Motor activity and the content of neuroactive amino acids in brain tissues

The influence of forced motor activity (swimming) on quantitative shifts in neuroactive amino acids (GABA, glutamic and aspartic acids and glycine) was studied in brain tissues of rats and cerebrospinal fluid of cats in health and brain circulation disturbances. The data obtained point to the elevation of the content of amino acids in the brain and appearance of GABA in the cerebrospinal fluid during brain ischemia.     

The content of free amino acids in the tissues of broiler chicks administered sodium humate in the ration]

Natrium humate introduction into ration of broilers activates the synthetic phase of protein exchange. The increase of protein amount in blood serum and chicken tissues, the pool decrease of free amino acids in blood and its simultaneous growth in muscles, increase of proteolysis level, the change in activity of peptide-hydrolase testify to this. In muscles the quantity of free amino acids ensuring the reamination increases considerably.     

Glutamate, calcium ion-chelating agents and the sodium and potassium ion contents of tissues from the brain

1. Salts of l-glutamate added to cerebral tissues maintained in glucose-saline-bicarbonate solutions cause the Na(+) content of the tissues to increase rapidly and K(+) to be lost. Entry of (22)Na(+) also is accelerated by l-glutamate and this acceleration is inhibited by low concentrations of tetrodotoxin. 2. Tissue Na(+) content and its rate of increase after the addition of l-glutamate are affected by the Ca(2+) of incubation media. 3. Very rapid and extensive entry of Na(+) to the tissue is caused by EDTA, and a moderate entry by citrate and ATP. Calculations of the concentration of free Ca(2+) in media after these additions indicate that Na(+) entry is sometimes associated with low Ca(2+) concentration, but that other substances, especially l-glutamate, act without greatly diminishing Ca(2+) concentration. 4. Experiments with 2,4-dinitrophenol and valinomycin are also reported and aspects of the Na(+) entry formulated and discussed.     

Excitatory amino acids as modulators of gonadotropin secretion

Summary The effects of quinolinic acid (QUIN) and quisqualate (QA) on the secretion of GnRH from MBH and LH and FSH from AP of 50 day old male rats have been evaluated by means of an in vitro perifusion technique.QUIN (100µM) is able to increase GnRH secretion with an action mediated by an NMDA receptor type, as shown by the inhibitory effect exerted by both a competitive (AP-5) and a non-competitive (MK-801) specific antagonist.QA per se at the concentrations tested (1–100µM) does not modify GnRH and gonadotropin secretion, but in the presence of a specific KA/QA receptor antagonist (DNQX) exerts a stimulatory effect at both levels.This observation might indicate that of the two QA receptor subtypes (ionotropic and metabotropic), this agonist binds to the metabotropic one with very low affinity: thus it is likely that a higher dose is required in order to have any effect on gonadotropin secretion. However, in the presence of DNQX, which binds to the ionotropic receptor, all the available QA can bind to the metabotropic one and can exert its action at MBH AP levels.     

Effect of dietary sulfur amino acids on the taurine content of rat tissues

Summary.  The effect of dietary sulfur amino acids on the taurine content of rat blood and tissues was investigated. Three types of diet were prepared for this study: a low-taurine diet (LTD), normal taurine diet (NTD; LTD + 0.5% Met), and high-taurine diet (HTD; LTD + 0.5% Met + 3% taurine). These diets had no differing effect on the growth of the rats. The concentration of taurine in the blood from the HTD- and NTD-fed rats was respectively 1,200% and 200% more than that from LTD-. In such rat tissues as the liver, the taurine content was significantly affected by dietary sulfur amino acids, resulting in a higher content with HTD and lower content with LTD. However, little or no effect on taurine content was apparent in the heart or eye. The activity for taurine uptake by the small intestine was not affected by dietary sulfur amino acids. The expression level of taurine transporter mRNA was altered only in the kidney under these dietary conditions: a higher expression level with LTD and lower expression level with HTD. Received January 8, 2002 Accepted January 18, 2002 Published online August 20, 2002 Authors' address: Dr. Hideo Satsu, Laboratory of Food Chemistry, Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan, Fax: +81-3-5841-8026 E-mail: asatsu@mail.ecc.u-tokyo.ac.jp Abbreviations: HTD, high-taurine diet; NTD, normal taurine diet; LTD, low-taurine diet; TAUT, taurine transporter; CSA, cysteine sulfinate; CDO, cysteine dioxygenase; CSAD, cysteine sulfinate decarboxylase; PBS, phosphate-buffered saline; DIDS, 4,4′-diisothiocyanostilbene-2′,2′-disulfonic acid     

Utilization in vivo of glucose and volatile fatty acids by sheep brain for the synthesis of acidic amino acids

1. Free glutamic acid, aspartic acid, glutamic acid from glutamine and, in some instances, the glutamic acid from glutathione and the aspartic acid from N-acetyl-aspartic acid were isolated from the brains of sheep and assayed for radioactivity after intravenous injection of [2-¹⁴C]glucose, [1-¹⁴C]acetate, [1-¹⁴C]butyrate or [2-¹⁴C]propionate. These brain components were also isolated and analysed from rats that had been given [2-¹⁴C]propionate. The results indicate that, as in rat brain, glucose is by far the best precursor of the free amino acids of sheep brain. 2. Degradation of the glutamate of brain yielded labelling patterns consistent with the proposal that the major route of pyruvate metabolism in brain is via acetyl-CoA, and that the short-chain fatty acids enter the brain without prior metabolism by other tissue and are metabolized in brain via the tricarboxylic acid cycle. 3. When labelled glucose was used as a precursor, glutamate always had a higher specific activity than glutamine; when labelled fatty acids were used, the reverse was true. These findings add support and complexity to the concept of the metabolic `compartmentation' of the free amino acids of brain. 4. The results from experiments with labelled propionate strongly suggest that brain metabolizes propionate via succinate and that this metabolic route may be a limited but important source of dicarboxylic acids in the brain.     

Locations of amino acids in brain slices from the rat. Tetrodotoxin-sensitive release of amino acids

1. Amino acids, particularly glutamate, gamma-aminobutyrate, aspartate and glycine, were released from rat brain slices on incubation with protoveratrine (especially in a Ca(2+)-deficient medium) or with ouabain or in the absence of glucose. Release was partially or wholly suppressed by tetrodotoxin. 2. Tetrodotoxin did not affect the release of glutamine under various incubation conditions, nor did protoveratrine accelerate it. 3. Protoveratrine caused an increased rate of formation of glutamine in incubated brain slices. 4. Increased K(+) in the incubation medium caused release of gamma-aminobutyrate, the process being partly suppressed by tetrodotoxin. 5. Incubation of brain slices in a glucose-free medium led to increased production of aspartate and to diminished tissue contents of glutamates, glutamine and glycine. 6. Use of tetrodotoxin to suppress the release of amino acids from neurons in slices caused by the joint action of protoveratrine and ouabain (the latter being added to diminish reuptake of amino acids), it was shown that the major pools of glutamate, aspartate, glycine, serine and probably gamma-aminobutyrate are in the neurons. 7. The major pool of glutamine lies not in the neurons but in the glia. 8. The tricarboxylic cycle inhibitors, fluoroacetate and malonate, exerted different effects on amino acid contents in, and on amino acid release from, brain slices incubated in the presence of protoveratrine. Fluoroacetate (3mm) diminished the content of glutamine, increased that of glutamate and gamma-aminobutyrate and did not affect respiration. Malonate (2mm) diminished aspartate and gamma-aminobutyrate content, suppressed respiration and did not affect glutamine content. It is suggested that malonate acts mainly on the neurons, and that fluoroacetate acts mainly on the glia, at the concentrations quoted. 9. Glutamine was more effective than glutamate as a precursor of gamma-aminobutyrate. 10. It is suggested that glutamate released from neurons is partly taken up by glia and converted there into glutamine. This is returned to the neurons where it is hydrolysed and converted into glutamate and gamma-aminobutyrate.     

A novel aminopeptidase from Burkholderia cepacia specific for acidic amino acids

An aminopeptidase specific for the N-terminal acidic residue (BcepAP) was purified from the cell extract of Burkholderia cepacia svr as a homotrimeric (subunit mass 66 kDa) molecule. It was identified as an unassigned peptidase of family M61. The only other member characterized so far from this family is a broad-specificity aminopeptidase of Sphingomonas capsulata (ScapAP) with preference for Gly or Ala residues. However, BcepAP exhibited narrow specificity and the preferred substrate was a peptide with an N-terminal Asp or Glu residue, which is quite unusual. The proteins assigned to this family were grouped separately on the basis of their homology to either BcepAP or ScapAP. It led the conclusion that BcepAP is a prototype of a new PepM61 subfamily, with a representative in other Proteobacteria , and to the prediction that members of the family share the ability to cleave N-terminal acidic residues of peptide substrates.