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Dauvilliers Y, Bogan RK, Šonka K, Partinen M, Foldvary-Schaefer N, Thorpy MJ. Calcium, Magnesium, Potassium, and Sodium Oxybates Oral Solution: A Lower-Sodium Alternative for Cataplexy or Excessive Daytime Sleepiness Associated with Narcolepsy. Nat Sci Sleep 2022; 14:531-546. [PMID: 35378745 PMCID: PMC8976528 DOI: 10.2147/nss.s279345] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/19/2021] [Accepted: 03/08/2022] [Indexed: 11/23/2022] Open
Abstract
Lower-sodium oxybate (LXB) is an oxybate medication approved to treat cataplexy or excessive daytime sleepiness (EDS) in patients with narcolepsy 7 years of age and older in the United States. LXB was developed as an alternative to sodium oxybate (SXB), because the incidence of cardiovascular comorbidities is higher in patients with narcolepsy and there is an elevated cardiovascular risk associated with high sodium consumption. LXB has a unique formulation of calcium, magnesium, potassium, and sodium ions, containing 92% less sodium than SXB. Whereas the active oxybate moiety is the same for LXB and SXB, their pharmacokinetic profiles are not bioequivalent; therefore, a phase 3 trial in participants with narcolepsy was conducted for LXB. This review summarizes the background on oxybate as a therapeutic agent and its potential mechanism of action on the gamma-aminobutyric acid type B (GABAB) receptor at noradrenergic and dopaminergic neurons, as well as at thalamocortical neurons. The rationale leading to the development of LXB as a lower-sodium alternative to SXB and the key efficacy and safety data supporting its approval for both adult and pediatric patients with narcolepsy are also discussed. LXB was approved in August 2021 in the United States for the treatment of idiopathic hypersomnia in adults. Potential future developments in the field of oxybate medications may include novel formulations and expanded indications for other diseases.
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Affiliation(s)
- Yves Dauvilliers
- Sleep and Wake Disorders Centre, Department of Neurology, Gui de Chauliac Hospital, Montpellier, France.,University of Montpellier, INSERM Institute Neuroscience Montpellier (INM), Montpellier, France
| | - Richard K Bogan
- University of South Carolina School of Medicine, Columbia, SC, USA
| | - Karel Šonka
- Department of Neurology, First Faculty of Medicine, Charles University and General University Hospital, Prague, Czech Republic
| | - Markku Partinen
- Helsinki Sleep Clinic, Terveystalo Healthcare, and Department of Clinical Neurosciences, University of Helsinki, Helsinki, Finland
| | | | - Michael J Thorpy
- Department of Neurology, Albert Einstein College of Medicine, Bronx, NY, USA
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2
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Crunelli V, Lőrincz ML, McCafferty C, Lambert RC, Leresche N, Di Giovanni G, David F. Clinical and experimental insight into pathophysiology, comorbidity and therapy of absence seizures. Brain 2020; 143:2341-2368. [PMID: 32437558 PMCID: PMC7447525 DOI: 10.1093/brain/awaa072] [Citation(s) in RCA: 94] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 12/19/2019] [Accepted: 01/31/2020] [Indexed: 12/24/2022] Open
Abstract
Absence seizures in children and teenagers are generally considered relatively benign because of their non-convulsive nature and the large incidence of remittance in early adulthood. Recent studies, however, show that 30% of children with absence seizures are pharmaco-resistant and 60% are affected by severe neuropsychiatric comorbid conditions, including impairments in attention, cognition, memory and mood. In particular, attention deficits can be detected before the epilepsy diagnosis, may persist even when seizures are pharmacologically controlled and are aggravated by valproic acid monotherapy. New functional MRI-magnetoencephalography and functional MRI-EEG studies provide conclusive evidence that changes in blood oxygenation level-dependent signal amplitude and frequency in children with absence seizures can be detected in specific cortical networks at least 1 min before the start of a seizure, spike-wave discharges are not generalized at seizure onset and abnormal cortical network states remain during interictal periods. From a neurobiological perspective, recent electrical recordings and imaging of large neuronal ensembles with single-cell resolution in non-anaesthetized models show that, in contrast to the predominant opinion, cortical mechanisms, rather than an exclusively thalamic rhythmogenesis, are key in driving seizure ictogenesis and determining spike-wave frequency. Though synchronous ictal firing characterizes cortical and thalamic activity at the population level, individual cortico-thalamic and thalamocortical neurons are sparsely recruited to successive seizures and consecutive paroxysmal cycles within a seizure. New evidence strengthens previous findings on the essential role for basal ganglia networks in absence seizures, in particular the ictal increase in firing of substantia nigra GABAergic neurons. Thus, a key feature of thalamic ictogenesis is the powerful increase in the inhibition of thalamocortical neurons that originates at least from two sources, substantia nigra and thalamic reticular nucleus. This undoubtedly provides a major contribution to the ictal decrease in total firing and the ictal increase of T-type calcium channel-mediated burst firing of thalamocortical neurons, though the latter is not essential for seizure expression. Moreover, in some children and animal models with absence seizures, the ictal increase in thalamic inhibition is enhanced by the loss-of-function of the astrocytic GABA transporter GAT-1 that does not necessarily derive from a mutation in its gene. Together, these novel clinical and experimental findings bring about paradigm-shifting views of our understanding of absence seizures and demand careful choice of initial monotherapy and continuous neuropsychiatric evaluation of affected children. These issues are discussed here to focus future clinical and experimental research and help to identify novel therapeutic targets for treating both absence seizures and their comorbidities.
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Affiliation(s)
- Vincenzo Crunelli
- Department of Physiology and Biochemistry, Faculty of Medicine and Surgery, University of Malta, Msida, Malta.,Neuroscience Division, School of Bioscience, Cardiff University, Museum Avenue, Cardiff, UK
| | - Magor L Lőrincz
- Neuroscience Division, School of Bioscience, Cardiff University, Museum Avenue, Cardiff, UK.,Department of Physiology, Faculty of Medicine, University of Szeged, Szeged, Hungary.,Department of Physiology, Anatomy and Neuroscience, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | - Cian McCafferty
- Department of Anatomy and Neuroscience, University College Cork, Cork, Ireland
| | - Régis C Lambert
- Sorbonne Université, CNRS, INSERM, Neuroscience Paris Seine and Institut de Biologie Paris Seine (NPS - IBPS), Paris, France
| | - Nathalie Leresche
- Sorbonne Université, CNRS, INSERM, Neuroscience Paris Seine and Institut de Biologie Paris Seine (NPS - IBPS), Paris, France
| | - Giuseppe Di Giovanni
- Department of Physiology and Biochemistry, Faculty of Medicine and Surgery, University of Malta, Msida, Malta.,Neuroscience Division, School of Bioscience, Cardiff University, Museum Avenue, Cardiff, UK
| | - François David
- Cerebral dynamics, learning and plasticity, Integrative Neuroscience and Cognition Center - UMR 8002, Paris, France
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3
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Bosch OG, Esposito F, Dornbierer D, von Rotz R, Kraehenmann R, Staempfli P, Quednow BB, Seifritz E. Prohedonic properties of gamma-hydroxybutyrate are associated with changes in limbic resting-state functional connectivity. Hum Psychopharmacol 2018; 33:e2679. [PMID: 30426556 DOI: 10.1002/hup.2679] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Revised: 09/27/2018] [Accepted: 09/28/2018] [Indexed: 12/22/2022]
Abstract
OBJECTIVE Gamma-hydroxybutyrate (GHB) is an endogenous GHB-/GABA-B receptor agonist and a narcolepsy treatment. However, GHB is also abused for its prohedonic effects. On a neuronal level, it was shown that GHB increases regional cerebral blood flow in limbic areas such as the right anterior insula (rAI) and the anterior cingulate cortex (ACC). We aimed to further explore the association between the subjective and neuronal signatures of GHB. METHOD We assessed subjective effects and resting-state functional connectivity (rsFC) of an rAI- and an ACC-seed in 19 healthy male subjects after GHB (35 mg/kg p.o.) using a placebo-controlled, double-blind, randomized, cross-over functional magnet resonance imaging design. RESULTS GHB increased subjective ratings for euphoria (p < 0.001) and sexual arousal (p < 0.01). Moreover, GHB increased rAI-rsFC to the right thalamus and the superior frontal gyrus and decreased ACC-rsFC to the bilateral paracentral lobule (all p < 0.05, cluster corrected). Moreover, GHB-induced euphoria was associated with rAI-rsFC to the superior frontal gyrus (p < 0.05, uncorrected). CONCLUSIONS GHB induces prohedonic effects such as euphoria and sexual arousal and in parallel modulates limbic rsFC with areas linked to regulation of mood, cognitive control, and sexual experience. These results further elucidate the drug's effects in neuropsychiatric disorders and as drug of abuse.
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Affiliation(s)
- Oliver G Bosch
- Department of Psychiatry, Psychotherapy and Psychosomatics, Psychiatric Hospital of the University of Zurich, Zurich, Switzerland.,Experimental and Clinical Pharmacopsychology, Department of Psychiatry, Psychotherapy and Psychosomatics, Psychiatric Hospital of the University of Zurich, Zurich, Switzerland
| | - Fabrizio Esposito
- Department of Medicine, Surgery and Dentistry "Scuola Medica Salernitana", University of Salerno, Baronissi, Italy
| | - Dario Dornbierer
- Department of Psychiatry, Psychotherapy and Psychosomatics, Psychiatric Hospital of the University of Zurich, Zurich, Switzerland.,Experimental and Clinical Pharmacopsychology, Department of Psychiatry, Psychotherapy and Psychosomatics, Psychiatric Hospital of the University of Zurich, Zurich, Switzerland
| | - Robin von Rotz
- Department of Psychiatry, Psychotherapy and Psychosomatics, Psychiatric Hospital of the University of Zurich, Zurich, Switzerland.,Experimental and Clinical Pharmacopsychology, Department of Psychiatry, Psychotherapy and Psychosomatics, Psychiatric Hospital of the University of Zurich, Zurich, Switzerland
| | - Rainer Kraehenmann
- Department of Psychiatry, Psychotherapy and Psychosomatics, Psychiatric Hospital of the University of Zurich, Zurich, Switzerland
| | - Philipp Staempfli
- Department of Psychiatry, Psychotherapy and Psychosomatics, Psychiatric Hospital of the University of Zurich, Zurich, Switzerland.,MR-Center of the Department of Psychiatry, Psychotherapy and Psychosomatics and the Department of Child and Adolescent Psychiatry, Psychiatric Hospital of the University of Zurich, Zurich, Switzerland
| | - Boris B Quednow
- Experimental and Clinical Pharmacopsychology, Department of Psychiatry, Psychotherapy and Psychosomatics, Psychiatric Hospital of the University of Zurich, Zurich, Switzerland.,Neuroscience Center Zurich, University and ETH, Zurich, Switzerland
| | - Erich Seifritz
- Department of Psychiatry, Psychotherapy and Psychosomatics, Psychiatric Hospital of the University of Zurich, Zurich, Switzerland.,Neuroscience Center Zurich, University and ETH, Zurich, Switzerland
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Postnatal expression of thalamic GABAA receptor subunits in the stargazer mouse model of absence epilepsy. Neuroreport 2018; 28:1255-1260. [PMID: 29099440 DOI: 10.1097/wnr.0000000000000909] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Absence seizures are known to originate from disruptions within the corticothalamocortical network; however, the precise underlying cellular and molecular mechanisms that induce hypersynchronicity and hyperexcitability are debated and likely to be complex and multifactorial. Recent studies implicate impaired thalamic GABAergic inhibition as a common feature in multiple animal models of absence epilepsy, including the well-established stargazer mouse model. Recently, we demonstrated region-specific increases in the whole tissue and synaptic levels of GABAA receptor (GABAAR) subunits α1 and β2, within the ventral posterior region of the thalamus in adult epileptic stargazer mice compared with nonepileptic control littermates. The objective of this study was to investigate whether such changes in GABAAR subunits α1 and β2 can be observed before the initiation of seizures, which occur around postnatal (PN) days 16-18 in stargazers. Semiquantitative western blotting was used to analyze the relative tissue level expression of GABAAR α1 and β2 subunits in the thalamus of juvenile stargazer mice compared with their nonepileptic control littermates at three different time points before the initiation of seizures. We show that there is a statistically significant increase in the expression of α1 and β2 subunits in the thalamus of stargazer mice, at the PN7-9 stage, compared with the control littermates, but not at PN10-12 and PN13-15 stages. These results suggest that an aberrant expression of GABAAR subunits α1 and β2 in the stargazers does not occur immediately before seizure onset and therefore is unlikely to directly contribute to the initiation of absence seizures.
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Benke D, Möhler H. Impact on GABA systems in monogenetic developmental CNS disorders: Clues to symptomatic treatment. Neuropharmacology 2017; 136:46-55. [PMID: 28764992 DOI: 10.1016/j.neuropharm.2017.07.030] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Revised: 07/26/2017] [Accepted: 07/28/2017] [Indexed: 12/26/2022]
Abstract
Animal studies of several single-gene disorders demonstrate that reversing the molecular signaling deficits can result in substantial symptomatic improvements in function. Focusing on the ratio of excitation to inhibition as a potential pathophysiological hallmark, seven single-gene developmental CNS disorders are reviewed which are characterized by a striking dysregulation of neuronal inhibition. Deficits in inhibition and excessive inhibition are found. The examples of developmental disorders encompass Neurofibromatosis type 1, Fragile X syndrome, Rett syndrome, Dravet syndrome including autism-like behavior, NONO-mutation-induced intellectual disability, Succinic semialdehyde dehydrogenase deficiency and Congenital nystagmus due to FRMD7 mutations. The phenotype/genotype correlations observed in animal models point to potential treatment options and will continue to inspire clinical research. Three drugs are presently in clinical trials: acamprosate and ganoxolon for Fragile X syndrome and SGS-742 for SSADH deficiency. This article is part of the "Special Issue Dedicated to Norman G. Bowery".
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Affiliation(s)
- Dietmar Benke
- Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland; Neuroscience Center Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland; Drug Discovery Network Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
| | - Hanns Möhler
- Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland; Neuroscience Center Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland; Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology (ETH), Vladimir-Prelog-Weg 10, 8023 Zurich, Switzerland.
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Synaptic changes in GABAA receptor expression in the thalamus of the stargazer mouse model of absence epilepsy. Neuroscience 2015; 306:28-38. [PMID: 26297893 DOI: 10.1016/j.neuroscience.2015.08.021] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2015] [Revised: 08/12/2015] [Accepted: 08/12/2015] [Indexed: 01/04/2023]
Abstract
Absence seizures are known to result from disturbances within the cortico-thalamocortical network, which remains partially synchronous under normal conditions but switches to a state of hypersynchronicity and hyperexcitability during absence seizures. There is evidence to suggest that impaired GABAergic inhibitory function within the thalamus could contribute to the generation of hypersynchronous oscillations in some animal models of absence epilepsy. Recently, we demonstrated region-specific alterations in the tissue expression level of GABAA receptors (GABA(A)Rs) α1 and β2 subunits within the thalamus of the stargazer mouse model of absence epilepsy. In the present study we investigated whether changes in these subunits also occur at synapses in the ventral posterior (VP) complex where they are components of phasic GABA(A)R receptors. Postembedding immunogold cytochemistry and electron microscopy were used to analyze the relative synaptic expression of α1 and β2 subunits in the VP thalamic region in epileptic stargazer mice compared to their non-epileptic littermates. We show that there is a significant increase in expression of α1 and β2 subunits (53.6% and 45.8%, respectively) at synapses in the VP region of stargazers, indicative of an increase in phasic GABA(A)Rs at thalamocortical (TC) relay neurons. Furthermore, we investigated whether tissue expression of GABA(A)R subunits α4 and δ, which constitute part of tonic GABA(A)Rs in the VP region, is altered in the stargazer mouse. Semi-quantitative Western blotting showed a significant increase in GABA(A)R α4 and δ subunits in the VP region of stargazer thalamus, which would indicate an increase in tonic GABA(A)R expression. Our findings show that there are changes in the levels of both phasic and tonic GABA(A)Rs in the VP thalamus; altered GABAergic inhibition within the VP could be one of many mechanisms contributing to the generation of absence seizures in this model.
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Venzi M, Di Giovanni G, Crunelli V. A critical evaluation of the gamma-hydroxybutyrate (GHB) model of absence seizures. CNS Neurosci Ther 2015; 21:123-40. [PMID: 25403866 PMCID: PMC4335601 DOI: 10.1111/cns.12337] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2014] [Revised: 09/13/2014] [Accepted: 09/17/2014] [Indexed: 12/13/2022] Open
Abstract
Typical absence seizures (ASs) are nonconvulsive epileptic events which are commonly observed in pediatric and juvenile epilepsies and may be present in adults suffering from other idiopathic generalized epilepsies. Our understanding of the pathophysiological mechanisms of ASs has been greatly advanced by the availability of genetic and pharmacological models, in particular the γ-hydroxybutyrate (GHB) model which, in recent years, has been extensively used in studies in transgenic mice. GHB is an endogenous brain molecule that upon administration to various species, including humans, induces not only ASs but also a state of sedation/hypnosis. Analysis of the available data clearly indicates that only in the rat does there exist a set of GHB-elicited behavioral and EEG events that can be confidently classified as ASs. Other GHB activities, particularly in mice, appear to be mostly of a sedative/hypnotic nature: thus, their relevance to ASs requires further investigation. At the molecular level, GHB acts as a weak GABA-B agonist, while the existence of a GHB receptor remains elusive. The pre- and postsynaptic actions underlying GHB-elicited ASs have been thoroughly elucidated in thalamus, but little is known about the cellular/network effects of GHB in neocortex, the other brain region involved in the generation of ASs.
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Affiliation(s)
- Marcello Venzi
- Neuroscience DivisionSchool of BioscienceCardiff UniversityCardiffUK
| | - Giuseppe Di Giovanni
- Neuroscience DivisionSchool of BioscienceCardiff UniversityCardiffUK
- Department of Physiology and BiochemistryMalta UniversityMsida, Malta
| | - Vincenzo Crunelli
- Neuroscience DivisionSchool of BioscienceCardiff UniversityCardiffUK
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8
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T-type Ca2+ channels in absence epilepsy. Pflugers Arch 2014; 466:719-34. [DOI: 10.1007/s00424-014-1461-y] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2014] [Accepted: 01/22/2014] [Indexed: 11/25/2022]
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9
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Seo S, Leitch B. Altered thalamic GABAA-receptor subunit expression in the stargazer mouse model of absence epilepsy. Epilepsia 2014; 55:224-32. [PMID: 24417662 DOI: 10.1111/epi.12500] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/29/2013] [Indexed: 01/11/2023]
Abstract
PURPOSE Absence seizures, also known as petit mal seizures, arise from disruptions within the cortico-thalamocortical network. Interconnected circuits within the thalamus consisting of inhibitory neurons of the reticular thalamic nucleus (RTN) and excitatory relay neurons of the ventral posterior (VP) complex, generate normal intrathalamic oscillatory activity. The degree of synchrony in this network determines whether normal (spindle) or pathologic (spike wave) oscillations occur; however, the cellular and molecular mechanisms underlying absence seizures are complex and multifactorial and currently are not fully understood. Recent experimental evidence from rodent models suggests that regional alterations in γ-aminobutyric acid (GABA)ergic inhibition may underlie hypersynchronous oscillations featured in absence seizures. The aim of the current study was to investigate whether region-specific differences in GABAA receptor (GABAAR) subunit expression occur in the VP and RTN thalamic regions in the stargazer mouse model of absence epilepsy where the primary deficit is in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) expression. METHODS Immunofluorescence confocal microscopy and semiquantitative Western blot analysis were used to investigate region-specific changes in GABAAR subunits in the thalamus of the stargazer mouse model of absence epilepsy to determine whether changes in GABAergic inhibition could contribute to the mechanisms underlying seizures in this model of absence epilepsy. KEY FINDINGS Immunofluorescence confocal microscopy revealed that GABAAR α1 and β2 subunits are predominantly expressed in the VP, whereas α3 and β3 subunits are localized primarily in the RTN. Semiquantitative Western blot analysis of VP and RTN samples from epileptic stargazers and their nonepileptic littermates showed that GABAAR α1 and β2 subunit expression levels in the VP were significantly increased (α1: 33%, β2: 96%) in epileptic stargazers, whereas α3 and β3 subunits in the RTN were unchanged in the epileptic mice compared to nonepileptic control littermates. SIGNIFICANCE These findings suggest that region-specific differences in GABAAR subunits in the thalamus of epileptic mice, specifically up-regulation of GABAARs in the thalamic relay neurons of the VP, may contribute to generation of hypersynchronous thalamocortical activity in absence seizures. Understanding region-specific differences in GABAAR subunit expression could help elucidate some of the cellular and molecular mechanisms underlying absence seizures and thereby identify targets by which drugs can modulate the frequency and severity of epileptic seizures. Ultimately, this information could be crucial for the development of more specific and effective therapeutic drugs for treatment of this form of epilepsy.
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Affiliation(s)
- Steve Seo
- Department of Anatomy, Brain Health Research Centre, Otago School of Medical Sciences, University of Otago, Dunedin, New Zealand
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Connelly WM, Errington AC, Crunelli V. γ-Hydroxybutyric acid (GHB) is not an agonist of extrasynaptic GABAA receptors. PLoS One 2013; 8:e79062. [PMID: 24244421 PMCID: PMC3823990 DOI: 10.1371/journal.pone.0079062] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Accepted: 09/25/2013] [Indexed: 02/07/2023] Open
Abstract
γ-Hydroxybutyric acid (GHB) is an endogenous compound and a drug used clinically to treat the symptoms of narcolepsy. GHB is known to be an agonist of GABAB receptors with millimolar affinity, but also binds with much higher affinity to another site, known as the GHB receptor. While a body of evidence has shown that GHB does not bind to GABAA receptors widely, recent evidence has suggested that the GHB receptor is in fact on extrasynaptic α4β1δ GABAA receptors, where GHB acts as an agonist with an EC50 of 140 nM. We investigated three neuronal cell types that express a tonic GABAA receptor current mediated by extrasynaptic receptors: ventrobasal (VB) thalamic neurons, dentate gyrus granule cells and striatal medium spiny neurons. Using whole-cell voltage clamp in brain slices, we found no evidence that GHB (10 µM) induced any GABAA receptor mediated current in these cell types, nor that it modulated inhibitory synaptic currents. Furthermore, a high concentration of GHB (3 mM) was able to produce a GABAB receptor mediated current, but did not induce any other currents. These results suggest either that GHB is not a high affinity agonist at native α4β1δ receptors, or that these receptors do not exist in classical areas associated with extrasynaptic currents.
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Affiliation(s)
- William M. Connelly
- Neuroscience Division, Cardiff School of Biosciences, Cardiff University, Cardiff, United Kingdom
- * E-mail: (WMC); (VC)
| | - Adam C. Errington
- Neuroscience Division, Cardiff School of Biosciences, Cardiff University, Cardiff, United Kingdom
| | - Vincenzo Crunelli
- Neuroscience Division, Cardiff School of Biosciences, Cardiff University, Cardiff, United Kingdom
- * E-mail: (WMC); (VC)
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Püttmann L, Stehr H, Garshasbi M, Hu H, Kahrizi K, Lipkowitz B, Jamali P, Tzschach A, Najmabadi H, Ropers HH, Musante L, Kuss AW. A novelALDH5A1mutation is associated with succinic semialdehyde dehydrogenase deficiency and severe intellectual disability in an Iranian family. Am J Med Genet A 2013; 161A:1915-22. [DOI: 10.1002/ajmg.a.36030] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2012] [Accepted: 04/15/2013] [Indexed: 01/20/2023]
Affiliation(s)
| | - Henning Stehr
- Department of Vertebrate Genomics; Max Planck Institute for Molecular Genetics; Berlin; Germany
| | - Masoud Garshasbi
- Department of Human Molecular Genetics; Max Planck Institute for Molecular Genetics; Berlin; Germany
| | - Hao Hu
- Department of Human Molecular Genetics; Max Planck Institute for Molecular Genetics; Berlin; Germany
| | - Kimia Kahrizi
- Genetics Research Center; University of Social Welfare and Rehabilitation Sciences; Tehran; Iran
| | - Bettina Lipkowitz
- Department of Human Molecular Genetics; Max Planck Institute for Molecular Genetics; Berlin; Germany
| | | | - Andreas Tzschach
- Department of Human Molecular Genetics; Max Planck Institute for Molecular Genetics; Berlin; Germany
| | - Hossein Najmabadi
- Genetics Research Center; University of Social Welfare and Rehabilitation Sciences; Tehran; Iran
| | - Hans-Hilger Ropers
- Department of Human Molecular Genetics; Max Planck Institute for Molecular Genetics; Berlin; Germany
| | - Luciana Musante
- Department of Human Molecular Genetics; Max Planck Institute for Molecular Genetics; Berlin; Germany
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Abstract
This review summarizes the findings obtained over the past 70 years on the fundamental mechanisms underlying generalized spike-wave (SW) discharges associated with absence seizures. Thalamus and cerebral cortex are the brain areas that have attracted most of the attention from both clinical and experimental researchers. However, these studies have often favored either one or the other structure in playing a major role, thus leading to conflicting interpretations. Beginning with Jasper and Penfield's topistic view of absence seizures as the result of abnormal functions in the so-called centrencephalon, we witness the naissance of a broader concept that considered both thalamus and cortex as equal players in the process of SW discharge generation. Furthermore, we discuss how recent studies have identified fine changes in cortical and thalamic excitability that may account for the expression of absence seizures in naturally occurring genetic rodent models and knockout mice. The end of this fascinating tale is presumably far from being written. However, I can confidently conclude that in the unfolding of this "novel," we have discovered several molecular, cellular, and pharmacologic mechanisms that govern forebrain excitability, and thus consciousness, during the awake state and sleep.
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Affiliation(s)
- Massimo Avoli
- Montreal Neurological Institute and Departments of Neurology & Neurosurgery, and of Physiology, McGill University, Montreal, Quebec, Canada.
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13
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Human aldo-keto reductase AKR7A2 protects against the cytotoxicity and mutagenicity of reactive aldehydes and lowers intracellular reactive oxygen species in hamster V79-4 cells. Chem Biol Interact 2011; 195:25-34. [PMID: 22001351 DOI: 10.1016/j.cbi.2011.09.007] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Revised: 09/26/2011] [Accepted: 09/27/2011] [Indexed: 12/16/2022]
Abstract
Aldo-keto reductase (AKR) enzymes are critical for the detoxication of endogenous and exogenous aldehydes. Previous studies have shown that the AKR7A2 enzyme is catalytically active toward aldehydes arising from lipid peroxidation, suggesting a potential role against the consequences of oxidative stress, and representing an important detoxication route in mammalian cells. The aim of this study was to determine the ability of AKR7A2 to protect cells against aldehyde cytotoxicity and genotoxicity and elucidate its potential role in providing resistance to oxidative stress. A transgenic mammalian cell model was developed in which AKR7A2 was overexpressed in V79-4 cells and used to evaluate the ability of AKR7A2 to provide resistance against toxic aldehydes. Results show that AKR7A2 provides increased resistance to the cytotoxicity of 4-hydroxynonenal (HNE) and modest resistance to the cytotoxicity of trans, trans-muconaldehyde (MUC) and methyglyoxal, but provided no protection against crotonaldehyde and acrolein. Cells expressing AKR7A2 were also found to be less susceptible to DNA damage, showing a decrease in mutation rate cause by 4-HNE compared to control cells. Furthermore, the role of the AKR7A2 enzyme on the cellular capability to cope with oxidative stress was assessed. V79 cells expressing AKR7A2 were more resistant to the redox-cycler menadione and were able to lower menadione-induced ROS levels in both a time and dose dependent manner. In addition, AKR7A2 was able to maintain intracellular GSH levels in the presence of menadione. Together these findings indicate that AKR7A2 is involved in cellular detoxication pathways and may play a defensive role against oxidative stress in vivo.
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Crunelli V, Cope DW, Terry JR. Transition to absence seizures and the role of GABA(A) receptors. Epilepsy Res 2011; 97:283-9. [PMID: 21889315 PMCID: PMC3227737 DOI: 10.1016/j.eplepsyres.2011.07.011] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Revised: 07/18/2011] [Accepted: 07/22/2011] [Indexed: 11/17/2022]
Abstract
Absence seizures appear to be initiated in a putative cortical ‘initiation site’ by the expression of medium-amplitude 5–9 Hz oscillations, which may in part be due to a decreased phasic GABAA receptor function. These oscillations rapidly spread to other cortical areas and to the thalamus, leading to fully developed generalized spike and wave discharges. In thalamocortical neurons of genetic models, phasic GABAA inhibition is either unchanged or increased, whereas tonic GABAA inhibition is increased both in genetic and pharmacological models. This enhanced tonic inhibition is required for absence seizure generation, and in genetic models it results from a malfunction in the astrocytic GABA transporter GAT-1. Contradictory results from inbred and transgenic animals still do not allow us to draw firm conclusions on changes in phasic GABAA inhibition in the GABAergic neurons of the nucleus reticularis thalami. Mathematical modelling may enhance our understanding of these competing hypotheses, by permitting investigations of their mechanistic aspects, hence enabling a greater understanding of the processes underlying seizure generation and evolution.
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Affiliation(s)
- Vincenzo Crunelli
- Neuroscience Division, School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3US, UK.
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15
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Crunelli V, Leresche N, Cope DW. GABAergic gain-of-function in absence seizures. Epilepsia 2010. [DOI: 10.1111/j.1528-1167.2010.02809.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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16
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Vardya I, Drasbek KR, Gibson KM, Jensen K. Plasticity of postsynaptic, but not presynaptic, GABAB receptors in SSADH deficient mice. Exp Neurol 2010; 225:114-22. [PMID: 20570675 DOI: 10.1016/j.expneurol.2010.05.022] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2009] [Revised: 04/26/2010] [Accepted: 05/27/2010] [Indexed: 12/28/2022]
Abstract
Succinic semialdehyde dehydrogenase (SSADH) deficiency is an autosomal-recessively inherited disorder of gamma-aminobutyrate (GABA) catabolism characterized by ataxia and epilepsy. Since SSADH is responsible for GABA break-down downstream of GABA transaminase, patients manifest high extracellular levels of GABA, as well as the GABA(B) receptor (GABA(B)R) agonist gamma-hydroxybutyrate (GHB). SSADH knockout (KO) mice display absence seizures, which progress into lethal tonic-clonic seizures at around 3weeks of age. It is hypothesized that desensitization of GABA(B)Rs plays an important role in the disease, although detailed studies of pre- and postsynaptic GABA(B)Rs are not available. We performed patch-clamp recordings from layer 2/3 pyramidal neurons in neocortical brain slices of wild-type (WT) and SSADH KO mice. Electrical stimulation of GABAergic fibers during wash in of the GABA(B)R agonist baclofen revealed no difference in presynaptic GABA(B)R mediated inhibition of GABA release between WT and SSADH KO mice. In contrast, a significant decrease in postsynaptic baclofen-induced potassium currents was seen in SSADH KO mice. This reduction was unlikely to be caused by accumulation of potassium, GABA or GHB in the brain slices, or an altered expression of regulators of G-protein signaling (RGS) proteins. Finally, adenosine-induced potassium currents were also reduced in SSADH KO mice, which could suggest heterologous desensitization of the G-protein dependent effectors, leading to a reduction in G-protein coupled inwardly rectifying potassium (GIRK) channel responses. Our findings indicate that high GABA and GHB levels desensitize postsynaptic, but not certain presynaptic, GABA(B)Rs, promoting a decrease in GIRK channel function. These changes could contribute to the development of seizures in SSADH KO mice and potentially also in affected patients.
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Affiliation(s)
- Irina Vardya
- Synaptic Physiology Laboratory, Department of Physiology and Biophysics, Aarhus University, Denmark
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17
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Bortolato M, Frau R, Orrù M, Fà M, Dessì C, Puligheddu M, Barberini L, Pillolla G, Polizzi L, Santoni F, Mereu G, Marrosu F. GABAB receptor activation exacerbates spontaneous spike-and-wave discharges in DBA/2J mice. Seizure 2010; 19:226-31. [DOI: 10.1016/j.seizure.2010.02.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2009] [Revised: 02/13/2010] [Accepted: 02/19/2010] [Indexed: 10/19/2022] Open
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18
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Wang X, Stewart L, Cortez MA, Wu Y, Velazquez JLP, Liu CC, Shen L, Snead OC. The circuitry of atypical absence seizures in GABA(B)R1a transgenic mice. Pharmacol Biochem Behav 2009; 94:124-30. [PMID: 19666047 DOI: 10.1016/j.pbb.2009.07.017] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/17/2009] [Revised: 07/20/2009] [Accepted: 07/28/2009] [Indexed: 01/30/2023]
Abstract
The objective of the current study was to determine the origin of the slow spike and wave discharges (SSWD) in the transgenic mouse with postnatal over-expression of the GABA(B) receptor subunit R1a (GABA(B)R1a(tg)), a mutant animal with a characteristic phenotype consisting of atypical absence seizures and cognitive dysfunction. Using simultaneous electrocorticographic (ECoG) recordings from cortical and depth electrodes in freely moving GABA(B)R1a(tg) mice, we showed that the SSWD in this model of atypical absence seizures arise exclusively from midline thalamus (MT), reticular nucleus of the thalamus (nRT), and the CA1 region of the hippocampus. Lesioning of the MT and nRT with ibotenic acid abolished SSWD. Microinjection of the GABA(B) receptor agonist, (-) baclofen, into MT and nRT exacerbated, and the GABA(B)R antagonist, CGP 35348 abolished, SSWD in the GABA(B)R1a(tg) mice. These data suggest that the nRT and MT are necessary for the generation of SSWD in the GABA(B)R1a(tg) model of atypical absence seizures, and indicate that GABA(B)R-mediated mechanisms within thalamus are necessary for the genesis of SSWD in atypical absence seizures. A putative cortico-thalamo-hippocampal circuit is proposed to explain the unique electrographic findings, ictal behavior, pharmacology, and impairment of cognition that characterize atypical absence seizures.
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Affiliation(s)
- Xiaomei Wang
- Neuroscience and Mental Health Program, Faculty of Medicine, University of Toronto, The Hospital for Sick Children, 555 University Avenue, Toronto, ON M5G1X8, Canada.
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19
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Mamelak M. Narcolepsy and depression and the neurobiology of gammahydroxybutyrate. Prog Neurobiol 2009; 89:193-219. [PMID: 19654034 DOI: 10.1016/j.pneurobio.2009.07.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2009] [Revised: 05/24/2009] [Accepted: 07/28/2009] [Indexed: 12/23/2022]
Abstract
A voluminous literature describes the relationship between disturbed sleep and depression. The breakdown of sleep is one of the cardinal features of depression and often also heralds its onset. Frequent arousals, periods of wakefulness and a short sleep onset REM latency are typical polysomnographic features of depression. The short latency to REM sleep has been attributed to the combination of a monoaminergic deficiency and cholinergic supersensitivity and these irregularities have been proposed to form the biological basis of the disorder. A similar imbalance between monoaminergic and cholinergic neurotransmission has been found in narcolepsy, a condition in which frequent awakenings, periods of wakefulness and short sleep onset REM latencies are also characteristic findings during sleep. In many cases of narcolepsy, this imbalance appears to result from a deficiency of hypocretin but once established, whether in depression or narcolepsy, this disequilibrium sets the stage for the dissociation or premature appearance of REM sleep and for the dissociation of the motor inhibitory component of REM sleep or cataplexy. In the presence of this monoaminergic/cholinergic imbalance, gammahydroxybutyrate (GHB) may acutely further reduce the latency of REM sleep and induce cataplexy, in both patients with narcolepsy or depression. On the other hand, the repeated nocturnal application of GHB in patients with narcolepsy improves the continuity of sleep, prolongs the latency to REM sleep and prevents cataplexy. Evidence to date suggests that GHB may restore the normal balance between monoaminergic and cholinergic neurotransmission. As such, the repeated use of GHB at night and the stabilization of sleep over time makes GHB an effective treatment for narcolepsy and a potentially effective treatment for depression.
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Affiliation(s)
- Mortimer Mamelak
- Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada.
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20
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Molnár T, Antal K, Nyitrai G, Emri Z. gamma-Hydroxybutyrate (GHB) induces GABA(B) receptor independent intracellular Ca2+ transients in astrocytes, but has no effect on GHB or GABA(B) receptors of medium spiny neurons in the nucleus accumbens. Neuroscience 2009; 162:268-81. [PMID: 19446011 DOI: 10.1016/j.neuroscience.2009.05.017] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2009] [Revised: 04/27/2009] [Accepted: 05/08/2009] [Indexed: 02/07/2023]
Abstract
We report on cellular actions of the illicit recreational drug gamma-hydroxybutyrate (GHB) in the brain reward area nucleus accumbens. First, we compared the effects of GHB and the GABA(B) receptor agonist baclofen. Neither of them affected the membrane currents of medium spiny neurons in rat nucleus accumbens slices. GABAergic and glutamatergic synaptic potentials of medium spiny neurons, however, were reduced by baclofen but not GHB. These results indicate the lack of GHB as well as postsynaptic GABA(B) receptors, and the presence of GHB insensitive presynaptic GABA(B) receptors in medium spiny neurons. In astrocytes GHB induced intracellular Ca(2+) transients, preserved in slices from GABA(B) receptor type 1 subunit knockout mice. The effects of tetrodotoxin, zero added Ca(2+) with/without intracellular Ca(2+) store depletor cyclopiazonic acid or vacuolar H-ATPase inhibitor bafilomycin A1 indicate that GHB-evoked Ca(2+) transients depend on external Ca(2+) and intracellular Ca(2+) stores, but not on vesicular transmitter release. GHB-induced astrocytic Ca(2+) transients were not affected by the GHB receptor-specific antagonist NCS-382, suggesting the presence of a novel NCS-382-insensitive target for GHB in astrocytes. The activation of astrocytes by GHB implies their involvement in physiological actions of GHB. Our findings disclose a novel profile of GHB action in the nucleus accumbens. Here, unlike in other brain areas, GHB does not act on GABA(B) receptors, but activates an NCS-382 insensitive GHB-specific target in a subpopulation of astrocytes. The lack of either post- or presynaptic effects on medium spiny neurons in the nucleus accumbens distinguishes GHB from many drugs and natural rewards with addictive properties and might explain why GHB has only a weak reinforcing capacity.
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Affiliation(s)
- T Molnár
- Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Pusztaszeri út 59-67.1025, Budapest, Hungary
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21
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Abstract
INTRODUCTION Benzodiazepine treatment of life-threatening gamma-hydroxybutyrate (GHB) withdrawal is frequently unsatisfactory. Animal studies suggest strongly that treatment with GABA(B) agonists, such as baclofen, will be a more effective strategy. METHODS A case report from the medical intensive care unit (ICU) of the university tertiary care hospital. RESULTS A 61-year-old woman was admitted to the medical ICU for severe withdrawal symptoms from chronic GHB use. This manifested as delirium, tremor, and seizures despite only small decreases in GHB dose and treatment with benzodiazepines. The addition of baclofen allowed the rapid sequential decreases in the GHB dose without seizure or delirium and resulted in long-term improvement of her tremor. CONCLUSIONS Baclofen, a GABA(B) agonist, may be a useful agent in the treatment of severe GHB withdrawal.
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Affiliation(s)
- Jennifer L LeTourneau
- Division of Pulmonary & Critical Care Medicine and Center for Intensive Care Research, Department of Medicine, Oregon Health & Science University, Biomedical Research Building (UHN-67), 3181 SW Sam Jackson Park Road, Portland, OR 97239-3098, USA
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22
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Ulrich D, Besseyrias V, Bettler B. Functional mapping of GABA(B)-receptor subtypes in the thalamus. J Neurophysiol 2007; 98:3791-5. [PMID: 17881477 DOI: 10.1152/jn.00756.2007] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The thalamus plays an important role in attention mechanisms and the generation of brain rhythms. gamma-Aminobutyric acid type B (GABA(B)) receptors are known to regulate the main output neurons of the thalamus, the thalamocortical relay (TCR) cells. However, the contributions of the two predominant GABA(B)-receptor subtypes, GABA(B(1a,2)) and GABA(B(1b,2)), to the control of TCR cell activity are unknown. Here, we used genetic and electrophysiological methods to investigate subtype-specific GABA(B) effects at the inputs to TCR cells. We found that mainly GABA(B(1a,2)) receptors inhibit the release of glutamate from corticothalamic fibers impinging onto TCR cells. In contrast, both GABA(B(1a,2)) and GABA(B(1b,2)) receptors efficiently inhibit the release of GABA from thalamic reticular nucleus (TRN) neurons onto TCR neurons. Likewise, both GABA(B(1a,2)) and GABA(B(1b,2)) receptors efficiently activate somatodendritic K(+) currents in TCR cells. In summary, our data show that GABA(B(1b,2)) receptors cannot compensate for the absence of GABA(B(1a,2)) receptors at glutamatergic inputs to TCR cells. This shows that the predominant association of GABA(B(1a,2)) receptors with glutamatergic terminals is a feature that is preserved at several brain synapses. Furthermore, our data indicate that the cognitive deficits observed with mice lacking GABA(B(1a,2)) receptors could to some extent relate to attention deficits caused by disinhibited release of glutamate onto TCR neurons.
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Affiliation(s)
- Daniel Ulrich
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, University of Basel, Basel, Switzerland.
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23
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Lyon RC, Johnston SM, Watson DG, McGarvie G, Ellis EM. Synthesis and catabolism of gamma-hydroxybutyrate in SH-SY5Y human neuroblastoma cells: role of the aldo-keto reductase AKR7A2. J Biol Chem 2007; 282:25986-92. [PMID: 17591773 DOI: 10.1074/jbc.m702465200] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
gamma-Hydroxybutyrate (GHB) is an endogenous metabolite synthesized in the brain. There is strong evidence to suggest that GHB has an important role as a neurotransmitter or neuromodulator. The human aldo-keto reductase AKR7A2 has been proposed previously to catalyze the NADPH-dependent reduction of succinic semialdehyde (SSA) to GHB in human brain. In this study we have used RNA interference to evaluate the role of AKR7A2 in GHB biosynthesis in human neuroblastoma SH-SY5Y cells. Quantitative reverse transcription-PCR analysis and immunoblotting revealed that short interfering RNA molecules directed against AKR7A2 led to a significant reduction in both AKR7A2 transcript and protein levels 72 h post-transfection. We have shown that reduced expression of AKR7A2 results in a 90% decrease in SSA reductase activity of cell extracts. Furthermore, we have shown using gas chromatography-mass spectrometry that a decrease in the level of AKR7A2 was paralleled with a significant reduction in intracellular GHB concentration. This provides conclusive evidence that AKR7A2 is the major SSA reductase in these cells. In contrast, short interfering RNA-dependent reduction in AKR7A2 levels had no effect on the GHB dehydrogenase activity of the extracts, and inhibitor studies suggest that another enzyme characteristic of an NAD-dependent alcohol dehydrogenase may be responsible for catalyzing this reverse reaction. Together these findings delineate pathways for GHB metabolism in the brain and will enable a better understanding of the relationship between GHB biosynthesis and catabolism in disease states and in drug overdose.
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Affiliation(s)
- Robert C Lyon
- Strathclyde Institute of Pharmacy and Biomedical Sciences, Univesity of Strathclyde, Glasgow G1 1XW, United Kingdom
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24
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Wu Y, Chan KFY, Eubanks JH, Guin Ting Wong C, Cortez MA, Shen L, Che Liu C, Perez Velazquez J, Tian Wang Y, Jia Z, Carter Snead O. Transgenic mice over-expressing GABA(B)R1a receptors acquire an atypical absence epilepsy-like phenotype. Neurobiol Dis 2007; 26:439-51. [PMID: 17363260 DOI: 10.1016/j.nbd.2007.01.013] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2006] [Revised: 12/19/2006] [Accepted: 01/28/2007] [Indexed: 11/21/2022] Open
Abstract
In this study, we tested whether over-expressing the GABA(B) receptor R1a subtype in transgenic mouse forebrain neurons would be sufficient to induce spontaneous absence seizures. As hypothesized, these transgenic mice develop spontaneous, recurrent, bilaterally synchronous, 3-6 Hz slow spike and wave discharges between 2 and 4 months of age. These discharges are blocked by ethosuximide and exacerbated by baclofen confirming their absence nature. The discharges occur coincident with absence-like behaviors such as staring, facial myoclonus, and whisker twitching. However, in contrast to typical absence epilepsy models, these mice move during the ictal event, display spike and wave discharges in both thalamocortical and limbic circuitry, exhibit impaired hippocampal synaptic plasticity, and display significantly impaired learning ability. Collectively, these features are more characteristic of the less common but more debilitating atypical form of absence epilepsy. Thus, these data support a role for the GABA(B)R1a receptor subtype in the etiology of atypical absence epilepsy.
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Affiliation(s)
- Ying Wu
- Program in Brain and Behavior, Hospital for Sick Children, University of Toronto, Toronto, ON, Canada
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25
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Velazquez JLP, Huo JZ, Dominguez LG, Leshchenko Y, Snead OC. Typical versus atypical absence seizures: network mechanisms of the spread of paroxysms. Epilepsia 2007; 48:1585-93. [PMID: 17484751 DOI: 10.1111/j.1528-1167.2007.01120.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
PURPOSE Typical absence seizures differ from atypical absence seizures in terms of semiology, EEG morphology, network circuitry, and cognitive outcome, yet have the same pharmacological profile. We have compared typical to atypical absence seizures, in terms of the recruitment of different brain areas. Our initial question was whether brain areas that do not display apparent paroxysmal discharges during typical absence seizures, are affected during the ictal event in terms of synchronized activity, by other, distant areas where seizure activity is evident. Because the spike-and-wave paroxysms in atypical absence seizures invade limbic areas, we then asked whether an alteration in inhibitory processes in hippocampi may be related to the spread seizure activity beyond thalamocortical networks, in atypical seizures. METHODS We used two models of absence seizures in rats: one of typical and the other of atypical absence seizures. We estimated phase synchronization, and evaluated inhibitory transmission using a paired-pulse paradigm. RESULTS In typical absence seizures, we observed an increase in synchronization between hippocampal recordings when spike-and-wave discharges occurred in the cortex and thalamus. This indicates that seizure activity in the thalamocortical circuitry enhances the propensity of limbic areas to synchronize, but is not sufficient to drive hippocampal circuitry into a full paroxysmal discharge. Lower paired-pulse depression was then found in hippocampus of rats that displayed atypical absence seizures. CONCLUSIONS These observations suggest that circuitries in brain areas that do not display apparent seizure activity become synchronized as seizures occur within thalamocortical circuitry, and that a weakened hippocampal inhibition may predispose to develop synchronization into full paroxysms during atypical absence seizures.
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Affiliation(s)
- Jose L Perez Velazquez
- Programme for Neuroscience and Mental Health and Division of Neurology, Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada.
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26
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Stewart LS, Bercovici E, Shukla R, Serbanescu I, Persad V, Mistry N, Cortez MA, Snead OC. Daily rhythms of seizure activity and behavior in a model of atypical absence epilepsy. Epilepsy Behav 2006; 9:564-72. [PMID: 17030024 DOI: 10.1016/j.yebeh.2006.08.019] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/28/2006] [Revised: 08/28/2006] [Accepted: 08/29/2006] [Indexed: 10/24/2022]
Abstract
We studied daily rhythms of chronic seizure activity and behavior in adult rats and mice treated with the cholesterol biosynthesis inhibitor AY-9944 (AY) during early postnatal development. Chronic atypical absence seizures were verified in the AY-treated animals by the presence of spontaneous 5- to 6-Hz slow spike-wave discharges (SSWDs) in the neocortex. General behavioral activity, as measured by total movements (TM), movement time (MT), ambulatory movement time (AMT), time spent in center of arena (CT), jumps (JFP), and rotational behavior (TURNS), were continuously recorded under a 12-hour light:12-hour dark photocycle. The average SSWD duration in AY-treated rats varied daily, with two peaks occurring at approximately dark phase and light phase onset. Mice treated with AY exhibited significant increases in all behavioral measures during the light and dark phases, with the exception of light-phase CT, which did not differ from that of controls. Consequently, the daily rhythm of total behavioral activity (TM) exhibited a significantly higher mean oscillation (mesor) and amplitude without evidence of phase shift compared with the TM rhythm of controls. The occurrence of SSWD activity in the AY model appears to be subject to regulation by biological timing mechanisms and, furthermore, associated with motor hyperactivity that does not alter the timing of behavioral rhythmicity.
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Affiliation(s)
- Lee S Stewart
- Brain and Behavior Research Program, The Hospital for Sick Children, Toronto, Ont., Canada
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27
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Molnár T, Fekete EK, Kardos J, Simon-Trompler E, Palkovits M, Emri Z. Metabolic GHB precursor succinate binds to gamma-hydroxybutyrate receptors: characterization of human basal ganglia areas nucleus accumbens and globus pallidus. J Neurosci Res 2006; 84:27-36. [PMID: 16673403 DOI: 10.1002/jnr.20867] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Binding of the metabolic gamma-hydroxybutyrate (GHB) precursor succinate to NCS-382-sensitive [3H]GHB-labeled sites in crude synaptosomal or purified synaptic membrane fractions prepared from the human nucleus accumbens (NA), globus pallidus (GP) and rat forebrain has been shown. This site can be characterized by binding of ethyl hemisuccinate and gap-junction blockers, including carbenoxolone hemisuccinate and beta-GRA. There was no significant binding interaction between GABAB receptor ligands (CGP 55845, (R)-baclofen) and these [3H]GHB-labeled sites. GHB, NCS-382 and succinate binding profile of [3H]GHB-labeled sites in rat forebrain, human NA or GP synaptic membranes were similar. The synaptic fraction isolated from the rat forebrain was characterized by GHB binding inhibition constants: Ki,NCS-382 = 1.2 +/- 0.2 microM, Ki,GHB = 1.6 +/- 0.3 microM and Ki,SUCCINATE = 212 +/- 66 microM. In crude membranes containing mainly extrasynaptic membranes, distinct GHB and GABAB receptor sites were found in the NA. By contrast, extrasynaptic GABAB receptor sites of rat forebrain and GP were GHB- and succinate-sensitive, respectively. The heterogeneity of GABAB sites found in native membranes indicates GABAB receptor-dependent differences in GHB action. Based on these findings, we suggest that succinate (and possibly drugs available as succinate salt derivatives) can mimic some of the actions of GHB.
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Affiliation(s)
- Tünde Molnár
- Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, HAS, Budapest, Hungary
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28
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Buzzi A, Wu Y, Frantseva MV, Perez Velazquez JL, Cortez MA, Liu CC, Shen LQ, Gibson KM, Snead OC. Succinic Semialdehyde Dehydrogenase Deficiency: GABAB receptor-mediated function. Brain Res 2006; 1090:15-22. [PMID: 16647690 DOI: 10.1016/j.brainres.2006.02.131] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2005] [Revised: 02/04/2006] [Accepted: 02/26/2006] [Indexed: 11/25/2022]
Abstract
The succinic semialdehyde dehydrogenase (SSADH) null mouse (SSADH(-/-)) represents a viable animal model for human SSADH deficiency and is characterized by markedly elevated levels of both gamma-hydroxybutyric acid (GHB) and gamma-aminobutyric acid (GABA) in brain, blood, and urine. In physiological concentrations, GHB acts at the GHB receptor (GHBR), but in high concentrations such as those observed in the brains of children with SSADH deficiency, GHB is thought to be a direct agonist at the GABABR receptor (GABABR). We tested the hypothesis that both GHBR and GABABR-mediated function are perturbed in SSADH deficiency. Therefore, we examined the high affinity binding site for GHB as well as the expression and function of the GABABR in mutant mice made deficient in SSADH (SSADH(-/-)). There was a significant decrease in binding of the specific GABABR antagonist, [3H]CGP-54626A at postnatal day (PN)7 and PN14 in SSADH(-/-) when compared to wild type control animals (SSADH(+/+)), particularly in hippocampus. GABABR-mediated synaptic potentials were decreased in SSADH(-/-). Immunoblot analysis of GABABR1a, R1b, and R2 in SSADH(-/-) indicated a trend towards a region-specific and time-dependent decrease of GABABR subunit protein expression. There was no difference between SSADH(-/-) and wild type in binding of either [3H]GHB or a specific GHBR antagonist to the GHBR. These data suggest that the elevated levels of GABA and GHB that occur in SSADH(-/-) lead to a use-dependent decrease in GABABR-mediated function and raise the possibility that this GHB- and GABA-induced perturbation of GABABR could play a role in the pathogenesis of the seizures and mental retardation observed in SSADH deficiency.
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MESH Headings
- Animals
- Binding Sites/genetics
- Brain/enzymology
- Brain/physiopathology
- Brain Chemistry/genetics
- Brain Diseases, Metabolic, Inborn/enzymology
- Brain Diseases, Metabolic, Inborn/genetics
- Brain Diseases, Metabolic, Inborn/physiopathology
- Disease Models, Animal
- GABA Antagonists/pharmacology
- Hydroxybutyrates/metabolism
- Mice
- Mice, Knockout
- Protein Subunits/genetics
- Receptors, GABA-B/genetics
- Receptors, GABA-B/metabolism
- Succinate-Semialdehyde Dehydrogenase/deficiency
- Succinate-Semialdehyde Dehydrogenase/genetics
- Synaptic Transmission/drug effects
- Synaptic Transmission/genetics
- Up-Regulation/genetics
- gamma-Aminobutyric Acid/metabolism
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Affiliation(s)
- Andrea Buzzi
- Brain and Behavior Program, Faculty of Medicine, University of Toronto, ON, Canada
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29
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Abstract
Spike-wave seizures are often considered a relatively "pure" form of epilepsy, with a uniform defect present in all patients and involvement of the whole brain homogeneously. Here, we present evidence against these common misconceptions. Rather than a uniform disorder, spike-wave rhythms arise from the normal inherent network properties of brain excitatory and inhibitory circuits, where they can be provoked by many different insults in several different brain networks. Here we discuss several different cellular and molecular mechanisms that may contribute to the generation of spike-wave seizures, particularly in idiopathic generalized epilepsy. In addition, we discuss growing evidence that electrical, neuroimaging, and molecular changes in spike-wave seizures do not involve the entire brain homogeneously. Rather, spike-wave discharges occur selectively in some thalamocortical networks, while sparing others. It is hoped that improved understanding of the heterogeneous defects and selective brain regions involved will ultimately lead to more effective treatments for spike-wave seizures.
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Affiliation(s)
- Hal Blumenfeld
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06520-8018, USA.
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Affiliation(s)
- O Carter Snead
- Department of Pediatrics, University of Toronto, and the Division of Neurology and the Brain and Behavior Research Program, Hospital for Sick Children, Toronto, ON, Canada
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31
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Cortez MA, Wu Y, Gibson KM, Snead OC. Absence seizures in succinic semialdehyde dehydrogenase deficient mice: a model of juvenile absence epilepsy. Pharmacol Biochem Behav 2005; 79:547-53. [PMID: 15582027 DOI: 10.1016/j.pbb.2004.09.008] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/17/2004] [Revised: 08/31/2004] [Accepted: 09/06/2004] [Indexed: 11/27/2022]
Abstract
The succinic semialdehyde dehydrogenase (SSADH) null mouse represents a viable animal model for human SSADH deficiency and is characterized by markedly elevated levels of both gamma-hydroxybutyric acid (GHB) and gamma-aminobutyric acid (GABA) in brain, blood, and urine. GHB is known to induce absence-like seizures and absence seizures have been reported to occur in children with SSADH deficiency. We tested the hypothesis that the phenotype of the SSADH(-/-) mouse shows absence-like seizures because of the inordinately high levels of GHB in the brain of this mutant animal. Sequential electrocorticographic (ECoG) and prolonged video ECoG recordings from chronically implanted electrodes were done on SSADH(-/-), SSADH(+/-), and SSADH(+/+) mice from postnatal day (P) 10 to (P) 21. Spontaneous, recurrent absence-like seizures appeared in the SSADH(-/-) during the second week of life and evolved into generalized convulsive seizures late in the third week of life that were associated with an explosive onset of status epilepticus which was lethal. The seizures in SSADH null mice were consistent with typical absence seizures in rodent with 7 Hz spike-and-wave discharge (SWD) recorded from thalamocortical circuitry, the onset/offset of which was time-locked with ictal behavior characterized by facial myoclonus, vibrissal twitching and frozen immobility. The absence seizures became progressively more severe from P14 to 18 at which time they evolved into myoclonic and generalized convulsive seizures that progressed into a lethal status epilepticus. The absence seizures in SSADH(-/-) were abolished by ethosuximide (ETX) and the GABA(B)R antagonist CGP 35348. The seizure phenotype in the SSADH(-/-) recapitulates that observed in human SSADH deficiency. Hence, SSADH(-/-) may be used to investigate the molecular mechanisms that underpin the pathogenesis of absence and generalized tonic-clonic seizures associated with SSADH deficiency. As well, the SSADH(-/-) may represent a unique animal model of the transition from absence to myoclonic and generalized convulsive seizures that is observed in up to 80% of patients with juvenile absence epilepsy.
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Affiliation(s)
- M A Cortez
- Division of Neurology, The Hospital for Sick Children, 555 University Avenue, Toronto, ON, M5G 1X8, Canada
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Wu Y, Ali S, Ahmadian G, Liu CC, Wang YT, Gibson KM, Calver AR, Francis J, Pangalos MN, Carter Snead O. Gamma-hydroxybutyric acid (GHB) and gamma-aminobutyric acidB receptor (GABABR) binding sites are distinctive from one another: molecular evidence. Neuropharmacology 2005; 47:1146-56. [PMID: 15567424 DOI: 10.1016/j.neuropharm.2004.08.019] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2004] [Revised: 07/26/2004] [Accepted: 08/17/2004] [Indexed: 10/26/2022]
Abstract
gamma-Hydroxybutyric Acid (GHB) is thought to be a weak partial agonist at the gamma-aminobutyric acid(B) Receptor (GABA(B)R), but the precise relationship of the GHB receptor (GHBR) to the GABA(B)R remains unclear. In order to test the hypothesis that the GHBR is not identical to the GABA(B)R, we conducted two groups of experiments. First, GABA(B)R subtype 1 (R1) and/or subtype 2 (R2) were over expressed in HEK 293 cells and membrane binding studies on the transfected cells done using [(3)H]GHB and [(3)H] (2E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene) ethanoic acid ([(3)H]NCS-382). The latter is a specific antagonist at the GHB binding site. Second, [(3)H]GHB and [(3)H]NCS-382 autoradiographic binding studies were done on the brains of mice in which the gene for GABA(B)R1a was deleted. Such mice do not have a functioning GABA(B)R. There was no detectable specific [(3)H]GHB or [(3)H]NCS-382 binding in HEK 293 cells transfected with GABA(B)R1, R2, or R1/R2. Binding to [(3)H]CGP54626A, a high affinity GABA(B)R antagonist, was absent in GABA(B)R1a(-/-) mice. There was no difference in [(3)H]NCS-382 binding observed in the brains of GABA(B)R1a(-/-), GABA(B)R1a(+/-) or GABA(B)R1a(+/+) mice. Specific [(3)H]GHB binding was observed in the brain of GABA(B)R1a(-/-) mice but was significantly lower than in wild type mice. These data support the hypothesis that the GHB binding site is separate and distinct from the GABA(B)R.
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Affiliation(s)
- Ying Wu
- Brain and Behavior Program, Hospital for Sick Children, University of Toronto, Toronto, ON, Canada M5G 1X8
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Ahmad S, Fowler LJ, Whitton PS. Effects of combined lamotrigine and valproate on basal and stimulated extracellular amino acids and monoamines in the hippocampus of freely moving rats. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 2005; 371:1-8. [PMID: 15660242 DOI: 10.1007/s00210-004-1008-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Received: 03/19/2004] [Accepted: 11/17/2004] [Indexed: 10/25/2022]
Abstract
The antiepileptic drugs sodium valproate (VPA) and lamotrigine (LTG) are increasingly used in combination in patients in whom monotherapy has failed to control seizures. Although these drugs are known to interact pharmacokinetically, several authors have proposed a pharmacodynamic interaction between the two. In order to investigate this we have studied the effects of combined treatment with LTG and VPA on basal and stimulated extracellular aspartate (ASP), glutamate (GLU), taurine (TAU), gamma amino butyric acid (GABA), 5-hydroxytryptamine (5-HT) and dopamine (DA) release in the hippocampus of freely moving rats using microdialysis. Additionally, we measured the possible effect of VPA on LTG in plasma, whole brain and dialysates. Neither LTG (10 mg/kg) nor VPA (300 mg/kg) given alone significantly altered basal levels of ASP, GLU or TAU. When given together, however, the two drugs significantly reduced extracellular ASP and GLU while increasing TAU levels. In the case of GABA, LTG was without effect on basal levels of the transmitter, but these increased following VPA and this persisted with both drugs. When transmitter release was stimulated by 50 muM veratridine, marked increases in the release of all amino acids occurred and this was decreased by LTG in all cases. VPA alone only altered GABA release, increasing it by approximately the same extent as basal GABA. For all of the amino acids studied, however, VPA reversed the decreases in release seen after LTG. VPA and LTG increased and decreased respectively basal 5-HT and DA. When given together the increase in extracellular 5-HT was greatly prolonged, but no effect on DA release was seen. When 5-HT release was evoked by veratridine this was increased by VPA and no other treatment. With DA, however, neither drug alone altered evoked release, but the two combined led to a marked increase. Co-administration of VPA with LTG showed no significant effect of this combination on LTG in any of the three compartments studied indicating that in this case a significant pharmacokinetic contribution to our findings is unlikely, which suggests that there is a probable pharmacodynamic interaction of the two drugs.
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Affiliation(s)
- Shagufta Ahmad
- Department of Pharmacology, School of Pharmacy, 29-39 Brunswick Square, London, WC1N 1AX, UK
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Wong CGT, Chan KFY, Gibson KM, Snead OC. Gamma-hydroxybutyric acid: neurobiology and toxicology of a recreational drug. ACTA ACUST UNITED AC 2004; 23:3-20. [PMID: 15298489 DOI: 10.2165/00139709-200423010-00002] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
gamma-Hydroxybutyric acid (GHB) is a short-chain fatty acid that occurs naturally in mammalian brain where it is derived metabolically from gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the brain. GHB was synthesised over 40 years ago and its presence in the brain and a number of aspects of its biological, pharmacological and toxicological properties have been elucidated over the last 20-30 years. However, widespread interest in this compound has arisen only in the past 5-10 years, primarily as a result of the emergence of GHB as a major recreational drug and public health problem in the US. There is considerable evidence that GHB may be a neuromodulator in the brain. GHB has multiple neuronal mechanisms including activation of both the gamma-aminobutyric acid type B (GABA(B)) receptor, and a separate GHB-specific receptor. This complex GHB-GABA(B) receptor interaction is probably responsible for the protean pharmacological, electroencephalographic, behavioural and toxicological effects of GHB, as well as the perturbations of learning and memory associated with supra-physiological concentrations of GHB in the brain that result from the exogenous administration of this drug in the clinical context of GHB abuse, addiction and withdrawal. Investigation of the inborn error of metabolism succinic semialdehyde deficiency (SSADH) and the murine model of this disorder (SSADH knockout mice), in which GHB plays a major role, may help dissect out GHB- and GABA(B) receptor-mediated mechanisms. In particular, the mechanisms that are operative in the molecular pathogenesis of GHB addiction and withdrawal as well as the absence seizures observed in the GHB-treated animals.
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Affiliation(s)
- C Guin Ting Wong
- Institute of Medical Sciences, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
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Castelli MP, Pibiri F, Carboni G, Piras AP. A review of pharmacology of NCS-382, a putative antagonist of gamma-hydroxybutyric acid (GHB) receptor. CNS DRUG REVIEWS 2004; 10:243-60. [PMID: 15492774 PMCID: PMC6741708 DOI: 10.1111/j.1527-3458.2004.tb00025.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Gamma-hydroxybutyric acid (GHB), a naturally occurring metabolite of gamma-aminobutyric acid (GABA), has been postulated to act as a specific agonist of GHB receptors and as well as a weak GABA(B) receptor agonist. To date, 6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylideneacetic acid (NCS-382), a semirigid compound structurally related to GHB, is the only compound reported to be an antagonist of the GHB receptor sites. In this article we review the in vivo and in vitro pharmacological properties of NCS-382 and its interaction with GHB and GABA(B) receptors. Binding studies have demonstrated that NCS-382 is a stereoselective ligand for GHB-binding sites, with both, the high and the low component of population, showing the same distribution of GHB receptors. Indeed, this compound did not display affinity for GABA(A), GABA(B), or any other known receptors, while conflicting data have been reported as to its selective antagonist action at GHB receptor. Only a few studies have shown that NCS-382 antagonizes GHB-induced effect, but a re-evaluation of all data reported in the literature suggests that the antagonistic effect of this compound could be due to an indirect action at GABA(B) receptors. As revealed by several behavioral studies, NCS-382 fails to antagonize GHB discriminative stimuli, GHB-induced inhibition of locomotor activity and ataxia or suppression of operant responses. Moreover, it is capable of either eliciting qualitatively similar effects to those of GHB or enhancing some actions of GHB. In addition, the NCS-382-sensitive electrophysiological effects of endogenous and exogenous GHB observed in vivo have not been completely replicated in vitro. The only electrophysiological action of GHB antagonized in vitro by NCS-382 required a previous blockade of GABA(B) receptors. We concluded that NCS-382 is a good ligand but not a selective antagonist for GHB receptor.
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Affiliation(s)
- M Paola Castelli
- B. B. Brodie Department of Neuroscience, University of Cagliari, 09042 Monserrato (CA) Italy.
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Schweitzer P, Roberto M, Madamba SG, Siggins GR. gamma-hydroxybutyrate increases a potassium current and decreases the H-current in hippocampal neurons via GABAB receptors. J Pharmacol Exp Ther 2004; 311:172-9. [PMID: 15152029 DOI: 10.1124/jpet.104.069534] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
gamma-Hydroxybutyrate (GHB) is used for the treatment of alcoholism and to induce absence seizures in animals, but it has also recently emerged as a drug of abuse. In hippocampal neurons, GHB may activate its own putative receptor as well as GABA(B) receptors to affect synaptic transmission. We used voltage-clamp recordings of rat CA1 pyramidal neurons to characterize the postsynaptic conductances affected by GHB and to further clarify the site of GHB action. Low concentrations of GHB (0.1-1 mM) did not affect postsynaptic properties, but 10 mM GHB elicited an outward current at resting potential by augmenting an inwardly rectifying potassium current and concomitantly decreased the hyperpolarization-activated H-current (I(h)). Like GHB, the selective GABA(B)-receptor agonist baclofen (20 microM) increased a potassium current and decreased I(h). In the presence of 10 mM GHB, the baclofen effects were largely occluded. The selective GABA(B) receptor antagonist CGP 55845 [3-N[1-(S)-(3,4-dichlorophenyl)ethyl]amino-2-(S)-hydroxypropyl-p-benzyl-phosphinic acid] blocked the effects of both GHB and baclofen, whereas the putative GHB receptor antagonist NCS-382 [(2E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene ethanoic acid] was ineffective. The GHB and baclofen effects were prevented in the presence of 200 microM barium, indicating that GHB augments a K(+) conductance, probably a G protein-coupled inwardly rectifying K(+) (GIRK) current. The decrease of I(h) by GHB and baclofen was also prevented by barium, suggesting that the diminution of I(h) is secondary to GIRK augmentation. Our results indicate that high GHB levels, which can be reached during abuse or intoxication, activate only GABA(B) receptors and not GHB receptors at the postsynaptic level to augment an inwardly rectifying K(+) current and decrease I(h).
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Affiliation(s)
- Paul Schweitzer
- The Scripps Research Institute, Department of Neuropharmacology, La Jolla, CA 92037, USA.
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Bekri S, Fossoud C, Plaza G, Guenne A, Salomons GS, Jakobs C, Van Obberghen E. The molecular basis of succinic semialdehyde dehydrogenase deficiency in one family. Mol Genet Metab 2004; 81:347-51. [PMID: 15059623 DOI: 10.1016/j.ymgme.2004.01.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2003] [Revised: 01/20/2004] [Accepted: 01/20/2004] [Indexed: 10/26/2022]
Abstract
Succinic semialdehyde dehydrogenase (SSADH) deficiency has predominantly neurological consequences, affecting psychomotor, speech and language development. Recently, two clinical reviews summarized the features of this disease and their relative frequency [Neurology 60 (2003) 1413; Ann. Neurol. 54 (2003) S73]. The molecular genetics of SSADH deficiency is still being explored. We describe the molecular basis of this defect in a Tunisian female child presenting with a mild phenotype. A small scale deletion in exon 10 of the gene led to a frameshift that predicts premature termination of the resulting putative protein. The parents were shown to be heterozygotes for this deletion, supporting its causative role.
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Affiliation(s)
- S Bekri
- Department of Biochemistry, Centre Hospitalier Universitaire de Nice, France.
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