GHB Receptor Research Articles

An Overview of the Putative Structural and Functional Properties of the GHBh1 Receptor through a Bioinformatics Approach.

The neurotransmitter γ-hydroxybutyric acid (GHB) is suggested to be involved in neuronal energy homeostasis processes, but the substance is also used as a recreational drug and as a prescription medication for narcolepsy. GHB has several high-affinity targets in the brain, commonly generalized as the GHB receptor. However, little is known about the structural and functional properties of GHB receptor subtypes. This opinion article discusses the literature on the putative structural and functional properties of the GHBh1 receptor subtype. GHBh1 contains 11 transmembrane helices and at least one intracellular intrinsically disordered region (IDR). Additionally, GHBh1 shows a 100% overlap in amino acid sequence with the Riboflavin (vitamin B2) transporter, which opens the possibility of a possible dual-function (transceptor) structure. Riboflavin and GHB also share specific neuroprotective properties. Further research into the GHBh1 receptor subtype may pave the way for future therapeutic possibilities for GHB.

Treatment of γ-Hydroxybutyrate (GHB) Overdose with the GABAB Antagonist SGS742.

High doses of the partial agonist of the GABA B receptor, γ-hydroxybutyric acid (GHB), causes respiratory depression that can lead to death. Previously, it has been shown that GABAB- receptor antagonism is able to prevent respiratory depression and sedation when inhibitors are pre-administered. In order to treat GHB overdoses, safety and efficacy of a treatment strategy at various times after GHB administration is necessary, in order to more closely replicate a true overdose situation. Preliminary studies developed an assay for SGS742 and determined its pharmacokinetics in rats. The effects of SGS742 on GHB-induced respiratory depression were evaluated when SGS742 administration was delayed 1 and 2 hours after intravenous or oral administration of GHB or γ-butyrolactone, a GHB prodrug. SGS742 reversed GHB-induced respiratory depression in a dose-dependent manner at both time points tested, with no effects on its toxicokinetics. However, some of the dosing paradigms resulted in toxicity in the form of tremors, seizures or abnormal movements. The tremors/seizures occurred in a manner that was dependent on both the dose and timing of SGS742 administration, and were not altered with pretreatment with gabazine, a GABAA receptor inhibitor, and only partially reduced with pretreatment with NCS382, a selective GHB receptor antagonist. Additional studies with a second GABAB antagonist SCH50911 demonstrated similar effects, producing reversal of respiratory depression but producing tremors and abnormal movements. Further studies are necessary in order to identify the potential use of GABAB antagonism as a treatment strategy for GHB overdoses. Significance Statement There is no current treatment for overdoses of the drug of abuse γ-hydroxybutyric acid (GHB). Since the toxicodynamic effects of GHB, including respiratory depression and lethality, are mediated through GABAB receptor agonism, GABAB receptor antagonists may represent a therapeutic strategy to treat overdoses. This study demonstrates that while GABAB receptor antagonists are effective as a pretreatment, they are less effective when administered at times after GHB administration and their administration is also associated with time- and dose-associated toxicity.

Current Insights on the Impact of Gamma-Hydroxybutyrate (GHB) Abuse.

Recreational gamma-hydroxybutyrate (GHB) use, although less common than other substance use, is increasingly recognised and is over-represented in emergency toxicology presentations. This narrative review summarizes GHB pharmacology, current patterns of use, potential harms and management of GHB toxicity and withdrawal. There is a complex interplay between GHB and GABA as GHB is both a prodrug and metabolite of GABA and GHB activates both GHB and GABA receptors. GHB is rapidly absorbed, with effects seen within minutes of ingestion. Metabolism is non-linear at higher doses. While GHB is listed as a controlled substance, its precursor’s gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD) are easily available as both have industrial applications. National surveys indicate low rates of GHB use, with identification of high-risk populations in men who have sex with men and polysubstance users. GHB is one of the three drugs most commonly used in chemsex. GHB is often co-ingested with other interacting psychoactive substances. Acute toxicity is dose-dependent, and management is supportive care. Withdrawal management is generally with benzodiazepines with addition of baclofen for more severe withdrawal. Barbiturates may have a role. Titration and tapering of pharmaceutical GHB is commonly used in the Netherlands. Complicated withdrawal with delirium may require intensive care and treatment with intravenous sedation. There are high rates of relapse after withdrawal and medications for longer-term management are currently being investigated. Chronic use is associated with poorer mental, physical and sexual health, social dysfunction and poor work performance. Laboratory detection is complicated as GHB is an endogenous substance with a short half-life, and therefore not often routinely assayed in the clinical setting. Future research should focus on improving GHB detection and management of GHB withdrawal and dependence. Interventions specific for high-risk groups should be developed and assessed.

Reader Response: Novel ALDH5A1 Variants and Genotype: Phenotype Correlation in SSADH Deficiency

In a recent article by DiBacco et al.,1 the authors reported novel pathologic ALDH5A1 variants in patients with succinic semialdehyde dehydrogenase (SSADH) deficiency. The novel pathologic variants caused clinical phenotyping disease in the participants. In these patients, the neurologic and psychiatric disorders were induced by a dysfunction of the GABAergic system, induced by an increase in gamma hydroxybutyric acid (GHB) levels. In these phenotype correlations of patients with novel genotype SSADH deficiency, the authors found an overall correlation between age and severity of epilepsy and presence of obsessive-compulsive disorder (OCD). They elegantly illustrated that epilepsy and OCD were more significantly prevalent in the adolescent/adult than in pediatric participants. This observation could derive from different expression of GHB receptors over the years.2 Furthermore, the GHB—involved in GABAergic and dopaminergic neurotransmissions2—could have an effect not only at the neuron level but also at the astrocyte level.2,3 Prolonged exposure to GHD caused an alteration of activity of astrocytes.3 Astroglial dysfunctions contribute to the pathogenesis of several neurologic and psychiatric disorders.4,5 These conditions—in particular an alteration of gliotransmission—could explain the different pathologic expressiveness of neuropsychiatric disorders over the years in these patients.

γ-Hydroxybutyric Acid: Pharmacokinetics, Pharmacodynamics, and Toxicology.

Gamma-hydroxybutyrate (GHB) is a short-chain fatty acid present endogenously in the brain and used therapeutically for the treatment of narcolepsy, as sodium oxybate, and for alcohol abuse/withdrawal. GHB is better known however as a drug of abuse and is commonly referred to as the "date-rape drug"; current use in popular culture includes recreational "chemsex," due to its properties of euphoria, loss of inhibition, amnesia, and drowsiness. Due to the steep concentration-effect curve for GHB, overdoses occur commonly and symptoms include sedation, respiratory depression, coma, and death. GHB binds to both GHB and GABAB receptors in the brain, with pharmacological/toxicological effects mainly due to GABAB agonist effects. The pharmacokinetics of GHB are complex and include nonlinear absorption, metabolism, tissue uptake, and renal elimination processes. GHB is a substrate for monocarboxylate transporters, including both sodium-dependent transporters (SMCT1, 2; SLC5A8; SLC5A12) and proton-dependent transporters (MCT1-4; SLC16A1, 7, 8, and 3), which represent significant determinants of absorption, renal reabsorption, and brain and tissue uptake. This review will provide current information of the pharmacology, therapeutic effects, and pharmacokinetics/pharmacodynamics of GHB, as well as therapeutic strategies for the treatment of overdoses. Graphical abstract.

γ-Hydroxybutyrate does not mediate glucose inhibition of glucagon secretion

Hypersecretion of glucagon from pancreatic α-cells strongly contributes to diabetic hyperglycemia. Moreover, failure of α-cells to increase glucagon secretion in response to falling blood glucose concentrations compromises the defense against hypoglycemia, a common complication in diabetes therapy. However, the mechanisms underlying glucose regulation of glucagon secretion are poorly understood and likely involve both α-cell–intrinsic and intraislet paracrine signaling. Among paracrine factors, glucose-stimulated release of the GABA metabolite γ-hydroxybutyric acid (GHB) from pancreatic β-cells might mediate glucose suppression of glucagon release via GHB receptors on α-cells. However, the direct effects of GHB on α-cell signaling and glucagon release have not been investigated. Here, we found that GHB (4–10 μm) lacked effects on the cytoplasmic concentrations of the secretion-regulating messengers Ca2+ and cAMP in mouse α-cells. Glucagon secretion from perifused mouse islets was also unaffected by GHB at both 1 and 7 mm glucose. The GHB receptor agonist 3-chloropropanoic acid and the antagonist NCS-382 had no effects on glucagon secretion and did not affect stimulation of secretion induced by a drop in glucose from 7 to 1 mm. Inhibition of endogenous GHB formation with the GABA transaminase inhibitor vigabatrin also failed to influence glucagon secretion at 1 mm glucose and did not prevent the suppressive effect of 7 mm glucose. In human islets, GHB tended to stimulate glucagon secretion at 1 mm glucose, an effect mimicked by 3-chloropropanoic acid. We conclude that GHB does not mediate the inhibitory effect of glucose on glucagon secretion.

Sodium oxybate (Xyrem) treatment in severely sleep-deprived child with Epstein–Barr virus encephalitis with lesion of sleep-wake regulation system: a case report

We present the effect of exogenous sodium oxybate (GHB) in a severely tormented boy unable to sleep and unable to be anesthetized due to a lesion in the sleep initiation system involving the tracks between the ventrolateral preoptic nucleus and the reticular system. We bypassed the system by using sodium oxybate's effect on the cortical GHB and GABAB receptors involved in the initiation and maintenance of sleep.

Discovery of 2-(Imidazo[1,2- b]pyridazin-2-yl)acetic Acid as a New Class of Ligands Selective for the γ-Hydroxybutyric Acid (GHB) High-Affinity Binding Sites.

Gabazine, a γ-aminobutyric acid type A (GABAA) receptor antagonist, has previously been reported to inhibit the binding of [3H]NCS-382, a representative ligand of the high-affinity binding site for the neuroactive substance γ-hydroxybutyric acid (GHB). We herein report a study on the structural determinants of gabazine for binding to (i) the orthosteric binding site of the GABAA receptor and (ii) the high-affinity GHB binding site. Expanding the structural diversity of available ligands for the high-affinity GHB binding sites, this study identified 2-(imidazo[1,2- b]pyridazin-2-yl)acetic acid as a novel ligand-scaffold leading to analogues with relatively high affinity ( Ki 0.19-2.19 μM) and >50 times selectivity for the [3H]NCS-382 over [3H]muscimol binding sites. These results highlight that gabazine interacts with the high-affinity GHB and orthosteric GABAA receptor binding sites differently and that distinct analogues can be generated to select between them. To facilitate further in vivo studies, a promising prodrug candidate for brain delivery was identified.

GHB receptors - a new trend in psychopharmacology?

Abstract Introduction: Gamma-hydroxybutyric acid (GHB) is commonly known as a recreation drug or the so-called “date rape drug”. It is also used in medicine to treat narcolepsy and alcohol addiction. GHB has an affinity for two types of receptors: GABAB and the relatively recently discovered GHB receptors. GHB receptors were first cloned in 2003 in mice and then in 2007 in humans. So far, evidence has been presented for their impact on dopaminergic transmission, which may imply that they play a role in the pathogenesis of diseases such as schizophrenia. At the same time, it has been demonstrated that benzamide antipsychotic drugs have an affinity for GHB receptors, which is why it is postulated that some of the effects of these drugs may result precisely from this affinity. Aim: The study presents the current state of knowledge about GHB receptors and their potential role in the pathogenesis of schizophrenia, and discusses drugs which show an affinity for this receptor. Material and method: The literature review was based on a search of articles indexed between 1965 and 2018 in Medline, Google Scholar, ScienceDirect and Research Gate databases. The following search terms were used: GHB receptor, GHB, sulpiride, and amisulpride. Result and discussion: 1. It is possible that GHB receptors are involved in the pathogenesis of schizophrenia, although more research is needed in this area. 2. Part of the effects of some benzamide antipsychotic drugs (such as amisulpride) may be due to their affinity for GHB receptors.

Succinic semialdehyde dehydrogenase deficiency, a disorder of GABA metabolism: an update on pharmacological and enzyme-replacement therapeutic strategies.

We present an update to the status of research on succinic semialdehyde dehydrogenase (SSADH) deficiency (SSADHD), a rare disorder of GABA metabolism. This is an unusual disorder featuring the accumulation of both GABA and its neuromodulatory analog, gamma-hydroxybutyric acid (GHB), and recent studies have advanced the potential clinical application of NCS-382, a putative GHB receptor antagonist. Animal studies have provided proof-of-concept that enzyme replacement therapy could represent a long-term therapeutic option. The characterization of neuronal stem cells (NSCs) derived from aldehyde dehydrogenase 5a1-/- (aldh5a1-/-) mice, the murine model of SSADHD, has highlighted NSC utility as an in vitro system in which to study therapeutics and associated toxicological properties. Gene expression analyses have revealed that transcripts encoding GABAA receptors are down-regulated and may remain largely immature in aldh5a1-/- brain, characterized by excitatory as opposed to inhibitory outputs, the latter being the expected action in the mature central nervous system. This indicates that agents altering chloride channel activity may be therapeutically relevant in SSADHD. The most recent therapeutic prospects include mTOR (mechanistic target of rapamycin) inhibitors, drugs that have received attention with the elucidation of the effects of elevated GABA on autophagy. The outlook for novel therapeutic trials in SSADHD continues to improve.

Toxicologic/transport properties of NCS-382, a γ-hydroxybutyrate (GHB) receptor ligand, in neuronal and epithelial cells: Therapeutic implications for SSADH deficiency, a GABA metabolic disorder

We report the in vitro assessment of pharmacotoxicity for the high-affinity GHB receptor ligand, NCS-382, using neuronal stem cells derived from mice with a targeted deletion of the aldehyde dehydrogenase 5a1 gene (succinic semialdehyde dehydrogenase(SSADH)-deficient mice). These animals represent a phenocopy of the human disorder of GABA metabolism, SSADH deficiency, that metabolically features accumulation of both GABA and the GABA-analog γ-hydroxybutyric acid in conjunction with a nonspecific neurological phenotype. We demonstrate for the first time using MDCK cells that NCS-382 is actively transported and capable of inhibiting GHB transport. Following these in vitro assays with in vivo studies in aldh5a1−/− mice, we found the ratio of brain/liver GHB to be unaffected by chronic NCS-382 administration (300mg/kg; 7 consecutive days). Employing a variety of cellular parameters (reactive oxygen and superoxide species, ATP production and decay, mitochondrial and lysosomal number, cellular viability and necrosis), we demonstrate that up to 1mM NCS-382 shows minimal evidence of pharmacotoxicity. As well, studies at the molecular level indicate that the effects of NCS-382 at 0.5mM are minimally toxic as evaluated using gene expression assay. The cumulative data provides increasing confidence that NCS-382 could eventually be considered in the therapeutic armament for heritable SSADH deficiency.

In vitro toxicological evaluation of NCS-382, a high-affinity antagonist of γ-hydroxybutyrate (GHB) binding

γ-Hydroxybutyric acid (GHB), a minor metabolite of the inhibitory neurotransmitter GABA, can accumulate to significant concentrations in the heritable disorder of GABA degradation, succinic semialdehyde dehydrogenase (SSADH) deficiency (SSADHD). Moreover, GHB may be employed in therapeutic settings (treatment of narcolepsy), as well as instances of illicit activity, including acquaintance sexual assault and the induction of euphoria. High-affinity binding sites for GHB in the brain have been identified, although the absolute identity of these receptors remains unclear. Pharmacological antagonism of GHB binding may have multiple instances of therapeutic relevance. The high affinity GHB receptor antagonist, NCS-382 (6,7,8,9-tetrahydro-5-hydroxy-5H-benzo-cyclohept-6-ylideneacetic acid) has not been piloted in humans. To address the potential clinical utility of NCS-382, we have piloted initial studies of its toxicology in HepG2 and primary hepatocyte cells. At high dose (0.5mM), NCS-382 showed no capacity for inhibition of microsomal CYPs (CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6 and 3A4) and minimal potential for activation of xenobiotic nuclear receptors. Additional cellular integrity and functional assays (viability, oxidative stress, apoptosis, ATP production) revealed little evidence for cytotoxicity, and a low degree of dysregulation of >370 genes actively engaged in the mediation of cellular toxicity. In vitro testing indicates a low probability of cellular toxicity associated with NCS-382.

A pharmacokinetic evaluation and metabolite identification of the GHB receptor antagonist NCS-382 in mouse informs novel therapeutic strategies for the treatment of GHB intoxication.

Gamma‐aminobutyric acid (GABA) is an endogenous inhibitory neurotransmitter and precursor of gamma‐hydroxybutyric acid (GHB). NCS‐382 (6,7,8,9‐tetrahydro‐5‐hydroxy‐5H‐benzo‐cyclohept‐6‐ylideneacetic acid), a known GHB receptor antagonist, has shown significant efficacy in a murine model of succinic semialdehyde dehydrogenase deficiency (SSADHD), a heritable neurological disorder featuring chronic elevation of GHB that blocks the final step of GABA degradation. NCS‐382 exposures and elimination pathways remain unknown; therefore, the goal of the present work was to obtain in vivo pharmacokinetic data in a murine model and to identify the NCS‐382 metabolites formed by mouse and human. NCS‐382 single‐dose mouse pharmacokinetics were established following an intraperitoneal injection (100, 300, and 500 mg/kg body weight) and metabolite identification was conducted using HPLC‐MS/MS. Kinetic enzyme assays employed mouse and human liver microsomes. Upon gaining an understanding of the NCS‐382 clearance mechanisms, a chemical inhibitor was used to increase NCS‐382 brain exposure in a pharmacokinetic/pharmacodynamic study. Two major metabolic pathways of NCS‐382 were identified as dehydrogenation and glucuronidation. The K m for the dehydrogenation pathway was determined in mouse (K m = 29.5 ± 10.0 μmol/L) and human (K m = 12.7 ± 4.8 μmol/L) liver microsomes. Comparable parameters for glucuronidation were >100 μmol/L in both species. Inhibition of NCS‐382 glucuronidation, in vivo, by diclofenac resulted in increased NCS‐382 brain concentrations and protective effects in gamma‐butyrolactone‐treated mice. These initial evaluations of NCS‐382 pharmacokinetics and metabolism inform the development of NCS‐382 as a potential therapy for conditions of GHB elevation (including acute intoxication & SSADHD).

Improvement in γ-hydroxybutyrate-induced contextual fear memory deficit by systemic administration of NCS-382.

Low, nonsedative doses of γ-hydroxybutyric acid (GHB) produce short-term anterograde amnesia in humans and memory impairments in experimental animals. We have previously shown that acute systemic treatment of GHB in adolescent female rats impairs the acquisition, but not the expression, of contextual fear memory while sparing both the acquisition and the expression of auditory cued fear memory. In the brain, GHB binds to specific GHB-binding sites as well as to γ-aminobutyric acid type B (GABAB) receptors. Although many of the behavioral effects of GHB at high doses have been attributed to its effects on the GABAB receptor, it is unclear which receptor mediates its relatively low-dose memory-impairing effects. The present study examined the ability of the putative GHB receptor antagonist NCS-382 to block the disrupting effects of GHB on fear memory in adolescent rat. Groups of rats received either a single dose of NCS-382 (3–10 mg/kg, intraperitoneally) or vehicle, followed by an injection of either GHB (100 mg/kg, intraperitoneally) or saline. All rats were trained in the fear paradigm, and tested for contextual fear memory and auditory cued fear memory. NCS-382 dose-dependently reversed deficits in the acquisition of contextual fear memory induced by GHB in adolescent rats, with 5 mg/kg of NCS-382 maximally increasing freezing to the context compared with the group administered GHB alone. When animals were tested for cued fear memory, treatment groups did not differ in freezing responses to the tone. These results suggest that low-dose amnesic effects of GHB are mediated by GHB receptors.

P.2.002 Rac1 GTPase and PAK activities in lateral amygdala constrain fear memory formation

COLOMBO, G., R. AGABIO, G. DIAZ, M. FÀ, C. LOBINA, R. REALI AND G. L. GESSA. γ-Hydroxybutyric acid intake in ethanol-preferring sP and -nonpreferring sNP rats. Physiol Behav 64(2) 197–202, 1998. γ-hydroxybutyric acid (GHB) and ethanol share several pharmacological similarities, suggesting that GHB may exert ethanol-like effects in the central nervous system. The present study was designed to test whether selectively bred ethanol-preferring rats would, unlike ethanol-nonpreferring ones, self-administer GHB, consistent with their higher preference for ethanol. Male ethanol-naive Sardinian alcohol-preferring (sP) and Sardinian alcohol-nonpreferring (sNP) rats were used. In Experiment 1, GHB solution (1% (w/v) in water) was initially offered as the sole fluid available for 14 consecutive days and then presented under the two-bottle, free-choice regimen, one bottle containing water and the other the GHB solution, for an additional 14 consecutive days. During the free-choice phase, high preference for GHB and intake of pharmacologically relevant daily doses of GHB developed in both rat lines, presumably because the 14-day no-choice period would unmask the reinforcing properties of GHB and lead to acquisition of GHB preference also in the supposedly less susceptible sNP rats. In Experiment 2, the forced GHB drinking phase was reduced to 3 days. Under the subsequent free-choice regimen, daily GHB preference and intake were initially low in both sP and sNP rats; however, after approximately 10 days, GHB preference and intake in sP rats rose progressively and then stabilized to significantly higher levels than in sNP rats throughout the entire free-choice phase. It is likely that episodic binges of GHB intake occurring during the first 10 days resulted in experiencing the reinforcing properties of GHB by sP but not sNP rats. The results of the present study suggest that a) sP rats are genetically more sensitive to the reinforcing effects of both ethanol and GHB than sNP rats; and b) disclosure of the higher sensitivity of sP rats to the reinforcing effects of GHB is a function of the length of the induction procedure. The results are also discussed in terms of differences in GHB receptors contributing to the predisposition to ethanol preference and avoidance, respectively.

Clinical Evaluation of Gamma Hydroxybutyric Acid (GHB) and its Glucuronide in Biological Matrices of Succinic Semi Aldehyde Dehydrogenase Deficient Patients

Gamma hydroxybutyric acid (GHB), an endogenous metabolite, is an agonist towards both GHB and GABAB receptors. GHB is elevated during illicit drug use and in patients with heritable succinic semialdehyde dehydrogenase (SSADH) deficiency, a disorder of GABA degradation. Previous reports have postulated that the glucuronide conjugate (GHB‐gluc) may represent a urinary biomarker for GHB intoxication. The objective of the present work was to examine the level of GHB‐gluc in SSADH‐deficient patients and its applicability as a potential clinical biomarker. Urine was quantified for GHB and GHB‐gluc on an AB Sciex 6500 mass spectrometer. Semi validation of the urine method was conducted using plasma and cerebrospinal fluid (CSF). SSADH patient urine, plasma and CSF and healthy volunteer control urine and plasma were collected and quantified for GHB and GHB‐gluc using LC‐MS/MS. Absolute quantification of GHB and GHB‐gluc in patient urine samples revealed an inverse correlation between GHB and GHB‐gluc (r2, 0.6; p value<0.05). Relative to control samples, the GHB‐gluc was only moderately elevated in patient samples (~15%). The GHB‐gluc was below the limit of quantification (25 ng/ml) in patient CSF and was not discernible between groups in plasma specimens. This work indicates that GHB‐conjugation may occur primarily in the kidney, or that a fraction of the GHB‐gluc is excreted in the bile.Acknowledgement: The generous support of the SSADH Association (www.ssadh.net) is gratefully acknowledged.

GHB for cataplexy: Possible mode of action.

The sleep disorder narcolepsy is caused by the loss of orexinergic neurones in the lateral hypothalamus. A troublesome symptom of narcolepsy is cataplexy, the sudden loss of muscle tone in response to strong emotions. It can be alleviated by antidepressants and sodium oxybate (γ-hydroxybutyric acid (GHB)). It is likely that the noradrenergic nucleus locus coeruleus (LC) is involved since it is essential for the maintenance of muscle tone, and ceases to fire during cataplectic attacks. Furthermore, alpha-2 adrenoceptors proliferate in the LC in cataplexy, probably due to 'heterologous denervation supersensitivity' resulting from the loss/weakening of the orexinergic input to the LC. This would lead to the sensitization of the autoinhibition mechanism of LC neurones mediated by inhibitory alpha-2 adrenoceptors ('autoreceptors'). Thus the excitatory input from the amygdala to the LC, activated by an emotional stimulus, would lead to the 'switching off' of LC activity via the supersensitive auto-inhibition mechanism. GHB is an agonist at both γ-aminobutyric acid (GABA) GABA (B) and GHB receptors that may be a subtype of an extrasynaptic GABA(A) receptor. GHB may prevent a cataplectic attack by dampening the tone of LC neurones via the stimulation of inhibitory extrasynaptic GABA receptors in the LC, and thus increasing the threshold for autoinhibition.

A critical evaluation of the gamma-hydroxybutyrate (GHB) model of absence seizures.

SummaryTypical 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.

Regional Fos-expression induced by γ-hydroxybutyrate (GHB): Comparison with γ-butyrolactone (GBL) and effects of co-administration of the GABAB antagonist SCH 50911 and putative GHB antagonist NCS-382

γ-Hydroxybutyrate (GHB) has a complex array of neural actions that include effects on its own high-affinity GHB receptor, the release of neuroactive steroids, and agonist actions at GABAA and GABAB receptors. We previously reported partial overlap in the c-Fos expression patterns produced by GHB and the GABAB agonist, baclofen in rats. The present study extends these earlier findings by examining the extent to which GHB Fos expression and behavioral sedation are prevented by (2S)-(+)-5,5-dimethyl-2-morpholineacetic acid (SCH 50911), a GABAB antagonist, and NCS-382, a putative antagonist at the high-affinity GHB receptor. We also compare Fos expression caused by GHB and its precursor γ-butyrolactone (GBL), which is a pro-drug for GHB but lacks the high sodium content of the parent GHB molecule. Both GHB (1000mg/kg) and GBL (600mg/kg) induced rapid sedation in rats that lasted over 90min and caused similar Fos expression patterns, albeit with GBL causing greater activation of the nucleus accumbens (core and shell) and dentate gyrus (granular layer). Pretreatment with SCH 50911 (100mg/kg) partly reversed the sedative effects of GHB and significantly reduced GHB-induced Fos expression in only four regions: the tenia tecta, lateral habenula, dorsal raphe and laterodorsal tegmental nucleus. NCS-382 (50mg/kg) had no effect on GHB-induced sedation or Fos expression. When given alone, both NCS-382 and SCH 50911 increased Fos expression in the bed nucleus of the stria terminalis, central amygdala, parasubthalamic nucleus and nucleus of the solitary tract. SCH 50911 alone affected the Islands of Calleja and the medial, central and paraventricular thalamic nuclei. Overall, this study shows a surprising lack of reversal of GHB-induced Fos expression by two relevant antagonists, both of which have marked intrinsic actions. This may reflect the limited doses tested but also suggests that GHB Fos expression reflects mechanisms independent of GHB and GABAB receptors.

Evaluation of drug–drug interactions of sodium oxybate with diclofenac: Results from a pharmacokinetic/pharmacodynamic study

To evaluate drug–drug interactions between sodium oxybate (SXB) and diclofenac with regard to pharmacokinetics (PK), pharmacodynamics (PD), and safety. SXB is the sodium salt of gamma hydroxybutyrate (GHB), a substrate for the monocarboxylate transporter that may be inhibited by diclofenac, which also binds to GHB receptors in the brain. Healthy volunteers were randomized to SXB + diclofenac placebo, SXB + diclofenac, or SXB placebo + diclofenac in a 3-period, double-blind, crossover design with a 2-day washout between periods. Diclofenac/placebo (50 mg immediate-release) was given qid every 4 h days 1 and 2, and 1 h before and 3 h after the first SXB dose day 3; SXB/placebo was given as two 3 g doses 4 h apart day 3. Blood and urine were sampled at predefined times for noncompartmental PK analysis. PD testing at the end of each treatment period included the Karolinska Sleepiness Scale (KSS), and several automated tests from CDR System (www.bracketglobal.com) including Simple Reaction Time, Digit Vigilance, Choice Reaction Time, Tracking, and Numeric Working Memory tasks. Safety was assessed at specified time points, and throughout the study. Of 22 subjects (77% male, 55% white, mean age 34.2±6.6 y), 20 completed the study. SXB PK were similar with and without diclofenac. Geometric LS mean percent ratios for SXB PK parameters with and without diclofenac were 106.7% for Cmax, 100.5% for AUC0-inf, and 94.8% for renal clearance; all 90% CIs were within the 80%-125% equivalence range, suggesting no PK drug-drug interaction. A similar lack of differences was observed for diclofenac PK. SXB induced sleepiness and attentional impairments. SXB + diclofenac had significantly less impairment at several time points compared with SXB alone on accuracy and speed on digit vigilance, choice reaction time, and power of attention (P<0.05). SXB effects on KSS and tracking performance were not reduced by diclofenac. The most common adverse events (AEs) were consistent with the drug profiles. AEs in &#8805;2 subjects with SXB + diclofenac (somnolence, n = 11; dizziness, n = 6; euphoric mood, n = 5; nausea, n = 5; headache, n = 4; vomiting, n = 3; dry mouth, n = 2; and feeling hot, n = 2) reflect a combined effect of both drugs. Co-administration of SXB and diclofenac did not significantly change the PK of either drug. Diclofenac co-administration appeared to reduce SXB-associated impairments to attention and information processing relative to SXB alone. AEs with SXB + diclofenac reflect combined drug effects. This study was sponsored by Jazz Pharmaceuticals, Inc.