Glutamine synthetase activity in Huntington's disease

Cerebellum in Alzheimer's disease and other neurodegenerative diseases: an emerging research frontier

The cerebellum is crucial for both motor and nonmotor functions. Alzheimer's disease (AD), alongside other dementias such as vascular dementia (VaD), Lewy body dementia (DLB), and frontotemporal dementia (FTD), as well as other neurodegenerative diseases (NDs) like Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and spinocerebellar ataxias (SCA), are characterized by specific and non-specific neurodegenerations in central nervous system. Previously, the cerebellum's significance in these conditions was underestimated. However, advancing research has elevated its profile as a critical node in disease pathology. We comprehensively review the existing evidence to elucidate the relationship between cerebellum and the aforementioned diseases. Our findings reveal a growing body of research unequivocally establishing a link between the cerebellum and AD, other forms of dementia, and other NDs, supported by clinical evidence, pathological and biochemical profiles, structural and functional neuroimaging data, and electrophysiological findings. By contrasting cerebellar observations with those from the cerebral cortex and hippocampus, we highlight the cerebellum's distinct role in the disease processes. Furthermore, we also explore the emerging therapeutic potential of targeting cerebellum for the treatment of these diseases. This review underscores the importance of the cerebellum in these diseases, offering new insights into the disease mechanisms and novel therapeutic strategies.

Glial Glutamine Homeostasis in Health and Disease

Glutamine is an essential cerebral metabolite. Several critical brain processes are directly linked to glutamine, including ammonia homeostasis, energy metabolism and neurotransmitter recycling. Astrocytes synthesize and release large quantities of glutamine, which is taken up by neurons to replenish the glutamate and GABA neurotransmitter pools. Astrocyte glutamine hereby sustains the glutamate/GABA-glutamine cycle, synaptic transmission and general brain function. Cerebral glutamine homeostasis is linked to the metabolic coupling of neurons and astrocytes, and relies on multiple cellular processes, including TCA cycle function, synaptic transmission and neurotransmitter uptake. Dysregulations of processes related to glutamine homeostasis are associated with several neurological diseases and may mediate excitotoxicity and neurodegeneration. In particular, diminished astrocyte glutamine synthesis is a common neuropathological component, depriving neurons of an essential metabolic substrate and precursor for neurotransmitter synthesis, hereby leading to synaptic dysfunction. While astrocyte glutamine synthesis is quantitatively dominant in the brain, oligodendrocyte-derived glutamine may serve important functions in white matter structures. In this review, the crucial roles of glial glutamine homeostasis in the healthy and diseased brain are discussed. First, we provide an overview of cellular recycling, transport, synthesis and metabolism of glutamine in the brain. These cellular aspects are subsequently discussed in relation to pathological glutamine homeostasis of hepatic encephalopathy, epilepsy, Alzheimer's disease, Huntington's disease and amyotrophic lateral sclerosis. Further studies on the multifaceted roles of cerebral glutamine will not only increase our understanding of the metabolic collaboration between brain cells, but may also aid to reveal much needed therapeutic targets of several neurological pathologies.

Quantitation of Glutamine Synthetase 1 Activity in Drosophila melanogaster

Protocols to assay the activity of glutamine synthetase (GS) are presented as they have been used in our laboratory to correlate the expression levels of the gene encoding Drosophila GS1 gene, the GS1 protein levels, and its activity in extracts of larvae and heads from Drosophila melanogaster. The assays are based on the glutamine synthetase-catalyzed formation of γ-glutamylhydroxylamine in the presence of ATP, L-glutamate, and hydroxylamine, in which hydroxylamine substitutes for ammonia in the reaction. Formation of γ-glutamylhydroxylamine is monitored spectrophotometrically in discontinuous assays upon complex formation with FeCl3. Fixed-time assays and those based on monitoring the time-course of product formation at different reaction times are described. The protocols can be adapted to quantify glutamine synthetase activity on biological materials other than Drosophila.

YAC128 mouse model of Huntington disease is protected against subtle chronic manganese (Mn)-induced behavioral and neuropathological changes

Manganese (Mn) is an essential micronutrient but excessive levels induce neurotoxic effects. Increasing evidence suggests a deficit of bioavailable Mn in Huntington disease (HD), an inherited neurodegenerative disease characterized by motor and cognitive disturbances. Previous studies have shown rescue of some molecular HD phenotypes by acute Mn exposure. This study simultaneously examined the potential for chronic Mn exposure to attenuate HD behavioral phenotypes, and for the HD genotype to offer protection against detrimental effects of chronic Mn exposure. In two independent studies a chronic Mn exposure paradigm was implemented in the YAC128 mouse model of HD and behavior was assessed at several timepoints. Study 1 exposed WT and YAC128 mice to twice weekly subcutaneous injections of 0, 5, 15, or 50 mg/kg MnCl[2] tetrahydrate from 12 to 32 weeks of age. A promising protective effect against motor coordination decline in 5 mg/kg MnCl[2] tetrahydrate-treated YAC128 mice was detected. Study 2 thus exposed WT and YAC128 mice to either 0 or 5 mg/kg MnCl[2] tetrahydrate from 12 to 52 weeks of age (with a partial randomized treatment crossover at 31 weeks). The same protective effect was not observed under these conditions at higher statistical power. We report subtle toxicological changes in exploratory behavior and total activity induced by chronic Mn exposure in WT mice only, despite similar total increases in brain Mn in WT and YAC128 mice. Further, chronic Mn treatment resulted in a 10-12 % decrease in striatal NeuN positive cell density in WT mice but not YAC128 mice, despite vehicle cell counts already being reduced compared to WT mice as expected for the HD genotype. The subtle changes observed in specific outcome measures, but not others, following long-term low-level Mn exposure in WT mice delineate the neurobehavioral and neuropathological effects at the threshold of chronic Mn toxicity. We conclude that these chronic low-dose Mn exposures do not significantly rescue behavioral HD phenotypes, but YAC2128 mice are protected against the subtle Mn-induced behavioral changes and decreased striatal neuron density observed in Mn-exposed WT mice.

Glutamate metabolism and recycling at the excitatory synapse in health and neurodegeneration

Glutamate is the primary excitatory neurotransmitter of the brain. Cellular homeostasis of glutamate is of paramount importance for normal brain function and relies on an intricate metabolic collaboration between neurons and astrocytes. Glutamate is extensively recycled between neurons and astrocytes in a process known as the glutamate-glutamine cycle. The recycling of glutamate is closely linked to brain energy metabolism and is essential to sustain glutamatergic neurotransmission. However, a considerable amount of glutamate is also metabolized and serves as a metabolic hub connecting glucose and amino acid metabolism in both neurons and astrocytes. Disruptions in glutamate clearance, leading to neuronal overstimulation and excitotoxicity, have been implicated in several neurodegenerative diseases. Furthermore, the link between brain energy homeostasis and glutamate metabolism is gaining attention in several neurological conditions. In this review, we provide an overview of the dynamics of synaptic glutamate homeostasis and the underlying metabolic processes with a cellular focus on neurons and astrocytes. In particular, we review the recently discovered role of neuronal glutamate uptake in synaptic glutamate homeostasis and discuss current advances in cellular glutamate metabolism in the context of Alzheimer's disease and Huntington's disease. Understanding the intricate regulation of glutamate-dependent metabolic processes at the synapse will not only increase our insight into the metabolic mechanisms of glutamate homeostasis, but may reveal new metabolic targets to ameliorate neurodegeneration.

Identification of Three Small Molecules That Can Selectively Influence Cellular Manganese Levels in a Mouse Striatal Cell Model

Manganese (Mn) is a biologically essential metal, critical as a cofactor for numerous enzymes such a glutamine synthetase and kinases such as ataxia-telangiectasia mutated (ATM). Similar to other essential metals such as iron and zinc, proper levels of Mn need to be achieved while simultaneously being careful to avoid excess levels of Mn that can be neurotoxic. A lifetime of occupational exposure to Mn can often lead to a Parkinsonian condition, also known as “manganism”, characterized by impaired gait, muscle spasms, and tremors. Despite the importance of its regulation, the mechanisms underlying the transport and homeostasis of Mn are poorly understood. Rather than taking a protein or gene-targeted approach, our lab recently took a high-throughput-screening approach to identify 41 small molecules that could significantly increase or decrease intracellular Mn in a neuronal cell model. Here, we report characterization of these small molecules, which we refer to as the “Mn toolbox”. We adapted a Fura-2-based assay for measuring Mn concentration and for measuring relative concentrations of other divalent metals: nickel, copper, cobalt, and zinc. Of these 41 small molecules, we report here the identification of three that selectively influence cellular Mn but do not influence the other divalent metals tested. The patterns of activity across divalent metals and the discovery of Mn-selective small molecules has potential pharmacological and scientific utility.

Glutamine Synthetase 1 Increases Autophagy Lysosomal Degradation of Mutant Huntingtin Aggregates in Neurons, Ameliorating Motility in a Drosophila Model for Huntington's Disease

Glutamine Synthetase 1 (GS1) is a key enzyme that catalyzes the ATP-dependent synthesis of l-glutamine from l-glutamate and is also member of the Glutamate Glutamine Cycle, a complex physiological process between glia and neurons that controls glutamate homeostasis and is often found compromised in neurodegenerative diseases including Huntington's disease (HD). Here we report that the expression of GS1 in neurons ameliorates the motility defects induced by the expression of the mutant Htt, using a Drosophila model for HD. This phenotype is associated with the ability of GS1 to favor the autophagy that we associate with the presence of reduced Htt toxic protein aggregates in neurons expressing mutant Htt. Expression of GS1 prevents the TOR activation and phosphorylation of S6K, a mechanism that we associate with the reduced levels of essential amino acids, particularly of arginine and asparagine important for TOR activation. This study reveals a novel function for GS1 to ameliorate neuronal survival by changing amino acids' levels that induce a "starvation-like" condition responsible to induce autophagy. The identification of novel targets that inhibit TOR in neurons is of particular interest for the beneficial role that autophagy has in preserving physiological neuronal health and in the mechanisms that eliminate the formation of toxic aggregates in proteinopathies.

Metabolomics studies in brain tissue: A review

Brain is still an organ with a composition to be discovered but beyond that, mental disorders and especially all diseases that curse with dementia are devastating for the patient, the family and the society. Metabolomics can offer an alternative tool for unveiling new insights in the discovery of new treatments and biomarkers of mental disorders. Until now, most of metabolomic studies have been based on biofluids: serum/plasma or urine, because brain tissue accessibility is limited to animal models or post mortem studies, but even so it is crucial for understanding the pathological processes. Metabolomics studies of brain tissue imply several challenges due to sample extraction, along with brain heterogeneity, sample storage, and sample treatment for a wide coverage of metabolites with a wide range of concentrations of many lipophilic and some polar compounds. In this review, the current analytical practices for target and non-targeted metabolomics are described and discussed with emphasis on critical aspects: sample treatment (quenching, homogenization, filtration, centrifugation and extraction), analytical methods, as well as findings considering the used strategies. Besides that, the altered analytes in the different brain regions have been associated with their corresponding pathways to obtain a global overview of their dysregulation, trying to establish the link between altered biological pathways and pathophysiological conditions.

Glutamine Synthetase: Role in Neurological Disorders

Glutamine synthetase (GS) is an ATP-dependent enzyme found in most species that synthesizes glutamine from glutamate and ammonia. In brain, GS is exclusively located in astrocytes where it serves to maintain the glutamate-glutamine cycle, as well as nitrogen metabolism. Changes in the activity of GS, as well as its gene expression, along with excitotoxicity, have been identified in a number of neurological conditions. The literature describing alterations in the activation and gene expression of GS, as well as its involvement in different neurological disorders, however, is incomplete. This review summarizes changes in GS gene expression/activity and its potential contribution to the pathogenesis of several neurological disorders, including hepatic encephalopathy, ischemia, epilepsy, Alzheimer's disease, amyotrophic lateral sclerosis, traumatic brain injury, Parkinson's disease, and astroglial neoplasms. This review also explores the possibility of targeting GS in the therapy of these conditions.

Manganese Is Essential for Neuronal Health

The understanding of manganese (Mn) biology, in particular its cellular regulation and role in neurological disease, is an area of expanding interest. Mn is an essential micronutrient that is required for the activity of a diverse set of enzymatic proteins (e.g., arginase and glutamine synthase). Although necessary for life, Mn is toxic in excess. Thus, maintaining appropriate levels of intracellular Mn is critical. Unlike other essential metals, cell-level homeostatic mechanisms of Mn have not been identified. In this review, we discuss common forms of Mn exposure, absorption, and transport via regulated uptake/exchange at the gut and blood-brain barrier and via biliary excretion. We present the current understanding of cellular uptake and efflux as well as subcellular storage and transport of Mn. In addition, we highlight the Mn-dependent and Mn-responsive pathways implicated in the growing evidence of its role in Parkinson's disease and Huntington's disease. We conclude with suggestions for future focuses of Mn health-related research.

Postmortem stability of brain GABAergic and glutamatergic receptors and enzymes under ecological conditions

Neurochemical biomarkers have emerged as useful tools for assessing the subclinical neurological impacts of environmental toxicants in birds and other wildlife. Careful consideration of biomarker stability is necessary before implementing their use on tissues from ecological studies, as receptors and enzymes in the brain may be affected by postmortem conditions. The goal of this study was to evaluate the postmortem stability of key GABAergic and glutamatergic receptors (N-methyl-D-aspartate (NMDA), gamma-aminobutyric acid (GABAA-benzodiazepine)) and enzymes (glutamine synthetase (GS), glutamic acid decarboxylase (GAD)) under environmentally relevant field and storage conditions to determine their suitability as biomarkers. We exposed chicken embryo brains to postmortem environmental and storage conditions typical for ecological studies (12, 24, and 48 h at 7 °C or 25 °C; 1, 4, and 8 weeks at -80 °C or -20 °C; 1 or 2 freeze thaw cycles), and measured [3H] MK-801 binding to the NMDA receptor, [3H] flunitrazipam binding to the GABAA-benzodiazepine receptor, GS activity, and GAD activity. We found that [3H] MK-801 binding is stable under all conditions studied. GAD activity was fairly stable under each storage and environmental temperatures for all durations, but was significantly less stable when stored at -20 °C than at -80 °C. [3H] flunitrazipam binding and GS activity were both impacted by environmental and storage temperature and duration, and might best be utilized in studies of samples with similar histories. Our findings here demonstrate that caution is warranted when comparing samples with different collection and storage histories, but that some biomarkers are fairly stable under various conditions.

Role of manganese in neurodegenerative diseases

Manganese (Mn) is an essential ubiquitous trace element that is required for normal growth, development and cellular homeostasis. Exposure to high Mn levels causes a clinical disease characterized by extrapyramidal symptom resembling idiopathic Parkinson's disease (IPD). The present review focuses on the role of various transporters in maintaining brain Mn homeostasis along with recent methodological advances in real-time measurements of intracellular Mn levels. We also provide an overview on the role for Mn in IPD, discussing the similarities (and differences) between manganism and IPD, and the relationship between α-synuclein and Mn-related protein aggregation, as well as mitochondrial dysfunction, Mn and PD. Additional sections of the review discuss the link between Mn and Huntington's disease (HD), with emphasis on huntingtin function and the potential role for altered Mn homeostasis and toxicity in HD. We conclude with a brief survey on the potential role of Mn in the etiologies of Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS) and prion disease. Where possible, we discuss the mechanistic commonalities inherent to Mn-induced neurotoxicity and neurodegenerative disorders.

Proteome profiles in medaka (Oryzias melastigma) liver and brain experimentally exposed to acute inorganic mercury

Mercury is a widespread and persistent pollutant occurring in a variety of forms in freshwater and marine ecosystems. Using the proteomic approach, this study examined the protein profiles of the medaka (Oryzias melastigma) liver and brain exposed to an acute mercuric chloride (HgCl(2)) concentration (1000μg/L) for 8h. The results showed that acute exposure of medaka to inorganic mercury enhanced metal accumulation in both the liver and brain, and a higher content of mercury was detected in the latter. Comparison of the two-dimensional electrophoresis protein profiles of HgCl(2)-exposed and non-exposed group revealed that altered protein expression was quantitatively detected in 20 spots in the brain and 27 in the liver. The altered protein spots were subjected to matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry analysis, with the resultant identification of 46 proteins. The proteins identified were involved in oxidative stress, cytoskeletonal assembly, signal transduction, protein modification, metabolism and other related functions (e.g. immune response, ionoregulation and transporting), highlighting the fact that inorganic mercury toxicity in fish seems to be complex and diverse. This study provided basic information to aid our understanding of the possible molecular mechanisms of acute inorganic mercury toxicity in aquatic organisms, as well as potential protein biomarker candidates for aquatic environmental monitoring.

Proteomic changes in the brains of Huntington's disease mouse models reflect pathology and implicate mitochondrial changes

Mouse models of Huntington's disease (HD) have been used extensively to recapitulate the pathological cascade of events in human HD. Mutant huntingtin interacts with many other proteins and has a well documented effect on gene expression. We were interested in whether changes in gene expression were translated into changes in the protein abundance in the brains of mouse models of HD. In two different HD knock in mouse models, the HdhQ150 and the HdhQ92, we detected changes in the abundance of proteins in mouse brain between wild-type and homozygous mutant animals. The numbers of changes detected rose with age and phenotypic severity. There were regional differences with most changes seen in the caudate and fewest in the cerebellum, reflecting the known pattern of gene expression changes in human HD and mouse models of HD and the known pathology. However, while some changes in the proteome followed changes in gene expression others did not directly reflect changes in gene expression seen in these animal models. Seven of the sixteen proteins detected have a known mitochondrial function, an enrichment of six-fold over that expected (p=0.001): these mitochondrial proteins show both increases and decreases in abundance implying that a straightforward alteration in mitochondrial number is unlikely to account for this finding.

In vitro and in vivo dose-dependent inhibition of methylmercury on glutamine synthetase in the brain of different species

Glutamine synthetase (GS) catalyzes the synthesis of glutamine from glutamate and ammonia and is associated with ischemic injury and neurological diseases. We investigated whether the in vitro and in vivo exposure to methylmercury (MeHg) produce changes in GS activity in the brain of different species. The brain in rats and mice was dissected into different regions for GS assay. MeHg levels in the brain tissues and blood of mice treated 2, 4 or 10 mg/kg MeHg were determined by a gas-chromatography/mass selective detector. In vitro exposure of MeHg (0.1-100 μM) produced dose-dependent decreases of GS activity in rat brains with 50% inhibition occurred at 10-20 μM. MeHg was a more potent GS inhibitor in vitro in the rat brain than other GS inhibitors (e.g., methionine sulfoximine, kainic acid). These effects were further confirmed using purified GS of sheep brains. In vivo GS activity was also inhibited in the hippocampus of mice given 4 or 10 mg/kg of MeHg. In mice concentration ratios of brain tissues to blood were 0.05-0.14 at 24 h post-dose. These data showed that MeHg produced significant changes in GS activity, indicating that GS is an effective biomarker for MeHg exposure.

Dysfunction of brain kynurenic acid metabolism in Huntington's disease: focus on kynurenine aminotransferases

The levels of the neuroprotective excitatory amino acid receptor antagonist kynurenic acid (KYNA) have been previously shown to be reduced in several regions of the brain of Huntington's disease (HD) patients. Thus, KYNA has been speculatively linked to the pathogenesis of HD. We have examined KYNA levels and the activity of its two biosynthetic enzymes (kynurenine aminotransferases (KAT) I and II) in 12 regions of brains from late-stage HD patients and control donors (n = 17 each). KYNA levels were measured in the original tissue homogenate. Using [3H]kynurenine as the substrate, enzyme activities were determined in dialyzed tissue homogenates. KYNA levels in the caudate nucleus decreased from 733 +/- 95 in controls to 401 +/- 62 fmol/mg tissue in HD (p < 0.01). The activity of both enzymes was highest in cortical areas (e.g. control frontal cortex: KAT I: 148 +/- 18 fmol/mg tissue/h; KAT II: 25 +/- 2 fmol/mg tissue/h). The activities of both KAT I and KAT II, when expressed per mg original weight, showed significant decreases (48-55%) in the HD putamen (p < 0.01). Trends toward lower enzyme activities and KYNA concentrations were detected in other brain areas as well. Kinetic analyses, performed in putamen and cerebellum, showed an approximately 3-fold increase in Km values for both KAT I and KAT II in the putamen only. Vmax values remained unchanged in the HD brain. These findings indicate a selective impairment in KYNA biosynthesis in the neostriatum of HD patients, possibly due to the loss of (an) endogenous KAT activator(s).(ABSTRACT TRUNCATED AT 250 WORDS)

Glutamine synthetase immunoreactivity in the human hippocampus is lamina-specific

Vibratome sections of immersion-fixed (4% paraformaldehyde) hippocampi from four autoptic cases without neuropathological findings were immunostained with a polyclonal anti-glutamine synthetase antibody. Immunoreactivity is restricted to astrocytes and has a layer-specific distribution: The highest levels are observed in the outer molecular layer of the fascia dentata, in the pyramidal cell layer and in the upper stratum oriens. The stratum radiatum displays particularly low immunoreaction. A conspicuous drop in immunoreactivity from the heavily stained outer molecular layer to its inner portion is marked by a clear-cut dividing line. The layer-specific staining pattern found corresponds to the laminated distribution of glutamate binding sites described by others.

The inhibition of glutamine synthetase in rat corpus striatum in vitro by methionine sulfoximine increases the neurotoxic effects of kainate and N-methyl-D-aspartate

Coronal slices of rat brain were incubated in Krebs bicarbonate medium containing kainate (300 microM), or N-methyl-D-aspartate (500 microM). Degeneration of striatal neurons by both these toxins was apparent after 40 min incubation, and was accompanied by a 33% (kainate) and 21% (N-methyl-D-aspartate) reduction in striatal glutamine synthetase activity. Pre-incubation of the slices with 500 microM L-methionine sulfoximine, an inhibitor of glutamine synthetase, for 20 min prior to the exposure to either kainate or N-methyl-D-aspartate, again showed extensive degeneration of striatal neurons, and a supra-additive reduction in glutamine synthetase activity in the tissue. The activity of the neuronal marker enzyme, neuron-specific enolase, was also reduced by pre-incubation of the slices with L-methionine sulfoximine before the addition of kainate or N-methyl-D-aspartate, but to a much lesser extent than glutamine synthetase. The results are discussed in terms of a possible mechanism of interaction between either kainate or N-methyl-D-aspartate, and glial cell metabolism.

Changes in nine enzyme markers for neurons, glia, and endothelial cells in agonal state and Huntington's disease caudate nucleus

Enzymes considered to be markers for neurons (angiotensin converting enzyme, thermolysin-like metalloendopeptidase, alanine aminopeptidase, and glutamate-oxaloacetate transaminase), glia (glutamine synthetase, pyruvate carboxylase, and beta-glucuronidase), and endothelial cells (alkaline phosphatase and plasminogen activator) were measured in caudate nucleus from 10 sudden death controls, eight agonal state controls, and 16 Huntington's disease patients. Glutamate-oxaloacetate transaminase was slightly reduced by agonal state. The four enzymes with a neuronal distribution were all correlatively reduced in Huntington's disease caudate nucleus. Glutamine synthetase activity was reduced and beta-glucuronidase mean activity increased over twofold in Huntington's disease caudate nucleus, with the two enzyme activities being inversely related. Pyruvate carboxylase was markedly affected by agonal state and was very variable in Huntington's disease caudate nucleus. The two endothelial enzymes were unaltered in Huntington's disease caudate nucleus. The findings are indicative of neuronal loss, an increased proportion of altered glia, and also of maintained vasculature in Huntington's disease caudate nucleus. Measurement of enzyme activities can help to delineate the types of cell altered in Huntington's disease.

Brain energy metabolism and dopaminergic function in Huntington's disease measured in vivo using positron emission tomography

A 48-year-old man with typical Huntington's disease was investigated with computed tomography (CT) and positron emission tomography. Regional cerebral blood flow, oxygen extraction, oxygen and glucose utilisation, L-Dopa uptake, and dopamine (D2) receptor binding were measured using several positron-labelled tracers. CT showed slight atrophy of the head of caudate but no cortical atrophy, although distinct frontal lobe dysfunction was present on psychometric testing. Oxygen and glucose metabolism and cerebral blood flow were decreased in the striata and to a lesser extent in frontal cortex. Cerebral blood flow was in the low normal range throughout the remainder of the brain. A normal metabolic ratio was found in all regions, since the changes in glucose utilisation paralleled those in oxygen consumption. The capacity of the striatum to store dopamine as assessed by L-[18F]-fluorodopa uptake was normal, but dopamine (D2) receptor binding was decreased when compared to normal subjects.

Increased alanine aminotransferase activity in the Huntington's disease putamen

The activities of both mitochondrial and cytosolic forms of alanine aminotransferase are markedly increased in Huntington's disease putamen autopsy samples. This increase was not observed in rats with kainic acid lesions of the striatum, and suggests a considerable alteration of glutamate and pyruvate metabolism as a feature of Huntington's disease.

Amino acids in autopsied human spinal cord. Selective changes in Friedreich's ataxia

The distribution of glycine, glutamate, aspartate, glutamine, and taurine was measured at autopsy in 10 normal human spinal cords, and in 4 spinal cords from Friedreich's Ataxia patients, using a sensitive double-isotope microassay of their dansyl derivatives. Transverse sections of spinal cord from cervical, thoracic, and lumbar levels were dissected to afford samples of gray matter, posterior columns, dorsal white matter, and ventral white matter. Levels of glycine, glutamate, and glutamine were found to be elevated in lumbar gray matter, being 2-3 times higher than those found in white matter structures. Aspartate and taurine, on the other hand, were found to be distributed more evenly in autopsied human spinal cord. Selective abnormalities of amino acid distribution in Friedreich's Ataxia included decreased glutamate and glutamine in lumbar gray matter and posterior columns and increased taurine content of lumbar spinal cord. These changes may be of pathophysiological significance in this hereditary neurodegenerative disease.

Chronic infusion of L-glutamate causes neurotoxicity in rat striatum

Chronic infusion of a high dose of monosodium glutamate (approximately 8 nmol/min) into the rat left striatum, over a period of 1 week, caused degeneration of striatal neurones. This was accompanied by a significant loss of neurochemical markers for both GABAergic and cholinergic interneurones. These results indicate that the sustained presence of elevated concentrations of glutamate will, in time, give rise to changes similar to those seen in human neurodegenerative disorders, such as Huntington's disease.

Reduced cortical glutamine concentrations in electrically kindled rats

The effect of kindling rats (with an electrical stimulus applied daily to the frontal cortex) on the concentrations of taurine, aspartate, glutamate, glutamine, and gamma-aminobutyric acid has been investigated. When compared with control groups, cortical glutamine concentrations were significantly decreased in kindled rats by approximately 20%. This decrease in glutamine directly correlated with the after-discharge duration (r = 0.84, p = 0.005). The significance of this in relation to glutamate metabolism and kindling is discussed here.

Glutamine synthetase and fructose-1, 6-diphosphatase activity in the putamen of control and Huntington's disease brain post mortem

There is a linear negative correlation between the activities of glutamine synthetase and fructose-1, 6-diphosphatase in normal Human putamen autopsy samples, and also in the Huntington's disease putamen. However, glutamine synthetase activity is reduced in choreic brain samples, while fructose-1, 6-diphosphatase activity is normal. The ratio of fructose-1, 6-diphosphatase to glutamine synthetase is therefore increased in Huntington's disease. The products of the two reactions, glutamine and fructose-6-phosphate, are the starting substrates for glycolipid and glycoprotein biosynthesis, via the glutamine:fructose-6-phosphate aminotransferase catalysed formation of glucoseamine-6-phosphate. The alternative metabolic route of fructose-6-phosphate leads to glycogen. The availability of glutamine, and the activity of glutamine synthetase may control fructose-6-phosphate metabolism, and the increased ratio of fructose-1,6-diphosphatase to glutamine synthetase in Huntington's disease may explain the accumulation of glycogen, and the reduction in ganglioside levels reported in this state.