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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 -
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 -
Reviews in the Neurosciences Aug 2020In this review, a series of experiments is presented, in which γ-amino butyric acid (GABA)ergic and glutamatergic effects on dopamine function in the rat nigrostriatal... (Review)
Review
In this review, a series of experiments is presented, in which γ-amino butyric acid (GABA)ergic and glutamatergic effects on dopamine function in the rat nigrostriatal and mesolimbic system was systematically assessed after pharmacological challenge with GABAA receptor (R) and and N-methyl d-aspartate (NMDA)R agonists and antagonists. In these studies, [123I]iodobenzamide binding to the D2/3R was mesured in nucleus accumbens (NAC), caudateputamen (CP), substantia nigra/ventral tegmental area (SN/VTA), frontal (FC), motor (MC) and parietal cortex (PC) as well as anterior (aHIPP) and posterior hippocampus (pHIPP) with small animal SPECT in baseline and after injection of either the GABAAR agonist muscimol (1 mg/kg), the GABAAR antagonist bicuculline (1 mg/kg), the NMDAR agonist d-cycloserine (20 mg/kg) or the NMDAR antagonist amantadine (40 mg/kg). Muscimol reduced D2/3R binding in NAC, CP, SN/VTA, THAL and pHIPP, while, after amantadine, decreases were confined to NAC, CP and THAL. In contrast, d-cycloserine elevated D2/3R binding in NAC, SN/VTA, THAL, frontal cortex, motor cortex, PC, aHIPP and pHIPP, while, after bicuculline, increases were confined to CP and THAL. Taken together, similar actions on regional dopamine levels were exterted by the GABAAR agonist and the NMDAR antagonist on the one side and by the GABAAR antagonist and the NMDAR agonist on the other, with agonistic action, however, affecting more brain regions. Thereby, network analysis suggests different roles of GABAARs and NMDARs in the mediation of nigrostriatal, nigrothalamocortical and mesolimbocortical dopamine function.
Topics: Animals; Bicuculline; Dopamine; Humans; Muscimol; Nucleus Accumbens; Rats; Receptors, GABA-A; Receptors, N-Methyl-D-Aspartate
PubMed: 32619197
DOI: 10.1515/revneuro-2019-0112 -
Neuron Nov 2023The neurotransmitter γ-aminobutyric acid (GABA) drives critical inhibitory processes in and beyond the nervous system, partly via ionotropic type-A receptors (GABARs)....
The neurotransmitter γ-aminobutyric acid (GABA) drives critical inhibitory processes in and beyond the nervous system, partly via ionotropic type-A receptors (GABARs). Pharmacological properties of ρ-type GABARs are particularly distinctive, yet the structural basis for their specialization remains unclear. Here, we present cryo-EM structures of a lipid-embedded human ρ1 GABAR, including a partial intracellular domain, under apo, inhibited, and desensitized conditions. An apparent resting state, determined first in the absence of modulators, was recapitulated with the specific inhibitor (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid and blocker picrotoxin and provided a rationale for bicuculline insensitivity. Comparative structures, mutant recordings, and molecular simulations with and without GABA further explained the sensitized but slower activation of ρ1 relative to canonical subtypes. Combining GABA with picrotoxin also captured an apparent uncoupled intermediate state. This work reveals structural mechanisms of gating and modulation with applications to ρ-specific pharmaceutical design and to our biophysical understanding of ligand-gated ion channels.
Topics: Humans; Receptors, GABA-A; Picrotoxin; Ligands; gamma-Aminobutyric Acid; Bicuculline; Binding Sites
PubMed: 37659407
DOI: 10.1016/j.neuron.2023.08.006 -
PloS One 2020Auditory steady-state responses (ASSRs) are states in which the electrical activity of the brain reacts steadily to repeated auditory stimuli. They are known to be...
Auditory steady-state responses (ASSRs) are states in which the electrical activity of the brain reacts steadily to repeated auditory stimuli. They are known to be useful for testing the functional integrity of neural circuits in the cortex, as well as for their capacity to generate synchronous activity in both human and animal models. Furthermore, abnormal gamma oscillations on ASSR are typically observed in patients with schizophrenia (SZ). Changes in neural synchrony may reflect aberrations in cortical gamma-aminobutyric acid (GABA) neurotransmission. However, GABA's impact and effects related to ASSR are still unclear. Here, we examined the effect of a GABAa receptor antagonist, (+)-bicuculline, on ASSR in free-moving rats. (+)-Bicuculline (1, 2 and 4 mg/kg, sc) markedly and dose-dependently reduced ASSR signals, consistent with current hypotheses. In particular, (+)-bicuculline significantly reduced event-related spectral perturbations (ERSPs) at 2 and 4 mg/kg between 10 and 30 minutes post-dose. Further, bicuculline (2 and 4 mg/kg) significantly and dose-dependently increased baseline gamma power. Furthermore, the occurrence of convulsions was consistent with the drug's pharmacokinetics. For example, high doses of (+)-bicuculline such as those greater than 880 ng/g in the brain induced convulsion. Additionally, time-dependent changes in ERSP with (+)-bicuculline were observed in accordance with drug concentration. This study partially unraveled the contribution of GABAa receptor signals to the generation of ASSR.
Topics: Animals; Auditory Cortex; Bicuculline; Convulsants; Evoked Potentials, Auditory; GABA-A Receptor Antagonists; Male; Rats; Rats, Sprague-Dawley; Receptors, GABA-A; Schizophrenia; Synaptic Transmission
PubMed: 32706815
DOI: 10.1371/journal.pone.0236363 -
International Journal of Molecular... Nov 2022Gamma-Aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the brain. It is produced by interneurons and recycled by astrocytes. In neurons, GABA...
Gamma-Aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the brain. It is produced by interneurons and recycled by astrocytes. In neurons, GABA activates the influx of Cl via the GABA receptor or efflux or K via the GABA receptor, inducing hyperpolarization and synaptic inhibition. In astrocytes, the activation of both GABA and GABA receptors induces an increase in intracellular Ca and the release of glutamate and ATP. Connexin 43 (Cx43) hemichannels are among the main Ca-dependent cellular mechanisms for the astroglial release of glutamate and ATP. However, no study has evaluated the effect of GABA on astroglial Cx43 hemichannel activity and Cx43 hemichannel-mediated gliotransmission. Here we assessed the effects of GABA on Cx43 hemichannel activity in DI NCT1 rat astrocytes and hippocampal brain slices. We found that GABA induces a Ca-dependent increase in Cx43 hemichannel activity in astrocytes mediated by the GABA receptor, as it was blunted by the GABA receptor antagonist bicuculline but unaffected by GABA receptor antagonist CGP55845. Moreover, GABA induced the Cx43 hemichannel-dependent release of glutamate and ATP, which was also prevented by bicuculline, but unaffected by CGP. Gliotransmission in response to GABA was also unaffected by pannexin 1 channel blockade. These results are discussed in terms of the possible role of astroglial Cx43 hemichannel-mediated glutamate and ATP release in regulating the excitatory/inhibitory balance in the brain and their possible contribution to psychiatric disorders.
Topics: Rats; Animals; Connexin 43; Astrocytes; Receptors, GABA-A; Bicuculline; Animals, Newborn; Cells, Cultured; Glutamic Acid; gamma-Aminobutyric Acid; Adenosine Triphosphate
PubMed: 36362410
DOI: 10.3390/ijms232113625 -
Neuroscience Research Nov 2022Altered inhibition/excitation (I/E) balance contributes to various brain disorders. Dysfunctional GABAergic interneurons enhance or reduce inhibition, resulting in I/E...
Altered inhibition/excitation (I/E) balance contributes to various brain disorders. Dysfunctional GABAergic interneurons enhance or reduce inhibition, resulting in I/E imbalances. Differences in short-term plasticity between excitation and inhibition cause frequency-dependence of the I/E ratio, which can be altered by GABAergic dysfunction. However, it is unknown whether I/E imbalances can be rescued pharmacologically using a single dose when the imbalance magnitude is frequency-dependent. Loss of PGC-1α (peroxisome proliferator activated receptor γ coactivator 1α) causes transcriptional dysregulation in hippocampal GABAergic interneurons. PGC-1α slices have enhanced baseline inhibition onto CA1 pyramidal cells, causing increased I/E ratio and impaired circuit function. High frequency stimulation reduces the I/E ratio and recovers circuit function in PGC-1α slices. Here we tested if using a low dose of bicuculline that can restore baseline I/E ratio can also rescue the frequency-dependent I/E imbalances in these mice. Remarkably, bicuculline did not reduce the I/E ratio below that of wild type during high frequency stimulation. Interestingly, bicuculline enhanced the paired-pulse ratio (PPR) of disynaptic inhibition without changing the monosynaptic inhibition PPR, suggesting that bicuculline modifies interneuron recruitment and not GABA release. Bicuculline improved CA1 output in PGC-1α slices, enhancing EPSP-spike coupling to wild type levels at high and low frequencies. Our results show that it is possible to rescue frequency-dependent I/E imbalances in an animal model of transcriptional dysregulation with a single treatment.
Topics: Animals; Bicuculline; Hippocampus; Interneurons; Mice; Mice, Knockout; PPAR gamma; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha
PubMed: 35842011
DOI: 10.1016/j.neures.2022.07.003 -
Acta Neurobiologiae Experimentalis 2022Studies have previously demonstrated a relationship between social status and anxiety disorders such as panic disorder. Repeated episodes of panic attacks do not occur...
Studies have previously demonstrated a relationship between social status and anxiety disorders such as panic disorder. Repeated episodes of panic attacks do not occur in combination with an actual fear stimulus or stressor. However, social ranking modulates the perception of the social signals of a threat or stressor. The hypothalamic nuclei are well‑known for their role in the elaboration of fear‑induced reactions. The dorsomedial hypothalamus (DMH) and the ventromedial hypothalamic (VMH) nuclei are hypothalamic subnuclei involved in the processing of threatening stimuli‑evoked aversive response and innate fear development. These structures are also located in the medial amygdala‑hypothalamus‑brainstem circuit that modulates innate fear‑induced defensive behaviors. This work aimed to investigate the relationship between social hierarchy and innate fear‑induced panic‑like responses in male rats. In our study, the dominance tube test was used to determine the social hierarchy. Then, DMH/VMH nuclei were unilaterally implanted with a guide cannula. After intra‑DMH/VMH injection of bicuculline (GABAA receptor antagonist), both innate fear induction and differences in dominant/subordinate rats were evaluated by the open field test. Intra‑DMH/VMH bicuculline increased the frequency of defensive immobility, forward escape movements, and crossing behaviors, as well as the duration of defensive immobility and forward escape movements in dominant rats. Subordinate rats showed a higher frequency of defensive attention, defensive immobility, and crossing than dominant rats. Additionally, dominant rats demonstrated a lower duration of defensive attention and defensive immobility than subordinate rats. Dominant rats seemed to adopt a form of innate‑fear characterized by increased proactivity with the environment. In contrast, subordinate rats exhibited a reactive form of innate‑fear characterized by passivity and freezing.
Topics: Animals; Male; Rats; Bicuculline; Fear; Hierarchy, Social; Rats, Wistar; Hypothalamus
PubMed: 35833813
DOI: 10.55782/ane-2022-012 -
The International Journal of... Feb 2022This study aimed to investigate the connection between the mutation of the transcription factor and impaired Ca-signaling, which reflects changes in neurotransmission...
OBJECTIVE
This study aimed to investigate the connection between the mutation of the transcription factor and impaired Ca-signaling, which reflects changes in neurotransmission in the cerebral cortex .
METHODS
We used mixed neuroglial cortical cell cultures derived from mutant mice. The cells were loaded with a fluorescent ratiometric calcium-sensitive probe Fura-2 AM and epileptiform activity was modeled by excluding magnesium ions from the external media or adding a GABA(A) receptor antagonist, bicuculline. Intracellular calcium dynamics were recorded using fluorescence microscopy. To identify the level of gene expression, the Real-Time PCR method was used.
RESULTS
It was found that cortical neurons isolated from homozygous () mice with the mutation demonstrate suppressed Ca signals in models of epileptiform activity . Wild-type cortical neurons are characterized by synchronous high-frequency and high-amplitude Ca oscillations occurring in all neurons of the network in response to Mg-free medium and bicuculline. But cortical neurons only single Ca pulses or attenuated Ca oscillations are recorded and only in single neurons, while most of the cell network does not respond to these stimuli. This signal deficiency of neurons correlates with a suppressed expression level of the genes encoding the subunits of NMDA, AMPA, and KA receptors; protein kinases PKA, JNK, CaMKII; and also the transcription factor Hif1α. These negative effects were partially abolished when neurons are grown in media with anti-inflammatory cytokine IL-10. IL-10 increases the expression of the above-mentioned genes but not to the level of expression in wild-type. At the same time, the amplitudes of Ca signals increase in response to the selective agonists of NMDA, AMPA and KA receptors, and the proportion of neurons responding with Ca oscillations to a Mg-free medium and bicuculline increases.
CONCLUSION
IL-10 restores neurotransmission in neuronal networks with the mutation by regulating the expression of genes encoding signaling proteins.
Topics: Animals; Bicuculline; Calcium; Cells, Cultured; Cerebral Cortex; Interleukin-10; Mice; N-Methylaspartate; Receptors, Glutamate; Transcription Factors; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid
PubMed: 32727246
DOI: 10.1080/00207454.2020.1803305 -
Neuropsychopharmacology : Official... Nov 2022Strategy switching is a form of cognitive flexibility that requires inhibiting a previously successful strategy and switching to a new strategy of a different...
Strategy switching is a form of cognitive flexibility that requires inhibiting a previously successful strategy and switching to a new strategy of a different categorical modality. It is dependent on dopamine (DA) receptor activation and release in ventral striatum and prefrontal cortex, two primary targets of ventral tegmental area (VTA) DA projections. Although the circuitry that underlies strategy switching early in learning has been studied, few studies have examined it after extended discrimination training. This may be important as DA activity and release patterns change across learning, with several studies demonstrating a critical role for substantia nigra pars compacta (SNc) DA activity and release once behaviors are well-learned. We have demonstrated that medial septum (MS) activation simultaneously increased VTA and decreased SNc DA population activity, as well as improved reversal learning via these actions on DA activity. We hypothesized that MS activation would improve strategy switching both early in learning and after extended training through its ability to increase VTA DA population activity and decrease SNc DA population activity, respectively. We chemogenetically activated the MS of male and female rats and measured their performance on an operant-based strategy switching task following 1, 10, or 15 days of discrimination training. Contrary to our hypothesis, MS activation did not affect strategy switching after 1 day of discrimination training. MS activation improved strategy switching after 10 days of training, but only in females. MS activation improved strategy switching in both sexes after 15 days of training. Infusion of bicuculline into the ventral subiculum (vSub) inhibited the MS-mediated decrease in SNc DA population activity and attenuated the improvement in strategy switching. Intra-vSub infusion of scopolamine inhibited the MS-mediated increase in VTA DA population activity but did not affect the improvement in strategy switching. Intra-vSub infusion of both bicuculline and scopolamine inhibited the MS-mediated effects on DA population activity in both the SNc and VTA and completely prevented the improvement in strategy switching. These data indicate that MS activation improves strategy switching once the original strategy has been sufficiently well-learned, and that this may occur via the MS's regulation of DA neuron responsivity.
Topics: Animals; Bicuculline; Dopamine; Dopaminergic Neurons; Female; Male; Rats; Scopolamine Derivatives; Substantia Nigra; Ventral Tegmental Area
PubMed: 35871093
DOI: 10.1038/s41386-022-01387-1