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Glutamate Excitotoxicity (glutamate + excitotoxicity)

Distribution by Scientific Domains

Life Sciences	52%
Medical Sciences	42%

Selected Abstracts

Enzymatic Degradation Protects Neurons from Glutamate Excitotoxicity

JOURNAL OF NEUROCHEMISTRY, Issue 3 2000
Christopher C. Matthews
Abstract: Several enzymes with the capacity to degrade glutamate have been suggested as possible neuroprotectants. We initially evaluated the kinetic properties of glutamate pyruvate transaminase (GPT; also known as alanine aminotransferase), glutamine synthetase, and glutamate dehydrogenase under physiologic conditions to degrade neurotoxic concentrations of glutamate. Although all three enzymes initially degraded glutamate rapidly, only GPT was able to reduce toxic (500 ,M) levels of glutamate into the physiologic (<20 ,M) range. Primary cultures of fetal murine cortical neurons were subjected to paradigms of either exogenous or endogenous glutamate toxicity to evaluate the neuroprotective value of GPT. Neuronal survival after exposure to added glutamate ranging from 100 to 500 ,M was improved significantly in the presence of GPT (,1 U/ml). Cultures were also exposed to the glutamate transporter inhibitor L- trans -pyrrolidine-2,4-dicarboxylate (PDC), which produces neuronal injury by elevating extracellular glutamate. GPT significantly reduced the toxicity of PDC. This reduction was associated with a reduction in the PDC-dependent rise in the medium concentration of glutamate. These results suggest that enzymatic degradation of glutamate by GPT can be an alternative to glutamate receptor blockade as a strategy to protect neurons from excitotoxic injury. [source]

Riluzole prolongs survival time and alters nuclear inclusion formation in a transgenic mouse model of Huntington's disease

MOVEMENT DISORDERS, Issue 4 2002
Johannes Schiefer MD
Abstract Glutamate excitotoxicity has been suggested to contribute to the pathogenesis of Huntington's disease (HD). Riluzole is a substance with glutamate antagonistic properties that is used for neuroprotective treatment in amyotrophic lateral sclerosis and which is currently tested in clinical trials for treatment of HD. R6/2 transgenic mice, which express exon 1 of the human HD gene with an expanded CAG triplet repeat, serve as a well-characterized mouse model for HD with progressing neurological abnormalities and limited survival. We treated R6/2 HD transgenic mice with riluzole orally beginning at a presymptomatic stage until death to investigate its potential neuroprotective effects in this mouse model and found that survival time in the riluzole group was significantly increased in comparison to placebo-treated transgenic controls. Additionally, the progressive weight loss was delayed and significantly reduced by riluzole treatment; behavioral testing of motor coordination and spontaneous locomotor activity, however, showed no statistically significant differences. We also examined the formation of the HD characteristic neuronal intranuclear inclusions (NII) immunohistologically. At a late disease stage, striatal NII from riluzole-treated transgenic mice showed profound changes in ubiquitination, i.e., NII were less ubiquitinated and surrounded by ubiquitinated micro-aggregates. Staining with antibodies directed against the mutated huntingtin revealed no significant difference in this component of NII. Taken together, these data suggest that riluzole is a promising candidate for neuroprotective treatment in human HD. © 2002 Movement Disorder Society [source]

Neuroprotection by donepezil against glutamate excitotoxicity involves stimulation of ,7 nicotinic receptors and internalization of NMDA receptors

BRITISH JOURNAL OF PHARMACOLOGY, Issue 1 2010
H Shen
BACKGROUND AND PURPOSE Glutamate excitotoxicity may be involved in ischaemic injury to the CNS and some neurodegenerative diseases, such as Alzheimer's disease. Donepezil, an acetylcholinesterase (AChE) inhibitor, exerts neuroprotective effects. Here we demonstrated a novel mechanism underlying the neuroprotection induced by donepezil. EXPERIMENTAL APPROACH Cell damage in primary rat neuron cultures was quantified by lactate dehydrogenase release. Morphological changes associated with neuroprotective effects of nicotine and AChE inhibitors were assessed by immunostaining. Cell surface levels of the glutamate receptor sub-units, NR1 and NR2A, were analyzed using biotinylation. Immunoblot was used to measure protein levels of cleaved caspase-3, total NR1, total NR2A and phosphorylated NR1. Immunoprecipitation was used to measure association of NR1 with the post-synaptic protein, PSD-95. Intracellular Ca2+ concentrations were measured with fura 2-acetoxymethylester. Caspase 3-like activity was measured using enzyme substrate, 7-amino-4-methylcoumarin (AMC)-DEVD. KEY RESULTS Levels of NR1, a core subunit of the NMDA receptor, on the cell surface were significantly reduced by donepezil. In addition, glutamate-mediated Ca2+ entry was significantly attenuated by donepezil. Methyllycaconitine, an inhibitor of ,7 nicotinic acetylcholine receptors (nAChR), inhibited the donepezil-induced attenuation of glutamate-mediated Ca2+ entry. LY294002, a phosphatidyl inositol 3-kinase (PI3K) inhibitor, had no effect on attenuation of glutamate-mediated Ca2+ entry induced by donepezil. CONCLUSIONS AND IMPLICATIONS Decreased glutamate toxicity through down-regulation of NMDA receptors, following stimulation of ,7 nAChRs, could be another mechanism underlying neuroprotection by donepezil, in addition to up-regulating the PI3K-Akt cascade or defensive system. [source]

Aberrant Control of Motoneuronal Excitability in Amyotrophic Lateral Sclerosis: Excitatory Glutamate,/,D -Serine vs.

CHEMISTRY & BIODIVERSITY, Issue 6 2010
-Aminobutanoic Acid (GABA), Inhibitory Glycine/
Abstract The mechanism underlying selective motoneuronal loss in amyotrophic lateral sclerosis (ALS) remains uncertain. The pathogenesis appears to be a complex and multifactorial process. Glutamate excitotoxicity to motoneuron is one of the most intensely investigated targets for the treatment of ALS, and excessive motoneuronal excitation by glutamate through ionotropic glutamate receptors has been mainly demonstrated. However, development of clinically effective drug targeting glutamate is sometimes difficult, because some aspects of glutamergic signals also could be beneficial, as the injured neurons attempt to recruit endogenous recovery. This review is focused on identifying other mechanisms of imbalanced excitation in ALS motoneurons including excitation-modulating D -serine and inhibitory glycine/GABA. Further, validation of these mechanisms might ultimately lead us to new therapeutic targets for ALS. [source]

Growth hormone-releasing peptide 6 protection of hypothalamic neurons from glutamate excitotoxicity is caspase independent and not mediated by insulin-like growth factor I

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2009
A. Delgado-Rubín
Abstract Treatment of the fetal hypothalamic neuronal cell line RCA-6 with growth hormone-releasing peptide 6, an agonist of the ghrelin receptor, or insulin-like growth factor I activates intracellular signalling cascades associated with anti-apoptotic actions. Abnormally high concentrations of glutamate provoke over-excitation of neurons leading to cell damage and apoptosis. Thus, the aim of this study was to investigate whether the administration of growth hormone-releasing peptide 6 and insulin-like growth factor I attenuates monosodium glutamate-induced apoptosis in RCA-6 neurons and the mechanisms involved. Two different mechanisms are involved in glutamate-induced cell death, one by means of caspase activation and the second through activation of a caspase-independent pathway of apoptosis mediated by the translocation of apoptosis-inducing factor. Growth hormone-releasing peptide 6 partially reversed glutamate-induced cell death but not the activation of caspases, suggesting blockage of the caspase-independent cell death pathway, which included interference with the translocation of apoptosis-inducing factor to the nucleus associated with the induction of Bcl-2. In contrast, the addition of insulin-like growth factor I to RCA-6 neurons abolished glutamate-induced caspase activation and cell death. These data demonstrate for the first time a neuroprotective role for growth hormone secretagogues in the caspase-independent cell death pathway and indicate that these peptides have neuroprotective effects independent of its induction of insulin-like growth factor I. [source]

Calcium ions in neuronal degeneration

IUBMB LIFE, Issue 9 2008
Urszula Wojda
Abstract Neuronal Ca2+ homeostasis and Ca2+ signaling regulate multiple neuronal functions, including synaptic transmission, plasticity, and cell survival. Therefore disturbances in Ca2+ homeostasis can affect the well-being of the neuron in different ways and to various degrees. Ca2+ homeostasis undergoes subtle dysregulation in the physiological ageing. Products of energy metabolism accumulating with age together with oxidative stress gradually impair Ca2+ homeostasis, making neurons more vulnerable to additional stress which, in turn, can lead to neuronal degeneration. Neurodegenerative diseases related to aging, such as Alzheimer's disease, Parkinson's disease, or Huntington's disease, develop slowly and are characterized by the positive feedback between Ca2+ dyshomeostasis and the aggregation of disease-related proteins such as amyloid beta, alfa-synuclein, or huntingtin. Ca2+ dyshomeostasis escalates with time eventually leading to neuronal loss. Ca2+ dyshomeostasis in these chronic pathologies comprises mitochondrial and endoplasmic reticulum dysfunction, Ca2+ buffering impairment, glutamate excitotoxicity and alterations in Ca2+ entry routes into neurons. Similar changes have been described in a group of multifactorial diseases not related to ageing, such as epilepsy, schizophrenia, amyotrophic lateral sclerosis, or glaucoma. Dysregulation of Ca2+ homeostasis caused by HIV infection or by sudden accidents, such as brain stroke or traumatic brain injury, leads to rapid neuronal death. The differences between the distinct types of Ca2+ dyshomeostasis underlying neuronal degeneration in various types of pathologies are not clear. Questions that should be addressed concern the sequence of pathogenic events in an affected neuron and the pattern of progressive degeneration in the brain itself. Moreover, elucidation of the selective vulnerability of various types of neurons affected in the diseases described here will require identification of differences in the types of Ca2+ homeostasis and signaling among these neurons. This information will be required for improved targeting of Ca2+ homeostasis and signaling components in future therapeutic strategies, since no effective treatment is currently available to prevent neuronal degeneration in any of the pathologies described here. © 2008 IUBMB IUBMB Life, 60(9): 575,590, 2008 [source]

Interleukin-1,: a bridge between inflammation and excitotoxicity?

JOURNAL OF NEUROCHEMISTRY, Issue 1 2008
Birgit Fogal
Abstract Interleukin-1 (IL-1) is a proinflammatory cytokine released by many cell types that acts in both an autocrine and/or paracrine fashion. While IL-1 is best described as an important mediator of the peripheral immune response during infection and inflammation, increasing evidence implicates IL-1 signaling in the pathogenesis of several neurological disorders. The biochemical pathway(s) by which this cytokine contributes to brain injury remain(s) largely unidentified. Herein, we review the evidence that demonstrates the contribution of IL-1, to the pathogenesis of both acute and chronic neurological disorders. Further, we highlight data that leads us to propose IL-1, as the missing mechanistic link between a potential beneficial inflammatory response and detrimental glutamate excitotoxicity. [source]

Preferential vulnerability of mesencephalic dopamine neurons to glutamate transporter dysfunction

JOURNAL OF NEUROCHEMISTRY, Issue 2 2008
Imane Nafia
Abstract Nigral depletion of the main brain antioxidant GSH is the earliest biochemical event involved in Parkinson's disease pathogenesis. Its causes are completely unknown but increasing number of evidence suggests that glutamate transporters [excitatory amino acid transporters (EAATs)] are the main route by which GSH precursors may enter the cell. In this study, we report that dopamine (DA) neurons, which express the excitatory amino acid carrier 1, are preferentially affected by EAAT dysfunction when compared with non-DA neurons. In rat embryonic mesencephalic cultures, l -trans-pyrrolidine-2,4-dicarboxylate, a substrate inhibitor of EAATs, is directly and preferentially toxic for DA neurons by decreasing the availability of GSH precursors and lowering their resistance threshold to glutamate excitotoxicity through NMDA-receptors. In adult rat, acute intranigral injection of l -trans-pyrrolidine-2,4-dicarboxylate induces a large regionally selective and dose-dependent loss of DA neurons and ,-synuclein aggregate formation. These data highlight for the first time the importance of excitatory amino acid carrier 1 function for the maintenance of antioxidant defense in DA neurons and suggest its dysfunction as a candidate mechanism for the selective death of DA neurons such as occurring in Parkinson's disease. [source]

Loss of metabotropic glutamate receptor-mediated regulation of glutamate transport in chemically activated astrocytes in a rat model of amyotrophic lateral sclerosis

JOURNAL OF NEUROCHEMISTRY, Issue 3 2006
Céline Vermeiren
Abstract Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by a selective loss of motor neurones accompanied by intense gliosis in lesioned areas of the brain and spinal cord. Glutamate-mediated excitotoxicity resulting from impaired astroglial uptake constitutes one of the current pathophysiological hypotheses explaining the progression of the disease. In this study, we examined the regulation of glutamate transporters by type 5 metabotropic glutamate receptor (mGluR5) in activated astrocytes derived from transgenic rats carrying an ALS-related mutated human superoxide dismutase 1 (hSOD1G93A) transgene. Cells from transgenic animals and wild-type littermates showed similar expression of glutamate,aspartate transporter and glutamate transporter 1 (GLT-1) after in vitro activation, whereas cells carrying the hSOD1 mutation showed a three-fold higher expression of functional mGluR5, as observed in the spinal cord of end-stage animals. In cells from wild-type animals, (S)-3,5-dihydroxyphenylglycine (DHPG) caused an immediate protein kinase C (PKC)-dependent up-regulation of aspartate uptake that reflected the activation of GLT-1. Although this effect was mimicked in both cultures by direct activation of PKC using phorbol myristate acetate, DHPG failed to up-regulate aspartate uptake in cells derived from the transgenic rats. The failure of activated mGluR5 to increase glutamate uptake in astrocytes derived from this animal model of ALS supports the theory of glutamate excitotoxicity in the pathogenesis of the disease. [source]

Neuroprotection by stem cell factor in rat cortical neurons involves AKT and NF,B

JOURNAL OF NEUROCHEMISTRY, Issue 1 2005
Krishnan M. Dhandapani
Abstract Stem cell factor (SCF) is a highly expressed cytokine in the central nervous system. In the present study, we demonstrate a neuroprotective role for SCF and its tyrosine kinase receptor, c-kit, against camptothecin-induced apoptosis and glutamate excitotoxicity in rat cortical neurons. This protection was blocked by pharmacological or molecular inhibition of either the MEK/ERK or PI3K/Akt signaling pathways. The importance of these pathways was further confirmed by the activation of both ERK, in a MEK-dependent manner, and Akt, via PI3K. Activation of Akt increased the binding of the p50 and p65 subunits of NF,B, which was also important for neuroprotection. Akt inhibition prevented NF,B binding, suggesting a role for Akt in SCF-induced NF,B. Pharmacological inhibition of NF,B or dominant negative I,B also prevented neuroprotection by SCF. SCF up-regulated the anti-apoptotic genes, bcl-2 and bcl-xL in an NF,B-dependent manner. Together, these findings demonstrate a neuroprotective role for SCF in cortical neurons, an effect that was mediated by Akt and ERK, as well as NF,B-mediated gene transcription. SCF represents a novel therapeutic target in the treatment of neurodegenerative disease. [source]

Heregulin upregulates the expression of nitric oxide synthase (NOS)-1 in rat cerebellar granule neurons via the ErbB4 receptor

JOURNAL OF NEUROCHEMISTRY, Issue 1 2001
Randy Krainock
Heregulin plays key roles in regulating cell number, determining fate and establishing pattern in the developing nervous system via specific receptors (ErbBs), including ErbB4. Two recent reports have shown that ErbB4 forms a complex with postsynaptic density proteins, which are, in turn, known to complex with nitric oxide synthase (NOS)-1. To reveal whether heregulin might regulate the expression of NOS-1, cultures enriched in cerebellar granule cells were exposed to heregulin for 72 h. This treatment resulted in an increase in NOS-1 protein (> 70%), an effect mediated by the ErbB4 receptor. While nitric oxide might mediate some of the downstream effects of heregulin in the nervous system, heregulin treatment neither enhanced granule cell survival, nor protected neurons from acute glutamate excitotoxicity. [source]

Bioenergetics of mitochondria in cultured neurons and their role in glutamate excitotoxicity

JOURNAL OF NEUROSCIENCE RESEARCH, Issue 15 2007
David G. Nicholls
Abstract The pathologic activation of NMDA receptors by glutamate is a major contributor to neuronal cell death after stroke. Receptor activation causes a massive influx of calcium into the neuron that is accumulated by the mitochondria. The favored hypothesis is that the calcium loaded mitochondria generate reactive oxygen species that damage and ultimately killed the neuron. In this review this hypothesis is critically re-examined with an emphasis on the role played by deficits in ATP generation. Novel techniques are developed to monitor the bioenergetic status of in situ mitochondria in cultured neurons. Applying these techniques to a model of glutamate excitotoxicity suggests that enhanced reactive oxygen species are a consequence rather than a cause of failed cytoplasmic calcium homeostasis (delayed calcium deregulation, [DCD]), but that prior oxidative damage facilitates DCD by damaging mitochondrial ATP generation. This impacts on current hypotheses relating to the neuroprotective effects of mild mitochondrial uncoupling. © 2007 Wiley-Liss, Inc. [source]

Alterations of chaperone protein expression in presenilin mutant neurons in response to glutamate excitotoxicity

PATHOLOGY INTERNATIONAL, Issue 9 2002
Izumi Maezawa
Mutations in the presenilin-1 (PS1) gene underlie the most common form of familial dementia of the Alzheimer type (DAT). We demonstrated previously that the expression of PS1 with a M146V mutation in transgenic mice potentiates glutamate toxicity to neurons, due to an altered calcium homeostasis. Here, using a subtractive cDNA library approach, we report the identification of several genes, the altered expression of which may be associated with this unique PS1 -related vulnerability to glutamate. The identified genes, including chaperonin subunit 2 and nucleophosmin 1/B23, are involved in the intracellular trafficking of proteins and ions. Northern blot analysis revealed that the effect of glutamate on calcium-binding proteins was augmented in neurons from PS1 mutation mice, compared with neurons from mice lacking other genes relevant to the pathogenesis of DAT (FE65 and APOE) or neurons from control wild-type mice. Interestingly, mRNA for two chaperone proteins were expressed at lower levels specifically in neurons from PS1 mutant mice. These findings suggest that PS1 mutations may, in part, contribute to the development of DAT via altered expression of chaperone proteins. [source]

Enhancing Intrinsic Cochlear Stress Defenses to Reduce Noise-Induced Hearing Loss,,§

THE LARYNGOSCOPE, Issue 9 2002
Richard D. Kopke COL MC USA
Abstract Objectives/Hypothesis Oxidative stress plays a substantial role in the genesis of noise-induced cochlear injury that causes permanent hearing loss. We present the results of three different approaches to enhance intrinsic cochlear defense mechanisms against oxidative stress. This article explores, through the following set of hypotheses, some of the postulated causes of noise-induced cochlear oxidative stress (NICOS) and how noise-induced cochlear damage may be reduced pharmacologically. 1) NICOS is in part related to defects in mitochondrial bioenergetics and biogenesis. Therefore, NICOS can be reduced by acetyl-L carnitine (ALCAR), an endogenous mitochondrial membrane compound that helps maintain mitochondrial bioenergetics and biogenesis in the face of oxidative stress. 2) A contributing factor in NICOS injury is glutamate excitotoxicity, which can be reduced by antagonizing the action of cochlear N -methyl-D-aspartate (NMDA) receptors using carbamathione, which acts as a glutamate antagonist. 3) Noise-induced hearing loss (NIHL) may be characterized as a cochlear-reduced glutathione (GSH) deficiency state; therefore, strategies to enhance cochlear GSH levels may reduce noise-induced cochlear injury. The objective of this study was to document the reduction in noise-induced hearing and hair cell loss, following application of ALCAR, carbamathione, and a GSH repletion drug D-methionine (MET), to a model of noise-induced hearing loss. Study Design This was a prospective, blinded observer study using the above-listed agents as modulators of the noise-induced cochlear injury response in the species chinchilla laniger. Methods Adult chinchilla laniger had baseline-hearing thresholds determined by auditory brainstem response (ABR) recording. The animals then received injections of saline or saline plus active experimental compound starting before and continuing after a 6-hour 105 dB SPL continuous 4-kHz octave band noise exposure. ABRs were obtained immediately after noise exposure and weekly for 3 weeks. After euthanization, cochlear hair cell counts were obtained and analyzed. Results ALCAR administration reduced noise-induced threshold shifts. Three weeks after noise exposure, no threshold shift at 2 to 4 kHz and <10 dB threshold shifts were seen at 6 to 8 kHz in ALCAR-treated animals compared with 30 to 35 dB in control animals. ALCAR treatment reduced both inner and outer hair cell loss. OHC loss averaged <10% for the 4- to 10-kHz region in ALCAR-treated animals and 60% in saline-injected-noise-exposed control animals. Noise-induced threshold shifts were also reduced in carbamathione-treated animals. At 3 weeks, threshold shifts averaged 15 dB or less at all frequencies in treated animals and 30 to 35 dB in control animals. Averaged OHC losses were 30% to 40% in carbamathione-treated animals and 60% in control animals. IHC losses were 5% in the 4- to 10-kHz region in treated animals and 10% to 20% in control animals. MET administration reduced noise-induced threshold shifts. ANOVA revealed a significant difference (P <.001). Mean OHC and IHC losses were also significantly reduced (P <.001). Conclusions These data lend further support to the growing body of evidence that oxidative stress, generated in part by glutamate excitotoxicity, impaired mitochondrial function and GSH depletion causes cochlear injury induced by noise. Enhancing the cellular oxidative stress defense pathways in the cochlea eliminates noise-induced cochlear injury. The data also suggest strategies for therapeutic intervention to reduce NIHL clinically. [source]

Current hypotheses for the underlying biology of amyotrophic lateral sclerosis,

ANNALS OF NEUROLOGY, Issue S1 2009
Jeffrey D. Rothstein MD
The mechanisms involved in selective motor neuron degeneration in amyotrophic lateral sclerosis remain unknown more than 135 years after the disease was first described. Although most cases have no known cause, mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1) have been implicated in a fraction of familial cases of the disease. Transgenic mouse models with mutations in the SOD1 gene and other ALS genes develop pathology reminiscent of the disorder, including progressive death of motor neurons, and have provided insight into the pathogenesis of the disease but have consistently failed to predict therapeutic efficacy in humans. However, emerging research has demonstrated that mutations and pathology associated with the TDP-43 gene and protein may be more common than SOD1 mutations in familial and sporadic ALS. Putative mechanisms of toxicity targeting motor neurons include oxidative damage, accumulation of intracellular aggregates, mitochondrial dysfunction, defects in axonal transport, growth factor deficiency, aberrant RNA metabolism, glial cell pathology, and glutamate excitotoxicity. Convergence of these pathways is likely to mediate disease onset and progression. Ann Neurol 2009;65 (suppl):S3,S9 [source]

Managing amyotrophic lateral sclerosis: Slowing disease progression and improving patient quality of life,

ANNALS OF NEUROLOGY, Issue S1 2009
Benjamin Rix Brooks MD
It is now possible to slow the disease progression of amyotrophic lateral sclerosis (ALS), but documented improvement in the quality of life of ALS patients has been difficult to quantitate. Putative mechanisms involved in motor neuron degeneration in ALS include oxidative damage, mitochondrial dysfunction, neuroinflammation, growth factor deficiency, and glutamate excitotoxicity. Several pharmacological agents that target these potential targets have demonstrated therapeutic potential in animal models with mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). Many treatments that have been moderately effective in this animal model have not been successfully translated into effective treatments for humans with ALS. Only the glutamate modulator riluzole has demonstrated efficacy in clinical trials and is approved for treating ALS. Combination treatments may represent a potential therapeutic strategy to more robustly prolong life and preserve function, but only vitamin E with riluzole has been formally studied in clinical trials, and to date, no combination treatments have been found to be more effective than currently available single agents. Ann Neurol 2009;65 (suppl):S17,S23 [source]

Glutamate receptors on myelinated spinal cord axons: I. GluR6 kainate receptors,

ANNALS OF NEUROLOGY, Issue 2 2009
Mohamed Ouardouz PhD
Objective The deleterious effects of glutamate excitotoxicity are well described for central nervous system gray matter. Although overactivation of glutamate receptors also contributes to axonal injury, the mechanisms are poorly understood. Our goal was to elucidate the mechanisms of kainate receptor,dependent axonal Ca2+ deregulation. Methods Dorsal column axons were loaded with a Ca2+ indicator and imaged in vitro using confocal laser-scanning microscopy. Results Activation of glutamate receptor 6 (GluR6) kainate receptors promoted a substantial increase in axonal [Ca2+]. This Ca2+ accumulation was due not only to influx from the extracellular space, but a significant component originated from ryanodine-dependent intracellular stores, which, in turn, depended on activation of L-type Ca2+ channels: ryanodine, nimodipine, or nifedipine blocked the agonist-induced Ca2+ increase. Also, GluR6 stimulation induced intraaxonal production of nitric oxide (NO), which greatly enhanced the Ca2+ response: quenching of NO with intraaxonal (but not extracellular) scavengers, or inhibition of neuronal NO synthase with intraaxonal N,-nitro-L-arginine methyl ester, blocked the Ca2+ increase. Loading axons with a peptide that mimics the C-terminal PDZ binding sequence of GluR6, thus interfering with the coupling of GluR6 to downstream effectors, greatly reduced the agonist-induced axonal Ca2+ increase. Immunohistochemistry showed GluR6/7 clusters on the axolemma colocalized with neuronal NO synthase and Cav1.2. Interpretation Myelinated spinal axons express functional GluR6-containing kainate receptors, forming part of novel signaling complexes reminiscent of postsynaptic membranes of glutamatergic synapses. The ability of such axonal "nanocomplexes" to release toxic amounts of Ca2+ may represent a key mechanism of axonal degeneration in disorders such as multiple sclerosis where abnormal accumulation of glutamate and NO are known to occur. Ann Neurol 2009 [source]