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M Maitre

Publications and source records attributed to M Maitre.

At least 91 records · Page 5Linked to original sources
PubMed1982

[Turnover of gamma-aminobutyric acid (GABA) in neurons and glial cells of the chick embryo in culture].

The turnover rates of gamma-aminobutyric acid (GABA) in cultured neurons and glial cells of Chicken embryo were measured by using a gas chromatography/mass spectrometric method. The method followed involved monitoring of the time course of changes in the enrichment of deuterium in GABA following incubation with pentadeuterated glutamate in the medium. The GABA turnover rate in neurons was found to be nearly eight fold greater than in glial cells.

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PubMed1982

High affinity binding sites for gamma-hydroxybutyric acid in rat brain.

The existence of a specific synthesizing enzyme for gamma-hydroxybutyric acid in rat brain has recently been reported. Here, for the first time, we demonstrate the presence of a high affinity, apparently specific binding site for this compound in the same tissue. This binding does not require Na+ and takes place optimally at pH 5.5. The bound gamma-hydroxybutyric acid is not displacable by GABA or baclofen. We report here on some structurally related compounds of GHB with a similar or better binding capacity than GHB itself. The number of binding sites increases with age up to adulthood and differs depending on the brain region. In primary tissue cultures of pure chicken neurones and glia, gamma-hydroxybutyric acid binding occurs exclusively in the neuronal preparations.

Animals↗
PubMed1982

Immunocytochemical evidence for the existence of GABAergic neurons in the nucleus raphe dorsalis. Possible existence of neurons containing serotonin and GABA.

It has been established that nerve cell bodies of the nucleus raphe dorsalis (NRD) belong to ascending 5-hydroxytryptamine systems. These neurons could be modulated by GABAergic interneurons or interposed GABA neurons. A high glutamate decarboxylase (GAD) activity in the NRD and a specific high-affinity uptake mechanism for GABA suggest the presence of GABA synthesizing elements in the NRD. Anti-GAD antibodies were used by an immunocytochemical procedure to demonstrate the presence of GABAergic elements. Anti-GAD antibodies were previously tested in the cerebellum and substantia nigra. Large amounts of GAD-positive reaction product were observed in the cytoplasm of some neurons (fusiform, ovoid or multipolar) or appeared as punctate deposits apposed to dendrites, soma and dispersed in the neuropil of the NRD. At the electron microscopic level, GAD-positive reaction product was observed within the cytoplasm of numerous somata in sections from colchicine-treated rats. GAD-positive staining was observed in numerous fibers or axonal terminals and two types of morphologically different fibers could be distinguished. The first displays small clear vesicles and few large granular vesicles (LGV) (80-100 nm), the second displays only clear round vesicles (40-60 nm). After 5,7-dihydroxytryptamine treatment (a neurotoxic for 5-HT terminals), the immunocytochemical labeling is much decreased. Some reactive neurons are still dispersed in the nucleus but the fibers containing LGV are no longer observed. These results strongly suggest that some neuronal elements in the NRD are morphologically, pharmacologically and anatomically similar to 5-HT neurons described at this level. Such cell elements could possess a double GABA and 5-HT potentiality. If this is not the case, a population of GABA neurons could be sensitive to 5,7-DHT and so have the capacity to take up 5-HT. The other reactive elements, insensitive to 5,7-DHT, could represent the GABAergic interneurons postulated at this level. Numerous GAD positive fibers or axon terminals were observed in synaptic contact with dendrites, axons or soma of other neurons. The chemical nature of the neuronal postsynaptic elements remains unknown. These findings strongly support the hypothesis for GABA-mediated inhibition in the NRD.

Animals↗
PubMed1982

Ontogeny and distribution of specific succinic semialdehyde reductase apoenzyme in the rat brain.

The ontogeny and distribution in rat brain of specific succinic semialdehyde reductase is described. This enzyme is probably responsible for the synthesis of gamma-hydroxybutyrate in brain. The highest activities and levels of apoenzyme are found in cerebellum, olfactory bulb, septum and median hypothalamus. During neonatal development, the enzyme activity remains stable at least until 63 days of age. As the levels of other enzymes of the GABA shunt pathway increase during this same period, this result indicates that there is a relative decrease in the reductive pathway of succinic semialdehyde catabolism during development leading to gamma-hydroxybutyrate synthesis, compared to the oxidative pathway leading to succinate.

Animals↗
PubMed1982

A high-affinity, Na+-dependent uptake system for gamma-hydroxybutyrate in membrane vesicles prepared from rat brain.

gamma-Hydroxybutyrate (GHB) is a compared with numerous neuropharmacological properties. The discovery of its biosynthetic system, together with its endogenous repartition, have prompted its possible implication in neurotransmission. The role is also supported by the existence, reported here, of a high-affinity uptake system for GHB (Km = 46.4 microM) in both purified brain plasma membrane vesicles and in the crude mitochondrial fraction. GHB uptake is dependent on a Na+ gradient but is independent of the membrane electrical potential. Cl- and K+ can also modulate the uptake. As an approach to determine the conformation required for GHB uptake, a series of related compounds, including aryl- or alkyl- derivatives, has been examined for ability to inhibit GHB uptake. The regional distribution of uptake is also indicative of its possible physiological role, since in striatum, an area where GHB has a known pharmacological effect on dopaminergic neurons, this uptake activity is the highest.

Animals↗
PubMed1981

Regional and subcellular localization in rat brain of the enzymes that can synthesize gamma-hydroxybutyric acid.

Rat brain contains two major NADPH-linked aldehyde reductases that can reduce succinate semialdehyde to 4-hydroxybutyrate. One of these enzymes appears to be fairly specific for succinate semialdehyde and is not significantly inhibited by classic aldehyde reductase inhibitors such as barbiturates. The other enzyme can reduce several aromatic aldehydes and is strongly inhibited by barbiturates and branched-chain fatty acids. Using one such inhibitor, it was possible to distinguish between and measure the two enzyme activities separately in various rat brain regions and in subcellular fractions. Both enzymes are mainly cytoplasmic but there is some activity in the synaptosomal fraction. The activity of the specific succinic semialdehyde reductase is highest in the cerebellum, where it represents 21% of the total activity, and lowest in the cortex, where it represents about 11% of the total activity.

Animals↗
PubMed1979

GABA binding processes in rat brain and liver.

Although these studies have provided some further insight into GABA binding processes associated with transport and receptor-activation, such attempts remain limited due to the lack of specificity of the ligands used to displace these components. Thus, BMI appeared to interact with both transport and synaptic receptor sites for GABA. Perhaps certain GABA-agonists (e.g., muscimol, isoguvacine) will be shown to interact more specifically with synaptic GABA-receptors? So-called "specific" binding of GABA and its analogues, or antagonists might not be the issue to be kept in focus in this type of experiment, especially since it cannot be separated into presynaptic, postsynaptic and non-synaptic components. The specificity of an interaction of ligand with membrane site may be determined by other requirements of the particular system concerned. In any case, it seems essential to examine the binding sites, themselves, in order to define more clearly which of these are involved in receptor-activation and in uptake. An approach involving the isolation and purification of GABA-receptors should provide evidence for specific binding of GABA to its postsynaptic receptors.

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