GHB Receptor Research Articles

Differentiating the discriminative stimulus effects of gamma-hydroxybutyrate and ethanol in a three-choice drug discrimination procedure in rats

Anecdotal reports indicate that GHB produces subjective effects similar to those of ethanol. However, recent investigations comparing the discriminative stimulus effects of GHB to those of ethanol suggest that the subjective effects of these substances may differ considerably. To explore further potential differences between GHB and ethanol, 16 male Sprague–Dawley rats were trained in a three-lever drug discrimination procedure to discriminate ethanol (1.0 g/kg, experiment 1; 1.5 g/kg, experiment 2) and GHB (300 mg/kg) from vehicle. Dose–response functions determined with both training compounds revealed a clear dissociation between the discriminative stimulus effects of these drugs. As expected, the GHB precursors gamma-butyrolactone and 1,4-butanediol produced full substitution for GHB. In addition, the GABA B receptor agonist baclofen substituted for GHB, whereas the benzodiazepine flunitrazepam and the NMDA receptor antagonist ketamine engendered greater responding on the ethanol-lever. GHB's discriminative stimulus effects were blocked by the GABA B receptor antagonist CGP-35348 but only partially blocked by the putative GHB receptor antagonist NCS 382. These findings are consistent with previous reports of GHB's discriminative stimulus effects in two-choice drug discrimination procedures and provide additional evidence that these effects are distinct from those of ethanol.

Effects of gamma hydroxybutyric acid on inhibition and excitation in rat neocortex

The mechanism by which the sedative and amnestic recreational drug gamma hydroxybutyric acid (GHB) acts is controversial. Some studies indicate that it acts at its unique receptor, while others demonstrate effects mediated through the GABA B receptor. We examined the effect of GHB on evoked GABA A receptor–mediated mono- and polysynaptic inhibitory postsynaptic currents (IPSCs) as well as on N-methyl- d-aspartate (NMDA) and AMPA-mediated excitatory postsynaptic currents (EPSCs) in layers II/III pyramidal cells of the frontal cortex of rat brain. One millimolar (mM) GHB suppressed monosynaptic IPSCs by 20%, whereas polysynaptic IPSCs were reduced by 56%. GHB (1 mM) also produced a significant suppression of NMDA-mediated EPSCs by 53% compared with 27% suppression of AMPA-mediated EPSCs. All effects of GHB on IPSCs and EPSCs were reversed by the specific GABA B antagonist CGP 62349, but not by the GHB receptor antagonist (2E)-5-hydroxy-5,7,8,9-tetrahydro-6 H-benzo[ a][7]annulen-6-ylidene ethanoic acid. Consistent with a presynaptic site of action, GHB reduced the frequency but not the amplitude of AMPA receptor–mediated mEPSCs and had no effect on postsynaptic currents evoked by direct application of NMDA. Finally, even though GHB appeared to be acting at presynaptic GABA B receptors, GHB and the GABA B agonist baclofen appeared to have opposite potencies for depression of NMDA- vs. AMPA-mediated EPSCs. GHB showed a preference for depressing NMDA responses while baclofen more potently suppressed AMPA responses. The suppression of NMDA more than AMPA responses by GHB at intoxicating doses may make it attractive as a recreational drug and may explain why GHB is abused and baclofen is not.

The Neuropharmacology of Sleep Disorders: Better Sleeping Through Chemistry?

Sleep and wake states involve interaction among many brain centers via multiple neurotransmitters, including dopamine, norepinephrine, hypocretin, acetylcholine, histamine and serotonin (wake promoting), and γ amino butyric acid (GABA) and melatonin (sleep promoting). Most medications for insomnia or hypersomnia act on elements of these neural systems. Initial treatment of insomnia includes sleep hygiene measures. Cognitive-behavioral therapy for insomnia is useful. Medications approved by the Food and Drug Administration for insomnia act on GABA receptors or on melatonin receptors. A frequent cause of insomnia is restless legs syndrome, which is linked to reduced dopaminergic activity in brain structures; idiopathic restless legs syndrome is best treated with dopamine agonists such as ropinerole or pramipexole. Excessive daytime sleepiness is most often due to insufficient sleep hours or sleep apnea but is also caused by medications, illnesses, narcolepsy, or idiopathic hypersomnia. Stimulants generally act through enhanced dopamine action (amphetamines, methylphenidate) or acetylcholine action (caffeine). Modafinil may act through enhanced central histamine, hypocretin, and possibly dopamine action. A newer agent, γ -hydroxybutyrate (GHB), acts on GABA and GHB receptors to consolidate sleep, improving daytime sleepiness in narcolepsy. Improving knowledge of sleep/wake mechanisms should lead to more specific and rational treatments for sleep disorders.

GHB: Drug of Abuse or Therapeutic Agent?

Gamma-hydroxybutyrate (GHB), first synthesized in the 1960s, is a water-soluble sedative able to cross the blood-brain barrier. Controversy still exists as to whether GHB should be considered a neurotransmitter or, simply, a neuromodulator; there is pharmacologic evidence both for a unique GHB receptor in the brain and for agonism at the G-protein–coupled GABAB receptor. When administered orally, …

Cloning and functional characterization of a gamma‐hydroxybutyrate receptor identified in the human brain

Two parent clones of a gamma-hydroxybutyrate (GHB) receptor, C12K32 and GHBh1, were isolated from a human frontal cortex cDNA library. The two clones differ by a deleted cytosine in C12K32. CHO cells transfected with either C12K32 or GHBh1 responded positively to submicromolar GHB stimulation. However, unlike C12K32, GHBh1 desensitizes rapidly on application of low concentrations of GHB. GHB receptor properties were then studied on C12K32 expressed in CHO cells. C12K32 bound GHB with a Kd of 114 nM and has no affinity for GABA or glutamate. GHB and NCS-382 displaced [3H]GHB with an IC50 of 53 +/- 8 and 120 +/- 18 nM, respectively. In patch-clamp experiments, GHB induced a dose-dependent response with an EC50 of 130 nM. This response was antagonized by NCS-382, was not reproduced by GABA, and was sensitive to the addition of GTP-gamma-S in the recording pipette. CHO cells transfected with C12K32 exhibited GTPgamma-35S binding with an EC50 of 462 nM for GHB and an IC50 of 2.9 microM for NCS-382. The present data led to the conclusion that both C12K32 and GHBh1 are two closely related isoforms of a human GHB receptor, GHBh1, that is described in the databank as the GPCR 172A.

Anti-aggressive effects of GHB in OF.1 strain mice: Involvement of dopamine D 2 receptors

Numerous studies indicate that gamma-hydroxybutyric acid (GHB) influences the endogenous dopamine system. Both GHB and most dopaminergic D 2 receptor antagonists are effective anti-aggressive agents in animal models. The present study aimed to investigate the effects of GHB on agonistic behaviour and to implicate D 2 dopamine receptor on these behaviours. For this purpose, the effects of GHB (80, 120 and 160 mg/kg, IP) and tiapride (60 mg/kg) administered alone or in combination were examined on agonistic behaviour elicited by ‘isolation’ in male mice. Individually housed mice were exposed to anosmic “standard opponents” 30 min after drug administration, and the encounters were videotaped and evaluated using an ethologically based analysis. The administration of 80 and 120 mg/kg of GHB reduced threat without impairing motor activity, but the administration of 160 mg/kg of GHB or the co-administration of GHB + tiapride (a selective D 2 receptor antagonist) significantly reduced threat and attack but concomitantly increased immobility. The co-administration of GHB + tiapride had different effects to those observed by the administration of these drugs separately. It is concluded that the anti-aggressive effect of GHB appears to be mediated, at least in part, by D 2 dopamine receptors. This anti-dopaminergic activity is an indirect effect, probably induced by the activation of GHB receptors of low affinity, and in this way, this compound would reduce levels of dopamine without blockading of D 2 postsynaptic dopamine receptors.

Immunohistochemical localization of a GHB receptor‐like protein isolated from rat brain

Gamma-hydroxybutyrate (GHB) is a substance derived from the metabolism of GABA and is heterogeneously distributed in various regions of the brain. This compound possesses a neuromodulatory role on several types of synapses, particularly those using GABA as a neurotransmitter. At physiological concentrations, this effect of GHB is mediated via specific receptors that induce neuronal hyperpolarization and bind radioactive GHB with a specific distribution, ontogenesis, kinetics, and pharmacology. A membrane protein that possesses six to seven transmembrane domains and which binds and is activated by micromolar amounts of GHB was recently cloned from rat brain hippocampus. In order to study the regional and cellular distribution of this receptor in rat brain, we selected several specific peptides belonging to the extracellular domains of the receptor to be used as specific immunogens to raise polyclonal antibodies in the rabbit. Among the antisera obtained, one of them gave particularly good results in terms of specificity and reactivity at high dilution. Immunohistochemical analyses, both at the confocal and electron microscopic level, showed receptor protein distribution closely resembling the distribution of GHB high-affinity binding sites, except for cerebellum, where GHB receptor(s) of lower affinity exist(s). In all regions studied the GHB receptor-like protein labeling appears to be distributed specifically in neurons and not in glial cells. At the cellular level the antibody specifically labels dendrites, and no immunoreactivity was detected in presynaptic endings or in axons. Accordingly, electron microscopy reveals strong labeling of postsynaptic densities and of neuronal cytosol.

Gamma-hydroxybutyrate – a drug of abuse

Gamma-hydroxybutyrate (GHB) is a drug of abuse that causes euphoria, anxiolysis, and hypnosis. The recent rise in the recreational intake of GHB, as well as its association with 'drug rape', has turned the attention to GHB in acute hospital settings. Acutely admitted GHB intoxicated patients may display various levels of sedation or coma, but may also show paradoxical agitation, combativeness, or self-injurious behaviors. The symptoms can be nonspecific and the definite diagnosis therefore normally relies on the detection of GHB in blood or body fluids, which is an analysis that may not be promptly available. As a basis for understanding the clinical features of GHB intoxication and abuse, we here review the pharmacological and neurophysiological knowledge about GHB, which stems from decades of clinical and basic GHB research. In addition, we discuss the latest discoveries in the quest for distinct GHB receptors in the brain, and their possible implications for future therapies of GHB abuse.

Metabolic GHB precursor succinate binds to γ‐hydroxybutyrate receptors: Characterization of human basal ganglia areas nucleus accumbens and globus pallidus

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.

Succinic Semialdehyde Dehydrogenase Deficiency: GABA B receptor-mediated function

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 GABA BR receptor (GABA BR). We tested the hypothesis that both GHBR and GABA BR-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 GABA BR in mutant mice made deficient in SSADH (SSADH −/−). There was a significant decrease in binding of the specific GABA BR antagonist, [ 3H]CGP-54626A at postnatal day (PN)7 and PN14 in SSADH −/− when compared to wild type control animals (SSADH +/+), particularly in hippocampus. GABA BR-mediated synaptic potentials were decreased in SSADH −/−. Immunoblot analysis of GABA BR1a, R1b, and R2 in SSADH −/− indicated a trend towards a region-specific and time-dependent decrease of GABA BR 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 GABA BR-mediated function and raise the possibility that this GHB- and GABA-induced perturbation of GABA BR could play a role in the pathogenesis of the seizures and mental retardation observed in SSADH deficiency.

Discriminative stimulus effects of flumazenil: perceptual masking by baclofen, and lack of substitution with gamma-hydroxybutyrate and its precursors 1,4-butanediol and gamma-butyrolactone

Pigeons trained to discriminate 0.1 mg/kg flumazenil, proposed as an in-vivo model to study interactions with diazepam-insensitive gamma-aminobutyric acid (GABA)A receptors, were tested with various GABAergic and non-GABAergic compounds. As a result of its pharmacological selectivity, the model was suitable for further examining previously reported flumazenil-like effects of gamma-hydroxybutyrate (GHB). Flumazenil and the GABAA negative modulator Ro 15-4513 produced 82-100% flumazenil-appropriate responding. Diazepam and the direct-acting GABAA agonists muscimol and 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-3-ol (THIP) produced 38-64% flumazenil-appropriate responding. GHB, its precursors 1,4-butanediol (1,4-BD) and gamma-butyrolactone (GBL), and the GABAB agonists baclofen and SKF97541 produced 0-24% flumazenil-appropriate responding. Baclofen shifted the flumazenil dose-response curve to the right and down, possibly involving perceptual masking of the discriminative stimulus effects of flumazenil by agonist activity at GABAB receptors. These masking effects of baclofen were blocked by the GABAB antagonist CGP35348. When CGP35348 was given together with GHB to block its GABAB agonist effects, GHB did not produce flumazenil-appropriate responding. Conceivably, effects of GHB at non-GABAB receptors (e.g. diazepam-sensitive GABAA receptors and GHB receptors) may interfere with the expression of its flumazenil-like discriminative stimulus effects. The asymmetric substitution between GHB and flumazenil is consistent with the hypothesis that the discriminative stimulus effects of GHB consist of several components, not all of which are mimicked by flumazenil.

Discriminative stimulus effects of GHB and GABA B agonists are differentially attenuated by CGP35348

The aim of this study was to examine the possible heterogeneity of mechanisms that contribute to the discriminative stimulus and rate-decreasing effects of γ-hydroxybutyrate (GHB). Dose effect curves were determined for GHB and two GABA B receptor agonists (baclofen and SKF97541) alone and together with the selective GABA B receptor antagonist CGP35348 in rats discriminating GHB. In a second study, GHB and SKF97541 dose effect curves were determined alone and together with baclofen. CGP35348 attenuated the discriminative stimulus and rate-decreasing effects of SKF97541 and baclofen to a greater extent than those of GHB. In the second study, baclofen enhanced the discriminative stimulus and rate-decreasing effects of GHB and SKF97541; however, the GHB dose effect curve was not shifted in a parallel manner. Taken together, these data suggest that multiple mechanisms, possibly including GHB receptors and GABA B receptor subtypes, are involved in the discriminative stimulus and rate-decreasing effects of GHB.

Microbial reduction of α-acetyl-γ-butyrolactone

Isomers of α-1′-hydroxyethyl-γ-butyrolactone can be considered as potential GHB receptor ligands designed by the molecular hybridization of GLB 2 and GHV 4. Using Aspergillus niger, Geotrichum candidum, and Kluyveromyces marxianus, it was possible to obtain (+)-(3 R,1′ S)-α-1′-hydroxyethyl-γ-butyrolactone in good to excellent conversions, diastereoisomeric and enantiomeric excesses. The corresponding enantiomer, (−)-(3 S,1′ S)-α-1′-hydroxyethyl-γ-butyrolactone was also produced in good conversion, and diastereoisomeric and enantiomeric excesses using Hansenula sp.

Metabolism of γ-hydroxybutyrate to d-2-hydroxyglutarate in mammals: further evidence for d-2-hydroxyglutarate transhydrogenase

γ-Hydroxybutyratic acid (GHB), and its prodrugs 4-butyrolactone and 1,4-butanediol, represent expanding drugs of abuse, although GHB is also used therapeutically to treat narcolepsy and alcoholism. Thus, the pathway by which GHB is metabolized is of importance. The goal of the current study was to examine GHB metabolism in mice with targeted ablation of the GABA degradative enzyme succinic semialdehyde dehydrogenase (SSADH −/− mice), in whom GHB persistently accumulates, and in baboons intragastrically administered with GHB immediately and persistently. Three hypotheses concerning GHB metabolism were tested: (1) degradation via mitochondrial fatty acid β-oxidation; (2) conversion to 4,5-dihydroxyhexanoic acid (a putative condensation product of the GHB derivative succinic semialdehyde); and (3) conversion to d-2-hydroxyglutaric acid ( d-2-HG) catalyzed by d-2-hydroxyglutarate transhydrogenase (a reaction previously documented only in rat). Both d-2-HG and 4,5-dihydroxyhexanoic acid were significantly increased in neural and nonneural tissue extracts derived from SSADH −/− mice. In vitro studies demonstrated the ability of 4,5-dihydroxyhexanoic acid to displace the GHB receptor ligand NCS-382 (IC 50 = 38 μmol/L), although not affecting GABA B receptor binding. Blood and urine derived from baboons administered with GHB also accumulated d-2-HG, but not 4,5-dihydroxyhexanoic acid. Our results indicate that d-2-HG is a prominent GHB metabolite and provide further evidence for the existence of d-2-hydroxyglutarate transhydrogenase in different mammalian species.

Discriminative Stimulus Effects of γ-Hydroxybutyrate: Role of Training Dose

gamma-Hydroxybutyrate (GHB) is a drug of abuse with actions at GHB and GABA receptors. This study examined whether the relative importance of GABA(A), GABA(B), and GHB receptors in the discriminative stimulus effects of GHB depends on the training dose. In comparison with a previous 100 mg/kg GHB-saline discrimination, pigeons were trained to discriminate either 178 or 56 mg/kg GHB from saline. Increasing the training dose shifted the GHB gradient to the right, and decreasing it shifted the gradient to the left. Similar shifts occurred with the GHB precursor gamma-butyrolactone, which substituted for GHB, and with the GABA(B) agonists baclofen and 3-aminopropyl(methyl)phosphinic acid hydrochloride (SKF97541) and the benzodiazepine diazepam, each of which produced at most 54 to 68% GHB-appropriate responding. The benzodiazepine antagonist flumazenil, the benzodiazepine inverse agonist ethyl 8-azido-6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-alpha]-[1,4]-benzodiazepine-3-carboxylate (Ro 15-4513), and the GHB receptor antagonist (2E)-5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene ethanoic acid (NCS-382) produced a maximum of 66 to 97% GHB-appropriate responding in animals discriminating 56 or 100 mg/kg GHB and a maximum of 1 to 49% in animals discriminating 178 mg/kg. NCS-382 did not attenuate the effects of GHB. The GABA(B) antagonist 3-aminopropyl(diethoxymethyl)phosphinic acid (CGP35348) blocked GHB at all training doses. The results suggest that increasing the training dose of GHB increases the pharmacological selectivity of its discriminative stimulus effects. At a high training dose, diazepam-insensitive GABA(A) receptors, for which flumazenil and Ro 15-4513 have affinity, may no longer be involved. Diazepam-sensitive GABA(A) receptors and GABA(B) receptors appear to play a similar role at all training doses. There was no evidence for GHB receptor involvement.

Drosophila GABA B receptors are involved in behavioral effects of γ-hydroxybutyric acid (GHB)

γ-hydroxybutyric acid (GHB) can be synthesized in the brain but is also a known drug of abuse. Although putative GHB receptors have been cloned, it has been proposed that, similar to the behavior-impairing effects of ethanol, the in vivo effects of pharmacological GHB may involve metabotropic γ-aminobutyric acid (GABA) GABA B receptors. We developed a fruitfly ( Drosophila melanogater) model to investigate the role of these receptors in the behavioral effects of exogenous GHB. Injecting GHB into male flies produced a dose-dependent motor impairment (measured with a computer-assisted automated system), which was greater in ethanol-sensitive cheapdate mutants than in wild-type flies. These effects of pharmacological concentrations of GHB require the presence and activation of GABA B receptors. The evidence for this was obtained by pharmacological antagonism of GABA B receptors with CGP54626 and by RNA interference (RNAi)-induced knockdown of the GABA B(1) receptor subtype. Both procedures inhibited the behavioral effects of GHB. GHB pretreatment diminished the behavioral response to subsequent GHB injections; i.e., it triggered GHB tolerance, but did not produce ethanol tolerance. On the other hand, ethanol pretreatment produced both ethanol and GHB tolerance. It appears that in spite of many similarities between ethanol and GHB, the primary sites of their action may differ and that recently cloned putative GHB receptors may participate in actions of GHB that are not mediated by GABA B receptors. These receptors do not have a Drosophila orthologue. Whether Drosophila express a different GHB receptor should be explored.

Novel Cyclic γ-Hydroxybutyrate (GHB) Analogs with High Affinity and Stereoselectivity of Binding to GHB Sites in Rat Brain

Gamma-hydroxybutyrate (GHB) is a psychotropic compound endogenous to the brain. Despite its potentially great physiological significance, its exact molecular mechanism of action is unknown. GHB is a weak agonist at GABA(B) receptors, but there is also evidence of specific GHB receptor sites, the molecular cloning of which remains a challenge. Ligands with high affinity and specificity for the reported GHB binding site are needed for pharmacological dissection of the GHB and GABA(B) effects and for mapping the structural requirements of the GHB receptor-ligand interactions. For this purpose, we have synthesized and assayed three conformationally restricted GHB analogs for binding against the GHB-specific ligand [3H]NCS-382 [(E,RS)-(6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylidene-)acetic acid] in rat brain homogenate. The cyclohexene and cyclopentene analogs, 3-hydroxycyclohex-1-enecarboxylic acid [(RS)-HOCHCA] and 3-hydroxycyclopent-1-enecarboxylic acid [(RS)-HOCPCA], were found to be high-affinity GHB ligands, with IC50 values in the nanomolar range, and had 9 and 27 times, respectively, higher affinity than GHB. The stereo-selectively synthesized R,R-isomer of the trans-cyclopropyl GHB analog, HOCPrCA, proved to have 10-fold higher affinity than its enantiomer. Likewise, the R-enantiomers of HOCHCA and HOCPCA selectively inhibited [3H]NCS-382 binding. The best inhibitor of these, (R)-HOCPCA, has an affinity 39 times higher than GHB and is thus among the best GHB ligands reported to date. Neither of the cycloalkenes showed any affinity (IC50 > 1 mM) for GABA(A) or GABA(B) receptors. These compounds show excellent potential as lead structures and novel tools for studying specific GHB receptor-mediated pharmacology.

γ-Hydroxybuttersäure — Neurotransmitter, Medikament und Droge

Gamma-hydroxybutyrate (GHB) is a short fatty acid and physiologic neurotransmitter. Initially, it was synthesized as a GABA agonist and used as a narcotic agent, because it rapidly induces sleep without major cardiovascular or respiratory side effects. Recently, a specific GHB receptor was identified, but while the clinical use of GHB as an anaesthetic was reduced due to putative pro-convulsive effects, it now is used to treat alcohol withdrawal and sleep disorders. Furthermore, GHB was postulated to be a regulator of energy metabolism, and tissue-protective effects were demonstrated in different animal models. Besides its clinical use, GHB (also called "liquid ecstasy") is increasingly consumed in the disco scene because of its mild sedative and euphoric effects. Intoxication from GHB is common with GHB users. For this reason and because GHB is not easy to detect, it is important to be aware of the symptoms of GHB intoxication. Moreover, some recent case reports document the danger of GHB dependence.

Ethers of 3-hydroxyphenylacetic acid as selective gamma-hydroxybutyric acid receptor ligands

Gamma-hydroxybutyric acid (GHB) is a drug of abuse, a therapeutic, and purportedly a neurotransmitter with a complex mechanism of action in vivo due to direct actions at GABA B as well as GHB receptors and because of its metabolism to GABA. Herein, we describe 3-ethers of 3-hydroxyphenylacetic acid, which have relatively high affinity at GHB sites, no significant affinity at GABA receptors, and would not be expected to be rapidly metabolized to GABAergic ligands. The selectivity of these compounds (UMB108, UMB109, and UMB119) could prove to be useful for studying the biology of GHB receptors, free from GABAergic effects.

Resuscitative Effect of a γ-Aminobutyric Acid B Receptor Antagonist on γ-Hydroxybutyric Acid Mortality in Mice

In the present study, a number of compounds were tested to evaluate their efficacy in exerting a protective effect on gamma-hydroxybutyric acid (GHB)-induced mortality in mice. The drugs investigated were the gamma-aminobutyric acid B (GABA B ) receptor antagonist SCH 50911, the GABA A receptor antagonist bicuculline, the benzodiazepine receptor antagonist flumazenil, the putative GHB receptor antagonist NCS-382, the opioid receptor antagonist naltrexone, and the amino acid and possible neuromodulator, taurine. All mice were initially treated with a lethal dose of GHB (7 g/kg, administered intragastrically). Once mice had displayed clear signs of GHB intoxication, animals from each group were treated acutely with either SCH 50911 (vehicle; 75, 150, and 300 mg/kg, administered intraperitoneally), bicuculline (vehicle; 2, 4, 6, and 8 mg/kg, administered intraperitoneally), flumazenil (vehicle; 1, 3, and 10 mg/kg, administered intraperitoneally), NCS-382 (vehicle; 50 and 200 mg/kg, administered intraperitoneally), naltrexone (vehicle; 3 and 10 mg/kg, administered intraperitoneally), or taurine (vehicle; 250 and 750 mg/kg, administered intraperitoneally). The various doses of each single drug were administered to 10 mice, randomly allocated throughout the experimental groups. Mortality was recorded every hour for the first 9 hours and subsequently 12, 18, and 24 hours after GHB injection. In each experiment, all vehicle-treated mice died within 24 hours of GHB injection. Doses of 150 and 300 mg/kg SCH 50911 produced a marked protection on GHB-induced mortality, evidenced by the death of only 0 of 10 and 2 of 10 mice in the 150- and 300-mg/kg SCH 50911 groups, respectively. In contrast, at all doses tested, bicuculline, flumazenil, NCS-382, naltrexone, and taurine were not observed to exert any protective effect on GHB-induced mortality (9 to 10/10 mice died in each treatment group). These results suggest an involvement of the GABA B receptor, at least in rodents, in the mediation of the lethal effects of GHB.