Effects of baclofen and gamma-hydroxybutyrate on rat striatal and mesolimbic 5-HT metabolism

Sodium oxybate: a potential new pharmacological option for the treatment of fibromyalgia syndrome

Fibromyalgia syndrome (FMS) is a common disorder, characterized by diffuse pain and tenderness, stiffness, fatigue, affective disorders and significant sleep pathology. A new set of diagnostic criteria have been developed which should make it easier for a busy clinician to diagnose the condition. US Food and Drug Administration (FDA) approved medications for the treatment of FMS have, for the most part, been geared to modulate the pain pathways to give the patient some degree of relief. A different kind of pharmacological agent, sodium oxybate (SXB), is described that is currently approved for the treatment of excessive daytime sleepiness and cataplexy in patients with narcolepsy. SXB, an endogenous metabolite of the inhibitory neurotransmitter gamma-hydroxybutyrate, is thought to act independently as a neurotransmitter with a presumed ability to modulate numerous other central nervous system neurotransmitters. In addition SXB has been shown to robustly increase slow wave sleep and decrease sleep fragmentation. Several large clinical trials have demonstrated SXB's ability to statistically improve pain, fatigue and a wide array of quality of life measurements of patients with fibromyalgia. SXB is not FDA approved to treat fibromyalgia.

Pharmacological aspects of the combined use of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) and gamma-hydroxybutyric acid (GHB): a review of the literature

Epidemiological studies show that the use of club drugs is on the rise. Furthermore, the last few decades have seen a rise in patterns of polydrug use. One of the combinations frequently used is ecstasy (MDMA) with gammahydroxybutyrate (GHB). For effective prevention it is important to be aware of this phenomenon and of the pharmacology of these drugs. The effects of the combination extend to different neurotransmitter systems, including serotonin, dopamine and noradrenaline. Studies investigating the effects of combinations of psychoactive substances are limited. In this review we describe the subjective effects of the MDMA/GHB combination. Furthermore, we review the individual actions of MDMA on serotonin, dopamine and noradrenaline systems. In addition, actions of GHB on these systems are discussed as a possible pharmacological basis for the interaction of both drugs. It is postulated that GHB attenuates the unpleasant or dysphoric effects of MDMA by its effect on the central dopaminergic system.

Sodium oxybate: neurobiology and clinical efficacy

Sodium oxybate is the sodium salt of γ-hydroxybutyrate (GHB), an endogenous short-chain fatty acid that is speculated to function as a neurotransmitter in the mammalian CNS. Pharmacodynamic effects of exogenously-administered sodium oxybate may include modulating the release of neurotransmitters, including γ-aminobutyric acid, dopamine, endogenous opioids and serotonin, and stimulating release of growth hormone. It is rapidly absorbed, with approximately 25% bioavailability and a plasma half-life of 40–60 min, necessitating twice-nightly dosing. Sodium oxybate is indicated for the treatment of cataplexy and excessive daytime sleepiness in patients with narcolepsy, and has been shown to improve disrupted night-time sleep and increase Stage 3 and 4 (slow-wave restorative) sleep in this patient population. The most common adverse events reported in clinical trials in patients with narcolepsy include headache, nausea, dizziness, nasopharyngitis, somnolence, vomiting and urinary incontinence.

Gamma-hydroxybutyrate increases tryptophan availability and potentiates serotonin turnover in rat brain

Gamma-hydroxybutyrate (GHB) is both a therapeutic agent and a recreative drug. It has sedative, anxiolytic and euphoric effects. These effects are believed to be due to GHB-induced potentiation of cerebral GABAergic and dopaminergic activities, but the serotonergic system might also be involved. In this study, we examine the effects of pharmacological doses of GHB on the serotonergic activity in rat brain. Administration of 4.0 mmol/kg i.p. GHB to rats induces an accumulation of tryptophan and 5-HIAA (5-hydroxyindole acetic acid) in the frontal cortex, striatum and hippocampus without causing significant change in the tissue serotonin content. In the extracellular space, GHB induced a slight decrease in serotonin release. The tryptophan and 5-HIAA accumulation induced by GHB is mimicked by the GHB receptor agonist para-chlorophenyl-transhydroxycrotonate (NCS-356) and blocked by NCS-382 (6,7,8,9-tetrahydro-5-[H]-benzocycloheptene-5-ol-4-ylidene acetic acid) a selective GHB receptor antagonist. GHB induces the accumulation of either a derivative of or [3H]-tryptophan itself in the extracellular space, possibly by increasing tryptophan transport across the blood-brain barrier. The blood content of certain neutral amino-acids, including tryptophan, is also increased by peripheral GHB administration. Some of the effect of GHB could be reproduced by baclofen and reduced by the GABAB antagonist CGP 35348. Taken together, these results indicate that the GHB-induced stimulation of tissue serotonin turnover may be due to an increase in tryptophan transport to the brain and in its uptake by serotonergic cells. As the serotonergic system may be involved in the regulation of sleep, mood and anxiety, the stimulation of this system by high doses of GHB may be involved in certain neuropharmacological events induced by GHB administration.

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.

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

gamma-Hydroxybutyric acid (GHB), a naturally occurring metabolite of GABA, is present in micromolar concentrations in various areas of the mammalian brain. Specific GHB binding sites, uptake system, synthetic and metabolizing enzymes have been identified in CNS. The present study shows the anatomical distribution of GHB binding sites in sections of primate (squirrel monkey) and human brain by radioligand quantitative autoradiography. In both species the highest densities of binding sites were found in the hippocampus, high to moderate densities in cortical areas (frontal, temporal, insular, cingulate and entorhinal) and low densities in the striatum; no binding sites were detected in the cerebellum. High density of GHB binding was found in the monkey amygdala. In addition the binding characteristics of [(3)H]GHB to membrane preparations of human brain cortex were examined. Scatchard analysis and saturation curves revealed both a high (K(d1) 92+/-4.4 nM; B(max1) 1027+/-110 fmol/mg protein) and a low-affinity binding site (K(d2) 916+/-42 nM; B(max2) 8770+/-159 fmol/mg protein). The present study is the first report on the autoradiographic distribution of specific GHB binding sites in the primate and human brain: such distribution is in both species in good agreement with the distribution found in the rat brain.

Characterization of the discriminative stimulus effects of gamma-hydroxybutyric acid as a means for unraveling the neurochemical basis of gamma-hydroxybutyric acid actions and its similarities to those of ethanol

The present paper reviews the drug discrimination studies, both from the literature and from this laboratory, conducted to investigate the pharmacological profile of the discriminative stimulus effects of gamma-hydroxybutyric acid. Collectively, the results of these studies suggest that: (1) the discriminative stimulus effects of gamma-hydroxybutyric acid are composed of different cues, each one being the effect of gamma-hydroxybutyric acid on a specific receptor system; (2) the proportion of each component cue varies as the training dose of gamma-hydroxybutyric acid is increased; (3) the gamma-aminobutyric acid B-mediated cue is a major ingredient of the mixed stimulus of gamma-hydroxybutyric acid, but it is more prominent at high training doses than at low training doses of gamma-hydroxybutyric acid; and (4) positive modulation of the gamma-aminobutyric acid A receptor is a relevant part of the discriminative stimulus effects of low gamma-hydroxybutyric acid doses. Finally, data indicating symmetrical generalization between the discriminative stimulus effects of a specific range of doses of gamma-hydroxybutyric acid and those of ethanol are discussed in regard to their further support of the hypothesis that gamma-hydroxybutyric acid may exert its antialcohol effects through a substitution mechanism.

Gamma-hydroxybutyric acid: an evaluation of its rewarding properties in rats and mice

Gamma-hydroxybutyric acid, an endogenous compound present in mammalian brain and supposed to be a neurotransmitter or neuromodulator, has been shown to affect several aspects of dependence from some drugs of abuse. It has been successfully used in clinical practice to alleviate both alcohol and opiate withdrawal symptoms. The aim of this study was to investigate whether gamma-hydroxybutyric acid possesses rewarding properties by means of conditioned place preference and intravenous self-administration paradigms. In the present study, gamma-hydroxybutyric acid induced conditioned place preference in rats, was intravenously self-administered by drug-naive mice, and altered cocaine intravenous self-administration in rats. Although to date the physiological role of this compound still remains unclear, there is no doubt that gamma-hydroxybutyric acid, in addition to its proved effect on alcohol and opiate dependence, possesses reinforcing properties of its own and may interfere with the neurochemical events in the rewarding effects produced by psychostimulant drugs. Our investigation points out the abuse liability of this drug, suggesting the use of particular precaution in handling gamma-hydroxybutyric acid as a clinically useful drug.

Involvement of GABA(A) and GABA(B) receptors in the mediation of discriminative stimulus effects of gamma-hydroxybutyric acid

The present study was designed to further investigate the pharmacological profile of the discriminative stimulus effects of gamma-hydroxybutyric acid (GHB). Drugs acting at the gamma-aminobutyric acid (GABA)B receptor (baclofen and CGP 35348), GABA(A)/benzodiazepine receptor complex (diazepam), N-methyl-D-aspartate (NMDA) receptor complex (dizocilpine), and cannabinoid receptor (WIN 55,212-2) were tested for substitution or blockade of the GHB interoceptive cue in rats trained to discriminate either 300 or 700 mg/kg of GHB i.g. from water in a T-maze, food-reinforced drug discrimination paradigm. Baclofen completely substituted for both training doses of GHB; however, its potency in substituting for GHB increased as the training dose of GHB was increased. CGP 35348 partially and completely blocked the cue elicited by 300 and 700 mg/kg of GHB, respectively. In contrast, diazepam partially substituted for 300 mg/kg of GHB, while failing to produce a GHB-appropriate response in the rat group trained to the higher GHB dose. Neither dizocilpine nor WIN 55,212-2 substituted for GHB. Collectively, these data suggest that: a) GHB produces a compound stimulus; and b) GABA(B)- and GABA(A)-mediated cues are prominent components of the mixed stimulus of GHB. However, the quality (i.e., the proportion of the component cues) of the stimulus varies as the training dose of GHB is increased; indeed, the contribution of the GABA(A)- and GABA(B)-mediated cues were smaller and greater, respectively, at 700 and 300 mg/kg of GHB training doses.

Gammahydroxybutyrate (GHB) receptor ligand effects on evoked synaptic field potentials in CA1 of the rat hippocampal slice

GHB produced a concentration-dependent depression of evoked synaptic field potentials (EFPs) recorded extracellularly in the CA1 region of the in vitro rat hippocampal slice. The concentration/response function revealed a threshold near 1 mM, with IC50 of 10.85 mM and a Hill coefficient of 1.29. The gamma-aminobutyric acid B-receptor (GABA-B) agonist baclofen also depressed the EFP, but even maximally effective concentrations of the GABA-B antagonist 2-hydroxy-saclofen (800 microM) could not completely block the GHB-induced EFP depression. Nor was GHB-induced EFP depression blocked by the GHB receptor "antagonist" NCS-382, which does not displace GABA-B receptor ligands. However, NCS-382 produced a concentration-dependent increase in EFP slope. The threshold concentration was about 100 microM but the maximally effective concentration, and thus the IC50, could not be determined in the perfusion slice system. NCS-382 may be an inverse agonist at hippocampal GHB receptors, or else endogenous hippocampal GHB receptor ligands medicate a tonic inhibition in CA1. At concentrations sufficient to induce EFP depression GHB did not alter pH. Although isosmotic sucrose did depress CA1 EFPs it was essentially ineffective at the IC50 for GHB. Gamma-butyrolactone, a prodrug of GHB, was only 1/20th as effective as GHB. This is consistent with previous data suggesting that GBL is freely permeable (does not substantially disturb tonicity) and that brain has very little capacity to either enzymatically convert the lactone to GHB or respond to the lactone itself.

Gamma-hydroxybutyric acid decreases intravenous cocaine self-administration in rats

Gamma-hydroxybutyric acid (GHB) is an endogenous compound present in mammalian brain suggested as a putative neurotransmitter, which has been shown to affect several aspects of dependence from various classes of drugs of abuse. In the present study, two sets of experiments were performed to investigate the effects of acute pretreatment with GHB on intravenous cocaine self-administration in rats. In the first experiment GHB was administered intragastrically at the doses of 175, 350, and 700 mg/kg to Long-Evans rats trained to self-administer cocaine using nose-poke as operandum. In the second experiment, GHB was administered intraperitoneally at the doses of 100, 200, and 400 mg/kg to Wistar rats trained to self-administer cocaine intravenously using lever-pressing as operandum. In both experiments acute pretreatment with GHB significantly and dose dependently reduced cocaine self-administration. The effectiveness of GHB was similar in both experiments, indicating that the effect of GHB on cocaine self-administration is independent of animal strain. route of administration, and type of operant response required. These results indicate that GHB reduces cocaine-seeking behavior in rats, modulating the acute reinforcing effect of cocaine. The clinical effectiveness of GHB in dependence from various classes of abused drugs warrants further studies to evaluate the possibility that GHB might represent a useful therapeutic agent for cocaine addiction in humans.

Sites of action of gamma-hydroxybutyrate (GHB)--a neuroactive drug with abuse potential

OBJECTIVE

This review highlights the biochemistry, pharmacology, and toxicology of the naturally-occurring fatty acid derivative, gamma-hydroxybutyrate (GHB). GHB is derived from gamma-aminobutyric acid (GABA) and is proposed to function as an inhibitory chemical transmitter in the central nervous system.

CONTENT

When administered in pharmacological doses, its powerful central nervous system depressant effects are readily observed. Although some of the neurophysiological actions of GHB could involve alterations in dopaminergic transmission in the basal ganglia, both its physiological and pharmacological actions are probably mediated through specific brain receptors for GHB. In addition, GHB might mediate some of its effects through interaction with the GABA(B) receptor. Experimentally, GHB has been used as a model for petit mal epilepsy; clinically, it has been used as a general anesthetic and as a drug to treat certain sleep disorders and related conditions. Owing to the purported ability of GHB to induce a state of euphoria, recreational use of this substance is popular. Although no deaths or long-term problems have been associated with GHB abuse, symptoms of GHB intoxication can be severe. The continued potential for GHB abuse makes it imperative for clinical toxicologists to be aware of the effects of this agent. Future research on the mechanism of action of GHB is needed to elucidate both its central nervous system depressant properties and its ability to effect a state of well-being.

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.

The ontogeny of [3H]gamma-hydroxybutyrate and [3H]GABAB binding sites: relation to the development of experimental absence seizures

gamma-Hydroxybutyric acid (GHB) is a naturally occurring compound which has the ability to induce generalized absence seizures when given to animals. There is growing evidence that both gamma-aminobutyric acid (GABA)B- and GHB-mediated mechanisms are involved in the pathogenesis of this phenomenon. Because of the fact that absence seizures are a disorder of children the ontogeny of [3H]GHB and [3H]GABAB binding and the developmental appearance of absence seizures in the GHB model of absence was ascertained and compared in developing rats. [3H]GABAB binding was present within the first 3 days of postnatal life and rose to levels which exceeded those found in adults, peaking between the 3rd and 5th postnatal week. [3H]GHB binding on the other hand did not appear until postnatal day 17 when it was detectable in the CA1 region of the hippocampus. There was a steady increase in [3H]GHB binding until adult levels were reached by postnatal day 40. Comparison of [3H]GABAB and [3H]GHB binding revealed that both sites were common to layer I-III of cortex, but otherwise differed in their regional distribution. There was an absolute concordance of the ontogeny of GHB-induced absence seizures with the developmental appearance of [3H]GHB binding in the superficial laminae of cortex; both appeared at postnatal day 18. These data support the hypotheses that the [3H]GHB and [3H]GABAB binding sites are separate from one another and suggest that maturational events in thalamus and cortex in the 3rd postnatal week are involved in the expression of GHB-induced absence seizures.

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.

Significance of gamma-hydroxybutyric acid in the brain

1. Administration of the endogenous compound gamma-hydroxybutyric acid (GHB) can induce a sleep-like state in experimental animals and, indeed, it has been used as a general anaesthetic in clinical medicine. 2. Although GHB appears to be a CNS depressant, there is evidence it possesses epileptiform activity resembling petit mal epilepsy. In the brain GHB is evidently derived from GABA, the final step being catalyzed by succinic semialdehyde reductase, a cytosolic NADP(+)-dependent enzyme. 3. Two different oxidoreductases, GHB dehydrogenase and hydroxyacid-ketoacid dehydrogenase, acting independently, are responsible for the reverse reaction when GHB is being metabolically inactivated. 4. Brain contains a Na(+)-dependent GHB uptake system which exhibits two components, one with a Km of 46 microM and the other with a Km of 325 microM. GHB also binds to receptor sites in brain homogenates and exhibits two distinct affinities. One binding site displays a Kd of 95 nM whereas the second site has a Kd of 16 microM. Binding to both sites is inhibited in the presence of NCS-382, a GHB receptor antagonist. 5. GHB might play a role as a neurotransmitter, particularly being involved in influencing dopamine release in the substantia nigra.

Effects of taurine, homotaurine and GABA on hypothalamic and striatal dopamine metabolism

To elucidate the effects of taurine on hypothalamic and striatal dopaminergic neurotransmission we compared its effects to those of gamma-aminobutyric acid (GABA) and homotaurine (a GABAA-receptor agonist) on hypothalamic and striatal concentrations of dopamine (DA) and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and, in the case of striatum, 3-methoxytyramine (3-MT) in rats. In addition, hypothalamic and striatal 5-hydroxytryptamine (5-HT) und 5-hydroxyindoleacetic acid, hypothalamic noradrenaline (NA) and 3-methoxy-4-hydroxyphenylglycol sulfate, and pituitary DA concentrations were also measured. The amino acids were injected into the lateral brain ventricles of conscious male rats in doses of 10 and 36 mumol/rat, and rat were sacrificed 15 and 60 min later, respectively. Homotaurine (by 11%) but not the other two amino acids elevated striatal DA, whereas hypothalamic DA was increased by both taurine (36%) and homotaurine (31%). All three amino acids at 36 mumol elevated striatal DOPAC, homotaurine (51%) more than taurine (31%) or GABA (30%), and hypothalamic DOPAC, both taurine (102%) and homotaurine (82%) clearly more than GABA (34%). Neither striatal nor hypothalamic HVA was altered by any of the amino acids. At 10 mumol the amino acids decreased striatal 3-MT by about 40%. At 36 mumol taurine and homotaurine reduced 3-MT by about 70%, whereas increasing the dose of GABA did not further reduce 3-MT. Both taurine and homotaurine at 36 mumol decreased hypothalamic NA content. Neither hypothalamic nor striatal 5-HT metabolism was altered. In the neurointermediate lobe of the pituitary gland taurine at 10 mumol but not at 36 mumol slightly (20%) increased DA.(ABSTRACT TRUNCATED AT 250 WORDS)

Gammahydroxybutyrate: an endogenous regulator of energy metabolism

Gammahydroxybutyrate is a naturally occurring metabolite of many mammalian tissues. Although its administration produces a wide range of pharmacological effects, its normal function has never been clearly defined. GHB can induce NREM and REM sleep, anaesthesia, hypothermia, and a trance-like state which has been considered a model for petit mal epilepsy. It markedly increases brain dopamine levels. It has been touted as a central neurotransmitter or neuromodulator, and high affinity brain receptors, as well as central mechanisms for its synthesis, uptake and release have been demonstrated in support of this. But GHB is also found in many peripheral tissues and in some of these in higher concentrations than in the brain. No explanation has been offered for its presence in these tissues. A number of studies indicate that GHB can reduce energy substrate consumption in both brain and peripheral tissues, and that it can protect these tissues from the damaging effects of anoxia or excessive metabolic demand. Indeed there is some evidence to suggest that endogenous GHB levels rise under these circumstances. GHB appears to act through the endogenous opioid system, since in the brain, at least, GHB raises dynorphin levels and its metabolic and pharmacological effects can be blocked by naloxone. These, and other observations detailed in this review, suggest that GHB may function naturally in the induction and maintenance of physiological states, like sleep and hibernation, in which energy utilization is depressed. GHB may also function naturally as an endogenous protective agent when tissue energy supplies are limited.

Gamma-hydroxybutyrate stimulation of the formation of cyclic GMP and inositol phosphates in rat hippocampal slices

The presence of gamma-hydroxybutyrate (GHB) (300-600 microM) in the incubation medium of rat hippocampal slices led to an increase of intracellular cyclic GMP and inositol phosphates. This phenomenon is dependent on the time and the dose of GHB used and might be the result of the stimulation of GHB receptor sites which are abundant in rat hippocampus. The increase of cyclic GMP and inositol phosphates is blocked by some anticonvulsants and opiate antagonists. These results seems to indicate that, like many substances inducing epileptic phenomena, GHB provokes neuronal depolarization in hippocampus which is accompanied by formation of cyclic GMP and inositol phosphates. The effect of opiate antagonists can be explained by the possible implication of an opiate synapse which mediates GHB effects in rat hippocampus.

Hypothermic effect of GABA in conscious stressed rats: its modification by cholinergic agonists and antagonists

gamma-Aminobutyric acid (GABA) intraperitoneally injected (i.p.) produced a dose-dependent hypothermia in restrained rats. GABA-induced hypothermia (1000 mg kg-1) was antagonized by pretreatment with atropine (2.5 and 10 mg kg-1 i.p.), hyoscine butylbromide (2.5 mg kg-1 i.p.), hexamethonium (0.75 mg kg-1 i.p.) or physostigmine (0.2 mg kg-1 s.c.). Hexamethonium (7.5 mg kg-1 i.p.) did not influence the hypothermia induced by GABA. The antagonism by physostigmine of GABA-induced hypothermia was attenuated by pretreatment of the rats with either alpha-methyl-p-tyrosine (200 mg kg-1 i.p.) or hexamethonium (7.5 mg kg-1 i.p.), but it was potentiated by either atropine (5 mg kg-1 i.p.) or hexamethonium (0.75 mg kg-1 i.p.). The data indicate that GABA-induced hypothermia may be partly mediated by acetylcholine release. Muscarinic receptors may play an important role in the effect of GABA. The results support the hypothesis of nicotinic presynaptic receptors modulating noradrenergic nerve endings that play a part in the hypothermic response of GABA.

Gammahydroxybutyric acid: central biochemical and behavioral effects in neonatal rats

Administration of gammahydroxybutyric acid (GHBA) to 4 days old animals caused a dose dependent decrease in locomotor activity. GHBA also induced a marked hypoventilation, irregular breathing and finally apnea, while heart rate was slightly increased. Changes in monoamine neurotransmitter turnover indicated an inhibition of dopamine (DA) neurotransmission. It is concluded that GHBA mechanisms in the neonatal rat brain are biochemically as well as functionally mature at an early age and that the effects on locomotor activity and respiratory regulation at least partly may involve interactions with central DA neurotransmission.

Monoamines as mediators of the antinociceptive effect of baclofen

The antinociceptive activity of baclofen was evaluated in rats using the tail flick and hot plate tests. When baclofen was administered intraperitoneally, pretreatment with depletors of monoamines and catecholamines (reserpine, alpha-MPT) produced a marked increase in antinociceptive activity in both tests. Blockade of noradrenergic and dopaminergic receptors with phentolamine, chlorpromazine and haloperidol produced similar increases. These agents were without intrinsic effect in these tests except for alpha-MPT which increased the tail flick latency slightly. Alterations in serotonergic function did not consistently alter the action of baclofen. When baclofen was administered intrathecally, pretreatment with reserpine and alpha-MPT produced minimal alterations in antinociceptive activity. It is likely that interactions between baclofen and monoamines occur at supraspinal sites.

Measurement of 5-hydroxytryptamine synthesis and metabolism in selected discrete regions of the rat brain using high performance liquid chromatography and electrochemical detection: pharmacological manipulations

High performance liquid chromatography coupled with electrochemical detection (LCEC) was employed to measure 5-hydroxytryptamine (5-HT), 5-hydroxyindole-3-acetic acid (5-HIAA) and 5-hydroxytryptophan (5-HTP) in the suprachiasmatic (SCN), medial preoptic (MPO) and arcuate (AN) nuclei as well as the median eminence (ME) and striatum (ST) of individual rat brains. Biochemical estimations of changes in 5-HT neuronal activity were made by measuring: (1) concentrations of 5-HT and 5-HIAA and (2) the rate of 5-HT synthesis (5-HTP accumulation following the administration of NSD 1015, an inhibitor of aromatic L-amino acid decarboxylase) after the administration of pharmacological agents known to influence these neurons. Pargyline increased the concentration of 5-HT and decreased the concentration of 5-HIAA while probenecid increased the concentration of 5-HIAA in all 5 brain regions. At both 2 and 24 hours after reserpine the concentration of 5-HT decreased, 5-HIAA increased or did not change, and the rate of 5-HT synthesis increased. In most of the brain regions blockers of 5-HT neuronal uptake (fluoxetine, chlorimipramine) did not influence 5-HT or 5-HIAA concentrations dramatically, but increased the rate of 5-HT synthesis. L-tryptophan generally increased the concentrations of 5-HT and 5-HIAA as well as the rate of accumulation of 5-HTP in all regions except the ME where 5-HIAA and 5-HTP concentrations both were unaffected. These results reveal that the method using LCEC is sensitive enough to detect pharmacologically-induced changes in 5-HT metabolism and synthesis in discrete regions of rat brain. The drugs examined in the present study generally caused similar changes in 5-HT dynamics in all 5 brain regions examined.

The effects of GABA-ergic drugs on enkephalin-induced motor seizure phenomena in the rat

1. The relationship between the effects of GABA-ergic drugs and D-ala2-met-enkephalinamide (DALA)-induced myoclonic contractions of inframandibular muscles has been studied in the rat. 2. GABA-ergic drugs altered enkephalin-induced myoclonic contractions in the following manner: (a) The GABA-mimetic drugs, muscimol, gabaculine and baclofen, decreased DALA-induced myoclonic contractions. (b) The GABA antagonist, bicuculline and the anticonvulsant substance, sodium valproate (dipropylacetic acid, DPA) potentiated DALA-induced myoclonic contractions. The potentiating effect of DPA is probably due to its opiate-like activity, since naloxone abolished this effect. 3. The modulatory effect of the GABA-mimetic drug on enkephalin-induced myoclonic contractions may give grounds for further study to test the possible use of other GABA-mimetic drugs and possibly opiate antagonists for the treatment of myoclonic syndromes.

Central cardiovascular effects of gamma-hydroxybutyric acid: interactions with noradrenaline, serotonin, dopamine and acetylcholine transmission

Gamma-hydroxybutyric acid (GHBA) increased arterial blood pressure and heart rate dose-dependently following intraperitoneal and intracerebroventricular administration to conscious rats. Cardiovascular responses to GHBA were completely prevented after pretreatment with reserpine or phenoxybenzamine and after a prehypothalamic brain transection. Intraperitoneal GHBA increased brain noradrenaline (NA) synthesis and utilization, particularly in the neocortex. Selective central NA depletion in combination with NA synthesis inhibition prevented the cardiovascular effects of GHBA. No overt interactions were observed with agents influencing 5-hydroxytryptamine (5-HT), dopamine (DA), or acetylcholine (Ach) transmission. Pentobarbitone but not diazepam or diphenylhydantoin abolished the hypertensive properties of GHBA. We conclude that the cardiovascular effects of GHBA are of central origin and that they are mediated via the peripheral sympathetic nervous system. They are dependent on an intact central NA transmission while there are few indications for a significant role of central DA-, 5-HT or Ach-mechanisms.

The effect of baclofen on the cardiovascular system of the rat

1 The cardiovascular responses to baclofen were investigated in anaesthetized rats. 2 Low doses of baclofen (less than 5 X 10(-8) mol), given intravenously, produced a transient fall in blood pressure and heart rate. Higher doses (greater than 5 X 10(-7) mol) produced a marked and prolonged increase in blood pressure accompanied by a rise in heart rate and cutaneous arterial dilatation. 3 The pressor and heart rate responses exhibited tachyphylaxis, and were abolished by hexamethonium, cervical cord section, reserpine-treatment and by a combination of alpha- and beta-adrenoceptor antagonists. 4 It is concluded that the increases in blood pressure and heart rate produced by high doses of baclofen are of central sympathetic origin.

Central cardiovascular and biochemical effects of baclofen in the conscious rat

Baclofen (beta-D-chlorophenyl-GABA, 1.25-10 mg kg-1 i.p.) elicited dose-dependent increases in blood pressure and heart rate in conscious rats. similar responses were observed after intracisternal or intracerebroventricular injections of baclofen 0.125-1 microgram kg-1. Baclofen i.p. was largely ineffective after spinal transection at C7. Pretreatment with phenoxybenzamine, bethanidine or hexamethonium antagonized the cardiovascular effects of i.p. baclofen. These actions were significantly attenuated after catecholamine depletion and synthesis inhibition by means of alpha-methyl-m-tyrosine and alpha-methyl-p-tyrosine. The responses to baclofen were not affected by bilateral adrenal demedullation but abolished by pentobarbitone anaesthesia. Hence, the cardiovascular effects of baclofen are probably evoked from central nervous structures and mediated via the sympathetic nervous system. In doses corresponding to those used in the circulatory studies i.p. baclofen increaed endogenous concentrations of brain DA and decreased DA utilization but only slightly affected brain NA concentrations and utilization.

The role of monoamines for the central effects of Baclofen on behavior of rats

Male albino rats given a bilateral injection of Baclofen (Lioresal) (12 micrograms/rat) in the cerebral ventricles showed a behavioral syndrome of activation + ataxia, paddling, tail-pinch hyperresponse and anesthesia. The phase of activation + ataxia was reduced by pretreatment of rats with H 44/68, FLA 63, reserpine, pimozide, phenoxybenzamine, oxypertine or chlorpromazine. The phase of paddling was reduced by pretreatment with FLA 63, reserpine, phenoxybenzamine, oxypertine, chlorpromazine, pimozide + phenoxybenzamine or apomorphine, while administration of clonidine instead of Baclofen caused paddling in non-pretreated rats. The phase of tail-pinch hyperresponse was reduced by reserpine, oxypertine, chlorpromazine or pimozide + phenoxybenzamine, while none of the pretreatments affected Baclofen-induced anesthesia. Drugs which affect mainly tryptaminergic or GABA-ergic functions failed to affect Baclofen-induced behaviors consistently. The findings suggest that dopaminergic and noradrenergic functions play a role in the central effects of Baclofen on behavior of rats.

Effects of baclofen on striatal 5-HT mediated by the nigrostriatal dopamine system

In rats, baclofen injected unilaterally into the substantia nigra increased dopamine (DA) and serotonin (5-HT) levels in the ipsilateral striata. Homovanillic acid levels first decreased and then increased to a maximum after 4 h. The content of 3,4-dihydroxyphenylacetic acid also increased after a latency of about 1 h. The effects of baclofen on striatal DA metabolism are consistent with the assumption that impulse flow in these DA neurones was diminshed by the drug. DA metabolites were also found in greater quantities in the contralateral striata, probably owing to compensatory activation of these DA neurones. Baclofen injected intranigrally did not increase the striatal 5-HT content in rats with a 6-hydroxydopamine-induced lesion of the nigrostriatal DA pathway. Our results suggest the presence of DA receptors on striatal 5-HT terminals or on interneurones synapsing axo-axonally with them.

Inhibition of nigral and neocortical cells by gamma-hydroxybutyrate: a microiontophoretic investigation

gamma-Hydroxybutyrate (GHB) and gamma-aminobutyrate (GABA) were applied microiontophoretically near spontaneously active cells in the substantia nigra and the neocortex of chloral hydrate-anaesthetized rats. Whereas GABA in "low doses" (i.e. 20 nA ejection currents) depressed the activity of cells in both areas, GBH reduced the firing rate only when the compound was expelled with two to three times higher ejection currents. Under these conditions GHB depressed about half of the nigral but the majority of the neocortical cells tested. The depressant action of GABA was readily antagonized by microiontophoretic bicuculline methiodide whereas the effects of GHB were resistant to this alkaloid. Intraperitoneally administered GHB in doses of 300 and 600 mg/kg reduced the firing rate of the majority of spontaneously active neocortical cells. In conclusion, GHB inhibits the firing of nigral and neocortical neurons. However its effects are not mediated through the activation of bicuculline-sensitive GABA receptors.