Glutamate Release In Rat Hippocampus Research Articles

5-HT1B receptor agonist CGS12066 presynaptically inhibits glutamate release in rat hippocampus

CGS12066, a 5-hydroxytryptamine 1B (5-HT1B) receptor agonist, has been reported to exhibit antidepressant activity. Considering that glutamatergic dysfunction is implicated in depression, the effect of CGS12066 on glutamate release in rat hippocampal nerve terminals and possible underlying mechanism were investigated. We observed that CGS12066 inhibited 4-aminopyridine (4-AP)-evoked glutamate release, and that a 5-HT1B receptor antagonist blocked this inhibition. Western blot analysis and immunocytochemistry confirmed the presence of presynaptic 5-HT1B receptor proteins. CGS12066-mediated inhibition of 4-AP-evoked glutamate release was completely abolished in the synaptosomes pretreated with inhibitors of Gi/Go-protein, adenylate cyclase (AC), and protein kinase A (PKA), namely pertussis toxin, MDL12330A, and H89, respectively. CGS12066 reduced the elevation of 4-AP-evoked intrasynaptosomal Ca2+ and cyclic AMP (cAMP) levels, but did not affect the synaptosomal membrane potential. Furthermore, in the presence of ω-conotoxin MVIIC, a N- and P/Q-type channel blocker, CGS12066-mediated inhibition of 4-AP-evoked glutamate release was markedly reduced; however, the intracellular Ca2+-release inhibitors dantrolene and CGP37157 did not affect the CGS12066 effect. Furthermore, CGS12066 reduced glutamatergic miniature excitatory postsynaptic current (mEPSC) frequency but did not affect mEPSC amplitude or glutamate-activated currents in hippocampal slices. Our data are the first to suggest that CGS12066 reduces AC/cAMP/PKA activation, through the activation of Gi/Go protein-coupled 5-HT1B receptors present on hippocampal nerve terminals, subsequently reducing Ca2+ entry through voltage-dependent Ca2+ channels and reducing 4-AP-evoked glutamate release. This investigation into the role of 5-HT1B receptors in glutamate release provides crucial information regarding the potential therapeutic role of 5-HT1B receptors for treating depression.

Ciproxifan, a histamine H3 receptor antagonist and inverse agonist, presynaptically inhibits glutamate release in rat hippocampus

Ciproxifan is an H3 receptor antagonist and inverse agonist with antipsychotic effects in several preclinical models; its effect on glutamate release has been investigated in the rat hippocampus. In a synaptosomal preparation, ciproxifan reduced 4-aminopyridine (4-AP)-evoked Ca2+-dependent glutamate release and cytosolic Ca2+ concentration elevation but did not affect the membrane potential. The inhibitory effect of ciproxifan on 4-AP-evoked glutamate release was prevented by the Gi/Go-protein inhibitor pertussis toxin and Cav2.2 (N-type) and Cav2.1 (P/Q-type) channel blocker ω-conotoxin MVIIC, but was not affected by the intracellular Ca2+-release inhibitors dantrolene and CGP37157. Furthermore, the phospholipase A2 (PLA2) inhibitor OBAA, prostaglandin E2 (PGE2), PGE2 subtype 2 (EP2) receptor antagonist PF04418948, and extracellular signal-regulated kinase (ERK) inhibitor FR180204 eliminated the inhibitory effect of ciproxifan on glutamate release. Ciproxifan reduced the 4-AP-evoked phosphorylation of ERK and synapsin I, a presynaptic target of ERK. The ciproxifan-mediated inhibition of glutamate release was prevented in synaptosomes from synapsin I-deficient mice. Moreover, ciproxifan reduced the frequency of miniature excitatory postsynaptic currents without affecting their amplitude in hippocampal slices. Our data suggest that ciproxifan, acting through the blockade of Gi/Go protein-coupled H3 receptors present on hippocampal nerve terminals, reduces voltage-dependent Ca2+ entry by diminishing PLA2/PGE2/EP2 receptor pathway, which subsequently suppresses the ERK/synapsin I cascade to decrease the evoked glutamate release.

Safinamide and glutamate release: New insights

s / Parkinsonism and Related Disorders 22 (2016) e149ee192 e177 Sciences, University of Ferrara, Ferrara, Italy; Consultant, Gallarate, Varese, Italy; RD Department of Medical Sciences, University of Ferrara, Ferrara, Italy; Consultant, Gallarate, Varese, Italy Objectives: Safinamide (Xadago®) is a novel drug recently approved as add-on therapy to levodopa in midto late-stage Parkinson's disease. Xadago® shows a unique dual mechanism of action: it has both dopaminergic properties (highly selective, potent and reversible inhibition of monoamine oxidase-B) and non-dopaminergic properties (state and usedependent sodium channel blockade causing inhibition of excessive glutamate release). The study aim was to evaluate the effect of safinamide on stimulated glutamate release in rat hippocampus at doses giving free brain concentrations able to block sodium channels and to provide a PK/PD approach to support its clinical relevance on overactive glutamate release inhibition. Methods: Glutamate release, stimulated by veratridine in the hippocampus of rats, was measured by in vivo microdialysis. Results: Safinamide was able to significantly inhibit the glutamate release in a dose-dependent manner and the relative measured free brain concentrations (0.3-2.2 mM) support the inhibition of sodium channels (2050% Ki. A functional blockade of sodium channels suggests that pharmacodynamically active concentrations of safinamide are available at the target sites in the brain: in rodents significant protection (50-70%) from convulsions was found when free brain concentration of 0.37-1.4 mM was reached. At the recommended clinical doses (50 and 100 mg) the estimated human free brain safinamide concentrations (0.21-1.92 mM) overlap the range of measured free brain concentrations effective in inhibiting overactive glutamate release in animals. Conclusions: These results clearly support the non-dopaminergic aspects of Xadago® mode of action in rats, likely relevant also in humans. P 6.004. 4I (N-(3-CHLORO-2-METHYLPHENYL) QUINOXALIN-2-CARBOXAMIDE), A NOVEL 5-HT3 RECEPTOR ANTAGONIST ALLEVIATES DEPRESSIVE BEHAVIOR EVOKED IN STREPTOZOTOCIN-INDUCED DIABETIC MICE: ROLE OF OXIDATIVE STRESS Deepali Gupta, Mahesh Radhakrishnan. Department of Pharmacy, Pilani,

Inhibitory effects of beta-amyloid on the nicotinic receptors which stimulate glutamate release in rat hippocampus: the glial contribution

We investigated on the neuronal nicotinic acetylcholine receptor subtypes involved in the cholinergic control of in vivo hippocampal glutamate (GLU), aspartate (ASP) and inhibitory γ-aminobutyric acid (GABA) overflow. We also investigated on the possible contribution of nicotinic acetylcholine receptors subtypes present on astrocytes in the regulation of the three neurotransmitter amino acids overflow using hippocampal gliosomes and on the effects of beta-amyloid (Aβ) 1–40 on the nicotinic control of amino acid neurotransmitter release. Nicotine was able to enhance the in vivo overflow of the three amino acids being more potent in stimulating GLU overflow. The α7 selective agonist PHA543613 induced an overflow very similar to that of nicotine. The α4β2 selective agonist 5IA85380 was significantly less potent in inducing GLU overflow while the overflow of ASP and GABA were almost inconsistent. Aβ1–40 inhibited the neurotransmitter overflow stimulated by PHA543613 but not the one evoked by 5IA85380. In hippocampal gliosomes nicotine elicited selectively GLU overflow which was also evoked by 5IA85380 and by the α7 selective agonist choline. Nicotine- and choline-induced glutamate overflow in gliosomes was inhibited by Aα1–40. In conclusion nicotine administration in vivo elicits hippocampal GLU release mostly through α7 nicotinic acetylcholine receptors likely present both on neurons and astrocytes. Aβ inhibitory effect on the nicotinic-control of GLU release seems to depend primarily to the inhibition of α7 nicotinic acetylcholine receptors functional responses.

Characterization of K+ depolarization evoked ATP, adenosine and glutamate release in rat hippocampus: a microelectrode biosensor study

Event Abstract Back to Event Characterization of K+ depolarization evoked ATP, adenosine and glutamate release in rat hippocampus: a microelectrode biosensor study Attila Heinrich1* and Beáta Sperlágh1 1 Institute of Experimental Medicine, Hungarian Academy of Sciences, Laboratory of Molecular Pharmacology, Hungary Glial cells are active players in information processing in the brain and both adenine nucleotides and nucleosides as well as glutamate play a key role in glia-neuron interactions. These 'gliotransmitters' signal either to astrocytes, where they generate Ca2+ waves, or to neurons, where they modulate synaptic transmission and neuronal excitability. However, the physiological trigger for the release of ATP from astrocytes and its mechanism is still unknown. In our study rat hippocampal slices were depolarized with 25 mM K+ and the release of ATP, adenosine and glutamate were recorded with enzymatic microelectrode biosensors. ATP and glutamate sensor exhibited a rapidly increasing current during K+ depolarization. In the presence of ARL67156 the extracellular level of ATP was encanced and the detected long lasting adenosine efflux was totally inhibited suggesting that generation of adenosine may arise from the extracellular breakdown of ATP. Ca2+-free medium abolished both ATP and adenosine release in response to K+ depolarization. ATP, adenosine and glutamate release was reduced in the presence of the Na+-channel blocker, TTX. Extracellular accumulation of ATP and adenosine were significantly decreased in the presence of NMDA receptor antagonist D-AP-5. High concentration of carbenoxolone, totally inhibited the ATP, adenosine and glutamate efflux, while in pannexin-selective low concentration CBX decreased only the adenosine efflux. Perfusion with the glia-selective toxin fluoroacetate significantly inhibited concentration of ATP, adenosine and glutamate. Our results demonstrate that ATP and adenosine release are mediated by axonal activation via NMDA receptors and probably derived from glial cells through different gap junction hemichannels. Although the efflux of adenosine did arise from previously released ATP, it is also released directly via pannexin hemichannels. ATP is released through gap junction hemichannel into extracellular space, before it is rapid breakdown to adenosine. Conference: IBRO International Workshop 2010, Pécs, Hungary, 21 Jan - 23 Jan, 2010. Presentation Type: Poster Presentation Topic: Cellular neuroscience Citation: Heinrich A and Sperlágh B (2010). Characterization of K+ depolarization evoked ATP, adenosine and glutamate release in rat hippocampus: a microelectrode biosensor study. Front. Neurosci. Conference Abstract: IBRO International Workshop 2010. doi: 10.3389/conf.fnins.2010.10.00046 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 20 Apr 2010; Published Online: 20 Apr 2010. * Correspondence: Attila Heinrich, Institute of Experimental Medicine, Hungarian Academy of Sciences, Laboratory of Molecular Pharmacology, Budapest, Hungary, heinrich@koki.hu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Attila Heinrich Beáta Sperlágh Google Attila Heinrich Beáta Sperlágh Google Scholar Attila Heinrich Beáta Sperlágh PubMed Attila Heinrich Beáta Sperlágh Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Different dynamic patterns of extracellular glutamate release in rat hippocampus after permanent or 30-min transient cerebral ischemia and histological correlation.

The extent and severity of neuronal damage is different in ischemia with reperfusion compared to ischemia and no reperfusion. To investigate the role of glutamate in cerebral ischemia-reperfusion injury, in vivo microdialysis was performed to examine the dynamic profile of glutamate in the hippocampus in a transient (30 min) or permanent middle cerebral artery occlusion (MCAo) in Wistar rats. The extracellular concentration of glutamate in the cornu ammonis (CA)1 sector of the ipsilateral hippocampus showed a significant but transient elevation of glutamate for both groups immediately following ischemic insult. The initial high peak in glutamate levels in the transient MCAo group was followed by two secondary elevations in glutamate at 50 min and 90 min after initialization of reperfusion. The histopathological outcome was also different in the two groups. The observation that glutamate releases occurred in the early reperfusion phase provided an evidence of additional excitotoxicity of glutamate and thereby a therapeutic base for extended use of glutamate antagonist in the ischemia-reperfusion injury.

Effects of Antiepileptic Drugs on K+‐Induced Glutamate Release and Spreading Depression in the Hippocampus Determined with an In Vivo Microdialysis Glutamate Biosensor (MGB)

Purpose: Glutamate is the principal excitatory neurotransmitter in the central nervous system, and excessive release of glutamate may produce seizures in patients with epilepsy and in various animal models of epilepsy. Glutamatergic transmission also plays an important role in the development of neuronal damage after a variety of insults to the brain, including those caused by status epilepticus. Thus, to clarify the effects of the antiepileptic drugs (AEDs) carbamazepine (CBZ) and zonisamide (ZNS) on the multiple components of hippocampal glutamate release, this study was carried out to determine the Ca2+‐ and K+‐evoked glutamate release in rat hippocampus with an in vivo microdialysis glutamate biosensor (MGB). Methods: The MGB was composed of a dialysis electrode (DE), a microdialysis probe, and a stainless steel recording electrode. The DE was filled with 100 U/ml of glutamate oxidase dissolved in a phosphate‐modified Ringer's solution (PMRS) containing (in mM): 145 Na+, 2.7 K+, 1.0 Mg2+, 154.4 C1− and adjusted with 4.3 mM phosphate buffer to pH 7.4. The MGB was implanted into the rat hippocampus (A =−5.8 L = 4.8, and V =−4.0 mm from Bregma). The perfusion rate was maintained at 1.0 μl/min, by using a modified Ringer's solution (MRS) composed of (in mM): 14.5 Na+, 2.7 K+, 1.2 Ca2+, 1.0 Mg2+, 154.4 Cl−, 0.2 ascorbate, and adjusted to pH 7.4 with 2 mM phosphate buffer and 1.1 mM Tris buffer. To study the effects of an increase in extracellular Ca+ or K+ levels (Ca2+‐ or K+‐evoked) on hippocampal glutamate release, MRS including either 3.4 mM Ca2+, 50 mM K+, 100 mM K+, 3.4 mM Ca2+, and 50 mM K+, Ca2+‐free, and 50 mM K+, or Ca2+‐free and 40 mM Mg2+ was infused for 60 min. To study the effects of CBZ and ZNS on basaMlippocampa1 extracellular glutamate levels, and on Ca2+‐ or K+‐evoked hippocampal glutamate release, 100 mM CBZ or 1 mM ZNS was dissolved in each perfusate. The neuronal firing frequencies were recorded with a telemeter set at a bandpass of 0.1–3 kHz and were fed into the computer as discharge rates. Results: An increase in the extracellular K+ levels produced concentration‐dependent increases in the extracellular glutamate levels in the hippocampus. This K+‐evoked glutamate release consisted of three components: an initial transient rise (ITR), a late gentle rise (LGR), and multiple phasic transient rises (MPTR). An increase in the extracellular Ca2+ levels did not affect hippocampal extracellular glutamate levels; however, it did enhance the K+‐evoked hippocampal glutamate release. Therapeutic concentrations of either CBZ and ZNS had no effect on basal extracellular glutamate levels in the hippocampus, whereas they did inhibit the K+‐evoked hippocampal glutamate release. Therapeutic concentrations of CBZ or ZNS also inhibited the stimulatory effects of Ca2+ on K+‐evoked hippocampal glutamate release. Conclusions: This study demonstrated that K+‐evoked hippocampal glutamate release consists of three phases: Ca2+‐dependent ITR, which was dependent on neuronal activity, and followed by the LGR and MPTR, which were Ca2+ dependent and neuronal activity independent (spreading depression). The inhibitory effect of ZNS on ITR was stronger than that of CBZ, whereas the inhibitory effects of CBZ on the series of LGR and MPTR of K+‐evoked hippocampal glutamate release were more effective than those of ZNS. The new method used in this study, the MGB, should be useful for studying the mechanisms of action of AEDs.

Inhibition of glutamate release in rat hippocampus by kynurenic acid does not protect CA1 cells from forebrain ischemia

We assessed the effect of a broad spectrum glutamatergic receptor antagonist, kynurenic acid (500 mg/kg) on ischemia-induced hippocampal glutamate release and neuronal damage. Kynurenic acid significantly decreased glutamate release during ischemia but had no effect on the hippocampal lesion. Some protection was observed in the cortex and in the striatum. These data suggested that the extracellular accumulation of glutamate during forebrain ischemia does not play a major role in the hippocampus.