bluuebunny/crossref_metadata_2025_split huggingface dataset:
MASS FRAGMENTOGRAPHIC DETERMINATION OF SOME ACIDIC AND ALCOHOLIC METABOLITES OF BIOGENIC AMINES IN THE RAT BRAIN
Authors: Karoum F. , Gillin J. C. , Wyatt R. J. 
Published: October 2006

Abstract—A mass fragmentographic procedure is described for the simultaneous quantification of a number of deaminated metabolites derived from tyramine, octopamine, dopamine, and norepinephrine. With this method, several of the metabolites were measured in normal rat brain. The results support the central nervous system origin of tyramine, octopamine and their metabolites. The concentration of the dopamine metabolite, homovanillic acid, in the rat brain was found to be about 15% higher than that of dihydroxyphenylacetic acid. As for the metabolites of norepinephrine, vanilmandelic acid concentration was found to be about 5% that of 3‐methoxy‐4‐hydroxyphenylglycol. The possible role of vanilmandelic acid in the CNS metabolism of norephrine is discussed.
THE INCORPORATION OF RADIOACTIVE AMINO ACIDS INTO BRAIN SUBCELLULAR PROTEINS DURING TRAINING
Authors: Hershkowitz M. , Wilson J. E. , Glassman E. 
Published: October 2006

Abstract—Total proteins, free amino acids, tritiated water and subcellular proteins of mouse brain were examined for changes in radioactivity during operant conditioning after subcutaneous administration of labelled amino acids. The conditioning was based on appetitive learning, using sweetened milk as a reward.During training and incorporation for 20‐30 min, both [3H]leucine and [1‐14C]leucine underwent a significant increase in catabolism, resulting in a decreased radioactivity in the free amino acids. [2‐2H]Methionine underwent a rapid loss of isotope, so that 90% of the radioactivity was in the form of tritiated water at the end of training, and this phenomenon masked any possible effect of training. The brain uptake of [35S]methionine increased during the training, resulting in an increased radioactivity in the proteins. Uptake of [3H]lysine increased slightly during training only after 1 h incorporation and not after 20 or 30 min, as judged from a time course of radioactivity in the free amino acids. Incorporation into nuclear proteins increased selectively during 20 min, and into nuclear and cytosol proteins after 60 min incorporations. It is concluded that changes in the observed rate of incorporation of a precursor into brain subcellular proteins under the influence of behaviour might be the result of changes in precursor catabolism or uptake, or both, and that each amino acid behaves in a different way. Even the same amino acid gives different results depending on the isotope and its position in the amino acid.
CHARACTERIZATION AND PROTEIN ANALYSIS OF MYELIN SUBFRACTIONS IN RAT BRAIN: DEVELOPMENTAL AND REGIONAL COMPARISONS
Authors: Zimmerman A. W. , Quarles R. H. , Webster H. de F. , Matthieu Jean‐Marie , Brady R. O. 
Published: October 2006

Abstract—Myelin preparations from the whole brains of 16‐day‐old rats and from cortical regions and brainstem, respectively, of 40‐day‐old rats were separated into light, medium and heavy subfractions on a discontinuous sucrose gradient by a procedure previously used for whole adult rat brain (Matthieu, et al., 1973). The total dry weight of myelin recovered from the 16‐day‐old rats was only 2·4mg/g fresh brain in comparison to 20 mg from adult brains. In 16‐day‐old rat brains, the percentage of the total myelin protein in the light fraction was higher than that found in adult brains; the percentage in the medium fraction was only one‐third that in adults; while the percentage in the heavy fraction was about the same at both ages. The heavy fraction from the 16‐day‐old rats contained less basic protein and proteolipid than the light fraction, and the levels of the 2′3′‐cyclic nucleotide 3′‐phosphohydrolase (CNP) and glycoprotein were less than half those in the light and medium fractions. Double labelling experiments with radioactive fucose indicated that the major labelled glycoprotein in the heavy and medium fractions had a slightly higher apparent mol. wt than that in the light fraction. Electron microscopy showed much readily identifiable, compact myelin in the light and medium fractions from the 16‐day‐old rats, whereas the heavy fraction contained more single membranous structures and much less multilamellar myelin. The yield of myelin/g fresh wt from brainstem of 40‐day‐old rats was 4‐fold higher than from cortical regions, and the percentage recovered in the light fraction was greater in the brainstem. In both regions basic proteins decreased from the light to the heavy fraction, whereas high mol. wt proteins, the glycoprotein and CNP increased. The biochemical and morphological results suggest that in both 16‐day‐old and young adult rats the light fraction is enriched multilamellar, compact myelin. In contrast, the heavy fraction at both ages is enriched in loose, uncompacted myelin and myelin‐related membranes, although the heavy fraction from 16‐day‐old rats also may be substantially contaminated with membranes which are unrelated to myelin.
ANALYSIS OF THE PREFERENTIAL RELEASE OF NEWLY SYNTHESIZED ACETYLCHOLINE BY CORTICAL SLICES FROM RAT BRAIN WITH THE AID OF TWO DIFFERENT LABELLED PRECURSORS
Authors: Molenaar P. C. , Polak R. L. 
Published: October 2006

Abstract—The release of newly synthesized acetylcholine (ACh) by cortical slices from rat brain in the presence of 25 mm‐KCl was studied. The slices were incubated for 5 min in a medium containing both [2‐14C]pyruvate and choline labelled with 3 deuterium atoms (choline‐d3) in order to label at the same time the acetyl moiety and the choline moiety of ACh. The non‐labelled ACh and the ACh‐d3 were measured by pyrolysis‐gas chromatography/mass spectrometry, and the [I4C]ACh by liquid scintillation counting. It was found that the newly formed [4C]ACh as well as the newly formed ACh‐d3 had a more than 2.5 times greater probability of being released than the preformed non‐labelled ACh. These findings strongly suggest that it is not simply the ACh synthesized immediately inside the nerve ending membrane from incoming undiluted labelled choline, which is preferentially released, but that all newly formed ACh has a greater probability of being released than preformed ACh. No preferential release of newly formed ACh was observed when the incubation medium contained 5.6 mm‐pyruvate instead of 10 mm‐glucose + 0.6 mm‐pyruvate. The cause of this difference remains unexplained.
REDUCTION OF γ‐AMINOBUTYRIC ACID LEVEL IN THE CAT CEREBRAL CORTEX BY AFFERENT ELECTRICAL STIMULATION
Authors: Lichtshtcin D. , Dobkin J. 
Published: October 2006

Abstract—Electrical stimulation for 30 s of one brachial plexus in cat (afferent electrical stimulation = AES) produced a 20% decrease in GABA level of the stimulated (contralateral) cerebral cortex as compared to the non‐stimulated (ipsilateral) cortex in the same animal. This change in GABA was reversed within a few seconds after cessation of stimulation. Inhibition of GABA catabolism by aminooxyacetic acid elevated considerably the cortical level of GABA but failed to prevent lowering GABA by AES. When AES was performed in preconvulsive condition induced by administration of picrotoxin, the decrease in GABA was negligible, while similar treatment with pentylenetetrazol had no influence on the decrease in GABA produced by AES. The observed lowering cortical GABA by AES is interpreted as being associated with some mechanism of the inhibitory transmitter inactivation.
SODIUM‐DEPENDENT HIGH AFFINITY CHOLINE UPTAKE: A REGULATORY STEP IN THE SYNTHESIS OF ACETYLCHOLINE
Authors: Simon J. R. , Atweh S. , Kuhar M. J. 
Published: October 2006

Abstract—The sodium‐dependent high affinity choline uptake into synaptosomes from rat brain has been studied after in vivo treatments which would alter the activity of cholinergic neurons. We utilized a number of treatments to reduce the activity of cholinergc neurons in the brain. Administration of pentobarbital (65 mg/kg), chloral hydrate (40 mg/kg) and γbutyrelactone (750 mg/kg) caused a 50‐80% reduction in sodium‐dependent high affinity choline uptake in several brain regions (30 min). This depression was not found 24 h after injection. Interruption of the cholinergic septal‐hippocampal or habenuleinterpeduncular tracts by lesions (10 min‐1 h) also caused a similar, large reduction in sodium‐dependent high affinity choline uptake in the hippocampus and the interpeduncular nucleus respectively.We reversed the inactivity after pentobarbital administration by direct electrical stimulation of the cholinergic septal‐hippocampal tract. Stimulation (40 Hz) for 10‐15 min completely reversed the depression in sodium‐dependent high affinity choline uptake. Stimulation at lower frequencies or for shorter times caused a partial reversal.Administration of pentylenetetrazol (75 mg/kg), a convulsant, was utilized to increase the activity of central cholinergic neurons. After drug administration, we found a large (60%) increase in sodium‐de‐pendent high affinity choline uptake. This increase was not found in the hippocampus when cholinergic afferents were interrupted by septal lesion prior to drug administration.We also examined the uptake after administration of cholinergic drugs. Oxotremorine (0.75 mg/kg), a muscarinic agonist which reduces acetylcholine release and turnover, caused a reduction in uptake. On the other hand, administration of scopolamine (5 mg/kg), a cholinergic antagonist which increases acetylcholine turnover, caused an increase in sodium‐dependent high affinity choline uptake. Addition of any drug utilized, drectly to uptake samples, did not alter uptake.We examined the conversion of [3H]choline to [3H]acetylcholine in hippocampal synaptosomes after septal lesion, pentylenetetrazol administration and in untreated controls. In all cases, 60‐70% of the total sodium‐dependent tritium content was present as [3H]acetylcholine. Evidence was presented that homoexchange is not or is less involved in choline uptake than in GABA uptake.A kinetic analysis of sodium‐dependent high affinity choline uptake was performed after all treatments. We found changes in Vmax, after all treatments, which were consistently in the same direction as the alterations in activity. The proposal is made that the sodium‐dependent high affinity choline uptake is coupled to cholinergic activity in such a way as to regulate the entry of choline for the maintenance of acetylcholine synthesis. The findings also lead us to propose that sodium‐dependent high affinity choline uptake in vitro be utilized as a rapid, relative measure of the activity of cholinergic nerve terminals in vivo.
INHIBITION OF THE UPTAKE OF GABA AND RELATED AMINO ACIDS IN RAT BRAIN SLICES BY THE OPTICAL ISOMERS OF NIPECOTIC ACID
Authors: Johnston G. A. R. , Krogsgaard‐Larsen P. , Stephanwn A. L. , Twitchin B. 
Published: October 2006

Abstract—R(‐)‐Nipecotic acid was a more potent inhibitor than the S(+)‐isomer of the uptake of GABA, (+)‐nipecotic acid, and β‐alanine in rat brain slices. (‐)‐Nipecotic acid was an order of magnitude more potent as an inhibitor of GABA uptake than as an inhibitor of β‐alanine uptake, whereas the (+)‐isomer was less selective. (–)‐Nipecotic acid was a weak inhibitor of L‐proline uptake and of rat brain acetylcholinesterase activity.Kinetic studies showed that both isomers of nipecotic acid were competitive inhibitors of GABA uptake when added at the same time as GABA, but non‐competitive inhibitors when preincubated with the tissue for 15 min before addition of GABA. The apparent slope inhibition constants, which were not influenced by preincubation, indicated that (–)‐nipecotic acid has an affinity for the carrier some 5 times higher than that for (+)‐nipecotic acid. (–)‐Nipecotic acid stimulated the release of preloaded radioactive GABA from rat brain slices. These observations indicate that (–)‐nipecotic acid is a substrate‐competitive inhibitor of GABA which combines with the GABA carrier and is taken up.(−)‐Nipecotic acid and (+)‐2,4‐diaminobutyric acid, on the basis of their absolute structures and inhibition kinetics, are proposed to interact in a similar way with the GABA transport system.
THE UPTAKE, METABOLISM AND RELEASE OF HOMOCHOLINE: STUDIES WITH RAT BRAIN SYNAPTOSOMES AND CAT SUPERIOR CERVICAL GANGLION
Authors: COLLIER B. , LOVAT S. , ILSON D. , BARKER L. A. , MITTAG T. W. 
Published: October 2006

Abstract—The accumulation of [3H]homocholine (3‐trimethylamino‐propan‐1‐01) by isolated synaptosomes prepared from rat brain was resolved kinetically into a high (KT= 3.0 μM) and a low (KT= 14.5 μM) affinity system. Although homocholine was not acetylated by solubilized choline acetyltransferase, 64% of the homocholine accumulated by intact synaptosomes via the high affinity uptake process was acetylated. Homocholine was also acetylated in the superior cervical ganglion of the cat, and the amount of acetylhomocholine formed was increased (12‐fold) by preganglionic nerve stimulation. In ganglia, acetylhomocholine was available for release by preganglionic nerve impulses, and its release was Ca2+‐dependent, It is concluded that homocholine can form a cholinergic false transmitter, and that the substrate specificity of choline acetyltransferase in vitro might be different from that in situ.
METABOLIC CHANGES ASSOCIATED WITH ISO‐OSMOTIC REGULATION IN BRAIN CORTEX SLICES
Authors: Fishman R. A. , Reiner M. , Chan P. H. 
Published: October 2006

Abstract— The metabolism of single, first cortical rat brain slices was studied in response to incubation in media of various osmolalities. There was an inverse relationship between osmolality and the magnitude of the increase in tissue water content, and a direct relationship between osmolality and inulin space. Brain sodium varied directly with the media sodium, but hyperosmolal sucrose and glucose resulted in a drop in brain sodium. Brain potassium was constant in hyperosmolal sodium media, but it fell in hypo‐osmolal media and hyperosmolal sucrose and glucose media.Hypo‐osmolality depressed the oxidation of [14C]glucose to 14CO2 whereas hyperosmolality obtained with sodium, sucrose, or glucose stimulated glucose oxidation. Lactate production was enhanced only by sodium hyperosmolality. Hypo‐osmolality caused a 70% drop in phosphocreatine and a minor decrease in energy charge potential, analagous to the effects of hypoxia. Hyperosmolality had no effect on energy metabolism.The total amino acid nitrogen released into the media was suppressed by hypo‐osmolality but was increased by hyperosmolal incubation. Hyperosmolality also increased production of ammonia fourfold.The time course of the change in tissue osmolality and ion content following incubation in hyperosmolal sodium media showed the tissue osmolality reached the media osmolality within 5 min, but it took 30 min for the tissue sodium to reach equilibrium with the media sodium. This indicates that unidentified or‘idiogenic osmoles’are induced transiently by hyperosmolality associated with changes in amino acid and ammonia metabolism.
PROPERTIES OF MEMBRANE‐BOUND DOPAMINES‐HYDROXYLASE IN CHROMAFFIN GRANULES FROM BOVINE ADRENAL MEDULLA
Authors: Aunis Dominique , Bouclier Martine , Pescheloche M. , Mandel P. 
Published: October 2006

Abstract— Properties of membrane‐bound and soluble dopamine‐β‐hydroxylase were studied. Both enzyme forms have identical affinities for tyramine as the substrate. Arrhenius plots of the membrane‐bound activity displayed a discontinuity at 29°C, the activation energy changing from 20,500 cal/mol below 29°C to 9500 cal/mol above 29°C. The soluble enzyme, like the purified enzyme, did not show discontinuities in Arrhenius plots, the activation energies being 18,500 cal/mol and 16,500 cal/mol respectively. The membrane‐bound enzyme showed a discontinuity in the pKm for tyramine versus reciprocal temperature plot, with a transition at 29°C, whereas the soluble enzyme failed to show such transition.The membrane‐bound dopamine‐β‐hydroxylase is solubilized by Triton X‐100 as well as by lysolecithin. Of lecithin, lysophosphatidyl ethanolamine and phosphatidyl serine, lysolecithin was the only phospholipid to induce solubilization of membrane‐bound dopamines β‐hydroxylase. The 29°C‐transition was not removed by treatment either with lysolecithin or with Triton X‐100 used at concentration of up to 2%. This could indicate a solubilization of dopamine‐β‐hydroxylase with an associated lipid moiety which cannot be dispersed from the enzyme molecule and which still affects the activation energy and Michaelis constant for tyramine.Results are discussed in terms of the relationship between lipid organization and enzyme activities; the significance of the solubilization by lysolecithin during exocytosis is considered in terms of the exocytosis process and fate of the chromaffin granule.
KINETIC STUDY OF GLUTAMATE TRANSPORT IN RAT BRAIN MITOCHONDRIA
Authors: Minn A. , Gayet J. 
Published: October 2006

Abstract— The experiments reported here confirm that glutamate can penetrate the inner membrane of isolated rat brain non‐synaptosomal mitochondria, either on a glutamate‐hydroxyl antiporter or on a glutamate‐aspartate antiporter.An inhibition of respiratory activity of mitochondria with glutamate as substrate was obtained in the presence of avenaciolide or N‐ethylmaleimide. Swelling of the mitochondria in iso‐osmotic NH4+‐l‐glutamate was inhibited in the presence of avenaciolide and N‐ethylmaleimide, but mersalyl, kainic acid, glisoxepide and amino‐oxyacetic acid had no effect on the glutamate‐hydroxyl exchange. Glutamate induced the reduction of intramitochondrial NAD(P), as estimated by double‐beam spectrophotometry, and this reduction was inhibited on the one hand by N‐ethylmaleimide, avenaciolide or fuscine, on the other hand by aminooxyacetic acid. A direct estimation of the penetration of l‐[14C]glutamate into brain mitochondria was performed by using the centrifugation‐stop procedure. This penetration followed saturation kinetics, with a mean apparent Km of 1.56 MM at pH 7.4 and at 20°C, the value of Knax was 4.34 nmol per min per mg protein in the same conditions. IV‐Ethylmaleimide slowed down the initial rate of glutamate penetration, and this inhibition appeared to be non‐competitive with a Ki of 0.7 Mm ‐at pH 7.4 and at 20°C. The entry of glutamate was pH‐dependent and it increased 2‐fold in the pH range of 7.4 to 6.4. A temperature‐dependence of glutamate transport was also shown between 2 and 25°C; the Arrhenius plot was a straight line, with a calculated EA of 12.8 kCal per mol of glutamate and a Q10 of 2.16. The activity of γ‐glutamyl transpeptidase was practically absent in these rat brain mitochondria.Oxidation of extramitochondrial NADH by the‘malate‐aspartate shuttle’reconstituted in vitro was followed in rat brain non‐synaptosomal mitochondria. In the absence of extramitochondrial malate or glutamate the ‘shuttle’ did not function, and in the absence of extramitochondrial aspartate the rate of NADH oxidation was low. Glutamine or γ‐aminobutyrate did not replace glutamate efficiently. A high inhibition of the‘malate‐aspartate shuttle’occurred in the presence of avenaciolide or mersalyl, and a moderate one in the presence of n‐ethylmaleimide, glisoxepide or n‐butylmalonate.Glutaminase activity in intact brain mitochondria was inhibited in the presence of extramitochondrial glutamate.
DIURNAL RHYTHM AND TURNOVER OF TRYPTOPHAN HYDROXYLASE IN THE PINEAL GLAND OF THE RAT
Authors: Sitaram B. R. , Lees G. J. 
Published: October 2006

AbstractTryptophan hydroxylase in the pineal gland of the rat was found to undergo a diurnal rhythm in activity with an elevated activity at night. The rhythm was abolished in constant light. Cycloheximide (15 mg/kg, i.p.), administered both at night and during the day, caused a rapid decay in activity suggesting that tryptophan hydroxylase was subject to a rapid turnover in vivo. The primary site of control appeared to be at the level of translation since actinomycin D had no effect. Some relevant properties of the enzyme were studied. Thiol‐containing compounds were shown to substantially protect pineal tryptophan hydroxylase from inactivation at 0°C but provided little protection at higher temperatures. The inactivation process appeared to be independent of oxygen. The activity of the enzyme, lost after ageing at 0°C. could be recovered by incubation with dithiothreitol under anaerobic conditions. Fresh enzyme, or enzyme inactivated at 37°C could not be activated by this process. A re‐examination of the action of p‐chlorophenylalanine (PCPA) on pineal tryptophan hydroxylase revealed that an irreversible inactivation occurred within 6h (25% of initial activity) followed by a recovery within 24 h. The rapid turnover of the enzyme is the probable reason for the failure of previous studies to observe an irreversible inhibition of this enzyme by PCPA.
THE EFFECTS OF 5‐HYDROXYTRYPTOPHAN AND 5‐HYDROXYTRYPTAMINE ON DOPAMINE SYNTHESIS AND RELEASE IN RAT BRAIN STRIATAL SYNAPTOSOMES1
Authors: Andrews David W. , Patrick Robert L. , Barchas Jack D. 
Published: October 2006

Abstract—The effects of 5‐hydroxytryptophan (5‐HTP) and serotonin (5‐HT) on dopamine synthesis and release in rat brain striatal synaptosomes have been examined and compared to the effects of tyramine and dopamine. Serotonin inhibited dopamine synthesis from tyrosine, with 25% inhibition occurring at 3 μM‐5‐HT and 60% inhibition at 200 μM. Dopamine synthesis from DOPA was also inhibited by 5‐HT, with 30% inhibition occurring at 200 μ. At 200 μM‐5‐HTP, dopamine synthesis from both tyrosine and DOPA was inhibited about 70%. When just the tyrosine hydroxylation step was measured in the intact synaptosome, 5‐HT, 5‐HTP, tyramine and dopamine all caused significant inhibition, but only dopamine inhibited soluble tyrosine hydroxylase [L‐tyrosine 3‐monooxygenase; L‐tyrosine, tetrahydropteridine oxygen oxidoreductase (3‐hydroxylating); EC 1.14.16.2] prepared from lysed synaptosomes. Particulate tyrosine hydroxylase was not inhibited by 10 μM‐5‐HT, but was about 20% inhibited by 200 μM‐5‐HT and 5‐HTP. At 200 μM both 5‐HT and 5‐HTP stimulated endogenous dopamine release. These experiments suggest that exposure of dopaminergic neurons to 5‐HT or 5‐HTP leads to an inhibition of dopamine synthesis, mediated in part by an intraneuronal displacement of dopamine from vesicle storage sites, leading to an increase in dopamine‐induced feedback inhibition of tyrosine hydroxylase, and in part by a direct inhibition of DOPA decarboxylation.