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Neuropharmacology Jul 2018gamma-Aminobutyric acid (GABA)-mediated inhibitory neurotransmission and the gene products involved were discovered during the mid-twentieth century. Historically,... (Review)
Review
gamma-Aminobutyric acid (GABA)-mediated inhibitory neurotransmission and the gene products involved were discovered during the mid-twentieth century. Historically, myriad existing nervous system drugs act as positive and negative allosteric modulators of these proteins, making GABA a major component of modern neuropharmacology, and suggesting that many potential drugs will be found that share these targets. Although some of these drugs act on proteins involved in synthesis, degradation, and membrane transport of GABA, the GABA receptors Type A (GABAR) and Type B (GABAR) are the targets of the great majority of GABAergic drugs. This discovery is due in no small part to Professor Norman Bowery. Whereas the topic of GABAR is appropriately emphasized in this special issue, Norman Bowery also made many insights into GABAR pharmacology, the topic of this article. GABAR are members of the ligand-gated ion channel receptor superfamily, a chloride channel family of a dozen or more heteropentameric subtypes containing 19 possible different subunits. These subtypes show different brain regional and subcellular localization, age-dependent expression, and potential for plastic changes with experience including drug exposure. Not only are GABAR the targets of agonist depressants and antagonist convulsants, but most GABAR drugs act at other (allosteric) binding sites on the GABAR proteins. Some anxiolytic and sedative drugs, like benzodiazepine and related drugs, act on GABAR subtype-dependent extracellular domain sites. General anesthetics including alcohols and neurosteroids act at GABAR subunit-interface trans-membrane sites. Ethanol at high anesthetic doses acts on GABAR subtype-dependent trans-membrane domain sites. Ethanol at low intoxicating doses acts at GABAR subtype-dependent extracellular domain sites. Thus GABAR subtypes possess pharmacologically specific receptor binding sites for a large group of different chemical classes of clinically important neuropharmacological agents. This article is part of the "Special Issue Dedicated to Norman G. Bowery".
Topics: Allosteric Regulation; Animals; GABA-A Receptor Agonists; GABA-A Receptor Antagonists; Humans; Receptors, GABA-A
PubMed: 29407219
DOI: 10.1016/j.neuropharm.2018.01.036 -
Trends in Biochemical Sciences Jun 2021GABA receptors are pentameric ligand-gated ion channels that mediate most fast neuronal inhibition in the brain. In addition to their important physiological roles, they... (Review)
Review
GABA receptors are pentameric ligand-gated ion channels that mediate most fast neuronal inhibition in the brain. In addition to their important physiological roles, they are noteworthy in their rich pharmacology; prominent drugs used for anxiety, insomnia, and general anesthesia act through positive modulation of GABA receptors. Direct structural information for how these drugs work was absent until recently. Efforts in structural biology over the past few years have revealed how important drug classes and natural products interact with the GABA receptor, providing a foundation for studies in dynamics and structure-guided drug design. Here, we review recent developments in GABA receptor structural pharmacology, focusing on subunit assemblies of the receptor found at synapses.
Topics: Ligand-Gated Ion Channels; Receptors, GABA-A
PubMed: 33674151
DOI: 10.1016/j.tibs.2021.01.011 -
Nature Jul 2018Fast inhibitory neurotransmission in the brain is principally mediated by the neurotransmitter GABA (γ-aminobutyric acid) and its synaptic target, the type A GABA...
Fast inhibitory neurotransmission in the brain is principally mediated by the neurotransmitter GABA (γ-aminobutyric acid) and its synaptic target, the type A GABA receptor (GABA receptor). Dysfunction of this receptor results in neurological disorders and mental illnesses including epilepsy, anxiety and insomnia. The GABA receptor is also a prolific target for therapeutic, illicit and recreational drugs, including benzodiazepines, barbiturates, anaesthetics and ethanol. Here we present high-resolution cryo-electron microscopy structures of the human α1β2γ2 GABA receptor, the predominant isoform in the adult brain, in complex with GABA and the benzodiazepine site antagonist flumazenil, the first-line clinical treatment for benzodiazepine overdose. The receptor architecture reveals unique heteromeric interactions for this important class of inhibitory neurotransmitter receptor. This work provides a template for understanding receptor modulation by GABA and benzodiazepines, and will assist rational approaches to therapeutic targeting of this receptor for neurological disorders and mental illness.
Topics: Benzodiazepines; Bicuculline; Binding, Competitive; Brain Chemistry; Cell Membrane; Cryoelectron Microscopy; Flumazenil; GABA Modulators; Glycosylation; HEK293 Cells; Humans; Immunoglobulin Fab Fragments; Ligands; Models, Molecular; Receptors, GABA-A; gamma-Aminobutyric Acid
PubMed: 29950725
DOI: 10.1038/s41586-018-0255-3 -
Nature Jan 2019Type-A γ-aminobutyric (GABA) receptors are ligand-gated chloride channels with a very rich pharmacology. Some of their modulators, including benzodiazepines and general...
Type-A γ-aminobutyric (GABA) 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 GABA receptors remains largely unknown. Here we report several high-resolution cryo-electron microscopy structures in which the full-length human α1β3γ2L GABA 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 GABA 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 GABA receptor modulators.
Topics: Allosteric Regulation; Alprazolam; Benzodiazepines; Bicuculline; Binding, Competitive; Cryoelectron Microscopy; Diazepam; GABA Modulators; Humans; Ligands; Models, Molecular; Nanostructures; Picrotoxin; Receptors, GABA-A; Signal Transduction
PubMed: 30602790
DOI: 10.1038/s41586-018-0832-5 -
Nature Sep 2020Most general anaesthetics and classical benzodiazepine drugs act through positive modulation of γ-aminobutyric acid type A (GABA) receptors to dampen neuronal activity...
Most general anaesthetics and classical benzodiazepine drugs act through positive modulation of γ-aminobutyric acid type A (GABA) receptors to dampen neuronal activity in the brain. However, direct structural information on the mechanisms of general anaesthetics at their physiological receptor sites is lacking. Here we present cryo-electron microscopy structures of GABA receptors bound to intravenous anaesthetics, benzodiazepines and inhibitory modulators. These structures were solved in a lipidic environment and are complemented by electrophysiology and molecular dynamics simulations. Structures of GABA receptors in complex with the anaesthetics phenobarbital, etomidate and propofol reveal both distinct and common transmembrane binding sites, which are shared in part by the benzodiazepine drug diazepam. Structures in which GABA receptors are bound by benzodiazepine-site ligands identify an additional membrane binding site for diazepam and suggest an allosteric mechanism for anaesthetic reversal by flumazenil. This study provides a foundation for understanding how pharmacologically diverse and clinically essential drugs act through overlapping and distinct mechanisms to potentiate inhibitory signalling in the brain.
Topics: Allosteric Regulation; Anesthetics, General; Barbiturates; Benzodiazepines; Bicuculline; Binding Sites; Binding, Competitive; Cryoelectron Microscopy; Diazepam; Electrophysiology; Etomidate; Flumazenil; GABA-A Receptor Antagonists; Humans; Ligands; Models, Molecular; Molecular Conformation; Molecular Dynamics Simulation; Phenobarbital; Picrotoxin; Propofol; Receptors, GABA-A; gamma-Aminobutyric Acid
PubMed: 32879488
DOI: 10.1038/s41586-020-2654-5 -
The Journal of Experimental Medicine Dec 2022Lethal intestinal tissue toxicity is a common side effect and a dose-limiting factor in chemoradiotherapy. Chemoradiotherapy can trigger DNA damage and induce...
Lethal intestinal tissue toxicity is a common side effect and a dose-limiting factor in chemoradiotherapy. Chemoradiotherapy can trigger DNA damage and induce P53-dependent apoptosis in LGR5+ intestinal stem cells (ISCs). Gamma-aminobutyric acid (GABA) and its A receptors (GABAAR) are present in the gastrointestinal tract. However, the functioning of the GABAergic system in ISCs is poorly defined. We found that GABAAR α1 (GABRA1) levels increased in the murine intestine after chemoradiotherapy. GABRA1 depletion in LGR5+ ISCs protected the intestine from chemoradiotherapy-induced P53-dependent apoptosis and prolonged animal survival. The administration of bicuculline, a GABAAR antagonist, prevented chemoradiotherapy-induced ISC loss and intestinal damage without reducing the chemoradiosensitivity of tumors. Mechanistically, it was associated with the reduction of reactive oxygen species-induced DNA damage via the L-type voltage-dependent Ca2+ channels. Notably, flumazenil, a GABAAR antagonist approved by the U.S. Food and Drug Administration, rescued human colonic organoids from chemoradiotherapy-induced toxicity. Therefore, flumazenil may be a promising drug for reducing the gastrointestinal side effects of chemoradiotherapy.
Topics: Animals; Bicuculline; Calcium; Chemoradiotherapy; Flumazenil; Humans; Intestines; Mice; Reactive Oxygen Species; Receptors, GABA-A; Stem Cells; Tumor Suppressor Protein p53; United States; gamma-Aminobutyric Acid
PubMed: 36125780
DOI: 10.1084/jem.20220541 -
Molecular Neurobiology May 2022Perineuronal nets (PNNs) are specialised extracellular matrix structures which preferentially enwrap fast-spiking (FS) parvalbumin interneurons and have diverse roles in...
Perineuronal nets (PNNs) are specialised extracellular matrix structures which preferentially enwrap fast-spiking (FS) parvalbumin interneurons and have diverse roles in the cortex. PNN maturation coincides with closure of the critical period of cortical plasticity. We have previously demonstrated that BDNF accelerates interneuron development in a c-Jun-NH-terminal kinase (JNK)-dependent manner, which may involve upstream thousand-and-one amino acid kinase 2 (TAOK2). Chondroitinase-ABC (ChABC) enzymatic digestion of PNNs reportedly reactivates 'juvenile-like' plasticity in the adult CNS. However, the mechanisms involved are unclear. We show that ChABC produces an immature molecular phenotype in cultured cortical neurons, corresponding to the phenotype prior to critical period closure. ChABC produced different patterns of PNN-related, GABAergic and immediate early (IE) gene expression than well-characterised modulators of mature plasticity and network activity (GABA-R antagonist, bicuculline, and sodium-channel blocker, tetrodotoxin (TTX)). ChABC downregulated JNK activity, while this was upregulated by bicuculline. Bicuculline, but not ChABC, upregulated Bdnf expression and ERK activity. Furthermore, we found that BDNF upregulation of semaphorin-3A and IE genes was TAOK mediated. Our data suggest that ChABC heightens structural flexibility and network disinhibition, potentially contributing to 'juvenile-like' plasticity. The molecular phenotype appears to be distinct from heightened mature synaptic plasticity and could relate to JNK signalling. Finally, we highlight that BDNF regulation of plasticity and PNNs involves TAOK signalling.
Topics: Bicuculline; Brain-Derived Neurotrophic Factor; Extracellular Matrix; Interneurons; Neuronal Plasticity; Parvalbumins
PubMed: 35233718
DOI: 10.1007/s12035-022-02772-z -
IUPHAR/BPS Guide To Pharmacology CITE Sep 2021The GABA receptor is a ligand-gated ion channel of the Cys-loop family that includes the nicotinic acetylcholine, 5-HT and strychnine-sensitive glycine receptors. GABA...
The GABA receptor is a ligand-gated ion channel of the Cys-loop family that includes the nicotinic acetylcholine, 5-HT and strychnine-sensitive glycine receptors. GABA receptor-mediated inhibition within the CNS occurs by fast synaptic transmission, sustained tonic inhibition and temporally intermediate events that have been termed 'GABA, slow' [45]. GABA receptors exist as pentamers of 4TM subunits that form an intrinsic anion selective channel. Sequences of six α, three β, three γ, one δ, three ρ, one ε, one π and one θ GABA receptor subunits have been reported in mammals [278, 235, 236, 283]. The π-subunit is restricted to reproductive tissue. Alternatively spliced versions of many subunits exist (e.g. α4- and α6- (both not functional) α5-, β2-, β3- and γ2), along with RNA editing of the α3 subunit [71]. The three ρ-subunits, (ρ1-3) function as either homo- or hetero-oligomeric assemblies [359, 50]. Receptors formed from ρ-subunits, because of their distinctive pharmacology that includes insensitivity to bicuculline, benzodiazepines and barbiturates, have sometimes been termed GABA receptors [359], [16, 235, 236]. Many GABA receptor subtypes contain α-, β- and γ-subunits with the likely stoichiometry 2α.2β.1γ [168, 235]. It is thought that the majority of GABA receptors harbour a single type of α- and β - subunit variant. The α1β2γ2 hetero-oligomer constitutes the largest population of GABA receptors in the CNS, followed by the α2β3γ2 and α3β3γ2 isoforms. Receptors that incorporate the α4- α5-or α 6-subunit, or the β1-, γ1-, γ3-, δ-, ε- and θ-subunits, are less numerous, but they may nonetheless serve important functions. For example, extrasynaptically located receptors that contain α6- and δ-subunits in cerebellar granule cells, or an α4- and δ-subunit in dentate gyrus granule cells and thalamic neurones, mediate a tonic current that is important for neuronal excitability in response to ambient concentrations of GABA [209, 272, 83, 19, 288]. GABA binding occurs at the β+/α- subunit interface and the homologous γ+/α- subunits interface creates the benzodiazepine site. A second site for benzodiazepine binding has recently been postulated to occur at the α+/β- interface ([254]; reviewed by [282]). The particular α-and γ-subunit isoforms exhibit marked effects on recognition and/or efficacy at the benzodiazepine site. Thus, receptors incorporating either α4- or α6-subunits are not recognised by 'classical' benzodiazepines, such as flunitrazepam (but see [356]). The trafficking, cell surface expression, internalisation and function of GABA receptors and their subunits are discussed in detail in several recent reviews [52, 140, 188, 316] but one point worthy of note is that receptors incorporating the γ2 subunit (except when associated with α5) cluster at the postsynaptic membrane (but may distribute dynamically between synaptic and extrasynaptic locations), whereas as those incorporating the δ subunit appear to be exclusively extrasynaptic. [16, 235, 3, 2] class the GABA receptors according to their subunit structure, pharmacology and receptor function. Currently, eleven native GABA receptors are classed as conclusively identified (., α1β2γ2, α1βγ2, α3βγ2, α4βγ2, α4β2δ, α4β3δ, α5βγ2, α6βγ2, α6β2δ, α6β3δ and ρ) with further receptor isoforms occurring with high probability, or only tentatively [235, 236]. It is beyond the scope of this Guide to discuss the pharmacology of individual GABA receptor isoforms in detail; such information can be gleaned in the reviews [16, 95, 168, 173, 143, 278, 216, 235, 236] and [9, 10]. Agents that discriminate between α-subunit isoforms are noted in the table and additional agents that demonstrate selectivity between receptor isoforms, for example β-subunit selectivity, are indicated in the text below. The distinctive agonist and antagonist pharmacology of ρ receptors is summarised in the table and additional aspects are reviewed in [359, 50, 145, 223]. Several high-resolution cryo-electron microscopy structures have been described in which the full-length human α1β3γ2L GABA 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 [198].
PubMed: 35005623
DOI: 10.2218/gtopdb/F72/2021.3 -
Experimental Physiology Apr 2015What is the topic of this review? This review focuses on the role of gap junctions and interneurones in sympathetic control at the spinal cord level. What advances does... (Review)
Review
What is the topic of this review? This review focuses on the role of gap junctions and interneurones in sympathetic control at the spinal cord level. What advances does it highlight? The review considers the importance of these local spinal circuits in contributing to rhythmic autonomic activity and enabling appropriate responses to homeostatic perturbations. Sympathetic control of end organs relies on the activity of sympathetic preganglionic neurones (SPNs) within the spinal cord. These SPNs exhibit heterogeneity with respect to function, neurochemistry, location, descending inputs and patterns of activity. Part of this heterogeneity is bestowed by local spinal circuitry. Our understanding of the role of these local circuits, including the significance of connections between the SPNs themselves through specialized gap junctions, is patchy. This report focuses on interneurones and gap junctions within these circuits. Gap junctions play a role in sympathetic control; they are located on SPNs in the intermediolateral cell column. Mefloquine, a chemical that blocks these gap junctions, reduces local rhythmic activity in the spinal cord slice and disrupts autonomic control in the working heart-brainstem preparation. The role that these gap junctions may play in health and disease in adult animals remains to be elucidated fully. Presympathetic interneurones are located in laminae V, VII and X and the intermediolateral cell column; those in lamina X are GABAergic and directly inhibit SPNs. The GABAergic inputs onto SPNs exert their effects through activation of synaptic and extrasynaptic receptors, which stabilize the membrane at negative potentials. The GABAergic interneurones contribute to rhythmic patterns of activity that can be generated in the spinal cord, because bicuculline reduces network oscillatory activity. These studies indicate that local spinal cord circuitry is critical in enabling appropriate levels and patterning of activity in sympathetic outflow. We need to understand how these circuits may be harnessed in the situation of spinal cord injury.
Topics: Animals; Biological Clocks; Feedback, Physiological; Gap Junctions; Humans; Interneurons; Models, Neurological; Nerve Net; Spinal Cord; Sympathetic Nervous System
PubMed: 25655449
DOI: 10.1113/EP085031 -
Epilepsia Jul 2019Currently prescribed antiepileptic drugs (AEDs) are ineffective in treating approximately 30% of epilepsy patients. Sulfasalazine (SAS) is an US Food and Drug...
OBJECTIVE
Currently prescribed antiepileptic drugs (AEDs) are ineffective in treating approximately 30% of epilepsy patients. Sulfasalazine (SAS) is an US Food and Drug Administration (FDA)-approved drug for the treatment of Crohn disease that has been shown to inhibit the cystine/glutamate antiporter system xc- (SXC) and decrease tumor-associated seizures. This study evaluates the effect of SAS on distinct pharmacologically induced network excitability and determines whether it can further decrease hyperexcitability when administered with currently prescribed AEDs.
METHODS
Using in vitro cortical mouse brain slices, whole-cell patch-clamp recordings were made from layer 2/3 pyramidal neurons. Epileptiform activity was induced with bicuculline (bic), 4-aminopyridine (4-AP) and magnesium-free (Mg -free) solution to determine the effect of SAS on epileptiform events. In addition, voltage-sensitive dye (VSD) recordings were performed to characterize the effect of SAS on the spatiotemporal spread of hyperexcitable network activity and compared to currently prescribed AEDs.
RESULTS
SAS decreased evoked excitatory postsynaptic currents (eEPSCs) and increased the decay kinetics of evoked inhibitory postsynaptic currents (eIPSCs) in layer 2/3 pyramidal neurons. Although application of SAS to bic and Mg -free-induced epileptiform activity caused a decrease in the duration of epileptiform events, SAS completely blocked 4-AP-induced epileptiform events. In VSD recordings, SAS decreased VSD optical signals induced by 4-AP. Co-application of SAS with the AED topiramate (TPM) caused a significantly further decrease in the spatiotemporal spread of VSD optical signals.
SIGNIFICANCE
Taken together this study provides evidence that inhibition of SXC by SAS can decrease network hyperexcitability induced by three distinct pharmacologic agents in the superficial layers of the cortex. Furthermore, SAS provided additional suppression of 4-AP-induced network activity when administered with the currently prescribed AED TPM. These findings may serve as a foundation to assess the potential for SAS or other compounds that selectively target SXC as an adjuvant treatment for epilepsy.
Topics: Animals; Anticonvulsants; Brain; Disease Models, Animal; Epilepsy; Excitatory Postsynaptic Potentials; Mice; Mice, Inbred C57BL; Patch-Clamp Techniques; Sulfasalazine
PubMed: 31211419
DOI: 10.1111/epi.16073