Magnetic Resonance Spectroscopy (MRS) in Alzheimer's Disease.

MRS is a noninvasive technique to measure different metabolites in the brain. Changes in the levels of certain metabolites can be used as surrogate markers for Alzheimer's disease. They can potentially be used for diagnosis, prediction of prognosis, or even assessing response to treatment.There are different techniques for MRS acquisitions including STimulated Echo Acquisition Mode (STEAM) and Point Resolved Spectroscopy (PRESS). In terms of localization, single or multi-voxel methods can be used. Based on current data: 1. NAA, marker of neuronal integrity and viability, reduces in AD with longitudinal changes over the time as the disease progresses. There are data claiming that reduction of NAA is associated with tau accumulation, early neurodegenerative processes, and cognitive decline. Therefore, it can be used as a stage biomarker for AD to assess the severity of the disease. With advancement of disease modifying therapies, there is a potential role for NAA in the future to be used as a marker of response to treatment. 2. mI, marker of glial cell proliferation and activation, is associated with AB pathology and has early changes in the course of the disease. The NAA/mI ratio can be predictive of AD development with high specificity and can be utilized in the clinical setting to stratify cases for further evaluation with PET for potential treatments. 3. The changes in the level of other metabolites such as Chol, Glu, Gln, and GABA are controversial because of the lack of standardization of MRS techniques, current technical limitations, and possible region specific changes. 4. Ultrahigh field MRS and more advanced techniques can overcome many of these limitations and enable us to measure more metabolites with higher accuracy. 5. Standardization of MRS techniques, validation of metabolites' changes against PET using PET-guided technique, and longitudinal follow-ups to investigate the temporal changes of the metabolites in relation to other biomarkers and cognition will be crucial to confirm the utility of MRS as a potential noninvasive biomarker for AD.

Distinguishing glutamate and glutamine in in vivo 1 H MRS based on nuclear spin singlet order filtering.

PURPOSE: The signals of glutamate (Glu) and glutamine (Gln) are often significantly overlapped in routine 1 H-MR spectra of human brain in vivo. Selectively probing the signals of Glu and Gln in vivo is very important for the study of the metabolisms in which Glu and Gln are involved. METHODS: The Glu-/Gln- targeted pulse sequences are developed to selectively probe the signals of Glu and Gln. The core part of the Glu-/Gln- targeted pulse sequences lies on the preparation of the nuclear spin singlet orders (SSOs) of the five-spin systems of Glu and Gln. The optimal control method is used to prepare the SSOs of Glu and Gln with high efficiency. RESULTS: The Glu-/Gln- targeted pulse sequences have been applied on phantoms to selectively probe the signals of Glu and Gln. Moreover, in the in vivo experiments, the signals of Glu and Gln in human brains of healthy subjects have been successfully probed separately. CONCLUSION: The developed Glu-/Gln- targeted pulse sequences can be used to distinguish the 1 H-MR signals of Glu and Gln in human brains in vivo. The optimal control method provides an effective way to prepare the SSO of a specific spin system with high efficiency and in turn selectively probe the signals of a targeted molecule.

Insulin Diminishes Superoxide Increase in Cytosol and Mitochondria of Cultured Cortical Neurons Treated with Toxic Glutamate.

Glutamate excitotoxicity is involved in the pathogenesis of many disorders, including stroke, traumatic brain injury, and Alzheimer's disease, for which central insulin resistance is a comorbid condition. Neurotoxicity of glutamate (Glu) is primarily associated with hyperactivation of the ionotropic N-methyl-D-aspartate receptors (NMDARs), causing a sustained increase in intracellular free calcium concentration ([Ca2+]i) and synchronous mitochondrial depolarization and an increase in intracellular superoxide anion radical (O2-•) production. Recently, we found that insulin protects neurons against excitotoxicity by decreasing the delayed calcium deregulation (DCD). However, the role of insulin in O2-• production in excitotoxicity still needs to be clarified. The present study aims to investigate insulin's effects on glutamate-evoked O2-• generation and DCD using the fluorescent indicators dihydroethidium, MitoSOX Red, and Fura-FF in cortical neurons. We found a linear correlation between [Ca2+]i and [O2-•] in primary cultures of the rat neuron exposed to Glu, with insulin significantly reducing the production of intracellular and mitochondrial O2-• in the primary cultures of the rat neuron. MK 801, an inhibitor of NMDAR-gated Ca2+ influx, completely abrogated the glutamate effects in both the presence and absence of insulin. In experiments in sister cultures, insulin diminished neuronal death and O2 consumption rate (OCR).

Single-Voxel Proton Magnetic Resonance Spectroscopy of the Thalamus in Idiopathic Epileptic Dogs and in Healthy Control Dogs.

The role of magnetic resonance spectroscopy (MRS) in the investigation of brain metabolites in epileptic syndromes in dogs has not been explored systematically to date. The aim of this study was to investigate metabolites in the thalamus in dogs affected by idiopathic epilepsy (IE) with and without antiepileptic drug treatment (AEDT) and to compare them to unaffected controls. Our hypothesis is that similar to humans with generalized epilepsy and loss of consciousness, N-acetyl aspartate (NAA) would be reduced, and glutamate-glutamine (Glx) would be increased in treated and untreated IE in comparison with the control group. In this prospective case-control study, Border Collie (BC) and Greater Swiss Mountain dog (GSMD) were divided into three groups: (1) healthy controls, IE with generalized tonic-clonic seizures with (2) and without (3) AEDT. A total of 41 BC and GSMD were included using 3 Tesla single-voxel proton MRS of the thalamus (PRESS localization, shortest TE, TR = 2000 ms, NSA = 240). After exclusion of 11 dogs, 30 dogs (18 IE and 12 healthy controls) remained available for analysis. Metabolite concentrations were estimated with LCModel using creatine as reference and compared using Kruskal-Wallis and Wilcoxon rank-sum tests. The Kruskal-Wallis test revealed significant differences in the NAA-to-creatine (p = 0.04) and Glx-to-creatine (p = 0.03) ratios between the three groups. The Wilcoxon rank-sum test further showed significant reduction in the NAA/creatine ratio in idiopathic epileptic dogs under AEDT compared to epileptic dogs without AEDT (p = 0.03) and compared to healthy controls (p = 0.03). In opposite to humans, Glx/creatine ratio was significantly reduced in dogs with IE under AEDT compared to epileptic dogs without AEDT (p = 0.03) and controls (p = 0.02). IE without AEDT and healthy controls did not show significant difference, neither in NAA/creatine (p = 0.60), nor in Glx-to-creatine (p = 0.55) ratio. In conclusion, MRS showed changes in dogs with IE and generalized seizures under AEDT, but not in those without AEDT. Based upon these results, MRS can be considered a useful advanced imaging technique for the evaluation of dogs with IE in the clinical and research settings.

Altered thalamic neurotransmitters metabolism and functional connectivity during the development of chronic constriction injury induced neuropathic pain.

BACKGROUND: To investigate the thalamic neurotransmitters and functional connections in the development of chronic constriction injury (CCI)-induced neuropathic pain. METHODS: The paw withdrawal threshold was measured by mechanical stimulation the right hind paw with the von frey hair in the rats of CCI-induced neuropathic pain. The N-acetylaspartate (NAA) and Glutamate (Glu) in thalamus were detected by magnetic resonance spectrum (MRS) process. The thalamic functional connectivity with other brain regions was scanned by functional magnetic resonance image (fMRI). RESULTS: The paw withdrawal threshold of the ipsilateral side showed a noticeable decline during the pathological process. Increased concentrations of Glu and decreased levels of NAA in the thalamus were significantly correlated with mechanical allodynia in the neuropathic pain states. The thalamic regional homogeneity (ReHo) decreased during the process of neuropathic pain. The functional connectivity among the thalamus with the insula and somatosensory cortex were significantly increased at different time points (7, 14, 21 days) after CCI surgery. CONCLUSION: Our study suggests that dynamic changes in thalamic NAA and Glu levels contribute to the thalamic functional connection hyper-excitation during CCI-induced neuropathic pain. Enhanced thalamus-insula functional connection might have a significant effect on the occurrence of neuropathic pain.

Molecular, Structural, Functional, and Pharmacological Sites for Vesicular Glutamate Transporter Regulation.

Vesicular glutamate transporters (VGLUTs) control quantal size of glutamatergic transmission and have been the center of numerous studies over the past two decades. VGLUTs contain two independent transport modes that facilitate glutamate packaging into synaptic vesicles and phosphate (Pi) ion transport into the synaptic terminal. While a transmembrane proton electrical gradient established by a vacuolar-type ATPase powers vesicular glutamate transport, recent studies indicate that binding sites and flux properties for chloride, potassium, and protons within VGLUTs themselves regulate VGLUT activity as well. These intrinsic ionic binding and flux properties of VGLUTs can therefore be modulated by neurophysiological conditions to affect levels of glutamate available for release from synapses. Despite their extraordinary importance, specific and high-affinity pharmacological compounds that interact with these sites and regulate VGLUT function, distinguish between the various modes of transport, and the different isoforms themselves, are lacking. In this review, we provide an overview of the physiologic sites for VGLUT regulation that could modulate glutamate release in an over-active synapse or in a disease state.

Astaxanthin Protects PC12 Cells against Homocysteine- and Glutamate-Induced Neurotoxicity.

Memory impairment has been shown to be associated with glutamate (Glu) excitotoxicity, homocysteine (Hcy) accumulation, and oxidative stress. We hypothesize that Glu and Hcy could damage neuronal cells, while astaxanthin (ATX) could be beneficial to alleviate the adverse effects. Using PC12 cell model, we showed that Glu and Hcy provoked a huge amount of reactive oxygen species (ROS) production, causing mitochondrial damage at EC50 20 and 10 mm, respectively. The mechanisms of action include: (1) increasing calcium influx; (2) producing ROS; (3) initiating lipid peroxidation; (4) causing imbalance of the Bcl-2/Bax homeostasis; and (5) activating cascade of caspases involving caspases 12 and 3. Conclusively, the damages caused by Glu and Hcy to PC12 cells can be alleviated by the potent antioxidant ATX.

Altered thalamic neurotransmitters metabolism and functional connectivity during the development of chronic constriction injury induced neuropathic pain

BACKGROUND: To investigate the thalamic neurotransmitters and functional connections in the development of chronic constriction injury (CCI)-induced neuropathic pain. METHODS: The paw withdrawal threshold was measured by mechanical stimulation the right hind paw with the von frey hair in the rats of CCI-induced neuropathic pain. The N-acetylaspartate (NAA) and Glutamate (Glu) in thalamus were detected by magnetic resonance spectrum (MRS) process. The thalamic functional connectivity with other brain regions was scanned by functional magnetic resonance image (fMRI). RESULTS: The paw withdrawal threshold of the ipsilateral side showed a noticeable decline during the pathological process. Increased concentrations of Glu and decreased levels of NAA in the thalamus were significantly correlated with mechanical allodynia in the neuropathic pain states. The thalamic regional homogeneity (ReHo) decreased during the process of neuropathic pain. The functional connectivity among the thalamus with the insula and somatosensory cortex were significantly increased at different time points (7, 14, 21 days) after CCI surgery. CONCLUSION: Our study suggests that dynamic changes in thalamic NAA and Glu levels contribute to the thalamic functional connection hyper-excitation during CCI-induced neuropathic pain. Enhanced thalamus-insula functional connection might have a significant effect on the occurrence of neuropathic pain.

Imaging of glutamate in acute traumatic brain injury using chemical exchange saturation transfer.

BACKGROUND: Chemical exchange saturation transfer (CEST) is an important contrast mechanism in the field of magnetic resonance imaging. Herein, we used CEST for glutamate (GluCEST) imaging to evaluate the Glu alterations in acute mild to moderate traumatic brain injury (TBI) and correlated such alterations with the cognitive outcome at 1-month postinjury. METHODS: Thirty-two patients with well-documented mild-to-moderate TBI and 15 healthy controls (HC group) underwent 3.0-Tesla magnetic resonance imaging (MRI) with GluCEST, and magnetic resonance spectroscopy (MRS) scans. The Montreal Cognitive Assessment (MoCA) examination was administered to all study subjects at 1-month postinjury for cognitive outcome acquisition and divided TBI patients into patients with good cognitive outcome (GCO group) and with poor cognitive outcome (PCO group). RESULTS: The GluCEST% values for the occipital gray matter (OGM) and bilateral parietooccipital white matter (PWM) were higher in the PCO group compared with the HC and GCO groups (P<0.05), whereas the GluCEST% value showed no significant differences between the GCO and HC groups (P>0.05). In comparison with HCs, TBI patients had a significantly increased GluCEST% value for the OGM and bilateral PWM (P<0.05). GluCEST performed better than MRS in the prediction of cognitive outcome for TBI patients (P<0.05). CONCLUSIONS: Glu is significantly increased in acute TBI and strongly correlates with the cognitive outcome at 1month postinjury. GluCEST may supply new insight into TBI and help to improve the accuracy of short-term outcome prediction.

Effects of Sub-Acute Manganese Exposure on Thyroid Hormone and Glutamine (Gln)/Glutamate (Glu)-γ- Aminobutyric Acid (GABA) Cycle in Serum of Rats.

Excessive manganese (Mn) exposure may adversely affect the central nervous system, and cause an extrapyramidal disorder known as manganism. The glutamine (Gln)/glutamate (Glu)-γ-aminobutyric acid (GABA) cycle and thyroid hormone system may be involved in Mn-induced neurotoxicity. However, the effect of Mn on the Gln/Glu-GABA cycle in the serum has not been reported. Herein, the present study aimed to investigate the effects of sub-acute Mn exposure on the Gln/Glu-GABA cycle and thyroid hormones levels in the serum of rats, as well as their relationship. The results showed that sub-acute Mn exposure increased serum Mn levels with a correlation coefficient of 0.733. Furthermore, interruption of the Glu/Gln-GABA cycle in serum was found in Mn-exposed rats, as well as thyroid hormone disorder in the serum via increasing serum Glu levels, and decreasing serum Gln, GABA, triiodothyronine (T3) and thyroxine (T4) levels. Additionally, results of partial correlation showed that there was a close relationship between serum Mn levels and the detected indicators accompanied with a positive association between GABA and T3 levels, as well as Gln and T4 levels in the serum of Mn-exposed rats. Unexpectedly, there was no significant correlation between serum Glu and the serum T3 and T4 levels. In conclusion, the results demonstrated that both the Glu/Gln-GABA cycle and thyroid hormone system in the serum may play a potential role in Mn-induced neurotoxicity in rats. Thyroid hormone levels, T3 and T4, have a closer relationship with GABA and Gln levels, respectively, in the serum of rats.

Electroacupuncture ameliorate learning and memory by improving N-acetylaspartate and glutamate metabolism in APP/PS1 mice.

OBJECTIVE: To explore the precise mechanism of electroacupuncture (EA) to delay cognitive impairment in Alzheimer disease. METHODS: N-Acetylaspartate (NAA), glutamate (Glu) and myoinositol (mI) metabolism were measured by magnetic resonance spectroscopy, learning and memory of APP/PS1 mouse was evaluated by the Morris water maze test and the step-down avoidance test, neuron survival number and neuronal structure in the hippocampus were observed by Nissl staining, and BDNF and phosphorylated TrkB detected by Western blot. RESULTS: EA at DU20 acupuncture significantly improve learning and memory in behavioral tests, up-regulate NAA, Glu and mI metabolism, increase the surviving neurons in hippocampus, and promote the expression of BDNF and TrkB in the APP/PS1 transgenic mice. CONCLUSION: These findings suggested that EA is a potential therapeutic for ameliorate cognitive dysfunction, and it might be due to EA could improve NAA and Glu metabolism by upregulation of BDNF in APP/PS1 mice.

Protective effect and mechanism of injection of glutamate into cerebellum fastigial nucleus on chronic visceral hypersensitivity in rats.

AIMS: We investigated the effects of chemical stimulation of cerebellum fastigial nucleus (FN) on the chronic visceral hypersensitivity (CVH) and its possible mechanism in rats. MAIN METHODS: We stimulated the FN by microinjecting glutamate into the FN, in order to explore whether the cerebellum fastigial nucleus played a role on CVH in rat. The model of CVH was established by colorectal distension (CRD) in neonatal rats. Abdominal withdrawal reflex (AWR) scores, pain threshold, and amplitude of electromyography (EMG) were used to assess the hyperalgesia. KEY FINDINGS: We showed that microinjection of l-glutamate (Glu) into the FN markedly attenuated hyperalgesia. The protective effect of FN was prevented by pretreatment with the glutamate decarboxylase inhibitor, 3-mercaptopropionic acid (3-MPA) into the FN or GABAA receptor antagonist, bicuculline (Bic) into the LHA (lateral hypothalamic area). The expressions of protein Bax, caspase-3 were decreased, but the expression of protein Bcl-2 was increased after chemical stimulation of FN. These results indicated that the FN participated in regulation of CVH, and was a specific area in the CNS for exerting protective effects on the CVH. In addition, LHA and GABA receptor may be involved in this process. SIGNIFICANCE: Our findings might provide a new and improved understanding of the FN function, and might show an effective treatment strategy for the chronic visceral hypersensitivity.

Emerging Trends in Pain Modulation by Metabotropic Glutamate Receptors.

Pain is an essential protective mechanism meant to prevent tissue damages in organisms. On the other hand, chronic or persistent pain caused, for example, by inflammation or nerve injury is long lasting and responsible for long-term disability in patients. Therefore, chronic pain and its management represents a major public health problem. Hence, it is critical to better understand chronic pain molecular mechanisms to develop innovative and efficient drugs. Over the past decades, accumulating evidence has demonstrated a pivotal role of glutamate in pain sensation and transmission, supporting glutamate receptors as promising potential targets for pain relieving drug development. Glutamate is the most abundant excitatory neurotransmitter in the brain. Once released into the synapse, glutamate acts through ionotropic glutamate receptors (iGluRs), which are ligand-gated ion channels triggering fast excitatory neurotransmission, and metabotropic glutamate receptors (mGluRs), which are G protein-coupled receptors modulating synaptic transmission. Eight mGluRs subtypes have been identified and are divided into three classes based on their sequence similarities and their pharmacological and biochemical properties. Of note, all mGluR subtypes (except mGlu6 receptor) are expressed within the nociceptive pathways where they modulate pain transmission. This review will address the role of mGluRs in acute and persistent pain processing and emerging pharmacotherapies for pain management.

Electroacupuncture ameliorate learning and memory by improving N -acetylaspartate and glutamate metabolism in APP/PS1 mice

OBJECTIVE: To explore the precise mechanism of electroacupuncture (EA) to delay cognitive impairment in Alzheimer disease. Methods N -Acetylaspartate (NAA), glutamate (Glu) and myoinositol (mI) metabolism were measured by magnetic resonance spectroscopy, learning and memory of APP/PS1 mouse was evaluated by the Morris water maze test and the step-down avoidance test, neuron survival number and neuronal structure in the hippocampus were observed by Nissl staining, and BDNF and phosphorylated TrkB detected by Western blot. RESULTS: EA at DU20 acupuncture significantly improve learning and memory in behavioral tests, up-regulate NAA, Glu and mI metabolism, increase the surviving neurons in hippocampus, and promote the expression of BDNF and TrkB in the APP/PS1 transgenic mice. CONCLUSION: These findings suggested that EA is a potential therapeutic for ameliorate cognitive dysfunction, and it might be due to EA could improve NAA and Glu metabolism by upregulation of BDNF in APP/PS1 mice.

Direct assessment of the metabolic origin of carbon atoms in glutamate from illuminated leaves using 13 C-NMR.

Glutamate (Glu) is the cornerstone of nitrogen assimilation and photorespiration in illuminated leaves. Despite this crucial role, our knowledge of the flux to Glu de novo synthesis is rather limited. Here, we used isotopic labelling with 13 CO2 and 13 C-NMR analyses to examine the labelling pattern and the appearance of multi-labelled species of Glu molecules to trace the origin of C-atoms found in Glu. We also compared this with 13 C-labelling patterns in Ala and Asp, which reflect citrate (and thus Glu) precursors, that is, pyruvate and oxaloacetate. Glu appeared to be less 13 C-labelled than Asp and Ala, showing that the Glu pool was mostly formed by 'old' carbon atoms. There were modest differences in intramolecular 13 C-13 C couplings between Glu C-2 and Asp C-3, showing that oxaloacetate metabolism to Glu biosynthesis did not involve C-atom redistribution by the Krebs cycle. The apparent carbon allocation increased with carbon net photosynthesis. However, when expressed relative to CO2 fixation, it was clearly higher at low CO2 while it did not change in 2% O2 , as compared to standard conditions. We conclude that Glu production from current photosynthetic carbon represents a small flux that is controlled by the gaseous environment, typically upregulated at low CO2 .

Physiological neuronal decline in healthy aging human brain - An in vivo study with MRI and short echo-time whole-brain (1)H MR spectroscopic imaging.

Knowledge of physiological aging in healthy human brain is increasingly important for neuroscientific research and clinical diagnosis. To investigate neuronal decline in normal aging brain eighty-one healthy subjects aged between 20 and 70years were studied with MRI and whole-brain (1)H MR spectroscopic imaging. Concentrations of brain metabolites N-acetyl-aspartate (NAA), choline (Cho), total creatine (tCr), myo-inositol (mI), and glutamine+glutamate (Glx) in ratios to internal water, and the fractional volumes of brain tissue were estimated simultaneously in eight cerebral lobes and in cerebellum. Results demonstrated that an age-related decrease in gray matter volume was the largest contribution to changes in brain volume. Both lobar NAA and the fractional volume of gray matter (FVGM) decreased with age in all cerebral lobes, indicating that the decreased NAA was predominantly associated with decreased gray matter volume and neuronal density or metabolic activity. In cerebral white matter Cho, tCr, and mI increased with age in association with increased fractional volume, showing altered cellular membrane turn-over, energy metabolism, and glial activity in human aging white matter. In cerebellum tCr increased while brain tissue volume decreased with age, showing difference to cerebral aging. The observed age-related metabolic and microstructural variations suggest that physiological neuronal decline in aging human brain is associated with a reduction of gray matter volume and neuronal density, in combination with cellular aging in white matter indicated by microstructural alterations and altered energy metabolism in the cerebellum.

Quantitative-profiling of neurotransmitter abnormalities in the disease progression of experimental diabetic encephalopathy rat.

Diabetic encephalopathy (DE) is one of the most prevalent chronic complications of diabetes mellitus (DM), with neither effective prevention nor proven therapeutic regimen. This study aims to uncover the potential dysregulation pattern of the neurotransmitters in a rat model of streptozotocin (STZ)-induced experimental DE. For that purpose, male Sprague-Dawley (SD) rats were treated with a single intraperitoneal injection of STZ. Cognitive performance was detected with the Morris water maze (MWM) test. Serum, cerebrospinal fluid (CSF), and brain tissues were collected to measure the levels of neurotransmitters. Compared with the control rats, the acetylcholine (ACh) levels in serum, CSF, hippocampus, and cortex were all significantly down-regulated as early as 6 weeks in the STZ treatment group. In contrast, the glutamate (Glu) levels were decreased in CSF and the hippocampus, but unaffected in the serum and cortex of STZ-treated rats. As for γ-aminobutyric acid (GABA), it was down-regulated in serum, but up-regulated in CSF, hippocampus, and the cortex in the STZ-treated group. The mRNA expressions of neurotransmitter-related rate limiting enzymes (including AChE, GAD1, and GAD2) and pro-inflammatory cytokines (including IL-1ß and TNF-α) were all increased in the DE rats. Our data suggest that DM induces isoform-dependent and tissue-specific neurotransmitter abnormalities, and that neuroinflammation may underlay the nervous system dysfunction observed in the progression of DE.

Investigating GluCEST and its specificity for pH mapping at low temperatures.

Chemical exchange saturation transfer (CEST) from glutamate to water (GluCEST) is a powerful tool for mapping glutamate concentration and intracellular pH. GluCEST could also be helpful to understand the physiology of lower aquatic vertebrates and invertebrates. Therefore, this study aimed to investigate the GluCEST effect and the exchange rate ksw from amine protons of glutamate to water in a broad range of temperatures (1-37°C) and pH (5.5-8.0). Z-spectra were measured from glutamate solutions at different pH values and temperatures and analysed by numerically solving the Bloch-McConnell equation. As expected, a strong dependence of the GluCEST effect and the determined ksw values on pH and temperature was observed. In addition, a strong dependence of the GluCEST effect on phosphate buffer concentration was confirmed. The in vitro data show that GluCEST is detectable in the whole temperature range, even at 1°C. An interpolation function for the exchange rate ksw was determined for the considered range of temperatures and pH values, showing a bijective relation between the exchange rate and pH at a given temperature. To investigate the specificity of GluCEST imaging at low temperatures, the CEST effect was investigated for several metabolites relevant for CEST imaging of the brain. As an example, the contribution of GluCEST to the total CEST effect at 3 ppm was estimated for zebrafish (Danio rerio). It is shown that also at lower temperatures glutamate is the major contributor to the total CEST effect, particularly if the experimental parameters are optimized.

Relation between modulation of the N-methyl-D-aspartate receptor and cyanide-induced neurotoxicity / 中国临床药理学与治疗学

Cyanide can activate the N-methyl-D-aspartate (NMDA) receptor by two approaches directly and indirectly. Firstly cyanide-induced depletion of energy is associated with the activation of NMDA receptors indirectly by increasing extracellular glutamate (Glu) and affecting cytosolic Ca 2+ homeostatic mechanisms. Secondly most likely as a conditioner of the NMDA receptor, cyanide enhances NMDA receptors responses by modulating redox sites of cysteine residue located in the subunit NR 1 or NR 2 of the NMDA receptor. NMDA receptor-induced neurotoxicity, initiated by the direct or indirect activation of NMDA receptor, leads to neuronal injury, apoptosis or necrosis finally. Therefore, it is believed that the activation of the NMDA receptor is presumably the key event in the mechanism of cyanide-induced neuronal injures.

Protective effect of tetrahydroxystilbene glucoside on hippocampal neurons damage induced by glutamate in rats / 中国康复理论与实践

@#ObjectiveTo observe the protective effect of tetrahydroxystilbene glucoside (TSG) on rats' hippocampal neuronal damage induced by glutamate (Glu) in the culture.MethodsHippocampus was isolated from newborn SD rats and dispersedly cultured in the medium for 9 days. Neurons were incubated with TSG (5—100μmol/L) for 24h, the cells were washed twice with Lock's solution without Mg2+,then Glu 500 μmol/L was added. Thirty min later, the reaction was terminated by washing the monolayer cells twice with the Lock's solution and then cultures were kept at 37℃ for 24h. Cell viability was measured by MTT method and cell membrane damage was determined by LDH leakage; with Fluo-3/AM as an intracellular calcium indicator and added into the bathing medium, fluorescent intensity of intracellular free calcium were observed through laser scanning confocal microscopy (LSCM).ResultsAfter the treatment with 5—100μmol/L TSG for 24h, the decrease of cell viability and the increase of LDH leakage caused by Glu was obviously resisted dose dependently. TSG inhibited increase of Ca2+ in cytoplasm, compared with model group.ConclusionTSG can significantly promote the cell viability and reduce the cell membrane damage in Glu treating hippocampal neurons. The neuroprotective activities of TGS is mediated by inhibiting Ca2+ overload in cytoplasm.