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Biomedical subjects

M Maitre

Publications and source records attributed to M Maitre.

At least 73 records · Page 4Linked to original sources
PubMed1987

Effect of anticonvulsant drugs on gamma-hydroxybutyrate release from hippocampal slices: inhibition by valproate and ethosuximide.

The effects of some anticonvulsant drugs have been investigated on gamma-hydroxybutyrate release from rat hippocampal and striatal slices. Sodium valproate and ethosuximide inhibited the depolarization-evoked release of gamma-hydroxybutyrate induced by 40 mM K+. The IC50 values for these two drugs are in the concentration range of valproate and ethosuximide that exists in rat brain after administration of anticonvulsant doses to the animals. Trimethadione and pentobarbital are without significant effects. It can be concluded that the inhibition of gamma-hydroxybutyrate release, particularly that observed for hippocampus, might explain the protective effect of valproate and ethosuximide on gamma-hydroxybutyrate-induced seizures and perhaps on other kinds of epileptoid phenomenon.

Animals↗
PubMed1987

Regional distribution of high-affinity gamma-[3H]hydroxybutyrate binding sites as determined by quantitative autoradiography.

The distribution of high-affinity binding sites for gamma-[3H]hydroxybutyrate in coronal sections of rat brain was studied by quantitative autoradiographic techniques. Binding sites for this naturally occurring substance, which may possibly have a neurotransmitter role, are concentrated in some restricted areas of the brain, particularly in the limbic system. The hippocampus (especially field CA1 of Ammon's horn, at 292 fmol/mg of tissue), septum (72 fmol/mg of tissue), and cortex (frontal, 113 fmol/mg of tissue; parietal, 103 fmol/mg of tissue; cingulate, 114 fmol/mg of tissue; and entorhinal, 134 fmol/mg of tissue) show pronounced labeling with gamma-[3H]hydroxybutyrate. Binding is much lower in caudatus-putamen (50 fmol/mg of tissue), thalamus, and hypothalamus. Caudal parts of the brain (cerebellum, pons, and medulla) are practically devoid of binding sites. These results strongly support a functional role of endogenous gamma-hydroxybutyrate in particularly restricted areas of the rat brain.

Animals↗
PubMed1985

Evidence for a role of high Km aldehyde reductase in the degradation of endogenous gamma-hydroxybutyrate from rat brain.

gamma-Hydroxybutyrate (GHB) is a putative neurotransmitter in brain. We have already demonstrated that it is transformed into gamma-aminobutyrate (GABA) by rat brain slices incubated under physiological conditions. This conversion occurs via a GABA-transaminase reaction. Therefore, succinic semialdehyde, the oxidative derivative of GHB, appears to be the primary catabolite of GHB degradation. Apparently, the kinetic characteristics and pH optimum of GHB dehydrogenase (high Km aldehyde reductase) in vitro do not favor a role for this enzyme in endogenous brain GHB oxidation. However, in the presence of glucuronate, glutamate, NADP and pyridoxal phosphate, pure GHB dehydrogenase, coupled to purified GABA-transaminase does produce GABA from GHB at an optimum pH close to the physiological value and with a low Km for GHB.

4-Aminobutyrate Transaminase↗
PubMed1985

Tryptophan 5-hydroxylase. Rapid purification from whole rat brain and production of a specific antiserum.

Tryptophan 5-hydroxylase (EC 1.14.16.4; L-tryptophan tetrahydropteridine: oxygen oxidoreductase) was purified to electrophoretic homogeneity from whole brain supernatant using the following steps: pteridine-argarose affinity chromatography, hydrophobic and finally hydroxyapatite chromatography. Exogenous catalase was necessary throughout most of the purification procedure in order to protect the enzyme against inactivation. The iron chelator desferrioxamine at a concentration of 10 microM or higher brought about an irreversible loss of enzyme activity of a partially purified preparation containing an excess of catalase, whereas this same chelator at a lower concentration afforded considerable protection of the enzyme's activity during the final purification stage despite the quasi-total absence of catalase and the presence of an excess of ferrous iron. Antiserum raised in the rabbit to purified tryptophan 5-hydroxylase appears to be monospecific for the enzyme after immunoadsorption of anti-catalase antibodies which were present due to the trace of catalase which remained in the final enzyme preparation.

Animals↗
PubMed1985

Specific immunolysis of serotonergic nerve terminals using an antiserum against tryptophan hydroxylase.

An antiserum to tryptophan hydroxylase purified from whole rat brain when incubated with rat striatal synaptosomes in the presence of complement caused release of 18% of LDH, 20% loss of potassium and 60% loss of tryptophan hydroxylase. Uptake of 5-HT was reduced by 60%. Anti-tryptophan hydroxylase alone, or complement alone were without action. The antiserum plus complement had no effect on DA uptake and did not release TH or GAD. These results suggest selective lysis of serotonergic nerve terminals had occurred. The antiserum plus complement reduced choline uptake by 45%. However, this did not seem due to lysis of cholinergic terminals, as ChAT was not released.

Animals↗
PubMed1985

gamma-Hydroxybutyrate uptake by rat brain striatal slices.

gamma-Hydroxybutyrate uptake by rat brain striatal slices was studied. The uptake was saturable with a Km of 702 +/- 107.10(-6) M. gamma-Hydroxybutyrate uptake was sodium dependent and inhibited by the omission of potassium. In addition, the effect of ouabain suggests that the transport is dependent on a cation gradient. Several analogues of gamma-hydroxybutyrate inhibit the transport system. GABA has no significant effect. This energy and cation dependent transport system is in favor of a transmitter or modulator role of gamma-hydroxybutyrate in the rat brain striatum.

Animals↗
PubMed1985

Conversion of gamma-hydroxybutyrate to gamma-aminobutyrate in vitro.

[3H]gamma-Hydroxybutyric acid [( 3H]GHB) at physiological concentration incubated with brain slices in Krebs-Ringer medium produced [3H]gamma-aminobutyric acid [( 3H]GABA). This compound was identified by its Rf values on thin-layer chromatograms and by analysis of the dansyl derivatives of the free amino acid fraction. No labelled glutamate could be detected. Brain slices incubated with labelled glutamate and nonradioactive GHB generated labelled 2-oxoglutarate, suggesting that gamma-aminobutyrate-2-oxoglutarate transaminase (GABA-T) is involved in catalyzing this reaction. Furthermore, specific inhibitors of GABA-T blocked the production of labelled GABA from labelled GHB and of labelled 2-oxoglutarate from labelled glutamate. Transformation of [3H]GHB into [3H]GABA was not inhibited by malonate, demonstrating that the succinate-linked pathway is not involved in the generation of GABA. The kinetic characteristics of the multienzyme system involved in GHB degradation studied in vitro are compatible with the production of GABA in vivo.

4-Aminobutyrate Transaminase↗
PubMed1984

A comparative study of L[3H]-glutamate and L[3H]-cysteine sulfinate binding sites in subcellular fractions of rat brain.

A comparative study of the binding of L-cysteine sulfinic acid (CSA) and L-glutamic acid (GLU) to various subcellular fractions of membranes from rat brain was made. Kinetic parameters were determined in all fractions for both types of binding. The effects of membrane preincubation, freezing, and thawing were also examined. The GLU and CSA specific binding levels increased in medium-density (C) and high-density (D) synaptic membranes as compared to the crude mitochondrial/synaptosomal membranes (wP2). Freezing and thawing reduced CSA binding in all tested subcellular fractions. GLU binding is reduced in wP2, C, and D. Binding to the "light" synaptic membranes (B) was not significantly affected, suggesting the presence of two GLU sites. Kinetics of the GLU binding indicated that the temperature-sensitive and -insensitive sites have Kd of 600 nM and 1,100/nM, respectively. Preincubation of fresh membranes conversely affected CSA and GLU binding to the various subcellular fractions, increasing CSA binding in wP2, B, C and decreasing it in D suggesting the existence of distinct sites for GLU and CSA. Preincubation of previously frozen membranes similarly modified CSA and GLU binding except in B fractions. CSA and GLU binding exhibited different pH sensitivities in both fresh and frozen membranes. These results indicate that multiple acid amino acid binding sites exist in membranes and that they can be differentiated according to their sensitivity to temperature. They also suggest the existence of distinct sites for CSA and GLU in fresh membranes, giving further support to the hypothesis that CSA may also serve a neurotransmitter role in the rat central nervous system.

Animals↗
PubMed1984

[Properties allowing the attribution to gamma-hydroxybutyrate the quality of neurotransmitter in the central nervous system].

gamma-Hydroxybutyrate (GHB) fulfills the main criteria of a neurotransmitter: it is unevenly distributed in C.N.S.; it is synthesized from succinic semi-aldehyde by a specific semi-aldehyde succinic reductase localized in neurons, in some dendrites and synaptic terminals; GHB is released by tissue slice depolarization, this release being reduced by 50-60% in a Ca++ free medium. Tetrodotoxin and verapamil strongly inhibited the depolarization evoked-release; high affinity heterogenously distributed binding sites for gamma-hydroxybutyrate exist in the brain. This binding does not require Na+. The bound gamma-hydroxybutyric acid is not displaceable by GABA or GABA agonists. Binding sites are enriched in the synaptosomal fraction; after micro-iontophoretic application, GHB exerts a depressant action on nigral and neocortical cells which is resistant to the presence of bicuculline methiodide. In neuronal cultures, GHB causes a hyperpolarization similar to that produced by GABA; high affinity uptake system for GHB exists both in purified plasma membrane vesicles and in brain tissue slices. This uptake is dependent on an Na+ gradient and is inhibited by ouabaïn and dinitrophenol; GABA does not modify GHB uptake by rat brain slices; GABA derived GHB has a turnover time almost three times faster than that of whole brain serotonin, 6-8 times as rapid as that of whole brain dopamine and 13-19 times as rapid as that of whole brain norepinephrine.

Animals↗
PubMed1983

Immunohistochemical evidence for the presence of gamma-aminobutyric acid and serotonin in one nerve cell. A study on the raphe nuclei of the rat using antibodies to glutamate decarboxylase and serotonin.

A specific and sensitive double immunocytochemical staining for the visualization of glutamate decarboxylase (GAD) and serotonin (5-HT) on the same brain section is developed. GAD is detected with specific GAD-antibodies by means of the unlabeled antibody enzyme, peroxidase anti-peroxidase, and serotonin with an antibody against the BSA-serotonin conjugate by an indirect immunofluorescent staining. The coexistence of GAD and 5-HT in the same perikaryon is demonstrated by a peroxidase reaction superimposed on fluorescent compounds. Cell bodies containing both antigens are observed in each raphe nuclei. However, the nucleus raphe dorsalis exhibits the largest number of cells containing either GAD alone or GAD and 5-HT together. An intracellular interaction between the metabolism of GABA and serotonin could be reasonably expected. The interactions between GABAergic and serotonergic systems must be thought of in terms of intracellular and/or transynaptic controls.

Animals↗
PubMed1983

Subcellular distribution of gamma-hydroxybutyrate binding sites in rat brain principal localization in the synaptosomal fraction.

gamma-Hydroxybutyrate binding sites, first described on crude membranes from rat brain, have been further studied on subcellular fractions. The nerve ending fraction (fraction C) exhibits the maximal capacity for GHB binding. The two classes of binding sites (high and low affinities) described for the crude membrane preparation are enriched in this synaptosomal fraction. This result is further evidence in favor of a role for GHB as a neurotransmitter or neuromodulator in rat brain.

Animals↗
PubMed1983

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.

Animals↗
PubMed1983

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.

Animals↗
PubMed1982

[Calcium-dependent liberation of gamma-hydroxybutyrate after depolarization of rat brain slices].

The release of gamma-hydroxybutyrate from preloaded Rat brain striatal slices was investigated. Potassium induced depolarisation caused an efflux of gamma-hydroxybutyrate in the incubation medium. This release is significantly decreased by a calcium free medium, containing magnesium salt and EGTA. Taking into account our previous results concerning synthesis, uptake and binding of gamma-hydroxybutyrate, this calcium-dependent release strongly suggest a possible role of gamma-hydroxybutyrate in neurotransmission in the C.N.S.

Animals↗