Glutamate Secretion Research Articles

The astrocyte excitability brief: From receptors to gliotransmission

Astrocytes do not merely serve as the supporting cast and scenery against which starring roles would be played by neurons. Rather, these glial cells are intimately involved in many of the brain’s functions by responding to neuronal activity and modulating it. Such interplay between two principle neural cells, neurons and astrocytes, is evidenced in bi-directional glutamatergic astrocyte–neuron signaling. A key feature in this signaling pathway is astrocytic excitability based on variations of cytosolic Ca2+. It enables astrocytes, through the activation of their glutamatergic receptors, to respond to the same signal used by nearby neurons in synaptic transmission. Furthermore, increases in cytosolic Ca2+ in astrocytes can subsequently lead to Ca2+-dependent exocytotic secretion of gliotransmitter glutamate that in turn can signal to adjacent neurons. Astrocytic secretory machinery includes an assortment of exocytotic proteins which governs a merger of secretory vesicles to the plasma membrane. A cumulative knowledge on astrocytic excitability will aid better understanding of operating procedures in the brain in health and disease.

Patterns of Amino Acid Metabolism by Proliferating Human Mesenchymal Stem Cells

The nutritional requirements of stem cells have not been determined; in particular, the amino acid metabolism of stem cells is largely unknown. In this study, we investigated the amino acid metabolism of human mesenchymal stem cells (hMSCs), with focus on two questions: Which amino acids are consumed and/or secreted by hMSCs and at what rates? To answer these questions, hMSCs were cultured on tissue culture plastic and in a bioreactor, and their amino acid profile was analyzed. The results showed that the kinetics of hMSCs growth and amino acid metabolism were significantly higher for hMSCs in tissue culture plastic than in the bioreactor. Despite differences in culture conditions, 8 essential and 6 nonessential amino acids were consumed by hMSCs in both tissue culture plastic and bioreactor cultures. Glutamine was the most consumed amino acid with significantly higher rates than for any other amino acid. The metabolism of nonessential amino acids by hMSCs deviated significantly from that of other cell lines. The secretion of alanine, glycine, glutamate, and ornithine by hMSCs showed that there is a strong overflow metabolism that can be due to the high concentrations of amino acids provided in the medium. In addition, the data showed that there is a metabolic pattern for proliferating hMSCs, which can contribute to the design of medium without animal serum for stem cells. Further, this study shows how to implement amino acid rates and metabolic principles in three-dimensional stem cell biology.

Influence of Intraventricular Application of Baclofen on Arterial Blood Pressure and Neurotransmitter Concentrations in the Hypothalamic Paraventricular Nucleus of Rats

The hypothalamic paraventricular nucleus (PVN) is a key site for regulating neuroendocrine functions in the magnocellular part and autonomic activities in the parvocellular part. Its anatomical proximity to the third ventricle could be a good target for intrathecal injection of baclofen. We investigated the correlation of intrathecal application of baclofen (a specific GABAB receptor agonist) and the release of epinephrine, norepinephrine, dopac, homovanillinic acid (HVA), glutamate and aspartate from the PVN. The decomposition products HVA, dopa and dopac of norepinephrine, epinephrine and dopamine, respectively, were used as parameters for the secretion of dopamine. We implanted a microdialysis probe in the PVN of 25 Wistar rats. In 13 rats, 1.5 μg baclofen was injected in the lateral ventricle and the equivalent quantity of Ringer's lactate solution injected in the remaining 12 rats as a control group. Neurotransmitters and amino acids were quantified by high-performance liquid chromatography. There was a conspicuous but not significant effect of baclofen concerning the secretion of epinephrine, norepinephrine, dopac, glutamate and aspartate from the PVN. A significant increase in HVA concentration was observed only in rats treated with baclofen compared with the control group. These findings suggest that baclofen influences the secretion of neurotransmitters and amino acids involved in autonomic activities mediated by GABAB receptors.

Ethanol reduces kainate-evoked glutamate secretion in rat hippocampal astrocytes

In this study we have used rat hippocampal astrocytes in culture to investigate the effect of ethanol on kainate-induced glutamate secretion. Our results show that kainate (10 μM to 500 μM) stimulated glutamate release from astrocytes. Preincubation of astrocytes in the presence of ethanol induced a concentration-dependent (1 mM–50 mM) inhibition of glutamate release caused by stimulation of cells with 100 μM kainate. Inhibition of alcohol-dehydrogenase, by preincubation of astrocytes in the presence of 4-methylpyrazole (1 mM), abolished ethanol-induced inhibition of glutamate release in response to kainate. On the other hand, preincubation of astrocytes in the presence of the antioxidant cinnamtannin B-1 (10 μM) also blocked ethanol inhibitory action on glutamate release in response to kainate. Ethanol (50 mM) reduced Ca 2+ mobilization in response to kainate, whereas cinnamtannin B-1 reversed the inhibitory action of ethanol on Ca 2+ mobilization by kainate. Our results are consistent with an inhibitory action of ethanol on glutamate secretion from hippocampal astrocytes. The inhibitory effects of ethanol are probably due to its oxidative metabolization, involves reactive oxygen species production, and a lower Ca 2+ mobilization by kainate. Taking into account the pivotal role that astrocytes play within the central nervous system, especially in relation to neurons, the negative effects of ethanol on the release of glutamate might affect neuron-glia communication in the hippocampus, which might lead to functional defects in the brain.

Follistatin-like 1 Suppresses Sensory Afferent Transmission by Activating Na+,K+-ATPase

Excitatory synaptic transmission is modulated by inhibitory neurotransmitters and neuromodulators. We found that the synaptic transmission of somatic sensory afferents can be rapidly regulated by a presynaptically secreted protein, follistatin-like 1 (FSTL1), which serves as a direct activator of Na(+),K(+)-ATPase (NKA). The FSTL1 protein is highly expressed in small-diameter neurons of the dorsal root ganglion (DRG). It is transported to axon terminals via small translucent vesicles and secreted in both spontaneous and depolarization-induced manners. Biochemical assays showed that FSTL1 binds to the α1 subunit of NKA and elevates NKA activity. Extracellular FSTL1 induced membrane hyperpolarization in cultured cells and inhibited afferent synaptic transmission in spinal cord slices by activating NKA. Genetic deletion of FSTL1 in small DRG neurons of mice resulted in enhanced afferent synaptic transmission and sensory hypersensitivity, which could be reduced by intrathecally applied FSTL1 protein. Thus, FSTL1-dependent activation of NKA regulates the threshold of somatic sensation.

A neurocomputational model of nicotine addiction based on reinforcement learning

Event Abstract Back to Event A neurocomputational model of nicotine addiction based on reinforcement learning Selin Metin1* and Neslihan Serap Sengor1 1 Istanbul Technical University, Türkiye In modeling nicotine addiction, we consider that addiction develops due to malfunctioning of reinforcement learning processes driven by metabolical modifications in the brain. We base our approach on the fact that addiction develops as a result of damaged reward mechanism. Excessive fondness for a substance causes compulsive seeking of that substance and opponent process theory is used in explaining the development of addiction. Nicotine blood level triggers the secretion of dopamine (DA) from the ventral tegmental area (VTA) due to a race with the naturally secreted acetylcholine (Ach) neurotransmitter. In return, glutamate secretion in learning processes is affected and it modifies behavioral choices. Chronic nicotine exposure stamps in the behavioral patterns modified by DA secretion and causes addiction development. The proposed computational model is developed using MATLAB in-house codes and realizes DA secretion from the VTA to the cortico-striato-thalamic (CST) loop using reinforcement learning. DA secretion, action selection, action evaluation, and value assignment subsystems are modeled as nonlinear dynamical systems. The dynamic behavior of these systems is investigated by bifurcation analysis using XPP in order to give an explanation of processes going on from dynamical system point of view. The action selection system uses competitive learning which is modified with VTA DA signaling affected by nicotine. Arithmetically increasing reward value affects the system in favor of selecting the smoking action. Error in expectation symbolizes the modifying effects of the neurotransmitters and changes the output of dorsal striatum, amplifies the emotional input, and updates the stimulus value. Past actions contribute to the evaluation process as the input from the previous action so the cumulative effects of the previous actions trigger the present action selection. During model execution, addictive, non-addictive, and indecisive behaviors are observed in simulation results. Addiction developed in 20/50 trials with an average of 346/1000 steps and standard deviation of 265.76. To improve the proposed model, reward should be computed as a dynamically changing function of model parameters. Also, the approach should be expanded to include the molecular basis of DA secretion mechanism from the VTA to the CST loop involving the relevant neurotransmitters to be able to give a more realistic model. Funding Information: This work is partially supported by BAP-ITU References [1] Gutkin, B.S., Dehaene, S., Changeux, J.P., “A Neurocomputational Hypothesis for Nicotine Addiction”, PNAS, vol.103, no.4, 1106-1111, Jan 24, 2006. [2] Metin, S., Sengor, N.S., A Neurocomputational Model of Nicotine Addiction Based on Reinforcement Learning, ICANN 2010, 20th International Conference on Artificial Neural Networks, (2010), pp: 15-18. Keywords: Dopamine, Neurons, networks and dynamical systems, reinforcement learning Conference: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011, Freiburg, Germany, 4 Oct - 6 Oct, 2011. Presentation Type: Poster Topic: neurons, networks and dynamical systems (please use "neurons, networks and dynamical systems" as keywords) Citation: Metin S and Sengor N (2011). A neurocomputational model of nicotine addiction based on reinforcement learning. Front. Comput. Neurosci. Conference Abstract: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011. doi: 10.3389/conf.fncom.2011.53.00058 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Aug 2011; Published Online: 04 Oct 2011. * Correspondence: Dr. Selin Metin, Istanbul Technical University, Istanbul, Türkiye, selinmetin@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Selin Metin Neslihan Serap Sengor Google Selin Metin Neslihan Serap Sengor Google Scholar Selin Metin Neslihan Serap Sengor PubMed Selin Metin Neslihan Serap Sengor Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

TRPV1 and Synaptic Transmission

Transient Receptor Potential Vanilloid Type 1 is a prominent "pain" receptor expressed in sensory afferent neurons. TRPV1 on peripheral nerve terminals detects a variety of noxious stimuli generated at sites of injury and inflammation, and in turn, drives the excitation and sensitization of C-fibers neurons. Significantly, TRPV1 is also located on the central terminals of sensory neurons projecting to the spinal cord and brainstem. These TRPV1 channels appear to stimulate the secretion of glutamate. Further, TRPV1 is expressed diffusely in the brain and there is emerging evidence for TRPV1 modulating transmission at various brain synapses. Here we discuss our current understanding of the potential roles for TRPV1 in synaptic transmission.

Adaptive Calcified Matrix Response of Dental Pulp to Bacterial Invasion Is Associated with Establishment of a Network of Glial Fibrillary Acidic Protein +/Glutamine Synthetase + Cells

We report evidence for anatomical and functional changes of dental pulp in response to bacterial invasion through dentin that parallel responses to noxious stimuli reported in neural crest-derived sensory tissues. Sections of resin-embedded carious adult molar teeth were prepared for immunohistochemistry, in situ hybridization, ultrastructural analysis, and microdissection to extract mRNA for quantitative analyses. In odontoblasts adjacent to the leading edge of bacterial invasion in carious teeth, expression levels of the gene encoding dentin sialo-protein were 16-fold greater than in odontoblasts of healthy teeth, reducing progressively with distance from this site of the carious lesion. In contrast, gene expression for dentin matrix protein-1 by odontoblasts was completely suppressed in carious teeth relative to healthy teeth. These changes in gene expression were related to a gradient of deposited reactionary dentin that displayed a highly modified structure. In carious teeth, interodontoblastic dentin sialo-protein(-) cells expressing glutamine synthetase (GS) showed up-regulation of glial fibrillary acidic protein (GFAP). These cells extended processes that associated with odontoblasts. Furthermore, connexin 43 established a linkage between adjacent GFAP(+)/GS(+) cells in carious teeth only. These findings indicate an adaptive pulpal response to encroaching caries that includes the deposition of modified, calcified, dentin matrix associated with networks of GFAP(+)/GS(+) interodontoblastic cells. A regulatory role for the networks of GFAP(+)/GS(+) cells is proposed, mediated by the secretion of glutamate to modulate odontoblastic response.

Dissection of mitogenic and neurodegenerative actions of cystine and glutamate in malignant gliomas.

Malignant glioma represents one of the most aggressive and lethal human neoplasias. A hallmark of gliomas is their rapid proliferation and destruction of vital brain tissue, a process in which excessive glutamate release by glioma cells takes center stage. Pharmacologic antagonism with glutamate signaling through ionotropic glutamate receptors attenuates glioma progression in vivo, indicating that glutamate release by glioma cells is a prerequisite for rapid glioma growth. Glutamate has been suggested to promote glioma cell proliferation in an autocrine or paracrine manner, in particular by activation of the (RS)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid hydrate (AMPA) subtype of glutamate receptors. Here, we dissect the effects of glutamate secretion on glioma progression. Glioma cells release glutamate through the amino-acid antiporter system X(c)(-), a process that is mechanistically linked with cystine incorporation. We show that disrupting glutamate secretion by interfering with the system X(c)(-) activity attenuates glioma cell proliferation solely cystine dependently, whereas glutamate itself does not augment glioma cell growth in vitro. Neither AMPA receptor agonism nor antagonism affects glioma growth in vitro. On a molecular level, AMPA insensitivity is concordant with a pronounced transcriptional downregulation of AMPA receptor subunits or overexpression of the fully edited GluR2 subunit, both of which block receptor activity. Strikingly, AMPA receptor inhibition in tumor-implanted brain slices resulted in markedly reduced tumor progression associated with alleviated neuronal cell death, suggesting that the ability of glutamate to promote glioma progression strictly requires the tumor microenvironment. Concerning a potential pharmacotherapy, targeting system X(c)(-) activity disrupts two major pathophysiological properties of glioma cells, that is, the induction of excitotoxic neuronal cell death and incorporation of cystine required for rapid proliferation.

Carboxypeptidase E cytoplasmic tail mediates localization of synaptic vesicles to the pre‐active zone in hypothalamic pre‐synaptic terminals

How synaptic vesicles (SVs) are localized to the pre-active zone (5-200 nm beneath the active zone) in the nerve terminal, which may represent the slow response SV pool, is not fully understood. Electron microscopy revealed the number of SVs located in the pre-active zone, was significantly decreased in hypothalamic neurons of carboxypeptidase E knockout (CPE-KO) mice compared with wild-type mice. Additionally, we found K(+)-stimulated glutamate secretion from hypothalamic embryonic neurons was impaired in CPE-KO mice. Biochemical studies indicate that SVs from the hypothalamus of wild-type mice and synaptic-like microvesicles from PC12 cells contain a transmembrane form of CPE, with a cytoplasmic tail (CPE(C10)), maybe involved in synaptic function. Yeast two-hybrid and pull-down experiments showed that the CPE cytoplasmic tail interacted with gamma-adducin, which binds actin enriched at the nerve terminal. Total internal reflective fluorescence (TIRF) microscopy using PC12 cells as a model showed that expression of GFP-CPE(C15) reduced the steady-state level of synaptophysin-mRFP containing synaptic-like microvesicles accumulated in the area within 200 nm from the sub-plasma membrane (TIRF zone). Our findings identify the CPE cytoplasmic tail, as a new mediator for the localization of SVs in the actin-rich pre-active zone in hypothalamic neurons and the TIRF zone of PC12 cells.

S100B and homocysteine in the acute alcohol withdrawal syndrome

Elevations of serum homocysteine levels are a consistent finding in alcohol addiction. Serum S100B levels are altered in different neuropsychiatric disorders but not well investigated in alcohol withdrawal syndromes. Because of the close connection of S100B to ACTH and glutamate secretion that both are involved in neurodegeneration and symptoms of alcoholism the relationship of S100B and homocysteine to acute withdrawal variables has been examined. A total of 22 male and 9 female inpatients (mean age 46.9 ± 9.7 years) with an ICD-10 diagnosis of alcohol addiction without relevant affective comorbidity were examined on admission and after 24, 48, and 120 h during withdrawal. S100B and homocysteine levels in serum were collected, and severity of withdrawal symptoms (AWS-scale), applied withdrawal medication, initial serum ethanol levels and duration of addiction were recorded. Serum S100B and homocysteine levels declined significantly (P < .05) over time. Both levels declined with withdrawal syndrome severity. Females showed a trend to a more intense decline in serum S100B levels compared to males at day 5 (P = .06). Homocysteine levels displayed a negative relationship to applied amount of clomethiazole (P < .05) and correlated with age of onset of addiction. No withdrawal seizures were recorded during the trial. As it is known for homocysteine, S100B revealed to decline rapidly over withdrawal treatment in alcoholism. This effect is more pronounced in female patients. S100B could be of relevance in the neurobiology of alcohol withdrawal syndromes. It may be indirectly related to the level of stress level or glutamatergic activity during alcohol withdrawal.

A model of direction selectivity in the starburst amacrine cell network

Displaced starburst amacrine cells (SACs) are retinal interneurons that exhibit GABAA receptor-mediated and Cl − cotransporter-mediated, directionally selective (DS) light responses in the rabbit retina. They depolarize to stimuli that move centrifugally through the receptive field surround and hyperpolarize to stimuli that move centripetally through the surround (Gavrikov et al, PNAS 100(26):16047–16052, 2003, PNAS 103(49):18793–18798, 2006). They also play a key role in the activity of DS ganglion cells (DS GC; Amthor et al, Vis Neurosci 19:495–509 2002; Euler et al, Nature 418:845–852, 2002; Fried et al, Nature 420:411– 414, 2002; Gavrikov et al, PNAS 100(26):16047–16052, 2003, PNAS 103(49):18793–18798, 2006; Lee and Zhou, Neuron 51:787–799 2006; Yoshida et al, Neuron 30:771–780, 2001). In this paper we present a model of strong DS behavior of SACs which relies on the GABA-mediated communication within a tightly interconnected network of these cells and on the glutamate signal that the SACs receive from bipolar cells (a presynaptic cell that receives input from cones). We describe how a moving light stimulus can produce a large, sustained depolarization of the SAC dendritic tips that point in the direction that the stimulus moves (i.e., centrifugal motion), but produce a minimal depolarization of the dendritic tips that point in the opposite direction (i.e., centripetal motion). This DS behavior, which is quantified based on the relative size and duration of the depolarizations evoked by stimulus motion at dendritic tips pointing in opposite directions, is robust to changes of many different parameter values and consistent with experimental data. In addition, the DS behavior is strengthened under the assumptions that the Cl− cotransporters Na + -K + -Cl − and K + -Cl − are located in different regions of the SAC dendritic tree (Gavrikov et al, PNAS 103(49):18793–18798, 2006) and that GABA evokes a long-lasting response (Gavrikov et al, PNAS 100(26):16047–16052, 2003, PNAS 103(49):18793–18798, 2006; Lee and Zhou, Neuron 51:787–799, 2006). A possible mechanism is discussed based on the generation of waves of local glutamate and GABA secretion, and their postsynaptic interplay as the waves travel between cell compartments.

Nigella sativaL. Seed Extract Modulates the Neurotransmitter Amino Acids Release in Cultured NeuronsIn Vitro

Nigella sativa L. (NS) has been used for medicinal purposes since ancient times. This study aimed to investigate the cytotoxicity of NS dry methanolic extract on cultured cortical neurons and its influence on neurotransmitter release, as well as the presence of excitatory (glutamate and aspartate) and inhibitory amino acids (gamma-aminobutyric acid—GABA—and glycine) in NS extract. Cultured rat cortical neurons were exposed to different times and concentrations of NS dry methanolic extract and cell viability was then determined by a quantitative colorimetric method. NS did not induce any toxicity. The secretion of different amino acids was studied in primary cultured cortical neurons by high-performance liquid chromatography (HPLC) using a derivation before injection with dansyl chloride. NS modulated amino acid release in cultured neurons; GABA was significantly increased whereas secretion of glutamate, aspartate, and glycine were decreased. The in vitro findings support the hypothesis that the sedative and depressive effects of NS observed in vivo could be based on changes of inhibitory/excitatory amino acids levels.

Cancer cells release glutamate via the cystine/glutamate antiporter

Although the amino acid glutamate is used as an intercellular signaling molecule for normal bone homeostasis, little is known regarding its possible role in the metabolic disruption characteristic of bone metastasis. We have previously shown in vitro that cancer cell lines relevant to bone metastasis release glutamate into the extracellular environment. This study demonstrates the expression of multiple glutamate transporters in cancer cell lines of non-central nervous system origin. Furthermore, we identify the molecular mechanism responsible for glutamate export and show that this system can be inhibited pharmacologically. By highlighting that glutamate secretion is a common biological feature of cancer cells, this study suggests that tumor-derived glutamate could interfere with glutamate-dependent intercellular signaling in normal bone. Pharmacological interference with cancer cell glutamate release may be a viable option for limiting host bone response to invading tumor cells in bone metastasis.

Commitment of 1-Methyl-4-phenylpyrinidinium Ion-induced Neuronal Cell Death by Proteasome-mediated Degradation of p35 Cyclin-dependent Kinase 5 Activator

The dysfunction of proteasomes and mitochondria has been implicated in the pathogenesis of Parkinson disease. However, the mechanism by which this dysfunction causes neuronal cell death is unknown. We studied the role of cyclin-dependent kinase 5 (Cdk5)-p35 in the neuronal cell death induced by 1-methyl-4-phenylpyrinidinium ion (MPP+), which has been used as an in vitro model of Parkinson disease. When cultured neurons were treated with 100 microM MPP+, p35 was degraded by proteasomes at 3 h, much earlier than the neurons underwent cell death at 12-24 h. The degradation of p35 was accompanied by the down-regulation of Cdk5 activity. We looked for the primary target of MPP+ that triggered the proteasome-mediated degradation of p35. MPP+ treatment for 3 h induced the fragmentation of the mitochondria, reduced complex I activity of the respiratory chain without affecting ATP levels, and impaired the mitochondrial import system. The dysfunction of the mitochondrial import system is suggested to up-regulate proteasome activity, leading to the ubiquitin-independent degradation of p35. The overexpression of p35 attenuated MPP+-induced neuronal cell death. In contrast, depletion of p35 with short hairpin RNA not only induced cell death but also sensitized to MPP+ treatment. These results indicate that a brief MPP+ treatment triggers the delayed neuronal cell death by the down-regulation of Cdk5 activity via mitochondrial dysfunction-induced up-regulation of proteasome activity. We propose a role for Cdk5-p35 as a survival factor in countering MPP+-induced neuronal cell death.

Unsuccessful Suicide Attempt of a 15 Year Old Adolescent with Ingestion of 5000 mg Modafinil

Modafinil (Provigil) is a wake-promoting drug approved for patients with narcolepsy or other causes of excessive daytime sleepiness. Each pill is 100 to 200 mg; maximal daily dose of modafinil in adults is 400 mg (the medication is not approved by the FDA for children younger than 16 years of age). We report the case of an adolescent who attempted to commit suicide by ingesting 50 pills of modafinil. The medication was prescribed for her mother to treat symptoms associated with multiple sclerosis. Approximately 2 hours following ingestion the patient complained of headache, nausea and abdominal pain. Her ECG demonstrated prolonged QTc interval. Observation for 72 hours revealed 24 hours of inability to sleep, tachycardia, and dyskinesia. There was no deterioration of kidney or liver functions, and no change in complete blood count or blood pressure.

Effects of extracellular calcium concentration on the glutamate release by bioactive glass (BG60S) preincubated osteoblasts

Glutamate released by osteoblasts sharing similarities with its role in neuronal transmission is a very new scientific concept which actually changed the understanding of bone physiology. Since glutamate release is a calcium (Ca2+)-dependent process and considering that we have previously demonstrated that the dissolution of bioactive glass with 60% of silicon (BG60S) can alter osteoblast Ca2+-signaling machinery, we investigated whether BG60S induces glutamate secretion in osteoblasts and whether it requires an increase in intracellular Ca2+. Here we showed that the extracellular Ca2+ increase due to BG60S dissolution leads to an intracellular Ca2+ increase in the osteoblast, through the activation of an inositol 1,4,5-triphosphate receptor (InsP3R) and a ryanodine receptor (RyR). Additionally, we also demonstrated that glutamate released by osteoblasts can be profoundly altered by BG60S. The modulation of osteoblast glutamate released by the extracellular Ca2+ concentration opens a new window in the field of tissue engineering, since many biomaterials used for bone repair are able to increase the extracellular Ca2+ concentration due to their dissolution products.

HFE polymorphisms affect cellular glutamate regulation

HFE gene variants are relatively common genetic variants in Caucasians. The H63D HFE genetic variant has been repeatedly associated with a number of neurodegenerative diseases. We developed neuroblastoma cell lines expressing different HFE polymorphisms to explore the mechanisms behind these associations. Here we tested the hypothesis that cells with the H63D variant have a phenotype that promotes glutamate toxicity. In support of this hypothesis, expression of H63D HFE is associated with increased calcium-induced glutamate secretion and decreased cellular glutamate uptake. The polymorphism-associated changes in glutamate secretion were mimicked by altering cellular iron. Additionally, intracellular calcium is altered in a genotype-specific manner which could further impact glutamate secretion. HFE-dependent effects on glutamate uptake were confirmed in astrocytoma cell lines with endogenous expression of HFE. The ability of minocycline and the antioxidant Trolox to increase glutamate uptake differed by HFE genotype and implicate oxidative stress in glutamate regulation. This study demonstrates HFE cellular effects that extend beyond iron regulation, and suggests that H63D HFE may promote glutamate toxicity.

Global Versus Local Perspectives on Schizophrenia

Back to table of contents Previous article Next article LETTERFull AccessGlobal Versus Local Perspectives on SchizophreniaSareh ZendehrouhFatemeh BakouieShahriar Gharibzadeh,Sareh ZendehrouhSearch for more papers by this authorFatemeh BakouieSearch for more papers by this authorShahriar GharibzadehSearch for more papers by this author,Published Online:1 Apr 2009AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail To the Editor: Recent neurobiological studies indicate that schizophrenia may be a neurodevelopmental and progressive disorder with multiple biochemical abnormalities involving dopamine, serotonin, glutamate, and gamma-aminobutyric acid secretion. In postmortem tissue studies, structural abnormalities and alterations in synaptic connectivity have been observed in the intracortical circuitry of the prefrontal dorsal cortex of schizophrenia patients. These morphological changes could be the sequelae of earlier environmental insults and genetic processes. There are probably multiple susceptibility genes, each of small effect, which act in conjunction with environmental factors as obstetric abnormalities, intrauterine infection, and abnormal nutrition. Candidate identified genes could influence neurodevelopment, synaptic plasticity, and neurotransmission. 1 The recent findings are consistent with notions that epigenetic factors play a major role in the disease process and epigenetic factors may continue to influence the expression of the affected genes in adulthood. 2 It is also demonstrated that schizophrenia is a dynamical disease—i.e., that important aspects of schizophrenia can be understood on the basis of concepts of the theory of nonlinear dynamical systems. 3 Chaotic dynamical systems are characterized by a lawful but delicate sensitivity to initial conditions. This leads to the observation that initially similar behaviors evolve into a striking divergence of behavioral patterns over time. Therefore, small differences in the input can result in an entirely different sequence of outputs. 4 We believe that genes act as initial conditions and environmental factors are the control parameters of a chaotic human brain system, which can force the system to special states with particular characteristics (e.g., schizophrenia). Since in chaotic dynamical systems, control parameters can direct the system to special states, environmental factors play a key role in aggravation or decline of schizophrenia symptoms. This complies with some reports that showed high relapse rate of schizophrenia in families that expressed high emotion, 5 which can be considered as a positive control factor. Based on our hypothesis, we propose that schizophrenia could be considered a chaotic model and the global features of the disease could be extracted instead of paying attention to local detailed features. In such a perspective, the manner of managing the disease will be changed. For example, we think that it is not necessary to include the effects of each part of the brain circuits and to correct any change in the amount of neurotransmitters; instead it is better to model the disease state as a chaotic system and recognize the interaction of different environmental factors, such as maternal health, birth complications, emotional states, familial relationships, etc., on it and try to minimize the pathological effects of them. We stress that it is not the compartments but the global interactions of different elements that play major roles in the disease and deserve attention. Modeling the behavior of schizophrenia on the basis of chaos theory to control the disease seems to be a good place to start.Biomedical Engineering, Amirkabir University of Technology, Tehran, Iran

Expression and localization of the Corynebacterium glutamicum NCgl1221 protein encoding an l-glutamic acid exporter

Corynebacterium glutamicum strains are used for the fermentative production of L-glutamate. Biotin limitation and addition of fatty acid ester surfactants can induce L-glutamic acid secretion. However, the mechanism of L-glutamate secretion remains unclear. It was recently reported that the NCgl1221 protein, a mechanosensitive channel homolog, was considered to be functional as an important L-glutamate exporter. However, the structure of the NCgl1221 protein has not been studied recently. In this study, we predicted the topology structure of the NCgl1221 protein by TopPred. We further analyzed the expression and localization of the NCgl1221 protein in the cytoplasmic membrane of both Escherichia coli and C. glutamicum cells by fusing green fluorescence protein (GFP) in the C terminus of the NCgl1221 protein. We found that the expressed fusion protein NCgl1221/GFP was visualized in the periphery of both E. coli and C. glutamicum cells under confocal microscope, which is consistent with a cytoplasmic membrane location. In contrast, GFP was ubiquitous in the cytoplasm of bacterial cells expressing GFP only. We herein provide the straightforward and obvious evidence to prove that NCgl1221 is confined to the cytoplasmic membrane. And NCgl1221 is a membrane protein having four transmembrane segments with its C terminus in the cytoplasm.