gamma-Hydroxybutyrate modulates synthesis and extracellular concentration of gamma-aminobutyric acid in discrete rat brain regions in vivo. (1/37)

gamma-Hydroxybutyrate possesses most of the properties of a neurotransmitter/neuromodulator that acts via specific pathways and receptors in brain. Beside its regulatory effects on dopaminergic transmission, gamma-hydroxybutyrate was thought for many years to interfere with gamma-aminobutyric acid (GABA)ergic processes in the brain. The present study demonstrates that in the rat frontal cortex in vivo, gamma-hydroxybutyrate or its agonist NCS-356 administered systemically at a high dose (500 mg/kg) increases GABA contents in dialysates via a mechanism blocked by the peripheral administration of the gamma-hydroxybutyrate antagonist NCS-382. Under the same conditions, the extracellular concentration of this amino acid was not modified in the hippocampus. However, when administered at a low dose (250 mg/kg), gamma-hydroxybutyrate decreases GABA content of the dialysates of the frontal cortex by an NCS-382-sensitive mechanism. Spontaneous [3H]GABA release was observed in the frontal cortex of rats at 160 min after i.p. [3H]-gamma-hydroxybutyrate administration. This result indicates that gamma-hydroxybutyrate in vivo could be the precursor of an extracellular GABA pool in the frontal cortex. After i.p. [3H]-gamma-hydroxybutyrate administration in the rat, the amino acid contents of several brain regions were quantified 160 min later, and the radioactivity in each region was measured. [3H]GABA, [3H]glutamate, and [3H]glycine were detected in most, but not all, of the brain regions studied. In particular, radioactive GABA was not detected in the hippocampus. The other amino acids were not labeled. These results show that gamma-hydroxybutyrate modulates the synthesis and the extracellular concentrations of GABA in specific regions of the rat brain. Identification of these GABA pools and determination of their functional role remain to be defined.  (+info)

Binding characteristics of the gamma-hydroxybutyric acid receptor antagonist [(3)H](2E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene) ethanoic acid in the rat brain. (2/37)

Radioligand binding studies with [(3)H](2E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene) ethanoic acid ([(3)H]NCS-382), an antagonist of gamma-hydroxybutyric acid (GHB) receptor, revealed specific binding sites in the rat cerebral cortex and hippocampus. However, there was very little binding in the rat cerebellum, heart, kidney, liver, and lung membranes. Binding was rapid and reached equilibrium in about 5 min. Scatchard analysis of saturation isotherms revealed two different populations of binding sites in the rat cerebral cortex (K(d1), 795 nM, B(max1), 25.4 pmol/mg of protein; K(d2), 21 microM; B(max2), 178 pmol/mg of protein) as well as in the rat hippocampus (K(d1), 441 nM; B(max1), 16.2 pmol/mg of protein; K(d2), 9.8 microM; B(max2), 255 pmol/mg of protein). (+/-)Baclofen (500 microM) and gamma-aminobutyric acid (100 microM) inhibited the binding only partially, whereas (+)bicuculline, muscimol, picrotoxinin, and phaclofen did not modify the binding. Interestingly, potassium chloride (100-300 mM) inhibited [(3)H]NCS-382 binding (34-56%), and this inhibitory effect was not affected by picrotoxinin. GHB and NCS-382 completely inhibited the [(3)H]NCS-382 (16 nM) binding in the rat cerebrocortical and hippocampal membranes, and NCS-382 was found to be about 10 times more potent than GHB in this regard. A variety of ligands for other receptors did not modify the [(3)H]NCS-382 binding, thereby suggesting selectivity of this radioligand for the GHB receptor sites in the brain. Based on these observations, [(3)H]NCS-382 seems to be a better radioligand than [(3)H]GHB for investigating the role of the GHB receptors in various pharmacological actions.  (+info)

Therapeutic intervention in mice deficient for succinate semialdehyde dehydrogenase (gamma-hydroxybutyric aciduria). (3/37)

Therapeutic intervention for human succinic semialdehyde dehydrogenase (SSADH) deficiency (gamma-hydroxybutyric aciduria) has been limited to vigabatrin (VGB). Pharmacologically, VGB should be highly effective due to 4-aminobutyrate-transaminase (GABA-transaminase) inhibition, lowering succinic semialdehyde and, thereby, gamma-hydroxybutyric acid (GHB) levels. Unfortunately, clinical efficacy has been limited. Because GHB possesses a number of potential receptor interactions, we addressed the hypothesis that antagonism of these interactions in mice with SSADH deficiency could lead to the development of novel treatment strategies for human patients. SSADH-deficient mice have significantly elevated tissue GHB levels, are neurologically impaired, and die within 4 weeks postnatally. In the current report, we compared oral versus intraperitoneal administration of VGB, CGP 35348 [3-aminopropyl(diethoxymethyl)phosphinic acid, a GABA(B) receptor antagonist], and the nonprotein amino acid taurine in rescue of SSADH-deficient mice from early death. In addition, we assessed the efficacy of the specific GHB receptor antagonist NCS-382 (6,7,8,9-tetrahydro-5-[H]benzocycloheptene-5-ol-6-ylideneacetic acid) using i.p. administration. All interventions led to significant lifespan extension (22-61%), with NCS-382 being most effective (50-61% survival). To explore the limited human clinical efficacy of VGB, we measured brain GHB and gamma-aminobutyric acid (GABA) levels in SSADH-deficient mice receiving VGB. Whereas high-dose VGB led to the expected elevation of brain GABA, we found no parallel decrease in GHB levels. Our data indicate that, at a minimum, GHB and GABA(B) receptors are involved in the pathophysiology of SSADH deficiency. We conclude that taurine and NCS-382 may have therapeutic relevance in human SSADH deficiency and that the poor clinical efficacy of VGB in this disease may relate to an inability to decrease brain GHB concentrations.  (+info)

A tertiary alcohol analog of gamma-hydroxybutyric acid as a specific gamma-hydroxybutyric acid receptor ligand. (4/37)

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.  (+info)

Effects of gamma-hydroxybutyrate (GHB) on schedule-controlled responding in rats: role of GHB and GABAB receptors. (5/37)

Gamma-hydroxybutyrate (GHB), a metabolite of gamma-aminobutyric acid (GABA), is an increasingly popular drug of abuse and was recently approved for the treatment of narcolepsy (Xyrem). GHB and GABA receptors have been implicated in mediating effects of GHB; however, the relative importance of each of these receptors is unclear. This study evaluated the effects of selective antagonists in combination with GHB and related compounds on schedule-controlled responding. Eight male Sprague-Dawley rats responded under a fixed-ratio schedule of food presentation. Cumulative dose-effect curves were generated and ED50 values calculated to evaluate the relative potency at decreasing responding. The rank-order potency was as follows: diazepam = baclofen > gamma-butyrolactone (GBL) > 1,4-butanediol (1,4-BDL) = GHB. All compounds decreased responding 20 min after administration. The duration of action of diazepam, GHB, and GBL was shorter than that of 1,4-BDL and baclofen. p-3-Aminopropyl-p-diethoxymethyl phosphinic acid (CGP 35348) antagonized the rate-decreasing effects of baclofen and not GHB; flumazenil antagonized the effects of diazepam and not GHB. The GHB receptor antagonist (2E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene ethanoic acid (NCS-382) did not attenuate the rate-decreasing effects of GHB, baclofen, or diazepam; larger doses of NCS-382 further decreased rate of responding when given in combination with each of these compounds. These studies show that GBL, 1,4-BDL, and GHB differ significantly in potency and duration of action. The ability of CGP 35348 to antagonize the rate-decreasing effects of baclofen may be limited by the involvement of multiple GABAB receptor subtypes and the lack of antagonism of GHB by NCS-382 may be due to its own GHB-like effects.  (+info)

Pathway-specific action of gamma-hydroxybutyric acid in sensory thalamus and its relevance to absence seizures. (6/37)

The systemic injection of gamma-hydroxybutyric acid (GHB) elicits spike and wave discharges (SWDs), the EEG hallmark of absence seizures, and represents a well established, widely used pharmacological model of this nonconvulsive epilepsy. Despite this experimental use of GHB, as well as its therapeutic use in narcolepsy and its increasing abuse, however, the precise cellular mechanisms underlying the different pharmacological actions of this drug are still unclear. Because sensory thalamic nuclei play a key role in the generation of SWDs and sleep rhythms, and because direct injection of GHB in the ventrobasal (VB) thalamus elicits SWDs, we investigated GHB effects on corticothalamic EPSCs and GABAergic IPSCs in VB thalamocortical (TC) neurons. GHB (250 microm-10 mm) reversibly decreased the amplitude of electrically evoked EPSCs and GABAA IPSCs via activation of GABAB receptors; however, approximately 60% of the IPSCs were insensitive to low (250 microm-1.0 mm) GHB concentrations. The putative GHB receptor antagonist NSC 382 applied alone had a number of unspecific effects, whereas it either had no action on, or further increased, the GHB-elicited effects on synaptic currents. Low GHB concentrations (250 microm) were also effective in increasing absence-like intrathalamic oscillations evoked by cortical afferent stimulation. These results indicate that low concentrations of GHB, similar to the brain concentrations that evoke SWDs in vivo, differentially affect excitatory and inhibitory synaptic currents in TC neurons and promote absence-like intrathalamic oscillations. Furthermore, the present data strengthen previous suggestions on the GHB mechanism of sleep promotion and will help focus future studies on the cellular mechanisms underlying its abuse.  (+info)

Synthesis of 1-benzothiepine and 1-benzazepine derivatives as orally active CCR5 antagonists. (7/37)

Quaternary ammonium benzocycloheptene compound 1 has previously been reported as a clinical candidate for an injectable CCR5 antagonist. In order to develop an orally active CCR5 antagonist, derivatives of tertiary amine benzocycloheptene 2, the chemical precursor to 1, were investigated. The benzocycloheptene ring was converted to benzothiepine and benzazepine rings and it was found that these changes could enhance the potency of tertiary amine derivatives. In particular, the 1-benzothiepine-1,1-dioxide 11b and the N-methyl-1-benzazepine 18 showed increased activity and good preliminary pharmacokinetic properties. The synthesis of 1-benzothiepine and 1-benzazepine derivatives and their activity are described.  (+info)

Metabolism of pyrogallol to purpurogallin by human erythrocytic hemoglobin. (8/37)

The aim of this study was to investigate the oxido-reductive reactions of human hemoglobin with pyrogallol and the metabolism of pyrogallol by the protein, which contains a protoporphyrin IX like cytochrome P-450. Pyrogallol, having three hydroxy groups at the adjacent positions in the benzene ring, oxidized human oxyhemoglobin to methemoglobin and reduced human methemoglobin to oxyhemoglobin. Since superoxide dismutase and catalase inhibited these reactions extensively, active oxygens such as superoxide and hydrogen peroxide were considered to be involved in the oxido-reductive reaction of human hemoglobin by pyrogallol. It was also found that the metabolism of pyrogallol to purpurogallin occurred quickly in human erythrocytes, i.e., when pyrogallol was added to human erythrocyte suspension, it oxidized intracellular hemoglobin and produced purpurogallin. The metabolism of pyrogallol to purpurogallin was explained by the pyrogallol oxidation with superoxide and hydrogen peroxide produced during the oxido-reductive reactions of human hemoglobin with pyrogallol. The present results show that human erythrocytes can metabolize pyrogallol, suggesting that the cells may be involved in the metabolism of some drugs in the human body.  (+info)

• 1
• 2
• 3
• 4
• 5