Quantitative autoradiographic distribution of gamma-hydroxybutyric acid binding sites in human and monkey brain

Prohedonic properties of gamma-hydroxybutyrate are associated with changes in limbic resting-state functional connectivity

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.

Effect of GHB-use and GHB-induced comas on dorsolateral prefrontal cortex functioning in humans

BACKGROUND

Gamma-hydroxybutyric acid (GHB) is a recreational drug associated with increasing numbers of GHB-dependent patients and emergency attendances often related to GHB-induced comas. Working memory (WM) deficits have been reported in association with GHB use, and animal studies have shown that GHB induces oxidative stress in vulnerable WM-related brain areas such as the dorsolateral prefrontal cortex (DLPFC). However, the effects of chronic GHB use and multiple GHB-induced comas on WM-related brain function in humans remains unknown.

METHODS

We recruited 27 GHB users with ≥4 GHB-induced comas (GHB-Coma), 27 GHB users who never experienced GHB-induced coma (GHB-NoComa), and 27 polydrug users who never used GHB (No-GHB). Participants performed an n-back WM task during functional magnetic resonance imaging (fMRI) to probe DLPFC functioning.

RESULTS

The GHB-Coma group had lower premorbid IQ (p = .006) than the GHB-NoComa group despite comparable age and education level. There were also group differences in the use of other drugs than GHB. Therefore, all group comparisons were adjusted for IQ and drug use other than GHB. Compared with the GHB-NoComa and the No-GHB groups, the GHB-Coma group showed increased activity in the right DLPFC (pSVC = 0.028) and increased functional connectivity of the right DLPFC with a cluster comprising the left anterior cingulate and medial frontal gyrus (pFWE = 0.003). No significant fMRI differences were observed between the GHB-NoComa and No-GHB groups. Due to technical problems, no behavioural data were collected.

DISCUSSION

These results suggest that multiple GHB-induced comas, but not GHB-use per se, are associated with alterations in WM-related brain function. Public awareness campaigns are required to minimize the potential adverse effects induced by GHB recreational use, and especially GHB-induced comas, even if no immediate side effects are experienced.

Adverse effects of GHB-induced coma on long-term memory and related brain function

BACKGROUND

Gamma-Hydroxybutyric acid (GHB) is a drug of abuse associated with increasing numbers of GHB-dependent patients and emergency attendances often related to GHB-induced coma. Animal studies suggest that GHB induces oxidative stress in the hippocampus, resulting in memory impairments. However, the consequences of chronic GHB use and GHB-induced coma on human brain function and cognition are unknown.

METHODS

We recruited 27 GHB users with ≥4 GHB-induced comas (GHB-Coma), 27 GHB users without a coma (GHB-NoComa), and 27 polydrug users who never used GHB (No-GHB). Participants completed verbal and spatial memory tests and an associative memory encoding task during functional magnetic resonance imaging (fMRI) to probe hippocampus functioning.

RESULTS

The GHB-Coma group showed a lower premorbid IQ (p = 0.006) and performed worse on the verbal memory test (p = 0.017) compared to the GHB-NoComa group, despite exhibiting similar levels of education. Compared with the other two groups, the GHB-Coma group showed lower left hippocampus (p_SVC = 0.044) and left lingual gyrus (p_FWE = 0.017) activity, and a trend for lower hippocampal functional connectivity with the left superior temporal cortex during performance of the associative memory encoding task (p_FWE = 0.063). No significant differences were observed between the GHB-NoComa group and the No-GHB group.

CONCLUSIONS

These results suggest that multiple GHB-induced comas, but not the use of GHB per se, are associated with alterations of memory performance and memory-related brain, although no causal link can be inferred from this cross-sectional study. The results highlight the need for public awareness to minimize the negative health consequences of recreational GHB use, in particular when related with GHB-induced comas.

Autoradiographic imaging and quantification of the high-affinity GHB binding sites in rodent brain using 3H-HOCPCA

GHB (γ-hydroxybutyric acid) is a compound endogenous to mammalian brain with high structural resemblance to GABA. GHB possesses nanomolar-micromolar affinity for a unique population of binding sites, but the exact nature of these remains elusive. In this study we utilized the highly selective GHB analogue, 3-hydroxycyclopent-1-enecarboxylic acid (HOCPCA) as a tritiated version (³H-HOCPCA) to radioactively label the specific GHB high-affinity binding site and gain further insight into the density, distribution and developmental profile of this protein. We show that, in low nanomolar concentrations, ³H-HOCPCA displays excellent signal-to-noise ratios using rodent brain autoradiography, which makes it a valuable ligand for anatomical quantification of native GHB binding site levels. Our data confirmed that ³H-HOCPCA labels only the high-affinity specific GHB binding site, found in high density in cortical and hippocampal regions. The experiments revealed markedly stronger binding at pH 6.0 (K_d 73.8 nM) compared to pH 7.4 (K_d 2312 nM), as previously reported for other GHB radioligands but similar B_max values. Using ³H-HOCPCA we analyzed the GHB binding protein profile during mouse brain development. Due to the high sensitivity of this radioligand, we were able to detect low levels of specific binding already at E15 in mouse brain, which increased progressively until adulthood. Collectively, we show that ³H-HOCPCA is a highly sensitive radioligand, offering advantages over the commonly used radioligand ³H-NCS-382, and thus a very suitable in vitro tool for qualitative and quantitative autoradiography of the GHB high-affinity site.

The behavioural profile of gamma-hydroxybutyrate, gamma-butyrolactone and 1,4-butanediol in humans

Gamma-hydroxybutyrate (GHB) is a putative neurotransmitter, a drug of abuse, and a medical treatment for narcolepsy and other neuropsychiatric disorders. Its precursors gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD) are endogenously converted to GHB and thereby exert their psychobehavioural effects. In humans, GHB has a wide spectrum of properties ranging from stimulation and euphoria in lower doses, to sedation, deep sleep, and coma after ingestion of high doses. However, behavioural studies in healthy volunteers remain scarce and are usually limited to psychomotor performance testing. Most available data arise from either qualitative studies with illicit users or clinical trials examining therapeutic properties of GHB (then usually termed sodium oxybate). Here, we present an overview of the behavioural effects of GHB, GBL, and 1,4-BD in these three populations. GHB and its precursors strongly influence behaviours related to core human autonomic functions such as control of food intake, sexual behaviour, and sleep-wake regulation. These effects are instrumentalised by illicit users and clinically utilised in neuropsychiatric disorders such as narcolepsy, fibromyalgia, and binge-eating syndrome. Considering the industry withdrawal from psychopharmacology development, repurposing of drugs according to their behavioural and clinical profiles has gained increasing relevance. As such, GHB seems to be an attractive candidate as an experimental therapeutic in depression.

Mechanisms for the Specific Properties of γ-Hydroxybutyrate in Brain

γ-Hydroxybutyrate (GHB) is both a natural brain compound with neuromodulatory properties at central GABAergic synapses (micromolar concentration range) and also a drug (Xyrem(R) ) clinically used for the treatment of various neurological symptoms (millimolar dose range). However, this drug has abuse potential and can be addictive for some patients. Here, we review the basic mechanistic role of endogenous GHB in brain as well as the properties and mechanisms of action for therapeutic clinical doses of exogenous GHB. Several hypotheses are discussed with a preference for a molecular mechanism that conciliates most of the findings available. This conciliatory model may help for the design of GHB-like drugs active at lower doses and devoid of major side effects.

Baclofen and gamma-hydroxybutyrate differentially altered behavior, EEG activity and sleep in rats

OBJECTIVES

Animal and human studies have shown that sleep may have an impact on functional recovery after brain damage. Baclofen (Bac) and gamma-hydroxybutyrate (GHB) have been shown to induce physiological sleep in humans, however, their effects in rodents are unclear. The aim of this study is to characterize sleep and electroencelphalogram (EEG) after Bac and GHB administration in rats. We hypothesized that both drugs would induce physiological sleep.

METHODS

Adult male Sprague-Dawley rats were implanted with EEG/electromyogram (EMG) electrodes for sleep recordings. Bac (10 or 20 mg/kg), GHB (150 or 300 mg/kg) or saline were injected 1 h after light and dark onset to evaluate time of day effect of the drugs. Vigilance states and EEG spectra were quantified.

RESULTS

Bac and GHB induced a non-physiological state characterized by atypical behavior and an abnormal EEG pattern. After termination of this state, Bac was found to increase the duration of non-rapid eye movement (NREM) and rapid eye movement (REM) sleep (∼90 and 10 min, respectively), reduce sleep fragmentation and affect NREM sleep episode frequency and duration (p<0.05). GHB had no major effect on vigilance states. Bac drastically increased EEG power density in NREM sleep in the frequencies 1.5-6.5 and 9.5-21.5 Hz compared to saline (p<0.05), while GHB enhanced power in the 1-5-Hz frequency band and reduced it in the 7-9-Hz band. Slow-wave activity in NREM sleep was enhanced 1.5-3-fold during the first 1-2 h following termination of the non-physiological state. The magnitude of drug effects was stronger during the dark phase.

CONCLUSION

While both Bac and GHB induced a non-physiological resting state, only Bac facilitated and consolidated sleep, and promoted EEG delta oscillations thereafter. Hence, Bac can be considered a sleep-promoting drug and its effects on functional recovery after stroke can be evaluated both in humans and rats.

The clinical toxicology of γ-hydroxybutyrate, γ-butyrolactone and 1,4-butanediol

INTRODUCTION

Gamma-hydroxybutyrate (GHB) and its precursors, gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD), are drugs of abuse which act primarily as central nervous system (CNS) depressants. In recent years, the rising recreational use of these drugs has led to an increasing burden upon health care providers. Understanding their toxicity is therefore essential for the successful management of intoxicated patients. We review the epidemiology, mechanisms of toxicity, toxicokinetics, clinical features, diagnosis, and management of poisoning due to GHB and its analogs and discuss the features and management of GHB withdrawal.

METHODS

OVID MEDLINE and ISI Web of Science databases were searched using the terms "GHB," "gamma-hydroxybutyrate," "gamma-hydroxybutyric acid," "4-hydroxybutanoic acid," "sodium oxybate," "gamma-butyrolactone," "GBL," "1,4-butanediol," and "1,4-BD" alone and in combination with the keywords "pharmacokinetics," "kinetics," "poisoning," "poison," "toxicity," "ingestion," "adverse effects," "overdose," and "intoxication." In addition, bibliographies of identified articles were screened for additional relevant studies including nonindexed reports. Non-peer-reviewed sources were also included: books, relevant newspaper reports, and applicable Internet resources. These searches produced 2059 nonduplicate citations of which 219 were considered relevant.

EPIDEMIOLOGY

There is limited information regarding statistical trends on world-wide use of GHB and its analogs. European data suggests that the use of GHB is generally low; however, there is some evidence of higher use among some sub-populations, settings, and geographical areas. In the United States of America, poison control center data have shown that enquiries regarding GHB have decreased between 2002 and 2010 suggesting a decline in use over this timeframe.

MECHANISMS OF ACTION

GHB is an endogenous neurotransmitter synthesized from glutamate with a high affinity for GHB-receptors, present on both on pre- and postsynaptic neurons, thereby inhibiting GABA release. In overdose, GHB acts both directly as a partial GABA(b) receptor agonist and indirectly through its metabolism to form GABA.

TOXICOKINETICS

GHB is rapidly absorbed by the oral route with peak blood concentrations typically occurring within 1 hour. It has a relatively small volume of distribution and is rapidly distributed across the blood-brain barrier. GHB is metabolized primarily in the liver and is eliminated rapidly with a reported 20-60 minute half-life. The majority of a dose is eliminated completely within 4-8 hours. The related chemicals, 1,4-butanediol and gamma butyrolactone, are metabolized endogenously to GHB. CLINICAL FEATURES OF POISONING: GHB produces CNS and respiratory depression of relatively short duration. Other commonly reported features include gastrointestinal upset, bradycardia, myoclonus, and hypothermia. Fatalities have been reported. MANAGEMENT OF POISONING: Supportive care is the mainstay of management with primary emphasis on respiratory and cardiovascular support. Airway protection, intubation, and/or assisted ventilation may be indicated for severe respiratory depression. Gastrointestinal decontamination is unlikely to be beneficial. Pharmacological intervention is rarely required for bradycardia; however, atropine administration may occasionally be warranted. WITHDRAWAL SYNDROME: Abstinence after chronic use may result in a withdrawal syndrome, which may persist for days in severe cases. Features include auditory and visual hallucinations, tremors, tachycardia, hypertension, sweating, anxiety, agitation, paranoia, insomnia, disorientation, confusion, and aggression/combativeness. Benzodiazepine administration appears to be the treatment of choice, with barbiturates, baclofen, or propofol as second line management options.

CONCLUSIONS

GHB poisoning can cause potentially life-threatening CNS and respiratory depression, requiring appropriate, symptom-directed supportive care to ensure complete recovery. Withdrawal from GHB may continue for up to 21 days and can be life-threatening, though treatment with benzodiazepines is usually effective.

Novel radioiodinated {gamma}-hydroxybutyric acid analogues for radiolabeling and Photolinking of high-affinity {gamma}-hydroxybutyric acid binding sites

γ-Hydroxybutyric acid (GHB) is a therapeutic drug, a drug of abuse, and an endogenous substance that binds to low- and high-affinity sites in the mammalian brain. To target the specific GHB binding sites, we have developed a (125)I-labeled GHB analog and characterized its binding in rat brain homogenate and slices. Our data show that [(125)I]4-hydroxy-4-[4-(2-iodobenzyloxy)phenyl]butanoate ([(125)I]BnOPh-GHB) binds to one site in rat brain cortical membranes with low nanomolar affinity (K(d), 7 nM; B(max), 61 pmol/mg protein). The binding is inhibited by GHB and selected analogs, but not by γ-aminobutyric acid. Autoradiography using horizontal slices from rat brain demonstrates the highest density of binding in hippocampus and cortical regions and the lowest density in the cerebellum. Altogether, the findings correlate with the labeling and brain regional distribution of high-affinity GHB sites or [(3)H](E,RS)-(6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylidene)acetic acid ([(3)H]NCS-382) binding sites. Using a (125)I-labeled photoaffinity derivative of the new GHB ligand, we have performed denaturing protein electrophoresis and detected one major protein band with an apparent mass of 50 kDa from cortical and hippocampal membranes. [(125)I]BnOPh-GHB is the first reported (125)I-labeled GHB radioligand and is a useful tool for in vitro studies of the specific high-affinity GHB binding sites. The related photoaffinity linker [(125)I]4-hydroxy-4-[4-(2-azido-5-iodobenzyloxy)phenyl]butanoate can be used as a probe for isolation of the elusive GHB binding protein.

Calcium and cAMP signaling induced by gamma-hydroxybutyrate receptor(s) stimulation in NCB-20 neurons

The NCB-20 neurohybridoma cells differentiated with dibutyryl-cyclic-AMP represent an interesting model to study several components of the gamma-hydroxybutyrate (GHB) system in brain. In particular, an active Na(+)-dependent uptake and a depolarization-evoked release of GHB is expressed by these cells, together with high affinity specific binding sites for this substance. However, only little is known about cellular mechanisms following GHB receptor(s) stimulation in these neurons. Electrophysiological data indicate that GHB can differently affect Ca(2+) currents. L-type calcium channels were typically inhibited by GHB when NCB-20 cells were depolarized. In contrast, when NCB-20 cells were at resting potential, GHB induced a specific Ca(2+) entry through T-type calcium channels. In this study, we investigated the effect induced on cytosolic free Ca(2+) level and cAMP production by GHB receptor(s) stimulated with micromolar concentrations of GHB or structural analogues of GHB. Ca(2+) movements studied by cellular imaging were dose-dependently increased but disappeared for GHB concentrations >25 microM. In addition, nanomolar doses of GHB inhibited forskolin-stimulated adenylate cyclase. This effect was also rapidly desensitized at higher GHB concentrations. Acting as an antagonist, NCS-382 decreased GHB receptor(s) mediated cAMP and calcium signals. The agonist NCS-356 mimicked GHB effects which were not affected by the GABA(B) receptor antagonist CGP-55-845. Our results reveal the occurrence of Ca(2+)-dependent adenylate cyclase inhibition in NCB-20 neurons after GHB receptor(s) stimulation by GHB concentrations <50 microM. Above this dose, GHB effects were inactivated. In addition, at GHB concentrations exceeding 50 microM, GTP-gammaS binding was also reduced, confirming the desensitization of GHB receptor(s). Taken together, these results support the existence in NCB-20 neurons of GHB receptors belonging to GPCR family that may recruit various G protein subtypes.

A single acute pharmacological dose of γ-hydroxybutyrate modifies multiple gene expression patterns in rat hippocampus and frontal cortex

γ-Hydroxybutyrate (GHB) is a natural brain neuromodulator that has its own enzymatic machinery for synthesis and degradation, release, and transport systems and several receptors that belong to the G protein-coupled receptor (GPCR) family. Targeting of this system with exogenous GHB is used in therapy to induce sleep and anesthesia and to reduce alcohol withdrawal syndrome. GHB is also popular as a recreational drug for its anxiolytic and mild euphoric effects. However, in both cases, GHB must be administered at high doses in order to maintain GHB concentrations in brain of ∼800-1,000 μM. These high concentrations are thought to be necessary for interactions with low-affinity sites on GABA(B) receptor, but the molecular targets and cellular mechanisms modulated by GHB remain poorly characterized. Therefore, to provide new insights into the elucidation of GHB mechanisms of action and open new tracks for future investigations, we explored changes of GHB-induced transcriptomes in rat hippocampus and prefrontal cortex by using DNA microarray studies. We demonstrate that a single acute anesthetic dose of 1 g/kg GHB alters a large number of genes, 121 in hippocampus and 53 in prefrontal cortex; 16 genes were modified simultaneously in both brain regions. In terms of molecular functions, the majority of modified genes coded for proteins or nucleotide binding sites. In terms of Gene Ontology (GO) functional categories, the largest groups were involved in metabolic processing for hippocampal genes and in biological regulation for prefrontal cortex genes. The majority of genes modified in both structures were implicated in cell communication processes. Western blot and immunohistochemical studies carried out on eight selected proteins confirmed the microarray findings.

Modafinil and γ-hydroxybutyrate have sleep state-specific pharmacological actions on hypocretin-1 physiology in a primate model of human sleep

Hypocretin-1 is a hypothalamic neuropeptide that is important in the regulation of wake and the lack of which results in the sleep disorder narcolepsy. Using a monkey that has consolidated wake akin to humans, we examined pharmacological manipulation of sleep and wake and its effects on hypocretin physiology. Monkeys were given the sleep-inducing γ-hydroxybutyrate (GHB) and the wake-inducing modafinil both in the morning and in the evening. Cerebrospinal fluid hypocretin-1 concentrations changed significantly in response to the drugs only when accompanied by a behavioral change (GHB-induced sleep in the morning or modafinil-induced wake in the evening). We also found that there was a large (180-fold) interindividual variation in GHB pharmacokinetics that explains variability in sleep induction in response to the drug. Our data indicate that the neurochemical concomitants of sleep and wake are capable of changing the physiological output of hypocretin neurons. Sleep independent of circadian timing is capable of decreasing cerebrospinal fluid hypocretin-1 concentrations. Furthermore, hypocretin neurons do not seem to respond to an 'effort' to remain awake, but rather keep track of time spent awake as a wake-promoting counterbalance to extended wakefulness.

Narcolepsy and depression and the neurobiology of gammahydroxybutyrate

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.

Comparative genomics of aldehyde dehydrogenase 5a1 (succinate semialdehyde dehydrogenase) and accumulation of gamma-hydroxybutyrate associated with its deficiency

Succinic semialdehyde dehydrogenase (SSADH; aldehyde dehydrogenase 5A1 [ALDH5A1]; locus 6p22) occupies a central position in central nervous system (CNS) neurotransmitter metabolism as one of two enzymes necessary for γ-aminobutyric acid (GABA) recycling from the synaptic cleft. Its importance is highlighted by the neurometabolic disease associated with its inherited deficiency in humans, as well as the severe epileptic phenotype observed in Aldh5a1^-/- knockout mice. Expanding evidence now suggests, however, that even subtle decreases in human SSADH activity, associated with rare and common single nucleotide polymorphisms, may produce subclinical pathological effects. SSADH, in conjunction with aldo-keto reductase 7A2 (AKR7A2), represent two neural enzymes responsible for further catabolism of succinic semialdehyde, producing either succinate (SSADH) or γ-hydroxybutyrate (GHB; AKR7A2). A GABA analogue, GHB is a short-chain fatty alcohol with unusual properties in the CNS and a long pharmacological history. Moreover, SSADH occupies a further role in the CNS as the enzyme responsible for further metabolism of the lipid peroxidation aldehyde 4-hydroxy-2-nonenal (4-HNE), an intermediate known to induce oxidant stress. Accordingly, subtle decreases in SSADH activity may have the capacity to lead to regional accumulation of neurotoxic intermediates (GHB, 4-HNE). Polymorphisms in SSADH gene structure may also associate with quantitative traits, including intelligence quotient and life expectancy. Further population-based studies of human SSADH activity promise to reveal additional properties of its function and additional roles in CNS tissue.

Gamma-butyrolactone (GBL) disruption of passive avoidance learning in the day-old chick appears to be due to its effect on GABAB not gamma-hydroxybutyric [corrected] acid (GHB) receptors

Gamma-butyrolactone (GBL) is a prodrug to gamma-hydroxybutyric acid (GHB) and metabolises to GHB when ingested. Discrimination stimulus studies report generalisation of effects of GHB to GBL. While amnesia is one of the most commonly reported symptoms of GHB's ingestion in human users, as yet few studies have examined this effect. Although an endogenous GHB specific receptor is present in the brain, several studies have indicated that the clinical effects of exogenous doses of GBL/GHB are due to its action on GABA(B) receptors rather than on the GHB receptor. In this series of studies, New Hampshire x White leghorn cockerels were trained using a modified version of the passive avoidance learning task. Subcutaneous injections of GBL induced a memory deficit by 10 min post-training, which persisted for at least 24 h. No effect on memory was seen with administration of the specific GHB agonist NCS-356 (gamma-p-chlorophenyl-trans-4-hydroxycrotonate). The GBL-induced memory deficit appeared similar to the deficit produced by baclofen, where the antagonist facilitated learning. Additionally, GBL-induced memory deficit was ameliorated by application of a GABA(B) antagonist. The results support the hypothesis that GBL exerts its influence on memory via the GABA(B) receptor rather than by the specific GHB receptor.

Novel high-affinity and selective biaromatic 4-substituted gamma-hydroxybutyric acid (GHB) analogues as GHB ligands: design, synthesis, and binding studies

Gamma-hydroxybutyrate (GHB) is a metabolite of gamma-aminobutyric acid (GABA) and has been proposed to function as a neurotransmitter or neuromodulator. GHB is used in the treatment of narcolepsy and is a drug of abuse. GHB binds to both GABA(B) receptors and specific high-affinity GHB sites in brain, of which the latter have not been linked unequivocally to function, but are speculated to be GHB receptors. In this study, a series of biaromatic 4-substituted GHB analogues, including 4'-phenethylphenyl, 4'-styrylphenyl, and 4'-benzyloxyphenyl GHB analogues, were synthesized and characterized pharmacologically in a [3H](E,RS)-(6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylidene)acetic acid ([3H]NCS-382) binding assay and in GABA(A) and GABA(B) receptor binding assays. The compounds were selective for the high-affinity GHB binding sites and several displayed Ki values below 100 nM. The affinity of the 4-[4'-(2-iodobenzyloxy)phenyl] GHB analogue 17b was shown to reside predominantly with the R-enantiomer (Ki = 22 nM), which has higher affinity than previously reported GHB ligands.

Characterization and pharmacology of the GHB receptor

Radioligand binding using [(3)H]NCS-382, an antagonist of the GHB receptor, revealed specific binding sites in the rat cerebrocortical and hippocampal membranes. Scatchard analysis of saturation isotherms revealed two different populations of binding sites. NCS-382 was about 10 times more potent than GHB in inhibiting [(3)H]NCS-382 binding. A variety of ligands for other receptors did not affect [(3)H]NCS-382 binding. Quantitative autoradiographic analysis of [(3)H]NCS-382 binding revealed similar characteristics. Thus [(3)H]NCS-382, being more potent and selective, offers advantage over [(3)H]GHB as a radioligand. Unlike GHB, several analogues of GHB such as UMB68 (a tertiary alcohol analogue of GHB), UMB86 (4-hydroxy-4-napthylbutanoic acid, sodium salt), UMB72 [4-(3-phenylpropyloxy)butyric acid, sodium salt], UMB73 (4-benzyloxybutyric acid, sodium salt), UMB66 (3-chloropropanoic acid), gamma-hydroxyvaleric acid (that is, GHV, a 4-methyl-substituted analogue of GHB), 3-HPA (3-hydroxyphenylacetic acid), and ethers of 3-hydroxyphenylacetic acid (UMB108, UMB109, and UMB119) displaced [(3)H]NCS-382 without affecting [(3)H]GABA binding to GABA(B) receptor. Thus these compounds offer an advantage over GHB as an experimental tool. Our study, aimed at exploring the potential involvement of the GHB receptor in the pharmacology of ethanol, indicated that ethanol does not affect [(3)H]NCS-382 binding in the rat brain, thereby suggesting that ethanol does not interact directly with the GHB receptor. Our study, aimed at exploring the involvement of the GHB receptor in the pathology of succinate semialdehyde dehydrogenase deficiency, which is known to cause elevation of GHB levels, revealed no change in the affinity, receptor density or displacement potency as determined by using [(3)H]NCS-382 as a radioligand in Aldh5a1(-/-) vs. Aldh5a1(+/+) mouse brain.

GC/MS profiling of gamma-hydroxybutyrate and precursors in various animal tissues using automatic solid-phase extraction. Preliminary investigations of its potential interest in postmortem interval determination

To quantify gamma-hydroxybutyrate (GHB) and its physiological metabolites, gamma-aminobutyric acid (GABA), 1,4-butanediol (1,4-BD), and gamma-butyrolactone (GBL) in various animal tissues (kidney, muscle, heart, liver, blood, brain cortex, thalamus, hypothalamus, hippocampus, or pons), an original gas chromatographic/mass spectrometric method with a automated solid-phase extraction by Oasis MCX cartridges on a Gilson Aspec Xli was developed. Using such apparatus allowed the limit of detection (LOD) of target compounds to be significantly lowered (LOD: 0.027, 0.025, and 5.7 microg/mL for GHB, 1,4-BD, and GABA, respectively, in 200 microL or microg of sample). After validation of each analytical step, the satisfactory performances of the apparatus in conjunction with the rapidity and ease of the extraction step make it suitable for simultaneous assay of GHB, 1,4-BD, GBL, and GABA. The method was used to test the correlation between GHB levels in tissues obtained at different times after death of male Sprague-Dawley rats and the postmortem interval. Preliminary results show a linear increase of GHB levels in relation to time of death in thoracic blood and central nervous system of animals kept at 15 and 20 degrees C.

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.

Metabolic GHB precursor succinate binds to gamma-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.

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.

Unravelling the brain targets of gamma-hydroxybutyric acid

Gamma-hydroxybutyric acid (GHB) is a naturally occurring gamma-aminobutyric acid (GABA) metabolite that has been proposed as a neurotransmitter/neuromodulator that acts via its own receptor (GHBR). Its exogenous administration, however, elicits central nervous system-dependent effects (e.g. memory impairment, increase in sleep stages 3 and 4, dependence, seizures and coma) that are mostly mediated by GABAB receptors. The past few years have seen important developments in our understanding of GHB neurobiology: a putative GHBR has been cloned; a transgenic model of GHB aciduria has been developed; GABAB receptor knockout mice and novel GHB analogs have helped to characterize the vast majority of exogenous GHB actions mediated by GABAB receptors; and some of the cellular mechanisms underlying the dependence/abuse properties of GHB, and its ability to elicit absence seizures and an increase in sleep stages 3 and 4, have been clarified. Nevertheless, the physiological significance of a brain GHB signaling pathway is still unknown, and there is an urgent need for a well-validated functional assay for GHBRs. Moreover, as GHB can also be metabolized to GABA, it remains to be seen whether the many GABAB receptor-mediated actions of GHB are caused by GHB itself acting directly on GABAB receptors or by a GHB-derived GABA pool (or both).

Gamma-hydroxybutyric acid (GHB) and the mesoaccumbens reward circuit: evidence for GABA(B) receptor-mediated effects

Gamma-hydroxybutyric acid (GHB) is a short-chain fatty acid naturally occurring in the mammalian brain, which recently emerged as a major recreational drug of abuse. GHB has multiple neuronal mechanisms including activation of both the GABA(B) receptor, and a distinct GHB-specific receptor. This complex GHB-GABA(B) receptor interaction is probably responsible for the multifaceted pharmacological, behavioral and toxicological profile of GHB. Drugs of abuse exert remarkably similar effects upon reward-related circuits, in particular the mesolimbic dopaminergic system and the nucleus accumbens (NAc). We used single unit recordings in vivo from urethane-anesthetized rats to characterize the effects of GHB on evoked firing in NAc "shell" neurons and on spontaneous activity of antidromically identified dopamine (DA) cells located in the ventral tegmental area. GHB was studied in comparison with the GABA(B) receptor agonist baclofen and antagonist (2S)(+)-5,5-dimethyl-2-morpholineacetic acid (SCH50911). Additionally, we utilized a GHB analog, gamma-(p-methoxybenzil)-gamma-hydroxybutyric acid (NCS-435), devoid of GABA(B) binding properties, but with high affinity for specific GHB binding sites. In common with other drugs of abuse, GHB depressed firing in NAc neurons evoked by the stimulation of the basolateral amygdala. On DA neurons, GHB exerted heterogeneous effects, which were correlated to the baseline firing rate of the cells but led to a moderate stimulation of the DA system. All GHB actions were mediated by GABA(B) receptors, since they were blocked by SCH50911 and were not mimicked by NCS-435. Our study indicates that the electrophysiological profile of GHB is close to typical drugs of abuse: both inhibition of NAc neurons and moderate to strong stimulation of DA transmission are distinctive features of diverse classes of abused drugs. Moreover, it is concluded that addictive and rewarding properties of GHB do not necessarily involve a putative high affinity GHB receptor.

Novel gamma-hydroxybutyric acid (GHB) analogs share some, but not all, of the behavioral effects of GHB and GABAB receptor agonists

gamma-Hydroxybutyrate (GHB), a therapeutic for narcolepsy and a drug of abuse, has several mechanisms of action that involve GHB and GABA(B) receptors, metabolism to GABA, and modulation of dopaminergic signaling. The aim of these studies was to examine the role of GHB and GABA(B) receptors in the behavioral effects of GHB. Three approaches were used to synthesize GHB analogs that bind selectively to GHB receptors and are not metabolized to GABA-active compounds. Radioligand binding assays identified UMB86 (4-hydroxy-4-napthylbutanoic acid, sodium salt), UMB72 [4-(3-phenylpropyloxy)butyric acid, sodium salt], UMB73 (4-benzyloxybutyric acid, sodium salt), 2-hydroxyphenylacetic acid, 3-hydroxyphenylacetic acid (3-HPA), and 4-hydroxy-4-phenylbutyric acid as compounds that displace [(3)H]NCS-382 [5-[(3)H]-(2E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7] annulen-6-ylidene) ethanoic acid] from GHB receptors at concentrations that do not markedly affect [(3)H]GABA binding to GABA(B) receptors. In rats and pigeons, GHB discriminative stimulus effects were not mimicked or attenuated by UMB86, UMB72, or 3-HPA up to doses that decreased responding. In mice, GHB, GHB precursors (gamma-butyrolactone and 1,4-butanediol) and GABA(B) receptor agonists [SKF97541 [3-aminopropyl(methyl)phosphinic acid hydrochloride] and baclofen] dose-dependently produced hypolocomotion, catalepsy, ataxia, and loss of righting. The GABA(B) receptor antagonist CGP35348 (3-aminopropyl(diethoxymethyl)phosphinic acid) attenuated catalepsy and ataxia that was observed after GHB and GABA(B) receptor agonists SKF97541 and baclofen. UMB86, UMB72, UMB73, and 3-HPA, like GHB, produced hypolocomotion, ataxia, and loss of righting; however, catalepsy was never observed with these compounds, which is consistent with the cataleptic effects of GHB being mediated by GABA(B) receptors. Ataxia that was observed with UMB86, UMB72, UMB73, and 3-HPA was not antagonized by CGP35348, suggesting that ataxia induced by these analogs is not mediated by GABA(B) receptors and might involve GHB receptors.

Gamma-hydroxybutyric acid: neurobiology and toxicology of a recreational drug

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.

A review of pharmacology of NCS-382, a putative antagonist of gamma-hydroxybutyric acid (GHB) receptor

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.

fMRI of generalized absence status epilepticus in conscious marmoset monkeys reveals corticothalamic activation

PURPOSE

A nonhuman primate model of generalized absence status epilepticus was developed for use in functional magnetic resonance imaging (fMRI) experiments to elucidate the brain mechanisms underlying this disorder.

METHODS

Adult male marmoset monkeys (Callithrix jacchus) were treated with gamma-butyrolactone (GBL) to induce prolonged absence seizures, and the resulting spike-wave discharges (SWDs) were analyzed to determine the similarity to the 3-Hz SWDs that characterize the disorder. In addition, blood-oxygenation-level-dependent (BOLD) fMRI was measured at 4.7 Tesla after absence seizure induction with GBL.

RESULTS

Electroencephalographic recordings during imaging showed 3-Hz SWDs typical of human absence seizures. This synchronized EEG pattern started within 15 to 20 min of drug administration and persisted for >60 min. In addition, pretreatment with the antiepileptic drug, ethosuximide (ESM), blocked the behavioral and EEG changes caused by GBL. Changes in BOLD signal intensity in the thalamus and sensorimotor cortex correlated with the onset of 3-Hz SWDs. The change in BOLD signal intensity was bilateral but heterogeneous, affecting some brain areas more than others. No significant negative BOLD changes were seen.

CONCLUSIONS

The BOLD fMRI data obtained in this marmoset monkey model of absence status epilepticus shows activation within the thalamus and cortex.

Evaluation of γ-Hydroxybutyric Acid for Genotoxicity in the Mouse Micronucleus Assay

Gamma-hydroxybutyric acid (GHB) is an endogenous compound found in the brain and other tissues of mammals. Neurotransmitter/neuromodulator functions have been ascribed to GHB, which has lately become a drug of abuse. In this study, we tested GHB for genotoxicity by measuring its ability to induce micronuclei in polychromatic erythrocytes (reticulocytes) in the peripheral blood of mice. Intraperitoneal injection with a dose of 25 mg/kg/day for 3 days or 50 mg/kg/day x 3 days resulted in a significant (by Dunnett's test) increase of 1.9- to 2.1-fold in micronuclei. However, because increases were small and because no consistent dose-dependent increase in induced micronuclear frequency could be demonstrated, our results do not conclusively show that GHB is an in vivo genotoxicant in mammals.

4‐Hydroxy‐trans‐2‐nonenoic acid is a γ‐hydroxybutyrate receptor ligand in the cerebral cortex and hippocampus

Elevated production of 4-hydroxy-trans-2-nonenal (HNE) occurs in numerous neurological disorders involving oxidative damage. HNE is metabolized to the non-toxic 4-hydroxy-trans-2-nonenoic acid (HNEAcid) by aldehyde dehydrogenases in the rat cerebral cortex. Based upon the structural similarity of HNEAcid to ligands of the gamma-hydroxybutyrate (GHB) receptor, we hypothesized that HNEAcid is an endogenous ligand for the GHB receptor. HNEAcid displaced the specific binding of the GHB receptor ligand (3)H-NCS382 (30 nm) in membrane preparations of human frontal cerebral cortex and whole rat cerebral cortex with IC(50s) of 3.9 +/- 1.1 and 5.6 +/- 1.2 micro m, respectively. Inhibition was attenuated when the carboxyl group of HNEAcid was replaced with an aldehyde or an alcohol. HNEAcid (300 micro m) did not displace the binding of beta-adrenergic receptor and GABA(B) receptor antagonists, demonstrating the selectivity of HNEAcid for the GHB receptor. HNEAcid is formed in homogenates of human frontal cortical gray matter in an NAD(+)-dependent (V(Max), 0.71 nmol/min/mg) and NADP(+)-dependent (V(Max), 0.12 nmol/min/mg) manner. Lastly, (3)H-NCS382 binding is elevated 2.7-fold with age in the cerebral cortex of rats. Our data demonstrate that an HNE metabolite, formed in rat and human brain, is a signaling molecule analogous to other bioactive lipid peroxidation products.

Presynaptic modulation of spontaneous inhibitory postsynaptic currents by gamma-hydroxybutyrate in the substantia nigra pars compacta

The regulation of GABA release from the inhibitory input to dopamine cells in the substantia nigra pars compacta (SNc) plays a key role in different reward-related behaviors. Gamma-hydroxybutyrate (GHB) has therapeutical properties in various psychiatric disorders, especially in alcohol abuse. GHB is also used as a drug of abuse, which induces sedation and euphoria. Using whole-cell patch-clamp recordings, we studied the effects of GHB on GABA release in the SNc by recording spontaneous inhibitory postsynaptic currents (sIPSCs) in brain slices of 21- to 25-day-old rats. We found that GHB depressed the frequency and amplitude of sIPSCs, while the frequency and the amplitude of miniature inhibitory postsynaptic currents (mIPSCs), recorded in the presence of TTX, were not affected. However, in the presence of high extracellular potassium (15 mM), which increases the contribution of voltage-dependent calcium channels, GHB induced a reduction in the frequency of the mIPSCs without any effect on their amplitude. All of these effects were GABA(B)-independent and they were blocked by the GHB receptor antagonist NCS-382. The present results indicate that GHB inhibits spontaneous inhibitory synaptic transmission recorded from dopaminergic neurons in the SNc likely by reducing voltage-dependent calcium influx involved in presynaptic GABA release.

From the street to the brain: neurobiology of the recreational drug gamma-hydroxybutyric acid

gamma-Hydroxybutyric acid (GHB) is a short-chain fatty acid that occurs naturally in the mammalian brain and is formed primarily from the precursor gamma-aminobutyric acid (GABA). The properties of GHB suggest that it has a neuromodulatory role in the brain and has the ability to induce several pharmacological and behavioral effects. GHB has been used clinically as an anesthetic and to treat alcoholism and narcolepsy. Furthermore, GHB has emerged recently as a major recreational drug of abuse. GHB appears to have dual mechanisms of action in the brain. Biochemical data suggest that the intrinsic neurobiological activity of GHB might be mediated through the GHB receptor, which is separate and distinct from the GABA(B) receptor. However, many of the pharmacological and clinical effects of exogenously administered GHB, including the properties of addiction, tolerance, withdrawal and intoxication, are probably mediated via the GABA(B) receptor, where GHB might act both directly as a partial agonist and indirectly through GHB-derived GABA.

Specific gamma-hydroxybutyrate-binding sites but loss of pharmacological effects of gamma-hydroxybutyrate in GABA(B)(1)-deficient mice

gamma-Hydroxybutyrate (GHB), a metabolite of gamma-aminobutyric acid (GABA), is proposed to function as a neurotransmitter or neuromodulator. gamma-Hydroxybutyrate and its prodrug, gamma-butyrolactone (GBL), recently received increased public attention as they emerged as popular drugs of abuse. The actions of GHB/GBL are believed to be mediated by GABAB and/or specific GHB receptors, the latter corresponding to high-affinity [3H]GHB-binding sites coupled to G-proteins. To investigate the contribution of GABAB receptors to GHB actions we studied the effects of GHB in GABAB(1)-/- mice, which lack functional GABAB receptors. Autoradiography reveals a similar spatial distribution of [3H]GHB-binding sites in brains of GABAB(1)-/- and wild-type mice. The maximal number of binding sites and the KD values for the putative GHB antagonist [3H]6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylidene acetic acid (NCS-382) appear unchanged in GABAB(1)-/- compared with wild-type mice, demonstrating that GHB- are distinct from GABAB-binding sites. In the presence of the GABAB receptor positive modulator 2,6-di-tert-butyl-4-(3-hydroxy-2,2-dimethyl-propyl)-phenol GHB induced functional GTPgamma[35S] responses in brain membrane preparations from wild-type but not GABAB(1)-/- mice. The GTPgamma[35S] responses in wild-type mice were blocked by the GABAB antagonist [3-[[1-(S)-(3,4dichlorophenyl)ethyl]amino]-2-(S)-hydroxy-propyl]-cyclohexylmethyl phosphinic acid hydrochloride (CGP54626) but not by NCS-382. Altogether, these findings suggest that the GHB-induced GTPgamma[35S] responses are mediated by GABAB receptors. Following GHB or GBL application, GABAB(1)-/- mice showed neither the hypolocomotion, hypothermia, increase in striatal dopamine synthesis nor electroencephalogram delta-wave induction seen in wild-type mice. It, therefore, appears that all studied GHB effects are GABAB receptor dependent. The molecular nature and the signalling properties of the specific [3H]GHB-binding sites remain elusive.

Selective gamma-hydroxybutyric acid receptor ligands increase extracellular glutamate in the hippocampus, but fail to activate G protein and to produce the sedative/hypnotic effect of gamma-hydroxybutyric acid

Two gamma-hydroxybutyric acid (GHB) analogues, trans-gamma-hydroxycrotonic acid (t-HCA) and gamma-(p-methoxybenzyl)-gamma-hydroxybutyric acid (NCS-435) displaced [3H]GHB from GHB receptors with the same affinity as GHB but, unlike GHB, failed to displace [3H]baclofen from GABAB receptors. The effect of the GHB analogues, GHB and baclofen, on G protein activity and hippocampal extracellular glutamate levels was compared. While GHB and baclofen stimulated 5'-O-(3-[35S]thiotriphospate) [35S]GTPgammaS binding both in cortex homogenate and cortical slices, t-HCA and NCS-435 were ineffective up to 1 mm concentration. GHB and baclofen effect was suppressed by the GABAB antagonist CGP 35348 but not by the GHB receptor antagonist NCS-382. Perfused into rat hippocampus, 500 nm and 1 mm GHB increased and decreased extracellular glutamate levels, respectively. GHB stimulation was suppressed by NCS-382, while GHB inhibition by CGP 35348. t-HCA and NCS-435 (0.1-1000 microm) locally perfused into hippocampus increased extracellular glutamate; this effect was inhibited by NCS-382 (10 microm) but not by CGP 35348 (500 microm). The results indicate that GHB-induced G protein activation and reduction of glutamate levels are GABAB-mediated effects, while the increase of glutamate levels is a GHB-mediated effect. Neither t-HCA nor NCS-435 reproduced GHB sedative/hypnotic effect in mice, confirming that this effect is GABAB-mediated. The GHB analogues constitute important tools for understanding the physiological role of endogenous GHB and its receptor.

A tertiary alcohol analog of gamma-hydroxybutyric acid as a specific gamma-hydroxybutyric acid receptor ligand

gamma-Hydroxybutyric acid (GHB) shows great promise as a treatment for sleeping disorders but is also increasingly abused. The exact mechanism of action of GHB is yet to be delineated, but it is known to interact with specific GHB binding sites or receptors, to act as a weak agonist at GABA(B) receptors, and that GHB undergoes metabolism to GABA. In drug discrimination studies, GABA(B) agonists, and to a lesser extent GABA(A)-positive modulators, substitute for GHB. To delineate the relative contributions of each receptor system to the profile of GHB, tertiary alcohol analogs of GHB and its homolog, 5-hydroxypentanoic acid (UMB58), were prepared (UMB68 and UMB75, respectively), which cannot be metabolized to GABA-active compounds. Binding studies against [(3)H]NCS-382 [(2E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene) ethanoic acid] showed that the tertiary alcohol analog of GHB (UMB68) has similar affinity to GHB, with the longer chain analogs possessing lower affinity. Against [(3)H]GABA, UMB68 showed no affinity (IC(50) >100 microM) at GABA(A) or GABA(B) receptors. In vivo studies showed that, at behaviorally active doses, rats trained to discriminate GHB did not recognize the novel ligands as GHB. Thus, UMB68 is a selective GHB receptor ligand in binding assays, will not undergo metabolism to GABA-active compounds, and does not show the same effects as GHB in vivo. These data suggest that, although UMB68 binds to the GHB receptor, it does not have the observed GABA receptor-mediated effects of GHB in vivo and could provide a novel tool for studying the pharmacology of the GHB receptor in the absence of complicating GABAergic effects.

Stereoselectivity of NCS-382 binding to gamma-hydroxybutyrate receptor in the rat brain

gamma-Hydroxybutyric acid (GHB), a naturally occurring metabolite of gamma-aminobutyric acid (GABA), has been postulated to act both as a specific agonist of GHB receptors and as a weak GABA(B) receptor agonist. The racemic compound 6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylideneacetic acid (RS-NCS-382), the only available antagonist of GHB receptors, has been resolved in two enantiomers, R- and S-; the potency of the latter to displace 4-hydroxy [2-3-(3)H] butyric acid ([(3)H]GHB) and [(3)H]NCS-382 from GHB receptors, on one hand, and [(3)H]baclofen from GABA(B) receptors on the other was compared in rat brain homogenates. R-NCS-382 was found to be twice and 60 times more potent than the RS- and S-forms, respectively, in displacing [(3)H]GHB and 2 and 14 times, respectively, in displacing [(3)H]NCS-382 from GHB binding. Neither RS-NCS-382 nor its enantiomers inhibited [(3)H]baclofen binding up to a concentration of 1 mM. Our results demonstrate that R-NCS-382 is the enantiomer of RS-NCS-382 with higher affinity for GHB receptors.

GABA(B) receptor-mediated increase of neurosteroids by gamma-hydroxybutyric acid

Among the pharmacological actions of gamma-hydroxybutyric acid (GHB), some may involve GABA(A) receptor-mediated mechanisms. GHB, however, fails to directly interact with sites for agonists and modulators on the GABA(A) receptor complex. We hypothesized that, in vivo, GHB may interfere with GABA(A) receptor function by altering the brain concentrations of the neurosteroids 3 alpha-hydroxy-5 alpha-pregnan-20-one (allopregnanolone, AP) and 3 alpha,21-dihydroxy-5 alpha-pregnan-20-one (allotetrahydrodeoxycorticosterone, THDOC), positive allosteric modulators of GABA-gated chloride currents. In male Wistar rats, GHB dose-dependently (75-1000 mg/kg, i.p.) increased AP, THDOC and their precursors pregnenolone and progesterone in brain cortex and hippocampus. The increases of AP (4-5 fold) and THDOC (3-4 fold) elicited by 300 mg/kg GHB peaked between 30 and 90 min and abated by 180 min. The selective GABA(B) receptor antagonist SCH 50911 (50 mg/kg, i.p.) prevented the action of GHB, while the GABA(B) receptor agonist baclofen (5-10 mg/kg) mimicked it. NCS-382 (50 mg/kg, i.p.), the purported selective antagonist of the GHB receptor, failed to antagonize GHB, but at 300 mg/kg increased brain cortical neurosteroids to the same extent as 300 mg/kg GHB; coadministration of GHB and NCS-382, however, failed to yield an additive effect. These results strongly suggest that GHB, via a GABA(B) receptor-mediated mechanism, increases the brain concentrations of neurosteroids, whose properties as amplifiers of the GABA-gated chloride conductances may play a role in the GABA(A) receptor-mediated pharmacological actions of GHB.

Central effects of 1,4-butanediol are mediated by GABA(B) receptors via its conversion into gamma-hydroxybutyric acid

The aliphatic alcohol 1,4-butanediol in converted into gamma-hydroxybutyric acid (GHB) via two enzymatic steps: first, it is oxidised by alcohol dehydrogenase in gamma-hydroxybutyraldehyde; second, the latter is transformed, likely by aldehyde dehydrogenase, into GHB. Initially, the present study compared the sedative/hypnotic effect of GHB and 1,4-butanediol, measured as loss of righting reflex. 1,4-Butanediol was more potent than GHB, presumably because of a more rapid penetration of the blood brain barrier. Further alcohol dehydrogenase inhibitors, 4-methylpyrazole and ethanol, totally prevented the sedative/hypnotic effect of 1,4-butanediol; the aldehyde dehydrogenase inhibitor disulfiram partially blocked the sedative/hypnotic effect of 1,4-butanediol. Finally, the sedative/hypnotic effect of 1,4-butanediol was antagonised by the GABA(B) receptor antagonists, SCH 50911 [(2S)(+)-5,5-dimethyl-2-morpholineacetic acid] and CGP 46381 [(3-aminopropyl)(cyclohexylmethyl)phosphinic acid], but not by the putative GHB receptor antagonist NCS-382 (6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylideneacetic acid), indicating that it is mediated by GABA(B) but not GHB receptors. Taken together, these results suggest that the sedative/hypnotic effect of 1,4-butanediol is mediated by its conversion in vivo into GHB which, in turn, binds to GABA(B) receptors. Accordingly 1,4-butanediol, unlike GHB, failed to displace [(3)H]GHB and [(3)H]baclofen in brain membranes.

Elevation of AKR7A2 (succinic semialdehyde reductase) in neurodegenerative disease

Elevated levels of oxidative stress or decreased antioxidant defense mechanisms may underlie the regionally increased oxidative damage to brain observed in many neurodegenerative disorders. Phase I detoxification pathways for reactive aldehydes generated from lipid peroxidation include aldehyde dehydrogenases, alcohol dehydrogenases and aldo-keto reductases (AKR). In the present study, we examined the cellular expression of AKR family member, succinic semialdehyde reductase (AKR7A2) that reduces toxic aldehydes as well as catalyzing the biosynthesis of the neuromodulator gamma-hydroxybutyrate (GHB). Our results show that in the cerebral cortex and hippocampus, AKR7A2 is primarily localized to glial cells, astrocytes and microglia. In the midbrain, AKR7A2 was found in glia and neuromelanin-containing neurons of the substantia nigra, and the periaqueductal gray. In sections of cerebral cortex and hippocampus from patients with AD and DLB, AKR7A2 immunoreactivity was elevated in reactive astrocytes and microglial cells. Furthermore, total AKR7A2 protein levels were elevated in the cerebral cortex of patients with AD versus control individuals. Our data suggest that reactive gliosis, as a response to injury, may affect GHB neuromodulatory pathways in neurodegenerative disease and elevate aldehyde detoxification pathways.

Role of GABA(B) receptors in the sedative/hypnotic effect of gamma-hydroxybutyric acid

The present study was aimed at identifying the receptor systems involved in the mediation of the sedative/hypnotic effect of gamma-hydroxybutyric acid (GHB) in DBA mice. Administration of the putative antagonist of the GHB binding site, 6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylideneacetic acid (NCS-382; 50-500 mg/kg, i.p.), significantly increased the duration of loss of righting reflex induced by GHB (1000 mg/kg, i.p.). In contrast, the GABA(B) receptor antagonists, (2S)(+)-5,5-dimethyl-2-morpholineacetic acid (SCH 50911; 25-100 mg/kg, i.p.) and (3-aminopropyl)(cyclohexylmethyl)phosphinic acid (CGP 46381; 12.5-150 mg/kg, i.p.), completely prevented the sedative/hypnotic effect of GHB. SCH 50911 (100 and 300 mg/kg, i.p.) was also capable to readily reverse the sedative/hypnotic effect of GHB (1000 mg/kg, i.p.) in mice that had lost the righting reflex. SCH 50911 (100 mg/kg, i.p.) also completely abolished the sedative/hypnotic effect of the GABA(B) receptor agonist, baclofen. These results indicate that the sedative/hypnotic effect of GHB is mediated by the stimulation of GABA(B) receptors and add further support to the hypothesis that the GABA(B) receptor constitutes a central site of action of GHB.

The many faces of ecstasy

References to the word ecstasy in popular culture can mean different things to different individuals. The most common form of ecstasy (3,4-methylenedioxymethamphetamine [MDMA]), is an amphetamine with some hallucinogenic properties at high doses. It is directly neurotoxic to the human brain and has been linked to a number of deaths worldwide. Deaths result from hyperthermia, hyponatremia, or cerebral edema. A naturally occurring metabolite of gamma-aminobutyric acid, gammahydroxybutyrate (GHB) is a potent central nervous system depressant. Although GHB is a Schedule I drug, analogs remain widely available for consumption. Acute intoxication with GHB or its analogs leads to coma and respiratory depression. Chronic use of GHB or its analogs is associated with a withdrawal syndrome characterized by autonomic excitation. Herbal ecstasy refers to ephedrine-containing preparations. Acute and chronic overdoses of herbal ecstasy have been linked to hypertension, tachydysrythmias, myocardial infarctions, cerebrovascular accidents, and deaths. There is no regulation of the ephedrine content of available herbal ecstasy products.

Gamma-hydroxybutyric acid in alcohol preference, dependence and withdrawal

Gamma-hydroxybutyric acid (GHB) is an endogenous constituent of the mammalian brain, where it likely functions as a neurotransmitter or a neuromodulator. Its exogenous administration exerts a number of pharmacological effects, including reduction of intensity of alcohol withdrawal syndrome and alcohol consumption in both laboratory animals and human alcoholics.The clinical studies conducted to date, although often testing samples of limited size, feature GHB as an effective, well-tolerated and safe drug for the treatment of alcohol dependence. Behavioural data in rats suggest that GHB may produce alcohol-like effects. This similarity may explain why GHB produces positively reinforcing properties, being subsequently self-administered by rodents and sometimes abused by humans (although episodes of self-directed intake of GHB appear to be a limited phenomenon in alcoholics); in addition it provides support to the hypothesis that GHB constitutes for alcoholism a replacement therapy similar to methadone in heroin addiction.