Glutamate Release In Brain Research Articles

Distinct acute stressors produce different intensity of anxiety-like behavior and differential glutamate release in zebrafish brain.

Anxiety disorder is one of the most well-characterized behavioral disorders in individuals subjected to acute or chronic stress. However, few studies have demonstrated how different types of stressors can modulate the neurochemical alterations involved in the generation of anxiety. In this study, we hypothesize that subjects exposed to different aversive stimuli (mechanical, chemical, and spatial restriction) present varied intensities of anxiety-like responses associated with distinct patterns of gamma-aminobutyric acid (GABA) and glutamate release in the brain. Adult zebrafish, Danio rerio (n = 60), were randomly divided into four experimental groups; control, acute restraint stress (ARS), conspecific alarm substance (CAS), and chasing with net (CN). After the stress protocols, the animals were individually transferred to a novel tank diving test for behavioral analysis. Subsequently, their brains were collected and subjected to GABA and glutamate release assay for quantification by HPLC. Our behavioral results showed that all aversive stimuli were capable of inducing anxiety-like behavior. However, the impact of anxiogenic behavior was more prominent in the CN and CAS groups when compared to ARS. This phenomenon was evident in all analyzed behavioral parameters (time on top, freezing, mean speed, maximum speed, and erratic swimming). Our data also showed that all aversive stimuli significantly decreased GABA release compared to the control group. Only animals exposed to CN and CAS presented an increase in extracellular glutamate levels. Different acute stressors induced different levels of anxiety-like behavior in zebrafish as well as specific alterations in GABAergic and glutamatergic release in the brain. These results demonstrate the complexity of anxiety disorders, highlighting that both behavioral and neurochemical responses are highly context-dependent.

PEDOT: Nafion Coated Microelectrode Biosensor for in Vivo Monitoring of Glutamate Release in Brain

L-Glutamic acid is one of the most prevalent excitatory signalling molecule in the central nervous system, plays a crucial role in a wide variety of brain functions such as memory, learning and neurological disorders like stroke, epilepsy and several other neurodegenerative diseases. In this study, we report on the design and development of an amperometric microelectrode based glutamate oxidase biosensor for real-time monitoring of L-glutamate in vivo in the mammalian brain. A Nafion and poly (3,4-ethylenedioxythiophene) (PEDOT) containing polymer composite has been electropolymerized onto 50μm Pt wire to act as a permselective membrane to selectively block common interfering substances in physiological conditions. In the second step, a mixture of glutamate oxidase entrapped in a biocompatible chitosan matrix was casted onto the surface of a Pt microelectrode. In the final step, ascorbate oxidase was coated onto the microelectrode to eliminate almost completely of any interference from high levels of extracellular ascorbic acid present in brain tissue. L-glutamate measurements were performed amperometrically at an applied potential of 0.6V vs Ag/AgCl. The miniaturized microelectrode biosensor showed a rapid steady state response to L-glutamate within 2 s. The biosensor also exhibited a very good linear dependence on the concentration of L-glutamate with a high sensitivity and excellent storage stability. We will discuss in detail, the biosensor fabrication and characterization together with performance characteristics and in vivo testing in intact rat brain tissue.

Association of Alterations in Gray Matter Volume With Reduced Evoked-Pain Connectivity Following Short-Term Administration of Pregabalin in Patients With Fibromyalgia.

Pregabalin (PGB) is an α2 δ calcium-channel subunit ligand that has previously been shown to reduce chronic pain in multiple conditions. Preclinical studies indicate that PGB may down-regulate brain glutamate release while also inhibiting astrocyte induction of glutamatergic synapse formation, and recent clinical findings support the notion that PGB modulates glutamatergic activity and functional brain connectivity in order to produce analgesia. The present study was undertaken to examine concurrent changes in brain gray matter volume (GMV) or evoked-pain connectivity in humans receiving PGB. Sixteen female fibromyalgia patients participated in a randomized double-blind 2-period crossover study of PGB versus placebo. Before and after each period, patients underwent high-resolution structural and evoked pressure-pain functional brain imaging. GMV was analyzed using voxel-based morphometry, and functional connectivity during evoked pressure-pain was assessed. PGB administration significantly reduced GMV within the posterior insula bilaterally, whereas there were no significant changes in insular GMV following placebo treatment. GMV reductions in the medial frontal gyrus were also observed when comparing PGB versus placebo treatment, and were associated with reduced clinical pain. These reductions in insular GMV were associated with concomitant reductions in connectivity to the default mode network, which was also associated with reduced clinical pain. Short-term PGB treatment altered brain structure and evoked-pain connectivity, and these decreases were associated with reduced clinical pain. We speculate that these fairly rapid changes in GMV may be related to brain neuroplasticity. It is unknown whether these effects are generalizable to other chronic pain states.

50 Hz hippocampal stimulation in refractory epilepsy: Higher level of basal glutamate predicts greater release of glutamate.

The effect of electrical stimulation on brain glutamate release in humans is unknown. Glutamate is elevated at baseline in the epileptogenic hippocampus of patients with refractory epilepsy, and increases during spontaneous seizures. We examined the effect of 50 Hz stimulation on glutamate release and its relationship to interictal levels in the hippocampus of patients with epilepsy. In addition, we measured basal and stimulated glutamate levels in a subset of these patients where stimulation elicited a seizure. Subjects (n = 10) were patients with medically refractory epilepsy who were undergoing intracranial electroencephalography (EEG) evaluation in an epilepsy monitoring unit. Electrical stimulation (50 Hz) was delivered through implanted hippocampal electrodes (n = 11), and microdialysate samples were collected every 2 min. Basal glutamate, changes in glutamate efflux with stimulation, and the relationships between peak stimulation-associated glutamate concentrations, basal zero-flow levels, and stimulated seizures were examined. Stimulation of epileptic hippocampi in patients with refractory epilepsy caused increases in glutamate efflux (p = 0.005, n = 10), and 4 of ten patients experienced brief stimulated seizures. Stimulation-induced increases in glutamate were not observed during the evoked seizures, but rather were related to the elevation in interictal basal glutamate (R(2) = 0.81, p = 0.001). The evoked-seizure group had lower basal glutamate levels than the no-seizure group (p = 0.04), with no stimulation-induced change in glutamate efflux (p = 0.47, n = 4). Conversely, increased glutamate was observed following stimulation in the no-seizure group (p = 0.005, n = 7). Subjects with an atrophic hippocampus had higher basal glutamate levels (p = 0.03, n = 7) and higher stimulation-induced glutamate efflux. Electrical stimulation of the epileptic hippocampus either increased extracellular glutamate efflux or induced seizures. The magnitude of stimulated glutamate increase was related to elevation in basal interictal glutamate, suggesting a common mechanism, possibly impaired glutamate metabolism. Divergent mechanisms may exist for seizure induction and increased glutamate in patients with epilepsy. These data highlight the potential risk of 50 Hz stimulation in patients with epilepsy.

Kynurenic acid: a metabolite with multiple actions and multiple targets in brain and periphery

It is usually assumed that kynurenic acid (KYNA) modifies neuronal function because it antagonizes the glycine site of the NMDA receptors and/or the neuronal cholinergic α7 nicotine receptors. It is not clear, however, whether the basal levels of KYNA found in brain extracellular spaces are sufficient to interact with these targets. Another reported target for KYNA is GPR35, an orphan receptor negatively coupled to G(i) proteins. GPR35 is expressed both in neurons and other cells (including glia, macrophages and monocytes). KYNA affinity for GPR35 in native systems has not been clarified and the low-affinity data widely reported in the literature for the interaction between KYNA and human or rat GPR35 have been obtained in modified expression systems. Possibly by interacting with GPR35, KYNA may also reduce glutamate release in brain and pro-inflammatory cytokines release in cell lines. The inhibition of inflammatory mediator release from both glia and macrophages may explain why KYNA has analgesic effects in inflammatory models. Furthermore, it may also explain why, KYNA administration (200mg/kg ip×3 times) to mice treated with lethal doses of LPS, significantly reduces the number of deaths. Finally, KYNA has been reported as an agonist of aryl hydrocarbon receptor (AHR), a nuclear protein involved in the regulation of gene transcription and able to cause immunosuppression after binding with dioxin. Thus, KYNA has receptors in the nervous and the immune systems and may play interesting regulatory roles in cell function.

Blood levels of glutamate oxaloacetate transaminase are more strongly associated with good outcome in acute ischaemic stroke than glutamate pyruvate transaminase levels

Ischaemic stroke is associated with an excessive release of glutamate in brain. GOT (glutamate-oxaloacetate transaminase) and GPT (glutamate-pyruvate transaminase) are two enzymes that are able to metabolize blood glutamate facilitating the lowering of extracellular levels of brain glutamate. Our aim was to study the association between blood levels of both enzymes and stroke outcome in patients with acute ischaemic stroke. We prospectively studied 365 patients with first ischaemic stroke<12 h. Glutamate, GOT and GPT levels were determined in blood samples obtained at admission. We considered functional outcome at 3 months [good outcome: mRS (modified Rankin Scale)≤2; poor outcome mRS >2], END (early neurological deterioration) in the first 72 h [increment ≥4 points in NIHSS (National Institutes of Health Stroke Scale)] and infarct volume [CT (computed tomography) at 36-72 h] as end points. We have found an inverse correlation between GOT and GPT levels and blood glutamate levels. Patients with poor outcome showed lower levels of GOT (11.9±8.2 compared with 22.7±10.2 m-units/ml, P<0.0001) and GPT (19.5±14.3 compared with 24.7±20.3 m-units/ml; P=0.004). A negative correlation has been found between GOT (Pearson coefficient=-0.477, P<0.0001) and GPT (Pearson coefficient=-0.116; P=0.027) levels and infarct volume. Patients with END showed higher levels of blood glutamate (381.7±97.9 compared with 237.6±114.0 μmol/l, P<0.0001) and lower levels of GOT (10.8±6.7 compared with 18.1±10.8 m-units/ml; P<0.0001). This clinical study shows an association between high blood GOT and GPT levels and good outcome in ischaemic stroke patients, this association being stronger for GOT than GPT levels.

Acupuncture attenuates extracellular glutamate level in global ischemia model of rat

Objectives: Acupuncture has been known to be effective in ischemia, and glutamate excitotoxicity is an important factor for the neuronal cell death. We examined the effect of acupuncture on glutamate level in the ischemic stroke model.Methods: A global ischemia was induced using the method of 11-vessel occlusion in rat. Rats were randomly divided into two groups: the control group (n=5, with 11-vessel occlusion) and the acupuncture group (n=5, with 11-vessel occlusion + acupuncture). The extracellular glutamate level was assessed using an intracerebral biosensor system measuring 256 samples per second. Simultaneously, the cerebral blood flow was measured and the electroencephalogram data were recorded. The time schedule of the experiment was as follows: 10 minutes of baseline measurement, 10 minutes of occlusion and 30 minutes of follow-up monitoring. Acupuncture stimulation was applied to the acupuncture points GB34 (Yangneungcheon) and GB39 (Hyeonjong) during the occlusion period.Results: In the control group, the extracellular glutamate level was changed as 135.19 ± 23.76 μM (mean ± standard deviation) from the baseline level. However, this increase was suppressed in the acupuncture group (72.20 ± 27.15 μM, p<0.01 versus the control group). The changes of cerebral blood flow and electroencephalogram were not significantly different between the groups.Discussion: This result suggests that the effect of acupuncture might be closely associated with modulation of the brain glutamate release in the ischemic condition.

Neuroprotection afforded by prior citicoline administration in experimental brain ischemia: effects on glutamate transport

Cytidine-5'-diphosphocholine (citicoline or CDP-choline), an intermediate in the biosynthesis of phosphatidylcholine, has shown beneficial effects in a number of CNS injury models including cerebral ischemia. Citicoline is the only neuroprotectant that has proved efficacy in patients with moderate to severe stroke. However, the precise mechanism by which citicoline is neuroprotective is not fully known. The present study was designed to search for mechanisms of citicoline neuroprotective properties using in vivo and in vitro models of brain ischemia. Focal brain ischemia was produced in male adult Fischer rats by occluding both the common carotid and middle cerebral arteries. Brain glutamate levels were determined at fixed intervals after occlusion. Animals were then sacrificed, and infarct volume and brain ATP levels were measured. As in vitro model of ischemia, rat cultured cortical neurones or astrocytes, isolated or in co-culture, were exposed to oxygen-glucose deprivation (OGD) either in the absence or in the presence of citicoline (1-100 microM). Viability was studied by measuring LDH release. Glutamate release and uptake, and ATP levels were also determined. Citicoline (0.5, 1 and 2 g/kg i.p. administered 1 h before the occlusion) produced a reduction of the infarct size measured at striatum (18, 27 and 42% inhibition, respectively, n = 8, P < 0.05 vs. ischemia), effect that correlated with the inhibition caused by citicoline on ischemia-induced increase in glutamate concentrations after the onset of the ischemia. Citicoline also inhibited ischemia-induced decrease in cortical and striatal ATP levels. Incubation of cultured rat cortical neurones with citicoline (10 and 100 microM) prevented OGD-induced LDH and glutamate release and caused a recovery in ATP levels after OGD, confirming our previous results. In addition, citicoline (100 microM) caused an increase in glutamate uptake and in EAAT2 glutamate transporter membrane expression in cultured rat astrocytes. Our present findings show novel mechanisms for the neuroprotective effects of citicoline, which cooperate to decrease brain glutamate release after ischemia.

A two-dimensional imaging biosensor to monitor enhanced brain glutamate release stimulated by nicotine

In this study, we have imaged and monitored real-time release of neurotransmitter glutamate from mouse brain slices stimulated by nicotine and physiological salts using a newly developed two-dimensional (2D) imaging biosensor. Nicotine, the addictive substance contained in cigarettes and other tobacco baring products, affects human body through interactions with both central and peripheral nervous system receptors and exists in various concentrations in body organs including the brain. The 2D imaging biosensor, designed for sensitive glutamate monitoring, is prepared through the use of a flat silica plate that is covalently attached with an enzyme, glutamate dehydrogenase (GDH). The 2D imaging biosensor can spatially resolve glutamate release and has a detection limit of 40 nM in detecting glutamate release from glutaminergic neurons in the brain slices. Using this biosensor, we have shown that the administration of nicotine (50 nM) on the brain slice stimulates repetitive glutamate release. To the best of our knowledge, this is the first time that a biosensor was used to define the vital role of nicotine in glutamate release. Physiological salts such as KCl and CaCl 2 have also been used to characterize the biosensor in measuring glutamate release. It is found in this study that nicotine stimulation is much more potent than physiological salts. The real-time detection of newly released glutamate from mouse brain slices clearly demonstrates the feasibility of the two-dimensional glutamate biosensor for real-time monitoring of dynamic glutamate release from living specimen.

Involvement of brain glutamate release in pyrogenic fever

Whether the glutamate release in the organum vasculosum laminae terminalis (OVLT) is attributable to genesis of a pyrogenic fever is unclear. The lack of information led us to evaluate the changes in glutamate concentrations of OVLT during the fever induced by staphylococcal enterotoxin A (SEA) in unanesthetized rabbits. Both the OVLT concentrations of glutamate and the colonic temperatures were simultaneously monitored during systemic injection of SEA, MK801 (an N-methyl- d-aspartate (NMDA) receptor channel blocker), ketamine (an NMDA receptor channel blocker), or normal saline. The extracellular dialysates in the brain were collected using a microdialysis probe previously placed in the OVLT region. The concentrations of glutamate in the microdialysates were measured by a high-pressure liquid chromatography in combination with a fluorescence detector. Systemic administration of SEA (30 ng kg −1 I.V.) increased both the concentrations of glutamate in the OVLT and the colonic temperatures. Glutamate appeared to rise slightly earlier than body temperature. Pretreatment or posttreatment with MK801 or ketamine significantly attenuated the SEA-induced augmenting glutamate release in the OVLT and fever in rabbits. The suppression of glutamate release appeared to start slightly earlier than temperature decline. In addition, the SEA-induced fever could be mimicked by direct injection of glutamate or SEA into the OVLT area. The fever induced by intra-OVLT injection of SEA or glutamate was significantly attenuated by pretreatment with an intra-OVLT dose of MK801 (5 μg) or ketamine (10 μg). The results suggest that glutamatergic pathways in the OVLT region are in pyrogenic fever genesis.

Limiting ischemic injury by inhibition of excitatory amino acid release.

Excitatory amino acids (EAAs) are important mediators of ischemic injury in stroke. N-Methyl-D-aspartate (NMDA) receptor antagonists have been shown to be very effective neuroprotective agents in animal models of stroke, but may have unacceptable toxicity for human use. An alternative approach is to inhibit the release of EAAs during stroke. BW1003C87 [5-(2,3,5-trichlorophenyl)-2,4-diaminopyrimidine], a drug that inhibits veratrine-induced release of the EAA glutamate in vitro, was tested in a rat model of proximal middle cerebral artery (MCA) occlusion. BW1003C87 significantly decreased ischemia-induced glutamate release in brain when given either 5 min before or 15 min following permanent MCA occlusion. Pretreated and posttreated rats had smaller infarct volumes and preserved glucose metabolism in the ischemic cortex at 24 h after MCA occlusion. BW1003C87 did not induce heat shock protein in the cingulate or retrosplenial cortex, suggesting that it does not injure neurons in these regions as do NMDA antagonists. These results demonstrate that drugs that inhibit glutamate release in ischemia may be nontoxic and show promise for the treatment of stroke.