria
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Liao YH, Lee HJ, Huang WJ, Fan PC, Chiou LC. Hispidulin alleviated methamphetamine-induced hyperlocomotion by acting at α6 subunit-containing GABAA receptors in the cerebellum. Psychopharmacology (Berl) 2016; 233:3187-99. [PMID: 27385415 DOI: 10.1007/s00213-016-4365-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Accepted: 06/09/2016] [Indexed: 12/25/2022]
Abstract
RATIONALE Hispidulin is a flavonoid we isolated from Clerodendrum inerme, an herb that effectively remitted a case of intractable motor tic disorders. Hispidulin was shown to be a positive allosteric modulator (PAM) of GABAA receptors, including the α6 subunit-containing subtype (α6GABAAR) that is predominantly expressed in cerebellar granule cells and insensitive to diazepam. OBJECTIVES We explored the action mechanism(s) of hispidulin using hyperdopaminergic mouse models induced by methamphetamine and apomorphine, based on the hyperdopaminergic nature of tic disorders. RESULTS Hispidulin significantly inhibited methamphetamine-induced hyperlocomotion (MIH) at i.p. doses without affecting apomorphine-induced hyperlocomotion and stereotypy behaviors or having significant benzodiazepine-like effects (BZLE), including sedation, anxiety, and motor impairment. When given by intracerebellar (i.c.b.) microinjection, hispidulin also alleviated MIH and this effect was prevented by i.c.b. coadministration of furosemide, an α6GABAAR antagonist, and mimicked by i.c.b. Ro 15-4513, an α6GABAAR PAM. Conversely, i.c.b. diazepam did not affect MIH while it reduced MIH at i.p. doses having significant BZLE. In a screening assay for 92 neurotransmitter receptors/degradation enzymes/transporters, hispidulin displayed significant (>50 % inhibition of radiolabeled ligand binding at 10 μM) binding affinity only at the benzodiazepine binding site of GABAARs (IC50 0.73∼1.78 μM) and catecholamine-o-methyl-transferase (COMT) (IC50 1.32 μM). OR-486, a more potent COMT inhibitor than hispidulin, did not affect MIH. CONCLUSIONS It is suggested that hispidulin alleviates MIH via acting as a PAM of cerebellar α6GABAARs, but not through COMT inhibition or affecting dopamine receptor responsiveness. Thus, selective α6GABAAR PAMs may have the potential to be a novel treatment for hyperdopaminergic disorders.
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Affiliation(s)
- Yu-Hsiang Liao
- Graduate Institute of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Hsin-Jung Lee
- Department of Pharmacology, College of Medicine, National Taiwan University, No. 1, Jen-Ai Rd., Section 1, Taipei, 100, Taiwan
| | - Wei-Jan Huang
- Graduate Institute of Pharmacognosy, Taipei Medical University, Taipei, Taiwan
| | - Pi-Chuan Fan
- Department of Pediatrics, National Taiwan University Hospital, Taipei, Taiwan
| | - Lih-Chu Chiou
- Graduate Institute of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan. .,Department of Pharmacology, College of Medicine, National Taiwan University, No. 1, Jen-Ai Rd., Section 1, Taipei, 100, Taiwan. .,Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan. .,Research Center for Chinese Medicine and Acupuncture, China Medical University, Taichung, Taiwan.
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Ihara Y, Tomonoh Y, Deshimaru M, Zhang B, Uchida T, Ishii A, Hirose S. Retigabine, a Kv7.2/Kv7.3-Channel Opener, Attenuates Drug-Induced Seizures in Knock-In Mice Harboring Kcnq2 Mutations. PLoS One 2016; 11:e0150095. [PMID: 26910900 PMCID: PMC4766199 DOI: 10.1371/journal.pone.0150095] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Accepted: 02/09/2016] [Indexed: 12/30/2022] Open
Abstract
The hetero-tetrameric voltage-gated potassium channel Kv7.2/Kv7.3, which is encoded by KCNQ2 and KCNQ3, plays an important role in limiting network excitability in the neonatal brain. Kv7.2/Kv7.3 dysfunction resulting from KCNQ2 mutations predominantly causes self-limited or benign epilepsy in neonates, but also causes early onset epileptic encephalopathy. Retigabine (RTG), a Kv7.2/ Kv7.3-channel opener, seems to be a rational antiepileptic drug for epilepsies caused by KCNQ2 mutations. We therefore evaluated the effects of RTG on seizures in two strains of knock-in mice harboring different Kcnq2 mutations, in comparison to the effects of phenobarbital (PB), which is the first-line antiepileptic drug for seizures in neonates. The subjects were heterozygous knock-in mice (Kcnq2Y284C/+ and Kcnq2A306T/+) bearing the Y284C or A306T Kcnq2 mutation, respectively, and their wild-type (WT) littermates, at 63–100 days of age. Seizures induced by intraperitoneal injection of kainic acid (KA, 12mg/kg) were recorded using a video-electroencephalography (EEG) monitoring system. Effects of RTG on KA-induced seizures of both strains of knock-in mice were assessed using seizure scores from a modified Racine’s scale and compared with those of PB. The number and total duration of spike bursts on EEG and behaviors monitored by video recording were also used to evaluate the effects of RTG and PB. Both Kcnq2Y284C/+ and Kcnq2A306T/+ mice showed significantly more KA-induced seizures than WT mice. RTG significantly attenuated KA-induced seizure activities in both Kcnq2Y284C/+ and Kcnq2A306T/+ mice, and more markedly than PB. This is the first reported evidence of RTG ameliorating KA-induced seizures in knock-in mice bearing mutations of Kcnq2, with more marked effects than those observed with PB. RTG or other Kv7.2-channel openers may be considered as first-line antiepileptic treatments for epilepsies resulting from KCNQ2 mutations.
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Affiliation(s)
- Yukiko Ihara
- Department of Pediatrics, School of Medicine, Fukuoka University, Fukuoka, Japan
| | - Yuko Tomonoh
- Department of Pediatrics, School of Medicine, Fukuoka University, Fukuoka, Japan
| | - Masanobu Deshimaru
- Department of Chemistry, Faculty of Science, Fukuoka University, Fukuoka, Japan
| | - Bo Zhang
- Department of Biochemistry, School of Medicine, Fukuoka University, Fukuoka, Japan
| | - Taku Uchida
- Central Research Institute for the Molecular Pathomechanisms of Epilepsy, Fukuoka University, Fukuoka City, Japan
| | - Atsushi Ishii
- Department of Pediatrics, School of Medicine, Fukuoka University, Fukuoka, Japan
| | - Shinichi Hirose
- Department of Pediatrics, School of Medicine, Fukuoka University, Fukuoka, Japan
- Central Research Institute for the Molecular Pathomechanisms of Epilepsy, Fukuoka University, Fukuoka City, Japan
- * E-mail:
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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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14
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Garrido-Acosta O, Meza-Toledo SE, Anguiano-Robledo L, Soriano-Ursúa MA, Correa-Basurto J, Davood A, Chamorro-Cevallos G. Anticonvulsant and Toxicological Evaluation of Parafluorinated/Chlorinated Derivatives of 3-Hydroxy-3-ethyl-3-phenylpropionamide. BIOMED RESEARCH INTERNATIONAL 2016; 2016:3978010. [PMID: 27006945 PMCID: PMC4783531 DOI: 10.1155/2016/3978010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/19/2015] [Revised: 01/21/2016] [Accepted: 01/26/2016] [Indexed: 02/07/2023]
Abstract
Although the anticonvulsant activity of 3-hydroxy-3-ethyl-3-phenylproionamide (HEPP) is well-known, its use is limited by the pharmacotoxicological profile. We herein tested its fluorinated and chlorinated derivatives (F-HEPP and Cl-HEPP) with two seizure models, maximal electroshock seizures (MES), and intraperitoneal pentylenetetrazole (PTZ) administration. Neurotoxicity was examined via the rotarod test. With in silico methods, binding was probed on possible protein targets-GABAA receptors and the sodium channel Nav1.2. The median effective doses (ED50) of HEPP, F-HEPP, and Cl-HEPP in the MES seizure model were 129.6, 87.1, and 62.0 mg/kg, respectively, and 66.4, 43.5, and in the PTZ seizure model 43.5 mg/kg. The HEPP-induced neurotoxic effect, which occurred at twice the ED50 against MES (p < 0.05), did not occur with F-HEPP or Cl-HEPP. Docking studies revealed that all tested ligands bound to GABAA receptors on a site near to the benzodiazepine binding site. However, on the sodium channel open pore Nav1.2, R-HEPP had interactions similar to those reported for phenytoin, while its enantiomer and the ligands F-HEPP and Cl-HEPP reached a site that could disrupt the passage of sodium. Our results show that, as anticonvulsant agents, parahalogen substituted compounds have an advantageous pharmacotoxicological profile compared to their precursor.
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Affiliation(s)
- Osvaldo Garrido-Acosta
- 1Facultad de Estudios Superiores Zaragoza, Universidad Nacional Autónoma de México, 15500 México City, DF, Mexico
- *Osvaldo Garrido-Acosta: and
| | - Sergio E. Meza-Toledo
- 2Laboratorio de Quimioterapia Experimental, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, 11350 México City, DF, Mexico
| | - Liliana Anguiano-Robledo
- 3Laboratorio de Farmacología Molecular, Sección de Estudios de Posgrado e Investigación, Escuela Superior de Medicina, Instituto Politécnico Nacional, 11340 México City, DF, Mexico
| | - Marvin A. Soriano-Ursúa
- 4Departamento de Fisiología, Escuela Superior de Medicina, Instituto Politécnico Nacional, 11340 México City, DF, Mexico
| | - José Correa-Basurto
- 5Laboratorio de Modelado Molecular y Diseño de Fármacos, Escuela Superior de Medicina, Instituto Politécnico Nacional, 11340 México City, DF, Mexico
| | - Asghar Davood
- 6Department of Medicinal Chemistry, Pharmaceutical Sciences Branch, Islamic Azad University, Tehran 19419, Iran
| | - Germán Chamorro-Cevallos
- 7Laboratorio de Toxicología Preclínica, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, 11350 México City, DF, Mexico
- *Germán Chamorro-Cevallos:
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15
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Gallos G, Yocum GT, Siviski ME, Yim PD, Fu XW, Poe MM, Cook JM, Harrison N, Perez-Zoghbi J, Emala CW. Selective targeting of the α5-subunit of GABAA receptors relaxes airway smooth muscle and inhibits cellular calcium handling. Am J Physiol Lung Cell Mol Physiol 2015; 308:L931-42. [PMID: 25659897 DOI: 10.1152/ajplung.00107.2014] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2014] [Accepted: 02/05/2015] [Indexed: 12/23/2022] Open
Abstract
The clinical need for novel bronchodilators for the treatment of bronchoconstrictive diseases remains a major medical issue. Modulation of airway smooth muscle (ASM) chloride via GABAA receptor activation to achieve relaxation of precontracted ASM represents a potentially beneficial therapeutic option. Since human ASM GABAA receptors express only the α4- and α5-subunits, there is an opportunity to selectively target ASM GABAA receptors to improve drug efficacy and minimize side effects. Recently, a novel compound (R)-ethyl8-ethynyl-6-(2-fluorophenyl)-4-methyl-4H-benzo[f]imidazo[1,5-a][1,4] diazepine-3-carboxylate (SH-053-2'F-R-CH3) with allosteric selectivity for α5-subunit containing GABAA receptors has become available. We questioned whether this novel GABAA α5-selective ligand relaxes ASM and affects intracellular calcium concentration ([Ca(2+)]i) regulation. Immunohistochemical staining localized the GABAA α5-subunit to human ASM. The selective GABAA α5 ligand SH-053-2'F-R-CH3 relaxes precontracted intact ASM; increases GABA-activated chloride currents in human ASM cells in voltage-clamp electrophysiology studies; and attenuates bradykinin-induced increases in [Ca(2+)]i, store-operated Ca(2+) entry, and methacholine-induced Ca(2+) oscillations in peripheral murine lung slices. In conclusion, selective subunit targeting of endogenous α5-subunit containing GABAA receptors on ASM may represent a novel therapeutic option to treat severe bronchospasm.
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Affiliation(s)
- George Gallos
- Department of Anesthesiology, College of Physicians and Surgeons of Columbia University, New York, New York;
| | - Gene T Yocum
- Department of Anesthesiology, College of Physicians and Surgeons of Columbia University, New York, New York
| | - Matthew E Siviski
- Department of Anesthesiology, College of Physicians and Surgeons of Columbia University, New York, New York
| | - Peter D Yim
- Department of Anesthesiology, College of Physicians and Surgeons of Columbia University, New York, New York
| | - Xiao Wen Fu
- Department of Anesthesiology, College of Physicians and Surgeons of Columbia University, New York, New York
| | - Michael M Poe
- Department of Chemistry, University of Wisconsin, Milwaukee, Wisconsin; and
| | - James M Cook
- Department of Chemistry, University of Wisconsin, Milwaukee, Wisconsin; and
| | - Neil Harrison
- Department of Anesthesiology, College of Physicians and Surgeons of Columbia University, New York, New York
| | - Jose Perez-Zoghbi
- Department of Cell Physiology and Molecular Biophysics; and Texas Tech University Health Sciences Center, Lubbock, Texas
| | - Charles W Emala
- Department of Anesthesiology, College of Physicians and Surgeons of Columbia University, New York, New York
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16
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Kulick C, Gutherz S, Kondratyev A, Forcelli PA. Ontogenic profile of seizures evoked by the beta-carboline DMCM (methyl-6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate) in rats. Eur J Pharmacol 2014; 740:662-8. [PMID: 24967532 DOI: 10.1016/j.ejphar.2014.06.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Revised: 06/10/2014] [Accepted: 06/16/2014] [Indexed: 10/25/2022]
Abstract
The beta-carboline, methyl-6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM), is a potent chemoconvulsant. While it has been utilized in adult rodents, it has not been previously examined for effects across postnatal development. DMCM is a negative allosteric modulator of benzodiazepine-sensitive GABAA receptors, receptor subtypes that are particularly enriched in limbic brain regions. This raises the possibility that DMCM may be particularly effective at evoking forebrain seizures, which is a challenge in neonatal animals due to the relative immaturity of the forebrain seizure network. The ability to selectebrain seizures is desirable when screening for drugs to use in temporal lobe epilepsy, which is characterized by seizures within the forebrain (limbic) network. To determine the profile of DMCM action across development, we examined the dose-dependent ability of DMCM to induce seizures in rats at P7, P10, P13, P14, P21 and in adulthood. We found that the highest sensitivity to DMCM occurred in P10, P13, and P14 rats. The lowest sensitivity occurred in P21 rats. Neonatal (P7) and adult (P60+) rats displayed moderate sensitivity. With moderate (0.2-0.4 mg/kg) doses of DMCM, we were able to reliably evoke limbic motor seizures without tonic-clonic components in animals as young as P7. These data support the utility of DMCM in assessing seizure threshold during development and raise the possibility for future exploration of DMCM as an agent to screen anticonvulsant drugs during the postnatal period.
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Affiliation(s)
- Catherine Kulick
- Department of Pharmacology and Physiology, Georgetown University, Washington, DC 20007, United States
| | - Samuel Gutherz
- Department of Pharmacology and Physiology, Georgetown University, Washington, DC 20007, United States
| | - Alexei Kondratyev
- Department of Pharmacology and Physiology, Georgetown University, Washington, DC 20007, United States; Department of Pediatrics, Georgetown University, School of Medicine, Washington, DC 20007, United States
| | - Patrick A Forcelli
- Department of Pharmacology and Physiology, Georgetown University, Washington, DC 20007, United States.
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17
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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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18
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Michaelson SD, Paulsen IM, Kozuska JL, Martin IL, Dunn SMJ. Importance of recognition loops B and D in the activation of human 5-HT₃ receptors by 5-HT and meta-chlorophenylbiguanide. Neuropharmacology 2013; 73:398-403. [PMID: 23810831 DOI: 10.1016/j.neuropharm.2013.06.017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 05/14/2013] [Accepted: 06/12/2013] [Indexed: 10/26/2022]
Abstract
The 5-HT₃ receptor is a cation selective member of the pentameric Cys-loop ligand-gated ion channels. While five subunits are known to exist, only two receptor subtypes have been significantly characterized: the homomeric receptor consisting of five A subunits and the heteromeric receptor containing both A and B subunits. The agonist recognition and activation of these receptors is orchestrated by six recognition loops three, A-C, on the principal subunit, and three, D-F, on the complementary subunit. In this study we have focused on the B loop of the principal subunit and loop D of the complementary subunit where aligned amino acids differ between the two subunits. A mutational analysis has been carried out using both 5-HT and m-chlorophenylbiguanide (mCPBG) to characterize receptor activation in the mutant receptors using two-electrode voltage clamp in Xenopus oocytes. The results show that the B loop W178I mutation of the 5-HT3A subunit markedly reduces the efficacy of mCPBG in both the homomeric and heteromeric receptors, while activation by 5-HT remains intact. Replacement of the D loop amino acid triplet RQY of the 5-HT3A subunit, with the aligned residues from the 5-HT3B subunit, QEV, converts 5-HT to a weak partial agonist in both the homomer and heteromer, but does not compromise activation by mCPBG. Exchange of the RQY triplet for the 5-HT3B subunit homologue, QEV, increases the Hill coefficient and decreases the EC₅₀ of this mutant when expressed with the wild type 5-HT3A subunit.
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Affiliation(s)
- S D Michaelson
- Department of Pharmacology, University of Alberta, 9-70 Medical Sciences Building, Edmonton, AB, Canada T6H 2H7
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19
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Kim KC, Kim P, Go HS, Choi CS, Park JH, Kim HJ, Jeon SJ, dela Pena IC, Han SH, Cheong JH, Ryu JH, Shin CY. Male-specific alteration in excitatory post-synaptic development and social interaction in pre-natal valproic acid exposure model of autism spectrum disorder. J Neurochem 2013; 124:832-43. [DOI: 10.1111/jnc.12147] [Citation(s) in RCA: 140] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Revised: 12/17/2012] [Accepted: 01/07/2013] [Indexed: 11/28/2022]
Affiliation(s)
- Ki Chan Kim
- Department of Pharmacology; College of Pharmacy; Seoul National University; Seoul Korea
- Center for Neuroscience Research; SMART Institute of Advanced Biomedical Sciences; Konkuk University; Seoul Korea
| | - Pitna Kim
- Center for Neuroscience Research; SMART Institute of Advanced Biomedical Sciences; Konkuk University; Seoul Korea
- School of Medicine; Konkuk University; Seoul Korea
| | - Hyo Sang Go
- Department of Pharmacology; College of Pharmacy; Seoul National University; Seoul Korea
- Center for Neuroscience Research; SMART Institute of Advanced Biomedical Sciences; Konkuk University; Seoul Korea
| | - Chang Soon Choi
- Center for Neuroscience Research; SMART Institute of Advanced Biomedical Sciences; Konkuk University; Seoul Korea
- School of Medicine; Konkuk University; Seoul Korea
| | - Jin Hee Park
- School of Medicine; Konkuk University; Seoul Korea
| | - Hee Jin Kim
- Department of Pharmacy; Sahmyook University; Seoul Korea
| | - Se Jin Jeon
- Department of Psychiatry; School of Medicine; University of California; Los Angeles California USA
| | | | - Seol-Heui Han
- Center for Neuroscience Research; SMART Institute of Advanced Biomedical Sciences; Konkuk University; Seoul Korea
- School of Medicine; Konkuk University; Seoul Korea
| | | | - Jong Hoon Ryu
- Department of Oriental Pharmaceutical Science; College of Pharmacy; Kyung Hee University; Seoul Korea
| | - Chan Young Shin
- Center for Neuroscience Research; SMART Institute of Advanced Biomedical Sciences; Konkuk University; Seoul Korea
- School of Medicine; Konkuk University; Seoul Korea
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20
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Richter L, de Graaf C, Sieghart W, Varagic Z, Mörzinger M, de Esch IJP, Ecker GF, Ernst M. Diazepam-bound GABAA receptor models identify new benzodiazepine binding-site ligands. Nat Chem Biol 2012; 8:455-64. [PMID: 22446838 DOI: 10.1038/nchembio.917] [Citation(s) in RCA: 151] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2011] [Accepted: 02/02/2012] [Indexed: 11/09/2022]
Abstract
Benzodiazepines exert their anxiolytic, anticonvulsant, muscle-relaxant and sedative-hypnotic properties by allosterically enhancing the action of GABA at GABA(A) receptors via their benzodiazepine-binding site. Although these drugs have been used clinically since 1960, the molecular basis of this interaction is still not known. By using multiple homology models and an unbiased docking protocol, we identified a binding hypothesis for the diazepam-bound structure of the benzodiazepine site, which was confirmed by experimental evidence. Moreover, two independent virtual screening approaches based on this structure identified known benzodiazepine-site ligands from different structural classes and predicted potential new ligands for this site. Receptor-binding assays and electrophysiological studies on recombinant receptors confirmed these predictions and thus identified new chemotypes for the benzodiazepine-binding site. Our results support the validity of the diazepam-bound structure of the benzodiazepine-binding pocket, demonstrate its suitability for drug discovery and pave the way for structure-based drug design.
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Affiliation(s)
- Lars Richter
- Department of Medicinal Chemistry, University of Vienna, Vienna, Austria
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21
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Alves R, Carvalho JGBD, Venditti MAC. High- and Low-Rearing Rats Differ in the Brain Excitability Controlled by the Allosteric Benzodiazepine Site in the GABA<sub>A</sub> Receptor. ACTA ACUST UNITED AC 2012. [DOI: 10.4236/jbbs.2012.23036] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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22
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Momosaki S, Hosoi R, Abe K, Inoue O. Remarkable selectivity of the in vivo binding of [3H]Ro15-4513 to α5 subtype of benzodiazepine receptor in the living mouse brain. Synapse 2011; 64:928-36. [PMID: 20506503 DOI: 10.1002/syn.20812] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
To evaluate the binding characteristics of [(3)H]Ro15-4513 with the central benzodiazepine (BZ) receptor, inhibition experiments of [(3)H]Ro15-1788 and [(3)H]Ro15-4513 were performed both in vitro and in vivo, using two BZ ligands, flunitrazepam (FNP), and ethyl-β-carboline-3-carboxylate (β-CCE). FNP inhibited the binding of [(3)H]Ro15-1788 and [(3)H]Ro15-4513 in a dose-dependent manner in the mouse cerebral cortex, hippocampus, and cerebellum, both in vitro and in vivo. β-CCE also inhibited the binding of [(3)H]Ro15-1788 and [(3)H]Ro15-4513 in all the aforementioned brain regions in vitro. However, in vivo, β-CCE inhibited the binding of [(3)H]Ro15-4513 in the cerebral cortex and cerebellum, but not in the hippocampus, even at an injected dose of up to 1mg/kg. In contrast, more than 50% of the in vivo binding of [(3)H]Ro15-1788 was inhibited by 1 mg/kg of β-CCE in all regions. The time-activity curve of [(3)H]Ro15-4513 in the hippocampus also showed no alteration of the peak uptake between the control group and 0.3 mg/kg of β-CCE coinjected group. These results indicated that the binding characteristics of [(3)H]Ro15-4513 with the BZ receptor differed markedly between the in vitro and in vivo condition, and the selectivity of [(3)H]Ro15-4513 binding to α5 subtype of BZ receptor in the mouse brain seemed to be remarkable under the in vivo condition.
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Affiliation(s)
- Sotaro Momosaki
- Division of Health Sciences, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan.
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23
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Use of multicomponent reactions in developing small-molecule tools to study GABAA receptor mechanism and function. Future Med Chem 2011; 3:243-50. [PMID: 21428818 DOI: 10.4155/fmc.10.302] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
We discuss the potential use of multicomponent reactions in developing small-molecule probes of GABA(A) receptor function. Two examples that illustrate this approach are presented: the synthesis of a class of compounds that specifically modulate the function of GABA(A) receptors containing the δ-subunit, and also 'caged' GABA derivatives. A caged GABA is a photolabile precursor of GABA that releases GABA upon photolysis.
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24
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Morlock EV, Czajkowski C. Different residues in the GABAA receptor benzodiazepine binding pocket mediate benzodiazepine efficacy and binding. Mol Pharmacol 2011; 80:14-22. [PMID: 21447642 DOI: 10.1124/mol.110.069542] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Benzodiazepines (BZDs) exert their therapeutic actions by binding to the GABA(A) receptor (GABA(A)R) and allosterically modulating GABA-induced chloride currents (I(GABA)). A variety of ligands with divergent structures bind to the BZD site, and the structural mechanisms that couple their binding to potentiation of I(GABA) are not well understood. In this study, we measured the effects of individually mutating 22 residues throughout the BZD binding pocket on the abilities of eszopiclone, zolpidem, and flurazepam to potentiate I(GABA). Wild-type and mutant α(1)β(2)γ(2) GABA(A)Rs were expressed in Xenopus laevis oocytes and analyzed using a two-electrode voltage clamp. GABA EC(50), BZD EC(50), and BZD maximal potentiation were measured. These data, combined with previous radioligand binding data describing the mutations' effects on BZD apparent binding affinities (J Neurosci 28:3490-3499, 2008; J Med Chem 51:7243-7252, 2008), were used to distinguish residues within the BZD pocket that contribute to BZD efficacy and BZD binding. We identified six residues whose mutation altered BZD maximal potentiation of I(GABA) (BZD efficacy) without altering BZD binding apparent affinity, three residues whose mutation altered binding but had no effect on BZD efficacy, and four residues whose mutation affected both binding and efficacy. Moreover, depending on the BZD ligand, the effects of some mutations were different, indicating that the structural mechanisms underlying the ability of BZD ligands with divergent structures to potentiate I(GABA) are distinct.
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Affiliation(s)
- Elaine V Morlock
- University of Wisconsin at Madison, 601 Science Drive, Madison, WI 53711, USA
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25
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Characterization of GABA(A) receptors expressed in glial cell membranes of adult mouse neocortex using a Xenopus oocyte microtransplantation expression system. J Neurosci Methods 2011; 198:77-83. [PMID: 21439322 DOI: 10.1016/j.jneumeth.2011.03.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2010] [Revised: 03/09/2011] [Accepted: 03/10/2011] [Indexed: 11/21/2022]
Abstract
Cell membranes isolated from nervous tissue can be easily injected into Xenopus oocytes, thereby effectively "microtransplanting" functional neurotransmitter receptors. This technique therefore allows a direct functional characterization of the original membrane receptor/ion channel proteins and the associated molecules while still embedded in their natural lipid environment. Cell membranes will contain components from different types of cells, i.e. neurons and glial cells, expressing their own receptors, with possibly different properties. To study the receptor properties of a single cell type, we injected oocytes with membranes isolated only from glia (gliosomes) of adult mouse neocortex and we focused our work on GABA(A) receptors incorporated in the oocyte cell membrane. We found that GABA(A)-activated currents allowed a good biophysical and pharmacological characterization of glial GABA(A) receptors. Therefore, the microtransplantation of gliosomes into oocytes can represent a good model to study the electrical and pharmacological properties of adult glial cells under different physiological and pathological conditions. Moreover, since gliosomes can be isolated from frozen tissues, this approach can be extended to post-mortem human tissues.
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You H, Kozuska JL, Paulsen IM, Dunn SM. Benzodiazepine modulation of the rat GABAA receptor α4β3γ2L subtype expressed in Xenopus oocytes. Neuropharmacology 2010; 59:527-33. [DOI: 10.1016/j.neuropharm.2010.07.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2010] [Revised: 06/23/2010] [Accepted: 07/08/2010] [Indexed: 10/19/2022]
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27
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Hanson SM, Morlock EV, Satyshur KA, Czajkowski C. Structural requirements for eszopiclone and zolpidem binding to the gamma-aminobutyric acid type-A (GABAA) receptor are different. J Med Chem 2009; 51:7243-52. [PMID: 18973287 DOI: 10.1021/jm800889m] [Citation(s) in RCA: 148] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
The sleep-aids zolpidem and eszopiclone exert their effects by binding to and modulating gamma-aminobutyric acid type-A receptors (GABA(A)Rs), but little is known about the structural requirements for their actions. We made 24 cysteine mutations in the benzodiazepine (BZD) binding site of alpha(1)beta(2)gamma(2) GABA(A)Rs and measured zolpidem, eszopiclone, and BZD-site antagonist binding. Mutations in gamma(2)loop D and alpha(1)loops A and B altered the affinity of all ligands tested, indicating that these loops are important for BZD pocket structural integrity. In contrast, gamma(2)loop E and alpha(1)loop C mutations differentially affected ligand affinity, suggesting that these loops are important for ligand selectivity. In agreement with our mutagenesis data, eszopiclone docking yielded a single model stabilized by several hydrogen bonds. Zolpidem docking yielded three equally populated orientations with few polar interactions, suggesting that unlike eszopiclone, zolpidem relies more on shape recognition of the binding pocket than on specific residue interactions and may explain why zolpidem is highly alpha(1)- and gamma(2)-subunit selective.
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Affiliation(s)
- Susan M Hanson
- Department of Physiology and Program in Molecular and Cellular Pharmacology, University of Wisconsin Madison, Madison, Wisconsin 53711, USA
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28
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Martyniuk CJ, Aris-Brosou S, Drouin G, Cahn J, Trudeau VL. Early evolution of ionotropic GABA receptors and selective regimes acting on the mammalian-specific theta and epsilon subunits. PLoS One 2007; 2:e894. [PMID: 17878929 PMCID: PMC1975676 DOI: 10.1371/journal.pone.0000894] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2007] [Accepted: 08/14/2007] [Indexed: 11/26/2022] Open
Abstract
Background The amino acid neurotransmitter GABA is abundant in the central nervous system (CNS) of both invertebrates and vertebrates. Receptors of this neurotransmitter play a key role in important processes such as learning and memory. Yet, little is known about the mode and tempo of evolution of the receptors of this neurotransmitter. Here, we investigate the phylogenetic relationships of GABA receptor subunits across the chordates and detail their mode of evolution among mammals. Principal Findings Our analyses support two major monophyletic clades: one clade containing GABAA receptor α, γ, and ε subunits, and another one containing GABAA receptor ρ, β, δ, θ, and π subunits. The presence of GABA receptor subunits from each of the major clades in the Ciona intestinalis genome suggests that these ancestral duplication events occurred before the divergence of urochordates. However, while gene divergence proceeded at similar rates on most receptor subunits, we show that the mammalian-specific subunits θ and ε experienced an episode of positive selection and of relaxed constraints, respectively, after the duplication event. Sites putatively under positive selection are placed on a three-dimensional model obtained by homology-modeling. Conclusions Our results suggest an early divergence of the GABA receptor subunits, before the split from urochordates. We show that functional changes occurred in the lineages leading to the mammalian-specific subunit θ, and we identify the amino acid sites putatively responsible for the functional divergence. We discuss potential consequences for the evolution of mammals and of their CNS.
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Affiliation(s)
- Christopher J. Martyniuk
- Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, Ontario, Canada
| | - Stéphane Aris-Brosou
- Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, Ontario, Canada
- Department of Mathematics and Statistics, University of Ottawa, Ottawa, Ontario, Canada
- * To whom correspondence should be addressed. E-mail:
| | - Guy Drouin
- Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, Ontario, Canada
| | - Joel Cahn
- Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, Ontario, Canada
| | - Vance L. Trudeau
- Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, Ontario, Canada
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29
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You H, Dunn SMJ. Identification of a domain in the delta subunit (S238-V264) of the alpha4beta3delta GABAA receptor that confers high agonist sensitivity. J Neurochem 2007; 103:1092-101. [PMID: 17711419 DOI: 10.1111/j.1471-4159.2007.04817.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have expressed the alpha4beta3delta and alpha4beta3gamma2L subtypes of the rat GABAA receptor in Xenopus oocytes and have investigated their agonist activation properties. GABA was a more potent agonist of the alpha4beta3delta receptor (EC50 approximately 1.4 micromol/L) than of the alpha4beta3gamma2L subtype (EC50 approximately 27.6 micromol/L). Other GABAA receptor agonists (muscimol, 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol, imidazole-4-amino acid) displayed similar subtype selectivity. The structural determinants underlying these differences have been investigated by co-expressing chimeric delta/gamma2L subunits with alpha4 and beta3 subunits. A stretch of amino acids in the delta subunit, S238-V264, is shown to play an important role in determining both agonist potency and the efficacies of full or partial agonists. This segment includes transmembrane domain 1 and the short intracellular loop that leads to the second transmembrane domain. The effects of the competitive antagonists, bicuculline and SR95531, and the channel blocker, picrotoxin, were not significantly affected by the incorporation of chimeric subunits. As the delta and gamma2L subunits have not been previously implicated directly in agonist binding, we suggest that the effects are likely to arise from changes in the transduction mechanisms that link agonist binding to channel activation.
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Affiliation(s)
- Haitao You
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
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Derry JMC, Paulsen IM, Davies M, Dunn SMJ. A single point mutation of the GABAA receptor α5-subunit confers fluoxetine sensitivity. Neuropharmacology 2007; 52:497-505. [PMID: 17045313 DOI: 10.1016/j.neuropharm.2006.07.036] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2005] [Revised: 06/26/2006] [Accepted: 07/19/2006] [Indexed: 01/05/2023]
Abstract
Fluoxetine has been reported to be a novel allosteric modulator of GABA(A) receptors with the notable exception of receptors that contain the alpha5-subunit isoform [Robinson, R.T., Drafts, B.C., Fisher, J.L., 2003. Fluoxetine increases GABA(A) receptor activity through a novel modulatory site. J. Pharmacol. Exp. Ther. 304, 978-984]. A mutagenic strategy has been used to investigate the structural basis for the insensitivity of this subunit. An alpha1/alpha5-subunit chimeragenesis approach first demonstrated the importance of the alpha1-subunit N-terminal sequence E165-D183 (corresponding to alpha5 E169-D187) in fluoxetine modulation. Specific amino acid substitutions in this domain subsequently revealed that a single mutation in the alpha5-subunit to the equivalent residue in alpha1 (T179A) was sufficient to confer fluoxetine sensitivity to the alpha5-containing receptor. However, the reciprocal mutation in the alpha1-subunit (A175T) did not result in a loss in sensitivity, suggesting the involvement of additional determinants for fluoxetine modulation. A comparative modeling approach was used to probe amino acids that may lie in close proximity to alpha1A175. This led serendipitously to the identification of a specific residue, alpha1F45, which, when mutated to an alanine, resulted in a significant decrease in potency for activation of the receptor by GABA and also reduced the efficacies of the partial agonists, THIP and P4S.
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Affiliation(s)
- Jason M C Derry
- Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
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Hansen RS, Paulsen I, Davies M. Determinants of amentoflavone interaction at the GABA(A) receptor. Eur J Pharmacol 2005; 519:199-207. [PMID: 16129428 DOI: 10.1016/j.ejphar.2005.06.036] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2005] [Accepted: 06/20/2005] [Indexed: 11/29/2022]
Abstract
We investigated the recognition properties of different GABA(A) receptor subtypes and mutant receptors for the biflavonoid amentoflavone, a constituent of St. John's Wort. Radioligand binding studies showed that amentoflavone recognition paralleled that of the classical benzodiazepine diazepam in that it had little or no affinity for alpha4- or alpha6-containing receptors. Lysine and alanine substitutions at position 101 of the rat alpha1 subunit resulted in a complete loss of competitive amentoflavone binding, but functional analysis of the alanine mutant expressed with beta2 and gamma2 subunits in Xenopus oocytes revealed no significant difference in the negative modulation of GABA-induced currents brought about by amentoflavone. Furthermore, elimination of the gamma subunit had no effect on the negative modulation of these currents. This negative modulation was also observed at alpha1beta1gamma2 GABA(A) receptors and is therefore not likely mediated by the loreclezole site. These results suggest a complex mechanism of amentoflavone interaction at GABA(A) receptors.
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Affiliation(s)
- Reena S Hansen
- Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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Criswell HE, Breese GR. A conceptualization of integrated actions of ethanol contributing to its GABAmimetic profile: a commentary. Neuropsychopharmacology 2005; 30:1407-25. [PMID: 15856077 DOI: 10.1038/sj.npp.1300750] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Early behavioral investigations supported the contention that systemic ethanol displays a GABAmimetic profile. Microinjection of GABA agonists into brain and in vivo electrophysiological studies implicated a regionally specific action of ethanol on GABA function. While selectivity of ethanol to enhance the effect of GABA was initially attributed an effect on type-I-benzodiazepine (BZD)-GABA(A) receptors, a lack of ethanol's effect on GABA responsiveness from isolated neurons with this receptor subtype discounted this contention. Nonetheless, subsequent work identified GABA(A) receptor subtypes, with limited distribution in brain, sensitive to enhancement of GABA at relevant ethanol concentrations. In view of these data, it is hypothesized that the GABAmimetic profile for ethanol is due to activation of mechanisms associated with GABA function, distinct from a direct action on the majority of postsynaptic GABA(A) receptors. The primary action proposed to account for ethanol's regional specificity on GABA transmission is its ability to release GABA from some, but not all, presynaptic GABAergic terminals. As systemic administration of ethanol increases neuroactive steroids, which can enhance GABA responsiveness, this elevated level of neurosteroids is proposed to magnify the effect of GABA released by ethanol. Additional factors contributing to the degree to which ethanol interacts with GABA function include an involvement of GABA(B) and other receptors that influence ethanol-induced GABA release, an effect of phosphorylation on GABA responsiveness, and a regional reduction of glutamatergic tone. Thus, an integration of these consequences induced by ethanol is proposed to provide a logical basis for its in vivo GABAmimetic profile.
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Affiliation(s)
- Hugh E Criswell
- Center For Alcohol Studies, UNC Neuroscience Center, Department of Psychiatry, University of North Carolina, School of Medicine, Chapel Hill, NC 27599-7178, USA.
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