Effects of subunit types of the cloned GABAA receptor on the response to a neurosteroid

doi:10.1016/0922-4106(91)90149-C

European Journal of Pharmacology: Molecular Pharmacology

Volume 206, Issue 1, 25 January 1991, Pages 77-80

https://doi.org/10.1016/0922-4106(91)90149-C Get rights and content

Abstract

Combinations of cloned GABA_A receptor subtypes, having the subunit combinations α1 + ß1 or α1 + ß1 + γ2 (i = 1. 2. 3). were expressed in Xenopus oocytes. The endogenous steroid 3α-hydroxy-5α-pregnan-20-one potentiates GABA currents induced therein by GABA. This potentiation was greater in the α1 + ß and α3 + ß1 than in the α2 + ß1 combinations. The presence of thee γ2-subunit increased the steroid potency in α1 + ß1 and α2 + ß1, but the combination α3 + ß1 + γ2 became much less steroid-sensitive. It is concluded that the steroid modification of the GABA_A receptor is strongly influenced by the α- and the γ2-subunit types.

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Cited by (137)

GABAa receptor subunits expression in silver catfish (Rhamdia quelen) brain and its modulation by Nectandra grandiflora Nees essential oil and isolated compounds
2019, Behavioural Brain Research
Citation Excerpt :
The γ2 subunit is highly expressed throughout developing and adult brain and is a component of almost 60% of all GABAa receptors [64,65]. This subunit is linked to receptor traffic, postsynaptic clustering, synaptic maintenance, GABA conductance [66–68], and modulates the GABAa sensitivity to neurosteroids [69]. A decrease in the γ2 subunit expression is observed in some types of epilepsy [70–72] and GABAa/γ2 knockdown mice have increased anxiety-like behavior [73].
Studies using silver catfish (Rhamdia quelen) as experimental models are often applied to screen essential oils (EO) with GABAergic-mediated effects. However, the expression of GABAa receptors in the silver catfish brain remains unknown. Thus, we assessed whether silver catfish express GABAa receptor subunits associated with sedation/anesthetic process and/or neurological diseases. Additionally, we evaluated the brain expression of GABAa receptor subunits in fish sedated with Nectandra grandiflora EO and its isolated compounds, the fish anesthetic (+)-dehydrofukinone (DHF), and dehydrofukinone epoxide (DFX), eremophil-11-en-10-ol (ERM) and selin-11-en-4-α-ol (SEL), which have GABAa-mediated anxiolytic-like effects in mice. The expression of the subunits gabra1, gabra2, gabra3, gabrb1, gabrd and gabrg2 in the silver catfish brain were assessed after a 24h-sedation bath by real time PCR. Since qPCR data rarely describes mechanisms of action, which are usually found through interactions with receptors, we also performed an antagonist-driven experiment using flumazenil (FMZ). Real-time PCR detected the mRNA expression of all targeted genes in R. quelen brain. The expression of gabra1 was decreased in fish sedated with ERM; EO increased gabra2, gabra3, gabrb1 and gabrg2 expression; SEL increased gabrb1, gabrd and gabrg2 expression. EO and compounds DFX, SEL and ERM induced sustained sedation in fish and FMZ-bath prompted the recovery from ERM- and DFX-induced sedation. Our results suggest that the EO, SEL, ERM and DFX sedative effects involve interaction with the GABAergic system. Our findings support the use of the silver catfish as robust and reliable experimental model to evaluate the efficacy of drugs with putative GABAergic-mediated effects.
Overlapping, but not identical, discriminative stimulus effects of the neuroactive steroid pregnanolone and ethanol
2008, Pharmacology Biochemistry and Behavior
Many behavioral effects of neuroactive steroids are mediated by GABA_A receptors; however, other receptors might be involved. Ethanol has a complex mechanism of action, and many of the same receptors have been implicated in the effects of neuroactive steroids and ethanol. The goal of this study was to determine whether actions of neuroactive steroids and ethanol at multiple receptors result in similar discriminative stimulus effects. Rats discriminated 5.6 mg/kg of pregnanolone while responding under a fixed-ratio 20 schedule of food presentation. Pregnanolone, flunitrazepam and pentobarbital produced > 80% pregnanolone-lever responding. In contrast, neither morphine nor the negative GABA_A modulator β-CCE substituted for pregnanolone up to doses that markedly decreased response rates. Ethanol substituted only in some rats; in other rats, ethanol produced < 20% pregnanolone-lever responding up to rate-decreasing doses. Thus, substitution of positive GABA_A modulators, and not morphine or β-CCE, for pregnanolone in all rats suggests that positive modulation of GABA_A receptors is important in the discriminative stimulus effects of pregnanolone. Although pregnanolone might have actions at other receptors, in addition to actions at GABA_A receptors, substitution of ethanol for pregnanolone only in some rats suggests that the mechanisms of action of pregnanolone and ethanol overlap, but are not identical.
Hormonal, neural, and genomic mechanisms for female reproductive behaviors, motivation, and arousal
2006, Knobil and Neill's Physiology of Reproduction
Role of the α subunit in the modulation of GABA<inf>A</inf> receptors by anabolic androgenic steroids
2005, Neuropharmacology
Neural transmission mediated by circuits expressing α₂ subunit-containing γ-aminobutyric acid type A (GABA_A) receptors is critical for the expression of behaviors known to be altered by anabolic androgenic steroids (AAS). Here we show that micromolar concentrations of AAS, which reflect levels found in steroid abusers, induce positive modulation of currents from α₂β₃γ_2L recombinant receptors elicited by pulses of GABA that mimic synaptic conditions in a manner that is mechanistically distinct from modulation induced at α₁β₃γ_2L receptors. Specifically, at α₂-containing receptors, the AAS, 17α-methyltestosterone (17α-MeT) enhanced peak current, slowed deactivation, diminished desensitization, and promoted entry of receptors into more distal states along the activation pathway. Analysis of GABA_A receptor-mediated synaptic currents in primary cortical neurons followed by single cell real-time RT-PCR demonstrated that 17α-MeT enhancement of synaptic currents is proportional to the ratio of α₂ to α₁ subunit mRNA. Finally, we show that the modulation elicited by AAS is not comparable to that produced by micromolar concentrations of other positive allosteric modulators at α₂-containing receptors. In sum, these data indicate that AAS elicit effects on GABA_A receptor function that depend significantly on α subunit composition and that the mechanism of AAS modulation of GABA_A receptors is distinct from that of other positive allosteric modulators.
Interaction between allopregnanolone and pregnenolone sulfate in modulating GABA-mediated synaptic currents in neurons from the rat medial preoptic nucleus
2005, Brain Research
Citation Excerpt :
Thus, it clearly seems possible that PregS may play a physiological role by antagonizing the potentiation induced by AlloP on GABAA receptors. As previously reported, in the micromolar range, AlloP acts as an agonist at the GABAA receptor in the absence of GABA [13,40,49], suggesting at least two distinct binding sites for AlloP [40]. In contrast, PregS has, to our knowledge, not been reported to affect GABAA receptors in the absence of agonists.
The two neurosteroids 3α-hydroxy-5α-pregnane-20-one (allopregnanolone; AlloP) and pregnenolone sulfate (PregS) affect neuronal GABA_A receptors differently. While AlloP mainly potentiates the currents through GABA_A receptors, PregS reduces such currents. The present study aimed at clarifying the interaction of AlloP and PregS at GABA_A receptors in neurons from the medial preoptic nucleus of male rat. AlloP has previously been shown to dramatically prolong GABA-mediated spontaneous inhibitory postsynaptic currents (sIPSCs) in these neurons. Here, by recording sIPSCs under voltage-clamp conditions with the perforated-patch technique, it was shown that PregS by itself did not significantly affect the amplitude or time course of such currents. However, PregS, in a concentration-dependent manner, reduced the AlloP-evoked prolongation of sIPSC decay when the two neurosteroids were applied together. In contrast to sIPSC amplitude and time course, sIPSC frequency was significantly reduced by 10 μM PregS alone. Further, although 1.0 μM AlloP alone induced a clear increase in sIPSC frequency, the frequency was not significantly different from control when 1.0 μM AlloP was applied in combination with 10 μM PregS. In addition to the effects on sIPSC parameters, PregS reduced the baseline current evoked by 1.0 μM AlloP in the absence of GABA application or synaptic activity. PregS by itself did not significantly affect the baseline current. The main effects of AlloP and PregS on the sIPSC time course were mimicked by a simplified model with AlloP assumed to reduce the rate of GABA unbinding from the receptor and PregS assumed to increase the rate of desensitization.
Hormonal, Neural, and Genomic Mechanisms for Female Reproductive Behaviors, Motivation, and Arousal
2005, Knobil and Neill's Physiology of Reproduction

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Short communicationEffects of subunit types of the cloned GABAA receptor on the response to a neurosteroid

Abstract

Potentiation of γ-aminobutyric-acid-activated chloride conductance by a steroid anaesthetic in cultured rat spinal neurons

J. Physiol.

Steroid modulation of the GABA/benzodrazepine receptor-linked chloride ionophore

Mol. Neurobiol.

Neurosteroids Oligodendrocyte mitochondria convert cholesterol to pregner olone

Nature

Science

Short communication
Effects of subunit types of the cloned GABA_A receptor on the response to a neurosteroid