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Palagini L, Bianchini C. Pharmacotherapeutic management of insomnia and effects on sleep processes, neural plasticity, and brain systems modulating stress: A narrative review. Front Neurosci 2022; 16:893015. [PMID: 35968380 PMCID: PMC9374363 DOI: 10.3389/fnins.2022.893015] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Accepted: 07/12/2022] [Indexed: 11/13/2022] Open
Abstract
IntroductionInsomnia is a stress-related sleep disorder, may favor a state of allostatic overload impairing brain neuroplasticity, stress immune and endocrine pathways, and may contribute to mental and physical disorders. In this framework, assessing and targeting insomnia is of importance.AimSince maladaptive neuroplasticity and allostatic overload are hypothesized to be related to GABAergic alterations, compounds targeting GABA may play a key role. Accordingly, the aim of this review was to discuss the effect of GABAA receptor agonists, short-medium acting hypnotic benzodiazepines and the so called Z-drugs, at a molecular level.MethodLiterature searches were done according to PRISMA guidelines. Several combinations of terms were used such as “hypnotic benzodiazepines” or “brotizolam,” or “lormetazepam” or “temazepam” or “triazolam” or “zolpidem” or “zopiclone” or “zaleplon” or “eszopiclone” and “insomnia” and “effects on sleep” and “effect on brain plasticity” and “effect on stress system”. Given the complexity and heterogeneity of existing literature, we ended up with a narrative review.ResultsAmong short-medium acting compounds, triazolam has been the most studied and may regulate the stress system at central and peripheral levels. Among Z-drugs eszopiclone may regulate the stress system. Some compounds may produce more “physiological” sleep such as brotizolam, triazolam, and eszopiclone and probably may not impair sleep processes and related neural plasticity. In particular, triazolam, eszopiclone, and zaleplon studied in vivo in animal models did not alter neuroplasticity.ConclusionCurrent models of insomnia may lead us to revise the way in which we use hypnotic compounds in clinical practice. Specifically, compounds should target sleep processes, the stress system, and sustain neural plasticity. In this framework, among the short/medium acting hypnotic benzodiazepines, triazolam has been the most studied compound while among the Z-drugs eszopiclone has demonstrated interesting effects. Both offer potential new insight for treating insomnia.
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Affiliation(s)
- Laura Palagini
- Psychiatry Division, Department of Neuroscience and Rehabilitation, University of Ferrara, Ferrara, Italy
- Department of Clinical and Experimental Medicine, University of Pisa, Pisa, Italy
- *Correspondence: Laura Palagini,
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Doble A, Canton T, Malgouris C, Stutzmann JM, Piot O, Bardone MC, Pauchet C, Blanchard JC. The mechanism of action of zopiclone. Eur Psychiatry 2020; 10 Suppl 3:117s-28s. [DOI: 10.1016/0924-9338(96)80093-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
Abstract
SummaryThe mechanism of action of the cyclopyrrolone hypnotic drug zopiclone involves allosteric modulation of the GABAAreceptor. Zopiclone displaces the binding of [3H]-flunitrazepam with an affinity of 28 nM, and enhances the binding of the channel blocker [35S]-TBPS. The binding of zopiclone, unlike that of hypnotic benzodiazepines, is not facilitated by GABA. Zopiclone does not distinguish between GABAA receptors containing different α-subunits (BZ1and BZ2phenotype). Studies with protein-modifying agents (egdiethylpyrocarbonate) and photoaffinity labelling suggest that cyclopyrrolones bind to a domain on the GABAA receptor different from the benzodiazepine binding domain. The consequence of this interaction with the GABAAreceptor is to potentiate responses to GABA, as can be demonstrated by electrophysiological methods. Subchronic treatment of mice with high doses of zopiclone does not produce the changes in sensitivity of the GABAAreceptor that are observed with hypnotic benzodiazepines.
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Licata SC, Rowlett JK. Abuse and dependence liability of benzodiazepine-type drugs: GABA(A) receptor modulation and beyond. Pharmacol Biochem Behav 2008; 90:74-89. [PMID: 18295321 DOI: 10.1016/j.pbb.2008.01.001] [Citation(s) in RCA: 122] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/03/2007] [Revised: 12/14/2007] [Accepted: 01/02/2008] [Indexed: 01/12/2023]
Abstract
Over the past several decades, benzodiazepines and the newer non-benzodiazepines have become the anxiolytic/hypnotics of choice over the more readily abused barbiturates. While all drugs from this class act at the GABA(A) receptor, benzodiazepine-type drugs offer the clear advantage of being safer and better tolerated. However, there is still potential for these drugs to be abused, and significant evidence exists to suggest that this is a growing problem. This review examines the behavioral determinants of the abuse and dependence liability of benzodiazepine-type drugs. Moreover, the pharmacological and putative biochemical basis of the abuse-related behavior is discussed.
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Affiliation(s)
- Stephanie C Licata
- McLean Hospital/Harvard Medical School, Behavioral Psychopharmacology Research Laboratory, 115 Mill Street, Belmont, MA 02478, United States.
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Horiuchi M, Kimura M, Tokumura M, Hasebe N, Arai T, Abe K. Absence of convulsive liability of doripenem, a new carbapenem antibiotic, in comparison with beta-lactam antibiotics. Toxicology 2006; 222:114-24. [PMID: 16549226 DOI: 10.1016/j.tox.2006.02.004] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2005] [Revised: 01/30/2006] [Accepted: 02/05/2006] [Indexed: 11/28/2022]
Abstract
beta-Lactam antibiotics have been suggested to have some degree of convulsive activity and neurotoxicity in experimental animals as well as in clinical situations. We examined the convulsive activities of a new carbapenem antibiotic, (+)-(4R,5S,6S)-6-[(1R)-1-hydroxyethyl]-4-methyl-7-oxo-3-[[(3S,5S)-5-[(sulfamoylamino)methyl]-3-pyrrolidinyl]thio]-1-azabicyclo[3.2.0]hept-2-ene-2-carboxic acid monohydrate (doripenem) using several animals and compared them with beta-lactam antibiotics. In intravenous (IV) injection studies, imipenem/cilastatin, at 400/400mg/kg produced seizure discharges on electroencephalogram (EEG) accompanied with clonic convulsions in rats. Meropenem showed only wet dog shaking behavior at 200 and 400mg/kg. Doripenem caused no changes in the EEG and behavior in rats at 400mg/kg. Imipenem/cilastatin IV potentiated the pentylenetetrazol (PTZ)-induced convulsions in mice at 250/250 mg/kg, while meropenem, panipenem/betamipron, cefazolin or doripenem did not cause any marked effects at up to 500 mg/kg. In mouse intracerebroventricular (ICV) injection studies, imipenem, panipenem and cefazolin induced clonic convulsions in a dose-dependent manner in mice. Doripenem and meropenem did not induce convulsions at up to 100 microg/mouse. In dog ICV injection studies, imipenem produced generalized seizure discharge with clonic convulsions at 100 microg/dog. Meropenem also produced spikes or seizure discharges at 100, 300 and 1,000 microg/dog. However, doripenem had no effects on the EEG and behavior in dogs at any doses. In in vitro binding studies, imipenem, panipenem, cefazolin and meropenem inhibited [(3)H]muscimol binding to the GABA(A) receptor in mouse brain homogenates while doripenem did not cause any inhibition at up to 10mM. In addition, doripenem had no influence on the anti-convulsant actions of valproic acid in the PTZ- or bicuculine-induced convulsive model. These results clearly indicate that doripenem has no convulsive activity, suggesting that its neurotoxicity may be negligible in clinical use.
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Affiliation(s)
- Masahito Horiuchi
- Department of Drug Safety Evaluation, Developmental Research Laboratories, Shionogi & Co., Ltd., 3-1-1 Futaba-cho, Toyonaka, Osaka 561-0825, Japan
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Abstract
Insomnia, an inability to initiate or maintain sleep, affects approximately one-third of the American population. Conventional benzodiazepines, such as triazolam and midazolam, were the treatment of choice for short-term insomnia for many years but are associated with adverse effects such as rebound insomnia, withdrawal and dependency. The newer hypnosedatives include zolpidem, zaleplon and zopiclone. These agents may be preferred over conventional benzodiazepines to treat short-term insomnia because they may be less likely to cause significant rebound insomnia or tolerance and are as efficacious as the conventional benzodiazepines. This review aims to summarise the published clinical drug interaction studies involving zolpidem, zaleplon and zopiclone. The pharmacokinetic and pharmacodynamic interactions that may be clinically important are highlighted. Clinical trials have studied potential interactions of zaleplon, zolpidem and zopiclone with the following types of drugs: cytochrome P450 (CYP) inducers (rifampicin), CYP inhibitors (azoles, ritonavir and erythromycin), histamine H(2) receptor antagonists (cimetidine and ranitidine), antidepressants, antipsychotics, antagonists of benzodiazepines and drugs causing sedation. Rifampicin significantly induced the metabolism of the newer hypnosedatives and decreased their sedative effects, indicating that a dose increase of these agents may be necessary when they are administered with rifampicin. Ketoconazole, erythromycin and cimetidine inhibited the metabolism of the newer hypnosedatives and enhanced their sedative effects, suggesting that a dose reduction may be required. Addition of ethanol to treatment with the newer hypnosedatives resulted in additive sedative effects without altering the pharmacokinetic parameters of the drugs. Compared with some of the conventional benzodiazepines, fewer clinically important interactions appear to have been reported in the literature with zaleplon, zolpidem and zopiclone. The fact that these drugs are newer to the market and have not been as extensively studied as the conventional benzodiazepines may be the reason for this. Another explanation may be a difference in CYP metabolism. While triazolam and midazolam are biotransformed almost entirely via CYP3A4, the newer hypnosedatives are biotransformed by several CYP isozymes in addition to CYP3A4, resulting in CYP3A4 inhibitors and inducers having a lesser effect on their biotransformation.
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Affiliation(s)
- Leah M Hesse
- Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, Massachusetts 02111, USA
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Abstract
GABA is the main inhibitory neurotransmitter of the CNS. It is well established that activation of GABA(A) receptors favors sleep. Three generations of hypnotics are based on these GABA(A) receptor-mediated inhibitory processes. The first and second generation of hypnotics (barbiturates and benzodiazepines respectively) decrease waking, increase slow-wave sleep and enhance the intermediate stage situated between slow-wave sleep and paradoxical sleep, at the expense of this last sleep stage. The third generation of hypnotics (imidazopyridines and cyclopyrrolones) act similarly on waking and slow-wave sleep but the slight decrease of paradoxical sleep during the first hours does not result from an increase of the intermediate stage. It has been shown that GABA(B) receptor antagonists increase brain-activated behavioral states (waking and paradoxical sleep: dreaming stage). Recently, a specific GABA(C) receptor antagonist was synthesized and found by i.c.v. infusion to increase waking at the expense of slow-wave sleep and paradoxical sleep. Since the sensitivity of GABA(C) receptors for GABA is higher than that of GABA(A) and GABA(B) receptors, GABA(C) receptor agonists and antagonists, when available for clinical practice, could open up a new era for therapy of troubles such as insomnia, epilepsy and narcolepsy. They could possibly act at lower doses, with fewer side effects than currently used drugs. This paper reviews the influence of different kinds of molecules that affect sleep and waking by acting on GABA receptors.
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Affiliation(s)
- Claude Gottesmann
- Laboratoire de Psychophysiologie, Faculté des Sciences, Université de Nice-Sophia Antipolis, 06108 Nice Cedex 2, France.
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Nordgren HK, Bodin K, Beck O. Chromatographic screening for zopiclone and metabolites in urine using liquid chromatography and liquid chromatography-mass spectrometry techniques. Ther Drug Monit 2002; 24:410-6. [PMID: 12021634 DOI: 10.1097/00007691-200206000-00014] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Zopiclone is a benzodiazepine-like hypnotic that was believed not to have any abuse potential. Nevertheless, during the past few years there have been an increasing number of reports on the abuse and misuse of zopiclone. Despite this, methods for screening analysis in urine are lacking. To investigate whether UV detection would be possible to use for this purpose, a liquid chromatography method with ultraviolet detection for analyzing zopiclone and its urinary metabolites was developed, with liquid chromatography-mass spectrometry for confirmation. The method was used for analyzing samples from subjects receiving methadone. The limits of detection were approximately 100 ng/mL in control urine samples and 500 ng/mL in urine samples from subjects receiving methadone. However, due to the high background in these patients' urine, a single therapeutic dose was impossible to detect.
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Affiliation(s)
- Helena K Nordgren
- Institution of Medicine, Department of Clinical Pharmacology, L7:05, Karolinska Institutet, S-171 76 Stockholm, Sweden.
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Carlson JN, Haskew R, Wacker J, Maisonneuve IM, Glick SD, Jerussi TP. Sedative and anxiolytic effects of zopiclone's enantiomers and metabolite. Eur J Pharmacol 2001; 415:181-9. [PMID: 11274997 DOI: 10.1016/s0014-2999(01)00851-2] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
We evaluated racemic zopiclone, its (S)- and (R)-enantiomers and a metabolite, (S)-desmethylzopiclone, for their actions on locomotor activity, rotarod performance, the elevated plus maze and the Vogel conflict test of anxiety, and electroconvulsive shock-induced seizures duration. Zopiclone and its (R)- and (S)-enantiomers reduced locomotor activity, and zopiclone and its (S)-enantiomer disrupted rotarod performance at 10 mg/kg. (S)-desmethylzopiclone did not alter these measures at doses of less than 200 mg/kg. (S)-desmethylzopiclone altered plus maze performance at the lowest dose of all the zopiclone derivatives tested, caused a dose-related effect on the Vogel conflict test and caused a dose-related reduction of electroconvulsive shock-induced seizure durations. The data indicate that (S)-desmethylzopiclone can bring about an anxiolytic effect without a substantial degree of central nervous system depression, and suggest that the agent may be particularly useful clinically in the treatment of anxiety.
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Affiliation(s)
- J N Carlson
- Center for Neuropharmacology and Neuroscience, Albany Medical College, Albany, NY 12208, USA.
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Davies M, Newell JG, Derry JM, Martin IL, Dunn SM. Characterization of the interaction of zopiclone with gamma-aminobutyric acid type A receptors. Mol Pharmacol 2000; 58:756-62. [PMID: 10999945 DOI: 10.1124/mol.58.4.756] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Zopiclone is a cyclopyrrolone that is used clinically as a hypnotic. Although this drug is known to interact with neuronal gamma-aminobutyric acid type A receptors, its binding site(s) within the receptor oligomer has been reported to be distinct from that of the classical benzodiazepines. After photoaffinity labeling with flunitrazepam, receptors in rat cerebellar membranes showed differentially reduced affinity for flunitrazepam and zopiclone by 50- and 3-fold, respectively. Because histidine 101 of the alpha-subunit is a major site of photolabeling, we have made specific substitutions of this residue and studied the consequences on the binding properties of zopiclone and diazepam using recombinant alpha1beta2gamma2-receptors transiently expressed in tsA201 cells. Both compounds showed similar binding profiles with receptors containing mutated alpha-subunits, suggesting a similar interaction with the residue at position 101. At alpha1beta2gamma3-receptors, flunitrazepam affinity was dramatically decreased by approximately 36-fold, whereas the affinity for zopiclone was decreased only 3-fold, suggesting a differential contribution of the gamma-subunit to the binding pocket. Additionally, we used electrophysiological techniques to examine the contribution of the gamma-subunit isoform in the receptor oligomer to ligand recognition using recombinant receptors expressed in Xenopus oocytes. Both compounds are agonists at alpha1beta2gamma2- and alpha1beta2gamma3-receptors, with flunitrazepam being more potent but less efficacious. In summary, these data suggest that histidine 101 of the alpha1-subunit plays a similar role in ligand recognition for zopiclone, diazepam, and flunitrazepam.
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Affiliation(s)
- M Davies
- Department of Pharmacology, Faculty of Medicine, University of Alberta, Edmonton, Alberta, Canada.
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Agitation in the ICU: part one Anatomical and physiologic basis for the agitated state. Crit Care 1999; 3:R35-R46. [PMID: 11094481 PMCID: PMC137231 DOI: 10.1186/cc348] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/1999] [Accepted: 06/06/1999] [Indexed: 12/21/2022] Open
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Hevers W, Lüddens H. The diversity of GABAA receptors. Pharmacological and electrophysiological properties of GABAA channel subtypes. Mol Neurobiol 1998; 18:35-86. [PMID: 9824848 DOI: 10.1007/bf02741459] [Citation(s) in RCA: 388] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The amino acid gamma-aminobutyric-acid (GABA) prevails in the CNS as an inhibitory neurotransmitter that mediates most of its effects through fast GABA-gated Cl(-)-channels (GABAAR). Molecular biology uncovered the complex subunit architecture of this receptor channel, in which a pentameric assembly derived from five of at least 17 mammalian subunits, grouped in the six classes alpha, beta, gamma, delta, sigma and epsilon, permits a vast number of putative receptor isoforms. The subunit composition of a particular receptor determines the specific effects of allosterical modulators of the GABAARs like benzodiazepines (BZs), barbiturates, steroids, some convulsants, polyvalent cations, and ethanol. To understand the physiology and diversity of GABAARs, the native isoforms have to be identified by their localization in the brain and by their pharmacology. In heterologous expression systems, channels require the presence of alpha, beta, and gamma subunits in order to mimic the full repertoire of native receptor responses to drugs, with the BZ pharmacology being determined by the particular alpha and gamma subunit variants. Little is known about the functional properties of the beta, delta, and epsilon subunit classes and only a few receptor subtype-specific substances like loreclezole and furosemide are known that enable the identification of defined receptor subtypes. We will summarize the pharmacology of putative receptor isoforms and emphasize the characteristics of functional channels. Knowledge of the complex pharmacology of GABAARs might eventually enable site-directed drug design to further our understanding of GABA-related disorders and of the complex interaction of excitatory and inhibitory mechanisms in neuronal processing.
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Affiliation(s)
- W Hevers
- Department of Psychiatry, University of Mainz, Germany
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Gottesmann C, Gandolfo G, Arnaud C, Gauthier P. The intermediate stage and paradoxical sleep in the rat: influence of three generations of hypnotics. Eur J Neurosci 1998; 10:409-14. [PMID: 9749703 DOI: 10.1046/j.1460-9568.1998.00069.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Paradoxical sleep in the rat, cat and mouse is preceded and sometimes followed by a short-lasting intermediate stage characterized by high-amplitude anterior cortex spindles and low-frequency hippocampal theta rhythm. Several neurophysiological arguments suggest that the intermediate stage corresponds to a brief functional disconnection of the forebrain from the brainstem. This paper is devoted to the review of quantitative and qualitative influences of three generations of hypnotics on the intermediate stage-paradoxical sleep couple. Barbiturates, first-generation hypnotics, extend the intermediate stage at the expense of paradoxical sleep. Three benzodiazepines are compared, two with a short half-life (triazolam and midazolam) and one with a long half-life (diazepam). They also decrease sleep occurrence latency and increase the intermediate stage at the expense of paradoxical sleep, except for midazolam, which increases both the intermediate stage and paradoxical sleep at low dose. Zolpidem and zopiclone, hypnotics of third generation, decrease paradoxical sleep but the intermediate stage never substitutes for paradoxical sleep. The results are discussed in relationship to the functional aspects of this turning-point period of sleep.
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Affiliation(s)
- C Gottesmann
- Laboratoire de Psychophysiologie, Faculté des Sciences, Université de Nice-Sophia Antipolis, Nice, France.
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Davies PA, Kirkness EF, Hales TG. Modulation by general anaesthetics of rat GABAA receptors comprised of alpha 1 beta 3 and beta 3 subunits expressed in human embryonic kidney 293 cells. Br J Pharmacol 1997; 120:899-909. [PMID: 9138697 PMCID: PMC1564547 DOI: 10.1038/sj.bjp.0700987] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
1. Radioligand binding and patch-clamp techniques were used to study the actions of gamma-aminobutyric acid (GABA) and the general anaesthetics propofol (2,6-diisopropylphenol), pentobarbitone and 5 alpha-pregnan-3 alpha-ol-20-one on rat alpha 1 and beta 3 GABAA receptor subunits, expressed either alone or in combination. 2. Membranes from HEK293 cells after transfection with alpha 1 cDNA did not bind significant levels of [35S]-tert-butyl bicyclophosphorothionate ([35S]-TBPS) (< 0.03 pmol mg-1 protein). GABA (100 microM) applied to whole-cells transfected with alpha 1 cDNA and clamped at -60 mV, also failed to activate discernible currents. 3. The membranes of cells expressing beta 3 cDNAs bound [35S]-TBPS (approximately 1 pmol mg-1 protein). However, the binding was not influenced by GABA (10 nM-100 microM). Neither GABA (100 microM) nor picrotoxin (10 microM) affected currents recorded from cells expressing beta 3 cDNA, suggesting that beta 3 subunits do not form functional GABAA receptors or spontaneously active ion channels. 4. GABA (10 nM-100 microM) modulated [35S]-TBPS binding to the membranes of cells transfected with both alpha 1 and beta 3 cDNAs. GABA (0.1 microM-1 mM) also dose-dependently activated inward currents with an EC50 of 9 microM recorded from cells transfected with alpha 1 and beta 3 cDNAs, clamped at -60 mV. 5. Propofol (10 nM-100 microM), pentobarbitone (10 nM-100 microM) and 5 alpha-pregnan-3 alpha-ol-20-one (1 nM-30 microM) modulated [35S]-TBPS binding to the membranes of cells expressing either alpha 1 beta 3 or beta 3 receptors. Propofol (100 microM), pentobarbitone (1 mM) and 5 alpha-pregnan-3 alpha-ol-20-one (10 microM) also activated currents recorded from cells expressing alpha 1 beta 3 receptors. 6. Propofol (1 microM-1 mM) and pentobarbitone (1 mM) both activated currents recorded from cells expressing beta 3 homomers. In contrast, application of 5 alpha-pregnan-3 alpha-ol-20-one (10 microM) failed to activate detectable currents. 7. Propofol (100 microM)-activated currents recorded from cells expressing either alpha 1 beta 3 or beta 3 receptors reversed at the Cl- equilibrium potential and were inhibited to 34 +/- 13% and 39 +/- 10% of control, respectively, by picrotoxin (10 microM). 5 alpha-Pregnan-3 alpha-ol-20-one (100 nM) enhanced propofol (100 microM)-evoked currents mediated by alpha 1 beta 3 receptors to 1101 +/- 299% of control. In contrast, even at high concentration 5 alpha-pregnan-3 alpha-ol-20-one (10 microM) caused only a modest facilitation (to 128 +/- 12% of control) of propofol (100 microM)-evoked currents mediated by beta 3 homomers. 8. Propofol (3-100 microM) activated alpha 1 beta 3 and beta 3 receptors in a concentration-dependent manner. For both receptor combinations, higher concentrations of propofol (300 microM and 1 mM) caused a decline in current amplitude. This inhibition of receptor function reversed rapidly during washout resulting in a "surge' current on cessation of propofol (300 microM and 1 mM) application. Surge currents were also evident following pentobarbitone (1 mM) application to cells expressing either receptor combination. By contrast, this phenomenon was not apparent following applications of 5 alpha-pregnan-3 alpha-ol-20-one (10 microM) to cells expressing alpha 1 beta 3 receptors. 9. These observations demonstrate that rat beta 3 subunits form homomeric receptors that are not spontaneously active, are insensitive to GABA and can be activated by some general anaesthetics. Taken together, these data also suggest similar sites on GABAA receptors for propofol and barbiturates, and a separate site for the anaesthetic steroids.
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Affiliation(s)
- P A Davies
- Department of Anesthesiology, UCLA Medical Center 90095, USA
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Reynolds JN, Maitra R. Propofol and flurazepam act synergistically to potentiate GABAA receptor activation in human recombinant receptors. Eur J Pharmacol 1996; 314:151-6. [PMID: 8957231 DOI: 10.1016/s0014-2999(96)00527-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The intravenous general anaesthetic propofol (2,6-di-isopropylphenol) is frequently combined with a benzodiazepine. There are clinical reports of synergism between these two agents for induction of general anaesthesia. To investigate a possible mechanism of this synergistic interaction between propofol and benzodiazepines, the effect of propofol and flurazepam on GABAA receptor function was examined in Xenopus oocytes expressing recombinant alpha 1 beta 2 gamma 2L and alpha 2 beta 2 gamma 2L receptor constructs. Potentiation of GABA receptor-activated current by low (1-10 microM) concentrations of propofol together with flurazepam (0.25-0.5 microM) was significantly greater than predicted by an additive response. Isobolographic analysis indicated a strong synergistic interaction between propofol and flurazepam at either of the receptor constructs examined. In contrast, the cyclopyrrolone derivative zopiclone, which produced a similar facilitation of GABA receptor-activated current compared to flurazepam, produced a less than additive potentiation when combined with propofol. Flurazepam significantly decreased the EC50 concentration of propofol for potentiation of GABA responses. Thus, flurazepam, in addition to facilitating GABA receptor activity on its own, also increases on its own, also increases the apparent affinity of the GABAA receptor complex to propofol, resulting in a greater than expected potentiation by the combination of propofol plus flurazepam.
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Affiliation(s)
- J N Reynolds
- Faculty of Medicine, Memorial University of Newfoundland, St. John's, Canada
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