gamma-Hydroxybutyrate modulates synthesis and extracellular concentration of gamma-aminobutyric acid in discrete rat brain regions in vivo.
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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)
Glucocorticoid effects on mesotelencephalic dopamine neurotransmission.
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Multiple neurochemical estimates were used to examine peripheral corticosterone (CORT) effects in dopaminergic terminal regions. Acute CORT administration, which elevated plasma CORT (5 h), slightly decreased dihydroxyphenylacetic acid (DOPAC) to dopamine (DA) ratios in the striatum but not in other regions examined. Two weeks of adrenalectomy (ADX) increased both medial prefrontal cortex DOPAC/DA and homovanillic acid (HVA)/DA and striatal HVA/DA. A reciprocal pattern of changes was observed with CORT replacement in ADX animals. In contrast, CORT replacement in ADX animals did not significantly influence tyrosine hydroxylase content, basal dihydroxyphenylalanine (DOPA) accumulation after NSD 1015 treatment or the decline in DA after alpha-methyl-para-tyrosine, suggesting that neither DA neuronal activity nor release are altered by CORT. Moreover, neither gamma-hydroxybutyric acid lactone-induced increases in DOPA accumulation or stress-induced increases in DA utilization were influenced by CORT replacement, indicating that neither autoreceptor regulation of DA synthesis nor acute stress regulation of DA utilization are changed by CORT. The findings are most consistent with direct inhibition of basal DA metabolism in the medial prefrontal cortex and striatum. The possible physiological and behavioral significance of this inhibition is being further explored. (+info)
Analysis of gamma-hydroxybutyrate (GHB) in urine by gas chromatography-mass spectrometry.
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A simple method for the direct analysis of gamma-hydroxybutyrate (GHB) from human urine is described. The method uses solid-phase extraction, liquid-liquid extraction, and silyl-derivatization, then gas chromatographic-mass spectrometric analysis using GHB-d6 as the internal standard. The method was linear from 5 to 500 mg/L, and coefficients of variation were less than 10%. Twenty-six urine specimens previously analyzed by an existing method were analyzed and yielded GHB concentrations ranging from 0 to 6100 mg/L; the results correlated between the two methods. Compared with existing methods, the method described here is superior because it is specific to GHB and can discriminate between GHB and gamma-butyrolactone. (+info)
Gamma-hydroxybutyrate and cocaine administration increases mRNA expression of dopamine D1 and D2 receptors in rat brain.
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The effects of acute and repeated gamma-hydroxybutyrate (GHB) and cocaine administration on D1 and D2 dopamine receptor mRNA expression were examined using in situ hybridization histochemistry in different rat brain structures rich in GHB receptors. Six hours after a single GHB administration (500 mg/kg i.p.), an increase in D1 and D2 mRNA expression was observed in almost all regions examined; whereas, acute cocaine injection (20 mg/kg i.p.) had no effect. Repeated exposure to GHB (500 mg/kg i.p. twice daily) for 10 days, followed by a 14-h withdrawal period, induced increasing effects on D1 and D2 dopamine receptor mRNA expression, similar to those caused by chronic treatment with cocaine (20 mg/kg i.p. once a day). These effects of GHB and cocaine on dopamine receptor mRNA expression could be a consequence, for both compounds, of the modulation of dopaminergic activity; thus, supporting the benefit of GHB in cocaine substitution therapy. (+info)
Determination of gamma-hydroxybutyrate (GHB) in biological specimens by gas chromatography--mass spectrometry.
(5/200)
A simple liquid-liquid extraction procedure for the analysis of gamma-hydroxybutyrate (GHB) in biological fluids without conversion to its lactone, gamma-butyrolactone, is described. Following derivatization to its di-TMS derivative, GHB was detected using gas chromatography-electron impact mass spectrometry. Diethylene glycol was used as the internal standard. The limit of quantitation in 1 mL of blood was 1 mg/L, and a linear response was observed over the concentration range 1 to 100 mg/L. Coefficients of variation for both intra-assay precision and interassay reproducibility ranged between 3.9 and 12.0%. GHB was detected in the blood of a sexual assault victim (3.2 mg/L), in the blood of two driving (DUI) cases (33 and 34 mg/L), and in the blood and urine of two nonfatal GHB-overdose cases (blood 130 and 221 mg/L; urine 1.6 and 2.2 g/L). The observed clinical symptoms ranged from confusion, disorientation, vomiting, and nystagmus to ataxia, sinus bradycardia, unconsciousness, and apnea. (+info)
gamma-aminobutyric acid type B receptors are expressed and functional in mammalian cardiomyocytes.
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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. (+info)
Modulation of absence seizures by the GABA(A) receptor: a critical rolefor metabotropic glutamate receptor 4 (mGluR4).
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Experimental absence seizures are associated with perturbations in the presynaptic release of GABA and glutamate within thalamocortical circuitry. The release of both glutamate and GABA is regulated by group III metabotropic glutamate receptors (mGluRs). Therefore, we examined the susceptibility of mice lacking the mGluR4 subtype of mGluR (mGluR4(-/-)) versus their wild-type controls (mGluR4(+/+)) to absence seizures induced either by gamma-hydroxybutyrate (GHB) or the GABA(B) agonist (-) baclofen or by low doses of the GABA(A) receptor (GABA(A)R) antagonists pentylenetetrazole, bicuculline, or picrotoxin. There was no difference between mGluR4(-/-) and mGluR4(+/+) mice in threshold to absence seizures induced by either GHB or (-) baclofen. In contrast, the mGluR4(-/-) mice were markedly resistant to absence seizures induced by low doses of GABA(A)R antagonists. No differences were observed between mGluR4(-/-) and mGluR4(+/+) mice in threshold to clonic or tonic seizures induced by higher doses of GABA(A)R antagonists, strychnine, or electroshock, indicating that seizure resistance in the mGluR4(-/-) mice was restricted solely to absence seizures. The resistance of mGluR4(-/-) mice to absence seizures induced by GABA(A)R antagonists was mimicked by bilateral administration of a mGluR4 antagonist into the nucleus reticularis thalami (nRT) of mGluR4(+/+) mice. Conversely, intra-nRT administration of a mGluR4 agonist in mGluR4(+/+) mice exacerbated GABA(A)R-induced absence seizures. These data indicate that the presence of mGluR4 within nRT is critical to GABAergic modulation of thalamocortical synchronization in normal and pathological states, such as generalized absence epilepsy. (+info)
Analysis of biofluids for gamma-hydroxybutyrate (GHB) and gamma-butyrolactone (GBL) by headspace GC-FID and GC-MS.
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The past few years have seen a dramatic increase in the abuse of gamma-hydroxybutyrate (GHB) and gamma-butyrolactone (GBL) in the United States. The abuse stems primarily from their euphoric and sedative properties, but these substances are also misused by bodybuilders as steroid alternatives. Recently there has been an alarming increase in the use of GHB and GBL in crimes of drug-facilitated sexual assault. A rapid and sensitive procedure was developed for the analysis of biofluids containing GHB and GBL. Two separate aliquots of a biological specimen were spiked with an alpha-methylene-gamma-butyrolactone internal standard solution. One of the aliquots was treated with concentrated sulfuric acid for cyclization of GHB to GBL and the other remained untreated. Both aliquots were extracted with methylene chloride and concentrated. Extracts were screened using automated headspace gas chromatography-flame-ionization detection (GC-FID). Qualitative findings were quantitated and confirmed in a manner similar to the GC-FID procedure with some modifications. A calibrated solution of GHB-d6 (or GBL-d6, when warranted) was added to the aliquots at a concentration approximating the level determined by the GC-FID screen. The extraction was as described with conversion of GHB to GBL, but analysis was by full-scan gas chromatography-mass spectrometry (El). Quantitation was performed by comparison of the area of the molecular ion of the parent drug (m/z 86) to that of the calibrated deuterated analogue (m/z 92). This analytical procedure allows for the rapid detection of GHB and GBL in biofluids. Its sensitivity has proven useful for the toxicological investigation of cases of drug-facilitated sexual assault. (+info)