Somatostatin and CCK-8 modulate release of striatal amino acids: role of dopamine receptors

The effects of somatostatin (SOM) and cholecystokinin octapeptide (CCK-8) on basal and potassium-evoked release of neurotransmitter amino acids were investigated in slices of rat caudate nucleus (CN) and, for comparison, cerebral cortex (CX). Endogenous aspartate (Asp), glutamate (Glu), glycine (Gly), and gamma-aminobutyric acid (GABA) were measured by high performance liquid chromatography. In both CN and CX, potassium (5-55 mM) produced a concentration-dependent increase in the release of Asp, Glu, Gly, and GABA in the presence of extracellular Ca2+. CCK-8 (1 microM) stimulated in CN the basal and K+-evoked release of Gly to 231% and 160% of control, respectively; this effect was blocked by sulpiride (SULP), a dopamine receptor antagonist. In contrast, SOM (1 microM) inhibited the K+-evoked release of Glu in CN by 26%, an effect that was not blocked by SULP. SOM and CCK-8 did not significantly affect the basal or K+ (35 mM)-evoked release of other amino acids in the CN or of any amino acids in CX. The results indicate that: CCK-8 facilitation of Gly release is dependent of Gly release is dependent on dopamine receptor activation, whereas the inhibition by SOM of Glu release is not: and the effects of SOM and CCK-8 are specific with respect to the brain region affected.     

The influence of glutamic and aminoacetic acids on the excitability of the liverwort Conocephalum conicum

Intracellular microelectrode measurements revealed that a resting potential (RP), an action potential (AP) and a calcium component of AP (named voltage transient, VT) can be influenced by glutamic acid (Glu) and aminoacetic acid (glycine, Gly) in the liverwort Conocephalum conicum. In the continuous presence of 5mM Glu or 5mM Gly, the RP hyperpolarized constantly and the plants became desensitized to the excitatory amino acids (Glu or Gly). Under such circumstances, the amplitudes of APs evoked by stimuli other than Glu or Gly grew, as did their calcium components (VTs). The sudden application of 1-15 mM Glu or Gly to a thallus not yet desensitized resulted in an excitation, i.e. a single AP or AP series. Aspartate (Asp) could not substitute for Glu in any way. Simultaneous action of both amino acids acted synergically to trigger APs. The same phenomenon was observed when glycine solution was enriched with N-methyl-D-aspartic acid (NMDA). Gly-induced APs were totally hindered by 1mM D-amino-5-phosphonopentanoic acid (AP5)--an inhibitor of ionotropic glutamate receptors of the NMDA kind. Glu-induced APs could be totally suppressed by 1mM AP5 as well as by 1mM 6,7-dinitroquinoxaline-2,3-dione (DNQX)--an inhibitor of AMPA/KA receptors. DNQX also completely blocked the calcium component of Glu-evoked APs. After DNQX treatment, the only response to Glu was a membrane potential hyperpolarization (like the Glu response in a desensitized plant). It was concluded that the Glu-induced depolarization and hyperpolarization are separate phenomena. The stimulatory effects of both Glu and Gly on liverwort excitability may be the consequences of an activation of a variety of ionotropic Glu receptor subtypes.     

青霉素G酰化酶β亚基Ser^579,Arg^580的定点突变研究

According to the comparison of amino acid sequence between PGA (Penicillin G Acylase) and PBPs (Penicillin Binding Protein), We suggest that No. 565-595 peptide fragment in beta-subunit of PGA may be a substrate-binding site of enzyme. Plasmid pTZGA was constructed by cloning the 2.6 kb PGA gene of pWGA into phagemid pTZ18U The technique of site-specific mutagenesis was used to study the role of residue No. 579 (Ser) and No. 580 (Arg) of PGA. Four kinds of mutants were obtained (Ser579-->Gly579, Arg580-->Gly580, Arg580-->Glu580, Arg580-->Lys580), both Glu580 and Gly580 mutants showed no activity of enzyme and Lys580 mutant remained 30% and Gly579 mutant kept 70% activity of wilde type. The same protein expression of four mutants according to the results of ELISA indicate that mutation does not affect the expression of PGA, but Arg580 residue may be essential for substrate-binding or catalysis of PGA.     

Ileal and total tract nutrient digestibility in blue foxes (Alopex lagopus) fed extruded diets containing different protein sources

This study compared apparent ileal and total tract digestibility of macronutrients and amino acids in blue foxes (Alopex lagopus) fed dry extruded diets. The control diet contained fish meal as the main protein source, while in the other diets 50% of the fish meal protein was replaced by not de-hulled solvent-extracted soybean meal, meat meal or bacterial protein meal. Ileal digestibility was obtained with animals modified with ileorectal anastomosis (IRA method). There were no significant differences in the average digestibility of CP, Lys, Trp, Val, Ala or Glu between IRA modified and intact animals. Average ileal digestibilities of His, Thr, Asp, Cys, Gly, Hyp, Pro, Ser, starch and total carbohydrates (CHO) were significantly lower compared with total tract values. Average ileal digestibility of Arg, Ile, Leu, Met, Phe, Tyr and crude fat was significantly higher than total tract digestibility. Digestibility measured in IRA modified animals showed less variability compared with values from intact animals. There were significant differences among diets in ileal as well as total tract digestibility of orude protein, most amino acids, starch and CHO, and in ileal digestibility of crude fat. Ileal crude protein digestibility of the diets ranged from 81.0-86.4% and total tract digestibility from 82.5-86.4%. Ileal amino acid digestibilities ranged from 70.1 (Asp) to 93.3% (Arg) and total tract values ranged from 72.8 (Cys) to 92.2% (Arg). Both ileal and total tract digestibilities of crude protein and most amino acids were significantly lower for diets containing meat meal or bacterial protein meal compared with the control fish meal-based diet and the diet with soybean meal. Although ileal digestibility may be more accurate than total tract digestibility in estimating the protein and amino acid supply in blue foxes, total tract digestibility may be acceptable because of numerically small differences between ileal and total tract digestibilities for protein and most amino acids. It was further concluded that ileal digestibilities of starch and CHO in the blue fox are lower than corresponding total tract digestibilities.     

Metabolism of some amino acids in relation to the photorespiratory nitrogen cycle of pea leaves

¹⁵N-labelled (amino group) asparagine (Asn), glutamate (Glu), alanine (Ala), aspartate (Asp) and serine (Ser) were used to study the metabolic role and the participation of each compound in the photorespiratory N cycle ofPisum sativum L. leaves. Asparagine was utilised as a nitrogen source by either deamidation or transamination, Glu was converted to Gln through NH₃ assimilation and was a major amino donor for transamination, and Ala was utilised by transamination to a range of amino acids. Transamination also provided a pathway for Asp utilisation, although Asp was also used as a substrate for Asn synthesis. In the photorespiratory synthesis of glycine (Gly), Ser, Ala, Glu and Asn acted as sources of amino-N, contributing, in the order given, 38, 28, 23, and 7% of the N for glycine synthesis; Asp provided less than 4% of the amino-N in glycine. Calculations based on the incorporation of¹⁵N into Gly indicated that about 60% (Ser), 20% (Ala), 12% (Glu) and 11% (Asn) of the N metabolised from each amino acid was utilised in the photorespiratory nitrogen cycle.Abbreviations Ala alamine - Asn asparagine - Asp aspartate - Glu glutamate - MOA methoxylamine - Ser serine     

The utilization of alanine, glutamic acid, and serine as amino acid substrates for glycine N-acyltransferase

The conjugation of benzoyl-CoA with the aliphatic and acidic amino acids by glycine N-acyltransferase, as well as the amides of the latter group, was investigated. Bovine and human liver benzoyl-amino acid conjugation were investigated using electrospray ionization tandem mass spectrometry (ESI-MS-MS). Bovine glycine N-acyltransferase catalyzed conjugation of benzoyl-CoA with Gly (Km(Gly) = 6.2 mM), Asn (Km(Asn) = 129 mM), Gln (Km(Gln) = 353 mM), Ala (Km(Ala) = 1573 mM), Glu (Km(Glu) = 1148 mM) as well as Ser in a sequential mechanism. In the case of the human form, conjugation with Gly (Km(Gly) = 6.4 mM), Ala (Km(Ala) = 997 mM), and Glu was detected. The presence of these alternative conjugates did not inhibit bovine glycine N-acyltransferase activity significantly. Considering the relatively low levels at which these conjugates are formed, it is unlikely that they will have a significant contribution to acyl-amino acid conjugation under normal conditions in vivo. However, their cumulative contribution to acyl-amino acid conjugation under metabolic disease states may prove to have a useful contribution to detoxification of elevated acyl-CoAs.     

Inhibition by Calmodulin Antagonists of [3H]MK-801 Binding in Brain Synaptic Membranes

In brain synaptic membranes not extensively washed, (+)-5-[3H]methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5, 10-imine ([3H]MK-801) binding was markedly inhibited in a concentration-dependent manner (at concentrations above 1 microM) by several compounds having antagonistic activity at the Ca(2+)-binding protein calmodulin. Scatchard analysis revealed that N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) inhibited the binding through a significant decrease in the density of binding sites without affecting the affinity at 10 microM. In membranes extensively washed and treated with a low concentration of Triton X-100, L-glutamic acid (Glu) drastically accelerated the initial association rate of [3H]MK-801 binding with glycine (Gly), almost doubling the initial association rate found in the presence of Glu alone. The addition of W-7 invariably reduced the initial association rate observed in the presence of either Glu alone or both Glu and Gly, without significantly altering the dissociation rate of bound [3H]-MK-801, irrespective of the presence of the two stimulatory amino acids. The maximal potencies of Glu, Gly, and spermidine in potentiating the binding were all attenuated by W-7. These results suggest that calmodulin antagonists may interfere with opening processes of an ion channel associated with an N-methyl-D-aspartate-sensitive subclass of excitatory amino acid receptors in rat brain.     

Effects of Prostaglandin E2 and Capsaicin on Behavior and Cerebrospinal Fluid Amino Acid Concentrations of Unanesthetized Rats: A Microdialysis Study

Abstract: Prostaglandin E₂ (PGE₂) delivered to the spinal cord produces an increased sensitivity to noxious (hyperalgesia) and innocuous (allodynia) stimuli. The mechanisms that underlie this effect remain unknown, but a PGE₂-evoked enhancement of spinal neurotransmitter release may be involved. To address this hypothesis, we examined the effect of PGE₂ on CSF concentrations of amino acids and also the modulatory effect of PGE₂ on capsaicin-evoked changes of spinal amino acid concentrations using a microdialysis probe placed in the lumbar subarachnoid space. Amino acids were quantified using HPLC with fluorescence detection. Addition of 1 mM, but not 10 or 100 µM, PGE₂ to the perfusate for a 10-min period (flow rate, 5 µl/min) evoked an immediate increase (80–100%) in glutamate (Glu), aspartate (Asp), taurine (Tau), glycine (Gly), and γ-aminobutyric acid (GABA) concentrations. Similarly, capsaicin infusion (0.1–10 µM) induced a dose-dependent increase in Glu, Asp, Tau, Gly, GABA, and ethanolamine levels. Significant increases in amino acid levels evoked by PGE₂ or capsaicin were associated with a touch-evoked allodynia. The combination of PGE₂ (10 µM) and capsaicin (0.1 or 1.0 µM) at concentrations that individually had no effect together evoked a significant increase (60–100%) in Glu, Asp, Tau, Gly, and GABA concentrations and produced tactile allodynia. These data demonstrate that spinally delivered PGE₂ or capsaicin substantially elevates CSF concentrations of both excitatory and inhibitory amino acids. The capacity of PGE₂ to enhance and prolong capsaicin-evoked amino acid concentrations may be one of the mechanisms by which spinal PGE₂ produces hyperalgesia and allodynia.     

Spontaneous release of endogenous aspartate and glutamate from rat striatal slices is increased following destruction of local neurons by ibotenic acid

We sought to determine in rat striatum whether the release of neurotransmitter amino acids aspartate (Asp), glutamate (Glu) and gamma-aminobutyric acid (GABA) were affected by local neurons. To do so, unilateral microinjections of ibotenic acid, an excitotoxin that destroys local neurons without affecting fibers of passage, were made into the striatum. Release of endogenous amino acids from lesioned and intact striatal slices were measured by HPLC one week later. The effectiveness and specificity of the lesion were confirmed by measuring the enzyme activity associated with extrinsic dopamine neurons (tyrosine hydroxylase; 111±14%), intrinsic GABA neurons (glutamic acid decarboxylase; 19±7%) and intrinsic acetylcholine neurons (choline acetyltransferase; 37±10%). Destruction of local striatal neurons markedly attenuated the release of GABA (41±12% of control) elicited by depolarization with K⁺ (35 mM), but did not significantly reduce the K⁺-evoked release of Asp (80±17%) and Glu (92±8%). However, spontaneous release of Asp and Glu was significantly greater than that observed in unlesioned tissue (159±18% and 209±27%, respectively), while the spontaneous release of GABA was not significantly reduced (75±43%). Although release of the neurotransmitter amino acids Asp, Glu and GABA were affected by the lesion, the release of the non-neurotransmitter amino acid tyrosine was unaffected. These data are consistent with the hypotheses that: 1) the predominant source of releasable stores of endogenous Asp and Glu in the striatum arises from extinsic neurons, and 2) that the spontaneous release of Asp and Glu from axon terminals in the striatum may be regulated, at least in part, by local inhibitory neurons.     

An Excitant Amino Acid Projection from the Medial Prefrontal Cortex to the Anterior Part of Nucleus Accumbens in the Rat

High-affinity uptake of neurotransmitter substrates in synaptosome-containing homogenates and tissue concentrations of amino acids were examined in subcortical areas 5-6 days after bilateral N-methyl-D-aspartate lesions confined to rat medial prefrontal cortex. D-[3H]Aspartate (32% of control) and [3H] gamma-aminobutyric acid ( [3H]GABA) (60% of control) uptakes were significantly reduced in medial prefrontal cortex, whereas [3H]choline (110% of control) uptake was unchanged, suggesting the production of axon-sparing lesions. The uptake of D-[3H]aspartate (76% of control), but not of [3H]GABA or [3H]choline, was significantly reduced in nucleus accumbens, with no concomitant reduction in amino acid concentrations. When examined in serial coronal sections, reduced D-[3H]aspartate uptake was confined to the most anterior 500 micron of nucleus accumbens (67% of contralateral sample). No significant reductions of uptake or amino acid concentrations were observed in caudate putamen or ventral tegmental area. These results suggest a role for glutamate or aspartate as neurotransmitters in projections from medial prefrontal cortex to anterior nucleus accumbens. Medial prefrontal cortex may represent the major excitatory cortical input to the nucleus accumbens.     

Effect of cysteine,glutamate and glycine supplementation to in vitro fertilization medium during bovine early embryo development

Glutathione (GSH) is an antioxidant synthesized from three constitutive amino acids (CAA): cysteine (Cys), glycine (Gly) and glutamate (Glu). Glutathione plays an important role in oocyte maturation, fertilization and early embryo development. This study aimed to investigate the effect of Cys (0.6 mM), Gly (0.6 mM) and Glu (0.9 mM) supplementation during in vitro fertilization (IVF) of cattle oocytes. In a Pilot Experiment, de novo synthesis of GSH in bovine zygote was evaluated using a modified TALP medium prepared without MEM-essential and MEM-non-essential amino acids (mTALP): mTALP + CAA (constitutive amino acids); mTALP + CAA+5 mMBSO (buthionine sulfoximide); mTALP + Cys + Gly; mTALP + Cys + Glu and mTALP + Gly + Glu. This evidence led us to investigate the impact of CAA supplementation to TALP medium (with essential and non-essential amino acids) on zygote viability, lipid peroxidation, total intracellular GSH content (include reduced and oxidized form; GSH-GSSG), pronuclear formation in zygotes and subsequent embryo development. IVF media contained a) TALP; b) TALP + Cys + Gly + Glu (TALP + CAA); c) TALP + Cys + Gly; d) TALP + Cys + Glu; e) TALP + Gly + Glu, were used. Total GSH-GSSG concentration was increased in TALP, TALP + CAA, and TALP + Cys + Gly. The viability of zygote was similar among treatments. Lipid peroxidation was increased in zygote fertilized with TALP + Cys + Gly; TALP + Cys + Glu; TALP + Gly + Glu and TALP + CAA. The percentage of penetrated oocytes decreased in TALP + CAA and TALP + Cys + Gly. The cleavage rate was lower in TALP + CAA and TALP + Gly + Glu. The percentage of embryos developing to the blastocyst stage was lower in TALP + Cys + Glu and TALP + CAA. In conclusion, we have demonstrated the synthesis of GSH during IVF. However, Cys, Gly and Glu supplementation to TALP medium had negative effects on embryonic development.     

Regional changes in the concentrations of glutamate,glycine, taurine,and GABA in the vitamin B-6 deficient developing rat brain: Association with neonatal seizures

It is well known that a dietary restriction of vitamin B-6 during gestation and lactation produces spontaneous seizures in neonatal animals. Since pyridoxal phosphate, one of the biologically active forms of vitamin B-6, is the cofactor for GAD the neonatal seizures have been attributed to low levels of brain GABA as a result of cofactor depletion. Although GABA levels are significantly lower in B-6 restricted neonatal rats with spontaneous seizures, seizure activity is not present in B-6 deficient adult rats or 28 day old rats in the present study, despite significantly low levels of brain GABA. These facts suggest that depletion of GABA is not the only biochemical alteration essential for the emergence of seizures. In the present study, the effect of vitamin B-6 undernutrition on the concentrations of the neuroactive amino acids, Glu, Gly, Tau, and GABA was determined in selected regions of the developing rat brain. The results show that the concentrations of Glu, Tau, and GABA were significantly lower and GLY significantly higher in selected brain regions of the B-6 restricted 14 day old rat compared to control tissue. Most of these changes were unique to 14 days of age, the time when spontaneous seizures are observed, and not present at 28 or 56 days of age when seizures are absent. This pattern of amino acid changes in the brain and the magnitude of the changes was consistent with those measured in a variety of chemically-induced animal models of epilepsy and in human epileptic foci. The regional distribution of amino acid changes was associated with brain regions which have been suggested to be responsible for the initiation and propagation of seizure activity. Two unique findings were also made in this study. First, there was a regional brain heterogeneity in the age-associated loss of brain Tau concentrations with the pons/medulla and substantia nigra appearing to be highly vulnerable and the hippocampus quite resistant to the loss of Tau. A second finding was the normalization of the neonatal GABA deficit in most brain regions by 56 days of age. The normalization of brain GABA was present in the face of continued dietary vitamin B-6 restriction. In summary, this study shows that the neuroactive amino acids Glu, Gly, Tau, and GABA are markedly altered in the seizure-prone vitamin B-6 restricted neonatal rat brain. The alterations in the brain concentration of Glu, Gly, and Tau may play an equally important role as GABA in the underlying mechanism of seizures associated with this condition.Abbreviations GAD Glutamic acid decarboxylase - GABA gamma-aminobutyric acid - Glu glutamate - Gly glycine - Tau taurine - CNS central nervous system - CTX cortex - HIPP hippocampus - C/P caudate/putamen - SN substantia nigra - Cb cerebellum - P/M pons/medulla     

Spontaneous missense mutations in the rplX gene for ribosomal protein L24 from Escherichia coli.

Temperature-resistant pseudorevertants of the temperature-sensitive Escherichia coli mutant KNS19, harboring a mutation in rplX, the gene for ribosomal protein L24, were isolated, cloned, and sequenced. The codon GAC for the amino acid Asp in the temperature-sensitive mutant corresponding to position 84 in the protein chain mutated either back to the wild type (Gly) or to codons for the amino acids Tyr and Glu. Furthermore, rplX genes from two other mutants with an altered protein L24 were cloned and sequenced. The mutations were localized at position 56 (Gly to Asp) and at position 62 (Glu to Lys) in the rplX gene. The latter two mutants lacked a conditional lethal phenotype. The results suggest that the amino acid Gly at positions 56 and 84 in the protein might be involved in loop formations.     

Brainstem activation of platelet-derived growth factor-beta receptor modulates the late phase of the hypoxic ventilatory response

The early phase of the biphasic ventilatory response to hypoxia in mammals is critically dependent on NMDA glutamate receptor activation within the nucleus of the solitary tract. However, the mechanisms underlying the subsequent development of the typical ventilatory roll-off are unclear and could underlie important roles in the functional and molecular adaptation to oxygen deprivation. Because the growth factor platelet-derived growth factor (PDGF)-BB can modulate the open channel probability of NMDA receptors by activating PDGF-beta receptors, its contribution to hypoxic ventilatory roll-off was examined. Administration of PDGF-BB, but not PDGF-AA, in the nucleus of the solitary tract was associated with significant attenuations of the early hypoxic ventilatory response in conscious rats. Furthermore, marked reductions in the magnitude of hypoxic ventilatory roll-off occurred in mice heterozygous for a mutation in the PDGF-beta receptor. Administration of a PDGF-beta receptor antagonist to wild-type littermates elicited similar declines in hypoxic ventilatory roll-off. The relative abundance of PDGF-beta receptors was confirmed in the nucleus of the solitary tract and other nuclei implicated in the hypoxic ventilatory response. In nucleus of the solitary tract lysates, PDGF-beta receptor tyrosine phosphorylation was temporally correlated with hypoxic ventilatory roll-off formation. Increased PDGF-B chain mRNA expression was induced by hypoxia in the nucleus of the solitary tract, and PDGF-B chain immunoreactivity colocalized with approximately 40% of nucleus of the solitary tract neurons, demonstrating hypoxia-induced c-Fos enhancements. Thus, PDGF-BB release and PDGF-beta receptor activation in the nucleus of the solitary tract are critical components of hypoxic ventilatory roll-off and may have important functional implications in processes underlying survival and acclimatization to hypoxic environments.     

Adsorption of amino acids on the magnetite-(111)-surface: a force field study

Magnetite (Fe₃O₄) is an important biomineral, e.g., used by magnetotactic bacteria. The connection between the inorganic magnetite-(111)-surface and the organic parts of the bacteria is the magnetosome membrane. The membrane is built by different magnetosome membrane proteins (MMPs), which are dominated by the four amino acids glycine (Gly), aspartic acid (Asp), leucine (Leu) and glutamic acid (Glu). Force field simulations of the interaction of the magnetite-(111)-surface and the main amino acid compounds offer the possibility to investigate if and how the membrane proteins could interact with the mineral surface thus providing an atomistic view on the respective binding sites. In a force field simulation the four amino acids were docked on the Fe-terminated magnetite-(111)-surface. The results show that it is energetically favorable for the amino acids to adsorb on the surface with Fe-O-distances between 2.6 Å and 4.1 Å. The involved O-atoms belong to the carboxyl-group (Asp and Glu) or to the carboxylate-group (Gly, Leu and Glu). Electrostatic interactions dominate the physisorption of the amino acids. During the simulations, according to the frequency of the best results, the global minimum for the docking interaction could be attained for all amino acids analyzed.     

Regional concentrations of transmitter amino acids after spinal cord ischaemia in the rabbit

Concentrations of Asp, Glu, Gly, GABA and Gln were studied in the ventral and dorsal horns of the rabbit spinal cord after ligation of the abdominal aorta. The most significant changes observed after 10, 20 and 40 min ischaemia were an increase in the Asp and GABA concentration in the ventral horns and an increase in the Asp, Gly and GABA concentration in the dorsal horns. These changes correspond to shifts in the relevant reactions under conditions of the altered redox equilibrium in the tissue during ischaemia. Four days after 10 min ischaemia, amino acid concentrations in the spinal cord were at the control levels. Four days after 20 and 40 min ischaemia Asp, Gly and GABA concentrations were decreased in the ventral horns and Asp, Gly, GABA and Glu concentrations in the dorsal horns. The percentually greater decrease in the concentration in the ventral horns may be associated with the greater morphological damage to these structures.     

Two Groups of Amino Acids Interact with GABA-A Receptors Coupled to t-[35S]Butylbicyclophosphorothionate Binding Sites: Possible Involvement with Seizures Associated with Hereditary Amino Acidemias

Seven L-amino acids (Trp, Arg, Lys, Met, Ile, Val, and Phe) partially (28-81%) reversed the inhibitory action of 1 microM gamma-aminobutyric acid (GABA) on t-[35S]butylbicyclophosphorothionate ([35S]TBPS) binding to rat brain membranes, with EC50 values ranging from 5 to 120 mM. D-Trp, D-Arg, D-Lys, D-Met, D-Val, and D-Phe were approximately equipotent with their L-isomers. Tyramine, phenethylamine, and tryptamine, the decarboxylation products of the aromatic amino acids (Tyr, Phe, and Trp, respectively), reversed the inhibitory action of 1 microM GABA on [35S]TBPS binding more potently than the parent amino acids (EC50 values = 1.5-3.0 mM). Human hereditary amino acidemias involving Arg, Lys, Ile, Val, and Phe are associated with seizures, and these amino acids and/or their metabolites may block GABA-A receptors. Five other L-amino acids (ornithine, His, Glu, Pro, and Ala) as well as Gly and beta-Ala inhibited [35S]TBPS binding with IC50 values ranging from 0.1 to 37 mM, and these inhibitions were reversed by the GABA-A receptor blocker R 5135 in all cases. The inhibitory effects of L-ornithine, L-Ala, L-Glu, and L-Pro were stereospecific, because the corresponding D-isomers were considerably less inhibitory. L-His, D-His, and L-Glu gave incomplete (plateau) inhibitions. Human hereditary amino acidemias involving L-ornithine, His, Pro, Gly, and beta-Ala are also associated with seizures, and we speculate that these GABA-mimetic amino acids may desensitize GABA-A receptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

血管紧张素—（1—7）在大鼠延髓头端腹外侧通过氨基酸类递质调节血压的作用

采用微量注射、微透析、高效液相色谱－荧光测定等技术和方法,观察和 血管紧张素－（1－7）[Ang-(1-7)]在延髓头端腹外侧（RVLM）与氨基酸类递质释放之间的关系,在麻醉大鼠RVLM注射Ang-(1-7)可引起血压升高,同时伴RVLM兴奋性氨基酸（EAA）释放增多;在RVLM注射Ang-(1-7)选择性受体拮抗剂Ang779可引起血压降低,同时伴RVLM EAA释放减少和抑制性氨基酸（IAA）释放增多,Ang-(1-7)的升压作用和Ang779的降压作用均可被相应的氨基酸受体拮抗剂部分阻娄。结果提示,Ang-(1-7)在RVLM的升压效庆可能部分是通过EAA释放增多所致;而Ang779在 RVLM的降压效应可能部分是通过EAA释放减少、IAA释放增多所致。     

EGCG Ameliorates the Suppression of Long-Term Potentiation Induced by Ischemia at the Schaffer Collateral-CA1 Synapse in the Rat

The function of Epigallocatechin gallate (EGCG), a main component of green tea, has been widely investigated, amelioration of synaptic transmission and neuroprotective effects against ischemia-induced brain damage among others. However, the mechanism underlying is still unveiled. We investigated the effects of EGCG on high frequency stimulation-induced long-term potentiation (LTP) in the Schaffer collateral-CA1 synapse with or without cerebral ischemia injury induced by middle cerebral artery occlusion (MCAO) in vivo to examine the possible relations between EGCG and synaptic transmission. Application of EGCG modulated synaptic transmission and produced a dose-dependent improvement of the induction of LTP. However, relative high-dose EGCG can block the induction of LTP at the Schaffer collateral-CA1 synapse in normal rat in vivo. In addition, the effects of EGCG were observed on the infarct volume and neurological deficit in rats subjected to MCAO; furthermore, the cell viability of primary cultured rat hippocampal and cortical neurons suffered from oxygen–glucose deprivation were evaluated with MTT and LDH assay, which showed significant neuroprotective properties in vitro. Surprisingly, the contents of the glutamate (Glu), glycine (Gly), and gamma-aminobutyric acid amino acids were totally disequilibrated before and after cerebral ischemia injury and could be rebalanced to original level by application of EGCG. Our results suggest that EGCG is able to improve the efficiency of synaptic transmission in cerebral ischemia injury with attenuated effect related to the neuroprotection of EGCG through regulating excitatory and inhibitory amino acid balance.