Alterations in the compartmentalized metabolism of glutamic acid with changed cerebral conditions

Imbalance of Individual Plasma Amino acids Relative to Valine and Taurine as Potential Markers of Childhood Malnutrition

In the present study a typical plasma amino acid profile for a defined population of healthy Venezuelan children was established and, further, the possibility was examined that deviations from such normalized amino acid patterns can be of use to warn of an impending nutritional deficiency, caused, in part, by adverse socio-economic conditions. This study comprised 152 children of both sexes ranging in age from 1 to 6 years. Classification into different socio-economic strata, ranging from impoverished to privileged, was evaluated by Graffar's method, as previously adapted by Mendez Castellano for Venezuela. The results of clinical and anthropometric examinations were used to group these children into 5 classes of nutritional sufficiency, ranging from adequate nutrition to severe undemutrition. The present data indicate that deviations in the plasma amino acid concentration profile, standardized for a defined population, can be used in combination with clinical evaluations to determine the type as well as the severity of inadequate nutrition. Abnormal ratios of several individual amino acids relative to Val and Tau may serve as early signs of (impending) undemutrition or malnutrition in children; the amino acid changes are detectable even in groups of children without any clinical signs but where sociological circumstances suggest a possibility of inadequate nutrition. Other uses for such plasma amino acid profiles may be to distinguish whether the detected amino acid abnormalities are of dietary or genetic origin, provided that the selected groups or individuals studied derive from a population with more or less the same genetic homogeneity and similar dietary customs.

Changes of amino acid and monoamine levels after neonatal 6-hydroxydopamine denervation in rat basal ganglia, substantia nigra, and Raphe nuclei

The effects of a neonatal dopaminergic deafferentation with the neurotoxin 6-hydroxydopamine (6-OHDA) on endogenous tissue levels of catecholamines, indoleamines, and amino acids were investigated in discrete rat brain regions. After producing the lesion at postnatal day 3 by intraventricular injections of 6-OHDA, with a desipramine pretreatment to protect noradrenaline neurons, the animals were kept for 3 months. Their brains were dissected to obtain samples of neostriatum, Globus pallidus, Substantia nigra, and Raphe nuclei, which were then analyzed by high-performance liquid chromatography, coupled either to electrochemical detection for aromatic monoamines, or to post-column ninhydrin derivatization with spectrophotometry for amino acids. The neonatal 6-OHDA treatment depleted dopamine (DA) levels in neostriatum, Globus pallidus, and Substantia nigra, but in Raphe nuclei DA was increased. The main metabolites of DA were also decreased in neostriatum, Globus pallidus, and Substantia nigra but remained unchanged in Raphe nuclei. Serotonin (5-HT) and its metabolite 5-hydroxy-indole-3-acetic acid increased in neostriatum and Raphe nuclei; in Substantia nigra there was a slight increase in 5-HT only. The 6-OHDA lesion caused heterogeneous alterations in amino acid contents, which varied according to the region. In the neostriatum there were increases of gamma-aminobutyric acid (GABA), aspartic acid, and glycine. In the Globus pallidus taurine, GABA, glutamic acid, glutamine, aspartic acid, serine, and alanine were elevated. In the Substantia nigra only increases in taurine, GABA, glutamic acid, and glutamine could be documented. This study shows important changes in amino acid levels and in some of their ratios, occurring in different anatomical subdivisions of the basal ganglia and related brainstem nuclei following a neonatal treatment with 6-OHDA. The results thus demonstrate major biochemical modifications in amino acids in the aftermath of a DA denervation and/or a 5-HT hyperinnervation during an early developmental period.

Determination of amino acids and monoamine neurotransmitters in caudate nucleus of seizure-resistant and seizure-prone BALB/c mice

Amino acid and monoamine concentrations were examined in tissue extracts of caudate nucleus of genetic substrains of BALB/c mice susceptible or resistant to audiogenic seizures. Amino acids [aspartate, glutamate, glycine, taurine, serine, gamma-aminobutyric acid (GABA)], monoamines, and related metabolites were separated by isocratic reverse-phase chromatography and detected by a coulometric electrode array system. In situ activity of tyrosine hydroxylase and tryptophan hydroxylase were determined by measuring the accumulation of L-DOPA and 5-hydroxytryptophan after administration of the decarboxylase inhibitor NSD-1015. Highly significant decreases in concentrations of both excitatory (glutamate and aspartate) and inhibitory amino acids (GABA and taurine) were observed in extracts of caudate nucleus of seizure-prone mice. Substantial decreases in concentrations of dopamine (DA) and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, were also noted. Decreased accumulation of L-DOPA after NSD-1015 administration provided evidence for decreased tyrosine hydroxylase activity and decreased DA synthesis in striatum of seizure-prone mice compared with seizure-resistant mice. Decreased concentrations of the DA metabolite 3-methoxytyramine (after NSD-1015 administration) suggested that DA release was also compromised in seizure-prone mice. No significant difference in 5-hydroxytryptophan accumulation in striatum of seizure-prone and seizure-resistant mice suggested that tryptophan hydroxylase activity and serotonin synthesis were not affected. The data suggest that seizure-prone BALB/c mice have a deficiency in intracellular content of both excitatory and inhibitory amino acids. The data also raise the issue of whether GABAergic interactions with the nigrostriatal DA system are important in the regulation of audiogenic seizure susceptibility.

Effects of soman-induced seizures on different extracellular amino acid levels and on glutamate uptake in rat hippocampus

Extracellular amino acid levels in CA3 and CA1 fields of rat hippocampus, an area highly sensitive to seizures, were determined by intracranial microdialysis during seizures induced by systemic administration of soman (o-1,2,2-trimethylpropyl methylphosphonofluoridate), a potent inhibitor of acetylcholinesterase. The glutamate uptake level was determined on another series of animals in hippocampus homogenates. An early and transient increase in the extracellular glutamate level occurred in CA3 within 30 min of seizures, with correlated brief elevations of taurine, glycine and glutamine levels. The glutamate level increased early in CA1, declined and then became more sustained (after 50 min of seizures). Apparent elevations of taurine, glycine and glutamine levels in CA1 accompanied changes in glutamate concentrations. Changes of glutamate level correlated with an increase in the glutamate uptake which rapidly declined after 40 min of seizures. The role of the transient release of glutamate in CA3 and of the sustained release in CA1 in prolonged soman-induced seizures is considered. The correlation between glutamate and other amino acid release is studied.

Long-lasting effects of audiogenic seizures on neurotransmitter amino acids in Rb mice

The existence of long-lasting (15-18 h) alterations of neurotransmitter amino acid levels following a single or repeated acoustic stimulations in audiogenic seizure-prone Rb1 and Rb2 mice and seizure-resistant Rb3 mice were investigated. The levels of glutamate, aspartate, glycine, taurine, and of some of their precursors: glutamine and serine were determined. Fourteen brain areas were examined. Alterations were found only in 6 brain areas (pons, olfactory bulbs, superior colliculus, inferior colliculus, olfactory tubercles and raphe). Most frequent occurring changes were observed in pons and olfactory tubercles. These changes concerned mainly the excitatory amino acids, glutamate, and aspartate. Alterations of taurine, glycine and serine were also recorded.

Changes with aging in the levels of amino acids in rat CNS structural elements. I. Glutamate and related amino acids

Glutamate and related amino acids were determined in 53 discrete brain areas of 3- and 29-month-old male Fischer 344 rats microdissected with the punch technique. The levels of amino acids showed high regional variation - the ratio of the highest to lowest level was 9 for aspartate, 5 for glutamate, 6 for glutamine, and 21 for GABA. Several areas were found to have all four amino acids at very high or at very low level, but also some areas had some amino acids at high, others at low level. With age, in more than half of the areas, significant changes could be observed; decrease occurred 5 times more frequently than increase. Changes occurred more often in levels of aspartate and GABA than in those of glutamate or glutamine. The regional levels of glutamate and its related amino acids show severalfold variations, with the levels tending to decrease in the aged brain.

Contributions of basic neurochemistry towards a novel concept of epilepsy

Epilepsy is an ancient disorder which treatment over the centuries has been guided by preconceptions regarding its origin. The major improvements in epilepsy management came following the discovery of the EEG and the development of seizure suppressing agents. These advances in diagnosis and anticonvulsant therapy have further ingrained the conviction that epilepsy is a disease of neurons. Evidence presented here is intended to support a different point of view which suggests that the metabolic modifications in epileptogenic tissue denote subtle alterations in the anatomical and biochemical relationship between neurons and their glial envelopes. As a result the extracellular environment of these cells contain higher than normal levels of glutamic acid. This creates an unnatural functional connectivity between neurons so that they establish abnormal synchronous activity between them and become hyperexcitable due to the depolarizing milieu. To compensate for these biochemical changes it is suggested that some thought might be given to epilepsy management by metabolic manipulation. The measures should be directed specifically towards improving the ability of glia to remove glutamic acid from the extracellular milieu. Two obvious possibilities are to enhance glial glutamine synthesis and to improve the interstitial "wash-out" of glutamic acid in epileptogenic epicenters. Such a therapy would anticipate to gradually diminish seizure incidence and susceptibility without, however, having a direct action on convulsive episodes per se. The approach must be considered an adjunct to current epilepsy treatment and not a substitute for the use of anticonvulsants.

Amphetamine stimulation of glutaminase is blocked by neuroleptics

The ability of several classes of neuroleptics to inhibit the activity of phosphate-activated glutaminase was studied in several brain regions. These agents decreased glutaminase activity only in the amygdala. Amphetamine elevated glutaminase activity in this region. This stimulation was not blocked by (-) butaclamol, but was blocked by (+) butaclamol, haloperidol, chlorpromazine or clozapine.

Potential locus and mechanism of blockade of conditioned avoidance responding by neuroleptics

In order to assess the possible loci of action of neuroleptics in blocking the acquisition of a one-way conditioned avoidance response, microinjections of three neuroleptics and seven putative neurotransmitters were made into several brain regions and their effects on this behavior were assessed. When injected into the amygdala, the ED50 values for haloperidol (0.128 nmol), chlorpromazine (1.04 nmol) and thioridazine (1.41 nmol) were appropriate in relation to their clinical potency. Injections of neurotransmitters were without effect except in a few cases. Most significantly, the intra-amygdaloid administration of glutamate diethyl ester (an antagonist at quisqualate-type receptors) produced a blockade of avoidance acquisition which, as in the case of the neuroleptics, was not diminished by pretreatment with atropine. Following intraperitoneal injection of chlorpromazine, a statistically-significant blockade of avoidance acquisition and of glutamate, released from slices of amygdala, was obtained at doses of 2 mg/kg or more. With haloperidol, comparable behavioral effects and release of glutamate were found at doses of 0.05 mg/kg or more. The depression of release of glutamate from amygdaloid slices could be attributed to glutamate derived from glutamine. These data suggest a possible role for glutamatergic transmission in the effects of neuroleptics.

[Biosynthesis of amino acids from glucose in the central nervous system in the Parkinson syndrome]

The incorporation of labelled carbon from glucose U-14C into CSF amino acids was investigated in three patients with Parkinson's disease and in three control persons with comparable age and physical stature. Comparing the specific radioactivities of serum and CSF one can postulate that the labelled amino acids found in the CSF are synthesized mainly by brain tissue. The resorption of glucose into the CNS and therefore the synthesis of amino acids from glucose was more rapid in controls; labelled alanine and glutamine appeared later in the CSF of the patients. As expected, in the controls the specific radioactivity of glutamic acid was found to be higher than that of glutamine, in patients the labelling of glutamine was higher as was that of serine, glycine, aspartic acid and asparagine. From our knowledge concerning the compartmentation of the metabolism of glutamate, we assume that in Parkinsonism the metabolic activity of neurons is reduced but that of astroglia is enhanced.

Alterations in the content of amino acid neurotransmitters before the onset and during the course of methoxypyridoxine-induced seizures in individual rabbit brain regions

In rabbits, generalized seizures were induced by methoxypyridoxine, and changes in amino acid concentrations of 15 brain regions were investigated before seizure onset and during the course of sustained epileptiform activity. As previously reported, gamma-aminobutyric acid (GABA) concentration decreased preictally in most regions. At the same time, taurine level was elevated in the hypothalamus, thalamus, hippocampus, caudatum, and frontal cortex. After 90 min of seizures, it was significantly decreased in the hypothalamus, periaqueductal grey, substantia nigra, frontal cortex, and cerebellum. Glycine content was reduced preictally only in the substantia nigra; after seizure onset its concentration rose in all brain areas. Glutamate content in the frontal cortex decreased before seizure onset; after 1.5 h of seizures, its concentration in cerebellum, caudatum, and hippocampus was reduced. Aspartate level was decreased in most areas after sustained seizures; in putamen, however, it was elevated. In contrast, glutamine content increased preictally in the superior colliculus and in all brain areas by approximately 200% after 90 min of seizures. Alanine and valine content also rose markedly in most brain areas after prolonged seizures, and threonine showed the same tendency. The single brain regions were observed to respond to methoxypyridoxine in highly individualistic ways. For example, the glycine content of the substantia nigra, which is believed to utilize this amino acid as a neurotransmitter, decreased preictally. The potential importance of the superior colliculus in seizure induction is considered in view of the early rise in glutamine level. The antagonistic preictal behavior of taurine and GABA is discussed with respect to synthesis, uptake from the blood, and antiepileptic properties.

Protein and taurine of maternal diets during the mouse neonatal period: permanent effects on cerebellar--brainstem amino acid levels in mature offspring

Neonatal malnutrition and/or undernutrition of limited duration appears to permanently influence steady state amino acid content of the adult mouse cerebellum and/or brainstem. Some of the changes seem related to the protein content of the milk (glutamine), whereas others reflect the taurine concentration in the milk during the neonatal period (glutamic acid and GABA). Adult levels of taurine, serine, and glycine in the cerebellum-brainstem may in part be influenced by the degree of growth retardation which occurred during the first 16 days of neonatal life. Provided the combined adult weight of the cerebellum and brainstem can be used as one criterion to determine growth retardation during the neonatal period, it appears justified to state that mice do not recover from malnutrition/undernutrition when subjected to such conditions during early infancy.