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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.
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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.
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2
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Maleeva G, Wutz D, Rustler K, Nin-Hill A, Rovira C, Petukhova E, Bautista-Barrufet A, Gomila-Juaneda A, Scholze P, Peiretti F, Alfonso-Prieto M, König B, Gorostiza P, Bregestovski P. A photoswitchable GABA receptor channel blocker. Br J Pharmacol 2019; 176:2661-2677. [PMID: 30981211 PMCID: PMC6609548 DOI: 10.1111/bph.14689] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2018] [Revised: 03/03/2019] [Accepted: 04/03/2019] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND AND PURPOSE Anion-selective Cys-loop receptors (GABA and glycine receptors) provide the main inhibitory drive in the CNS. Both types of receptor operate via chloride-selective ion channels, though with different kinetics, pharmacological profiles, and localization. Disequilibrium in their function leads to a variety of disorders, which are often treated with allosteric modulators. The few available GABA and glycine receptor channel blockers effectively suppress inhibitory currents in neurons, but their systemic administration is highly toxic. With the aim of developing an efficient light-controllable modulator of GABA receptors, we constructed azobenzene-nitrazepam (Azo-NZ1), which is composed of a nitrazepam moiety merged to an azobenzene photoisomerizable group. EXPERIMENTAL APPROACH The experiments were carried out on cultured cells expressing Cys-loop receptors of known subunit composition and in brain slices using patch-clamp. Site-directed mutagenesis and molecular modelling approaches were applied to evaluate the mechanism of action of Azo-NZ1. KEY RESULTS At visible light, being in trans-configuration, Azo-NZ1 blocked heteromeric α1/β2/γ2 GABAA receptors, ρ2 GABAA (GABAC ), and α2 glycine receptors, whereas switching the compound into cis-state by UV illumination restored the activity. Azo-NZ1 successfully photomodulated GABAergic currents recorded from dentate gyrus neurons. We demonstrated that in trans-configuration, Azo-NZ1 blocks the Cl-selective ion pore of GABA receptors interacting mainly with the 2' level of the TM2 region. CONCLUSIONS AND IMPLICATIONS Azo-NZ1 is a soluble light-driven Cl-channel blocker, which allows photo-modulation of the activity induced by anion-selective Cys-loop receptors. Azo-NZ1 is able to control GABAergic postsynaptic currents and provides new opportunities to study inhibitory neurotransmission using patterned illumination.
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Affiliation(s)
- Galyna Maleeva
- INSERM, INS, Institut de Neurosciences des Systèmes, Aix-Marseille University, Marseille, France
| | - Daniel Wutz
- Institute of Organic Chemistry, University of Regensburg, Regensburg, Germany
| | - Karin Rustler
- Institute of Organic Chemistry, University of Regensburg, Regensburg, Germany
| | - Alba Nin-Hill
- Departament de Química Inorgànica i Orgànica (Secció de Química Orgànica) and Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, Barcelona, Spain
| | - Carme Rovira
- Departament de Química Inorgànica i Orgànica (Secció de Química Orgànica) and Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, Barcelona, Spain.,Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
| | - Elena Petukhova
- Department of Normal Physiology, Kazan State Medical University, Kazan, Russia
| | - Antoni Bautista-Barrufet
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Barcelona, Spain
| | - Alexandre Gomila-Juaneda
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Barcelona, Spain
| | - Petra Scholze
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Franck Peiretti
- INSERM 1263, INRA 1260, C2VN, Aix-Marseille Université, Marseille, France
| | - Mercedes Alfonso-Prieto
- Department of Computational Biomedicine, Institute for Advanced Simulations IAS-5 and Institute of Neuroscience and Medicine INM-9, Forschungszentrum Jülich GmbH, Jülich, Germany.,Cécile and Oskar Vogt Institute for Brain Research, Medical Faculty, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Burkhard König
- Institute of Organic Chemistry, University of Regensburg, Regensburg, Germany
| | - Pau Gorostiza
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Barcelona, Spain.,Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain.,Network Biomedical Research Center in Biomaterials, Bioengineering and Nanomedicine (CIBER-BBN), Spain
| | - Piotr Bregestovski
- INSERM, INS, Institut de Neurosciences des Systèmes, Aix-Marseille University, Marseille, France.,Department of Normal Physiology, Kazan State Medical University, Kazan, Russia.,Institute of Neurosciences, Kazan State Medical University, Kazan, Russia
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3
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Amakhin DV, Soboleva EB, Zaitsev AV. Cephalosporin antibiotics are weak blockers of GABAa receptor-mediated synaptic transmission in rat brain slices. Biochem Biophys Res Commun 2018; 499:868-874. [DOI: 10.1016/j.bbrc.2018.04.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2018] [Accepted: 04/02/2018] [Indexed: 10/17/2022]
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4
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Bink H, Sedigh-Sarvestani M, Fernandez-Lamo I, Kini L, Ung H, Kuzum D, Vitale F, Litt B, Contreras D. Spatiotemporal evolution of focal epileptiform activity from surface and laminar field recordings in cat neocortex. J Neurophysiol 2018; 119:2068-2081. [PMID: 29488838 DOI: 10.1152/jn.00764.2017] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
New devices that use targeted electrical stimulation to treat refractory localization-related epilepsy have shown great promise, although it is not well known which targets most effectively prevent the initiation and spread of seizures. To better understand how the brain transitions from healthy to seizing on a local scale, we induced focal epileptiform activity in the visual cortex of five anesthetized cats with local application of the GABAA blocker picrotoxin while simultaneously recording local field potentials on a high-resolution electrocorticography array and laminar depth probes. Epileptiform activity appeared in the form of isolated events, revealing a consistent temporal pattern of ictogenesis across animals with interictal events consistently preceding the appearance of seizures. Based on the number of spikes per event, there was a natural separation between seizures and shorter interictal events. Two distinct spatial regions were seen: an epileptic focus that grew in size as activity progressed, and an inhibitory surround that exhibited a distinct relationship with the focus both on the surface and in the depth of the cortex. Epileptiform activity in the cortical laminae was seen concomitant with activity on the surface. Focus spikes appeared earlier on electrodes deeper in the cortex, suggesting that deep cortical layers may be integral to recruiting healthy tissue into the epileptic network and could be a promising target for interventional devices. Our study may inform more effective therapies to prevent seizure generation and spread in localization-related epilepsies. NEW & NOTEWORTHY We induced local epileptiform activity and recorded continuous, high-resolution local field potentials from the surface and depth of the visual cortex in anesthetized cats. Our results reveal a consistent pattern of ictogenesis, characterize the spatial spread of the epileptic focus and its relationship with the inhibitory surround, and show that focus activity within events appears earliest in deeper cortical layers. These findings have potential implications for the monitoring and treatment of refractory epilepsy.
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Affiliation(s)
- Hank Bink
- Department of Bioengineering, University of Pennsylvania , Philadelphia, Pennsylvania.,Center for Neuroengineering and Therapeutics, University of Pennsylvania , Philadelphia, Pennsylvania
| | - Madineh Sedigh-Sarvestani
- Department of Neuroscience, Perelman School of Medicine, University of Pennsylvania , Philadelphia, Pennsylvania
| | - Ivan Fernandez-Lamo
- Department of Neuroscience, Perelman School of Medicine, University of Pennsylvania , Philadelphia, Pennsylvania
| | - Lohith Kini
- Department of Bioengineering, University of Pennsylvania , Philadelphia, Pennsylvania.,Center for Neuroengineering and Therapeutics, University of Pennsylvania , Philadelphia, Pennsylvania
| | - Hoameng Ung
- Department of Bioengineering, University of Pennsylvania , Philadelphia, Pennsylvania.,Center for Neuroengineering and Therapeutics, University of Pennsylvania , Philadelphia, Pennsylvania
| | - Duygu Kuzum
- Department of Electrical and Computer Engineering, University of California San Diego , La Jolla, California
| | - Flavia Vitale
- Center for Neuroengineering and Therapeutics, University of Pennsylvania , Philadelphia, Pennsylvania.,Department of Neurology, Hospital of the University of Pennsylvania , Philadelphia, Pennsylvania.,Department of Physical Medicine and Rehabilitation, Perelman School of Medicine, University of Pennsylvania , Philadelphia, Pennsylvania
| | - Brian Litt
- Department of Bioengineering, University of Pennsylvania , Philadelphia, Pennsylvania.,Center for Neuroengineering and Therapeutics, University of Pennsylvania , Philadelphia, Pennsylvania.,Department of Neurology, Hospital of the University of Pennsylvania , Philadelphia, Pennsylvania
| | - Diego Contreras
- Center for Neuroengineering and Therapeutics, University of Pennsylvania , Philadelphia, Pennsylvania.,Department of Neuroscience, Perelman School of Medicine, University of Pennsylvania , Philadelphia, Pennsylvania
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5
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Activation of GABA A receptors controls mesiotemporal lobe epilepsy despite changes in chloride transporters expression: In vivo and in silico approach. Exp Neurol 2016; 284:11-28. [DOI: 10.1016/j.expneurol.2016.07.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Revised: 07/12/2016] [Accepted: 07/16/2016] [Indexed: 12/16/2022]
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6
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Manayi A, Nabavi SM, Daglia M, Jafari S. Natural terpenoids as a promising source for modulation of GABAergic system and treatment of neurological diseases. Pharmacol Rep 2016; 68:671-9. [PMID: 27110875 DOI: 10.1016/j.pharep.2016.03.014] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2015] [Revised: 02/28/2016] [Accepted: 03/24/2016] [Indexed: 02/06/2023]
Abstract
γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter reducing neural excitability in the mammalian central nervous system (CNS) with three subclasses of receptors. Several conventional drugs and compounds modulate the GABAergic system, demonstrating different pharmacological effects. In this review, interactions of natural terpenoids with the GABAergic system are highlighted with relation to disorders like anxiety, insomnia, convulsion, pain, and cognitive deficits. Terpenoids with various structures affect the function of the GABAergic system via dissimilar mechanisms. Most of the discussed compounds interact with GABA receptors, but especially with the GABAA subtype. This may be due to the fact that researchers tend to assess the interaction of compounds using GABAA receptors. However, bilobalide, a sesquiterpene, showed anticonvulsant properties through the activation of glutamic acid decarboxylase (GAD) enzyme, which is a key enzyme in biosynthesis of GABA. Therefore, further studies evaluating and comparing terpenoids of different classes and their interaction with the GABA system, along with their pharmacokinetic properties, could be worthwhile in future studies.
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Affiliation(s)
- Azadeh Manayi
- Medicinal Plants Research Center, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran
| | - Seyed Mohammad Nabavi
- Applied Biotechnology Research Center, Baqiyatallah University of Medical Sciences, Tehran, Iran
| | - Maria Daglia
- Department of Drug Sciences, Medicinal Chemistry and Pharmaceutical Technology Section, University of Pavia, Pavia, Italy
| | - Samineh Jafari
- Department of Pharmacognosy, Faculty of Pharmacy, Zanjan University of Medical Sciences, Zanjan, Iran.
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7
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Sieghart W. Allosteric modulation of GABAA receptors via multiple drug-binding sites. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2014; 72:53-96. [PMID: 25600367 DOI: 10.1016/bs.apha.2014.10.002] [Citation(s) in RCA: 143] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
GABAA receptors are ligand-gated ion channels composed of five subunits that can be opened by GABA and be modulated by multiple pharmacologically and clinically important drugs. Over the time, hundreds of compounds from different structural classes have been demonstrated to modulate, directly activate, or inhibit GABAA receptors, and most of these compounds interact with more than one binding site at these receptors. Crystal structures of proteins and receptors homologous to GABAA receptors as well as homology modeling studies have provided insights into the possible location of ligand interaction sites. Some of these sites have been identified by mutagenesis, photolabeling, and docking studies. For most of these ligands, however, binding sites are not known. Due to the high flexibility of GABAA receptors and the existence of multiple drug-binding sites, the unequivocal identification of interaction sites for individual drugs is extremely difficult. The existence of multiple GABAA receptor subtypes with distinct subunit composition, the contribution of distinct subunit sequences to binding sites of different receptor subtypes, as well as the observation that even subunits not directly contributing to a binding site are able to influence affinity and efficacy of drugs, contribute to a unique pharmacology of each GABAA receptor subtype. Thus, each receptor subtype has to be investigated to identify a possible subtype selectivity of a compound. Although multiple binding sites make GABAA receptor pharmacology even more complicated, the exploitation of ligand interaction with novel-binding sites also offers additional possibilities for a subtype-selective modulation of GABAA receptors.
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Affiliation(s)
- Werner Sieghart
- Department of Molecular Neurosciences, Center for Brain Research, Medical University Vienna, Vienna, Austria.
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8
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Carta V, Pangerl M, Baur R, Puthenkalam R, Ernst M, Trauner D, Sigel E. A pentasymmetric open channel blocker for Cys-loop receptor channels. PLoS One 2014; 9:e106688. [PMID: 25184303 PMCID: PMC4153658 DOI: 10.1371/journal.pone.0106688] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Accepted: 07/31/2014] [Indexed: 11/30/2022] Open
Abstract
γ-Aminobutyric acid type A receptors (GABAA receptors) are chloride ion channels composed of five subunits, mediating fast synaptic and tonic inhibition in the mammalian brain. These receptors show near five-fold symmetry that is most pronounced in the second trans-membrane domain M2 lining the Cl- ion channel. To take advantage of this inherent symmetry, we screened a variety of aromatic anions with matched symmetry and found an inhibitor, pentacyanocyclopentdienyl anion (PCCP-) that exhibited all characteristics of an open channel blocker. Inhibition was strongly dependent on the membrane potential. Through mutagenesis and covalent modification, we identified the region α1V256-α1T261 in the rat recombinant GABAA receptor to be important for PCCP- action. Introduction of positive charges into M2 increased the affinity for PCCP- while PCCP- prevented the access of a positively charged molecule into M2. Interestingly, other anion selective cys-loop receptors were also inhibited by PCCP-, among them the Drosophila RDL GABAA receptor carrying an insecticide resistance mutation, suggesting that PCCP- could serve as an insecticide.
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Affiliation(s)
- Valentina Carta
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
| | - Michael Pangerl
- Department of Chemistry, Ludwig-Maximilians-Universität München and Center of Integrated Protein Science, Munich, Germany
| | - Roland Baur
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
| | - Roshan Puthenkalam
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Margot Ernst
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Dirk Trauner
- Department of Chemistry, Ludwig-Maximilians-Universität München and Center of Integrated Protein Science, Munich, Germany
| | - Erwin Sigel
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
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9
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Christensen RK, Petersen AV, Schmitt N, Perrier JF. Fast detection of extrasynaptic GABA with a whole-cell sniffer. Front Cell Neurosci 2014; 8:133. [PMID: 24860433 PMCID: PMC4030185 DOI: 10.3389/fncel.2014.00133] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Accepted: 04/28/2014] [Indexed: 11/16/2022] Open
Abstract
Gamma-amino-butyric acid (GABA) is the main inhibitory transmitter of the brain. It operates by binding to specific receptors located both inside and outside synapses. The extrasynaptic receptors are activated by spillover from GABAergic synapses and by ambient GABA in the extracellular space. Ambient GABA is essential for adjusting the excitability of neurons. However, due to the lack of suitable methods, little is known about its dynamics. Here we describe a new technique that allows detection of GABA transients and measurement of the steady state GABA concentration with high spatial and temporal resolution. We used a human embryonic kidney (HEK) cell line that stably expresses GABAA receptors composed of α1, β2, and γ2 subunits. We recorded from such a HEK cell with the whole-cell patch-clamp technique. The presence of GABA near the HEK cell generated a measurable electric current whose magnitude increased with concentration. A fraction of the current did not inactivate during prolonged exposition to GABA. This technique, which we refer to as a “sniffer” allows the measurement of ambient GABA concentration inside nervous tissue with a resolution of few tens of nanomolars. In addition, the sniffer detects variations in the extrasynaptic GABA concentration with millisecond time resolution. Pilot experiments demonstrate that the sniffer is able to report spillover of GABA induced by synaptic activation in real time. This is the first report on a GABA sensor that combines the ability to detect fast transients and to measure steady concentrations.
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Affiliation(s)
- Rasmus K Christensen
- Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen Copenhagen, Denmark
| | - Anders V Petersen
- Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen Copenhagen, Denmark
| | - Nicole Schmitt
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen Copenhagen, Denmark
| | - Jean-François Perrier
- Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen Copenhagen, Denmark
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10
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Stepanyuk AR, Borisyuk AL, Tsugorka TM, Belan PV. Different pools of postsynaptic GABAA receptors mediate inhibition evoked by low- and high-frequency presynaptic stimulation at hippocampal synapses. Synapse 2014; 68:344-54. [PMID: 24677449 DOI: 10.1002/syn.21742] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Revised: 03/16/2014] [Accepted: 03/21/2014] [Indexed: 11/12/2022]
Abstract
Patterns of short-term synaptic plasticity could considerably differ between synapses of the same axon. This may lead to separation of synaptic receptors transmitting either low- or high-frequency signals and, therefore, may have functional consequences for the information transfer in the brain. Here, we estimated a degree of such separation at hippocampal GABAergic synapses using a use-dependent GABAA receptor antagonist, picrotoxin, to selectively suppress a pool of GABAA receptors monosynaptically activated during the low-frequency stimulation. The relative changes in postsynaptic responses evoked by the high-frequency stimulation before and after such block were used to estimate the contribution of this GABAA receptor pool to synaptic transmission at high frequencies. Using this approach, we have shown that IPSCs evoked by low-frequency (0.2 Hz) stimulation and asynchronous currents evoked by high-frequency (20-40 Hz) stimulation are mediated by different pools of postsynaptic GABAA receptors. Thus, our findings suggest that inhibition produced by a single hippocampal interneuron may be selectively routed to different postsynaptic targets depending on the presynaptic discharge frequency.
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Affiliation(s)
- Andrey R Stepanyuk
- Department of General Physiology of the Nervous System, Bogomoletz Institute of Physiology, 4 Bogomoletz street, Kiev, 01024, Ukraine; State Key Laboratory of Molecular and Cellular Biology, Bogomoletz Institute of Physiology, 4 Bogomoletz street, Kiev, 01024, Ukraine
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11
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Bright DP, Smart TG. Methods for recording and measuring tonic GABAA receptor-mediated inhibition. Front Neural Circuits 2013; 7:193. [PMID: 24367296 PMCID: PMC3852068 DOI: 10.3389/fncir.2013.00193] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Accepted: 11/18/2013] [Indexed: 01/12/2023] Open
Abstract
Tonic inhibitory conductances mediated by GABAA receptors have now been identified and characterized in many different brain regions. Most experimental studies of tonic GABAergic inhibition have been carried out using acute brain slice preparations but tonic currents have been recorded under a variety of different conditions. This diversity of recording conditions is likely to impact upon many of the factors responsible for controlling tonic inhibition and can make comparison between different studies difficult. In this review, we will firstly consider how various experimental conditions, including age of animal, recording temperature and solution composition, are likely to influence tonic GABAA conductances. We will then consider some technical considerations related to how the tonic conductance is measured and subsequently analyzed, including how the use of current noise may provide a complementary and reliable method for quantifying changes in tonic current.
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Affiliation(s)
- Damian P Bright
- Department of Neuroscience, Physiology and Pharmacology, University College London London, UK
| | - Trevor G Smart
- Department of Neuroscience, Physiology and Pharmacology, University College London London, UK
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12
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Carpenter TS, Lau EY, Lightstone FC. Identification of a possible secondary picrotoxin-binding site on the GABA(A) receptor. Chem Res Toxicol 2013; 26:1444-54. [PMID: 24028067 DOI: 10.1021/tx400167b] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The type A GABA receptors (GABARs) are ligand-gated ion channels (LGICs) found in the brain and are the major inhibitory neurotransmitter receptors. Upon binding of an agonist, the GABAR opens and increases the intraneuronal concentration of chloride ions, thus hyperpolarizing the cell and inhibiting the transmission of the nerve action potential. GABARs also contain many other modulatory binding pockets that differ from the agonist-binding site. The composition of the GABAR subunits can alter the properties of these modulatory sites. Picrotoxin is a noncompetitive antagonist for LGICs, and by inhibiting GABAR, picrotoxin can cause overstimulation and induce convulsions. We use addition of picrotoxin to probe the characteristics and possible mechanism of an additional modulatory pocket located at the interface between the ligand-binding domain and the transmembrane domain of the GABAR. Picrotoxin is widely regarded as a pore-blocking agent that acts at the cytoplasmic end of the channel. However, there are also data to suggest that there may be an additional, secondary binding site for picrotoxin. Through homology modeling, molecular docking, and molecular dynamics simulations, we show that binding of picrotoxin to this interface pocket correlates with these data, and negative modulation occurs at the pocket via a kinking of the pore-lining helices into a more closed orientation.
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Affiliation(s)
- Timothy S Carpenter
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory , 7000 East Avenue, Livermore, California 94550, United States
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13
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Qin Z, Luo J, VandeVrede L, Tavassoli E, Fa' M, Teich AF, Arancio O, Thatcher GRJ. Design and synthesis of neuroprotective methylthiazoles and modification as NO-chimeras for neurodegenerative therapy. J Med Chem 2012; 55:6784-801. [PMID: 22779770 DOI: 10.1021/jm300353r] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Learning and memory deficits in Alzheimer's disease (AD) result from synaptic failure and neuronal loss, the latter caused in part by excitotoxicity and oxidative stress. A therapeutic approach is described that uses NO-chimeras directed at restoration of both synaptic function and neuroprotection. 4-Methylthiazole (MZ) derivatives were synthesized, based upon a lead neuroprotective pharmacophore acting in part by GABA(A) receptor potentiation. MZ derivatives were assayed for protection of primary neurons against oxygen-glucose deprivation and excitotoxicity. Selected neuroprotective derivatives were incorporated into NO-chimera prodrugs, coined nomethiazoles. To provide proof of concept for the nomethiazole drug class, selected examples were assayed for restoration of synaptic function in hippocampal slices from AD-transgenic mice, reversal of cognitive deficits, and brain bioavailability of the prodrug and its neuroprotective MZ metabolite. Taken together, the assay data suggest that these chimeric nomethiazoles may be of use in treatment of multiple components of neurodegenerative disorders, such as AD.
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Affiliation(s)
- Zhihui Qin
- Department of Medicinal Chemistry and Pharmacognosy, University of Illinois College of Pharmacy, University of Illinois at Chicago , 833 S. Wood Street, Chicago, Illinois 60612-7231, United States
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14
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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] [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 ρ1 GABAC receptors expressed in Xenopus oocytes using two-electrode voltage clamp. The ginkgolides were moderately potent antagonists with IC50s 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 ρ1 GABAC 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.
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Abstract
Ongoing interactions among cortical neurons often manifest as network-level synchrony. Understanding the spatiotemporal dynamics of such spontaneous synchrony is important because it may (1) influence network response to input, (2) shape activity-dependent microcircuit structure, and (3) reveal fundamental network properties, such as an imbalance of excitation (E) and inhibition (I). Here we delineate the spatiotemporal character of spontaneous synchrony in rat cortex slice cultures and a computational model over a range of different E-I conditions including disfacilitated (antagonized AMPA, NMDA receptors), unperturbed, and disinhibited (antagonized GABA(A) receptors). Local field potential was recorded with multielectrode arrays during spontaneous burst activity. Synchrony among neuronal groups was quantified based on phase-locking among recording sites. As network excitability was increased from low to high, we discovered three phenomena at an intermediate excitability level: (1) onset of synchrony, (2) maximized variability of synchrony, and (3) neuronal avalanches. Our computational model predicted that these three features occur when the network operates near a unique balanced E-I condition called "criticality." These results were invariant to changes in the measurement spatial extent, spatial resolution, and frequency bands. Our findings indicate that moderate average synchrony, which is required to avoid pathology, occurs over a limited range of E-I conditions and emerges together with maximally variable synchrony. If variable synchrony is detrimental to cortical function, this is a cost paid for moderate average synchrony. However, if variable synchrony is beneficial, then by operating near criticality the cortex may doubly benefit from moderate mean and maximized variability of synchrony.
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Stepanyuk AR, Borisyuk AL, Belan PV. Efficient maximum likelihood estimation of kinetic rate constants from macroscopic currents. PLoS One 2012; 6:e29731. [PMID: 22242142 PMCID: PMC3248447 DOI: 10.1371/journal.pone.0029731] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2011] [Accepted: 12/03/2011] [Indexed: 01/24/2023] Open
Abstract
A new method is described that accurately estimates kinetic constants, conductance and number of ion channels from macroscopic currents. The method uses both the time course and the strength of correlations between different time points of macroscopic currents and utilizes the property of semiseparability of covariance matrix for computationally efficient estimation of current likelihood and its gradient. The number of calculation steps scales linearly with the number of channel states as opposed to the cubic dependence in a previously described method. Together with the likelihood gradient evaluation, which is almost independent of the number of model parameters, the new approach allows evaluation of kinetic models with very complex topologies. We demonstrate applicability of the method to analysis of synaptic currents by estimating accurately rate constants of a 7-state model used to simulate GABAergic macroscopic currents.
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Affiliation(s)
- Andrey R. Stepanyuk
- Bogomoletz Institute of Physiology, Kiev, Ukraine
- State Key Laboratory of Molecular and Cellular Biology, Kiev, Ukraine
| | - Anya L. Borisyuk
- Bogomoletz Institute of Physiology, Kiev, Ukraine
- State Key Laboratory of Molecular and Cellular Biology, Kiev, Ukraine
| | - Pavel V. Belan
- Bogomoletz Institute of Physiology, Kiev, Ukraine
- State Key Laboratory of Molecular and Cellular Biology, Kiev, Ukraine
- * E-mail:
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17
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Cid M, Vilcaes A, Rupil L, Salvatierra N, Roth G. Participation of the GABAergic system on the glutamate release of frontal cortex synaptosomes from Wistar rats with experimental autoimmune encephalomyelitis. Neuroscience 2011; 189:337-44. [DOI: 10.1016/j.neuroscience.2011.05.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2010] [Revised: 05/05/2011] [Accepted: 05/05/2011] [Indexed: 11/16/2022]
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