bluuebunny/crossref_metadata_2025_split huggingface dataset:
NET PRODUCTION OF γ‐AMINOBUTYRIC ACID IN ASTROCYTES IN PRIMARY CULTURES DETERMINED BY A SENSITIVE MASS SPECTROMETRIC METHOD
Authors: Wu P. H. , Durden D. A. , Hertz L. 
Published: October 2006

Abstract—A sensitive and specific high resolution mass spectrometric method, using a deuterium labelled internal standard, was developed for the quantitation of GABA in biological materials. GABA was converted to the DNS‐γ‐butyrolactam, isolated by thin layer chromatography and quantitated by the integrated ion current procedure. The method was used to measure the GABA content of cultured astrocytes (0.0545 nmol/mg protein, depending upon the culturing conditions), of fresh media (0.02–0.04 μM) and of conditioned media (after culturing in the absence of added GABA: 0.02–1.8 μM, depending upon the culturing conditions). An estimate of the rate of GABA production was obtained from the concentration in conditioned media and in the cells when GABA degradation was inhibited by AOAA (13 μM). The production of GABA was negligible in the cells grown under ordinary conditions but increased to 0.3 nmol/h per mg protein in cells which had been grown in the presence of 0.25 mM‐ dibutyryl cyclic AMP for 1 week. This value is of the same order of magnitude as the GAD activity observed in extraneurónal tissue. However, the GABA production measured mass spectrometrically was much lower than that of labelled GABA from [U‐14C]glutamate. The latter value was non‐reproducible and varied from one batch of radioactive glutamate to another.
THE CHARACTERIZATIO OF MONOAMINE OXIDASE IN CULTURED MAMMALIAN CELLS
Authors: Powell J. F. , Craig I. W. 
Published: October 2006

Abstract—The expression of monoamine oxidase (MAO) in a variety of mammalian cells has been investigated employing tryptamine as substrate. The enzyme present in those cell lines having sufficient activity for detailed analysis exhibited a monophasic response to the inhibitor clorgyline. On this basis the cell lines examined were found to express only A, or only B, type activity. Hypoxanthineguanine phosphoribosyl transferase (HGPRT) deficient derivatives of both MAO type A, or MAOtype B, expressing cells were examined. The HGPRT status of the cells appeared to have little influence on the expression of the enzyme.
LOCATING THE MAJOR GLYCOPROTEIN (Po PROTEIN) IN THE X‐RAY PROFILE OF FROG SCIATIC‐NERVE MYELIN
Authors: Blaurock A. E. , Nelander J. C. 
Published: October 2006

AbstractSome detailed X‐ray profiles have been put forward for frog sciatic‐nerve myelin in the past 8 y. In this paper we interpret one of these. Much of the myelin protein is located in the extracellular half of the membrane. On the basis of a chemical analysis and other recently published data indicating the sidedness of some myelin proteins, we suggest that the major glycoprotein (Po protein) is inserted into the extracellular half of the myelin bilayer and that it extends into the extracellular space. Our interpretation is consistent with known physical properties of the Po protein. Other myelin proteins have not yet been located.Electron densities and average hydrophobicities of some myelin proteins have been calculated, as well as electron densities and scattering powers of some myelin lipids.
FREE 3‐METHOXY‐4‐HYDROXYPHENYLETHYLENEGLYCOL IN THE CENTRAL NERVOUS SYSTEM OF THE RAT: SEMI‐AUTOMATED FLUOROMETRIC ASSAY, TURNOVER AND EFFECTS OF DRUGS
Authors: Adégr J.‐P. , Korf J. 
Published: October 2006

AbstractA semi‐automated fluorometric assay technique for free 3‐methoxy‐4‐hydroxyphenylethyl‐eneglycol (MOPEG) in rat brain and spinal cord is described.The method is based on a simple manually‐performed two‐step purification procedure using column chromatography on Sephadex G 10 and DEAE‐Sephadex A 25 (borate form) respectively. After isolation MOPEG is converted into a fluorophore in a continuous flow system using ethylene diamine condensation in the presence of an oxidant. The MOPEG assay is highly sensitive (detection limit 2 ng/sample) and linear, with an overall recovery of approx 75%.Specificity is demonstrated by testing a number of compounds and confirmed by gas chromatography‐mass spectrometry analysis. Treatment with clozapine and haloperidol (both neuroleptics), reser‐pine (impairing intraneuronal storage) or phenoxybenzamine (α‐adrenoceptor blocking agent) increased the content of MOPEG both in brain and spinal cord. Cerebral levels of MOPEG were decreased after injection of a single dose of the tricyclic antidepressant desipramine and after chronic destruction of the locus coeruleus by electrolytic lesion or by the administration of the neurotoxic drug 6‐hydroxy‐dopamine. Animals killed by microwave irradiation did not show lower MOPEG contents in brain than decapitated animals.These results indicate that MOPEG is a measure for changes in central noradrenaline turnover and that drugs affect MOPEG in the brain and spinal cord similarly. Fractional rate constants of MOPEG in the rat brain and spinal cord were estimated with the exponential decline curves produced by treatment with pargyline. Turnover rates of 193 pmol/g/h and 167 pmol/g/h in the brain and spinal cord respectively were calculated.
THE EFFECT OF DELTA‐AMINOLAEVULINIC ACID ON THE UPTAKE AND EFFLUX OF [3H]GABA IN RAT BRAIN SYNAPTOSOMES
Authors: Brennan M. J. W. , Cantrill R. C. 
Published: October 2006

Abstract§‐Aminolaevulinic acid (§‐ALA) is an omega amino acid which can be considered as an analogue of γ‐aminobutyric acid (GABA). We have examined the effect of §‐ALA on [3H]GABA uptake and release in the synaptosome fraction of rat cerebral cortex and report:(1) High concentrations of §‐ALA (0.75‐5 mM) stimulated [3H]GABA release very markedly, the stimulation with 1mM and 5mM‐§‐ALA exceeding the maximum obtainable with unlabelled GABA;(2) Low concentrations of §‐ALA (0.1‐0.5 mM) produced little stimulation of [3H]GABA efflux, less than that produced by similar concentrations of unlabelled GABA;(3) 0.1 mM‐§‐ALA reduced the stimulation of [3H]GABA efflux elicited by 55 mM‐K+ and the combination of 1 mM‐§‐ALA and 55mM‐K+ produced a lower stimulation of efflux than 1 mM‐§‐ALA alone;(4) §‐ALA inhibits [3H]GABA uptake in a linearly competitive fashion and inhibition is maximal at 0.5 mM‐§‐ALA.These results are discussed in relation to the neuronal high affinity GABA transport mechanism and inhibition of the synaptosomal Na+ and K+ ‐dependent ATPase. It is also postulated that §‐ALA increases the chloride conductance of the synaptosomal membrane, possibly by acting on presynaptic GABA receptors.
CHARACTERIZATION OF TAURINE UPTAKE BY NEURONAL AND GLIAL CELLS IN CULTURE
Authors: Borg J. , Balcar V. J. , Mark J. , Mandel P. 
Published: October 2006

AbstractUptake of [35S]taurine was studied in parallel on glial and neuronal cells maintained in continuous culture, including transformed neuronal cells. Both glial and neuronal taurine uptake systems were concentrative, highly sodium‐dependent and inhibited by closely related structural analogues such as hypotaurine, β‐alanine and GABA. Strychnine was found to be a potent inhibitor of taurine uptake, especially in the glial cells, while parachloromercuriphenylsulphonate was more efficient on the neuronal clones. In contrast with uptake by neuroblastoma cells, the glial transport was dependent on the presence of calcium in the incubation medium.
Evolution du taux de quelques acides aminés libres cérébraux au cours de l'encéphalopathie hépatique chez le rat porteur dune anastomose porto‐cave Brain amino acids changes during hepatic encephalopathy in the rat with portocaval anastomosis
Authors: Tangapregassom M. J. , Lantin N. , Salomon F. , Bismuth H. , Grange D. 
Published: October 2006

AbstractThe free amino acid contents of rat brain have been estimated in animals with portocaval shunt and sham operated up to 1, 2, 3, 5 and 6 weeks after operation. The cyclic amino acid levels (Phe, Tyr and His) were consistently raised from the first to the last weeks. The aliphatic amino acid contents (Ala, Gly, GABA, Lys and Arg) were not found to be significantly different from those of sham operated animals during the first 3 weeks, but they dropped significantly during the 5th and 6th postoperative weeks. Consideration is given to the possibility that the increase of brain cyclic amino acids and delayed fall of aliphatic amino acid contents may explain other results (i.e. drop of sleep and pain thresholds) which have been described in animals with a similar portocaval shunt.
INTERACTION OF LEUCINE, GLUCOSE, AND KETONE METABOLISM IN RAT BRAIN IN VITRO
Authors: Palaiologos G. , Koivisto V. A. , Felig P. 
Published: October 2006

AbstractBrain cortex slices from fed, 48 h and 120 h fasted rats were incubated and 14CO2 was measured from (a) [U‐14C]glucose (5 mm) either alone or in the presence of l‐lcucine (0.1 or 1 mm), and (b) [U‐14C]leucine or [l‐14C]leucine at 0.1 or 1 mm with or without glucose (5 mm). In other experiments, sodium dl‐3‐hydroxybutyrate (3‐OHB) or acetoacetate (AcAc) at 1 or 5 mm were added in the above incubation mixture. The rate of conversion of [U14C]glucose to CO2 was decreased 20% by leucine at 1 mm and 30–50% by 3‐OHB at 1 or 5 mm but not by leucine at 0.1 mm. The effects of 3‐OHB and of leucine (1 mm) were not additive. The effects of leucine were similar in the fed and fasted rats. The rate of conversion of [U‐14C]leucine or [l‐,4C]leucine to 14CO2 at 0.1 mm and 1.0 mm was increased by glucose (35%) in the fed or fasted rats. Ketone bodies in the absence of glucose had no effect on leucine oxidation. However, the stimulatory effect of glucose on the rate of conversion of leucine to CO2 was inhibited by 3‐OHB at 5 mm. These results suggest that (a) leucine in increased concentrations (1 mm) may reduce glucose oxidation by brain cortex while itself becoming an oxidative fuel for brain, and (b) leucine oxidation by brain may be influenced by the prevailing glucose and ketone concentrations.
THE COMPLEX BINDING OF γ‐AMINOBUTYRIC ACID TO A RAT BRAIN SYNAPTIC MEMBRANE PREPARATION
Authors: Winkler M. H. , Nicklas W. J. , Berl S. 
Published: October 2006

AbstractThe association of γ‐aminobutyric acid (GABA) with rat brain synaptic membranes is complex and involves more than one set of binding sites. This fact is suggested by the form of experimentally determined binding curves and confirmed by the destruction of one set of homogenous sites by covalent modifications with iodine. The difference in binding of GABA by two sets of membranes which have been exhaustively iodinated in the presence and absence of an excess of GABA corresponds to 1/6 of the binding expressed by uniodinated membranes after equilibration with 0.25 μm‐GABA. This difference appears to be the result of the expression of a homogeneous set of independent sites, each of which contains an iodinatable'residue that is protected by bound GABA.Examination of the factors leading to the retention of radioactive ligand by a synaptic membrane preparation is suggestive of a method for determining the maximum number of binding sites for a given ligand and for evaluating solution space without displacing the bound species or adding a presumably inert tracer. Three additional measurements of retention of high ligand concentration are shown to be sufficient for the determination. Employment of the method facilitates the investigation of the interaction of the membrane preparations with individual agonists and antagonists.
THE ACTIVITY OF PARTIAL REACTIONS IN THE CHAIN ELONGATION OF PALMITOYL‐CoA AND STEAROYL‐CoA BY MOUSE BRAIN MICROSOMES
Authors: Bernert John T. , Bourre Jean‐Marie , Baumann Nicole A. , Sprecher Howard 
Published: October 2006

AbstractPartial reactions in the overall chain elongation of palmitoyl‐CoA and stearoyl‐CoA by mouse brain microsomes have been analyzed. The rate of the initial condensation reaction between palmitoyl‐CoA and malonyl‐CoA was more than 5 times greater than the rate obtained with stearoyl‐CoA, and in both cases good agreement between condensation and overall chain elongation rates was observed.By contrast, both β‐hydroxyoctadecanoyl‐CoA and β‐hydroxyeicosanoyl‐CoA were quite rapidly dehydrated by brain microsomes at similar rates. Similar results were obtained with 2‐trans‐octadecenoyl‐CoA and 2‐trans‐eicosenoyl‐CoA in which both substrates were rapidly reduced at nearly the same rate in the presence of NADPH. In all cases, intermediate reactions subsequent to condensation were much more rapid than overall chain elongation. These results suggest that the mechanism of malonyl‐CoA‐dependent fatty acid chain elongation in brain microsomes is similar to that observed in other tissues, and are consistent with an overall regulation of chain elongation mediated primarily by the initial condensation reaction.
BIOPTERIN V. DE NOVO SYNTHESIS OF DIHYDROBIOPTERIN: EVIDENCE FOR ITS QUINONOID STRUCTURE AND LACK OF DEPENDENCE OF ITS REDUCTION TO TETRAHYDROBIOPTERIN ON DIHYDROFOLATE REDUCTASE
Authors: Gál E. M. , Bybee J. A. , Sherman A. D. 
Published: October 2006

AbstractSamples of quinonoid‐l‐erythrodihydrobiopterin (q‐BH2) and quinonoid‐6‐methyl‐dihydro‐pterin (q‐6‐MPH2) were prepared by oxidation of l‐erythro‐5,6,7,8‐tetrahydrobiopterin (BH4) and 5,6,7,8‐tetrahydro‐6‐methylpterin (6‐MPH4) and separated from D‐erythro‐7,8‐dihydrobiopterin (7,8‐BH2) and 6‐methyl‐7,8‐dihydropterin (7,8‐6‐MPH2) as well as from the tetrahydropterins on phosphocellulose column by high‐pressure liquid chromatography. The quinonoid dihydropterins were identified and quantitated by scan of their ultraviolet absorption and fluorescence emission spectra through their rearrangement to their 7,8‐tautomer and also by gas chromatography of their rapidly synthesized trimethylsilyl derivative. Identification was also achieved by the enzymatic reduction of [3H]q‐BH2to [3H]BH4 by dihydrofolate reductase (DHFR). Direct proof for the enzymatic synthesis of the q‐BH2 from GTP or from 2‐amino‐6‐(5′‐triphosphoribosyl)‐amino‐5‐ or ‐6‐formamido‐6‐hydroxypyrimi‐dine (FPyd‐P3) was obtained by isolation of the compound which was identical in all respects to the q‐BH2 obtained by chemical synthesis from BH4. The reduction of enzymatically synthesized q‐BH2 by dihydropteridine reductase (DHPR) to BH4 was not inhibited by methotrexate (MTX). When the enzymatically synthesized q‐BH2 was converted to 7,8‐BH2, it was reduced only by DHFR. This reduction, however, was inhibited by MTX. On the biosynthetic pathway from GTP to dihydrobiopterin, the enzyme responsible for the appearance of the quinonoid structure is the d‐erythro‐dihydroneopterin triphosphate synthetase, the product of which (quinonoid d‐erythro‐dihydroneopterin triphosphate) is converted to quinonoid dihydrobiopterin by l‐erythro‐dihydrobiopterin synthetase. Experiments in vivo established that DHFR does not participate in the reduction of dihydrobiopterin to tetra‐hydrobiopterin when the former is synthesized from GTP de novo. MTX at 5 × 10−6M exerted no inhibition on the reduction of the biosynthetic dihydrobiopterin to tetrahydrobiopterin in vivo, yet completely inhibited the reduction of intraventricularly injected tritiated dihydrofolate ([3H]FH2) to tritiated tetrahydrofolate ([3H]FH4).
RELATIONSHIP BETWEEN THE 4‐AMINOBUTYRATE BYPATH AND THE OXIDATION OF 2‐OXOGLUTARATE IN RAT BRAIN MITOCHONDRIA
Authors: Lopes‐Cardozo M. , Albers R. W. 
Published: October 2006

Abstract— A method is described to evaluate simultaneously the contributions of 2‐oxoglutarate oxidation and the GABA bypath to succinate production in isolated rat brain mitochondria.2‐Oxoglutarate oxidation is under respiratory control whereas the activity of the GABA shunt is but slightly affected by the mitochondrial energy state.The oxidation of GABA is half‐maximal with 5mm‐GABA. GABA does not affect 2‐oxoglutarate oxidation. 1 mm‐2‐oxoglutarate is optimal for GABA oxidation, whereas higher concentrations inhibit the shunt activity.The rate of GABA oxidation observed in vitro (5 nmol/min.mg mitochondrial protein) is comparable to the activity of the shunt under in viuo conditions.The control and the compartmentation of GABA oxidation are discussed.
LACTOPEROXIDASE‐COUPLED IODINATION OF BOVINE CHROMAFFIN GRANULES
Authors: Blakeborough P. , Louis C. F. 
Published: October 2006

Abstract— Chromaffin granules were iodinated with lactoperoxidase at either their external or internal membrane surfaces. When iodination of internal soluble granule proteins and membrane phospholipids was minimized, the majority of the membrane proteins, including the 83,000 component, were iodinated. Components with molecular weights 63,000, 61,000, 51,000, 44,000, 32,000, 26,000 and 19,000 had a higher 125I specific activity than did the other membrane components, suggesting they were more accessible at the outer membrane surface than were the other components. In the presence of detergent, the iodination of all membrane components was increased more than 10‐fold; the incorporation of 125I was now similar to their Coomassie Blue staining intensity in disc gels, indicating that all components were equally accessible to lactoperoxidase. In the presence of detergent, iodine incorporation into the MW 83,000 and 16,000 components was stimulated approx 100‐fold.The MW 83,000, 63,000, 61,000 and 37,000 components incorporated significant amounts of 125I when granule membranes were iodinated from their internal surface, suggesting these components have a portion of their polypeptide chain accessible at the inner membrane surface. Thus the MW 83,000 component, which we identified as dopamine β hydroxylase, and the MW 63,000/61,000 components, which are part of the membrane ATPase, can be iodinated from both membrane surfaces. This would suggest that these are transmembrane proteins. However, the major portion of all the proteins in this membrane were inaccessible to lactoperoxidase at either membrane surface.
POST‐MORTEM CHANGES IN HIGH AFFINITY CHOLINE UPTAKE
Authors: Klemm Nikolai , Kuhar Michael J. 
Published: October 2006

Abstract— When animals were killed by decapitation and the heads kept refrigerated at 2–4°C. high affinity choline uptake was maintained up to 3 days post‐mortem. At 5 days post‐mortem, there was a significant reduction in uptake. In tissues kept at 2–4°C for 1 day, the ionic dependence, drug sensitivity and kinetic parameters of uptake were identical to that of control tissues. At 3 days post‐mortem, intact synaptosomal profiles, although with features characteristic of degenerating neuronal tissues, were observed in electronmicroscopic studies. In tissues maintained at room temperature, however, the uptake activity was nearly completely gone by 1 day. It is concluded that high affinity choline uptake is maintained for days, a surprisingly long time, in tissues kept in the cold immediately after death.When pentylenetetrazol or pentobarbital were administered to rats in order to activate or depress the choline uptake, it was found that the activity‐related changes in choline uptake undergo a reversal in post‐mortem tissues. The changes in uptake were significantly lost by 10min post‐mortem and totally absent by 30min post‐mortem. In vitro studies with whole hippocampi indicate that the postmortem reversal in activity‐related changes in uptake is temperature‐dependent. It is concluded that because of post‐mortem reversals in activity‐related states of uptake the true magnitude of these activity‐related changes in uptake may be underestimated by existing methods of assay. Acetylcholine levels in synaptosomal preparations did not clearly correlate with levels of choline uptake.
DEVELOPMENTAL CHANGES IN THE DISTRIBUTION OF 3‐HYDROXY‐3‐METHYLGLUTARYL COENZYME A REDUCTASE AMONG SUBCELLULAR FRACTIONS OF RAT BRAIN 1
Authors: MALTESE WILLIAM A. , VoLPE JOSEPH J. 
Published: October 2006

Abstract—The distribution of 3‐hydroxy‐3‐methylglutaryl coenzyme A (HMG‐CoA) reductase (EC 1.1.1.34) relative to that of several biochemical markers has been studied in subcellular fractions prepared from the brains of rats, aged 4 days to adult, by differential centrifugation. In the brains of 10‐day‐old animals fractions which sedimented at 800 g (P1 and 9000 g (P2) contained 28% and 65% respectively of the total reductase activity. A similar distribulion of the microsomal marker, NADPH‐cytochrome c reductase, suggested that the HMG‐CoA reductase activity in the low‐speed pellets was due to substantial contamination of these fractions with endoplasmic reticulum. When P2 was fractionated on a discontinuous sucrose gradient, the distributions of protein, RNA and NADPH‐cytochrome c reductase paralleled that of HMG‐CoA reductase, indicaling a non‐specific association of endoplasmic reliculum and HMG‐CoA reductase with all of the structures sedimenting in P2. As brain maturation proceeded and a greater percentage of total brain protein (primarily associated with myelin) sedimenled in P1, the subcellular distributions of HMG‐CoA reductase and the microsomal marker changed in a parallel way. By 21 days P1 contained nearly all of the reductase activity. Because the specific activity of HMG‐CoA reductase in P1 decreased steadily between 4 and 21 days, while the specific activity of 2′:3′‐cyclic nucleotide 3′‐phosphohydrolase in this fraction increased in a coordinate fashion, we conclude that the reductase is not an integral component of myelin, and probably is associated exclusively with the endoplasmic reticulum included in P1. In view of the developmental changes in the distribution of HMG‐CoA reductase among subcellular fraclions, we suggest that whole homogenates (or comparable tissue extracts) should be utilized to evaluate reductase activity in the developing brain.
LEVELS OF NOREPINEPHRINE AND DOPAMINE IN MOUSE BRAIN REGIONS FOLLOWING MICROWAVE INACTIVATION‐RAPID POST‐MORTEM DEGRADATION OF STRIATAL DOPAMINE IN DECAPITATED ANIMALS
Authors: Blank C. LeRoy , Sasa Suleiman , Isernhagen Rick , Meyerson Laurence R. , Wassil David , Wong Peter , Modak Arvind T. , Stavinoha William B. 
Published: October 2006

Abstract—The effects of 2 methods of killing on norepinephrine and dopamine in mouse brain regions were examined. One method utilized decapitation, while the other method utilized heating with microwave irradiation concentrated on the head. The norepinephrine and dopamine contents of the cerebellum, medulla‐pons, midbrain, diencephalon, hippocampus, corpus striatum, and cerebral cortex were determined by methods using liquid chromatography with electrochemical detection. Dopamine content in striatum was also quantitated by the method of gas chromatography with mass fragmentography. A significantly lower value for decapitated animals, as compared to the microwave heated group, was found only for dopamine exclusively in the striatum.Activities of the enzymes tyrosine hydroxylase, DO PA decarboxylase, monoamine oxidase, and catechol‐o‐methyltransferase in the striatum were also examined. These enzymes were totally inactivated by the microwave heating, except catechol‐o‐methyltransferase which was decreased approx 80%. These results support either (1) the existence of a substantial pool of dopamine in the striatum with a very rapid turnover rate or (2) a decapitation‐related release and destruction of striatal dopamine. Measurements of 3‐methoxytyramine in the striatum exhibit post‐mortem increases corresponding to the decreases of dopamine. Use of the rapid tissue enzyme inactivation technique suggests that in vivo levels of this O‐methylated dopamine metabolite are an order of magnitude lower than the results normally obtained after killing by decapitation.