Identification of GABA accumulating neurons in the dorsal raphe nucleus]

A possible GABAergic innervation of the nucleus raphe dorsalis (NRD) was investigated by measuring glutamate decarboxylase activity in the NRD after lesioning the afferents of this nucleus. The slight decrease found in the enzymatic activity suggests that these afferents have a minor participation in the GABA innervation of the NRD and implies the existence of an intrinsic GABAergic system in this nucleus. This local innervation was demonstrated by radio-autography and shows fibers, axonal varicosities and cell bodies which accumulate 3H GABA in the caudal part of this nucleus.     

Proline synthesis from glutamate in the mitochondria isolated from a blowfly,Aldrichina grahami

Summary Proline biosynthesis from glutamate was demonstrated in a cell free system prepared from blowfly abdomen. The biosynthetic activity was found mainly in the mitochondrial fraction. The biosynthesis of proline from glutamate required ATP, NADPH and Mg⁺⁺ as cofactors.     

Effects of D-alpha-aminoadipate on physiologically evoked responses of cat dorsal horn neurones.

Microelectrophoretic administration of D-alpha-aminoadipate reversibly reduced excitatory responses of cat dorsal horn neurones evoked by iontophoretic glutamate and non-noxious peripheral stimuli but did not influence similar responses evoked by noxious peripheral stimuli or iontophoretic substance P.     

Reduction of high affinity glutamate uptake in rat hippocampus by two polyamine-like toxins isolated from the venom of the predatory wasp Philanthus triangulum F

Two components of the venom of the predatory wasp Philanthus triangulum F. significantly reduce--to a greater or less extent--the high affinity uptake of glutamate in rat hippocampus. A concentration of 10 microM delta-PTX caused a reduction of 74%, while the other component, beta-PTX, at the same concentration, caused a reduction of 18%. Hence the effect of delta-PTX on high affinity glutamate uptake in the hippocampus is comparable with its effect on high affinity glutamate uptake in insect neuromuscular junctions. Contrary to our previous findings that beta-PTX has no effect on high affinity glutamate uptake in insect glutamatergic terminal axons, however, beta-PTX significantly reduces high affinity glutamate uptake in the hippocampus, albeit less effectively than delta-PTX.     

Renal ammoniagenesis in kidney slices from rats undergoing glycerol-induced acute tubular necrosis

Summary Compared to control, kidney slices from rats undergoing glycerol-induced ATN produce less ammonia from glutamate, but show no difference when glutamine is substrate. However, gluconeogenesis from glutamine, like glutamate, is decreased in acute tubular necrosis (ATN). We conclude that renal ammoniagenesis is influenced by ATN. Glycerol-induced ATN causes a relative increase in glutamine deamidation and a decrease in glutamate deamination.Supported by a grant from the American Kidney Fund.     

Involvement of extrasynaptic glutamate in physiological and pathophysiological changes of neuronal excitability

Glutamate is the most abundant neurotransmitter of the central nervous system, as the majority of neurons use glutamate as neurotransmitter. It is also well known that this neurotransmitter is not restricted to synaptic clefts, but found in the extrasynaptic regions as ambient glutamate. Extrasynaptic glutamate originates from spillover of synaptic release, as well as from astrocytes and microglia. Its concentration is magnitudes lower than in the synaptic cleft, but receptors responding to it have higher affinity for it. Extrasynaptic glutamate receptors can be found in neuronal somatodendritic location, on astroglia, oligodendrocytes or microglia. Activation of them leads to changes of neuronal excitability with different amplitude and kinetics. Extrasynaptic glutamate is taken up by neurons and astrocytes mostly via EAAT transporters, and astrocytes, in turn metabolize it to glutamine. Extrasynaptic glutamate is involved in several physiological phenomena of the central nervous system. It regulates neuronal excitability and synaptic strength by involving astroglia; contributing to learning and memory formation, neurosecretory and neuromodulatory mechanisms, as well as sleep homeostasis.The extrasynaptic glutamatergic system is affected in several brain pathologies related to excitotoxicity, neurodegeneration or neuroinflammation. Being present in dementias, neurodegenerative and neuropsychiatric diseases or tumor invasion in a seemingly uniform way, the system possibly provides a common component of their pathogenesis. Although parts of the system are extensively discussed by several recent reviews, in this review I attempt to summarize physiological actions of the extrasynaptic glutamate on neuronal excitability and provide a brief insight to its pathology for basic understanding of the topic.     

Glutamate synthase: a complex iron-sulfur flavoprotein

Glutamate synthase is a complex iron-sulfur flavoprotein that forms l-glutamate from l-glutamine and 2-oxoglutarate. It participates with glutamine synthetase in ammonia assimilation processes. The known structural and biochemical properties of glutamate synthase from Azospirillum brasilense, a nitrogen-fixing bacterium, will be discussed in comparison to those of the ferredoxin-dependent enzyme from photosynthetic tissues and of the eukaryotic reduced pyridine nucleotide-dependent form of glutamate synthase in order to gain insight into the mechanism of the glutamate synthase reaction. Sequence analyses also revealed that the small subunit of bacterial glutamate synthase may be the prototype of a novel class of flavin adenine dinucleotide- and iron-sulfur-containing oxidoreductase widely used as an enzyme subunit or domain to transfer reducing equivalents from NAD(P)H to an acceptor protein or protein domain. Received 10 November 1998, received after revision 10 December 1998; accepted 10 December 1998     

Control of respiration by nitric oxide in Keilin-Hartree particles,mitochondria and SH-SY5Y neuroblastoma cells

The pattern of cytochrome c oxidase inhibition by nitric oxide (NO) was investigated polarographically using Keilin-Hartree particles, mitochondria and human neuroblastoma cells. NO reacts with purified cytochrome c oxidase forming either a nitrosyl- or a nitrite-inhibited derivative, displaying distinct kinetics and light sensitivity of respiration recovery in the absence of free NO. Keilin-Hartree particles or cells, respiring either on endogenous substrates alone or in the presence of ascorbate, as well as state 3and state 4mitochondria respiring on glutamate and malate, displayed the rapid recovery characteristic of the nitrite derivative. All systems, when respiring in the presence of tetramethyl-p-phenylenediamine, were characterised by the slower, light-sensitive recovery typical of the nitrosyl derivative. Together the results suggest that the reaction of NO with cytochrome c oxidase in situ follows two alternative inhibition pathways, depending on the electron flux through the respiratory chain.Received 1 April 2003; received after revision 22 May 2003; accepted 3 June 2003     

Glutamate transporters in the biology of malignant gliomas

Malignant gliomas are relentless tumors that offer a dismal clinical prognosis. They develop many biological advantages that allow them to grow and survive in the unique environment of the brain. The glutamate transporters system x _c ^? and excitatory amino acid transporters (EAAT) are emerging as key players in the biology and malignancy of these tumors. Gliomas manipulate glutamate transporter expression and function to alter glutamate homeostasis in the brain, which supports their own growth, invasion, and survival. As a consequence, malignant cells are able to quickly destroy and invade surrounding normal brain. Recent findings are painting a larger picture of these transporters in glioma biology, and as such are providing opportunities for clinical intervention for patients. This review will detail the current understanding of glutamate transporters in the biology of malignant gliomas and highlight some of the unique aspects of these tumors that make them so devastating and difficult to treat.     

Presynaptic effects of spider toxins: increase of high affinity uptake in the arthropod peripheral glutamatergic system

In contrast to the reported effects of polyamines on the high affinity neurotransmitter uptake, two polyamine-like spider toxins significantly increase the high affinity uptake of glutamate as demonstrated with high resolution autoradiography. The effects of both spider toxins were compared to those of a polyamine toxin from the wasp Philanthus triangulum, which is known to inhibit the high affinity glutamate uptake.     

Presynaptic effects of spider toxins: Increase of high affinity uptake in the arthropod peripheral glutamatergic system

In contrast to the reported effects of polyamines on the high affinity neurotransmitter uptake, two polyamine-like spider toxins significantly increase the high affinity uptake of glutamate as demonstrated with high resolution autoradiography. The effects of both spider toxins were compared to those of a polyamine toxin from the waspPhilanthus triangulum, which is known to inhibit the high affinity glutamate uptake.     

Glutamate synthase: a fascinating pathway from L-glutamine to L-glutamate

Glutamate synthase is a multicomponent iron-sulfur flavoprotein belonging to the class of N-terminal nucleophile amidotransferases. It catalyzes the conversion of L-glutamine and 2-oxoglutarate into two molecules of L-glutamate. In recent years the X-ray structures of the ferredoxin-dependent glutamate synthase and of the a subunit of the NADPH-dependent glutamate synthase have become available. Thanks to X-ray crystallography, it is now known that the ammonia reaction intermediate is transferred via an intramolecular tunnel from the amidotransferase domain to the synthase domain over a distance of about 32Å. Although ammonia channeling is a recurrent theme for N-terminal nucleophile and triad-type amidotransferases, the molecular mechanisms of ammonia transfer and its control are different for each known amidotransferase. This review focuses on the intriguing mechanism of action and self-regulation of glutamate synthase with a special focus on the structural data.Received 8 August 2003; received after revision 15 September 2003; accepted 17 September 2003     

Towards an understanding of the role of glutamate in neurodegenerative disorders: energy metabolism and neuropathology

It is thought that impairment, of energy metabolism that results in deterioration of membrane function, leading to loss of the Mg²⁺ block on NMDA receptors, and allowing persistent activation of these receptors by glutamate, might be a cause of neuronal death in neurodegenerative disorders. Studies in rodents using mitochondrial respiratory chain toxins, such as aminooxyacetic acid, 1-methyl-4-phenylpyridinium, malonic acid and 3-nitropropionic acid, suggest that such processes may indeed be involved in neurotoxicity. Striatal and nigral degeneration induced by mitochondrial toxins in rodents resembles the neuropathology seen in humans suffering from Huntington's or Parkinson's disease, and can be prevented either by decortication or by NMDA receptor antagonists. Such experimental observations suggest that glutamate may be involved in neuronal death leading to neurodegenerative disorders in humans. If so, glutamate antagonists may offer a therapeutic approach for retarding the progression of these disabling disorders.     

Regeneration of feline dorsal roots

Résumé La régénération des racines postérieures, précédemment sectionées, a lieu exclusivement dans leur parties neurilemmales. Se servant d'une méthode modifiée d'anastomose des racines, leur régénération fonctionelle est démonstrée par des techniques électrophysiologiques.     

Action of glutamic acid and of some glutamate analogues on the molluscan central neurones

Summary The effects of L-glutamic acid and of some glutamate analogues have been studied on the central nervous system of the snailHeobania vermiculata, using conventional electrophysiological techniques. The glutamate H-response had the mean equilibrium value of-(57±4) mV and was associated with a Cl^– conductance change. The D-response to glutamate application showed an involvement of sodium ions. Aspartate was agonist of glutamate action and displayed similar equilibrium value of the H-response, whereas quisqualate H-response was non-invertible.The authors wish to express their thanks to Prof. A. Curatolo for his continual interest and advice, and to Dr J. Stinnakre for the criticism of the text.     

Mitochondria as the conductor of metabolic signals for insulin exocytosis in pancreatic beta-cells

Mitochondrial metabolism is crucial for the coupling of glucose recognition to the exocytosis of the insulin granules. This is illustrated by in vitro and in vivo observations discussed in the present review. Mitochondria generate ATP, which is the main coupling messenger in insulin secretion. However, the subsequent Ca2+ signal in the cytosol is necessary but not sufficient for full development of sustained insulin secretion. Hence, mitochondria generate ATP and other coupling factors serving as fuel sensors for the control of the exocytotic process. Numerous studies have sought to identify the factors that mediate the amplifying pathway over the Ca2+ signal in glucose-stimulated insulin secretion. Predominantly, these factors are nucleotides (GTP, ATP, cAMP, NADPH), although metabolites have also been proposed, such as long-chain acyl-CoA derivatives and glutamate. Hence, the classical neurotransmitter glutamate receives a novel role, that of an intracellular messenger or co-factor in insulin secretion. This scenario further highlights the importance of glutamate dehydrogenase, a mitochondrial enzyme well recognized to play a key role in the control of insulin secretion. Therefore, additional putative messengers of mitochondrial origin are likely to participate in insulin secretion.     

Reduction of high affinity glutamate uptake in rat hippocampus by two polyamine-like toxins isolated from the venom of the predatory waspphilanthus triangulum F

Summary Two components of the venom of the predatory waspPhilanthus triangulum F. significantly reduce — to a greater or less extent — the high affinity uptake of glutamate in rat hippocampus. A concentration of 10 M -PTX caused a reduction of 74%, while the other component, -PTX, at the same concentration, caused a reduction of 18%. Hence the effect of -PTX on high affinity glutamate uptake in the hippocampus is comparable with its effect on high affinity glutamate uptake in insect neuromuscular junctions. Contrary to our previous findings that -PTX has no effect on high affinity glutamate uptake in insect glutamatergic terminal axons, however, -PTX significantly reduces high affinity glutamate uptake in the hippocampus, albeit less effectively than -PTX.     

A method for the determination of glutamate oxaloacetate transaminase in sperm plasma from boars and bulls.

A method is described for the determination of glutamate oxaloacetate transaminase (GOT) activity in sperm plasma from boars and bulls as a test for fertilizing ability.     

Physiological studies on the effects of nutritional imbalance on the central nervous system. II. Effects of thiamine deficiency on oxidative enzymes in the brain of chicken, Gallus domesticus.

The activitiy levels of succinate dehydrogenase, glutamate dehydrogenase and pyruvate dehydrogenase in the fore, mid and hind brain regions of the thiamine deficient chicken, Gallus domesticus were determined. The activity levels of succinate dehydrogenase and glutamate dehydrogenase in all the 3 regions of brain showed augmentation on inducing thiamine deficiency. In contrast the activity levels of pyruvate dehydrogenase decreased in the brain of thiamine deficient animals. It is suggested that these changes in the oxidative enzymes indicate disturbance caused in the operation of the tricarboxylic acid cycle in thiamine deficiency.     

Physiological studies on the effects of nutritional imbalance on the central nervous system. II. Effects of thiamine deficiency on oxidative enzymes in the brain of chicken,Gallus domesticus

Summary The activity levels of succinate dehydrogenase, glutamate dehydrogenase and pyruvate dehydrogenase in the fore, mid and hind brain regions of the thiamine deficient chicken,Gallus domesticus were determined. The activity levels of scccinate dehydrogenase and glutamate dehydrogenase in all the 3 regions of brain showed augmentation on inducing thiamine deficiency. In contrast the activity levels of pyruvate dehydrogenase decreased in the brain of thiamine deficient animals. It is suggested that these changes in the oxidative enzymes indicate disturbance caused in the operation of the tricarboxylic acid cycle in thiamine deficiency.