1
|
Bukanova JV, Solntseva EI, Skrebitsky VG. Factors promoting the release of picrotoxin from the trap in the GABA(A) receptor pore. Neurochem Int 2024; 175:105703. [PMID: 38395151 DOI: 10.1016/j.neuint.2024.105703] [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: 12/05/2023] [Revised: 01/31/2024] [Accepted: 02/21/2024] [Indexed: 02/25/2024]
Abstract
Picrotoxin (PTX), a convulsant of plant origin, has been used in many studies as research tool. PTX is the open channel blocker of the GABAA receptor (GABAAR). Being in the pore, PTX initiates transfer of the channel to the closed state and thus it falls into the "trap". The consequence of this PTX trapping is so-called aftereffect, i.e. continuation of the blockade of the GABA-induced chloride current (IGABA) after removal of PTX from the external solution. The present work shows that the positive allosteric modulators (PAMs) of the GABAA receptor, allopregnanolone (Allo) and zolpidem (Zolp) as well as a high concentration of GABA shortened the PTX aftereffect. Experiments were carried out on isolated Purkinje neurons of the rat cerebellum using the whole-cell patch-clamp method. IGABA was induced by applications of 5 μM GABA (EC30) for 1 s with 30 s intervals. 50 μM PTX completely blocked IGABA, and recovery upon PTX washout occurred with a time constant (τrec) of 20.2 min. 1 μM Allo reduced the blocking effect of PTX by 30% and accelerated the recovery of IGABA by almost 10 times (τrec = 2.4 min). 0.5 μM Zolp did not change the IGABA block in the presence of PTX but accelerated the recovery of IGABA by more than 3 times (τrec = 5.6 min). Increasing the GABA concentration to 20 μM did not change the blocking effect of PTX, but accelerated recovery by 6 times (τrec = 3.3 min). The mechanism of the shortening of the PTX aftereffect is presumably the expansion of the GABAAR pore in the presence of PAMs and a high concentration of the agonist and, as a consequence, the escape of PTX from the "trap". The work describes new pharmacological properties of Allo and Zolp.
Collapse
Affiliation(s)
- Julia V Bukanova
- Brain Research Institute, Research Center of Neurology, Moscow, Russia
| | - Elena I Solntseva
- Brain Research Institute, Research Center of Neurology, Moscow, Russia.
| | | |
Collapse
|
2
|
Yamaguchi J, Andrade MA, Truong TT, Toney GM. Glutamate Spillover Dynamically Strengthens Gabaergic Synaptic Inhibition of the Hypothalamic Paraventricular Nucleus. J Neurosci 2024; 44:e1851222023. [PMID: 38154957 PMCID: PMC10869154 DOI: 10.1523/jneurosci.1851-22.2023] [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: 09/29/2022] [Revised: 12/16/2023] [Accepted: 12/20/2023] [Indexed: 12/30/2023] Open
Abstract
The hypothalamic paraventricular nucleus (PVN) is strongly inhibited by γ-aminobutyric acid (GABA) from the surrounding peri-nuclear zone (PNZ). Because glutamate mediates fast excitatory transmission and is substrate for GABA synthesis, we tested its capacity to dynamically strengthen GABA inhibition. In PVN slices from male mice, bath glutamate applied during ionotropic glutamate receptor blockade increased PNZ-evoked inhibitory postsynaptic currents (eIPSCs) without affecting GABA-A receptor agonist currents or single-channel conductance, implicating a presynaptic mechanism(s). Consistent with this interpretation, bath glutamate failed to strengthen IPSCs during pharmacological saturation of GABA-A receptors. Presynaptic analyses revealed that glutamate did not affect paired-pulse ratio, peak eIPSC variability, GABA vesicle recycling speed, or readily releasable pool (RRP) size. Notably, glutamate-GABA strengthening (GGS) was unaffected by metabotropic glutamate receptor blockade and graded external Ca2+ when normalized to baseline amplitude. GGS was prevented by pan- but not glial-specific inhibition of glutamate uptake and by inhibition of glutamic acid decarboxylase (GAD), indicating reliance on glutamate uptake by neuronal excitatory amino acid transporter 3 (EAAT3) and enzymatic conversion of glutamate to GABA. EAAT3 immunoreactivity was strongly localized to presumptive PVN GABA terminals. High bath K+ also induced GGS, which was prevented by glutamate vesicle depletion, indicating that synaptic glutamate release strengthens PVN GABA inhibition. GGS suppressed PVN cell firing, indicating its functional significance. In sum, PVN GGS buffers neuronal excitation by apparent "over-filling" of vesicles with GABA synthesized from synaptically released glutamate. We posit that GGS protects against sustained PVN excitation and excitotoxicity while potentially aiding stress adaptation and habituation.
Collapse
Affiliation(s)
- Junya Yamaguchi
- Department of Cellular & Integrative Physiology, University of Texas Health San Antonio, San Antonio 78229-3900, Texas
| | - Mary Ann Andrade
- Department of Cellular & Integrative Physiology, University of Texas Health San Antonio, San Antonio 78229-3900, Texas
| | - Tamara T Truong
- Department of Cellular & Integrative Physiology, University of Texas Health San Antonio, San Antonio 78229-3900, Texas
| | - Glenn M Toney
- Department of Cellular & Integrative Physiology, University of Texas Health San Antonio, San Antonio 78229-3900, Texas
- Center for Biomedical Neuroscience, University of Texas Health San Antonio, San Antonio 78229-3900, Texas
| |
Collapse
|
3
|
Beltrán González AN, López Pazos MI, Del Vas M, Calvo DJ. Negative modulation of the GABA Aρ1 receptor function by histamine. Eur J Pharmacol 2023; 955:175880. [PMID: 37406850 DOI: 10.1016/j.ejphar.2023.175880] [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: 01/10/2023] [Revised: 06/12/2023] [Accepted: 06/26/2023] [Indexed: 07/07/2023]
Abstract
Besides its function as a local mediator of the immune response, histamine can play a role as a neurotransmitter and neuromodulator. Histamine actions are classically mediated through four different G protein-coupled receptor subtypes but non-classical actions were also described, including effects on many ligand-gated ion channels. Previous evidence indicated that histamine acts as a positive modulator on diverse GABAA receptor subtypes, such as GABAAα1β2γ2, GABAAα2β3γ2, GABAAα3β3γ2, GABAAα4β3γ2 and GABAAα5β3γ2. Meanwhile, its effects on GABAAρ1 receptors, known to stand for tonic currents in retinal neurons, had not been examined before. The effects of histamine on the function of human homomeric GABAAρ1 receptors were studied here, using heterologous expression in Xenopus laevis oocytes followed by the electrophysiological recording of GABA-evoked Cl- currents. Histamine inhibited GABAAρ1 receptor-mediated responses. Effects were reversible, independent of the membrane potential, and strongly dependent on both histamine and GABA concentration. A rightward parallel shift in the concentration-response curve for GABA was observed in the presence of histamine, without substantial change in the maximal response or the Hill coefficient. Results were compatible with a competitive antagonism of histamine on the GABAAρ1 receptors. This is the first report of inhibitory actions exerted by histamine on an ionotropic GABA receptor.
Collapse
Affiliation(s)
- Andrea N Beltrán González
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Fisiología, Biología Molecular y Neurociencias (IFIByNE), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad de Buenos Aires (UBA), Ciudad Autónoma de Buenos Aires, Argentina
| | - Manuel I López Pazos
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Fisiología, Biología Molecular y Neurociencias (IFIByNE), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad de Buenos Aires (UBA), Ciudad Autónoma de Buenos Aires, Argentina
| | - Mariana Del Vas
- Instituto de Agrobiotecnología y Biología Molecular (IABIMO), Instituto Nacional de Tecnología Agropecuaria (INTA), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
| | - Daniel J Calvo
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Fisiología, Biología Molecular y Neurociencias (IFIByNE), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad de Buenos Aires (UBA), Ciudad Autónoma de Buenos Aires, Argentina.
| |
Collapse
|
4
|
Bellavite P. Neuroprotective Potentials of Flavonoids: Experimental Studies and Mechanisms of Action. Antioxidants (Basel) 2023; 12:antiox12020280. [PMID: 36829840 PMCID: PMC9951959 DOI: 10.3390/antiox12020280] [Citation(s) in RCA: 20] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Revised: 01/23/2023] [Accepted: 01/25/2023] [Indexed: 01/31/2023] Open
Abstract
Neurological and neurodegenerative diseases, particularly those related to aging, are on the rise, but drug therapies are rarely curative. Functional disorders and the organic degeneration of nervous tissue often have complex causes, in which phenomena of oxidative stress, inflammation and cytotoxicity are intertwined. For these reasons, the search for natural substances that can slow down or counteract these pathologies has increased rapidly over the last two decades. In this paper, studies on the neuroprotective effects of flavonoids (especially the two most widely used, hesperidin and quercetin) on animal models of depression, neurotoxicity, Alzheimer's disease (AD) and Parkinson's disease are reviewed. The literature on these topics amounts to a few hundred publications on in vitro and in vivo models (notably in rodents) and provides us with a very detailed picture of the action mechanisms and targets of these substances. These include the decrease in enzymes that produce reactive oxygen and ferroptosis, the inhibition of mono-amine oxidases, the stimulation of the Nrf2/ARE system, the induction of brain-derived neurotrophic factor production and, in the case of AD, the prevention of amyloid-beta aggregation. The inhibition of neuroinflammatory processes has been documented as a decrease in cytokine formation (mainly TNF-alpha and IL-1beta) by microglia and astrocytes, by modulating a number of regulatory proteins such as Nf-kB and NLRP3/inflammasome. Although clinical trials on humans are still scarce, preclinical studies allow us to consider hesperidin, quercetin, and other flavonoids as very interesting and safe dietary molecules to be further investigated as complementary treatments in order to prevent neurodegenerative diseases or to moderate their deleterious effects.
Collapse
|
5
|
Hodapp A, Kaiser ME, Thome C, Ding L, Rozov A, Klumpp M, Stevens N, Stingl M, Sackmann T, Lehmann N, Draguhn A, Burgalossi A, Engelhardt M, Both M. Dendritic axon origin enables information gating by perisomatic inhibition in pyramidal neurons. Science 2022; 377:1448-1452. [PMID: 36137045 DOI: 10.1126/science.abj1861] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Information processing in neuronal networks involves the recruitment of selected neurons into coordinated spatiotemporal activity patterns. This sparse activation results from widespread synaptic inhibition in conjunction with neuron-specific synaptic excitation. We report the selective recruitment of hippocampal pyramidal cells into patterned network activity. During ripple oscillations in awake mice, spiking is much more likely in cells in which the axon originates from a basal dendrite rather than from the soma. High-resolution recordings in vitro and computer modeling indicate that these spikes are elicited by synaptic input to the axon-carrying dendrite and thus escape perisomatic inhibition. Pyramidal cells with somatic axon origin can be activated during ripple oscillations by blocking their somatic inhibition. The recruitment of neurons into active ensembles is thus determined by axonal morphological features.
Collapse
Affiliation(s)
- Alexander Hodapp
- Institute of Physiology and Pathophysiology, Medical Faculty, Heidelberg University, Heidelberg, Germany
| | - Martin E Kaiser
- Institute of Physiology and Pathophysiology, Medical Faculty, Heidelberg University, Heidelberg, Germany
| | - Christian Thome
- Institute of Physiology and Pathophysiology, Medical Faculty, Heidelberg University, Heidelberg, Germany.,Institute of Anatomy and Cell Biology, Medical Faculty, Johannes Kepler University, Linz, Austria.,Institute for Stem Cell Biology and Regenerative Medicine, Stanford University, Stanford, CA, USA
| | - Lingjun Ding
- Institute of Neurobiology, University of Tübingen, Tübingen, Germany.,Werner-Reichardt Centre for Integrative Neuroscience, Tübingen, Germany.,Graduate Training Centre of Neuroscience, IMPRS, Tübingen, Germany
| | - Andrei Rozov
- Institute of Physiology and Pathophysiology, Medical Faculty, Heidelberg University, Heidelberg, Germany.,Federal Center of Brain Research and Neurotechnologies, Moscow, Russian Federation.,OpenLab of Neurobiology, Kazan Federal University, Kazan, Russian Federation
| | - Matthias Klumpp
- Institute of Physiology and Pathophysiology, Medical Faculty, Heidelberg University, Heidelberg, Germany
| | - Nikolas Stevens
- Institute of Physiology and Pathophysiology, Medical Faculty, Heidelberg University, Heidelberg, Germany
| | - Moritz Stingl
- Institute of Physiology and Pathophysiology, Medical Faculty, Heidelberg University, Heidelberg, Germany
| | - Tina Sackmann
- Institute of Physiology and Pathophysiology, Medical Faculty, Heidelberg University, Heidelberg, Germany
| | - Nadja Lehmann
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, Heidelberg, Germany
| | - Andreas Draguhn
- Institute of Physiology and Pathophysiology, Medical Faculty, Heidelberg University, Heidelberg, Germany
| | - Andrea Burgalossi
- Institute of Neurobiology, University of Tübingen, Tübingen, Germany.,Werner-Reichardt Centre for Integrative Neuroscience, Tübingen, Germany
| | - Maren Engelhardt
- Institute of Anatomy and Cell Biology, Medical Faculty, Johannes Kepler University, Linz, Austria.,Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, Heidelberg, Germany
| | - Martin Both
- Institute of Physiology and Pathophysiology, Medical Faculty, Heidelberg University, Heidelberg, Germany
| |
Collapse
|
6
|
Choudhary S, Abongwa M, Kashyap SS, Verma S, Mair GR, Kulke D, Martin RJ, Robertson AP. Nodulisporic acid produces direct activation and positive allosteric modulation of AVR-14B, a glutamate-gated chloride channel from adult Brugia malayi. Proc Natl Acad Sci U S A 2022; 119:e2111932119. [PMID: 35969762 PMCID: PMC9407656 DOI: 10.1073/pnas.2111932119] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2021] [Accepted: 06/13/2022] [Indexed: 11/18/2022] Open
Abstract
Glutamate-gated chloride channels (GluCls) are unique to invertebrates and are targeted by macrocyclic lactones. In this study, we cloned an AVR-14B GluCl subunit from adult Brugia malayi, a causative agent of lymphatic filariasis in humans. To elucidate this channel's pharmacological properties, we used Xenopus laevis oocytes for expression and performed two-electrode voltage-clamp electrophysiology. The receptor was gated by the natural ligand L-glutamate (effective concentration, 50% [EC50] = 0.4 mM) and ivermectin (IVM; EC50 = 1.8 nM). We also characterized the effects of nodulisporic acid (NA) on Bma-AVR-14B and NA-produced dual effects on the receptor as an agonist and a type II positive allosteric modulator. Here we report characterization of the complex activity of NA on a nematode GluCl. Bma-AVR-14B demonstrated some unique pharmacological characteristics. IVM did not produce potentiation of L-glutamate-mediated responses but instead, reduced the channel's sensitivity for the ligand. Further electrophysiological exploration showed that IVM (at a moderate concentration of 0.1 nM) functioned as an inhibitor of both agonist and positive allosteric modulatory effects of NA. This suggests that IVM and NA share a complex interaction. The pharmacological properties of Bma-AVR-14B indicate that the channel is an important target of IVM and NA. In addition, the unique electrophysiological characteristics of Bma-AVR-14B could explain the observed variation in drug sensitivities of various nematode parasites. We have also shown the inhibitory effects of IVM and NA on adult worm motility using Worminator. RNA interference (RNAi) knockdown suggests that AVR-14 plays a role in influencing locomotion in B. malayi.
Collapse
Affiliation(s)
- Shivani Choudhary
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011
| | - Melanie Abongwa
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011
| | - Sudhanva S. Kashyap
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011
| | - Saurabh Verma
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011
| | - Gunnar R. Mair
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011
| | - Daniel Kulke
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011
| | - Richard J. Martin
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011
| | - Alan P. Robertson
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011
| |
Collapse
|
7
|
Singla RK, Dhir V, Madaan R, Kumar D, Singh Bola S, Bansal M, Kumar S, Dubey AK, Singla S, Shen B. The Genus Alternanthera: Phytochemical and Ethnopharmacological Perspectives. Front Pharmacol 2022; 13:769111. [PMID: 35479320 PMCID: PMC9036189 DOI: 10.3389/fphar.2022.769111] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Accepted: 02/21/2022] [Indexed: 12/14/2022] Open
Abstract
Ethnopharmacological relevance: The genus Alternanthera (Amaranthaceae) comprises 139 species including 14 species used traditionally for the treatment of various ailments such as hypertension, pain, inflammation, diabetes, cancer, microbial and mental disorders. Aim of the review: To search research gaps through critical assessment of pharmacological activities not performed to validate traditional claims of various species of Alternanthera. This review will aid natural product researchers in identifying Alternanthera species with therapeutic potential for future investigation. Materials and methods: Scattered raw data on ethnopharmacological, morphological, phytochemical, pharmacological, toxicological, and clinical studies of various species of the genus Alternanthera have been compiled utilizing search engines like SciFinder, Google Scholar, PubMed, Science Direct, and Open J-Gate for 100 years up to April 2021. Results: Few species of Alternanthera genus have been exhaustively investigated phytochemically, and about 129 chemical constituents related to different classes such as flavonoids, steroids, saponins, alkaloids, triterpenoids, glycosides, and phenolic compounds have been isolated from 9 species. Anticancer, antioxidant, antibacterial, CNS depressive, antidiabetic, analgesic, anti-inflammatory, and immunomodulator effects have been explored in the twelve species of the genus. A toxicity study has been conducted on 3 species and a clinical study on 2 species. Conclusions: The available literature on pharmacological studies of Alternanthera species reveals that few species have been selected based on ethnobotanical surveys for scientific validation of their traditional claims. But most of these studies have been conducted on uncharacterized and non-standardized crude extracts. A roadmap of research needs to be developed for the isolation of new bioactive compounds from Alternanthera species, which can emerge out as clinically potential medicines.
Collapse
Affiliation(s)
- Rajeev K. Singla
- Institutes for Systems Genetics, Frontiers Science Center for Disease-related Molecular Network, West China Hospital, Sichuan University, Chengdu, China
- iGlobal Research and Publishing Foundation, New Delhi, India
| | - Vivek Dhir
- Chitkara College of Pharmacy, Chitkara University Punjab, Rajpura, India
| | - Reecha Madaan
- Chitkara College of Pharmacy, Chitkara University Punjab, Rajpura, India
- *Correspondence: Bairong Shen, ; Reecha Madaan,
| | - Deepak Kumar
- Department of Health and Family Welfare, Civil Hospital, Rampura Phul, India
| | - Simranjit Singh Bola
- Akal College of Pharmacy and Technical Education, Mastuana Sahib, Sangrur, India
| | - Monika Bansal
- Akal College of Pharmacy and Technical Education, Mastuana Sahib, Sangrur, India
| | - Suresh Kumar
- Department of Pharmaceutical Sciences and Drug Research, Punjabi University, Patiala, India
| | | | - Shailja Singla
- iGlobal Research and Publishing Foundation, New Delhi, India
| | - Bairong Shen
- Institutes for Systems Genetics, Frontiers Science Center for Disease-related Molecular Network, West China Hospital, Sichuan University, Chengdu, China
- *Correspondence: Bairong Shen, ; Reecha Madaan,
| |
Collapse
|
8
|
Ríos JL, Schinella GR, Moragrega I. Phenolics as GABA A Receptor Ligands: An Updated Review. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27061770. [PMID: 35335130 PMCID: PMC8953830 DOI: 10.3390/molecules27061770] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Revised: 03/02/2022] [Accepted: 03/03/2022] [Indexed: 11/16/2022]
Abstract
Natural products can act as potential GABA modulators, avoiding the undesirable effects of traditional pharmacology used for the inhibition of the central nervous system such as benzodiazepines (BZD). Phenolics, especially flavonoids and phlorotannins, have been considered as modulators of the BZD-site of GABAA receptors (GABAARs), with sedative, anxiolytic or anticonvulsant effects. However, the wide chemical structural variability of flavonoids shows their potential action at more than one additional binding site on GABAARs, which may act either negatively, positively, by neutralizing GABAARs, or directly as allosteric agonists. Therefore, the aim of the present review is to compile and discuss an update of the role of phenolics, namely as pharmacological targets involving dysfunctions of the GABA system, analyzing both their different compounds and their mechanism as GABAergic modulators. We focus this review on articles written in English since the year 2010 until the present. Of course, although more research would be necessary to fully establish the type specificity of phenolics and their pharmacological activity, the evidence supports their potential as GABAAR modulators, thereby favoring their inclusion in the development of new therapeutic targets based on natural products. Specifically, the data compiled in this review allows for the directing of future research towards ortho-dihydroxy diterpene galdosol, the flavonoids isoliquiritigenin (chalcone), rhusflavone and agathisflavone (biflavonoids), as well as the phlorotannins, dieckol and triphlorethol A. Clinically, flavonoids are the most interesting phenolics due to their potential as anticonvulsant and anxiolytic drugs, and phlorotannins are also of interest as sedative agents.
Collapse
Affiliation(s)
- José-Luis Ríos
- Departament de Farmacologia, Facultat de Farmàcia, Universitat de València, Av. Vicent Andrés Estellés s/n, Burjassot, 46100 Valencia, Spain
- Correspondence:
| | - Guillermo R. Schinella
- Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata BA1900, Argentina;
- Instituto de Ciencias de la Salud, UNAJ-CICPBA, Florencio Varela BA1888, Argentina
| | - Inés Moragrega
- Departament de Psicobiologia, Facultat de Psicologia, Universitat de València, Av. Blasco Ibáñez 21, 46010 Valencia, Spain;
| |
Collapse
|
9
|
Germann AL, Reichert DE, Burbridge AB, Pierce SR, Evers AS, Steinbach JH, Akk G. Analysis of Modulation of the ρ1 GABA A Receptor by Combinations of Inhibitory and Potentiating Neurosteroids Reveals Shared and Distinct Binding Sites. Mol Pharmacol 2020; 98:280-291. [PMID: 32675382 DOI: 10.1124/mol.120.119842] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2020] [Accepted: 07/07/2020] [Indexed: 11/22/2022] Open
Abstract
The ρ1 GABAA receptor is prominently expressed in the retina and is present at lower levels in several brain regions and other tissues. Although the ρ1 receptor is insensitive to many anesthetic drugs that modulate the heteromeric GABAA receptor, it maintains a rich and multifaceted steroid pharmacology. The receptor is negatively modulated by 5β-reduced steroids, sulfated or carboxylated steroids, and β-estradiol, whereas many 5α-reduced steroids potentiate the receptor. In this study, we analyzed modulation of the human ρ1 GABAA receptor by several neurosteroids, individually and in combination, in the framework of the coagonist concerted transition model. Experiments involving coapplication of two or more steroids revealed that the receptor contains at least three classes of distinct, nonoverlapping sites for steroids, one each for the inhibitory steroids pregnanolone (3α5βP), 3α5βP sulfate, and β-estradiol. The site for 3α5βP can accommodate the potentiating steroid 5αTHDOC. The findings are discussed with respect to receptor modulation by combinations of endogenous neurosteroids. SIGNIFICANCE STATEMENT: The study describes modulation of the ρ1 GABAA receptor by neurosteroids. The coagonist concerted transition model was used to determine overlap of binding sites for several inhibitory and potentiating steroids.
Collapse
Affiliation(s)
- Allison L Germann
- Departments of Anesthesiology (A.L.G., A.B.B., S.R.P., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.) and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - David E Reichert
- Departments of Anesthesiology (A.L.G., A.B.B., S.R.P., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.) and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Ariel B Burbridge
- Departments of Anesthesiology (A.L.G., A.B.B., S.R.P., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.) and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Spencer R Pierce
- Departments of Anesthesiology (A.L.G., A.B.B., S.R.P., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.) and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Alex S Evers
- Departments of Anesthesiology (A.L.G., A.B.B., S.R.P., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.) and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Joe Henry Steinbach
- Departments of Anesthesiology (A.L.G., A.B.B., S.R.P., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.) and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Gustav Akk
- Departments of Anesthesiology (A.L.G., A.B.B., S.R.P., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.) and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| |
Collapse
|
10
|
Zhou X, Li G, Yang B, Wu J. Quercetin Enhances Inhibitory Synaptic Inputs and Reduces Excitatory Synaptic Inputs to OFF- and ON-Type Retinal Ganglion Cells in a Chronic Glaucoma Rat Model. Front Neurosci 2019; 13:672. [PMID: 31293381 PMCID: PMC6604910 DOI: 10.3389/fnins.2019.00672] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Accepted: 06/12/2019] [Indexed: 01/28/2023] Open
Abstract
Background Glaucoma is a neurodegenerative disease caused by excitotoxic injury of retinal ganglion cells (RGCs). In our previous model of high intraocular pressure, prepared by injecting magnetic beads into the anterior chamber, we demonstrated that an important natural dietary flavonoid compound (quercetin) can improve RGC function. However, it is unclear whether quercetin can improve the synaptic function of RGCs and how quercetin regulates synaptic transmission in rat models of chronic glaucoma. Methods A rat model of chronic glaucoma was prepared by electrocoagulation of the superior scleral vein. Electrophysiological electroretinography was used to detect the photopic negative response (PhNR). The whole-cell patch-clamp technique was used to clamp ON- and OFF- type RGCs in sections from normal retinas and from retinas that had been subjected to glaucoma for 4 weeks. Results Quercetin can reverse the decrease in PhNR amplitude caused by chronic glaucoma. The baseline frequency of miniature GABAergic inhibitory postsynaptic currents (mIPSCs) in the RGCs of glaucomatous retinal slices was lower than that of the control group. The frequencies of miniature excitatory postsynaptic currents (mEPSCs) were not significantly different between control and glaucomatous RGCs. The baseline frequencies of GABAergic mIPSCs and mEPSCs in OFF-type glaucomatous RGCs were greater than those in ON-type glaucomatous RGCs. Quercetin increased miniature GABAergic inhibitory neurotransmission to RGCs and decreased miniature glutamatergic excitatory neurotransmission, reducing the excitability of the RGCs themselves, thus alleviating the excitability of RGCs in glaucomatous slices. Conclusion Quercetin may be a promising therapeutic agent for improving RGC survival and function in glaucomatous neurodegeneration. Quercetin exerted direct protective effects on RGCs by increasing inhibitory neurotransmission and decreasing excitatory neurotransmission to RGCs, thus reducing excitotoxic damage to those cells in glaucoma.
Collapse
Affiliation(s)
- Xujiao Zhou
- Eye Institute, Eye and ENT Hospital, State Key Laboratory of Medical Neurobiology, Institutes of Brain Science and Collaborative Innovation Center for Brain Science, Shanghai Medical College, Fudan University, Shanghai, China.,Shanghai Key Laboratory of Visual Impairment and Restoration, Shanghai, China.,NHC Key Laboratory of Myopia, Key Laboratory of Myopia, Chinese Academy of Medical Sciences, Fudan University, Shanghai, China
| | - Gang Li
- Eye Institute, Eye and ENT Hospital, State Key Laboratory of Medical Neurobiology, Institutes of Brain Science and Collaborative Innovation Center for Brain Science, Shanghai Medical College, Fudan University, Shanghai, China.,Shanghai Key Laboratory of Visual Impairment and Restoration, Shanghai, China.,NHC Key Laboratory of Myopia, Key Laboratory of Myopia, Chinese Academy of Medical Sciences, Fudan University, Shanghai, China
| | - Boqi Yang
- Eye Institute, Eye and ENT Hospital, State Key Laboratory of Medical Neurobiology, Institutes of Brain Science and Collaborative Innovation Center for Brain Science, Shanghai Medical College, Fudan University, Shanghai, China.,Shanghai Key Laboratory of Visual Impairment and Restoration, Shanghai, China.,NHC Key Laboratory of Myopia, Key Laboratory of Myopia, Chinese Academy of Medical Sciences, Fudan University, Shanghai, China
| | - Jihong Wu
- Eye Institute, Eye and ENT Hospital, State Key Laboratory of Medical Neurobiology, Institutes of Brain Science and Collaborative Innovation Center for Brain Science, Shanghai Medical College, Fudan University, Shanghai, China.,Shanghai Key Laboratory of Visual Impairment and Restoration, Shanghai, China.,NHC Key Laboratory of Myopia, Key Laboratory of Myopia, Chinese Academy of Medical Sciences, Fudan University, Shanghai, China.,Department of Ophthalmology and Vision Science, Eye and ENT Hospital, Fudan University, Shanghai, China
| |
Collapse
|
11
|
Masiulis S, Desai R, Uchański T, Serna Martin I, Laverty D, Karia D, Malinauskas T, Zivanov J, Pardon E, Kotecha A, Steyaert J, Miller KW, Aricescu AR. GABA A receptor signalling mechanisms revealed by structural pharmacology. Nature 2019; 565:454-459. [PMID: 30602790 PMCID: PMC6370056 DOI: 10.1038/s41586-018-0832-5] [Citation(s) in RCA: 330] [Impact Index Per Article: 66.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Accepted: 11/23/2018] [Indexed: 01/02/2023]
Abstract
Type-A γ-aminobutyric (GABAA) receptors are ligand-gated chloride channels with a very rich pharmacology. Some of their modulators, including benzodiazepines and general anaesthetics, are among the most successful drugs in clinical use and are common substances of abuse. Without reliable structural data, the mechanistic basis for the pharmacological modulation of GABAA receptors remains largely unknown. Here we report several high-resolution cryo-electron microscopy structures in which the full-length human α1β3γ2L GABAA receptor in lipid nanodiscs is bound to the channel-blocker picrotoxin, the competitive antagonist bicuculline, the agonist GABA (γ-aminobutyric acid), and the classical benzodiazepines alprazolam and diazepam. We describe the binding modes and mechanistic effects of these ligands, the closed and desensitized states of the GABAA receptor gating cycle, and the basis for allosteric coupling between the extracellular, agonist-binding region and the transmembrane, pore-forming region. This work provides a structural framework in which to integrate previous physiology and pharmacology research and a rational basis for the development of GABAA receptor modulators.
Collapse
Affiliation(s)
- Simonas Masiulis
- MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, UK.
| | - Rooma Desai
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
| | - Tomasz Uchański
- Structural Biology Brussels, Vrije Universiteit Brussel (VUB), Brussels, Belgium
- VIB-VUB Center for Structural Biology, VIB, Brussels, Belgium
| | - Itziar Serna Martin
- Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Duncan Laverty
- MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, UK
| | - Dimple Karia
- Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Tomas Malinauskas
- Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Jasenko Zivanov
- MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, UK
| | - Els Pardon
- Structural Biology Brussels, Vrije Universiteit Brussel (VUB), Brussels, Belgium
- VIB-VUB Center for Structural Biology, VIB, Brussels, Belgium
| | - Abhay Kotecha
- Materials and Structural Analysis, Thermo Fisher Scientific, Eindhoven, The Netherlands
| | - Jan Steyaert
- Structural Biology Brussels, Vrije Universiteit Brussel (VUB), Brussels, Belgium
- VIB-VUB Center for Structural Biology, VIB, Brussels, Belgium
| | - Keith W Miller
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
| | - A Radu Aricescu
- MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, UK.
- Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK.
| |
Collapse
|
12
|
Quercetin Reduces Cortical GABAergic Transmission and Alleviates MK-801-Induced Hyperactivity. EBioMedicine 2018; 34:201-213. [PMID: 30057312 PMCID: PMC6116474 DOI: 10.1016/j.ebiom.2018.07.031] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2018] [Revised: 07/11/2018] [Accepted: 07/20/2018] [Indexed: 02/06/2023] Open
Abstract
An imbalance between neuronal excitation and inhibition represents a core feature in multiple neuropsychiatry disorders, necessitating the development of novel strategies to calibrate the excitatory–inhibitory balance of therapeutics. Here we identify a natural compound quercetin that reduces prefrontal cortical GABAergic transmission and alleviates the hyperactivity induced by glutamatergic N-methyl-d-aspartate receptor antagonist MK-801. Quercetin markedly reduced the GABA-activated currents in a noncompetitive manner in cultured cortical neurons, and moderately inhibited spontaneous and electrically-evoked GABAergic inhibitory postsynaptic current in mouse prefrontal cortical slices. Notably, systemic and prefrontal-specific delivery of quercetin reduced basal locomotor activity in addition to alleviated the MK-801-induced hyperactivity. The effects of quercetin were not exclusively dependent on α5-subunit-containing A type GABA receptors (GABAARs), as viral-mediated, region-specific genetic knockdown of the α5-subunit in prefrontal cortex improved the MK-801-evoked psychotic symptom but reserved the pharmacological responsivity to quercetin. Both interventions together completely normalized the locomotor activity. Together, quercetin as a negative allosteric GABAAR modulator exerted antipsychotic activity, facilitating further therapeutic development for the excitatory–inhibitory imbalance disorders.
Collapse
|
13
|
Gielen M, Corringer P. The dual-gate model for pentameric ligand-gated ion channels activation and desensitization. J Physiol 2018; 596:1873-1902. [PMID: 29484660 PMCID: PMC5978336 DOI: 10.1113/jp275100] [Citation(s) in RCA: 73] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2018] [Revised: 01/17/2018] [Accepted: 01/17/2018] [Indexed: 12/15/2022] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) mediate fast neurotransmission in the nervous system. Their dysfunction is associated with psychiatric, neurological and neurodegenerative disorders such as schizophrenia, epilepsy and Alzheimer's disease. Understanding their biophysical and pharmacological properties, at both the functional and the structural level, thus holds many therapeutic promises. In addition to their agonist-elicited activation, most pLGICs display another key allosteric property, namely desensitization, in which they enter a shut state refractory to activation upon sustained agonist binding. While the activation mechanisms of several pLGICs have been revealed at near-atomic resolution, the structural foundation of desensitization has long remained elusive. Recent structural and functional data now suggest that the activation and desensitization gates are distinct, and are located at both sides of the ion channel. Such a 'dual gate mechanism' accounts for the marked allosteric effects of channel blockers, a feature illustrated herein by theoretical kinetics simulations. Comparison with other classes of ligand- and voltage-gated ion channels shows that this dual gate mechanism emerges as a common theme for the desensitization and inactivation properties of structurally unrelated ion channels.
Collapse
Affiliation(s)
- Marc Gielen
- Channel Receptors UnitInstitut PasteurCNRS UMR 3571ParisFrance
| | | |
Collapse
|
14
|
Beltrán González AN, Vicentini F, Calvo DJ. Negative modulation of the GABA A ρ1 receptor function by l-cysteine. J Neurochem 2017; 144:50-57. [PMID: 29023772 DOI: 10.1111/jnc.14237] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2017] [Revised: 09/12/2017] [Accepted: 10/04/2017] [Indexed: 11/28/2022]
Abstract
l-Cysteine is an endogenous sulfur-containing amino acid with multiple and varied roles in the central nervous system, including neuroprotection and the maintenance of the redox balance. However, it was also suggested as an excitotoxic agent implicated in the pathogenesis of neurological disorders such as Parkinson's and Alzheimer's disease. l-Cysteine can modulate the activity of ionic channels, including voltage-gated calcium channels and glutamatergic NMDA receptors, whereas its effects on GABAergic neurotransmission had not been studied before. In the present work, we analyzed the effects of l-cysteine on responses mediated by homomeric GABAA ρ1 receptors, which are known for mediating tonic γ-aminobutyric acid (GABA) responses in retinal neurons. GABAA ρ1 receptors were expressed in Xenopus laevis oocytes and GABA-evoked chloride currents recorded by two-electrode voltage-clamp in the presence or absence of l-cysteine. l-Cysteine antagonized GABAA ρ1 receptor-mediated responses; inhibition was dose-dependent, reversible, voltage independent, and susceptible to GABA concentration. Concentration-response curves for GABA were shifted to the right in the presence of l-cysteine without a substantial change in the maximal response. l-Cysteine inhibition was insensitive to chemical protection of the sulfhydryl groups of the ρ1 subunits by the irreversible alkylating agent N-ethyl maleimide. Our results suggest that redox modulation is not involved during l-cysteine actions and that l-cysteine might be acting as a competitive antagonist of the GABAA ρ1 receptors.
Collapse
Affiliation(s)
- Andrea N Beltrán González
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Ciudad Autónoma de Buenos Aires, Argentina
| | - Florencia Vicentini
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Ciudad Autónoma de Buenos Aires, Argentina
| | - Daniel J Calvo
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Ciudad Autónoma de Buenos Aires, Argentina
| |
Collapse
|
15
|
Shen ML, Wang CH, Chen RYT, Zhou N, Kao ST, Wu DC. Luteolin inhibits GABAA receptors in HEK cells and brain slices. Sci Rep 2016; 6:27695. [PMID: 27292079 PMCID: PMC4904371 DOI: 10.1038/srep27695] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Accepted: 05/24/2016] [Indexed: 11/23/2022] Open
Abstract
Modulation of the A type γ-aminobutyric acid receptors (GABAAR) is one of the major drug targets for neurological and psychological diseases. The natural flavonoid compound luteolin (2-(3,4-Dihydroxyphenyl)- 5,7-dihydroxy-4-chromenone) has been reported to have antidepressant, antinociceptive, and anxiolytic-like effects, which possibly involve the mechanisms of modulating GABA signaling. However, as yet detailed studies of the pharmacological effects of luteolin are still lacking, we investigated the effects of luteolin on recombinant and endogenous GABAAR-mediated current responses by electrophysiological approaches. Our results showed that luteolin inhibited GABA-mediated currents and slowed the activation kinetics of recombinant α1β2, α1β2γ2, α5β2, and α5β2γ2 receptors with different degrees of potency and efficacy. The modulatory effect of luteolin was likely dependent on the subunit composition of the receptor complex: the αβ receptors were more sensitive than the αβγ receptors. In hippocampal pyramidal neurons, luteolin significantly reduced the amplitude and slowed the rise time of miniature inhibitory postsynaptic currents (mIPSCs). However, GABAAR-mediated tonic currents were not significantly influenced by luteolin. These data suggested that luteolin has negative modulatory effects on both recombinant and endogenous GABAARs and inhibits phasic rather than tonic inhibition in hippocampus.
Collapse
Affiliation(s)
- Mei-Lin Shen
- Graduate Institute of Chinese Medicine, China Medical University, Taichung, Taiwan
| | - Chen-Hung Wang
- Graduate Institute of Clinical Medical Science, China Medical University, Taichung, Taiwan
| | - Rita Yu-Tzu Chen
- Translational Medicine Research Center, China Medical University Hospital, Taichung, Taiwan
| | - Ning Zhou
- Graduate Institute of Clinical Medical Science, China Medical University, Taichung, Taiwan.,Translational Medicine Research Center, China Medical University Hospital, Taichung, Taiwan
| | - Shung-Te Kao
- Graduate Institute of Chinese Medicine, China Medical University, Taichung, Taiwan
| | - Dong Chuan Wu
- Graduate Institute of Clinical Medical Science, China Medical University, Taichung, Taiwan.,Translational Medicine Research Center, China Medical University Hospital, Taichung, Taiwan
| |
Collapse
|
16
|
The Combined Extract of Zingiber officinale and Zea mays (Purple Color) Improves Neuropathy, Oxidative Stress, and Axon Density in Streptozotocin Induced Diabetic Rats. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2015; 2015:301029. [PMID: 25969689 PMCID: PMC4410543 DOI: 10.1155/2015/301029] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/25/2014] [Accepted: 03/10/2015] [Indexed: 01/01/2023]
Abstract
Based on the protective effect of the combined extract of purple waxy corn and ginger (PWCG) on oxidative stress related disorders in diabetic condition, we aimed to determine the effect of PWCG on the functional, biochemical, and structural change of the lesion nerve in streptozotocin- (STZ-) diabetic rats. PWCG at doses of 100, 200, and 300 mg·kg−1 BW were orally given to STZ-diabetic rats which were subjected to chronic constriction (CCI) at right sciatic nerve for 21 days. The blood sugar was assessed before and at the end of study whereas the sciatic function index (SFI), paw withdrawal threshold intensity (PWTI), and paw withdrawal latency (PWL) were assessed every 3 days until the end of study. At the end of study, the determination of nerve conduction velocity (NCV), axon density, oxidative stress status, and aldose reductase (AR) activity of the lesion nerve were performed. It was found that PWCG improved SFI, PWTI, PWL, and NCV together with the improved oxidative stress status and the axon density in the lesion nerve. No changes of AR activity or blood sugar level were observed. Therefore, PWCG might improve the functional and structural changes in STZ-diabetic rats plus CCI via the improved oxidative stress status.
Collapse
|
17
|
Snell HD, Gonzales EB. Amiloride and GMQ Allosteric Modulation of the GABA-A ρ1 Receptor: Influences of the Intersubunit Site. J Pharmacol Exp Ther 2015; 353:551-9. [PMID: 25829529 DOI: 10.1124/jpet.115.222802] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Accepted: 03/31/2015] [Indexed: 11/22/2022] Open
Abstract
Amiloride, a diuretic used in the treatment of hypertension and congestive heart failure, and 2-guanidine-4-methylquinazoline (GMQ) are guanidine compounds that modulate acid-sensing ion channels. Both compounds have demonstrated affinity for a variety of membrane proteins, including members of the Cys-loop family of ligand-gated ion channels, such as the heteromeric GABA-A αβγ receptors. The actions of these guanidine compounds on the homomeric GABA-A ρ1 receptor remains unclear, especially in light of how many GABA-A αβγ receptor modulators have different effects in the GABA-A ρ1 receptors. We sought to characterize the influence of amiloride and GMQ on the human GABA-A ρ1 receptors using whole-cell patch-clamp electrophysiology. The diuretic amiloride potentiated the human GABA-A ρ1 GABA-mediated current, whereas GMQ antagonized the receptor. Furthermore, a GABA-A second transmembrane domain site, the intersubunit site, responsible for allosteric modulation in the heteromeric GABA-A receptors mediated amiloride's positive allosteric actions. In contrast, the mutation did not remove GMQ antagonism but only changed the guanidine compound's potency within the human GABA-A ρ1 receptor. Through modeling and introduction of point mutations, we propose that the GABA-A ρ1 intersubunit site plays a role in mediating the allosteric effects of amiloride and GMQ.
Collapse
Affiliation(s)
- Heather D Snell
- Department of Pharmacology and Neuroscience (H.D.S., E.B.G.), Institute for Aging and Alzheimer's Disease Research (E.B.G.), and Cardiovascular Research Institute (E.B.G.), University of North Texas Health Science Center, Fort Worth, Texas
| | - Eric B Gonzales
- Department of Pharmacology and Neuroscience (H.D.S., E.B.G.), Institute for Aging and Alzheimer's Disease Research (E.B.G.), and Cardiovascular Research Institute (E.B.G.), University of North Texas Health Science Center, Fort Worth, Texas
| |
Collapse
|
18
|
Beltrán González AN, Pomata PE, Goutman JD, Gasulla J, Chebib M, Calvo DJ. Benzodiazepine modulation of homomeric GABAAρ1 receptors: differential effects of diazepam and 4'-chlorodiazepam. Eur J Pharmacol 2014; 743:24-30. [PMID: 25246015 DOI: 10.1016/j.ejphar.2014.09.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Revised: 09/09/2014] [Accepted: 09/10/2014] [Indexed: 11/26/2022]
Abstract
GABA(A) receptors (GABA(A)Rs) are ligand-gated ion channels that mediate inhibitory neurotransmission in the central nervous system (CNS). They are members of the Cys-loop receptor family and display marked structural and functional heterogeneity. Many GABA(A)Rs receptor subtypes are allosterically modulated by benzodiazepines (BDZs), which are drugs extensively used as anxiolytics, sedative-hypnotics and anticonvulsants. One high-affinity site and at least three additional low-affinity sites for BDZ recognition have been identified in several heteromeric and homomeric variants of the GABA(A)Rs (e.g.: α1β2γ2, α1β2/3, β3, etc.). However, the modulation of homomeric GABA(A)ρRs by BDZs was not previously revealed, and these receptors, for a long a time, were assumed to be fully insensitive to the actions of these drugs. In the present study, human homomeric GABA(A)ρ1 receptors were expressed in Xenopus oocytes and GABA-evoked responses electrophysiologically recorded in the presence or absence of BDZs. GABA(A)ρ1 receptor-mediated responses were modulated by diazepam and 4'-chlorodiazepam in the micromolar range, in a concentration-dependent, voltage-independent and reversible manner. Diazepam produced potentiating effects on GABA-evoked Cl(-) currents and 4'-Cl diazepam induced biphasic effects depending on the GABA concentration, whereas Ro15-4513 and alprazolam were negative modulators. BDZ actions were insensitive to flumazenil. Other BDZs showed negligible activity at equivalent experimental conditions. Our results suggest that GABA(A)ρ1 receptor function can be selectively and differentially modulated by BDZs.
Collapse
Affiliation(s)
- Andrea N Beltrán González
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Vuelta de Obligado 2490, Ciudad Autónoma de Buenos Aires CP 1428, Argentina
| | - Pablo E Pomata
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Vuelta de Obligado 2490, Ciudad Autónoma de Buenos Aires CP 1428, Argentina
| | - Juan D Goutman
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Vuelta de Obligado 2490, Ciudad Autónoma de Buenos Aires CP 1428, Argentina
| | - Javier Gasulla
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Vuelta de Obligado 2490, Ciudad Autónoma de Buenos Aires CP 1428, Argentina
| | - Mary Chebib
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Vuelta de Obligado 2490, Ciudad Autónoma de Buenos Aires CP 1428, Argentina
| | - Daniel J Calvo
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Vuelta de Obligado 2490, Ciudad Autónoma de Buenos Aires CP 1428, Argentina.
| |
Collapse
|
19
|
Differential effects of quercetin glycosides on GABAC receptor channel activity. Arch Pharm Res 2014; 38:108-14. [DOI: 10.1007/s12272-014-0409-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2014] [Accepted: 05/06/2014] [Indexed: 10/25/2022]
|
20
|
Characteristics of quercetin interactions with liposomal and vacuolar membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:254-65. [DOI: 10.1016/j.bbamem.2013.08.014] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2013] [Revised: 08/02/2013] [Accepted: 08/25/2013] [Indexed: 01/07/2023]
|
21
|
Calero CI, Beltrán González AN, Gasulla J, Alvarez S, Evelson P, Calvo DJ. Quercetin antagonism of GABAAρ₁ receptors is prevented by ascorbic acid through a redox-independent mechanism. Eur J Pharmacol 2013; 714:274-80. [PMID: 23916728 DOI: 10.1016/j.ejphar.2013.07.044] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Revised: 07/02/2013] [Accepted: 07/18/2013] [Indexed: 10/26/2022]
Abstract
Quercetin is a natural flavonoid widely distributed in plants that acts as a neuroprotective agent and modulates the activity of different synaptic receptors and ion channels, including the ionotropic GABA receptors. GABA(Aρ₁) receptors were shown to be antagonized by quercetin, but the mechanisms underlying these antagonistic actions are still unknown. We have analyzed here if the antagonistic action produced by quercetin on GABA(Aρ₁) receptors was related to its redox activity or due to alternative mechanism/s. Homomeric GABA(Aρ₁) receptors were expressed in frog oocytes and GABA-evoked responses electrophysiologically recorded. Quercetin effects on GABA(Aρ₁) receptors were examined in the absence or presence of ascorbic acid. Chemical protection of cysteines by selective sulfhydryl reagents and site directed mutagenesis experiments were also used to determine ρ₁ subunit residues involved in quercetin actions. Quercetin antagonized GABA(Aρ₁) receptor responses in a dose-dependent, fast and reversible manner. Quercetin inhibition was prevented in the presence of ascorbic acid, but not by thiol reagents that modify the extracellular Cys-loop of these receptors. H141, an aminoacidic residue located near to the ρ₁ subunit GABA binding site, was involved in the allosteric modulation of GABA(Aρ₁) receptors by several agents including ascorbic acid. Quercetin similarly antagonized GABA-evoked responses mediated by mutant (H141D)GABA(Aρ₁) and wild-type receptors, but prevention exerted by ascorbic acid on quercetin effects was impaired in mutant receptors. Taken together the present results suggest that quercetin antagonistic actions on GABA(Aρ₁) receptors are mediated through a redox-independent allosteric mechanism.
Collapse
Affiliation(s)
- Cecilia I Calero
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Consejo Nacional de Investigaciones Científicas y Técnicas, Vuelta de Obligado 2490, C1428ADN Ciudad Autónoma de Buenos Aires, Argentina.
| | | | | | | | | | | |
Collapse
|
22
|
Kosari-Nasab M, Babri S, Fatehi-Gharehlar L, Doosti MH, Pakzad S. Involvement of GABAergic system in regulation of the anxiolytic- and antidepressant-like effects of Scrophularia striata extract in rats. PHARMACEUTICAL BIOLOGY 2013; 51:581-588. [PMID: 23373710 DOI: 10.3109/13880209.2012.749924] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
CONTEXT Neuropsychiatric disorders, like anxiety and depression, are global problems for clinical researchers in neurology. Recently, some authors have shown neuroprotective and anti-inflammatory effects of Scrophularia striata Boiss (Scrophulariaceae) extract in rodents. OBJECTIVE The purpose of the current study was to investigate the effects of S. striata extract on anxiety and depressant-like behaviors and find a possible mechanism for these impacts. MATERIALS AND METHODS In this study, the elevated plus-maze (EPM) and forced swimming test (FST), which are useful models for selective identification of anxiolytic and antidepressant drug effects in rodents, were used. We investigated the effects of S. striata ethanol extract at different doses (20, 50, 100, 160 and 220 mg/kg) on anxiety and depression behaviors in the EPM and FST, and then we assessed the role of γ-aminobutyric acid (GABA)A receptor in modulation of the effects of S. striata extract in the brain. RESULTS Our results showed that effective doses of S. striata (100 and 160 mg/kg) increased the percentages of open arm time and entries in the EPM and decreased immobility time in the FST in comparison with control group, indicating anxiolytic and antidepressant effects, respectively. Moreover, intracerebroventricular administration of GABAA receptor agonist (muscimol; 1 µg/rat) enhanced the impact of S. striata, and GABAA receptor antagonist (bicuculline; 1 µg/rat) blocked these effects in rats, indicating that significant interactions existed between S. striata and the GABAergic system in the brain. DISCUSSION AND CONCLUSION Findings of this study suggest that anxiolytic and antidepressant effects of S. striata may be modulated via the GABAergic system.
Collapse
Affiliation(s)
- Morteza Kosari-Nasab
- Laboratory of Plant Biotechnology, Hayyan Research Institute, University of Tabriz, Tabriz, Iran
| | | | | | | | | |
Collapse
|
23
|
Lee BH, Hwang SH, Choi SH, Kim HJ, Lee JH, Lee SM, Ahn YG, Nah SY. Inhibitory Effects of Ginsenoside Metabolites, Compound K and Protopanaxatriol, on GABAC Receptor-Mediated Ion Currents. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2013; 17:127-32. [PMID: 23626474 PMCID: PMC3634089 DOI: 10.4196/kjpp.2013.17.2.127] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Revised: 02/25/2013] [Accepted: 03/05/2013] [Indexed: 12/29/2022]
Abstract
Ginsenosides, one of the active ingredients of Panax ginseng, show various pharmacological and physiological effects, and they are converted into compound K (CK) or protopanaxatriol (M4) by intestinal microorganisms. CK is a metabolite derived from protopanaxadiol (PD) ginsenosides, whereas M4 is a metabolite derived from protopanaxatriol (PT) ginsenosides. The γ-aminobutyric acid receptorC (GABAC) is primarily expressed in retinal bipolar cells and several regions of the brain. However, little is known of the effects of ginsenoside metabolites on GABAC receptor channel activity. In the present study, we examined the effects of CK and M4 on the activity of human recombinant GABAC receptor (ρ1) channels expressed in Xenopus oocytes by using a 2-electrode voltage clamp technique. In oocytes expressing GABAC receptor cRNA, we found that CK or M4 alone had no effect in oocytes. However, co-application of either CK or M4 with GABA inhibited the GABA-induced inward peak current (IGABA). Interestingly, pre-application of M4 inhibited IGABA more potently than CK in a dose-dependent and reversible manner. The half-inhibitory concentration (IC50) values of CK and M4 were 52.1±2.3 and 45.7±3.9 µM, respectively. Inhibition of IGABA by CK and M4 was voltage-independent and non-competitive. This study implies that ginsenoside metabolites may regulate GABAC receptor channel activity in the brain, including in the eyes.
Collapse
Affiliation(s)
- Byung-Hwan Lee
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
| | | | | | | | | | | | | | | |
Collapse
|
24
|
RETRACTED ARTICLE: Involvement of the GABA-Ergic System in Anxiolytic and Antidepressive Effects of the Scrophularia striata Extract in Rats. NEUROPHYSIOLOGY+ 2013. [DOI: 10.1007/s11062-013-9333-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
|
25
|
Huang SH, Lewis TM, Lummis SC, Thompson AJ, Chebib M, Johnston GA, Duke RK. Mixed antagonistic effects of the ginkgolides at recombinant human ρ1 GABAC receptors. Neuropharmacology 2012; 63:1127-39. [PMID: 22828636 PMCID: PMC3465557 DOI: 10.1016/j.neuropharm.2012.06.067] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2011] [Revised: 06/18/2012] [Accepted: 06/24/2012] [Indexed: 11/26/2022]
Abstract
The diterpene lactones of Ginkgo biloba, ginkgolides A, B and C are antagonists at a range of Cys-loop receptors. This study examined the effects of the ginkgolides at recombinant human ρ(1) GABA(C) receptors expressed in Xenopus oocytes using two-electrode voltage clamp. The ginkgolides were moderately potent antagonists with IC(50)s in the μM range. At 10 μM, 30 μM and 100 μM, the ginkgolides caused rightward shifts of GABA dose-response curves and reduced maximal GABA responses, characteristic of noncompetitive antagonists, while the potencies showed a clear dependence on GABA concentration, indicating apparent competitive antagonism. This suggests that the ginkgolides exert a mixed-type antagonism at the ρ(1) GABA(C) receptors. The ginkgolides did not exhibit any obvious use-dependent inhibition. Fitting of the data to a number of kinetic schemes suggests an allosteric inhibition as a possible mechanism of action of the ginkgolides which accounts for their inhibition of the responses without channel block or use-dependent inhibition. Kinetic modelling predicts that the ginkgolides exhibit saturation of antagonism at high concentrations of GABA, but this was only partially observed for ginkgolide B. It also suggests that there may be different binding sites in the closed and open states of the receptor, with a higher affinity for the receptor in the closed state.
Collapse
Affiliation(s)
- Shelley H. Huang
- Discipline of Pharmacology, School of Medical Sciences, Faculty of Medicine, University of Sydney, Australia
| | - Trevor M. Lewis
- School of Medical Sciences, University of New South Wales, Australia
| | - Sarah C.R. Lummis
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Andrew J. Thompson
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Mary Chebib
- Faculty of Pharmacy, University of Sydney, Australia
| | - Graham A.R. Johnston
- Discipline of Pharmacology, School of Medical Sciences, Faculty of Medicine, University of Sydney, Australia
| | - Rujee K. Duke
- Discipline of Pharmacology, School of Medical Sciences, Faculty of Medicine, University of Sydney, Australia
| |
Collapse
|
26
|
Hollands EC, Dale TJ, Baxter AW, Meadows HJ, Powell AJ, Clare JJ, Trezise DJ. Population Patch-Clamp Electrophysiology Analysis of Recombinant GABAA α1β3γ2 Channels Expressed in HEK-293 Cells. ACTA ACUST UNITED AC 2009; 14:769-80. [DOI: 10.1177/1087057109335675] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
γ-Amino butyric acid (GABA)—activated Cl— channels are critical mediators of inhibitory postsynaptic potentials in the CNS. To date, rational design efforts to identify potent and selective GABAA subtype ligands have been hampered by the absence of suitable high-throughput screening approaches. The authors describe 384-well population patch-clamp (PPC) planar array electrophysiology methods for the study of GABAA receptor pharmacology. In HEK293 cells stably expressing human α1β3γ2 GABAA channels, GABA evoked outward currents at 0 mV of 1.05 ± 0.08 nA, measured 8 s post GABA addition. The IGABA was linear and reversed close to the theoretical ECl (—56 mV). Concentration-response curve analysis yielded a mean pEC50 value of 5.4 and Hill slope of 1.5, and for a series of agonists, the rank order of potency was muscimol > GABA > isoguvacine. A range of known positive modulators, including diazepam and pentobarbital, produced concentration-dependent augmentation of the GABA EC 20 response (1 µM). The competitive antagonists bicuculline and gabazine produced concentration-dependent, parallel, rightward displacement of GABA curves with pA2 and slope values of 5.7 and 1.0 and 6.7 and 1.0, respectively. In contrast, picrotoxin (0.2-150 µM) depressed the maximal GABA response, implying a non-competitive antagonism. Overall, the pharmacology of human α1β3γ2 GABAA determined by PPC was highly similar to that obtained by conventional patch-clamp methods. In small-scale single-shot screens, Z′ values of >0.5 were obtained in agonist, modulator, and antagonist formats with hit rates of 0% to 3%. The authors conclude that despite the inability of the method to resolve the peak agonist responses, PPC can rapidly and usefully quantify pharmacology for the α1β3γ2 GABAA isoform. These data suggest that PPC may be a valuable approach for a focused set and secondary screening of GABAA receptors and other slow ligand-gated ion channels. ( Journal of Biomolecular Screening 2009:769-780)
Collapse
Affiliation(s)
- Emma C. Hollands
- Biochemical & Cellular Targets, Molecular Discovery Research, GlaxoSmithKline R&D, Harlow, Essex, United Kingdom
| | - Tim J. Dale
- Biochemical & Cellular Targets, Molecular Discovery Research, GlaxoSmithKline R&D, Harlow, Essex, United Kingdom
| | - Andrew W. Baxter
- Biochemical & Cellular Targets, Molecular Discovery Research, GlaxoSmithKline R&D, Harlow, Essex, United Kingdom
| | - Helen J. Meadows
- Biochemical & Cellular Targets, Molecular Discovery Research, GlaxoSmithKline R&D, Harlow, Essex, United Kingdom
| | - Andrew J. Powell
- Biochemical & Cellular Targets, Molecular Discovery Research, GlaxoSmithKline R&D, Harlow, Essex, United Kingdom
| | - Jeff J. Clare
- Biochemical & Cellular Targets, Molecular Discovery Research, GlaxoSmithKline R&D, Harlow, Essex, United Kingdom
| | - Derek J. Trezise
- Biochemical & Cellular Targets, Molecular Discovery Research, GlaxoSmithKline R&D, Harlow, Essex, United Kingdom,
| |
Collapse
|
27
|
Abdel-Halim H, Hanrahan JR, Hibbs DE, Johnston GAR, Chebib M. A molecular basis for agonist and antagonist actions at GABA(C) receptors. Chem Biol Drug Des 2008; 71:306-27. [PMID: 18312293 DOI: 10.1111/j.1747-0285.2008.00642.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We modelled the N-terminal ligand-binding domain of the rho1 GABA(C) receptor based on the Lymnaea stagnalis acetylcholine-binding protein (L-AChBP) crystal structure using comparative modelling and validated using flexible docking guided by known mutagenesis studies. A range of known rho1 GABA(C) receptor ligands comprising seven full agonists, 10 partial agonists, 43 antagonists and 12 inactive molecules were used to evaluate and validate the models. Of the 50 models identified, six models that allowed flexible ligand docking in accordance with the experimental data were selected and used to study detailed receptor-ligand interactions. The most refined model to accommodate all known active ligands featured a cavity comprising of a volume of 488 A(3). A detailed analysis of the interaction between the rho1 GABA(C) receptor model and the docked ligands revealed possible H-bonds and cation-pi interactions between the different ligands and binding site residues. Based on quantum mechanical/molecular mechanical (QM/MM) calculations, the model showed distinctive conformations of loop C that provided a molecular basis for agonist and antagonist actions. Agonists elicit loop C closure, while a more open loop C was observed upon antagonist binding. The model differentiates the role for key residues known to be involved in either binding and/or gating.
Collapse
Affiliation(s)
- Heba Abdel-Halim
- Faculty of Pharmacy, The University of Sydney, Sydney, NSW 2006, Australia
| | | | | | | | | |
Collapse
|
28
|
Carland JE, Johnston GAR, Chebib M. Relative impact of residues at the intracellular and extracellular ends of the human GABAC rho1 receptor M2 domain on picrotoxinin activity. Eur J Pharmacol 2008; 580:27-35. [PMID: 18031737 DOI: 10.1016/j.ejphar.2007.10.036] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2006] [Revised: 10/12/2007] [Accepted: 10/16/2007] [Indexed: 11/18/2022]
Abstract
The relative impact on picrotoxinin activity of residues at the intracellular (2' and 6' residues) and extracellular (15' and 17' residues) ends of the second transmembrane (M2) domain of the human gamma-aminobutyric acid-C (GABA(C)) rho1 receptor was investigated. A series of GABA(C) rho1 subunits were produced containing either single or multiple mutations at the positions of interest. Wild-type and mutant subunits (containing one or more of the following mutations: P2'S, T6'M, I15'N, G17'H) were expressed in Xenopus oocytes and characterized using agonists, partial agonists and antagonists. Changes in agonist activity were observed for mutant receptors. Most notably, mutation at the 2' position resulted in decreased agonist potency, while mutation at the 15' and 17' residues increased agonist potency. The affinity of the competitive antagonist (1,2,5,6-tetrahydropyridine-4-yl)methylphosphinic acid (TPMPA) was unchanged compared to wild-type at all mutant receptors. Of the four residues studied, mutation of residues at the 2' and 6' positions had the greatest impact on picrotoxinin activity. Inclusion of the P2'S mutation typically produced receptors with increased picrotoxinin potency, while the T6'M mutation reduced picrotoxinin potency. Picrotoxinin is a mixed antagonist at wild-type and all mutant receptors, with the exception of the double mutant rho1P2'S/T6'M receptors at which the non-competitive component was isolated. It is proposed that the contribution of M2 domain residues to picrotoxinin activity is potentially two-fold: (1) their role as a potential picrotoxinin binding site within the pore; and (2) they are critical for receptor activation properties of the receptor, thus may alter the allosteric mechanism of picrotoxinin.
Collapse
Affiliation(s)
- Jane E Carland
- Faculty of Pharmacy, A15, The University of Sydney, NSW 2006, Australia
| | | | | |
Collapse
|
29
|
Sun H, Cheng XP, You-Ye Z, Jiang P, Zhou JN. Quercetin subunit specifically reduces GlyR-mediated current in rat hippocampal neurons. Neuroscience 2007; 148:548-59. [PMID: 17664043 DOI: 10.1016/j.neuroscience.2007.06.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2007] [Revised: 06/04/2007] [Accepted: 06/08/2007] [Indexed: 10/23/2022]
Abstract
Quercetin is a substance of low molecular weight found in vascular plants with a wide range of biological activities including antioxidative and anti-inflammatory activities. In the present study, the effects of quercetin on native glycine receptors (GlyRs) in cultured rat hippocampal neurons were investigated using a whole-cell patch-clamp technique. Quercetin reversibly and concentration-dependently depressed glycine-induced current (I(Gly)), with an IC50 of 10.7+/-0.24 microM and a Hill coefficient of 1.08+/-0.12. Quercetin depressed maximum I(Gly) and significantly changed the EC50 for glycine and the Hill coefficient. Kinetic analysis indicated that quercetin accelerated the rates of desensitization. Interestingly, after the end of glycine with quercetin coapplication, a transient rebound occurred. The quercetin effects also displayed voltage-dependence, being greater at positive membrane potentials. These effects suggested that quercetin may act as an open channel blocker. Furthermore, in the sequential application protocol, quercetin inhibited the peak amplitude of I(Gly) to a macroscopic degree while slowing GlyR desensitization. These effects implied that quercetin has a depressant effect independent of GlyR channel's opening, which maybe caused by an allosteric mechanism. Strikingly, quercetin inhibited the amplitude of recombinant-induced current mediated by alpha2-, alpha2beta-, alpha3- and alpha3beta-GlyRs but had no effects on alpha1- and alpha1beta-GlyRs that were expressed in HEK293T cells. We also investigated the effects of quercetin on I(Gly) in spinal neurons during development in vitro. The extent of blockade by quercetin on I(Gly) was slighter in spinal neurons than in hippocampal neurons in a development-dependent manner. Taken together, our results suggest that quercetin has possible effects in information processing within a neuronal network by inhibition of I(Gly) and may be useful as a pharmacological probe for identifying the subunit types of GlyRs.
Collapse
Affiliation(s)
- Hao Sun
- Hefei National Laboratory for Physical Sciences at Microscale and Department of Neurobiology and Biophysics, School of Life Science, University of Science and Technology of China, Anhui, China
| | | | | | | | | |
Collapse
|
30
|
Li W, Jin X, Covey DF, Steinbach JH. Neuroactive steroids and human recombinant rho1 GABAC receptors. J Pharmacol Exp Ther 2007; 323:236-47. [PMID: 17636008 DOI: 10.1124/jpet.107.127365] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The gamma-aminobutyric acid type C (GABAC) receptor is structurally related to the GABAA receptors, yet quite distinct physiologically and pharmacologically. Neuroactive steroids are known to be potent and efficacious modulators of the GABAA receptor, but they are less well characterized in their actions on the GABAC receptor. We have examined the actions of neuroactive steroids and analogs on rho1 (GABAC) receptors expressed in Xenopus laevis oocytes, with two goals in mind. First, we tested a larger number of endogenous steroids, to determine whether particularly potent steroids could be found. Second, we examined the structure-activity relationship for steroid actions, and some mechanistic features, to determine the possible numbers of steroid binding sites and mechanisms of action. In total, 41 compounds were examined. Estradiols are inhibitors, essentially equipotent with picrotoxinin. No endogenous steroid tested was highly efficacious at potentiation. The results of the structure-activity studies and the effects of two mutations to the second transmembrane region of the rho1 GABAC receptor indicate that there are several mechanisms by which steroids can inhibit the receptor. Surprisingly, estradiol shares some features with picrotoxin. Inhibition by negatively charged compounds was not sensitive to membrane potential, and inhibition by all compounds tested was reduced at higher concentrations of GABA. The data indicate that the binding sites mediating potentiation and inhibition differ from each other and that there are several (three or more) mechanisms for producing inhibition.
Collapse
Affiliation(s)
- Wenjun Li
- Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO, USA
| | | | | | | |
Collapse
|
31
|
Baruchi I, Ben-Jacob E. Towards neuro-memory-chip: imprinting multiple memories in cultured neural networks. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 75:050901. [PMID: 17677014 DOI: 10.1103/physreve.75.050901] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2006] [Indexed: 05/16/2023]
Abstract
We show that using local chemical stimulations it is possible to imprint persisting (days) multiple memories (collective modes of neuron firing) in the activity of cultured neural networks. Microdroplets of inhibitory antagonist are injected at a location selected based on real-time analysis of the recorded activity. The neurons at the stimulated locations turn into a focus for initiating synchronized bursting events (the collective modes) each with its own specific spatiotemporal pattern of neuron firing.
Collapse
Affiliation(s)
- Itay Baruchi
- School of Physics and Astronomy, Raymond & Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University, Tel-Aviv, Israel
| | | |
Collapse
|
32
|
Akk G, Covey DF, Evers AS, Steinbach JH, Zorumski CF, Mennerick S. Mechanisms of neurosteroid interactions with GABA(A) receptors. Pharmacol Ther 2007; 116:35-57. [PMID: 17524487 PMCID: PMC2047817 DOI: 10.1016/j.pharmthera.2007.03.004] [Citation(s) in RCA: 120] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2007] [Accepted: 03/29/2007] [Indexed: 11/20/2022]
Abstract
Neuroactive steroids have some of their most potent actions by augmenting the function of GABA(A) receptors. Endogenous steroid actions on GABA(A) receptors may underlie important effects on mood and behavior. Exogenous neuroactive steroids have potential as anesthetics, anticonvulsants, and neuroprotectants. We have taken multiple approaches to understand more completely the interaction of neuroactive steroids with GABA(A) receptors. We have developed many novel steroid analogues in this effort. Recent work has resulted in synthesis of new enantiomer analogue pairs, novel ligands that probe various properties of the steroid pharmacophore, fluorescent neuroactive steroid analogues, and photoaffinity labels. Using these tools, combined with receptor binding and electrophysiological assays, we have begun to untangle the complexity of steroid actions at this important class of ligand-gated ion channel.
Collapse
Affiliation(s)
- Gustav Akk
- Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110
| | - Douglas F. Covey
- Department of Molecular Biology & Pharmacology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110
| | - Alex S. Evers
- Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110
- Department of Molecular Biology & Pharmacology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110
| | - Joe Henry Steinbach
- Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110
- Department of Anatomy & Neurobiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110
| | - Charles F. Zorumski
- Department of Anatomy & Neurobiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110
- Department of Psychiatry, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110
| | - Steven Mennerick
- Department of Anatomy & Neurobiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110
- Department of Psychiatry, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110
| |
Collapse
|
33
|
Sedelnikova A, Erkkila BE, Harris H, Zakharkin SO, Weiss DS. Stoichiometry of a pore mutation that abolishes picrotoxin-mediated antagonism of the GABAA receptor. J Physiol 2006; 577:569-77. [PMID: 16990398 PMCID: PMC1890441 DOI: 10.1113/jphysiol.2006.120287] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Picrotoxin, a potent antagonist of the inhibitory central nervous system GABAA and glycine receptors, is believed to interact with residues that line the central ion pore. These pore-lining residues are in the second transmembrane domain (TM2) of each of the five constituent subunits. One of these amino acids, a threonine at the 6' location, when mutated to phenylalanine, abolishes picrotoxin sensitivity. It has been suggested that this threonine, via hydrogen bonding, directly interacts with the picrotoxin molecule. We previously demonstrated that this mutation, in the alpha, beta or gamma subunit, can impart picrotoxin resistance to the GABA receptor. Since the functional pentameric GABA receptor contains two alpha subunits, two beta subunits and one gamma subunit, it is not clear how many alpha and beta subunits must carry this mutation to impart the resistant phenotype. In this study, by coexpression of mutant alpha or beta subunits with their wild-type counterparts in various defined ratios, we demonstrate that any single subunit carrying the 6' mutation imparts picrotoxin resistance. Implications of this finding in terms of the mechanism of antagonism are considered.
Collapse
Affiliation(s)
- Anna Sedelnikova
- Department of Physiology, UTHSCSA, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA
| | | | | | | | | |
Collapse
|
34
|
Chimenti F, Cottiglia F, Bonsignore L, Casu L, Casu M, Floris C, Secci D, Bolasco A, Chimenti P, Granese A, Befani O, Turini P, Alcaro S, Ortuso F, Trombetta G, Loizzo A, Guarino I. Quercetin as the active principle of Hypericum hircinum exerts a selective inhibitory activity against MAO-A: extraction, biological analysis, and computational study. JOURNAL OF NATURAL PRODUCTS 2006; 69:945-9. [PMID: 16792415 DOI: 10.1021/np060015w] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The methanol extract from Hypericum hircinum leaves exhibited in vitro inhibition of monoamine oxidases (MAO). Bioassay-guided fractionation led to the isolation of quercetin and five compounds identified for the first time from H. hircinum. Quercetin was the only compound with a selective inhibitory activity against MAO-A, with an IC50 value of 0.010 microM. To explain MAO selective inhibition at the molecular level, a computational study was carried out by conformational search and docking techniques using recently determined crystallographic models of both enzymatic isoforms. An in vivo study in mice was carried out using the forced swimming test in order to elucidate the behavioral effects of quercetin.
Collapse
Affiliation(s)
- Franco Chimenti
- Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive, Università degli Studi di Roma La Sapienza, P.le A. Moro 5, 00185 Rome, Italy
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
35
|
Li W, Covey DF, Alakoskela JM, Kinnunen PKJ, Steinbach JH. Enantiomers of neuroactive steroids support a specific interaction with the GABA-C receptor as the mechanism of steroid action. Mol Pharmacol 2006; 69:1779-82. [PMID: 16527905 DOI: 10.1124/mol.106.022863] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neuroactive steroids can either potentiate or inhibit a variety of membrane channels. Most studies have suggested that the effects are mediated by specific association of the steroid with the affected channel. However, a recent study of the rho1 (GABA-C) receptor (Mol Pharmacol 66:56-69, 2004) concluded that the actions were consistent with an action of the steroid in the lipid bilayer to alter the lateral pressure profile in the membrane. The enantiomers of an optically active compound are expected to have identical physical properties, including interactions with hydrophobic portions of the cell membrane. We have used two pairs of enantiomers (pregnanolone and ent-pregnanolone, allopregnanolone and ent-allopregnanolone) and show that the ability to potentiate (allopregnanolone) or inhibit (pregnanolone) the rho1 receptor is enantioselective. Therefore, these results strongly suggest that the actions of these neuroactive steroids are mediated by interactions with chiral regions of the target protein, rather than by a change in membrane properties (including lateral pressure).
Collapse
Affiliation(s)
- Wenjun Li
- Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | | | | | | | | |
Collapse
|
36
|
Goutman JD, Escobar AL, Calvo DJ. Analysis of macroscopic ionic currents mediated by GABArho1 receptors during lanthanide modulation predicts novel states controlling channel gating. Br J Pharmacol 2006; 146:1000-9. [PMID: 16231008 PMCID: PMC1751227 DOI: 10.1038/sj.bjp.0706411] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Lanthanide-induced modulation of GABA(C) receptors expressed in Xenopus oocytes was studied. We obtained two-electrode voltage-clamp recordings of ionic currents mediated by recombinant homomeric GABArho(1) receptors and performed numerical simulations of kinetic models of the macroscopic ionic currents.GABA-evoked chloride currents were potentiated by La(3+), Lu(3+) and Gd(3+) in the micromolar range. Lanthanide effects were rapid, reversible and voltage independent. The degree of potentiation was reduced by increasing GABA concentration.Lu(3+) also induced receptor desensitization and decreased the deactivation rate of GABArho(1) currents. In the presence of 300 microM Lu(3+), dose-response curves for GABA-evoked currents showed a significant enhancement of the maximum amplitude and an increase of the apparent affinity. The rate of onset of TPMPA and picrotoxin antagonism of GABArho(1) receptors was modulated by Lu(3+). These results suggest that the potentiation of the anionic current was the result of a direct lanthanide-receptor interaction at a site capable of allosterically modulating channel properties. Based on kinetic schemes, which included a second open state and a nonconducting desensitized state that closely reproduced the experimental results, two nonexclusive probable models of GABArho(1) channels gating are proposed.
Collapse
Affiliation(s)
- Juan D Goutman
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales (FCEyN), Universidad de Buenos Aires (UBA), Vuelta de Obligado 2490, CP 1428 Ciudad Autónoma de Buenos Aires, Argentina
| | - Ariel L Escobar
- Department of Physiology, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6551, U.S.A
| | - Daniel J Calvo
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales (FCEyN), Universidad de Buenos Aires (UBA), Vuelta de Obligado 2490, CP 1428 Ciudad Autónoma de Buenos Aires, Argentina
- Author for correspondence:
| |
Collapse
|
37
|
Huang SH, Duke RK, Chebib M, Sasaki K, Wada K, Johnston GAR. Mixed antagonistic effects of bilobalide at ρ1 GABAC receptor. Neuroscience 2006; 137:607-17. [PMID: 16300902 DOI: 10.1016/j.neuroscience.2005.08.071] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2005] [Revised: 08/16/2005] [Accepted: 08/26/2005] [Indexed: 11/28/2022]
Abstract
Bilobalide was found to be a moderately potent antagonist with a weak use-dependent effect at recombinant human rho(1) GABA(C) receptors expressed in Xenopus oocytes using two-electrode voltage clamp methodology. Antagonism of bilobalide at homomeric rho(1) GABA(C) receptors appeared to be mixed. At low concentration, bilobalide (3 microM) caused a parallel right shift and surmountable GABA maximal response of the GABA dose-response curve characteristic of a competitive antagonist. At high concentrations, bilobalide (10-100 microM) caused nonparallel right shifts and reduced maximal GABA responses of GABA dose-response curves characteristic of a noncompetitive antagonist. The potency of bilobalide appears to be dependent on the concentrations of GABA and was more potent at lower GABA concentrations. The mechanism of action of bilobalide at rho(1) GABA(C) receptors appears to be similar to that of the chloride channel blocker picrotoxinin.
Collapse
Affiliation(s)
- S H Huang
- Adrien Albert Laboratory of Medicinal Chemistry, Department of Pharmacology D06, Faculty of Medicine, The University of Sydney, NSW 2006, Australia
| | | | | | | | | | | |
Collapse
|
38
|
Alakuijala A, TalviOja K, Pasternack A, Pasternack M. Functional characterization of rat ρ2 subunits expressed in HEK 293 cells. Eur J Neurosci 2005; 21:692-700. [PMID: 15733087 DOI: 10.1111/j.1460-9568.2005.03880.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
GABA(C) receptors are thought to be homo- or heteropentamers composed of rho1, rho2 and rho3 subunits. Previous work on rat rho2 subunits expressed in Xenopus oocytes has suggested that they do not form functional homo-oligomeric GABA(C) receptors, but do combine with rho1 or rho3 subunits to form hetero-oligomers. These findings are difficult to interpret because both human and mouse rho2 subunits do form functional homo-oligomeric receptors. Also, many regions of the rat brain express solely rho2 subunit transcripts which, according to presently available evidence, would not result in expression of functional GABA(C) receptors. We show here that homomeric rat rho2 receptors can be expressed in HEK 293 cells. Homo-oligomeric rat rho2 receptors expressed in mammalian cells matured slowly and displayed small but detectable GABA-induced currents with slow kinetics. Rat rho2 receptors also had a decreased sensitivity to picrotoxin and a marked sensitivity to the GABA(C) receptor agonist cis-aminocrotonic acid. Our results demonstrate for the first time the expression of functional homomeric rat rho2 receptors, and suggest that rho(2) subunits may contribute to brain function, including in areas not expressing other rho subunits.
Collapse
Affiliation(s)
- Anniina Alakuijala
- Institute of Biotechnology, PO Box 56, FI-00014 University of Helsinki, Finland
| | | | | | | |
Collapse
|
39
|
Abstract
Picrotoxin is a plant alkaloid that is often used to block the activity of neuronal GABA and glycine receptors. However, the mechanism by which picrotoxin inhibits these receptors is still in debate. In this study, we investigated the picrotoxin inhibition on perch-rho subunits expressed heterologously in Xenopus laevis oocytes, and on native GABA(C) receptors of perch bipolar cells. Both competitive and noncompetitive mechanisms were observed for picrotoxin inhibition of the GABA(C) receptor. In oocytes expressing the rho1A subunit, terminating simultaneously the coapplication of GABA and picrotoxin induced a large rebound of membrane current. In addition, picrotoxin significantly accelerated the kinetics of GABA responses, particularly in the relaxation (offset) phase of GABA currents. Both current rebound and the large acceleration of GABA relaxation were unique to picrotoxin inhibition and were not observed with the competitive antagonist (1,2,5,6-tetrahydropyridin-4-yl)-methylphosphinic acid or the allosteric modulator zinc. The change in kinetics induced by picrotoxin was also observed on receptors formed by other GABA rho subunits, as well as on the GABA(C) receptors of retinal bipolar cells. Based on these observations, we proposed a model in which picrotoxin binds to the GABA(C) receptor in both channel open and closed states. Overall, this model provides a remarkably good approximation of the experimental findings we observed for picrotoxin inhibition of GABA(C) receptors. These results support an allosteric mechanism of picrotoxin inhibition of ligand-gated chloride channels.
Collapse
Affiliation(s)
- Haohua Qian
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, 1855 West Taylor St., Chicago, IL 60612, USA
| | | | | | | |
Collapse
|
40
|
Schmitt DE, Hill RH, Grillner S. The spinal GABAergic system is a strong modulator of burst frequency in the lamprey locomotor network. J Neurophysiol 2004; 92:2357-67. [PMID: 15190090 DOI: 10.1152/jn.00233.2004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The spinal network coordinating locomotion is comprised of a core of glutamate and glycine interneurons. This network is modulated by several transmitter systems including spinal GABA interneurons. The purpose of this study is to explore the contribution of GABAergic neurons to the regulation of locomotor burst frequency in the lamprey model. Using gabazine, a competitive GABAA antagonist more specific than bicuculline, the goal was to provide a detailed analysis of the influence of an endogenous activation of GABAA receptors on fictive locomotion, as well as their possible interaction with GABAB and involvement of GABAC receptors. During N-methyl-D-aspartate (NMDA)-induced fictive locomotion (ventral root recordings in the isolated spinal cord), gabazine (0.1-100 microM) significantly increased the burst rate up to twofold, without changes in regularity or "burst quality." Gabazine had a proportionately greater effect at higher initial burst rates. Picrotoxin (1-7.5 microM), a less selective GABAA antagonist, also produced a pronounced increase in frequency, but at higher concentrations, the rhythm deteriorated, likely due to the unspecific effects on glycine receptors. The selective GABAB antagonist CGP55845 also increased the frequency, and this effect was markedly enhanced when combined with the GABAA antagonist gabazine. The GABAC antagonist (1,2,5,6-tetrahydropyridine-4-yl)methylphosphinic acid (TPMPA) had no effect on locomotor bursting. Thus the spinal GABA system does play a prominent role in burst frequency regulation in that it reduces the burst frequency by < or =50%, presumably due to presynaptic and soma-dendritic effects documented previously. It is not required for burst generation, but acts as a powerful modulator.
Collapse
Affiliation(s)
- David E Schmitt
- Nobel Inst. for Neurophysiology, Dept. of Neuroscience, Karolinska Institutet, SE 17177 Stockholm, Sweden
| | | | | |
Collapse
|