Acute metabolic effects of taurine on the enzymes metabolizing glutamate and gaba

100 mg of taurine per kg body weight had been administered intraperitoneally and 30 min after the administration the animals were sacrificed. Glutamate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, glutaminase, glutamine synthetase, glutamate decarboxylase and GABA aminotransferase along with the content of glutamate and GABA in cerebral cortex, cerebellum and brain stem were studied and compared with the same obtained in the rats treated with normal saline in place of taurine. The results indicated a significant decrease in the activity of glutamate dehydrogenase in cerebral cortex and cerebellum and a significant increase in brain stem. Glutaminase and glutamine synthetase were found to increase significantly both in cerebral cortex and cerebellum. The activities of glutamate decarboxylase was found to increase in all the three regions along with a significant decrease in GABA aminotransferase while the content of glutamate showed a decrease in all the three brain regions, the content of GABA was observed to increase significantly. The above effects of taurine on the metabolism of glutamate and GABA are discussed in relation to the functional role of GABA and glutamate. The results indicate that taurine administration would result in a state of inhibition in brain.     

Content of dicarboxylic acids and GABA in normal suslik brain and under the effect of oxygen at higher pressure

The content of glutamic, asparaginic and gamma-aminobutyric (GABA) acids in norm and under hyperoxia was determined in different cerebral areas of susliks living in places at different heights above sea level. In susliks at a height of 1700-2000 m above sea level the content of glutamate aspartate and GABA lowers significantly as compared to that in susliks at a height of 500-600 m above sea level. Under the effect of oxygen 6 at. ga at the 22nd minute on the average there occur convulsions in susliks living both in high mountains and middle mountains. Acute oxygen poisoning is not accompanied by noticeable shifts in the content of free dicarboxylic amino acids in the studied cerebral areas of middle-mountain susliks and is characterized only by an increase of the GABA content in the cerebellum. In high-mountain susliks the content of glutamate under these conditions increases in great cerebral hemispheres, while the asparate content lowers in cerebral hemispheres and cerebellum. In the latter the drop in the content of GABA is statistically significant.     

Amino acid concentrations and selected enzyme activities in rat auditory,olfactory, and visual systems

Homogenates of specific brain regions of three sensory systems (auditory, olfactory, and visual) were prepared from pigmented Long-Evans Hooded rats and assayed for amino acid concentrations and activities of glutaminase, aspartate aminotransferase (total, cytosolic, and, by difference, mitochondrial), malate dehydrogenase, lactate dehydrogenase, and choline acetyltransferase. Comparing the quantitative distributions among regions revealed significant correlations between AAT and aspartate, between glutaminase and glutamate, between glutamate and glutamine, and between AAT plus glutaminase, or glutaminase alone, and the sum of aspartate, glutamate, and GABA, suggesting a metabolic pathway involving the synthesis of a glutamate pool as precursor to aspartate and GABA. Of the inhibitory transmitter amino acids, GABA concentrations routinely exceeded those of glycine, but glycine concentrations were relatively high in brainstem auditory structures.     

Chronic metabolic effects of ammonia in mouse brain.

Chronic ammonia toxicity in experimental mice was induced by exposing them for 2 and 5 days to 5 % (v/v) ammonia solution. The enzymes concerned with glutamate metabolism (aspartate-, alanine- and tyrosine aminotransferases, glutamate dehydrogenase and glutamine synthetase) and (Na+ + K+)-ATPase were estimated in the three regions of brain (cerebellum, cerebral cortex and brain stem) and in liver. Glutamate, aspartate, alanine, glutamine and GABA, RNA and protein were also estimated in the three regions of brain and liver. A significant rise in the activity of (Na+ + K+)-ATPase in all the three regions of brain along with a fall in the activity of alanine aminotransferase was noticed. Changes in the activities of other enzymes were also observed. A significant increase in alanine and a decrease in glutamic acid was observed while no change was observed in the content of other amino acids belonging to the glutamate family. As a result of this, changes in the ratios of glutamate/glutamine and glutamate + aspartate/GABA was observed. The results indicated that the brain was in a state of more depression and less of excitation. Under these conditions the liver tissue was showing a profound rise in the activity of the enzymes of glutamate metabolism. The results are further discussed.     

Symmetrical distribution of amino acid neurotransmitters in the right and left cerebral cortex of the rat

The level and activity of seven amino acids were examined in both the right and left areas of the cerebral cortex of the rat in order to determine their respective symmetrical distribution. In the first experiment, alanine, glycine, threonine, serine, GABA, aspartate, and glutamate were measured in six different regions of the cortex: medial, sulcal, and dorsal prefrontal as well as parietal, temporal, and occipital. The differences in the level of these amino acids in symmetrical regions of either side of the cortex were not statistically significant. In the second experiment, the in vivo synthesis from the [¹⁴C]glucose precursor of three amino acids, glutamate, glutamine, and GABA was measured using the cortical push-pull perfusion technique in the freely moving rat. Although differences in synthesis were found between the prefrontal and parietal areas of the cortex, no changes occurred between right and left hemispheres. These results indicate that for the resting levels of the amino acids examined in this study, no differential asymmetric distribution exists between right or left cortical regions of the rat's brain.     

Dichloroacetate (DCA) reduces brain lactate but increases brain glutamine in experimental cerebral malaria: a 1H-NMR study

Recent findings that levels of brain lactate and alanine were elevated in murine cerebral malaria led us to investigate the effect of dichloroacetate (DCA; 60 mg/kg), an activator of pyruvate dehydrogenase, on the levels of brain metabolites, and on the survival of mice infected with Plasmodium berghei ANKA which normally causes lethal cerebral malaria. DCA significantly reduced brain lactate and alanine levels when administered to infected mice, had no effect on the TCA cycle-related metabolites glutamate, GABA and aspartate and was associated with increased brain glutamine levels: 40% of mice thus treated survived the normally lethal infection.     

Acute and short term effects of ethanol on the metabolism of glutamic acid and GABA in rat brain

Although alcoholic intoxication is attributed to its pharmacological effects on the cell membranes in brain, the rapid metabolic utilisation of the same alters the metabolism of brain affecting the metabolism of glutamate and GABA which have varied metabolic roles besides serving a major proportion of synaptic activity. A study on the effects of ethanol, both acute and short-term, on glutamate (glu) and GABA metabolism in various regions of rat brain was carried out. Increased activities of glutamic acid decarboxylase (GAD) and aspartic acid aminotransferase (AST) in all brain regions, but decreased activity of glutamic acid dehydrogenase (GDH) in cerebral cortex (CC) and cerebellum (CB) following ethanol administration in brain was observed. Differential effects of ethanol were also obtained on the contents of glu and aspartate (asp), which were increased in CC, CB, and brain stem (BS) regions, as opposed to GABA content, which, although found to increase in acute toxicity, showed a decrease in all of the above brain regions in short-term toxicity. It is concluded that the above changes in glu, asp and GABA represent the consequences of metabolic utilization of alcohol in the brain, probably more a state of cerebral excitation than depression, and the changes may be a compensatory phenomenon.     

Neuroactive Amino Acids in Focally Epileptic Human Brain: A Review

Studies of neuroactive amino acids and their regulatory enzymes in surgically excised focally epileptic human brain are reviewed. Concentrations of glutamate, aspartate and glycine are significantly increased in epileptogenic cerebral cortex. The activities of the enzymes, glutamate dehydrogenase and aspartate aminotransferase, involved in glutamate and aspartate metabolism are also increased. Polyamine synthesis is enhanced in epileptogenic cortex and may contribute to the activation of N-methyl-D-aspartate (NMDA) receptors. Nuclear magnetic resonance spectroscopy (NMRS) reveals that patients with poorly controlled complex partial seizures have a significant diminution in occipital lobe gamma aminobutyric acid (GABA) concentration. The activity of the enzyme GABA-aminotransaminase (GABA-T) which catalyzes GABA degredation is not altered in epileptogenic cortex. NMRS studies show that vigabatrin, a GABA-T inhibitor and effective antiepileptic, significantly increases brain GABA. Glutamate decarboxylase (GAD), responsible for GABA synthesis, is diminished in interneurons in discrete regions of epileptogenic cortex and hippocampus. In vivo microdialysis performed in epilepsy surgery patients provides measurements of extracellular amino acid levels during spontaneous seizures. Glutamate concentrations are higher in epileptic hippocampi and increase before seizure onset reaching potentially excitotoxic levels. Frontal or temporal cortical epileptogenic foci also release aspartate, glutamate and serine particularly during intense seizures or status epilepticus. GABA in contrast, exhibits a delayed and feeble rise in the epileptic hippocampus possibly due to a reduction in the number and/or efficiency of GABA transporters.     

Dichloroacetate (DCA) reduces brain lactate but increases brain glutamine in experimental cerebral malaria: a 1H-NMR study

Abstract

Recent findings that levels of brain lactate and alanine were elevated in murine cerebral malaria led us to investigate the effect of dichloroacetate (DCA; 60 mg/kg), an activator of pyruvate dehydrogenase, on the levels of brain metabolites, and on the survival of mice infected with Plasmodium berghei ANKA which normally causes lethal cerebral malaria. DCA significantly reduced brain lactate and alanine levels when administered to infected mice, had no effect on the TCA cycle-related metabolites glutamate, GABA and aspartate and was associated with increased brain glutamine levels: 40% of mice thus treated survived the normally lethal infection.     

γ-Aminobutyric Acid Metabolism and Behavioral Effects After Intraventricular Injection of Spermine in Chicks

Effects of intraventricularly injected spermine on behavior and electrocortical activity and gamma-aminobutyric acid (GABA) metabolism after a single dose of 1.13 mumol/animal were studied. Decrease in locomotor activity, sedation or sleep, and electrocortical synchronization that lasted approximately 2 h were observed. In addition spermine caused a significant increase in GABA content in diencephalon and brainstem, 30 min after administration. Concomitantly a significant increase of glutamate decarboxylase (GAD) activity was observed in cerebral hemispheres, diencephalon, and brainstem. Reduction in gamma-aminobutyrate: alpha-oxoglutarate amino-transferase (GABA-T) levels occurred in the diencephalon along with a significant increase of GABA-T in the brainstem. The present results demonstrate that spermine has the capacity to affect GABA metabolism and are in favor of the suggestion that endogenous polyamines may modulate GABAergic mechanisms.     

Glutamate decarboxylase activity and GABA binding in the brain synaptic membranes in rats with compensatory activation of hypothalamo-pituitary-adrenal system in stress

The reaction of the rat adrenal cortex and medulla to stress was absent under conditions of compensatory activations of function of hypothalamic-pituitary-adrenal system. At the same time, glutamate decarboxylase activity was increased in the hypothalamus, decreased in the hyppocampus, and remained unchanged in medulla oblongata and cortex of cerebral hemispheres of hemiadrenalectomized rats after stress as compared to rats without stress. On the contrary, the intensity of specific GABA binding by synaptic membranes of medulla oblongata of hemiadrenalectomized rats was increased in response to stress effect it was decreased in the cortex of cerebral hemispheres, and remained unchanged in the hyppocampus.     

Studies on the GABAergic system in astrocytoma and neuroblastoma cells in culture

The GABAergic system was investigated in C-6 astrocytoma cells and C-1300 neuroblastoma cells in culture and compared to that in mouse brain. The activities of glutamate decarboxylase, GABA-transaminase, succinic semialdehyde dehydrogenase and glutamate dehydrogenase were measured. In the cultured cells, only glutamate dehydrogenase activity was equal or greater than that of mouse cerebral cortex. Glutamate decarboxylase in both cell lines was 2%, while GABA-transaminase and succinic semialdehyde dehydrogenase activities were less than 20% of those found in brain. In spite of the disparate enzyme activities, GABA, glutamate, and -ketoglutarate concentrations were similar in the cell lines and cerebral cortex. The anticonvulsant drugs sodium valproate and aminooxyacetic acid increased cortical GABA concentrations but either had no effect or decreased GABA in the cells in a complete medium. The convulsant isoniazid decreased GABA in mouse brain but had no effect in either cell line. In the absence of pyridoxal in the medium, some drug effects could be induced in the cultured cells. It is concluded that the differing responses of the GABAergic system in the mouse brain and cell lines may be attributed in part to the fact that the cells do not represent an integrated system and are of tumor origin.     

Bilobalide prevents reduction of gamma-aminobutyric acid levels and glutamic acid decarboxylase activity induced by 4-O-methylpyridoxine in mouse hippocampus

We previously reported that bilobalide, a constituent of Ginkgo biloba L. leaves, protected mice against convulsions induced by 4-O-methylpyridoxine (MPN). To elucidate the mechanism of the anticonvulsant activity of bilobalide, this study examined the effect of bilobalide on MPN-induced changes in the levels of gamma-aminobutyric acid (GABA) and glutamate, and in the activity of glutamic acid decarboxylase (GAD) in the hippocampus, cerebral cortex and striatum of the mouse. GABA levels and GAD activity in the hippocampus and cerebral cortex were significantly enhanced by bilobalide treatment (30 mg/kg, p.o., for 4 days) alone. MPN significantly decreased GABA levels and GAD activity in the three brain regions tested compared with those in the control. Pretreatment with bilobalide effectively suppressed the MPN-induced reduction in GABA levels and GAD activity in the hippocampus and cerebral cortex. On the other hand, there were no significant differences in the glutamate levels in the three regions despite various treatments. These results suggested that bilobalide prevents MPN-induced reduction in GABA levels through potentiation by bilobalide of GAD activity, and this effect of bilobalide contributes to its anticonvulsant effect against MPN-induced convulsions.     

Effects of ammonia on monoamine oxidase and enzymes of GABA metabolism in mouse brain.

Acute and chronic ammonia toxicity was produced in the mice by intraperitoneal injection of ammonium chloride (200 mg/kg) and by exposure of mice to ammonia vapours (5% v/v) continuously for 2 days and 5 days respectively. The ammonia content was elevated in the cerebellum, cerebral cortex and brain stem and in liver. In acute ammonia intoxication there was a decrease in the monoamine oxidase (MAO) activity in all the three regions of brain. In chronic ammonia toxicity (2 days of exposure) a significant increase in the activity of MAO was observed in the cerebral cortex while in cerebellum and brain stem there was a significant decrease. In cerebral cortex and cerebellum there was a rise in the activity of MAO as a result of exposure to ammonia vapours for 5 days. A significant decrease was observed in the activity of glutamate decarboxylase (GAD) in all the three regions of the brain both in acute and chronic ammonia toxicity (2 days). There was a decrease in the activity of this enzyme only in the cerebral cortex in the animals exposed to ammonia for 5 days. The activity of GABA-aminotransferase (GABA-T) showed a significant rise in cerebellum and a fall in the brain stem in acute ammonia toxicity. In chronic ammonia toxicity GABA-T showed a rise in all the three regions of brain. Chronic ammonia toxicity produced a significant decrease in the content of glutamate in all the three regions without a significant change in the content of aspartate. GABA and glutamine. The content of alanine increased in all the three regions of brain under these experimental conditions. The ratio of glutamate + aspartate/GABA and glutamate/glutamine showed a decrease in all the three regions as a result of ammonia toxicity.     

Quantification of the GABA Shunt and the Importance of the GABA Shunt Versus the 2-Oxoglutarate Dehydrogenase Pathway in GABAergic Neurons

Abstract: We investigated the activity of the cerebral GABA shunt relative to the overall cerebral tricarboxylic acid (TCA) cycle and the importance of the GABA shunt versus 2-oxoglutarate dehydrogenase for the conversion of 2-oxoglutarate into succinate in GABAergic neurons. Awake mice were dosed with [1-¹³C]glucose, and brain extracts were analyzed by ¹³C NMR spectroscopy. The percent enrichments of GABA C-2 and glutamate C-4 were the same: 5.0 ± 1.6 and 5.1 ± 0.2%, respectively (mean ± SD). This, together with previous data, indicates that the flux through the GABA shunt relative to the overall cerebral TCA cycle flux equals the GABA/glutamate pool size ratio, which in the mouse is 17%. It has previously been shown that under the experimental conditions used in this study, the ¹³C labeling of aspartate from [1-¹³C]glucose specifically reflects the metabolic activity of GABAergic neurons. In the present study, the reduction in the formation of [¹³C]aspartate during inhibition of the GABA shunt by γ-vinyl-GABA indicated that not more than half the flux from 2-oxoglutarate to succinate in GABAergic neurons goes via the GABA shunt. Therefore, because fluxes through the GABA shunt and 2-oxoglutarate dehydrogenase in GABAergic neurons are approximately the same, the TCA cycle activity of GABAergic neurons could account for one-third of the overall cerebral TCA cycle activity in the mouse. Treatment with γ-vinyl-GABA, which increased GABA levels dramatically, caused changes in the ¹³C labeling of glutamate and glutamine, which indicated a reduction in the transfer of glutamate from neurons to glia, implying reduced glutamatergic neurotransmission. In the most severely affected animals these alterations were associated with convulsions.     

The effect of diethyl- -fluoroglutarate on phosphates and glutamate in slices of rabbit cerebral cortex

Abstract— The diethyl ester of α-fluoroglutarate (DEFG), an inhibitor of glutamate dehydrogenase, was prepared, and its effect on glutamate and phosphates in slices of rabbit cerebral cortex was examined. The primary effect of the drug on cortical slices incubating in a Krebs-Ringer glucose medium was to decrease the tissue levels of glutamate in association with decreased levels and turnover of high-energy phosphates. Assimilation of exogenous glutamate by the slices was partially blocked in the presence of the drug and severely depressed oxidative phosphorylation resulted when glutamate and DEFG were both present in the incubation mixture. The results suggested a significant relationship between the activity of cerebral glutamate dehydrogenase and oxidative phosphorylation. During incubation in a Krebs-Ringer glucose medium the endogenous pool of free amino acids in the cortical slice partitioned with the medium. Little or no glutamate, aspartate or GABA was present in the medium after incubation, but glycine, alanine, threonine, serine and glutamine did partition to varying degrees, with over one-half of the glutamine present in the incubation medium. With the exception of ‘leakage’ of aspartate, the partitioning patterns were relatively unaffected by the presence of added glutamate or DEFG.     

Developmental change of endogenous glutamate and gamma-glutamyl transferase in cultured cerebral cortical interneurons and cerebellar granule cells,and in mouse cerebral cortex and cerebellum in vivo

The developmental change of endogenous glutamate, as correlated to that of gamma-glutamyl transferase and other glutamate metabolizing enzymes such as phosphate activated glutaminase, glutamate dehydrogenase and aspartate, GABA and ornithine aminotransferases, has been investigated in cultured cerebral cortex interneurons and cerebellar granule cells. These cells are considered to be GABAergic and glutamatergic, respectively. Similar studies have also been performed in cerebral cortex and cerebellum in vivo. The developmental profiles of endogenous glutamate in cultured cerebral cortex interneurons and cerebellar granule cells corresponded rather closely with that of gamma-glutamyl transferase and not with other glutamate metabolizing enzymes. In cerebral cortex and cerebellum in vivo the developmental profiles of endogenous glutamate, gamma-glutamyl transferase and phosphate activated glutaminase corresponded with each other during the first 14 days in cerebellum, but this correspondence was less good in cerebral cortex. During the time period from 14 to 28 days post partum the endogenous glutamate concentration showed no close correspondence with any particular enzyme. It is suggested that gamma-glutamyltransferase regulates the endogenous glutamate concentration in culture neurons. The enzyme may also be important for regulation of endogenous glutamate in brain in vivo and particularly in cerebellum during the first 14 days post partum. Gamma-glutamyl transferase in cultured neurons and brain tissue in vivo appears to be devoid of maleate activated glutaminase.Abbreviations used Asp-T aspartate aminotransferase (EC 2.6.1.1) - GABA-T GABA aminotransferase (EC 2.6.1.19) - GAD glutamate decarboxylase (EC 4.1.1.15) - gamma-GT gamma-glutamyl transferase (gamma-glutamyl transpeptidase) (EC. 2.3.2.2) - Glu glutamate - GDH glutamate dehydrogenase (EC 1.4.1.3) - GS glutamine synthetase (EC 6.3.1.2) - MAG maleate activated glutaminase - Orn-T ornithine aminotransferase (EC 2.6.1.13) - PAG phosphate activated glutaminase (EC 3.5.1.1)     

Changes in regional levels of putative neurotransmitter amino acids in brain under unilateral forebrain ischemia

The levels of the neurotransmitter amino acids glutamate, aspartate, and GABA were determined in different brain regions during ischemia and post-ischemic recirculation periods using the unilateral carotid artery occlusion model of stroke in gerbils. The levels of glutamate, aspartate and GABA in ischemic hemisphere were increased significantly by 10 min of ischemia and later declined with time. Reperfusion for 30 min following 10 min. of ischemia further enhanced the levels of glutamate and aspartate. Increase in GABA levels were found during early periods of reperfusion. Regional variations in the changes of amino acids' levels were noticed following ischemia. Hippocampus showed the highest increase in glutamate levels followed by striatum and cerebral cortex. Aspartate levels in striatum and hippocampus increased during 10 min ischemia (46% and 30%) and recirculation (70% and 79%), whereas in cerebral cortex the levels were doubled only during recirculation. Ischemia induced elevations of GABA levels were observed in cerebral cortex (68%) and in hippocampus (30%), and the levels were normalized during recirculation. No changes in GABA levels were found in striatum. It is suggested that the large increase in the levels of excitatory neurotransmitter amino acids in brain regions specially in hippocampus during ischemia and recirculation may be one of the causal factors for ischemic brain damage.     

Transmitter amino acid release from rat neocortex: Complete versus incomplete ischemia models

Release of the excitotoxic amino acids, glutamate and aspartate, from the ischemic rat cerebral cortex was compared in two models; the seven vessel occlusion model (7VO) of complete cerebral ischemia and the four vessel occlusion model (4VO) of incomplete cerebral ischemia. Amino acid efflux into cortical superfusates was measured using cortical cups placed on both hemispheres. Whereas a 20 min period of ischemia causes a pronounced release of glutamate and aspartate from the 4VO model, efflux was significantly reduced in the 7VO model. Release of the inhibitory transmitter GABA, was similar in the two models. This result suggests that excitotoxic amino acid efflux into the extracellular spaces of the cerebral cortex may be enhanced by the residual blood flow in an incomplete ischemia.Special issue dedicated to Dr. Sidney Ochs.     

Regional Amino Acid Distribution in Relation to Function in Insulin Hypoglycaemia

The amino acids glutamate, aspartate, gamma-aminobutyric acid (GABA), and glutamine were measured as their dansyl derivatives in whole brain and specific brain regions by a sensitive double-labelling technique at various times during the development of hypoglycaemic encephalopathy. Hypoglycaemia was induced by administration of insulin (100 i.u./kg) to 24-h fasted rats. No significant changes in glutamate, GABA, or glutamine were detected in whole brain at any time up to and including the onset of hypoglycaemic convulsions. In cerebral cortex, however, GABA levels were reduced to 65% or normal prior to the appearance of neurological symptoms of hypoglycaemia. Onset of symptoms (severe catalepsy and loss of righting reflex, but before the onset of convulsions) was accompanied by marked decreases of glutamate and glutamine in striatum and hippocampus. These regions, in addition to cerebral cortex, show the greatest vulnerability to hypoglycaemic insult, according to previous anatomical studies. Aspartate levels were significantly increased (p less than 0.01) in the cerebral cortex of convulsing animals, confirming a previous report. No changes were detectable in any of the amino acids studied in medulla-pons at any time during the progression of hypoglycaemia. Cerebral cortex and striatum showed a selective net loss of amino acids (2.2 and 3.5 mumol/g. respectively) prior to the onset of insulin-hypoglycaemic convulsions.