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  • 1
    Electronic Resource
    Electronic Resource
    THE DISTRIBUTION OF AMINO ACIDS, Na+ AND K+ FROM SURFACE TO CENTRE IN INCUBATED SLICES OF MOUSE BRAIN (1974)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 22 (1974), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: —The effect of tissue damage on the uptake of amino acids by brain slices was investigated by measuring uptake in slices of different thickness and measuring the distribution of [14C]-labelled amino acid on the surface and in the centre of incubated slices. The uptake of glutamate, aspartate, and GABA was greater in 0.1 mm-thick slices than in 0.42 mm-thick slices in short and in long (up to 120 min) incubations; the uptake of other amino acids was equal or greater in the 0.42 mm-thick slices. The water content of incubated slices did not change greatly from surface to centre; inulin space was greater at the surface, and in slices from cortex, especially higher at the cut surface. Na+ and K+ concentrations were also higher at the surface. In the rest of the slice space, inulin, Na+ and K+ distribution was quite uniform. The distribution of ATP was inhomogeneous: in thinner slices the centre concentration was higher; in thicker slices the centre concentration was lower. Amino acid uptake initially (at 5 min) was higher at the surface, especially in the thicker slices; after longer time (30 min) incubation, the distribution of lysine and leucine was uniform, and glutamate uptake was greater at the surface. The inhomogeneity of distribution increased with increasing thickness of the slices. We concluded that the uptake of some amino acids (perhaps those for which, beside a low affinity transport, also a higher affinity transport system exists) is greater in thinner slices and greater on the surface of slices, and there is an initially inhomogeneous distribution during amino acid uptake. The uptake on the surface constitutes only a small portion of the total uptake, and tissue damage does not explain the greater uptake of amino acids by slices in comparison to the brain in vivo. This shows the higher transport capacity of cells in the brain and emphasizes the importance of mechanisms controlling the metabolite composition of the extracellular fluid in finally influencing the metabolite composition of the brain itself.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1974.tb04325.x
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  • 2
    Electronic Resource
    Electronic Resource
    REGIONAL AND SUBCELLULAR DISTRIBUTION OF CHOLINE ACETYLTRANSFERASE IN THE BRAIN OF RATS (1973)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 21 (1973), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: —Homogenates of corpus striatum, cerebral cortex and hypothalamus excised from rat brain were fractionated on discontinuous Ficoll and sucrose density gradients, and the distribution of choline acetyltransferase (ChAc) in the mitochondrial and synaptosomal fractions was determined. In the hypothalamic and cortical regions the fractions enriched in synaptosomes showed much higher activity of ChAc than those containing mainly mitochondria. On the other hand, the corpus striatum showed an equal distribution of ChAc activity in those two fractions. The localization of ChAc was also studied in the postnuclear supernatants obtained from three brain regions, using continuous sucrose density gradients. The distribution of ChAc was compared to that of monoamine oxidase (MAO), potassium and protein. When the pellets obtained from the fractions collected from the gradient were suspended in sucrose, the peak of ChAc activity was close to that of MAO in all three brain regions. When 0.1 mm EDTA +1% butanol was used in order to liberate the occluded form of ChAc, the maximum liberation occurred in lighter fractions, resulting in a shift of the activity peak toward the top of the gradient. This was found with fractions from hypothalamic and cortical regions. In the striatum, the liberated ChAc remained in the same fractions as the occluded enzyme. The results indicate that ChAc is liberated only in those fractions where it is present in synaptosomes. In agreement with the results on the discontinuous gradients this occurs in particles of lower density than mitochondria in cortex and hypo-thalamus, but in particles of similar density to mitochondria in the corpus striatum, indicating regional differences in the distribution of ChAc in the brain. K+ containing particles centrifuged in less dense fractions than those containing ChAc, indicating that synaptosomes are heterogeneous with respect to these two marker substances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1973.tb06024.x
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  • 3
    Electronic Resource
    Electronic Resource
    THE EFFECT OF ELEVATED AMINO ACIDS ON AMINOTRANSFERASE LEVELS IN BRAIN AND LIVER OF THE MOUSE (1974)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 23 (1974), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— Adult mice were fed standard diets that were enriched with selected amino acids, i.e. 3% methionine, 6% valine, or 8% lysine. These diets caused the following changes in the amino acid pool of the brain measured at 7 and 21 days. The high methionine diet resulted in 50-fold higher levels of methionine and cysteine and somewhat lower levels of serine and glutamine. The valine and lysine-enriched diets also caused 2- to 4-fold increases in valine and lysine contents of brain, respectively. In spite of the large changes in amino acid levels, however, there were essentially no changes in aspartate: α-ketoglutarate, alanine: α-ketoglutarate, ornithine: α-ketoglutarate, methionine: α-ketoglutarate, and the branched chain aminotransferase activities of brain 3, 10, and 21 days after the onset of the dietary regimen. In contrast, these diets produced significant changes in some of these enzyme activities in liver. Changes in liver included a 2-fold increase in ornithine and alanine aminotransferase activities with the methionine-enriched diet. Liver ornithine aminotransferase activity also increased slightly in animals fed the valine-enriched or lysine-enriched diet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1974.tb06059.x
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  • 4
    Electronic Resource
    Electronic Resource
    PROTEIN AND PEPTIDE HYDROLASES OF THE RAT HYPOTHALAMUS AND PITUITARY (1974)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 22 (1974), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Peptide and peptidyl-peptide hydrolase activities were measured in the cerebral cortex, adenoand neurohypophysis, anterior and posterior regions of the hypothalamus to assess regional differences in peptide hormone turnover. In general all enzyme activities were higher in the pituitary except for the monoacyl arylamidase which was lower, and neutral proteinase which was distributed more evenly in all regions. Of the enzymes measured the highest activities occurred in the presence of the di- and tripeptide substrates (aminopeptidases); this activity was some 20-60-fold higher than the acid and neutral proteinases. Comparison of the peptide-amide substrates revealed the highest activity with the monoacyl derivative which was five-fold higher than the dipeptidyl, and 50-fold higher than the tripeptidyl (hormonal) factor Pro-Leu-Gly. NH2. Analysis of the breakdown products of the hormonal factor indicated inactivation by N-terminal release of Pro, Leu with Gly. NH2 as the final product. Regional differences in enzyme content in neurosecretory areas suggest that this plays a role in the turnover of specific hormones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1974.tb04288.x
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  • 5
    Electronic Resource
    Electronic Resource
    MEASUREMENTS OF RATES OF PROTEIN SYNTHESIS IN RAT BRAIN SLICES (1974)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 22 (1974), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The use of tracer concentrations of labelled amino acids to measure incorporation in incubated slices of brain results in wide fluctuations with time in the specific activity of the precursor. Using concentrations of about 1 mm of labelled amino acid facilitates the accurate measurement of rates of synthesis. These higher precursor levels in the medium decrease the fluctuations in free amino acid specific activity due to dilution by endogenous amino acid and the production of amino acid by protein degradation, and decrease the lag in incorporation due to transport phenomena. Concentrations of 1 mm amino acid in the medium did not inhibit protein synthesis; with valine, leucine, phenylalanine, lysine and histidine, incorporation rates were similar when measured at trace concentrations and at 1 mm medium levels. The source of amino acid for protein synthesis appears to be intracellular. No evidence could be found for the preferential use of extracellular medium amino acid. The rate of incorporation of amino acids in incubated slices of rat brain was 0.087 per cent of the protein amino acid/h.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1974.tb04300.x
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  • 6
    Electronic Resource
    Electronic Resource
    METABOLISM OF AMINO ACIDS IN INCUBATED SLICES OF MOUSE BRAIN (1970)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 17 (1970), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 〈list xml:id="l1" style="custom"〉1Slices of mouse brain were incubated with [U-14C]alanine, valine, leucine, phenylalanine, proline, histidine, lysine, arginine or aspartic acid, and the extent of metabolism was estimated by analyses utilizing paper chromatography of the tissue extracts and with an amino acid analyser.〈list xml:id="l2" style="custom"〉2The metabolism of Ala and Asp was high; of Leu and Pro, moderate; and of Lys, Arg and Phe, low; the metabolism of Val and His was not significant. The time-course of metabolism in most cases showed varying rates, indicating heterogeneous metabolic compartments for the amino acids.〈list xml:id="l3" style="custom"〉3Production of CO2 was high from Asp, moderate from Ala, and low from Leu; the other amino acids were not oxidized to CO2 to any significant extent. A large portion of the metabolized label was trapped in the form of Glu or Asp.〈list xml:id="l4" style="custom"〉4Metabolism increased with increasing concentration of amino acid to some extent and was largely inhibited by omission of glucose, by anaerobic conditions, or by cyanide. Although these conditions also inhibit uptake, the time-course and extent of inhibition uptake and metabolism were different.〈list xml:id="l5" style="custom"〉5With Asp, Ala and Phe, metabolism was lowest in slices from pons-medulla; the brain area exhibiting the highest metabolism differed for each amino acid. The metabolism of Asp was lower in brain samples from newborn than in those from adults; the metabolism of Leu was higher in slices from newborn brain.〈list xml:id="l6" style="custom"〉6The results indicate that the majority of the amino acids can be metabolized in brain tissue and that the metabolic rates are influenced by a number of factors, among them the level of amino acids and the level of available energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1970.tb03379.x
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  • 7
    Electronic Resource
    Electronic Resource
    DISTRIBUTION OF AMINO ACIDS AND OF EXO- AND ENDOPEPTIDASES ALONG VERTEBRATE AND INVERTEBRATE NERVES (1970)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 17 (1970), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— The proximo-distal gradients for representative peptidases, peptidylpeptide hydrolases, and amino acids were measured in segments of peripheral nerve from invertebrates and vertebrates and in the lobster brain and ventral cord.Crustacean nerve was characterized by a large pool of free amino acids totaling 100–200 μmoles/g wet wt. In lobster nerve, the principal free amino acid was aspartic acid which comprised 55 per cent of the free pool, whereas in the rat sciatic nerve it comprised only 5 per cent. The principal free amino acid in rat sciatic nerve was taurine (32 per cent of the pool) and in lobster brain glycine comprised 30 per cent of the pool. No consistent patterns emerged for the gradients along the nerves for amino acids and hydrolytic enzymes. In the leg nerve of the lobster, concentrations of aspartic acid and arginine were higher in the proximal region, and concentrations of proline and alanine were higher in the distal region. Concentrations of most amino acids were higher in the proximal regions of crab nerve, of lobster brain and ventral cord, and of rat sciatic nerve.Rat sciatic nerve exhibited a pronounced proximo-distal increase in activity of aminopeptidase (Leu-Gly-Gly). In lobster leg nerve, activity of neutral proteinase was higher in the proximal segment, whereas activity of acid proteinase was higher in the distal segment. The best examples of proximo-distal gradients were found in lobster brain and ventral cord; activities of endopeptidases, arylamidases (Leu- and Arg-βNA), and aminopeptidase were higher in the supra-esophageal ganglia or cephalothorax segments than in the distal regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1970.tb00501.x
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  • 8
    Electronic Resource
    Electronic Resource
    THE UPTAKE OF AMINO ACIDS BY THE INTACT OLFACTORY BULB OF THE MOUSE: A COMPARISON WITH TISSUE SLICE PREPARATIONS (1973)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 20 (1973), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— Intact olfactory bulbs from 8- to 15-day-old mice were compared to slices of olfactory bulb and cerebral hemisphere with respect to uptake of amino acids, respiratory rate, levels of ATP, retention of sodium and potassium, and extracellular space. The uptake of amino acids was lower in intact bulbs than in slice preparations, both in regard to initial rates of uptake and to final steady state levels, at external amino acid concentrations from 0·2 to 2·0mM. Uptake was lower in bulbs attached to brain than in those separated from it and somewhat higher in the half of the bulb closer to the cut surface. In all preparations the uptake of glutamic acid and glycine was highest, uptake of histidine and valine was intermediate, and uptake of lysine was lowest. These differences between intact bulbs and slices could not be correlated with differences in respiratory rate, levels of ATP, or changes in levels of Na+ or K+ ions. Increases in dextran and inulin spaces, however, were greatest in preparations having the highest rates of amino acid uptake. Although for several amino acids the maximal velocity of uptake (Vmax) was 4-fold higher in slices of bulb than in intact bulbs, the affinity of amino acids to their carrier systems (Km) was similar, an indication that the same transport process was operative in both cases. On the basis of these results we propose that intact olfactory bulbs incubated in vitro possess a regulatory mechanism for the limitation of amino acid uptake that is absent or diminished in slices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1973.tb00087.x
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  • 9
    Electronic Resource
    Electronic Resource
    FORMATION OF ASPARAGINE FROM ASPARTIC ACID IN RAT BRAIN (1970)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 17 (1970), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The synthesis of asparagine in rat brain was studied both in vitro and in vivo. A conversion in vitro of about 2 per cent of the added l-[14C]aspartic acid into asparagine was found after a 2 h incubation with the 100,000 g supernatant fraction from brain. This corresponded to a formation of 4·8 nmol of asparagine/mg of protein/h. The reaction required ATP and glutamine, and was linear with time during the 2 h incubation. When the crude mitochondrial fraction was added to the incubation mixture the reaction was inhibited, probably because of the presence of ATPase activity in the mitochondrial preparation. Inhibition by the reaction product seemed unlikely since removal of endogenous asparagine did not stimulate the reaction; only when asparagine was added at levels of 0·5 or 1·0 mm was significant inhibition found. Ammonium chloride was less effective than glutamine as an amide donor. Endogenous asparaginase (EC 3.5.1.1.) activity was low in the in vitro preparation and did not significantly affect the conversion. Synthesis of asparagine from aspartic acid did not occur in slices of brain nor was there a significant conversion of aspartic acid or glucose to asparagine after their intracerebral administration in vivo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1970.tb03361.x
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  • 10
    Electronic Resource
    Electronic Resource
    DEVELOPMENTAL CHANGES IN Na+, K+ AND ATP AND IN THE LEVELS AND TRANSPORT OF AMINO ACIDS IN INCUBATED SLICES OF RAT BRAIN (1971)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 18 (1971), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— 〈list xml:id="l1" style="custom"〉1Upon incubation, slices of brain tissue took up fluid; the degree of swelling increased with increasing age. No sweiling occurred in slices from foetal brain. Since this swelling was associated with increases in the inulin space, the percentage of inulin space in slices at the end of incubation increased during brain development.2Most of the capacity for ion transport seemed to be absent from foetal brain. In vivo and in slices, Na+ was very high and K+ was very low in comparison to levels at other ages. There was a rapid change around birth, but no significant change at later ages. Upon incubation, Na+ levels increased in other slices, but not in slices of foetal brain.3Upon incubation of the slices, ATP levels were restored to levels close to those in the living brain; there were no significant alterations in available energy during development to explain changes in amino acid transport.4The composition of the free pool of cerebral amino acids in vivo changed with development, with some compounds (glutamic acid and related compounds) increasing, others (mostly‘essential’amino acids) decreasing, with age. These changes were not linear with time, and the level of a compound might exhibit several peaks during development.5The uptake (influx) of taurine, glutamate and glycine into brain slices increased rapidly during the foetal and early neonatal periods, reached a maximum between 2 and 3 weeks of postnatal age and then declined to adult levels. The levels of steady-state uptake with glycine also exhibited a maximal peak at 2-3 weeks of postnatal age. Steady-state uptake of taurine and glutamate reached adult levels by about 3 weeks of age.6The pattern of inhibition of amino acid transport by two specific amino acid analogues changed during development for some amino acids (GABA, glycine and glutamate), indicating an alteration in substrate specificity.7The results demonstrate complex changes in cerebral amino acid transport during development, with several maxima or minima and with changes in specificity for at least some compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1971.tb12042.x
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