Gamma-hydroxybutyrate, succinic semialdehyde and sleep

Sleep, plasticity and the pathophysiology of neurodevelopmental disorders: the potential roles of protein synthesis and other cellular processes

Sleep is important for neural plasticity, and plasticity underlies sleep-dependent memory consolidation. It is widely appreciated that protein synthesis plays an essential role in neural plasticity. Studies of sleep-dependent memory and sleep-dependent plasticity have begun to examine alterations in these functions in populations with neurological and psychiatric disorders. Such an approach acknowledges that disordered sleep may have functional consequences during wakefulness. Although neurodevelopmental disorders are not considered to be sleep disorders per se, recent data has revealed that sleep abnormalities are among the most prevalent and common symptoms and may contribute to the progression of these disorders. The main goal of this review is to highlight the role of disordered sleep in the pathology of neurodevelopmental disorders and to examine some potential mechanisms by which sleep-dependent plasticity may be altered. We will also briefly attempt to extend the same logic to the other end of the developmental spectrum and describe a potential role of disordered sleep in the pathology of neurodegenerative diseases. We conclude by discussing ongoing studies that might provide a more integrative approach to the study of sleep, plasticity, and neurodevelopmental disorders.

Evaluation of the reinforcing and discriminative stimulus effects of 1,4-butanediol and gamma-butyrolactone in rhesus monkeys

Metabolic precursors and prodrugs of gamma-hydroxybutyrate (GHB), including 1,4-butanediol (BDL) and gamma-butyrolactone (GBL), have sedative and anesthetic effects and might have positive reinforcing effects. BDL and GBL were evaluated using behavioral procedures that measure positive reinforcing effects and discriminative stimulus effects of drugs that modulate gamma-aminobutyric acid (GABA) at the GABA(A) receptor complex. One group of rhesus monkeys could respond for saline or the barbiturate methohexital (i.v.) in a self-administration paradigm. Two other groups of monkeys discriminated the barbiturate pentobarbital (i.g.) or the benzodiazepine midazolam (s.c.) from saline in a drug discrimination paradigm; another group of monkeys was treated with the benzodiazepine diazepam (5.6 mg/kg/day, p.o.) and discriminated the benzodiazepine antagonist flumazenil (s.c.) from vehicle. In self-administration experiments, methohexital and not BDL (0.1-3.2 mg/kg/injection) or GBL (0.1-3.2 mg/kg/injection) reliably maintained responding above saline levels. BDL and GBL, up to doses that suppressed responding, did not substitute for pentobarbital, midazolam or flumazenil. The onset of action for both drugs to decrease response rate was delayed (90 min for GBL and 150 min for BDL). These results suggest that any abuse-related effects of BDL and GBL are qualitatively different from the abuse-related effects of GABA(A) receptor modulators and further indicate that BDL and GBL do not have positive reinforcing effects in rhesus monkeys experienced with self-administration of a short-acting sedative-hypnotic.

GHB: a new and novel drug of abuse

There has been increasing attention in the United States to problems of abuse of gamma-hydroxybutyrate (GHB), with some evidence for problems in other parts of the world as well. In vitro and animal research show that, while GHB shares some properties with abused central nervous system depressant drugs, it has unique aspects of its pharmacology as well, including actions at a specific neural receptor which probably mediates many of its effects. Abuse potential assessment of GHB using standard animal models has not yielded a picture of a highly abusable substance, but little human testing has yet been done. Very little systematic data exist on tolerance and dependence with GHB, but both have been seen in human users. Quantitative data on the prevalence of GHB abuse is incomplete, but various qualitative measures indicate that a mini-epidemic of abuse began in the late 1980s and continues to the present. GHB is often included with the group of 'club drugs', and can be used as an intoxicant. It also has been used as a growth promoter and sleep aid and has been implicated in cases of 'date rape', usually in combination with alcohol. Undoubtedly the easy availability of GHB and some of its precursors has contributed to its popularity. Recent changes in the control status of GHB in the US may reduce its availability with as yet unknown consequences for the scope of the public health problem. Drug abuse experts need to familiarize themselves with GHB as possibly representing a new type of drug abuse problem with some unique properties.

Immunohistochemical studies of the localization of neurons containing the enzyme that synthesizes dopamine, GABA, or gamma-hydroxybutyrate in the rat substantia nigra and striatum

gamma-Hydroxybutyrate (GHB) is an endogenous metabolite of gamma-aminobutyric acid (GABA), which is synthesized in the neuronal compartment of the central nervous system. This substance possesses several properties that support its role as a neurotransmitter/neuromodulator in brain. In particular, it is synthesized by a specific pathway that transforms GABA into succinic semialdehyde via GABA-T activity; then succinic semialdehyde is converted into GHB by a specific succinic semialdehyde reductase (SSR). The last enzyme is considered as a marker for neurons that synthesize GHB. This compound binds in brain to receptors whose distribution, ontogenesis, kinetics, and pharmacology are specific. Endogenous GHB, but also GHB exogenously administered to rats, participate in the regulation of dopaminergic activity of the nigrostriatal pathway. To investigate the distribution of GHB neurons in this pathway and the anatomic relationships between dopaminergic and GHB neurons, immunocytochemical identification of dopamine, GABA, and GHB neurons was carried out in the substantia nigra and striatum of the rat. The following markers for these neurons were used: anti-tyrosine hydroxylase (TH) antibodies for dopamine neurons, anti-glutamate decarboxylase (GAD) antibodies for GABA neurons, and anti-succinic semialdehyde reductase (SSR) antibodies for GHB neurons. GABA neurons were studied because GAD and SSR co-exist frequently in the same neuron, and GABA alone also exerts its own regulatory effects on dopaminergic neurons. This study reveals the co-existence of GAD/SSR and GAD/SSR/TH in numerous neurons of the substantia nigra. However, some neurons appear to be only GAD or SSR positive. In the striatum, TH-positive terminals surround many GHB neurons. GAD innervation is abundant in close contact with unlabeled neurons in the caudate-putamen, whereas distinct SSR-positive punctuates are also present. The existence of SSR-reactive synapses and neurons was confirmed in the striatum at the electron microscopic level. On the basis of these results, a clear anatomo-functional relationship between GHB and dopamine networks cannot be defined; however, we propose the modulation by GHB of striatal intrinsic neurons that could then interfere with the presynaptic control of dopaminergic activity.

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.

gamma-aminobutyric acid type B receptors are expressed and functional in mammalian cardiomyocytes

gamma-Hydroxybutyrate (GHB), an anesthetic adjuvant analog of gamma-aminobutyrate (GABA), depresses cell excitability in hippocampal neurons by inducing hyperpolarization through the activation of a prominent inwardly rectifying K(+) (Kir3) conductance. These GABA type B (GABA(B))-like effects are clearly shown at high concentrations of GHB corresponding to blood levels usually reached during anesthesia and are mimicked by the GABA(B) agonist baclofen. Recent studies of native GABA(B) receptors (GABA(B)Rs) have favored the concept that GHB is also a selective agonist. Furthermore, cloning has demonstrated that GABA(B)Rs assemble heteromeric complexes from the GABA(B)R1 and GABA(B)R2 subtypes and that these assemblies are activated by GHB. The surprisingly high tissue content, together with anti-ischemic and protective effects of GHB in the heart, raises the question of a possible influence of GABA(B) agonists on excitable cardiac cells. In the present study, we provide electrophysiological evidence that GHB activates an inwardly rectifying K(+) current in rat ventricular myocytes. This effect is mimicked by baclofen, reversibly inhibited by GABA(B) antagonists, and prevented by pertussis toxin pretreatment. Both GABA(B)R1 and GABA(B)R2 are detected in cardiomyocytes by Western blotting and are shown to coimmunoprecipitate. Laser scanning confocal microscopy discloses an even distribution of the two receptors in the sarcolemma and along the transverse tubular system. Hence, we conclude that GABA(B)Rs are distributed not only in neuronal tissues but also in the heart, where they can be activated and induce electrophysiological alterations through G-protein-coupled inward rectifier potassium channels.

Ability of baclofen in reducing alcohol intake and withdrawal severity: I--Preclinical evidence

BACKGROUND

The similarities between the pharmacological effects of the gamma-aminobutyric acid receptor agonist, baclofen, and the alcohol-substituting agent, gamma-hydroxybutyric acid, led us to investigate whether baclofen was capable of reducing (a) ethanol withdrawal syndrome in ethanol-dependent rats and (b) voluntary ethanol intake in ethanol-preferring rats.

METHODS

In experiment 1, Wistar rats were rendered physically dependent on ethanol by the repeated administration of intoxicating doses of ethanol for 6 consecutive days. Baclofen was acutely administered intraperitoneally at doses of 10, 20, and 40 mg/kg. In experiment 2, baclofen (0, 2.5, 5, and 10 mg/kg, intraperitoneally) was administered once a day for 14 consecutive days to ethanol-preferring sP rats that had continuous access to ethanol (10%, v/v) and water under the two-bottle free choice regimen.

RESULTS

In experiment 1, baclofen dose-dependently decreased the intensity of ethanol withdrawal signs; furthermore, 20 mg/kg of baclofen protected from audiogenic seizures in ethanol-withdrawn rats. In experiment 2, baclofen selectively and dose-dependently reduced voluntary ethanol intake; a compensatory increase in water intake left total fluid intake virtually unchanged.

CONCLUSIONS

These results are in close agreement with those of a preliminary clinical study and suggest that baclofen may constitute a novel therapeutic agent for alcoholism.

Evaluation of the reinforcing and discriminative stimulus effects of gamma-hydroxybutyrate in rhesus monkeys

Gamma-hydroxybutyrate (GHB) is a metabolite of GABA that is present in the CNS and fulfils at least some of the criteria for a neurotransmitter. Its effects are generally similar to those of CNS depressants and include ataxia, sleep and anesthesia. It has also been suggested that GHB is a drug of abuse. The present experiment was designed to evaluate GHB in procedures predictive of abuse and dependence potential in rhesus monkeys. Three monkeys were surgically prepared with indwelling silicone venous catheters and allowed to self-administer methohexital or saline in twice-daily experimental sessions. Other groups of monkeys were trained in drug discrimination paradigms to discriminate D-amphetamine (AMPH; n = 4), pentobarbital (PB; n = 3) or triazolam (n = 3) from saline. Another group was maintained on diazepam daily and trained to discriminate flumazenil from saline (n = 2). GHB (0.01-10 mg/kg per injection) maintained self-administration marginally above saline levels at one dose (3.2 or 10 mg/kg) in two of the three monkeys tested. GHB (1.0-178 mg/kg, subcutaneously (s.c.) or intragastrically (i.g.)) did not reliably substitute as a discriminative stimulus for any of the training conditions. Taken together with previous results, the present experiment suggests that GHB has, at most, low potential for abuse.

Sulpiride, but not haloperidol, up-regulates gamma-hydroxybutyrate receptors in vivo and in cultured cells

Five days of gamma-hydroxybutyrate (GHB) administration (3 x 500 mg kg(-1) day(-1) i.p.) to rats resulted in a significant decrease in the density of GHB receptors measured in the whole rat brain without modification of their corresponding affinity. Similar administration of (-)-sulpiride (2 X 100 mg kg(-1) day(-1) i.p. for 5 days) induces an up-regulation of GHB receptors without change in their dissociation constants (Kd). Haloperidol (2 X 2 mg day(-1) i.p. for 5 days) showed no effect. Administered chronically via osmotic minipumps directly into the lateral ventricles, (-)-sulpiride (60 microg day(-1) for 7 days) and GHB (600 microg day(-1) for 7 days) up-regulated and down-regulated rat brain GHB receptors, respectively. Finally, in a mouse hybridoma cell line (NCB-20 cells) expressing GHB receptors, the treatment of these cells with 1 mM GHB, 100 microM (-)-sulpiride or 1 mM GABA decreases, increases and induces no change, respectively, in the density of GHB receptors after 3 days of treatments. These results indicate that chronic GHB treatment modifies the expression of its receptor and that sulpiride also induces plastic changes in GHB receptors perhaps via antagonistic properties.

The gamma-hydroxybutyrate signalling system in brain: organization and functional implications

gamma-Hydroxybutyrate is a metabolite of GABA which is synthesized and accumulated by neurons in brain. This substance is present in micromolar quantities in all brain regions investigated as well as in several peripheral organs. Neuronal depolarization releases gamma-hydroxybutyrate into the extracellular space in a Ca(2+)-dependent manner. Gamma-hydroxybutyrate high-affinity receptors are present only in neurons, with a restricted specific distribution in the hippocampus, cortex and dopaminergic structures of rat brain (the striatum in general, olfactory bulbs and tubercles, frontal cortex, dopaminergic nuclei A9, A10 and A12). Stimulation of these receptors with low amounts of gamma-hydroxybutyrate induces in general hyperpolarizations in dopaminergic structures with a reduction of dopamine release. However, in the hippocampus and the frontal cortex, it seems that gamma-hydroxybutyrate induces depolarization with an accumulation of cGMP and an increase in inositol phosphate turnover. Some of the electrophysiological effects of GHB are blocked by NCS-382, a gamma-hydroxybutyrate receptor antagonist while some others are strongly attenuated by GABAB receptors antagonists. Gamma-hydroxybutyrate penetrates freely into the brain when administered intravenously or intraperitoneally. This is a unique situation for a molecule with signalling properties in the brain. Thus, the gamma-hydroxybutyrate concentration in brain easily can be increased more than 100 times. Under these conditions, gamma-hydroxybutyrate receptors are saturated and probably desensitized and down-regulated. It is unlikely that GABAB receptors could be stimulated directly by GHB. Most probably, GABA is released in part under the control of GHB receptors in specific pathways expressing GABAB receptors. Alternatively, GABAB receptors might be specifically stimulated by the GABA formed via the metabolism of gamma-hydroxybutyrate in brain. In animals and man, these GHBergic and GABAergic potentiations induce dopaminergic hyperactivity (which follows the first phase of dopaminergic terminal hyperpolarization), a strong sedation with anaesthesia and some EEG changes with epileptic spikes. It is presumed that, under pathological conditions (hepatic failure, alcoholic intoxication, succinic semialdehyde dehydrogenase defects), the rate of GHB synthesis or degradation in the peripheral organ is modified and induces increased GHB levels which could interfere with the normal brain mechanisms. This pathological status could benefit from treatments with gamma-hydroxybutyric and/or GABAB receptors antagonists. Nevertheless, the regulating properties of the endogenous gamma-hydroxybutyrate system on the dopaminergic pathways are a cause for the recent interest in synthetic ligands acting specifically at gamma-hydroxybutyrate receptors and devoid of any role as metabolic precursor of GABA in brain.

Synaptic vesicle-associated glutamate decarboxylase: identification and relationship to insulin-dependent diabetes mellitus

Glutamic acid decarboxylase (GAD) catalyzes the biosynthesis of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). GAD has been suggested as an autoantigen in insulin-dependent diabetes mellitus and stiff-man syndrome. Recently, three forms of membrane-associated GAD (MGAD) have been characterized in porcine brain, but the subcellular localization and function of these proteins are unknown. We present evidence that GAD activity is associated with synaptic vesicles from porcine brain. These vesicles contain a 60 kDa protein recognized by serum from patients with insulin-dependent diabetes mellitus, probably MGADII, as shown by subcellular fractionation and immunoblotting. These results raise the possibility that the association of MGADII with synaptic vesicles may be crucial for its role as an autoantigen in insulin-dependent diabetes mellitus.

Gamma-hydroxybutyrate: an overview of the pros and cons for it being a neurotransmitter and/or a useful therapeutic agent

Gamma-hydroxybutyrate (GHB) is a catabolite in brain of gamma-aminobutyrate (GABA) and is also found in nonneuronal tissues. It is present in the brain at about one thousandth of the concentration of its parent compound. High affinity and specific uptake, and energy dependent transport systems for GHB have been described in brain in addition to a class of high affinity binding sites, functional at a rather unphysiologically low pH. Administration of large doses of GHB to animals and man leads to sedation, and at the highest doses, anaesthesia. These effects are prominent when GHB brain levels are over one hundred-fold the endogenous levels. In some animals, GHB administration also induces an electroencephalographic and behavioural changes resembling that of human petit mal epilepsy. GHB has been used in man as an anaesthetic adjuvant. GHB lowers cerebral energy requirements and may play a neuroprotective role. Administered GHB profoundly effects the cerebral dopaminergic system by a mechanism which remains to be unravelled. GHB has been tested with success on alcoholic patients where it attenuates the withdrawal syndrome. It is indicated here that in this situation, it may owe its effect by acting as a pro-drug of the neurotransmitter GABA into which it can be transformed. As administration of GHB, a GABAB receptor agonist and a natural opioid peptide all elicit similar abnormal EEG phenomena, it may be suggested that they are acting via a common pathway. The petit mal epileptic effects of GHB might be ascribed to its direct, or indirect agonist properties after transformation to a pool of GABA at the GABAB receptor or via interactions at its own binding sites linked to a similar series of biochemical events. Some anticonvulsant drugs, the opiate antagonist naloxone and a synthetic structural GHB analogue antagonise certain behavioural effects of GHB administration. It is postulated that GHB exerts some of its effects via transformation to GABA pools, and that substances which inhibit this process antagonise its effects by blocking GABA formation. GHB has been proposed as a neurotransmitter, although straightforward evidence for this role is lacking. Evidence for and against GHB, as a neurotransmitter, is reviewed here together with a discussion of its potential as a therapeutically useful drug.

Epileptogenic spikes and seizures but not high voltage spindles are induced by local frontal cortical application of gamma-hydroxybutyrate

Combining the methods of microdialysis and EEG recording, we have examined the effect of unilaterally, intracortically applied gamma-hydroxybutyrate (GHB) on frontal cortical EEG activity in freely moving rats. GHB, a natural endogenous GABA metabolite, is known to induce rhythmic spike and wave activity, resembling generalized petit mal epilepsy. Without GHB, spontaneous high voltage spindles (HVS, 6-9 Hz) were observed during awake and immobile behavior in most of the animals (HVS rats), while others never had any HVS. In those both groups of animals intracortical application of GHB induced epileptogenic spikes (< 0.5 Hz) behaviorally accompanied by occasional myoclonic jerks and epileptic discharges (< 2 Hz) with behavioral convulsions and contraversive movements towards the left hindlimb (seizures) but did not induce HVS or spike and waves, as reported after systemic application. In the group of rats with spontaneous occurring HVS the amplitude of the HVS on the side of the microdialysis probe was suppressed by GHB and GHB-induced spikes invading the contralateral cortex frequently triggered and terminated local HVS. The results point to different neural mechanisms for the generation of HVS and spikes and epileptic discharges (seizures) induced after local intracortical application of GHB.

gamma-Hydroxybutyric acid in the treatment of alcohol dependence: a double-blind study

The effect of gamma-hydroxybutyric acid on alcohol consumption and alcohol craving in alcoholics was investigated in a randomized double-blind study versus placebo. Patients were treated as outpatients during a three month period either with gamma-hydroxybutyric acid (50 mg/kg/day, divided into three daily doses) or with placebo. Of the 82 alcoholics that entered the study, 71 completed it, 36 in the gamma-hydroxybutyric acid and 35 in the placebo group. Alcohol consumption was assessed by the subject's self report. At the 3rd month of treatment, 11 patients in the gamma-hydroxybutyric acid group referred to be abstinent and 15 referred controlled drinking; while in the placebo group only two and six patients referred abstinence and controlled drinking, respectively. Serum-gammaglutamyl-transferase activity correlated with the admitted alcohol consumption. Gamma-hydroxybutyric acid treatment decreased alcohol craving during the 3 months of treatment. Transient side effects were noted by six patients on gamma-hydroxybutyric acid and two on placebo. The results suggest that gamma-hydroxybutyric acid may be useful in the treatment of alcohol dependence.

Anti-sedative and anti-cataleptic properties of NCS-382, a gamma-hydroxybutyrate receptor antagonist

NCS-382 possesses antagonistic properties at gamma-hydroxybutyrate receptor sites. Its effect on the sedative/cataleptic behaviour observed in rats after gamma-hydroxybutyrate administration was investigated. NCS-382 diminished, in a dose-dependent manner, the sedative and/or cataleptic effects of gamma-hydroxybutyrate, as revealed by a variety of sensorimotor tests. These results indicate that the well-known sedative/anaesthetic effects induced by gamma-hydroxybutyrate administration are provoked via stimulation of a specific class(es) of gamma-hydroxybutyrate receptors which exist in the rat brain and which could mediate a local stimulation of opiate synthesis and release.

gamma-Hydroxybutyric acid-induced seizures bear no relation to core temperature

The hypothesis that the absencelike seizures induced by gamma-hydroxybutyrate (GHB) are secondary to the effect of this drug on body temperature was tested using the prodrug of GHB, gamma-butyrolactone (GBL). Dosages of GBL less than 400 mg/kg produced a consistent profound hypothermia associated with bilaterally synchronous spike-wave discharges (SWD), whereas higher doses were associated with a more complex effect on core temperature associated with an EEG pattern of burst suppression. The threshold dose for the hypothermia and SWD was the same, but the temperature changes occurred later and lasted longer than the SWD induced by GHB. Rats aged less than 28 days were less sensitive to the hypothermia but more sensitive to the SWD produced by GHB than adult animals. The antiepileptic drug (AED) ethosuximide (ESM), known to attenuate GHB-induced SWD did so, but had no effect on the hypothermia, whereas GHB-induced hypothermia, but not SWD, was blocked by raising the ambient temperature from 26 degrees to 32 degrees C. These data do not support the hypothesis that GHB-induced absencelike seizure activity is a result of the hypothermia produced by this drug. Rather they suggest that the SWD and hypothermia are caused by separate, independent mechanisms.

Localization studies of gamma-hydroxybutyrate receptors in rat striatum and hippocampus

Quantitative autoradiography using [3H] gamma-hydroxybutyrate was used in combination with anatomic and neurotoxic lesions to localize the gamma-hydroxybutyrate (GHB) receptors in the striatum and hippocampus of rat brain. 6-Hydroxydopamine (6-OHDA) lesions of the nigro-striatal pathway failed to reduce [3H] gamma-hydroxybutyrate binding in the striatum. In contrast, kainic acid (KA) lesions of the caudate-putamen (CPu) resulted in about 45% loss of binding. For hippocampus, lesions of septo-hippocampal pathway did not modify receptor density but intrahippocampal kainic acid injection largely attenuated (50%) [3H] GHB binding. These results demonstrate that gamma-hydroxybutyrate receptors in the CPu and dorsal hippocampus are principally located on intrinsic neurons which may participate in the functional expression of the role gamma-hydroxybutyrate has in these structures.

Electroencephalographic investigations in rabbits of drugs acting at GABA-benzodiazepine-barbiturate/picrotoxin receptors complex

This paper describes the EEG profiles, observed in rabbits, of drugs which affect GABA synaptic activity at GBB complex. Drugs which enhance GABA synaptic activity induce sedation associated with EEG synchronization. However, muscimol, THIP, GHB and baclofen induce signs of CNS stimulation (light tremors of the forelimbs, chewing, light nystagmus and hyperpnea) associated with EEG spikes. Signs of light stimulation (chewing and jerks of the head) also occur after BDZs and barbiturates, and are associated with the presence of 12-24 and 20-25 Hz waves, respectively. Drugs which reduce GABA synaptic activity (bicuculline, inverse BDZ agonists, PTZ, picrotoxin and Ro 5-3663) induce three dose-dependent stages of EEG changes: trains of slow waves, trains of spike-and-wave complexes and paroxysmal activity in the rostral encephalic structures without apparent changes of the electrical activity in the spinal cord. The first two stages are associated with a behavioral state of alert and the third stage with tonico-clonic convulsions. Among the inverse BDZ agonists, DMCM and beta-CCM elicit all three stages, whereas FG 7142 and beta-CCE induce only the first two and CGS 8216 only the first. The BDZ antagonists Ro 15-1788 and Ro 15-3505 (0.2-30 mg/kg IV) do not significantly affect the EEG pattern. However, they selectively inhibit the effects of diazepam and of the inverse BDZ agonists. In both cases, the inhibition is observed with doses as low as 0.2 mg/kg IV and leads to an EEG desynchronization. The possible involvement of the modifications of GABA synaptic activity in the etiology of both petit mal and grand mal epilepsies is discussed.

Acute and short term effects of ethanol on the metabolism of glutamic acid and GABA in rat brain

Although alcoholic intoxication is attributed to its pharmacological effects on the cell membranes in brain, the rapid metabolic utilisation of the same alters the metabolism of brain affecting the metabolism of glutamate and GABA which have varied metabolic roles besides serving a major proportion of synaptic activity. A study on the effects of ethanol, both acute and short-term, on glutamate (glu) and GABA metabolism in various regions of rat brain was carried out. Increased activities of glutamic acid decarboxylase (GAD) and aspartic acid aminotransferase (AST) in all brain regions, but decreased activity of glutamic acid dehydrogenase (GDH) in cerebral cortex (CC) and cerebellum (CB) following ethanol administration in brain was observed. Differential effects of ethanol were also obtained on the contents of glu and aspartate (asp), which were increased in CC, CB, and brain stem (BS) regions, as opposed to GABA content, which, although found to increase in acute toxicity, showed a decrease in all of the above brain regions in short-term toxicity. It is concluded that the above changes in glu, asp and GABA represent the consequences of metabolic utilization of alcohol in the brain, probably more a state of cerebral excitation than depression, and the changes may be a compensatory phenomenon.

Ontogeny of gamma-hydroxybutyric acid. II. Electroencephalographic effects

The ontogeny of petit mal-like seizures induced by gamma-hydroxybutyrate (GHB) was investigated. The prodrug of GHB, gamma-butyrolactone (GBL) was administered in varying dosages under continuous EEG monitoring from cortical and depth electrodes to rats varying in postnatal age from 1 to 85 days. The brain pharmacokinetics of GHB were determined at various ages as was the effect of ethosuximide on GBL-induced EEG changes. In adult rats, GBL produced a predictable sequence of electrical events beginning with spike bursts and progressing to polyspiking separated by low voltage activity. In 1-day-old rats, GBL produced voltage suppression with stupor. Poorly organized spiking appeared at postnatal day 3 and by day 9 marked burst suppression with polyspiking separated by low voltage activity was noted. However, the full array of electrical events seen in adult rats did not appear until day 28. Ethosuximide was ineffective against GHB seizure until the third postnatal week of life. GHB had a longer half-life in brain in the first week of postnatal life. These data suggest that in the rodent, petit mal-like seizure activity may require a fully mature brain and raise the possibility of different mechanisms being responsible for the various stages of EEG changes induced by GBL.

Depolarization-evoked release of gamma-hydroxybutyrate from rat brain slices

The release of gamma-hydroxybutyrate from preloaded rat brain striatal slices was investigated. K+-induced depolarization caused an efflux of gamma-hydroxybutyrate of about 50 fmol min-1 mg-1 (wet weight), but in a Ca2+-free medium containing Mg2+, the evoked release was reduced by 50-60%. The release was higher when 100 microM veratridine was used as a depolarizing agent. The efflux of gamma-hydroxybutyrate is related to veratridine and K+ concentration, and is strongly inhibited by 10 microM tetrodotoxin. The Ca2+ channel blocker verapamil induces a large decrease in the efflux of gamma-hydroxybutyrate after both K+- and veratridine-induced depolarization. These results are in favour of a possible transmitter function for gamma-hydroxybutyrate in rat striatum.

Central injections of the GABA-transaminase inhibitor ethanolamine-O-sulfate (EOS): effects on brain [14C]2-deoxy-D-glucose uptake and behavior in rats

Brain glucose utilization was examined 24 h after single intracisternal injections of the GABA-transaminase inhibitor ethanolamine-O-sulfate (EOS) in rats. Qualitative autoradiography indicated a pronounced and homogeneous depression in [14C]2-deoxy-D-glucose ([14C]2DG) uptake throughout the brains of rats treated with 200 or 400 micrograms EOS. Quantitative scintillation counting of 14C in 9 brain areas of other rats confirmed the marked, generalized decrease in label uptake 24 h after EOS. Food intake measurements confirmed previous reports of dose-dependent anorexia after EOS. Rats treated with the 200 micrograms dose showed decreased open-field activity 24 h after injection but no other deficits in various tests of sensorimotor function or in tail-pinch-induced feeding. Rats treated with the 400 micrograms dose also showed deficits in open-field activity, plus deficits in orientation to touch stimuli, longer latencies than controls in catalepsy tests, and faster habituation of startle responses to sound. This group showed normal feeding responses to tail-pinch stimulation in the presence of solid food but not in the presence of liquid food. It was concluded that sensorimotor deficits may play some role in the anorexigenic effects of EOS but are probably not their primary cause. The discrepancy between the apparent degree of depression of brain glucose utilization and the comparatively mild behavioral deficits observed would suggest the possibility that metabolic fuels other than glucose may be mobilized following central EOS treatment.

Positive cooperativity in high affinity binding sites for gamma-hydroxybutyric acid in rat brain

High affinity binding sites for gamma-hydroxybutyrate have recently been shown to exist on crude membranes of rat brain. These sites exhibit a dissociation constant of 95 nM and a capacity of 557 fentomoles per mg protein. However, after more extensive washing of the crude membrane fraction and performing binding experiments at a lower concentration of radioactive GHB (below 20 nM), the existence of another binding site for GHB with a higher affinity than previously described was discovered. The data concerning this binding site are in favour of positive cooperative binding characteristics. This binding site may play a role in the mediation of the multiple physiological and pharmacological effects of GHB in the rat CNS and its presence provides additional evidence in favour of a neuromodulator or neurotransmitter role of GHB.

gamma-Hydroxybutyrate: cerebral metabolic, vascular, and protective effects

The cerebral protection afforded by each of several preparations of gamma-hydroxybutyrate (GHB) was examined in the hypoxic (FiO2 = 0.05) mouse model. The greatest increase in survival time (85%) occurred after pretreatment with 300 mg/kg given as buffered gamma-butyrolactone (GBL). Compared with previous studies employing the same hypoxic model, this increase was less than that observed with certain barbiturates and equal to that observed with certain anesthetics. The cerebral and systemic metabolic and vascular effects of each of several preparations of GHB were examined in a canine model. The cerebral metabolic rate for oxygen (CMRO2) tended to increase after GHB 100 mg/kg, then progressively decreased after cumulative doses of 600 mg/kg and 1100 mg/kg. The greatest depression in CMRO2 (48%) occurred with 1100 mg/kg given as unbuffered GBL. With each preparation and at every dose, a reduction in cerebral blood flow (CBF) exceeded the reduction in CMRO2. The major systemic effect was an almost two-thirds reduction in cardiac output at the largest doses. Assuming no species difference the cerebral protection observed with GHB is probably limited by both the reduction in cardiac output and the unfavorable relationship of cerebral oxygen supply to demand (CBF/CMRO2). Brain biopsies taken after the cumulative dose of GHB 1100 mg/kg showed a trend toward lower phosphocreatine levels and higher lactate and lactate/pyruvate levels than in untreated dogs.

Effects of gamma-hydroxybutrate and gamma-butyrolactone on cerebral energy metabolism during exposure and recovery from hypoxemia-oligemia

Cerebral hypoxia-oligemia was produced by lowering of the arterial PO2 to 30 mm Hg and by right common carotid artery occlusion in rats who were pretreated with intravenous Krebs' solution, gamma-hydroxybutyrate (GHB) (500 mg/kg) or gamma-butyrolactone (GBL) (300 mg/kg). At 0.5 h exposure the right cerebral hemisphere of animals receiving Krebs', GHB or GBL showed equivalent decreases of ATP and phosphocreatine and increase of ADP, AMP and lactate which indicated that these depressant drugs had no beneficial effect on the energy metabolism of the acutely hypoxic-oligemic brain. In a second series of rats in which Krebs' solution, GHB or GBL were administered to animals during the early recovery period from 0.5 h hypoxic-oligemic exposure, the brain metabolic patterns of the right hemisphere indicated that GHB retarded the restitution of energy phosphates and the oxidation of the accumulated lactate; whereas, GBL led to a delayed metabolic deterioration. It is concluded that GHB and GBL do not beneficially alter cerebral energy metabolism during acute hypoxia-oligemia and that their administration during restitution may result in metabolic alterations which suggest an unfavorable effect.

gamma-Hydroxybutyric acid is not a GABA-mimetic agent in the spinal cord

gamma-Hydroxybutyric acid (GHB), a pharmacologically active central nervous system constituent, has been postulated to function as a gamma-aminobutyric acid (GABA) agonist. This hypothesis was tested directly on GABAergic synapses in isolated, superfused frog spinal cord. Addition of GHB to the superfusate produced effects on primary afferent terminals that were distinctly different from the effects of GABA. Thus, although both compounds depressed dorsal root potentials, GHB hyperpolarized terminals while GABA depolarized the same structures. The GABA responses were antagonized by bicuculline and picrotoxin, but these alkaloids did not change GHB's actions. In addition, GHB altered neither high-affinity uptake by cord slices, nor potassium-evoked release of tritiated GABA from them. GHB did not directly release GABA from spinal slices preloaded with [3H]GABA. These observations suggest that the central nervous system actions of GHB are not dependent upon its ability to activate GABAergic synapses or to modify GABAergic mechanisms.

The elimination of pollution by a non inhalational technique

A method is described whereby major surgery can be accomplished without inhalational anaesthtic agents, thus completely eliminating operating room pollution. The method is based on the balanced use of three intravenous agents--morphine, alcuronium and gamma-hydroxybutyrate (GHB). In the dose chosen for GHB, reliable unconsciousness can be produced for surgery of any length, and using physostigmine as an antidote, patients can be wakened within ten minutes. The advantages are convenience, simplicity of equipment, low cost, absence of pollution and good patient acceptance. The disadvantages are a certain incidence of hypertension and in this series, a small failure rate with the antidote.

Reversal of the anaesthetic action of sodium gamma-hydroxybutyrate

Physostigmine was administered intravenously to 25 patients, anaesthetised with sodium gamma-hydroxybutyrate (GHB), and their emergence from anesthesia was studied. Physostigmine (2 mg) brought about rapid, safe, reliable and sustained awakening after a "latent period" varying from 2-10 minutes (mean 6-2 minutes+/-S.D. 2-2) in 24 patients. In the one patient not awake at 10 minutes, a second dose of physostigmine produced awakening in an additional 8 minutes. No serious side effects were attributable to the physostigmine. This finding may warrant a reconsideration of the place of GHB in anaesthetic practice.