GABAA Receptors as Broadcasters of Sexually Differentiating Signals in the Brain

Background Gamma-aminobutyric acid type A (GABAA) receptors, the major inhibitory receptors in the brain, are important targets of many drugs, including general anesthetics. These compounds exert multiple effects on GABAA receptors, including direct activation, prolongation of deactivation kinetics, and reduction of inhibitory postsynaptic current amplitudes. However, the degree to which these actions occur differs for different agents and synapses, possibly because of subunit-specific effects on postsynaptic receptors. In contrast to benzodiazepines and intravenous anesthetics, there is little information available about the subunit dependency of actions of volatile anesthetics. Therefore, the authors studied in detail the effects of isoflurane on recombinant GABAA receptors composed of several different subunit combinations. Methods Human embryonic kidney 293 cells were transiently transfected with rat complementary DNAs of alpha1beta2, alpha1beta2gamma2L, alpha1beta2gamma2S, alpha5beta3, or alpha5beta3gamma2S subunits. Using rapid application and whole cell patch clamp techniques, cells were exposed to 10- and 2,000-ms pulses of gamma-aminobutyric acid (1 mm) in the presence or absence of isoflurane (0.25, 0.5, 1.0 mm). Anesthetic effects on decay kinetics, peak amplitude, net charge transfer and rise time were measured. Statistical significance was assessed using the Student t test or one-way analysis of variance followed by the Tukey post hoc test. Results Under control conditions, incorporation of a gamma2 subunit conferred faster deactivation kinetics and reduced desensitization. Isoflurane slowed deactivation, enhanced desensitization, and reduced peak current amplitude in alphabeta receptors. Coexpression with a gamma2 subunit caused these effects of isoflurane to be substantially reduced or abolished. Although the two gamma2 splice variants imparted qualitatively similar macroscopic kinetic properties, there were significant quantitative differences between effects of isoflurane on deactivation and peak current amplitude in gamma2S- versus gamma2L-containing receptors. The net charge transfer resulting from brief pulses of gamma-aminobutyric acid was decreased by isoflurane in alphabeta but increased in alphabetagamma receptors. Conclusions The results indicate that subunit composition does substantially influence modulation of GABAA receptors by isoflurane. Specifically, the presence of a gamma2 subunit and the identity of its splice variant are important factors in determining physiologic and pharmacologic properties. These results may have functional implications in understanding how anesthetic effects on specific types of GABAA receptors in the brain contribute to changes in brain function and behavior.

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The desensitization pathway of GABAA receptors, one subunit at a time

10.1101/2020.05.18.101287 ◽

2020 ◽

Cited By ~ 1

Author(s):

Marc Gielen ◽

Nathalie Barilone ◽

Pierre-Jean Corringer

Keyword(s):

Gabaa Receptors ◽

Synergistic Effects ◽

Kinetic Modelling ◽

Concerted Mechanism ◽

Inhibitory Synaptic Transmission ◽

Asymmetric Pattern ◽

Gaba Binding ◽

Conformational Landscape ◽

Fast Activation ◽

The Brain

AbstractGABAA receptors mediate most inhibitory synaptic transmission in the brain of vertebrates. Following GABA binding and fast activation, these receptors undergo a slower desensitization, whose conformational pathway remains largely elusive. To explore the mechanism of desensitization, we used concatemeric α1β2γ2 GABAA receptors to selectively introduce gain-of-desensitization mutations one subunit at a time. A library of twenty-six mutant combinations was generated and their bi-exponential macroscopic desensitization rates measured. Introducing mutations at the different subunits shows a strongly asymmetric pattern with a key contribution of the γ2 subunit, and combining mutations results in marked synergistic effects indicating a non-concerted mechanism. Kinetic modelling indeed suggests a pathway where subunits move independently, the desensitization of two subunits being required to occlude the pore. Our work thus hints towards a very diverse and labile conformational landscape during desensitization, with potential implications in physiology and pharmacology.

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Contrasting strategies for anoxic brain survival--glycolysis up or down.

Journal of Experimental Biology ◽

10.1242/jeb.200.2.411 ◽

1997 ◽

Vol 200 (2) ◽

pp. 411-419 ◽

Cited By ~ 20

Author(s):

P L Lutz ◽

G E Nilsson

Keyword(s):

Electrical Activity ◽

Gabaa Receptors ◽

Glycolytic Enzymes ◽

Brain Blood Flow ◽

Gamma Aminobutyric Acid ◽

Channel Arrest ◽

Sensory Activities ◽

High Level ◽

And Control ◽

The Brain

Anoxia-tolerant turtles and carp (Carassius) exhibit contrasting strategies for anoxic brain survival. In the turtle brain, the energy consumption is deeply depressed to the extent of producing a comatose-like state. Brain metabolic depression is brought about by activating channel arrest to reduce ion flux and through the release of inhibitory gamma-aminobutyric acid (GABA) and the upregulation of GABAA receptors. Key glycolytic enzymes are down-regulated during prolonged anoxia. The result is a suppression of neurotransmission and a substantial depression in brain electrical activity. By contrast, Carassius remain active during anoxia, though at a reduced level. As in the turtle, there is an adenosine-mediated increase in brain blood flow but, in contrast to the turtle, this increase is sustained throughout the anoxic period. Key glycolytic enzymes are up-regulated and anaerobic glycolysis is enhanced. There is no evidence of channel arrest in Carassius brain. The probable result is that electrical activity in the brain is not suppressed but instead maintained at a level sufficient to regulate and control the locomotory and sensory activities of the anoxic carp. The key adaptations permitting the continued high level of glycolysis in Carassius are the production and excretion of ethanol as the glycolytic end-product, which avoids self-pollution by lactate produced during glycolysis that occurs in other vertebrates.

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The desensitization pathway of GABAA receptors, one subunit at a time

Nature Communications ◽

10.1038/s41467-020-19218-6 ◽

2020 ◽

Vol 11 (1) ◽

Cited By ~ 1

Author(s):

Marc Gielen ◽

Nathalie Barilone ◽

Pierre-Jean Corringer

Keyword(s):

Gabaa Receptors ◽

Synergistic Effects ◽

Kinetic Modelling ◽

Concerted Mechanism ◽

Inhibitory Synaptic Transmission ◽

Asymmetric Pattern ◽

Gaba Binding ◽

Conformational Landscape ◽

Fast Activation ◽

The Brain

Abstract GABAA receptors mediate most inhibitory synaptic transmission in the brain of vertebrates. Following GABA binding and fast activation, these receptors undergo a slower desensitization, the conformational pathway of which remains largely elusive. To explore the mechanism of desensitization, we used concatemeric α1β2γ2 GABAA receptors to selectively introduce gain-of-desensitization mutations one subunit at a time. A library of twenty-six mutant combinations was generated and their bi-exponential macroscopic desensitization rates measured. Introducing mutations at the different subunits shows a strongly asymmetric pattern with a key contribution of the γ2 subunit, and combining mutations results in marked synergistic effects indicating a non-concerted mechanism. Kinetic modelling indeed suggests a pathway where subunits move independently, the desensitization of two subunits being required to occlude the pore. Our work thus hints towards a very diverse and labile conformational landscape during desensitization, with potential implications in physiology and pharmacology.

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GABAA Receptor-Mediated Sleep-Promoting Effect of Saaz–Saphir Hops Mixture Containing Xanthohumol and Humulone

Molecules ◽

10.3390/molecules26237108 ◽

2021 ◽

Vol 26 (23) ◽

pp. 7108

Author(s):

Byungjick Min ◽

Yejin Ahn ◽

Hyeok-Jun Cho ◽

Woong-Kwon Kwak ◽

Hyung Joo Suh ◽

...

Keyword(s):

Gabaa Receptor ◽

Gabaa Receptors ◽

Sleep Disturbances ◽

Nrem Sleep ◽

Sleep Time ◽

Promoting Effect ◽

Amino Butyric Acid ◽

Gabaa Receptor Antagonist ◽

Gaba Content ◽

The Brain

Hops contain flavonoids that have sedative and sleep-promoting activities such as α-acid, β-acid, and xanthohumol. In this study, the sleep-enhancing activity of a Saaz–Saphir hops mixture was measured. In the caffeine-induced insomnia model, the administration of a Saaz–Saphir mixture increased the sleep time compared to Saaz or Saphir administration alone, which was attributed to the increase in NREM sleep time by the δ-wave increase. Oral administration of the Saaz–Saphir mixture for 3 weeks increased the γ-amino butyric acid (GABA) content in the brain and increased the expression of the GABAA receptor. As the GABA antagonists picrotoxin and bicuculline showed a decrease in sleep activity, it was confirmed that the GABAA receptor was involved in the Saaz–Saphir mixture activity. In addition, the GABAA receptor antagonist also reduced the sleep activity induced by xanthohumol and humulone contained in the Saaz–Saphir mixture. Therefore, xanthohumol and humulone contained in the Saaz–Saphir mixture showed sleep-promoting activity mediated by the GABAA receptors. The mixture of the Saaz and Saphir hop varieties may thus help mitigate sleep disturbances compared to other hop varieties.

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Co-localization of GABAA receptors and benzodiazepine receptors in the brain shown by monoclonal antibodies

Nature ◽

10.1038/314168a0 ◽

1985 ◽

Vol 314 (6007) ◽

pp. 168-171 ◽

Cited By ~ 258

Author(s):

P. Schoch ◽

J. G. Richards ◽

P. Häring ◽

B. Takacs ◽

C. Stähli ◽

...

Keyword(s):

Monoclonal Antibodies ◽

Gabaa Receptors ◽

Benzodiazepine Receptors ◽

The Brain

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Fos-like immunoreactivity in the brain associated with freezing or escape induced by inhibition of either glutamic acid decarboxylase or GABAA receptors in the dorsal periaqueductal gray

Brain Research ◽

10.1016/j.brainres.2005.05.068 ◽

2005 ◽

Vol 1051 (1-2) ◽

pp. 100-111 ◽

Cited By ~ 48

Author(s):

Karina Genaro Borelli ◽

Cristina Ferreira-Netto ◽

Norberto Cysne Coimbra ◽

Marcus Lira Brandão

Keyword(s):

Glutamic Acid ◽

Glutamic Acid Decarboxylase ◽

Gabaa Receptors ◽

Periaqueductal Gray ◽

Acid Decarboxylase ◽

Dorsal Periaqueductal Gray ◽

The Brain

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Subchronic Administration of Noopept and Semax Peptides Increases the Density of Cortical GABAA-Receptors in the Brain of BALB/c Mice

Neurochemical Journal ◽

10.1134/s1819712421030120 ◽

2021 ◽

Vol 15 (3) ◽

pp. 260-265

Author(s):

E. V. Vasil’eva ◽

A. A. Abdullina ◽

G. I. Kovalev

Keyword(s):

Gabaa Receptors ◽

The Brain

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Identification of Dihydromyricetin and Metabolites in Serum and Brain Associated with Acute Anti-Ethanol Intoxicating Effects in Mice

International Journal of Molecular Sciences ◽

10.3390/ijms22147460 ◽

2021 ◽

Vol 22 (14) ◽

pp. 7460

Author(s):

Eileen Carry ◽

Dushyant Kshatriya ◽

Joshua Silva ◽

Daryl L. Davies ◽

Bo Yuan ◽

...

Keyword(s):

Gabaa Receptors ◽

Xenopus Oocytes ◽

Total Serum ◽

Loss Of Righting Reflex ◽

Righting Reflex ◽

Rapid Clearance ◽

Poor Absorption ◽

Gabaergic Activity ◽

The Brain ◽

Putative Mechanism

Dihydromyricetin is a natural bioactive flavonoid with unique GABAA receptor activity with a putative mechanism of action to reduce the intoxication effects of ethanol. Although dihydromyricetin’s poor oral bioavailability limits clinical utility, the promise of this mechanism for the treatment of alcohol use disorder warrants further investigation into its specificity and druggable potential. These experiments investigated the bioavailability of dihydromyricetin in the brain and serum associated with acute anti-intoxicating effects in C57BL/6J mice. Dihydromyricetin (50 mg/kg IP) administered 0 or 15-min prior to ethanol (PO 5 g/kg) significantly reduced ethanol-induced loss of righting reflex. Total serum exposures (AUC0→24) of dihydromyricetin (PO 50 mg/kg) via oral (PO) administration were determined to be 2.5 µM × h (male) and 0.7 µM × h (female), while intraperitoneal (IP) administration led to 23.8-fold and 7.2- increases in AUC0→24 in male and female mice, respectively. Electrophysiology studies in α5β3γ2 GABAA receptors expressed in Xenopus oocytes suggest dihydromyricetin (10 µM) potentiates GABAergic activity (+43.2%), and the metabolite 4-O-methyl-dihydromyricetin (10 µM) negatively modulates GABAergic activity (−12.6%). Our results indicate that administration route and sex significantly impact DHM bioavailability in mice, which is limited by poor absorption and rapid clearance. This correlates with the observed short duration of DHM’s anti-intoxicating properties and highlights the need for further investigation into mechanism of DHM’s potential anti-intoxicating properties.

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