Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Aspartate

  • acetyl aspartate
  • n-acetyl aspartate

  • Terms modified by Aspartate

  • aspartate amino transferase
  • aspartate aminotransferase
  • aspartate aminotransferase activity
  • aspartate aminotransferase level
  • aspartate level
  • aspartate receptor
  • aspartate residue
  • aspartate transaminase
  • aspartate transferase

  • Selected Abstracts

    Reduction in glutamate uptake is associated with extrasynaptic NMDA and metabotropic glutamate receptor activation at the hippocampal CA1 synapse of aged rats

    AGING CELL, Issue 5 2010
    Brigitte Potier
    Summary This study aims to determine whether the regulation of extracellular glutamate is altered during aging and its possible consequences on synaptic transmission and plasticity. A decrease in the expression of the glial glutamate transporters GLAST and GLT-1 and reduced glutamate uptake occur in the aged (24,27 months) Sprague,Dawley rat hippocampus. Glutamatergic excitatory postsynaptic potentials recorded extracellularly in ex vivo hippocampal slices from adult (3,5 months) and aged rats are depressed by DL-TBOA, an inhibitor of glutamate transporter activity, in an N -Methyl- d- Aspartate (NMDA)-receptor-dependent manner. In aged but not in young rats, part of the depressing effect of DL-TBOA also involves metabotropic glutamate receptor (mGluRs) activation as it is significantly reduced by the specific mGluR antagonist d-methyl-4-carboxy-phenylglycine (MCPG). The paired-pulse facilitation ratio, a functional index of glutamate release, is reduced by MCPG in aged slices to a level comparable to that in young rats both under control conditions and after being enhanced by DL-TBOA. These results suggest that the age-associated glutamate uptake deficiency favors presynaptic mGluR activation that lowers glutamate release. In parallel, 2 Hz-induced long-term depression is significantly decreased in aged animals and is fully restored by MCPG. All these data indicate a facilitated activation of extrasynaptic NMDAR and mGluRs in aged rats, possibly because of an altered distribution of glutamate in the extrasynaptic space. This in turn affects synaptic transmission and plasticity within the aged hippocampal CA1 network. [source]

    Transport characteristics of N -acetyl- l -aspartate in rat astrocytes: involvement of sodium-coupled high-affinity carboxylate transporter NaC3/NaDC3-mediated transport system

    Takuya Fujita
    Abstract We investigated in the present study the transport characteristics of N -acetyl- l -aspartate in primary cultures of astrocytes from rat cerebral cortex and the involvement of NA+ -coupled high-affinity carboxylate transporter NaC3 (formerly known as NaDC3) responsible for N -acetyl- l -aspartate transport. N -acetyl- l -aspartate transport was NA+ -dependent and saturable with a Michaelis,Menten constant (Km) of ,110 µm. NA+ -activation kinetics revealed that the NA+ to- N -acetyl- l -aspartate stoichiometry was 3 : 1 and concentration of Na+ necessary for half-maximal transport (KNAm) was 70 mm. NA+ -dependent N -acetyl- l -aspartate transport was competitively inhibited by succinate with an inhibitory constant (Ki) of 14.7 µm, which was comparable to the Km value of NA+ -dependent succinate transport (29.4 µm). l -Aspartate also inhibited NA+ -dependent [14C]N -acetyl- l -aspartate transport with relatively low affinity (Ki = 2.2 mm), whereas N -acetyl- l -aspartate was not able to inhibit NA+ -dependent aspartate transport in astrocytes. In addition, Li+ was found to have a significant inhibitory effect on the NA+ -dependent N -acetyl- l -aspartate transport in a concentration-dependent manner. Furthermore, RT,PCR and western blot analyses revealed that NaC3 is expressed in primary cultures of astrocytes. Taken collectively, these results indicate that NaC3 expressed in rat cerebrocortical astrocytes is responsible for NA+ -dependent N -acetyl- l -aspartate transport. This transporter is likely to be an essential prerequisite for the metabolic role of N -acetyl- l -aspartate in the process of myelination. [source]

    How does photorespiration modulate leaf amino acid contents?

    PLANT CELL & ENVIRONMENT, Issue 7 2002
    A dual approach through modelling, metabolite analysis
    Abstract The aim of this work was to establish the quantitative impact of photorespiration on leaf amino acid contents. Attached leaves of wheat and potato were incubated for 30,40 min under defined conditions in which net CO2 uptake (A) was manipulated by irradiance, ambient CO2 or ambient O2. The incubated portion of the leaf was sampled by a rapid-quench method and photorespiratory flux (vo) was modelled from the measured rate of net CO2 uptake. In both wheat and potato, the ratio between glycine and serine showed a strong positive correlation with vo. Aspartate and alanine correlated negatively with vo but glutamate and glutamine showed less clear relationships. In potato, glutamate and glutamine did not correlate clearly with either A or vo. In wheat, glutamine showed a general increase with A but no relationship with vo, whereas 2-oxoglutarate contents correlated positively with vo and negatively with A. As a result, glutamine : glutamate and glutamine : 2-oxoglutarate increased with net CO2 uptake in wheat, observations that are attributed primarily to imperfect and variable coupling between the supply of NH3 in primary nitrogen assimilation and the associated delivery of 2-oxoglutarate to the chloroplast. A simple theoretical analysis is used to illustrate the potentially marked impact of primary nitrogen assimilation on leaf glutamine, even against a background of high rates of photorespiratory ammonia recycling. [source]

    Integrin ,IIb,3:ligand interactions are linked to binding-site remodeling

    PROTEIN SCIENCE, Issue 8 2006
    Roy R. Hantgan
    Abstract This study tested the hypothesis that high-affinity binding of macromolecular ligands to the ,IIb,3 integrin is tightly coupled to binding-site remodeling, an induced-fit process that shifts a conformational equilibrium from a resting toward an open receptor. Interactions between ,IIb,3 and two model ligands,echistatin, a 6-kDa recombinant protein with an RGD integrin-targeting sequence, and fibrinogen's ,-module, a 30-kDa recombinant protein with a KQAGDV integrin binding site,were measured by sedimentation velocity, fluorescence anisotropy, and a solid-phase binding assay, and modeled by molecular graphics. Studying echistatin variants (R24A, R24K, D26A, D26E, D27W, D27F), we found that electrostatic contacts with charged residues at the ,IIb/,3 interface, rather than nonpolar contacts, perturb the conformation of the resting integrin. Aspartate 26, which interacts with the nearby MIDAS cation, was essential for binding, as D26A and D26E were inactive. In contrast, R24K was fully and R24A partly active, indicating that the positively charged arginine 24 contributes to, but is not required for, integrin recognition. Moreover, we demonstrated that priming,i.e., ectodomain conformational changes and oligomerization induced by incubation at 35°C with the ligand-mimetic peptide cHarGD,promotes complex formation with fibrinogen's ,-module. We also observed that the ,-module's flexible carboxy terminus was not required for ,IIb,3 integrin binding. Our studies differentiate priming ligands, which bind to the resting receptor and perturb its conformation, from regulated ligands, where binding-site remodeling must first occur. Echistatin's binding energy is sufficient to rearrange the subunit interface, but regulated ligands like fibrinogen must rely on priming to overcome conformational barriers. [source]

    Critical catalytic functional groups in the mechanism of aspartate-,-semialdehyde dehydrogenase

    Julio Blanco
    Aspartate-,-semialdehyde dehydrogenase (ASADH) catalyzes the reductive dephosphorylation of ,-aspartyl phosphate to l -aspartate-,-semialdehyde in the aspartate biosynthetic pathway. This pathway is not found in humans or other eukaryotic organisms, yet is required for the production of threonine, isoleucine, methionine and lysine in most microorganisms. The mechanism of this enzyme has been examined through the structures of two active-site mutants of ASADH from Haemophilus influenzae. Replacement of the enzyme active-site cysteine with serine (C136S) leads to a dramatic loss of catalytic activity caused by the expected decrease in nucleophilicity, but also by a change in the orientation of the serine hydroxyl group relative to the cysteine thiolate. In contrast, in the H277N active-site mutant the introduced amide is oriented in virtually the same position as that of the histidine imidazole ring. However, a shift in the position of the bound reaction intermediate to accommodate this shorter asparagine side chain, coupled with the inability of this introduced amide to serve as a proton acceptor, results in a 100-fold decrease in the catalytic efficiency of H277N relative to the native enzyme. These mutant enzymes have the same overall fold and high structural identity to native ASADH. However, small perturbations in the positioning of essential catalytic groups or reactive intermediates have dramatic effects on catalytic efficiency. [source]

    HPLC determination of acidic d -amino acids and their N -methyl derivatives in biological tissues

    Mara Tsesarskaia
    Abstract d -Aspartate (d -Asp) and N -methyl- d -aspartate (NMDA) occur in the neuroendocrine systems of vertebrates and invertebrates, where they play a role in hormone release and synthesis, neurotransmission, and memory and learning. N -methyl- d -glutamate (NMDG) has also been detected in marine bivalves. Several methods have been used to detect these amino acids, but they require pretreatment of tissue samples with o -phthaldialdehyde (OPA) to remove primary amino acids that interfere with the detection of NMDA and NMDG. We report here a one-step derivatization procedure with the chiral reagent N-, -(5-fluoro-2,4-dinitrophenyl)-(d or l)-valine amide, FDNP-Val-NH2, a close analog of Marfey's reagent but with better resolution and higher molar absorptivity. The diastereomers formed were separated by HPLC on an ODS-Hypersil column eluted with TFA/water,TFA/MeCN. UV absorption at 340 nm permitted detection levels as low as 5,10 pmol. d -Asp, NMDA and NMDG peaks were not obscured by other primary or secondary amino acids; hence pretreatment of tissues with OPA was not required. This method is highly reliable and fast (less than 40 min HPLC run). Using this method, we detected d -Asp, NMDA and NMDG in several biological tissues (octopus brain, optical lobe and bucchal mass; foot and mantle of the mollusk Scapharca broughtonii), confirming the results of other researchers. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Novel Enantioselective Receptors for N-Protected Glutamate and Aspartate

    Andrea Ragusa
    Abstract A series of chiral bisthiourea macrocycles 1,4 have been prepared and their binding properties with various dicarboxylate salts have been examined by using NMR titration and isothermal calorimetry experiments. Macrocycle 1, in particular, favours the 1:1 binding of N-protected L -glutamate and aspartate, but favours 1:2 binding of the corresponding D -amino acids in polar solvents (dimethyl sulfoxide and acetonitrile). The macrocycles, however, do not bind carboxylates at all in the less competitive solvent chloroform. The binding properties of these macrocyles are sensitive to small structural changes as demonstrated by the altered binding properties of macrocycles 2,4 compared with 1. [source]

    Blockade of the central generator of locomotor rhythm by noncompetitive NMDA receptor antagonists in Drosophila larvae

    Daniel Cattaert
    Abstract The noncompetitive antagonists of the vertebrate N -methyl- D -aspartate (NMDA) receptor dizocilpine (MK 801) and phencyclidine (PCP), delivered in food, were found to induce a marked and reversible inhibition of locomotor activity in Drosophilamelanogaster larvae. To determine the site of action of these antagonists, we used an in vitro preparation of the Drosophila third-instar larva, preserving the central nervous system and segmental nerves with their connections to muscle fibers of the body wall. Intracellular recordings were made from ventral muscle fibers 6 and 7 in the abdominal segments. In most larvae, long-lasting (>1 h) spontaneous rhythmic motor activities were recorded in the absence of pharmacological activation. After sectioning of the connections between the brain and abdominal ganglia, the rhythm disappeared, but it could be partially restored by perfusing the muscarinic agonist oxotremorine, indicating that the activity was generated in the ventral nerve cord. MK 801 and PCP rapidly and efficiently inhibited the locomotor rhythm in a dose-dependent manner, the rhythm being totally blocked in 2 min with doses over 0.1 mg/mL. In contrast, more hydrophilic competitive NMDA antagonists had no effect on the motor rhythm in this preparation. MK 801 did not affect neuromuscular glutamatergic transmission at similar doses, as demonstrated by monitoring the responses elicited by electrical stimulation of the motor nerve or pressure applied glutamate. The presence of oxotremorine did not prevent the blocking effect of MK 801. These results show that MK 801 and PCP specifically inhibit centrally generated rhythmic activity in Drosophila, and suggest a possible role for NMDA-like receptors in locomotor rhythm control in the insect CNS. © 2001 John Wiley & Sons, Inc. J Neurobiol 48: 58,73, 2001 [source]

    High-sensitivity detection of biological amines using fast Hadamard transform CE coupled with photolytic optical gating

    ELECTROPHORESIS, Issue 17 2007
    Kevin L. Braun
    Abstract Here, we report the first utilization of Hadamard transform CE (HTCE), a high-sensitivity, multiplexed CE technique, with photolytic optical gating sample injection of caged fluorescent labels for the detection of biologically important amines. Previous implementations of HTCE have relied upon photobleaching optical gating sample injection of fluorescent dyes. Photolysis of caged fluorescent labels reduces the fluorescence background, providing marked enhancements in sensitivity compared to photobleaching. Application of fast Hadamard transform CE (fHTCE) for fluorescein-based dyes yields a ten-fold higher sensitivity for photolytic injections compared to photobleaching injections, due primarily to the reduced fluorescent background provided by caged fluorescent dyes. Detection limits as low as 5,pM (ca. 18,molecules per injection event) were obtained with on-column LIF detection using fHTCE in less than 25,s, with the capacity for continuous, online separations. Detection limits for glutamate and aspartate below 150,pM (1,2,amol/injection event) were obtained using photolytic sample injection, with separation efficiencies exceeding 1×106,plates/m and total multiplexed separation times as low as 8,s. These results strongly support the feasibility of this approach for high-sensitivity dynamic chemical monitoring applications. [source]

    Determination of amino acids in rat vitreous perfusates by capillary electrophoresis

    ELECTROPHORESIS, Issue 17 2004
    Kongthong Thongkhao-On
    Abstract In vivo determinations of amino acids are important for improving our understanding of physiological states of biological tissue function and dysfunction. However, the chemically complex matrix of different biological fluids complicates the assay of this important class of molecules. We introduce a method for characterizing the amino acid composition of submicroliter volumes of vitreous humor perfusates. Low-flow push-pull perfusion sampling is compatible with collecting small volume samples in a complicated matrix that are potentially difficult to separate. An efficient, sensitive, and rapid analysis of amino acids from in vivo perfusates of the vitreous is presented with 3-(4-carboxybenzoyl)-2-quinoline-carboxaldehyde (CBQCA) derivatitation and capillary electrophoresis (CE) separation with laser-induced fluorescence detection (LIF). Derivatization with CBQCA for up to 2 h provided high sensitivity and low detection limits at the nM level. Seventeen amino acids including D -serine (D -Ser) and D -aspartate (D -Asp) were resolved in less than 10 min. Importantly, D -Ser is separated from its enantiomeric pair. Characterization of vitreal amino acids with this assay technique will be useful for understanding ocular diseases and physiological mechanisms in vision. [source]

    In vivo simultaneous monitoring of ,-aminobutyric acid, glutamate, and L -aspartate using brain microdialysis and capillary electrophoresis with laser-induced fluorescence detection: Analytical developments and in vitro/in vivo validations

    ELECTROPHORESIS, Issue 18 2003
    Valérie Sauvinet
    Abstract ,-Aminobutyric acid (GABA), glutamate (Glu), and L -aspartate (L -Asp) are three major amino acid neurotransmitters in the central nervous system. In this work, a method for the separation of these three neurotransmitters in brain microdialysis samples using a commercially available capillary electrophoresis (CE) system has been developed. Molecules were tagged on their primary amine function with the fluorogene agent naphthalene-2,3-dicarboxaldehyde (NDA), and, after separation by micellar electrokinetic chromatography, were detected by laser-induced fluorescence using a 442 nm helium-cadmium laser. The separation conditions for the analysis of derivatized neurotransmitters in standard solutions and microdialysates have been optimized, and this method has been validated on both pharmacological and analytical basis. The separation of GABA, Glu, and L -Asp takes less than 10 min by using a 75 mmol/L borate buffer, pH 9.2, containing 70 mmol/L SDS and 10 mmol/L hydroxypropyl-,-cyclodextrin and +,25 kV voltage. The detection limits were 3, 15 nmol/L and, 5 nmol/L for GABA, Glu, and L -Asp, respectively. Moreover, submicroliter samples can be analyzed. This method allows a simple, rapid and accurate measurement of the three amino acid neurotransmitters for the in vivo brain monitoring using microdialysis sampling. [source]

    On-line biosensors for simultaneous determination of glucose, choline, and glutamate integrated with a microseparation system

    ELECTROPHORESIS, Issue 18 2003
    Guoyue Shi
    Abstract An effective microseparation system integrated with ring-disc electrodes and two microfluidic devices was fabricated for in vivo determination using a microdialysis pump. The major interference of ascorbic acid (AA) was excluded by direct oxidation with ascorbate oxidase. Glucose, glutamate, and choline were successfully determined simultaneously through the biosensors modified with a bilayer of osmium-poly(4-vinylpyridine)gel-horseradish peroxidase (Os-gel-HRP)/glucose oxidase (GOD), glutamate oxidase (GlutaOD) or choline oxidase (ChOD). To stabilize the biosensors, 0.2% polyethylenimine (PEI) was mixed with the oxidases. The cathodic currents of glucose, glutamate, and choline biosensors started to increase after the standard solutions were injected into the microseparation system. The on-line biosensors show a wide calibration range (10,7,10,5 mol/L) with a detection limit of 10,8 mol/L at the working potential of ,50 mV. The variations of glucose, glutamate, and choline were determined simultaneously in a free moving rat when we perfused the medial frontal cortex with 100 ,mol/L N -methyl- D -aspartate (NMDA) solution, which is the agonist of the NMDA receptor. [source]

    A high-throughput on-line microdialysis-capillary assay for D -serine

    ELECTROPHORESIS, Issue 7-8 2003
    Kylie B. O'Brien
    Abstract A high-throughput method is described for the analysis of D -serine and other neurotransmitters in tissue homogenates. Analysis is performed by microdialysis-capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection in a sheath flow detection cell. Sample pretreatment is not required as microdialysis sampling excludes proteins and cell fragments. Primary amines are derivatized on-line with o -phthaldialdehyde (OPA) in the presence of ,-mercaptoethanol followed by on-line CE-LIF analysis. Under the separation conditions described here, D -serine is resolved from L -serine and other primary amines commonly found in biological samples. Each separation requires less than 22 s. Eliminating the need for sample pretreatment and performing the high-speed CE analysis on-line significantly reduces the time required for D -serine analysis when compared with traditional methods. This method has been used to quantify D -serine levels in larval tiger salamander retinal homogenates, as well as dopamine, ,-amino- n -butyric acid (GABA), glutamate and L -aspartate. D -serine release from an intact retina was also detected. [source]

    Perinatal exposure to bisphenol-A changes N -methyl- D -aspartate receptor expression in the hippocampus of male rat offspring

    Xiao-Hong Xu
    Abstract Bisphenol-A (BPA) is one of the most common environmental endocrine disrupters with mixed estrogen agonist/antagonist properties. The toxicity of BPA has been extensively evaluated in a variety of tests in rodents, including developmental and reproductive toxicity, and carcinogenicity. The objective of the present study is to evaluate whether or not perinatal maternal exposure to BPA at 0.05, 0.5, 5, 50, and 200 mg/kg/d affects N -methyl- D -aspartate (NMDA) receptor (NMDAR) subunits NR1, NR2A, 2B, estrogen receptor beta (ER,), and aromatase cytochrome P450 (P450arom) protein expressions of hippocampus in male rat offspring during postnatal development. Western-blotting analyses showed that perinatal exposure to BPA significantly affected the expression of NMDAR subunits. At the lower doses of 0.05 to 50 mg/kg/d, BPA concentration dependently inhibited the expression of NMDAR subunits. However, at the higher dose (200 mg/kg/d), the effects of BPA on these subunits were different, with a stronger inhibition of NR1 expression and a slighter inhibition of NR2A, 2B expression when compared with those at the lower dosage of BPA. In addition, perinatal exposure to BPA inhibited the expression of ER, protein, but increased P450arom protein expression in a concentration-dependent manner, especially during the early postnatal period (the first 1,3 postnatal weeks). No significant influence of BPA on P450arom was observed at postnatal week 8. These data suggest that environmental BPA exposure may affect the development of the brain, enhancing the local biosynthesis of estrogen in the brain, inhibiting ER, and NMDAR expressions. Environ. Toxicol. Chem. 2010;29:176,181. © 2009 SETAC [source]

    Deletions in 16p13 including GRIN2A in patients with intellectual disability, various dysmorphic features, and seizure disorders of the rolandic region

    EPILEPSIA, Issue 9 2010
    Constanze Reutlinger
    Summary Seizure disorders of the rolandic region comprise a spectrum of different epilepsy syndromes ranging from benign rolandic epilepsy to more severe seizure disorders including atypical benign partial epilepsy/pseudo-Lennox syndrome, electrical status epilepticus during sleep, and Landau-Kleffner syndrome. Centrotemporal spikes are the unifying electroencephalographic hallmark of these benign focal epilepsies, indicating a pathophysiologic relationship between the various epilepsies arising from the rolandic region. The etiology of these epilepsies is elusive, but a genetic component is assumed given the heritability of the characteristic electrographic trait. Herein we report on three patients with intellectual disability, various dysmorphic features, and epilepsies involving the rolandic region, carrying previously undescribed deletions in 16p13. The only gene located in the critical region shared by all three patients is GRIN2A coding for the alpha-2 subunit of the neuronal N -methyl- d -aspartate (NMDA) receptor. [source]

    Model of cryptogenic infantile spasms after prenatal corticosteroid priming

    EPILEPSIA, Issue 2010
    Libor Velí
    Summary Infantile spasms (IS) is a devastating epilepsy syndrome of childhood. IS occurs in 3,12-month-old infants and is characterized by spasms, interictal electroencephalography (EEG) hypsarrhythmia, and profound mental retardation. Hormonal therapy [adrenocorticotropic hormone (ACTH), corticosteroids] is frequently used, but its efficacy is tainted by severe side effects. For research of novel therapies, a validated animal model of IS is required. We propose the model of spastic seizures triggered by N -methyl- d -aspartate (NMDA) in infant rats prenatally exposed to betamethasone. The spasms have remarkable similarity to human IS, including motor flexion spasms, ictal EEG electrodecrement, and responsiveness to ACTH. Interestingly, the spasms do not involve the hippocampus. Autoradiographic metabolic mapping as well as tagging of the areas of neuronal excitation with c-fos indicates a strong involvement of hypothalamic structures such as the arcuate nucleus, which has significant bilateral connections with other hypothalamic nuclei as well as with the brainstem. [source]

    Epileptiform synchronization in the cingulate cortex

    EPILEPSIA, Issue 3 2009
    Gabriella Panuccio
    Summary Purpose:, The anterior cingulate cortex (ACC),which plays a role in pain, emotions and behavior,can generate epileptic seizures. To date, little is known on the neuronal mechanisms leading to epileptiform synchronization in this structure. Therefore, we investigated the role of excitatory and inhibitory synaptic transmission in epileptiform activity in this cortical area. In addition, since the ACC presents with a high density of opioid receptors, we studied the effect of opioid agonism on epileptiform synchronization in this brain region. Methods:, We used field and intracellular recordings in conjunction with pharmacological manipulations to characterize the epileptiform activity generated by the rat ACC in a brain slice preparation. Results:, Bath-application of the convulsant 4-aminopyridine (4AP, 50 ,M) induced both brief and prolonged periods of epileptiform synchronization resembling interictal- and ictal-like discharges, respectively. Interictal events could occur more frequently before the onset of ictal activity that was contributed by N -methyl- d -aspartate (NMDA) receptors. Mu-opioid receptor activation abolished 4AP-induced ictal events and markedly reduced the occurrence of the pharmacologically isolated GABAergic synchronous potentials. Ictal discharges were replaced by interictal events during GABAergic antagonism; this GABA-independent activity was influenced by subsequent mu-opioid agonist application. Conclusions:, Our results indicate that both glutamatergic and GABAergic signaling contribute to epileptiform synchronization leading to the generation of electrographic ictal events in the ACC. In addition, mu-opioid receptors appear to modulate both excitatory and inhibitory mechanisms, thus influencing epileptiform synchronization in the ACC. [source]

    Electrical and Chemical Long-term Depression Do Not Attenuate Low-Mg2+,induced Epileptiform Activity in the Entorhinal Cortex

    EPILEPSIA, Issue 4 2005
    Jörg Solger
    Summary:,Purpose: Low-frequency electrical and magnetic stimulation of cortical brain regions has been shown to reduce cortical excitability and to decrease the susceptibility to seizures in humans and in vivo models of epilepsy. The induction of long-term depression (LTD) or depotentiation of a seizure-related long-term potentiation has been proposed to be part of the underlying mechanism. With the low-Mg2+ -model of epilepsy, this study investigated the effect of electrical LTD, chemical LTD, and depotentiation on the susceptibility of the entorhinal cortex to epileptiform activity. Methods: The experiments were performed on isolated entorhinal cortex slices obtained from adult Wistar rats and mice. With extracellular recording techniques, we studied whether LTD induced by (a) three episodes of low-frequency paired-pulse stimulation (3 × 900 paired pulses at 1 Hz), and by (b) bath-applied N -methyl- d -aspartate (NMDA, 20 ,M) changes time-to-onset, duration, and frequency of seizure-like events (SLEs) induced by omitting MgSO4 from the artificial cerebrospinal fluid. Next we investigated the consequences of depotentiation on SLEs themselves by applying low-frequency stimulation after onset of low-Mg2+,induced epileptiform activity. Results: LTD, induced either by low-frequency stimulation or by bath-applied NMDA, had no effect on time-to-onset, duration, and frequency of SLEs compared with unconditioned slices. Low-frequency stimulation after onset of SLEs did not suppress but induced SLEs that lasted for the time of stimulation and were associated with a simultaneous increase of the extracellular K+ concentration. Conclusions: Our study demonstrates that neither conditioning LTD nor brief low-frequency stimulation decreases the susceptibility of the entorhinal cortex to low-Mg2+,induced epileptiform activity. The present study does not support the hypothesis that low-frequency brain stimulation exerts its anticonvulsant effect via the induction of LTD or depotentiation. [source]

    Voltage-Dependent Block of N -Methyl- d -Aspartate Receptors by the Novel Anticonvulsant Dibenzylamine, a Bioactive Constituent of l -(+)-,-Hydroxybutyrate

    EPILEPSIA, Issue 10 2003
    Sean D. Donevan
    Summary:,Purpose: Previously we demonstrated that l -(+)-,-hydroxybutyrate (L-BHB), acetoacetate (ACA), acetone, and dibenzylamine (DBA) were anticonvulsant in an audiogenic seizure,susceptible model, and that DBA was a bioactive contaminant identified in commercial lots of L-BHB. In the present study, we asked whether these effects could be mediated by ionotropic glutamate or ,-aminobutyric acidA (GABAA) receptors. Methods: We studied the effects of both stereoisomers of BHB (as well as the racemate), ACA, and DBA on N -methyl- d -aspartate (NMDA), ,-amino-3-hydroxy-5methyl-4-isoxazole-proprionic acid (AMPA), and GABAA receptors in cultured rodent neocortical neurons by using whole-cell voltage-clamp recording techniques. Results: Only L-BHB and DBA exerted a concentration- and voltage-dependent block of NMDA-evoked currents, whereas none of the tested substrates affected AMPA- or GABA-activated currents. The kinetics of whole-cell block by L-BHB and DBA were similar, providing additional evidence that DBA is responsible for the anticonvulsant activity of L-BHB. Conclusions: BHB and ACA do not exert direct actions on GABAA or ionotropic glutamate receptors in cultured neocortical neurons. In addition, we provide additional evidence that DBA is responsible for the anticonvulsant activity of L-BHB, and that this action may be mediated in part by voltage-dependent blockade of NMDA receptors. [source]

    Epilepsy-induced Changes in Signaling Systems of Human and Rat Postsynaptic Densities

    EPILEPSIA, Issue 2 2003
    Ursula Wyneken
    Summary: ,Purpose: To study seizure-induced changes in signaling proteins present in postsynaptic densities (PSDs) isolated from human epileptic neocortex and from rat cortex in which seizures were induced by injection of kainic acid. Methods: We performed Western blot analysis of signaling proteins in PSDs isolated from cortical tissue. Results: Seizures induce a strong upregulation of TrkB, the receptor for brain-derived neurotrophic factor (BDNF), whereas components of the N -methyl- d -aspartate (NMDA)-receptor complex are downregulated in both human and rat PSDs. Conclusions: These data show that long-term changes in PSD composition occur as a consequence of epileptic seizure activity. [source]

    A Short-echo-time Proton Magnetic Resonance Spectroscopic Imaging Study of Temporal Lobe Epilepsy

    EPILEPSIA, Issue 9 2002
    Robert J. Simister
    Summary: ,Purpose: We used short-echo-time proton magnetic resonance spectroscopy imaging (MRSI) to study metabolite concentration variation through the temporal lobe in patients with temporal lobe epilepsy (TLE) with and without abnormal MRI. Methods: MRSI was performed at TE = 30 ms to study 10 control subjects, 10 patients with TLE and unilateral hippocampal sclerosis, and 10 patients with TLE and unremarkable MRI (MRI negative). We measured the concentrations of N -acetyl aspartate +N -acetyl aspartyl-glutamate (NAAt), creatine (Cr), choline (Cho), glutamate + glutamine (Glx), and myoinositol, in the anterior, middle, and posterior medial temporal lobe (MTL), and in the posterior lateral temporal lobe. Segmented volumetric T1 -weighted MRIs gave the tissue composition of each MRSI voxel. Normal ranges were defined as the control mean ± 3 SD. Results: In the hippocampal sclerosis group, seven of 10 had abnormally low NAAt in the ipsilateral anterior MTL. In the MRI-negative group, four of 10 had low NAAt in the middle MTL voxel ipsilateral to seizure onset. Metabolite ratios were less sensitive to abnormality than was the NAAt concentration. Group analysis showed low NAAt, Cr, and Cho in the anterior MTL in hippocampal sclerosis. Glx was elevated in the anterior voxel contralateral to seizure onset in the MRI-negative group. Metabolite concentrations were influenced by voxel position and tissue composition. Conclusions: (a) Low NAAt, Cr, and Cho were features of the anterior sclerotic hippocampus, whereas low NAAt was observed in the MRI-negative group in the middle MTL region. The posterior temporal lobe regions were not associated with significant metabolite abnormality; (b) The two patient groups demonstrated different metabolite profiles across the temporal lobe, with elevated Glx a feature of the MRI-negative group; and (c) Voxel tissue composition and position influenced obtained metabolite concentrations. [source]

    Low Concentration of DL-2-Amino-5-phosphonovalerate Induces Epileptiform Activity in Guinea Pig Hippocampal Slices

    EPILEPSIA, Issue 10 2001
    Ali Gorji
    Summary: , Purpose: The specific mechanisms by which low concentrations of cyclosporine induce seizures and low concentrations of phencyclidine provoke behavioral excitation remain to be elucidated. Both compounds block N -methyl- d -aspartate (NMDA) receptors. The aim of this study was to determine if low concentrations of the NMDA-receptor blockers increase the seizure susceptibility. Methods: Guinea pig hippocampal slices were exposed to artificial cerebrospinal fluid containing the NMDA blocker dl -2-amino-5-phosphono-valerate (APV; 0.1,10 ,M). Extracellular field potentials were recorded from CA1 and CA3 regions. Results: Low concentrations of APV induced epileptiform burst discharges (0.1,0.25 ,M), whereas higher doses failed to decrease the seizure threshold (1,10 ,M). Conclusions: The results indicate that the excitatory effect of low concentrations NMDA blockers may play a role in the neurotoxicity of aforementioned substances. [source]

    The Anticonvulsant SGB-017 (ADCI) Blocks Voltage-Gated Sodium Channels in Rat and Human Neurons: Comparison with Carbamazepine

    EPILEPSIA, Issue 3 2000
    Lucy Sun
    Summary: Purpose: SGB-017 (ADCI) is a novel anticonvul-sant that blocks both voltage-activated sodium channels and N -methyl- d -aspartate (NMDA)-receptor-gated channels. Results by Rogawski et al. suggested that SGB-017 produces its anticonvulsant action primarily by inhibition of NMDA-receptor channels. However, SGB-017 is effective in several animal models of epilepsy that are unresponsive to NMDA antagonists. These results indicate that block of NMDA-receptor channels is not the only mechanism contributing to its anticonvulsant activity. Thus the effects of SGB-017 on neu-ronal sodium channels were investigated. Methods: Whole cell voltage-clamp techniques were used to record sodium currents in freshly dissociated rat superior cervical ganglion (SCG) and hippocampal neurons and cultured human NT2 neurons. The effects of SGB-017 on the amplitude of sodium currents, elicited by a depolarizing pulse to 0 mV from different holding potentials, were measured and compared with those of carbamazepine (CBZ). Results: SGB-017 inhibited sodium currents in rat SCG and hippocampal neurons with a similar potency to CBZ. Like CBZ, the inhibition of sodium channels by SGB-017 was voltage dependent. Its median inhibitory concentration (IC50) for inhibition of sodium channels at depolarized holding potentials is similar to that for its inhibition of NMDA receptor channels. In human hNT2 neurons, SGB-017 was more potent than CBZ at inhibiting sodium currents. Conclusions: SGB-017 produces its anticonvulsant activity by blocking both sodium- and NMDA-receptor channels in a voltage- and use-dependent manner. The combination of these two mechanisms of action makes SGB-017 an effective AED in several different animal models of epilepsy. [source]

    Neuropsychiatric disturbances in SLE are associated with antibodies against NMDA receptors

    R. Omdal
    To determine whether neuropsychiatric manifestations in patients with systemic lupus erythematosus (SLE) are influenced by antibodies against the human N-methyl- d -aspartate (NMDA) receptor types NR2a or NR2b. A decapeptide was synthesized containing a sequence motif present in the extracellular ligand-binding domain of NMDA receptors NR2a and NR2b, bound by the monoclonal murine anti-DNA antibody R4A. In an ELISA with the murine monoclonal R4v as positive control, plasma samples of 57 patients with SLE were examined for the anti-peptide (anti-NR2) antibody after the patients had been subjected to comprehensive psychological and cognitive testing. Poor performance on the Visual Paired Associates test (immediate), the Grooved Pegboard test, as well as high scores on the Beck Depression Inventory, and scales D-2 (depression), Pd-4 (psychopathic deviate), Sc-8 (schizophrenia), and Ma-9 (hypomania) of the MMPI-2 were significantly associated with elevated levels of anti-NR2 antibodies. The findings in several domains indicate an association between anti-NR2 antibodies and depressed mood in addition to decreased short-time memory and learning. Antibodies to NMDA receptors thus may represent one of several mechanisms for cerebral dysfunction in patients with SLE. [source]

    Impairment of CaMKII activation and attenuation of neuropathic pain in mice lacking NR2B phosphorylated at Tyr1472

    Shinji Matsumura
    Abstract Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a key mediator of long-term potentiation (LTP), which can be triggered by N -methyl- d -aspartate (NMDA) receptor-mediated Ca2+ influx. We previously demonstrated that Fyn kinase-mediated phosphorylation of NR2B subunits of NMDA receptors at Tyr1472 in the dorsal horn was involved in a neuropathic pain state even 1 week after nerve injury. Here we show that Y1472F-KI mice with a knock-in mutation of the Tyr1472 site to phenylalanine did not exhibit neuropathic pain induced by L5 spinal nerve transection, whereas they did retain normal nociceptive responses and induction of inflammatory pain. Phosphorylation of NR2B at Tyr1472 was only impaired in the spinal cord of Y1472F-KI mice among the major phosphorylation sites. There was no difference in the Ca2+ response to glutamate and sensitivity to NMDA receptor antagonists between naive wild-type and Y1472F-KI mice, and the Ca2+ response to glutamate was attenuated in the Y1472F-KI mice after nerve injury. Autophosphorylation of CaMKII at Thr286 was markedly impaired in Y1472F-KI mice after nerve injury, but there was no difference in phosphorylation of CaMKII at Thr305 or protein kinase C, at Thr674, and activation of neuronal nitric oxide synthase and microglia in the superficial layer of spinal cord between wild-type and Y1472F-KI mice after the operation. These results demonstrate that the attenuation of neuropathic pain is caused by the impaired NMDA receptor-mediated CaMKII signaling in Y1472F-KI mice, and suggest that autophosphorylation of CaMKII at Thr286 plays a central part not only in LTP, but also in persistent neuropathic pain. [source]

    High-frequency gamma oscillations coexist with low-frequency gamma oscillations in the rat visual cortex in vitro

    Olaleke O. Oke
    Abstract Synchronization of neuronal activity in the visual cortex at low (30,70 Hz) and high gamma band frequencies (> 70 Hz) has been associated with distinct visual processes, but mechanisms underlying high-frequency gamma oscillations remain unknown. In rat visual cortex slices, kainate and carbachol induce high-frequency gamma oscillations (fast-,; peak frequency , 80 Hz at 37°C) that can coexist with low-frequency gamma oscillations (slow-,; peak frequency , 50 Hz at 37°C) in the same column. Current-source density analysis showed that fast-, was associated with rhythmic current sink-source sequences in layer III and slow-, with rhythmic current sink-source sequences in layer V. Fast-, and slow-, were not phase-locked. Slow-, power fluctuations were unrelated to fast-, power fluctuations, but were modulated by the phase of theta (3,8 Hz) oscillations generated in the deep layers. Fast-, was spatially less coherent than slow-,. Fast-, and slow-, were dependent on ,-aminobutyric acid (GABA)A receptors, ,-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and gap-junctions, their frequencies were reduced by thiopental and were weakly dependent on cycle amplitude. Fast-, and slow-, power were differentially modulated by thiopental and adenosine A1 receptor blockade, and their frequencies were differentially modulated by N -methyl- d -aspartate (NMDA) receptors, GluK1 subunit-containing receptors and persistent sodium currents. Our data indicate that fast-, and slow-, both depend on and are paced by recurrent inhibition, but have distinct pharmacological modulation profiles. The independent co-existence of fast-, and slow-, allows parallel processing of distinct aspects of vision and visual perception. The visual cortex slice provides a novel in vitro model to study cortical high-frequency gamma oscillations. [source]

    N -methyl- d -aspartate, hyperpolarization-activated cation current (Ih) and ,-aminobutyric acid conductances govern the risk of epileptogenesis following febrile seizures in rat hippocampus

    Mohamed Ouardouz
    Abstract Febrile seizures are the most common types of seizure in children, and are generally considered to be benign. However, febrile seizures in children with dysgenesis have been associated with the development of temporal lobe epilepsy. We have previously shown in a rat model of dysgenesis (cortical freeze lesion) and hyperthermia-induced seizures that 86% of these animals developed recurrent seizures in adulthood. The cellular changes underlying the increased risk of epileptogenesis in this model are not known. Using whole cell patch-clamp recordings from CA1 hippocampal pyramidal cells, we found a more pronounced increase in excitability in rats with both hyperthermic seizures and dysgenesis than in rats with hyperthermic seizures alone or dysgenesis alone. The change was found to be secondary to an increase in N -methyl- d -aspartate (NMDA) receptor-mediated excitatory postsynaptic currents (EPSCs). Inversely, hyperpolarization-activated cation current was more pronounced in naďve rats with hyperthermic seizures than in rats with dysgenesis and hyperthermic seizures or with dysgenesis alone. The increase in GABAA -mediated inhibition observed was comparable in rats with or without dysgenesis after hyperthermic seizures, whereas no changes were observed in rats with dysgenesis alone. Our work indicates that in this two-hit model, changes in NMDA receptor-mediated EPSCs may facilitate epileptogenesis following febrile seizures. Changes in the hyperpolarization-activated cation currents may represent a protective reaction and act by damping the NMDA receptor-mediated hyperexcitability, rather than converting inhibition into excitation. These findings provide a new hypothesis of cellular changes following hyperthermic seizures in predisposed individuals, and may help in the design of therapeutic strategies to prevent epileptogenesis following prolonged febrile seizures. [source]

    Dopamine modulation of excitatory currents in the striatum is dictated by the expression of D1 or D2 receptors and modified by endocannabinoids

    Véronique M. André
    Abstract Striatal medium-sized spiny neurons (MSSNs) receive glutamatergic inputs modulated presynaptically and postsynaptically by dopamine. Mice expressing the gene for enhanced green fluorescent protein as a reporter gene to identify MSSNs containing D1 or D2 receptor subtypes were used to examine dopamine modulation of spontaneous excitatory postsynaptic currents (sEPSCs) in slices and postsynaptic N -methyl- d -aspartate (NMDA) and ,-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) currents in acutely isolated cells. The results demonstrated dopamine receptor-specific modulation of sEPSCs. Dopamine and D1 agonists increased sEPSC frequency in D1 receptor-expressing MSSNs (D1 cells), whereas dopamine and D2 agonists decreased sEPSC frequency in D2 receptor-expressing MSSNs (D2 cells). These effects were fully (D1 cells) or partially (D2 cells) mediated through retrograde signaling via endocannabinoids. A cannabinoid 1 receptor (CB1R) agonist and a blocker of anandamide transporter prevented the D1 receptor-mediated increase in sEPSC frequency in D1 cells, whereas a CB1R antagonist partially blocked the decrease in sEPSC frequency in D2 cells. At the postsynaptic level, low concentrations of a D1 receptor agonist consistently increased NMDA and AMPA currents in acutely isolated D1 cells, whereas a D2 receptor agonist decreased these currents in acutely isolated D2 cells. These results show that both glutamate release and postsynaptic excitatory currents are regulated in opposite directions by activation of D1 or D2 receptors. The direction of this regulation is also specific to D1 and D2 cells. We suggest that activation of postsynaptic dopamine receptors controls endocannabinoid mobilization, acting on presynaptic CB1Rs, thus modulating glutamate release differently in glutamate terminals projecting to D1 and D2 cells. [source]

    Attention , oscillations and neuropharmacology

    Gustavo Deco
    Abstract Attention is a rich psychological and neurobiological construct that influences almost all aspects of cognitive behaviour. It enables enhanced processing of behaviourally relevant stimuli at the expense of irrelevant stimuli. At the cellular level, rhythmic synchronization at local and long-range spatial scales complements the attention-induced firing rate changes of neurons. The former is hypothesized to enable efficient communication between neuronal ensembles tuned to spatial and featural aspects of the attended stimulus. Recent modelling studies suggest that the rhythmic synchronization in the gamma range may be mediated by a fine balance between N -methyl- d -aspartate and ,-amino-3-hydroxy-5-methylisoxazole-4-propionate postsynaptic currents, whereas other studies have highlighted the possible contribution of the neuromodulator acetylcholine. This review summarizes some recent modelling and experimental studies investigating mechanisms of attention in sensory areas and discusses possibilities of how glutamatergic and cholinergic systems could contribute to increased processing abilities at the cellular and network level during states of top-down attention. [source]

    Metabotropic glutamate receptor 1 activity generates persistent, N -methyl- d -aspartate receptor-dependent depression of hippocampal pyramidal cell excitability

    J. P. Clement
    Abstract Metabotropic glutamate receptors (mGluRs) are involved in many forms of neuronal plasticity. In the hippocampus, they have well-defined roles in long-lasting forms of both synaptic and intrinsic plasticity. Here, we describe a novel form of long-lasting intrinsic plasticity that we call (S)-3,5-dihydroxyphenylglycine (DHPG)-mediated long-term depression of excitability (DHPG-LDE), and which is generated following transient pharmacological activation of group I mGluRs. In extracellular recordings from hippocampal slices, DHPG-LDE was expressed as a long-lasting depression of antidromic compound action potentials (cAPs) in CA1 or CA3 cells following a 4-min exposure to the group I mGluR agonist (S)-DHPG. A similar phenomenon was also seen for orthodromic fibre volleys evoked in CA3 axons. In single-cell recordings from CA1 pyramids, DHPG-LDE was manifest as persistent failures in antidromic action potential generation. DHPG-LDE was blocked by (S)-(+)- a -amino-4-carboxy-2-methylbenzeneacetic acid (LY367385), an antagonist of mGluR1, but not 2-methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP), an mGluR5 inhibitor. Although insensitive to antagonists of ,-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate/kainate and ,-aminobutyric acidA receptors, DHPG-LDE was blocked by antagonists of N -methyl- d -aspartate (NMDA) receptors. Similarly, in single-cell recordings, DHPG-mediated antidromic spike failures were eliminated by NMDA receptor antagonism. Long after (S)-DHPG washout, DHPG-LDE was reversed by mGluR1 antagonism. A 4-min application of (S)-DHPG also produced an NMDA receptor-dependent persistent depolarization of CA1 pyramidal cells. This depolarization was not solely responsible for DHPG-LDE, because a similar level of depolarization elicited by raising extracellular K+ increased the amplitude of the cAP. DHPG-LDE did not involve HCN channels or protein synthesis, but was eliminated by blockers of protein kinase C or tyrosine phosphatases. [source]