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Abstract
The inhibitory glycine receptor is a member of the Cys-loop superfamily of ligand-gated ion channels. It is the principal mediator of rapid synaptic inhibition in the spinal cord and brainstem and plays an important role in the modulation of higher brain functions including vision, hearing, and pain signaling. Glycine receptor function is controlled by only a few agonists, while the number of antagonists and positive or biphasic modulators is steadily increasing. These modulators are important for the study of receptor activation and regulation and have found clinical interest as potential analgesics and anticonvulsants. High-resolution structures of the receptor have become available recently, adding to our understanding of structure-function relationships and revealing agonistic, inhibitory, and modulatory sites on the receptor protein. This Review presents an overview of compounds that activate, inhibit, or modulate glycine receptor function in vitro and in vivo.
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Affiliation(s)
- Ulrike Breitinger
- Department of Biochemistry, German University in Cairo, New Cairo 11835, Egypt
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2
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Jones MJ, Dawson A, Hales TG, Hunter WN. A Structural Rationale for N-Methylbicuculline Acting as a Promiscuous Competitive Antagonist of Inhibitory Pentameric Ligand-Gated Ion Channels. Chembiochem 2020; 21:1526-1533. [PMID: 31859406 DOI: 10.1002/cbic.201900680] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2019] [Indexed: 11/07/2022]
Abstract
Bicuculline, a valued chemical tool in neurosciences research, is a competitive antagonist of specific GABAA receptors and affects other pentameric ligand-gated ion channels including the glycine, nicotinic acetylcholine and 5-hydroxytryptamine type 3 receptors. We used a fluorescence-quenching assay and isothermal titration calorimetry to record low-micromolar dissociation constants for N-methylbicuculline interacting with acetylcholine-binding protein and an engineered version called glycine-binding protein (GBP), which provides a surrogate for the heteromeric interface of the extracellular domain of the glycine receptor (GlyR). The 2.4 Å resolution crystal structure of the GBP:N-methylbicuculline complex, sequence and structural alignments reveal similarities and differences between GlyR and the GABAA receptor-bicuculline interactions. N-methylbicuculline displays a similar conformation in different structures, but adopts distinct orientations enforced by interactions and steric blocks with key residues and plasticity in the binding sites. These features explain the promiscuous activity of bicuculline against the principal inhibitory pentameric ligand-gated ion channels in the CNS.
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Affiliation(s)
- Mathew J Jones
- Division of Biological Chemistry and Drug Discovery School of Life Sciences, University of Dundee, Dow St, Dundee, DD1 5EH, UK
| | - Alice Dawson
- Division of Biological Chemistry and Drug Discovery School of Life Sciences, University of Dundee, Dow St, Dundee, DD1 5EH, UK
| | - Tim G Hales
- Division of Systems Medicine, School of Medicine, Ninewells Hospital, University of Dundee, Dundee, DD1 9SY, UK
| | - William N Hunter
- Division of Biological Chemistry and Drug Discovery School of Life Sciences, University of Dundee, Dow St, Dundee, DD1 5EH, UK
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3
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Exercise Plus Pharmacological Neuromodulation of Synaptic Inhibition Enhance Motor Function Recovery After Ischemic Stroke. Neuroscience 2020; 430:12-24. [PMID: 31982464 DOI: 10.1016/j.neuroscience.2020.01.012] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2019] [Revised: 01/07/2020] [Accepted: 01/08/2020] [Indexed: 11/23/2022]
Abstract
The objective of this study was to examine the interactive effects of exercise and low-level inhibition of GABAA receptors on the recovery of motor function and BDNF expression in the primary motor cortex (M1) of a stroke rat model. Male Sprague-Dawley rats were divided into five groups: sham (SHAM), control (CON), exercise (EX), bicuculline (BIC), and bicuculline plus exercise (BICEX) groups. All rats, except those in the SHAM group, underwent middle cerebral artery occlusion (MCAO) surgery to induce an ischemic stroke. GABAA receptor antagonist, bicuculline (0.25 mg/kg, i.p.), was administered to the BIC and BICEX groups. The EX and BICEX groups exercised on a treadmill (11 m/min for 30 min). Each intervention started 3 days after the MCAO surgery and was carried out every day for 2 weeks. Following the intervention, bilateral M1 BDNF mRNA and protein expression levels were assessed using qRT-PCR and ELISA. Marginal recovery was found in the EX and BIC groups, whereas motor function recovery was enhanced with exercise in the presence of BIC administration specifically in the BICEX group. Furthermore, BDNF protein level in the ipsilateral M1 was significantly higher in the BICEX group than in other groups. This study indicated that exercise combined with low-level inhibition of GABAA receptors after stroke could facilitate the recovery of motor function accompanied by BDNF upregulation in the ipsilateral M1. Therefore, this study provides a novel insight of pharmacological neuromodulation into stroke rehabilitation.
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Mazzone GL, Nistri A. Modulation of extrasynaptic GABAergic receptor activity influences glutamate release and neuronal survival following excitotoxic damage to mouse spinal cord neurons. Neurochem Int 2019; 128:175-185. [PMID: 31051211 DOI: 10.1016/j.neuint.2019.04.018] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Revised: 04/08/2019] [Accepted: 04/30/2019] [Indexed: 12/14/2022]
Abstract
Excitotoxic levels of released glutamate trigger a cascade of deleterious cellular events leading to delayed neuronal death. This phenomenon implies extensive dysregulation in the balance between network excitation and inhibition. Our hypothesis was that enhancing network inhibition should prevent excitotoxicity and provide neuroprotection. To test this notion, we used mouse organotypic spinal slice cultures and explored if excitotoxicity caused by the potent glutamate analogue kainate was blocked by pharmacological increase in GABAA receptor activity. To this end we monitored (with a biosensor) real-time glutamate release following 1 h kainate application and quantified neuronal survival 24 h later. Glutamate release evoked by kainate was strongly decreased by the allosteric GABAA modulator midazolam (10 nM) or the GABA agonist THIP (10 μM), leading to neuroprotection. On the contrary, much higher glutamate release was induced by the GABA antagonist bicuculline (20 μM) that inhibits synaptic and extrasynaptic GABAA receptors. Gabazine (20 μM), an antagonist of synaptic GABAA receptors, had no effect on glutamate release or neuroprotection. No effect was observed with the glycine antagonist strychnine or the glycine agonist L-alanine. These findings indicate that enhancement of GABA receptor activity was an effective tool to counteract excitotoxic death in spinal networks. In view of the potent activity by THIP, preferentially acting on extrasynaptic GABAA receptors, the present data imply a significant role for extrasynaptic GABAA receptors in sparing spinal cord neurons from injury.
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Affiliation(s)
- Graciela L Mazzone
- Instituto de Investigaciones en Medicina Traslacional (IIMT), CONICET-Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina.
| | - Andrea Nistri
- Neuroscience Dept., International School for Advanced Studies (SISSA), Trieste, Italy
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Zhang J, Chen X, Kårbø M, Zhao Y, An L, Wang R, Wang K, Huang Z. Anticonvulsant effect of dipropofol by enhancing native GABA currents in cortical neurons in mice. J Neurophysiol 2018; 120:1404-1414. [DOI: 10.1152/jn.00241.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Temporal lobe epilepsy (TLE), the most common pharmacoresistant focal epilepsy disorder, remains a major unmet medical need. Propofol is used as a short-acting medication for general anesthesia and refractory status epilepticus with issues of decreased consciousness and memory loss. Dipropofol, a derivative of propofol, has been reported to exert antioxidative and antibacterial activities. Here we report that dipropofol exerted anticonvulsant activity in a mouse model of kainic acid-induced seizures. Whole cell patch-clamp recordings of brain slices from the medial entorhinal cortex (mEC) revealed that dipropofol hyperpolarized the resting membrane potential and reduced the number of action potential firings, resulting in suppression of cortical neuronal excitability. Furthermore, dipropofol activated native tonic GABAA currents of mEC layer II stellate neurons in a dose-dependent manner with an EC50 value of 9.3 ± 1.6 μM (mean ± SE). Taken together, our findings show that dipropofol activated GABAA currents and exerted anticonvulsant activities in mice, thus possessing developmental potential for new anticonvulsant therapy. NEW & NOTEWORTHY The anticonvulsant effect of dipropofol was shown in a mouse model of kainic acid-induced seizures. Whole cell patch-clamp recordings of brain slices showed suppression of cortical neuronal excitability by dipropofol. Dipropofol activated the native tonic GABAA currents in a dose-dependent manner.
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Affiliation(s)
- Jingliang Zhang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking University Health Science Center, Beijing, China
| | - Xiaoling Chen
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking University Health Science Center, Beijing, China
| | - Matti Kårbø
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking University Health Science Center, Beijing, China
| | - Yi Zhao
- Tech-Development Department, Xi’an Libang Pharmaceutical Company, Xi’an, China
| | - Long An
- Tech-Development Department, Xi’an Libang Pharmaceutical Company, Xi’an, China
| | - Rutao Wang
- Tech-Development Department, Xi’an Libang Pharmaceutical Company, Xi’an, China
| | - KeWei Wang
- Department of Pharmacology, Qingdao University School of Pharmacy, Qingdao, China
| | - Zhuo Huang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking University Health Science Center, Beijing, China
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Albers HE, Walton JC, Gamble KL, McNeill JK, Hummer DL. The dynamics of GABA signaling: Revelations from the circadian pacemaker in the suprachiasmatic nucleus. Front Neuroendocrinol 2017; 44:35-82. [PMID: 27894927 PMCID: PMC5225159 DOI: 10.1016/j.yfrne.2016.11.003] [Citation(s) in RCA: 72] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2016] [Revised: 10/16/2016] [Accepted: 11/22/2016] [Indexed: 12/31/2022]
Abstract
Virtually every neuron within the suprachiasmatic nucleus (SCN) communicates via GABAergic signaling. The extracellular levels of GABA within the SCN are determined by a complex interaction of synthesis and transport, as well as synaptic and non-synaptic release. The response to GABA is mediated by GABAA receptors that respond to both phasic and tonic GABA release and that can produce excitatory as well as inhibitory cellular responses. GABA also influences circadian control through the exclusively inhibitory effects of GABAB receptors. Both GABA and neuropeptide signaling occur within the SCN, although the functional consequences of the interactions of these signals are not well understood. This review considers the role of GABA in the circadian pacemaker, in the mechanisms responsible for the generation of circadian rhythms, in the ability of non-photic stimuli to reset the phase of the pacemaker, and in the ability of the day-night cycle to entrain the pacemaker.
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Affiliation(s)
- H Elliott Albers
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Neuroscience Institute, Georgia State University, Atlanta, GA 30302, United States.
| | - James C Walton
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Neuroscience Institute, Georgia State University, Atlanta, GA 30302, United States
| | - Karen L Gamble
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35294, United States
| | - John K McNeill
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Neuroscience Institute, Georgia State University, Atlanta, GA 30302, United States
| | - Daniel L Hummer
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Department of Psychology, Morehouse College, Atlanta, GA 30314, United States
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Kuenzel K, Friedrich O, Gilbert DF. A Recombinant Human Pluripotent Stem Cell Line Stably Expressing Halide-Sensitive YFP-I152L for GABAAR and GlyR-Targeted High-Throughput Drug Screening and Toxicity Testing. Front Mol Neurosci 2016; 9:51. [PMID: 27445687 PMCID: PMC4923258 DOI: 10.3389/fnmol.2016.00051] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Accepted: 06/13/2016] [Indexed: 01/29/2023] Open
Abstract
GABAARs and GlyRs are considered attractive drug targets for therapeutic intervention and are also increasingly recognized in the context of in vitro neurotoxicity (NT) and developmental neurotoxicity (DNT) testing. However, systematic human-specific GABAAR and GlyR-targeted drug screening and toxicity testing is hampered due to lack of appropriate in vitro models that express native GABAARs and GlyRs. We have established a human pluripotent stem cell line (NT2) stably expressing YFP-I152L, a halide-sensitive variant of yellow fluorescent protein (YFP), allowing for fluorescence-based functional analysis of chloride channels. Upon stimulation with retinoic acid, NT2 cells undergo neuronal differentiation and allow pharmacological and toxicological evaluation of native GABAARs and GlyRs at different stages of brain maturation. We applied the cell line in concentration-response experiments with the neurotransmitters GABA and glycine as well as with the drugs strychnine, picrotoxin, fipronil, lindane, bicuculline, and zinc and demonstrate that the established in vitro model is applicable to GABAAR and GlyR-targeted pharmacological and toxicological profiling. We quantified the proportion of GABAAR and GlyR-sensitive cells, respectively, and identified percentages of approximately 20% each within the overall populations, rendering the cells a suitable model for systematic in vitro GABAAR and GlyR-targeted screening in the context of drug development and NT/DNT testing.
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Affiliation(s)
- Katharina Kuenzel
- Department of Chemical and Biological Engineering, Institute of Medical Biotechnology, Friedrich-Alexander-Universität Erlangen-NürnbergErlangen, Germany; Erlangen Graduate School in Advanced Optical Technologies, Friedrich-Alexander-Universität Erlangen-NürnbergErlangen, Germany
| | - Oliver Friedrich
- Department of Chemical and Biological Engineering, Institute of Medical Biotechnology, Friedrich-Alexander-Universität Erlangen-NürnbergErlangen, Germany; Erlangen Graduate School in Advanced Optical Technologies, Friedrich-Alexander-Universität Erlangen-NürnbergErlangen, Germany
| | - Daniel F Gilbert
- Department of Chemical and Biological Engineering, Institute of Medical Biotechnology, Friedrich-Alexander-Universität Erlangen-NürnbergErlangen, Germany; Erlangen Graduate School in Advanced Optical Technologies, Friedrich-Alexander-Universität Erlangen-NürnbergErlangen, Germany
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8
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Clarke RBC, Söderpalm B, Lotfi A, Ericson M, Adermark L. Involvement of Inhibitory Receptors in Modulating Dopamine Signaling and Synaptic Activity Following Acute Ethanol Exposure in Striatal Subregions. Alcohol Clin Exp Res 2015; 39:2364-74. [DOI: 10.1111/acer.12895] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2015] [Accepted: 09/01/2015] [Indexed: 12/15/2022]
Affiliation(s)
- Rhona B. C. Clarke
- Addiction Biology Unit; Institute of Neuroscience and Physiology; Department of Psychiatry and Neurochemistry; Sahlgrenska Academy; University of Gothenburg; Gothenburg Sweden
| | - Bo Söderpalm
- Addiction Biology Unit; Institute of Neuroscience and Physiology; Department of Psychiatry and Neurochemistry; Sahlgrenska Academy; University of Gothenburg; Gothenburg Sweden
- Beroendekliniken; Sahlgrenska University Hospital; Gothenburg Sweden
| | - Amir Lotfi
- Addiction Biology Unit; Institute of Neuroscience and Physiology; Department of Psychiatry and Neurochemistry; Sahlgrenska Academy; University of Gothenburg; Gothenburg Sweden
| | - Mia Ericson
- Addiction Biology Unit; Institute of Neuroscience and Physiology; Department of Psychiatry and Neurochemistry; Sahlgrenska Academy; University of Gothenburg; Gothenburg Sweden
| | - Louise Adermark
- Addiction Biology Unit; Institute of Neuroscience and Physiology; Department of Psychiatry and Neurochemistry; Sahlgrenska Academy; University of Gothenburg; Gothenburg Sweden
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9
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Juárez EH, Ochoa-Cortés F, Miranda-Morales M, Espinosa-Luna R, Montaño LM, Barajas-López C. Selectivity of antagonists for theCys-loop native receptors for ACh, 5-HT and GABA in guinea-pig myenteric neurons. ACTA ACUST UNITED AC 2013; 34:1-8. [DOI: 10.1111/aap.12016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Revised: 07/30/2013] [Accepted: 08/16/2013] [Indexed: 11/29/2022]
Affiliation(s)
- E. H. Juárez
- División de Biología Molecular; Instituto Potosino de Investigación Científica y Tecnológica; San Luis Potosí SLP México
| | - F. Ochoa-Cortés
- División de Biología Molecular; Instituto Potosino de Investigación Científica y Tecnológica; San Luis Potosí SLP México
| | - M. Miranda-Morales
- Departamento de Neurobiología Celular y Molecular; Instituto de Neurobiología; Universidad Nacional Autónoma de México; Campus Juriquilla Querétaro Querétaro México
| | - R. Espinosa-Luna
- División de Biología Molecular; Instituto Potosino de Investigación Científica y Tecnológica; San Luis Potosí SLP México
| | - L. M. Montaño
- Departamento de Farmacología; Facultad de Medicina; Universidad Nacional Autónoma de México; México DF México
| | - C. Barajas-López
- División de Biología Molecular; Instituto Potosino de Investigación Científica y Tecnológica; San Luis Potosí SLP México
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Li P, Slaughter M. Glycine receptor subunit composition alters the action of GABA antagonists. Vis Neurosci 2007; 24:513-21. [PMID: 17659095 DOI: 10.1017/s0952523807070368] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2007] [Accepted: 04/11/2007] [Indexed: 11/07/2022]
Abstract
GABA receptor antagonists produce an unexpectedly significant inhibition of native glycine receptors in retina and in alpha1 or alpha2 homomeric glycine receptors (GlyRs) expressed in HEK 293 cells. In this study we evaluate this phenomenon in heteromeric glycine receptors, formed by mixing alpha1, alpha2, and beta subunits. Picrotoxinin, picrotin, SR95531, and bicuculline are all more effective antagonists at GlyRs containing alpha2 subunits than alpha1 subunits. Inclusion of beta subunits reduces the inhibitory potency of picrotoxinin and picrotin but increases the potency of SR95531 and bicuculline. As a result of these two factors, bicuculline is particularly poor at discriminating GABA and glycine receptors. Picrotin, which has been reported to be inactive at GABA receptors, blocks glycine currents in retina and in HEK293 cells, suggesting its utility as a selective glycine antagonist. However, picrotin is a more potent inhibitor of GABA than glycine in retinal neurons. We also tested if GABA and glycine receptor subunits can combine to form functional receptors. If GABAAR gamma2S subunits are co-expressed with GlyR alpha subunits, the mixed receptor is glycine-sensitive and GABA-insensitive. But the mixed receptor exhibits a non-competitive picrotoxinin inhibition that is not observed in the homomeric GlyRs. This suggests that glycine and GABA subunits can co-assemble to form functional glycine receptors.
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Affiliation(s)
- Ping Li
- Department of Physiology and Biophysics, University at Buffalo, Buffalo, New York 14214, USA
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Miranda-Morales M, García-Hernández LM, Ochoa-Cortés F, Espinosa-Luna R, Naranjo-Rodríguez EB, Barajas-López C. Cross-talking between 5-HT3 and GABAA receptors in cultured myenteric neurons. Synapse 2007; 61:732-40. [PMID: 17568409 DOI: 10.1002/syn.20411] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
We recorded whole-cell ion currents induced by gamma-aminobutyric acid (I(GABA)) and serotonin (I(5-HT)) to investigate and characterize putative interactions between GABA(A) and 5-HT(3) receptors in myenteric neurons from the guinea pig small intestine. I(GABA) and I(5-HT) were inhibited by bicuculline and ondansetron, respectively. Currents induced by the simultaneous application of both, GABA and 5-HT (I(GABA+5-HT)) were significantly lower than the sum of I(GABA) and I(5-HT), indicating the existence of a current occlusion. Such an occlusion was observed when GABA(A) and 5-HT(3) receptors are virtually saturated. Kinetics, and pharmacological properties of I(GABA+5-HT) indicate that they are mediated by activation of both, GABA(A) and 5-HT(3) channels. GABA did not alter I(5-HT) in neurons without GABA(A) channels, in the presence of bicuculline (a GABA(A) receptor antagonist) or at the reversal potential for I(GABA). Similarly, 5-HT did not modify I(GABA) in neurons in which 5-HT(3) channels were absent, after inhibiting 5-HT(3) channels with ondansetron (a 5-HT(3) receptor antagonist) or at the reversal potential for I(5-HT). Current occlusion was observed as soon as GABA(A) and 5-HT(3) channels were being activated, in the absence of Ca(2+), at low temperature (11 degrees C), and after adding staurosporine (a protein kinase inhibitor) to the pipette solution. Our proposal is that GABA(A) and 5-HT(3) channels are organized in clusters and within these, both channels can cross-inhibit each other, likely by allosteric interactions between these proteins.
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Stehr CM, Linbo TL, Incardona JP, Scholz NL. The Developmental Neurotoxicity of Fipronil: Notochord Degeneration and Locomotor Defects in Zebrafish Embryos and Larvae. Toxicol Sci 2006; 92:270-8. [PMID: 16611622 DOI: 10.1093/toxsci/kfj185] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Fipronil is a phenylpyrazole insecticide designed to selectively inhibit insect gamma-aminobutyric acid (GABA) receptors. Although fipronil is often used in or near aquatic environments, few studies have assessed the effects of this neurotoxicant on aquatic vertebrates at sensitive life stages. We explored the toxicological effects of fipronil on embryos and larvae using the zebrafish (Danio rerio) experimental model system. Embryos exposed to fipronil at nominal concentrations at or above 0.7 microM (333 mug/l) displayed notochord degeneration, shortening along the rostral-caudal body axis, and ineffective tail flips and uncoordinated muscle contractions along the body axis in response to touch. This phenotype closely resembles zebrafish locomotor mutants of the accordion class and is consistent with loss of reciprocal inhibitory neurotransmission by glycinergic commissural interneurons in the spinal cord. Consistent with the hypothesis that notochord degeneration may be due to abnormal mechanical stress from muscle tetany, the expression patterns of gene and protein markers specific to notochord development were unaffected by fipronil. Moreover, the degenerative effects of fipronil (1.1 microM) were reversed by coexposure to the sodium channel blocker MS-222 (0.6mM). The notochord effects of fipronil were phenocopied by exposure to 70 microM strychnine, a glycinergic receptor antagonist. In contrast, exposure to gabazine, a potent vertebrate GABA(A) antagonist, resulted in a hyperactive touch response but did not cause notochord degeneration. Although specifically developed to target insect GABA receptors with low vertebrate toxicity, our results suggest that fipronil impairs the development of spinal locomotor pathways in fish by inhibiting a structurally related glycine receptor subtype. This represents an unanticipated and potentially novel mechanism for fipronil toxicity in vertebrates.
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Affiliation(s)
- Carla M Stehr
- Ecotoxicology and Environmental Fish Health Program, Northwest Fisheries Science Center, National Oceanic and Atmospheric Administration Fisheries, 2725 Montlake Boulevard East, Seattle, WA 98112, USA
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Dougherty KJ, Bannatyne BA, Jankowska E, Krutki P, Maxwell DJ. Membrane receptors involved in modulation of responses of spinal dorsal horn interneurons evoked by feline group II muscle afferents. J Neurosci 2005; 25:584-93. [PMID: 15659594 PMCID: PMC1890036 DOI: 10.1523/jneurosci.3797-04.2005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Modulatory actions of a metabotropic 5-HT1A&7 membrane receptor agonist and antagonist [(+/-)-8-hydroxy-2-(di-n-propylamino)-tetralin; N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane-carboxamide] and an ionotropic 5-HT3 membrane receptor agonist and antagonist [2-methyl-serotonin (2-Me 5-HT); N-(1-azabicyclo[2.2.2]oct-3-yl)-6-chloro-4-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-8-carboxamide hydrochloride] were investigated on dorsal horn interneurons mediating reflex actions of group II muscle afferents. All drugs were applied ionophoretically in deeply anesthetized cats. Effects of agonists were tested on extracellularly recorded responses of individual interneurons evoked by electrical stimulation of group II afferents in a muscle nerve. Effects of antagonists were tested against the depression of these responses after stimulation of raphe nuclei. The results show that both 5-HT1A&7 and 5-HT3 membrane receptors are involved in counteracting the activation of dorsal horn interneurons by group II afferents. Because only quantitative differences were found within the sample of the tested neurons, these results suggest that modulatory actions of 5-HT on excitatory and inhibitory interneurons might be similar. The relationship between 5-HT axons and axons immunoreactive for the 5-HT3A receptor subunit, which contact dorsal horn interneurons, was analyzed using immunofluorescence and confocal microscopy. Contacts from both types of axons were found on all interneurons, but their distribution and density varied, and there was no obvious relationship between them. In two of six interneurons, 5-HT3A-immunoreactive axons formed ring-like arrangements around the cell bodies. In previous studies, axons possessing 5-HT3 receptors were found to be excitatory, and as 2-Me 5-HT depressed transmission to dorsal horn interneurons, the results indicate that 5-HT operates at 5-HT3 receptors presynaptic to these neurons to depress excitatory transmission.
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MESH Headings
- 8-Hydroxy-2-(di-n-propylamino)tetralin/pharmacology
- Animals
- Bicuculline/pharmacology
- Bridged Bicyclo Compounds, Heterocyclic/pharmacology
- Cats
- Electric Stimulation
- Evoked Potentials/drug effects
- Evoked Potentials/physiology
- Immunohistochemistry
- Interneurons/drug effects
- Interneurons/physiology
- Iontophoresis
- Muscles/innervation
- Oxazines/pharmacology
- Piperazines/pharmacology
- Posterior Horn Cells/drug effects
- Posterior Horn Cells/physiology
- Pyridines/pharmacology
- Raphe Nuclei/physiology
- Receptor, Serotonin, 5-HT1A/drug effects
- Receptor, Serotonin, 5-HT1A/physiology
- Receptors, GABA-A/drug effects
- Receptors, GABA-A/physiology
- Receptors, Serotonin/drug effects
- Receptors, Serotonin/physiology
- Receptors, Serotonin, 5-HT3/drug effects
- Receptors, Serotonin, 5-HT3/physiology
- Serotonin/analogs & derivatives
- Serotonin/pharmacology
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Wang P, Slaughter MM. Effects of GABA receptor antagonists on retinal glycine receptors and on homomeric glycine receptor alpha subunits. J Neurophysiol 2005; 93:3120-6. [PMID: 15728760 DOI: 10.1152/jn.01228.2004] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Glycinergic and GABAergic inhibition are juxtaposed at one retinal synaptic layer yet likely perform different functions. These functions have usually been evaluated using receptor antagonists. In examining retinal glycine receptors, we were surprised to find that commonly used concentrations of GABA antagonists blocked significant fractions of the glycine current. In retinal amacrine and ganglion cells, the competitive GABAA receptor antagonists (bicuculline and SR95531) were also competitive GlyR antagonists. Picrotoxinin produced a noncompetitive inhibition of retinal GlyRs. [1,2,5,6-tetrahydropyridine-4-yl] methylphosphinic acid, the GABACR antagonist, did not inhibit glycine receptors. All three GABAA receptor antagonists were competitive inhibitors of homomeric alpha1 or alpha2 GlyRs expressed in human embryonic kidney cells (HEK293) cells. Interestingly, bicuculline was much more effective at alpha2 GlyRs and might be used to separate glycine receptor subtypes. Thus commonly used concentrations of GABA antagonists do not unambiguously differentiate GABA and glycine pathways. Picrotoxinin inhibition of GABAC receptors requires two amino acids in the second transmembrane region (TM2): 2' serine and 6' threonine. Although TM2 regions in GABA and glycine receptors are highly homologous, neither 2' serine nor 6' threonine is essential for picrotoxinin sensitivity in glycine receptors.
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Affiliation(s)
- Peiyuan Wang
- Dept. of Physiology and Biophysics, 124 Sherman Hall, Buffalo, NY 14214, USA
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Halliwell RF, Su J, Demuro A, Martinez-Torres A, Miledi R. Characterization of the interaction between a novel convulsant agent, norbiphen, and GABA(A) and other ligand-gated ion channels. Neuropharmacology 2002; 43:778-87. [PMID: 12367622 DOI: 10.1016/s0028-3908(02)00173-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
A hybrid molecule composed of the antimicrobial, norfloxacin, linked to the non-steroidal anti-inflammatory drug (NSAID), biphenylacetic acid, which we have termed norbiphen, is a lethal convulsant in vivo and an antagonist of rodent GABA(A) receptors in vitro. In the present study, the selectivity, molecular site(s) and mechanism of action of this novel convulsant were investigated using electrophysiological techniques. Sub-maximal GABA-evoked currents recorded from rodent hippocampal neurons were reversibly inhibited by norbiphen (1 microM) to 5+/-2% of control whereas glutamate, NMDA and glycine activated responses were little or unaffected. Sub-maximal GABA-evoked currents recorded from oocytes expressing recombinant human alpha1beta2gamma2s or alpha1beta2 GABA(A) receptors were also reversibly inhibited by norbiphen (1-1000 nM) with an IC(50) (+/-s.e.m.) of 5.7+/-1 and 8.8+/-1 nM, respectively. Similarly, GABA currents recorded from alpha1beta1gamma2s, alpha1beta1 and beta2gamma2s receptors were inhibited with IC(50)s of 16.1+/-1, 18.8+/-1 and 4.2+/-1 nM, respectively. In contrast, norbiphen (100 nM) had little or no effect at rho1 GABA(C) homomers. At alpha1beta2gamma2s receptors, norbiphen had no affect on the GABA reversal potential, and inhibition was not voltage-dependent, suggesting that this compound does not act at the ion channel. The GABA concentration response curve was shifted in a competitive-like fashion by norbiphen (10-300 nM) and a Schild analysis of these data yielded a slope of 0.94+/-0.1 and a pA(2) of 7.77. Our data reveal a novel, selective and highly potent antagonist of GABA(A) receptors. Norbiphen should be a valuable agent in future studies of this receptor complex.
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Affiliation(s)
- R F Halliwell
- School of Biological & Biomedical Sciences, University of Durham, UK.
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Davies DL, Machu TK, Guo Y, Alkana RL. Ethanol Sensitivity in ATP-Gated P2X Receptors Is Subunit Dependent. Alcohol Clin Exp Res 2002. [DOI: 10.1111/j.1530-0277.2002.tb02604.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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