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Mishra M, Singh R, Mukherjee S, Sharma D. Dehydroepiandrosterone's antiepileptic action in FeCl3-induced epileptogenesis involves upregulation of glutamate transporters. Epilepsy Res 2013; 106:83-91. [PMID: 23891458 DOI: 10.1016/j.eplepsyres.2013.06.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Revised: 06/06/2013] [Accepted: 06/25/2013] [Indexed: 10/26/2022]
Abstract
Dehydroepiandrosterone (DHEA), a neuroactive androgen steroid, has antiepileptic action in iron-induced experimental epilepsy (which models post-traumatic clinical epilepsy). In iron-induced epilepsy increased extracellular glutamate resulting from its reduced glial uptake due to the down-regulation (decreased expression) of transporters (glial and or neuronal) is active during epileptogenesis. The present study was aimed at determining whether the mechanism of antiepileptic action of DHEA involved upregulation (increased expression) of glutamate transporters. Iron-induced epileptogenesis was performed in rats by FeCl3 injection into the cerebral cortex. DHEA was administered intraperitoneally to the iron-induced epileptic rats for 7, 14 and 21 days. Levels of glutamate transporters mRNAs expression were measured using quantitative PCR in the hippocampus during the chronic phase of iron-induced epileptogenesis. There were significant reductions in the glutamate transporter mRNAs in epileptogenesis. DHEA treatment resulted in a significant elevation of glutamate transporters: GLT-1, GLAST and EACC-1 mRNA indicating that the DHEA treatment induced upregulation of these transporters. The results are of significance in respect of the mechanism of the antiepileptic action of neurosteroids and the glutamate transporters as therapeutic targets in glutamatergic epileptogenesis.
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Affiliation(s)
- Monika Mishra
- Neurobiology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
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2
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Eid T, Tu N, Lee TSW, Lai JCK. Regulation of astrocyte glutamine synthetase in epilepsy. Neurochem Int 2013; 63:670-81. [PMID: 23791709 DOI: 10.1016/j.neuint.2013.06.008] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2012] [Revised: 05/28/2013] [Accepted: 06/08/2013] [Indexed: 11/20/2022]
Abstract
Astrocytes play a crucial role in regulating and maintaining the extracellular chemical milieu of the central nervous system under physiological conditions. Moreover, proliferation of phenotypically altered astrocytes (a.k.a. reactive astrogliosis) has been associated with many neurologic and psychiatric disorders, including mesial temporal lobe epilepsy (MTLE). Glutamine synthetase (GS), which is found in astrocytes, is the only enzyme known to date that is capable of converting glutamate and ammonia to glutamine in the mammalian brain. This reaction is important, because a continuous supply of glutamine is necessary for the synthesis of glutamate and GABA in neurons. The known stoichiometry of glutamate transport across the astrocyte plasma membrane also suggests that rapid metabolism of intracellular glutamate via GS is a prerequisite for efficient glutamate clearance from the extracellular space. Several studies have indicated that the activity of GS in astrocytes is diminished in several brain disorders, including MTLE. It has been hypothesized that the loss of GS activity in MTLE leads to increased extracellular glutamate concentrations and epileptic seizures. Understanding the mechanisms by which GS is regulated may lead to novel therapeutic approaches to MTLE, which is frequently refractory to antiepileptic drugs. This review discusses several known mechanisms by which GS expression and function are influenced, from transcriptional control to enzyme modification.
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Affiliation(s)
- Tore Eid
- Department of Laboratory Medicine, Yale University School of Medicine, New Haven, CT 06520, United States.
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Shin EJ, Jeong JH, Chung YH, Kim WK, Ko KH, Bach JH, Hong JS, Yoneda Y, Kim HC. Role of oxidative stress in epileptic seizures. Neurochem Int 2011; 59:122-37. [PMID: 21672578 PMCID: PMC3606551 DOI: 10.1016/j.neuint.2011.03.025] [Citation(s) in RCA: 294] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2010] [Revised: 03/27/2011] [Accepted: 03/28/2011] [Indexed: 11/16/2022]
Abstract
Oxidative stress resulting from excessive free-radical release is likely implicated in the initiation and progression of epilepsy. Therefore, antioxidant therapies aimed at reducing oxidative stress have received considerable attention in epilepsy treatment. However, much evidence suggests that oxidative stress does not always have the same pattern in all seizures models. Thus, this review provides an overview aimed at achieving a better understanding of this issue. We summarize work regarding seizure models (i.e., genetic rat models, kainic acid, pilocarpine, pentylenetetrazol, and trimethyltin), oxidative stress as an etiologic factor in epileptic seizures (i.e., impairment of antioxidant systems, mitochondrial dysfunction, involvement of redox-active metals, arachidonic acid pathway activation, and aging), and antioxidant strategies for seizure treatment. Combined, this review highlights pharmacological mechanisms associated with oxidative stress in epileptic seizures and the potential for neuroprotection in epilepsy that targets oxidative stress and is supported by effective antioxidant treatment.
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Affiliation(s)
- Eun-Joo Shin
- Neuropsychopharamcology and Toxicology Program, College of Pharmacy, Kangwon National University, Chunchon 200-701, South Korea
| | - Ji Hoon Jeong
- Department of Pharmacology, College of Medicine, Chung-Ang University, Seoul 156-756, South Korea
| | - Yoon Hee Chung
- Department of Anatomy, College of Medicine, Chung-Ang University, Seoul 156-756, South Korea
| | - Won-Ki Kim
- Department of Neuroscience, College of Medicine, Korea University, Seoul 136-705, South Korea
| | - Kwang-Ho Ko
- Pharmacology Laboratory, College of Pharmacy, Seoul National University, Seoul 143-701, South Korea
| | - Jae-Hyung Bach
- Neuropsychopharamcology and Toxicology Program, College of Pharmacy, Kangwon National University, Chunchon 200-701, South Korea
| | - Jau-Shyong Hong
- Neuropharmacology Section, Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA
| | - Yukio Yoneda
- Laboratory of Molecular Pharmacology, Division of Pharmaceutical Sciences, Kanazawa University Graduate School of Natural Science and Technology, Kanazawa, Ishikawa 920-1192, Japan
| | - Hyoung-Chun Kim
- Neuropsychopharamcology and Toxicology Program, College of Pharmacy, Kangwon National University, Chunchon 200-701, South Korea
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González-Martínez JA, Ying Z, Prayson R, Bingaman W, Najm I. Glutamate clearance mechanisms in resected cortical dysplasia. J Neurosurg 2011; 114:1195-202. [DOI: 10.3171/2010.10.jns10715] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Object
Changes in the expression of glutamate transporters (GLTs) may play a role in the expression of epileptogenicity. Previous studies have shown an increased number of neuronal GLTs in human dysplastic neurons. The expression of glial and neuronal GLTs and glutamine synthetase (GS) in balloon cells (BCs) and BC-containing cortical dysplasia has not been studied.
Methods
The authors analyzed neocortical samples that were resected in 5 patients who had cortical dysplasia–induced medically intractable focal epilepsy and who underwent extraoperative prolonged electrocorticographic (ECoG) recordings. The expressions of glial (GLT1/EAAT2) and neuronal (EAAT3, EAAC1) GLTs and GS proteins were immunohistochemically studied in all 5 resected samples. The authors also assessed in situ colocalization of GLTs and GS with neuronal and glial markers.
Results
Balloon cell–containing cortical dysplasia lesions did not exhibit ictal patterns on prolonged extraoperative ECoG recordings. There was a differential expression of glial and neuronal GLTs in BCs and dysplastic neurons: the majority of BCs highly expressed glial but not neuronal GLTs. Dysplastic neurons showed increased immunohistochemical staining with neuronal EAAT3 but not with EAAT2/GLT1. Moreover, only glial fibrillary acidic protein–positive BCs also expressed GS.
Conclusions
There is a differential GLT expression in dysplastic and balloon cells. The presence of glial GLTs and GS in balloon cell cortical dysplasia suggests a possible antiepileptic role for BCs and is consistent with the reported increased epileptogenicity in GLT1-deficient animals.
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Affiliation(s)
| | | | - Richard Prayson
- 2Department of Surgical Pathology, Cleveland Clinic, Cleveland, Ohio
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Ueda Y, Kitamoto A, Willmore LJ, Kojima T. Hippocampal gene network analysis in an experimental model of posttraumatic epilepsy. Neurochem Res 2010; 36:1323-8. [PMID: 21191651 DOI: 10.1007/s11064-010-0386-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/22/2010] [Indexed: 11/25/2022]
Abstract
In the present study, we performed comprehensive gene expression and gene network analyses using a DNA microarray to elucidate the molecular events responsible for the pathology of posttraumatic epilepsy at the partial seizure stage. We used an experimental posttraumatic epilepsy model of amygdalar focal FeCl(3)-injected rats and compared gene expression profiles in the hippocampus at the partial seizure stage (less than stage 3 on Racine's convulsion scale) and that of sham-operated animals. At the partial seizure stage, upregulation of phospholipase A2 (PLA2) and lipid metabolism were observed, which have been reported to be caused by brain injury and seizures in previous studies. Furthermore, significant upregulation of genes related to inflammation and the immune system was observed. These molecular changes in PLA2 and lipid metabolism may be related to seizure propagation.
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Affiliation(s)
- Yuto Ueda
- Section of Psychiatry, Department of Clinical Neuroscience, Faculty of Medicine, University of Miyazaki, Miyazaki, 889-1692, Japan
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Abstract
Incidence of Seizures in the Acute Phase of Stroke: A Population-based Study. Szaflarski JP, Rackley AY, Kleindorfer DO, Khoury J, Woo D, Miller R, Alwell K, Broderick JP, Kissela BM. Epilepsia 2008;49(6):974–981. Purpose The incidence of seizures within 24 h of acute stroke has not been studied extensively. We aimed to establish the incidence of acute poststroke seizures in a biracial cohort and to determine whether acute seizure occurrence differs by race/ethnicity, stroke subtype, and/or stroke localization. Methods We identified all stroke cases between July 1993 and June 1994 and in 1999 within the population of the Greater Cincinnati metropolitan region. Patients with a prior history of seizures/epilepsy were excluded from analysis. Results A total of 6044 strokes without a history of seizure(s) were identified; 190 (3.1%) had seizures within the first 24 h of stroke onset. Of ICH/SAH patients, 8.4% had a seizure within the first 24 h of stroke onset ( p ≤ 0.0001 vs all other stroke subtype). Of the patients with ischemic stroke, we observed higher incidence of seizures in cardioembolic versus small or large vessel ischemic ( p = 0.02) strokes. Patients with seizures experienced higher mortality than patients without seizures ( p < 0.001) but seizures were not an independent risk factor of mortality at 30 days after stroke. Independent risk factors for seizure development included hemorrhagic stroke, younger age, and prestroke Rankin score of ≥1. Race/ethnicity or localization of the ischemic stroke did not influence the risk for seizure development in the studied population. Discussion The overall incidence of acute seizures after stroke was 3.1%, with a higher incidence seen in hemorrhagic stroke, younger patients, and those presenting with higher prestroke Rankin scores. Acute seizures were associated with a higher mortality at 30 days after stroke.
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Abnormal expressions of glutamate transporters and metabotropic glutamate receptor 1 in the spontaneously epileptic rat hippocampus. Brain Res Bull 2010; 81:510-6. [DOI: 10.1016/j.brainresbull.2009.10.008] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2009] [Revised: 10/11/2009] [Accepted: 10/11/2009] [Indexed: 11/22/2022]
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Willmore LJ, Ueda Y. Posttraumatic epilepsy: hemorrhage, free radicals and the molecular regulation of glutamate. Neurochem Res 2008; 34:688-97. [PMID: 18785008 DOI: 10.1007/s11064-008-9841-3] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2008] [Accepted: 08/22/2008] [Indexed: 11/29/2022]
Abstract
Traumatic brain injury causes development of posttraumatic epilepsy. Bleeding within neuropil is followed by hemolysis and deposition of hemoglobin in neocortex. Iron from hemoglobin and transferring is deposited in brains of patients with posttraumatic epilepsy. Iron compounds form reactive free radical oxidants. Microinjection of ferric ions into rodent brain results in chronic recurrent seizures and liberation of glutamate into the neuropil, as is observed in humans with epilepsy. Termination of synaptic effects of glutamate is by removal via transporter proteins. EAAC-1 is within neurons while GLT-1 and GLAST are confined to glia. Persistent down regulation of GLAST production is present in hippocampal regions in chronic seizure models. Down regulation of GLAST may be fundamental to a sequence of free radical reactions initiated by brain injury with hemorrhage. Administration of antioxidants to animals causes interruption of the sequence of brain injury responses induced by hemorrhage, suggesting that such a strategy needs to be evaluated in patients with traumatic brain injury.
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Affiliation(s)
- L J Willmore
- Department of Neurology & Psychiatry, Saint Louis University School of Medicine, 1402 South Grand Blvd., St. Louis, MI 63104, USA.
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Mauguière F. [Epileptogenicity and evaluation of epileptic risk]. Neurochirurgie 2007; 53:156-62. [PMID: 17507046 DOI: 10.1016/j.neuchi.2007.03.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2007] [Accepted: 03/22/2007] [Indexed: 11/18/2022]
Abstract
Epilepsy is the more frequent clinical manifestation of hemispheric cavernomas in 50 to 75% of symptomatic cases; the annual risk of a first seizure is evaluated from 1.5 to 2.5%. As for all epileptogenic lesions, many questions arise: Is the pathologic tissue or the perilesional cortex responsible for the epileptic symptoms? Is the risk related with the topography of the lesion? Is the prognosis of the epilepsy related with the number of seizures? Can the epilepsy become drug-resistant? Can surgical treatment cure the epilepsy? When surgery is indicated, should lesionectomy alone or lesionectomy plus perilesional tissue resection be performed? The iron and the hemosiderin deposits induce metabolic perturbations and tissue reorganization (gliosis and sclerosis) around the cavernoma. These cortical modifications seem to be responsible for the epileptic discharges but this is difficult to demonstrate. Epileptic discharges have been recorded in the perilesional tissue in only one study of the literature. Drug therapy can usually control the seizures, but it appears that surgery is more effective when the epilepsy is recent and the seizures are not too frequent. For these reasons it would appear licit to propose the resection of the lesion when the surgical risk is not too great. In case of drug-resistant epilepsy, the same function-targeted surgical strategy may be used as for the management of any severe epilepsy.
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Affiliation(s)
- F Mauguière
- Service de neurologie fonctionnelle et d'épileptologie, hôpital neurologique, groupement hospitalier Est, hospices civils de Lyon (HCL), 59 boulevard Pinel 69394, Lyon cedex 03, France.
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Ueda Y, Doi T, Nagatomo K, Willmore LJ, Nakajima A. Functional role for redox in the epileptogenesis: molecular regulation of glutamate in the hippocampus of FeCl3-induced limbic epilepsy model. Exp Brain Res 2007; 181:571-7. [PMID: 17486325 DOI: 10.1007/s00221-007-0954-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2007] [Accepted: 03/31/2007] [Indexed: 12/01/2022]
Abstract
We used western blotting to measure the quantity of glutamate and gamma-aminobutyric acid (GABA) transporters proteins within hippocampal tissue obtained from rats who had undergone epileptogenesis. Chronic seizures were induced by amygdalar injection of FeCl(3). We found that the glial glutamate transporters GLAST and GLT-1 were down-regulated at 60 days after initiation of chronic and recurrent seizures. However, the neuronal glutamate transporter EAAC-1 and the GABA transporter GAT-3 were increased. We performed in vivo microdialysis in freely moving animals to estimate in vivo redox state. We found that the hippocampal tissues were oxidized, resulting in even further impairment of glutamate transport. Our data show that epileptogenesis in rats resulting in chronic and recurrent seizures is associated with collapse of glutamate regulation caused by both the molecular down-regulation of glial glutamate transporters combined with the functional failure due to oxidation.
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Affiliation(s)
- Yuto Ueda
- Section of Psychiatry, Department of Clinical Neuroscience, Faculty of Medicine, University of Miyazaki, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan.
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Ueda Y, Doi T, Nagatomo K, Tokumaru J, Takaki M, Willmore LJ. Effect of levetiracetam on molecular regulation of hippocampal glutamate and GABA transporters in rats with chronic seizures induced by amygdalar FeCl3 injection. Brain Res 2007; 1151:55-61. [PMID: 17408599 DOI: 10.1016/j.brainres.2007.03.021] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2006] [Revised: 03/06/2007] [Accepted: 03/07/2007] [Indexed: 10/23/2022]
Abstract
Enhancement of the glutamatergic excitatory synaptic transmission efficacy in the FeCl3 induced epilepsy model is associated with changes in the levels of glutamate and GABA transporter proteins. This study examined the effect of levetiracetam (LEV) on glutamate overflow and glutamate/GABA transporters expression in rats with epileptogenesis induced by the amygdalar injection of 1.0 microl of 100 mM FeCl3 (epileptic rat) and in control rats receiving amygdalar acidic saline injection (non-epileptic rat). In amygdalar acidic saline injected rats, 40 mM KCl-evoked glutamate overflow was significantly suppressed by both 32 and 100 microM LEV co-perfusion. In unilateral amygdalar FeCl3 injected rats, 32 microM LEV was ineffective, but the 100 microM LEV statistically suppressed glutamate overflow. Western blotting was employed to determine the hippocampal expression of glutamate/GABA transporters in epileptic or non-epileptic rats. The rats were treated for 14 days with 54 mg/kg LEV or vehicle intraperitoneally injection. Following 14 days of treatment, the ipsilateral hippocampus was removed for a Western blot analysis. In non-epileptic rats, the expression increased for all of the glutamate and GABA transporters (GLAST, GLT-1, EAAC-1, GAT-1 and GAT-3) while the glutamate transporter regulating protein (GTRAP3-18) decreased in comparison to those of normal rats that were treated with the vehicle. In epileptic rats receiving LEV, the EAAC-1 and GAT-3 levels increased while GTRAP3-18 (89%) decreased in comparison to those of the epileptic rats treated with the vehicle. GTRAP3-18 inhibitor regulates glutamate-binding affinity to EAAC-1. The anti-epileptic action of LEV may be partially due to a reduction of glutamate-induced excitotoxicity and an enhancement of the GABAergic inhibition as observed with the inhibitory effect on the 40 mM KCl-evoked glutamate overflow. These conclusions are supported by the increase in the expression of glial glutamate transporters (GLAST and GLT-1), and the increase in the expression of EAAC-1 and GAT-3 associated with a decrease in GTRAP3-18. The increased expression of EAAC-1 and the decreased expression of GTRAP3-18 in association with the up-regulation of GAT-3 due to such continual LEV administration was thus found to enhance GABA synthesis and reverse the transport of GABA both in non-epileptic and epileptic rats. The suppression of glutamate excitation and the enhancement of GABA inhibition in the rats with continual LEV administration is a result of the up-regulation of glutamate and GABA transporters with the down-regulation of GTRAP3-18. These observations together demonstrated the critical molecular mechanism of the anti-epileptic activity of LEV.
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Affiliation(s)
- Yuto Ueda
- Section of Psychiatry, Department of Clinical Neuroscience, Faculty of Medicine, University of Miyazaki, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan.
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Voutsinos-Porche B, Koning E, Clément Y, Kaplan H, Ferrandon A, Motte J, Nehlig A. EAAC1 glutamate transporter expression in the rat lithium-pilocarpine model of temporal lobe epilepsy. J Cereb Blood Flow Metab 2006; 26:1419-30. [PMID: 16538232 DOI: 10.1038/sj.jcbfm.9600295] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Glutamate excitotoxicity has been involved in the pathophysiology of epilepsy. Normal functioning of glutamate transporters clears the synaptically released glutamate to prevent excitotoxic neuronal death. Using densitometric immunohistochemical analysis, we examined the temporal expression of the neuronal glutamate transporter (EAAC1) in the lithium-pilocarpine rat model of temporal lobe epilepsy. During the acute period of lithium-pilocarpine-induced status epilepticus, EAAC1 transporter expression increased in the pyramidal neurons of cornus ammonis (CA)1, CA2 and CA3 (fields of the hippocampus), in dentate gyrus (DG) granule cells and in olfactory tubercle (Tu). During the latent period, EAAC1 expression was strongly expressed in the DG granular and molecular layers, Tu, cerebral cortex and septum, and went back to control levels in CA1, CA2 and CA3 layers. The overexpression of EAAC1 occurred mainly in structures prone to develop Fluoro-Jade-B-positive degenerating neurons. It is, however, not clear to what extent the overexpression of EAAC1 contributes to epileptogenesis and in which area it may represent a preventive or compensatory or response to injury.
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Doi T, Ueda Y, Tokumaru J, Willmore LJ. Molecular regulation of glutamate and GABA transporter proteins by clobazam during epileptogenesis in Fe+++-induced epileptic rats. ACTA ACUST UNITED AC 2005; 142:91-6. [PMID: 16274841 DOI: 10.1016/j.molbrainres.2005.09.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2005] [Revised: 08/03/2005] [Accepted: 09/17/2005] [Indexed: 11/20/2022]
Abstract
To assess the molecular effects of the antiepileptic drug clobazam (CLB, 1,5-benzodiazepine), a benzodiazepine effective in the management of epilepsy, we performed a series of experiments using rats with chronic, spontaneous recurrent seizures induced by amygdalar injection of FeCl(3). Experimental animals were treated for 14 days with CLB. We then measured the expression of glutamate and GABA transporter proteins and evaluated the changes that occurred in these proteins using both experimental and control animals. CLB treatment was associated with an increase in the production of GLT-1 in the contra-lateral hippocampus of animals receiving amygdalar FeCl(3) and CLB treatment. CLB treatment up-regulated the GABA transporter GAT3 in the contra-lateral hippocampus of animals with chronic, recurrent seizures. In contrast, CLB had no effect on the expression of EAAC1 and GAT1 in the hippocampus or the cortex in control animal groups. Chronic epileptogenesis may be associated with down-regulation of the production of glial excitatory amino acid transporters, GLAST and GLT-1, proteins that cause increase in the basal extracellular concentrations of glutamate. Elevated GABA transporter expression results in increased reverse transport of GABA to the extracellular space during periods of excitation. In addition to allosteric activation of GABA(A) receptors, this study suggests that CLB might exhibit its antiepileptic action by increasing GLT-1 expression and GAT3 in the hippocampus of rats with chronic seizures.
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Affiliation(s)
- Taku Doi
- Department of Psychiatry, Miyazaki Medical College, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan.
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Gorter JA, Mesquita ARM, van Vliet EA, da Silva FHL, Aronica E. Increased expression of ferritin, an iron-storage protein, in specific regions of the parahippocampal cortex of epileptic rats. Epilepsia 2005; 46:1371-9. [PMID: 16146431 DOI: 10.1111/j.1528-1167.2005.11505.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
PURPOSE Iron accumulation in the brain has been associated with neurodegenerative disorders, including epilepsy. In our previous SAGE study, we showed that ferritin, an iron-storage protein, was one of the genes (Ferritin-H) that showed overexpression before the chronic epileptic phase. In this study we used ferritin as indicator for disturbed iron homeostasis to acquire insight into whether this could play a role in the pathogenesis of temporal lobe epilepsy. METHODS With immunocytochemistry, we studied the regional and cellular distribution of ferritin protein in an animal model for temporal lobe epilepsy in which spontaneous seizures develop a few weeks after electrically induced status epilepticus (SE). RESULTS Increased ferritin expression was observed in regions known to be vulnerable to cell death, mainly in reactive microglial cells of epileptic rats. Ferritin expression after SE was initially high, especially throughout the hippocampus, but decreased over time. In the chronic epileptic phase, it was still upregulated in regions where extensive cell loss occurs during the early acute and latent period. Within the parahippocampal region, the most persistent ferritin overexpression was present in microglial cells in layer III of the medial entorhinal area. The upregulation was most extensive in rats that had developed a progressive form of epilepsy with frequent seizures (approximately five to 10 seizures per day). CONCLUSIONS The fact that ferritin upregulation is still present in specific limbic regions in chronic epileptic rats, when neuronal loss is absent or minimal, suggests a role of iron in the pathogenesis and progression of epilepsy.
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Affiliation(s)
- Jan A Gorter
- Center for Neuroscience, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, The Netherlands.
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Brem F, Hirt AM, Simon C, Wieser HG, Dobson J. Low temperature magnetic analysis in the identification of iron compounds from human brain tumour tissue. ACTA ACUST UNITED AC 2005. [DOI: 10.1088/1742-6596/17/1/010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Brem F, Hirt AM, Simon C, Wieser HG, Dobson J. Characterization of iron compounds in tumour tissue from temporal lobe epilepsy patients using low temperature magnetic methods. Biometals 2005; 18:191-7. [PMID: 15954745 DOI: 10.1007/s10534-004-6253-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Excess iron accumulation in the brain has been shown to be related to a variety of neurodegenerative diseases. However, identification and characterization of iron compounds in human tissue is difficult because concentrations are very low. For the first time, a combination of low temperature magnetic methods was used to characterize iron compounds in tumour tissue from patients with mesial temporal lobe epilepsy (MTLE). Induced magnetization as a function of temperature was measured between 2 and 140 K after cooling in zero-field and after cooling in a 50 mT field. These curves reveal an average blocking temperature for ferritin of 10 K and an anomaly due to magnetite at 48 K. Hysteresis measurements at 5 K show a high coercivity phase that is unsaturated at 7 T, which is typical for ferritin. Magnetite concentration was determined from the saturation remanent magnetization at 77 K. Hysteresis measurements at various temperatures were used to examine the magnetic blocking of magnetite and ferritin. Our results demonstrate that low temperature magnetic measurements provide a useful and sensitive tool for the characterisation of magnetic iron compounds in human tissue.
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Affiliation(s)
- Franziska Brem
- ETH-Hönggerberg, Institute of Geophysics, CH-8093 Zurich, Switzerland.
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Hasegawa D, Matsuki N, Fujita M, Ono K, Orima H. Kinetics of glutamate and gamma-aminobutyric acid in cerebrospinal fluid in a canine model of complex partial status epilepticus induced by kainic acid. J Vet Med Sci 2005; 66:1555-9. [PMID: 15644607 DOI: 10.1292/jvms.66.1555] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
An imbalance of excitatory and inhibitory transmitters in the brain has been suggested to cause epileptic seizures. In this study, we investigated the kinetics of glutamate (GLU) and gamma-aminobutyric acid (GABA) in cerebrospinal fluid (CSF-GLU and CSF-GABA, respectively) using a high performance liquid chromatography (HPLC) in a canine model of complex partial status epilepticus (CPSE) induced by the microinjection of kainic acid (KA) into the unilateral amygdala. During the acute phase (3, 6, 12 and 48 hr after the onset of CPSE), CSF-GLU was significantly increased, while CSF-GABA was decreased, although not significantly. In the chronic phase, both CSF-GLU and CSF-GABA were significantly lower than normal at 72 hr after the onset of CPSE, and their levels returned to normal at 2 months. Results of the present study demonstrate that CSF-GLU is gradually increased in relation with seizure severity, and suggested the possibility that CSF-GABA was consistently decreased during CPSE induced by KA in dogs.
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Affiliation(s)
- Daisuke Hasegawa
- Department of Veterinary Radiology, Nippon Veterinary and Animal Science University, 1-7-1 Kyonan-cho, Musashino-shi, Tokyo 180-8602, Japan
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18
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Junker H, Späte K, Suofu Y, Walther R, Schwarz G, Kammer W, Nordheim A, Walker LC, Runge U, Kessler C, Popa-Wagner A. Proteomic Identification of the Involvement of the Mitochondrial Rieske Protein in Epilepsy. Epilepsia 2005; 46:339-43. [PMID: 15730530 DOI: 10.1111/j.0013-9580.2005.46904.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE Kindled seizures are widely used to model epileptogenesis, but the molecular mechanisms underlying the attainment of kindling status are largely unknown. Recently we showed that achievement of kindling status in the Sprague-Dawley rat is associated with a critical developmental interval of 25 +/- 1 days; the identification of this long, well-defined developmental interval for inducing kindling status makes possible a dissection of the cellular and genetic events underlying this phenomenon and its relation to normal and pathologic brain function. METHODS By using proteomics on cerebral tissue from our new rat kindling model, we undertook a global analysis of protein expression in kindled animals. Some of the identified proteins were further investigated by using immunohistochemistry. RESULTS We report the identification of a modified variant of the Rieske iron-sulfur protein, a component of the mitochondrial cytochrome bc1 complex, whose isoelectric point is shifted toward more alkaline values in the hippocampus of kindled rats. By immunohistochemistry, the Rieske protein is well expressed in the hippocampus, except in the CA1 subfield, an area of selective vulnerability to seizures in humans and animal models. We also noted an asymmetric, selective expression of the Rieske protein in the subgranular neurons of the dorsal dentate gyrus, a region implicated in neurogenesis. CONCLUSIONS These results indicate that the Rieske protein may play a role in the response of neurons to seizure activity and could give important new insights into the molecular pathogenesis of epilepsy.
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Affiliation(s)
- Heike Junker
- Institutes of Biochemistry, Ernst-Moritz-Arndt-University, Greifswald, Germany
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19
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Abstract
Although iron plays an important role in many aspects of human neurophysiology, it also can be toxic under certain circumstances. Anomalous amounts of iron are known to be associated with most types of neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases. To date, little is known about the specific iron compounds present in this tissue and there is recent evidence to suggest that some forms are magnetic. This raises important questions with regard to the role of magnetic iron compounds in disease initiation and progression and, indeed, the origin of these compounds. This paper reviews recent work on the identification and analysis of magnetic iron compounds associated with neurological disorders.
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Affiliation(s)
- Jon Dobson
- Centre for Science and Technology in Medicine, Keele University, Hartshill, Stoke-on-Trent, United Kingdom.
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Williamson A, Patrylo PR, Lee S, Spencer DD. Physiology of human cortical neurons adjacent to cavernous malformations and tumors. Epilepsia 2004; 44:1413-9. [PMID: 14636349 DOI: 10.1046/j.1528-1157.2003.23603.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE Focal neocortical seizures can be associated with a number of specific pathologies including supratentorial tumors and cavernous malformations (CMs), both of which are highly epileptogenic. METHODS To begin to address the question of whether these lesions have different mechanisms of epileptogenesis, we used intracellular recordings from neurons adjacent to intracerebral neoplasms and cerebral CMs. Developmental anomalies were not included in this study. RESULTS Neurons adjacent to CMs had a greater propensity to show large (>5 mV), complex spontaneous synaptic events than did neurons neighboring neoplastic substrates (50 vs. 4.7% of cells and 75 and 8% of patients, respectively; p < 0.004; p < 0.05). Both spontaneous excitatory and inhibitory events were noted. In contrast, in tissue adjacent to tumors, low-amplitude (<3 mV) spontaneous excitatory activity predominated. Neurons neighboring CMs also exhibited more excitable responses to synaptic stimulation, with multiple action potentials riding on prolonged excitatory postsynaptic potentials (EPSPs) being evoked in 71% of these cells, versus 32% of cells from the tumor group; p < 0.05. In studies using hippocampal tissue, we noted a similar pattern of spontaneous activity in tissue adjacent to CMs. CONCLUSIONS These data suggest that CMs may induce seizure activity via a different pathophysiologic mechanism(s) than glial tumors.
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Affiliation(s)
- Anne Williamson
- Department of Neurosurgery, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
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21
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Ueda Y, Nakajima A, Tokumaru J. Antioxidant ability and lipid peroxidation in the hippocampus with epileptogenesis induced by Fe3+ injection into the amygdaloid body of rats. Neurochem Res 2004; 28:1895-900. [PMID: 14649733 DOI: 10.1023/a:1026136211759] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
To analyze antioxidant ability and lipid peroxidation in the hippocampus of rats in an interictal state of FeCl3-induced epileptogenesis, the hippocampal eliminating decay ratio of exogenously applied nitroxide radical (3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (carbamoyl-PROXYL)) by electron paramagnetic resonance (EPR) spectroscopy, and the thiobarbituric reactive substances (TBARS) level in the hippocampus were measured. The prolonged half-life of electron paramagnetism of carbamoyl-PROXYL in the hippocampus of rats with chronic FeCl3-induced epileptogenesis revealed decreased antioxidant ability, which supports the vulnerability against oxidative stress. In addition, TBARS level (marker of lipid peroxidation) was increased in the hippocampus of rats injected with FeCl3 compared with that of control. This study revealed that repetitive seizures resulted in the decreased hippocampal antioxidant ability with lipid peroxidation and explained the regional vulnerability to oxidative stress in the limbic system with epileptogenesis.
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Affiliation(s)
- Yuto Ueda
- Department of Psychiatry, Miyazaki Medical College, 5200 Kihara, Kiyotake, Miyazaki, Japan.
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22
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Zhang G, Raol YSH, Hsu FC, Brooks-Kayal AR. Long-term alterations in glutamate receptor and transporter expression following early-life seizures are associated with increased seizure susceptibility. J Neurochem 2003; 88:91-101. [PMID: 14675153 DOI: 10.1046/j.1471-4159.2003.02124.x] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Prolonged seizures in early childhood are associated with an increased risk of development of epilepsy in later life. The mechanism(s) behind this susceptibility to later development of epilepsy is unclear. Increased synaptic activity during development has been shown to permanently alter excitatory neurotransmission and could be one of the mechanisms involved in this increased susceptibility to the development of epilepsy. In the present study we determine the effect of status-epilepticus induced by lithium/pilocarpine at postnatal day 10 (P10 SE) on the expression of glutamate receptor and transporter mRNAs in hippocampal dentate granule cells and protein levels in dentate gyrus of these animals in adulthood. The results revealed a decrease in glutamate receptor 2 (GluR2) mRNA expression and protein levels as well as an increase in protein levels for the excitatory amino acid carrier 1 (EAAC1) in P10 SE rats compared to controls. Expression of glutamate receptor 1 (GluR1) mRNA was decreased in both P10 SE rats and identically handled, lithium-injected littermate controls compared to naive animals, and GluR1 protein levels were significantly lower in lithium-controls than in naive rats, suggesting an effect of either the handling or the lithium on GluR1 expression. These changes in EAA receptors and transporters were accompanied by an increased susceptibility to kainic acid induced seizures in P10 SE rats compared to controls. The current data suggest that early-life status-epilepticus can result in permanent alterations in glutamate receptor and transporter gene expression, which may contribute to a lower seizure threshold.
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Affiliation(s)
- Guojun Zhang
- Division of Neurology, Pediatric Regional Epilepsy Program, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104, USA
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23
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Ueda Y, Doi T, Tsuru N, Tokumaru J, Mitsuyama Y. Expression of glutamate transporters and ionotropic glutamate receptors in GLAST knockout mice. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 2002; 104:120-6. [PMID: 12225864 DOI: 10.1016/s0169-328x(02)00325-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
In order to investigate the molecular mechanism underlying high seizure susceptibility of GLAST knockout mice, we carried out Western blotting for the expression of GLT-1, EAAC-1, and several kinds of glutamate receptors in the hippocampus and the cortex. Although no significant difference was observed between GLAST (+/+) and (-/-) mice in terms of expression of GLT-1 and EAAC-1 in the hippocampus, these proteins were over-expressed in the frontal cortex in GLAST (-/-) mice (GLT-1, about 210% increase; EAAC-1, about 180% increase). Expression of hippocampal Glu-R1 and Glu-R2 in GLAST (-/-) mice was remarkably increased (Glu-R1, about 140% increase; Glu-R2, about 160% increase), while Glu-R3 and NMDA receptors levels (NMDA-R1, 2A and 2B) were equal to those in control. Cortical levels of Glu-R1, -R2 and -R3 receptors in GLAST (-/-) mice were remarkably decreased (Glu-R1, about 60% decrease; Glu-R2, about 60% decrease; Glu-R3, about 70% decrease), while NMDA receptors were remarkably increased in comparison to those in GLAST (+/+) mice (N-R1, about 150% increase; N-R2A, about 150% increase; N-R2B, about 140% increase). These data suggest that the increased susceptibility to seizures in GLAST (-/-) mice might be derived from increased expression of Glu-R1 in the hippocampus coupled with decreased cortical expression of Glu-R2 and increased NMDA-R1 and -2A, -2B expression.
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Affiliation(s)
- Yuto Ueda
- Department of Psychiatry, Miyazaki Medical College, Miyazaki, Japan.
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Crino PB, Jin H, Shumate MD, Robinson MB, Coulter DA, Brooks-Kayal AR. Increased expression of the neuronal glutamate transporter (EAAT3/EAAC1) in hippocampal and neocortical epilepsy. Epilepsia 2002; 43:211-8. [PMID: 11906504 PMCID: PMC2441873 DOI: 10.1046/j.1528-1157.2002.35001.x] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE To define the changes in gene and protein expression of the neuronal glutamate transporter (EAAT3/EAAC1) in a rat model of temporal lobe epilepsy as well as in human hippocampal and neocortical epilepsy. METHODS The expression of EAAT3/EAAC1 mRNA was measured by reverse Northern blotting in single dissociated hippocampal dentate granule cells from rats with pilocarpine-induced temporal lobe epilepsy (TLE) and age-matched controls, in dentate granule cells from hippocampal surgical specimens from patients with TLE, and in dysplastic neurons microdissected from human focal cortical dysplasia specimens. Immunolabeling of rat and human hippocampi and cortical dysplasia tissue with EAAT3/EAAC1 antibodies served to corroborate the mRNA expression analysis. RESULTS The expression of EAAT3/EAAC1 mRNA was increased by nearly threefold in dentate granule cells from rats with spontaneous seizures compared with dentate granule cells from control rats. EAAT3/EAAC1 mRNA levels also were high in human dentate granule cells from patients with TLE and were significantly elevated in dysplastic neurons in cortical dysplasia compared with non-dysplastic neurons from postmortem control tissue. No difference in expression of another glutamate transporter, EAAT2/GLT-1, was observed. Immunolabeling demonstrated that EAAT3/EAAC1 protein expression was enhanced in dentate granule cells from both rats and humans with TLE as well as in dysplastic neurons from human cortical dysplasia tissue. CONCLUSIONS Elevations of EAAT3/EAAC1 mRNA and protein levels are present in neurons from hippocampus and neocortex in both rats and humans with epilepsy. Upregulation of EAAT3/EAAC1 in hippocampal and neocortical epilepsy may be an important modulator of extracellular glutamate concentrations and may occur as a response to recurrent seizures in these cell types.
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Affiliation(s)
- Peter B Crino
- PENN Epilepsy Center, Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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25
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Gorter JA, Van Vliet EA, Proper EA, De Graan PNE, Ghijsen WEJM, Lopes Da Silva FH, Aronica E. Glutamate transporters alterations in the reorganizing dentate gyrus are associated with progressive seizure activity in chronic epileptic rats. J Comp Neurol 2002; 442:365-77. [PMID: 11793340 DOI: 10.1002/cne.10101] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The expression of glial and neuronal glutamate transporter proteins was investigated in the hippocampal region at different time points after electrically induced status epilepticus (SE) in the rat. This experimental rat model for mesial temporal lobe epilepsy is characterized by cell loss, gliosis, synaptic reorganization, and chronic seizures after a latent period. Despite extensive gliosis, immunocytochemistry revealed only an up-regulation of both glial transporters localized at the outer aspect of the inner molecular layer (iml) in chronic epileptic rats. The neuronal EAAC1 transporter was increased in many somata of individual CA1-3 neurons and granule cells that had survived after SE; this up-regulation was still present in the chronic epileptic phase. In contrast, a permanent decrease of EAAC1 immunoreactivity was observed in the iml of the dentate gyrus. This permanent decrease in EAAC1 expression, which was only observed in rats that experienced progressive spontaneous seizure activity, could lead to abnormal glutamate levels in the iml once new abnormal glutamatergic synaptic contacts are formed by means of sprouted mossy fibers. Considering the steady growth of reorganizing mossy fibers in the iml, the absence of a glutamate reuptake mechanism in this region could contribute to progression of spontaneous seizure activity, which occurs with a similar time course.
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Affiliation(s)
- Jan A Gorter
- Swammerdam Institute for Life Sciences, University of Amsterdam, 1098 SM, Amsterdam, The Netherlands.
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26
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Ingram EM, Wiseman JW, Tessler S, Emson PC. Reduction of glial glutamate transporters in the parietal cortex and hippocampus of the EL mouse. J Neurochem 2001; 79:564-75. [PMID: 11701760 DOI: 10.1046/j.1471-4159.2001.00612.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
There is extensive experimental evidence indicating a crucial role for glutamate in epileptogenesis and epileptic activity. The glial glutamate transporters GLT1 and GLAST are proposed to account for the majority of extracellular glutamate re-uptake. In the present study, polyclonal antibodies specific to GLT1 and GLAST were generated and characterized, revealing distribution patterns for the two transporters confirming those previously reported. In situ hybridization and immunoblotting were then used to compare levels of these two transporters in the parietal cortex and hippocampus of unstimulated and stimulated EL mice with DDY control mice. Additionally, HPLC determined tissue glutamate concentrations in the same regions of these animals. These experiments revealed reductions in GLT1 mRNA and protein in the parietal cortex of unstimulated and stimulated EL mice compared with DDY controls, accompanied by an increase in tissue glutamate concentration in the stimulated EL mice group. GLT1 mRNA was also reduced in the CA3 hippocampal subfield of both unstimulated and stimulated EL mice. GLAST protein was reduced in the hippocampus of the stimulated EL mice group, while no changes in GLAST mRNA or protein were detected in the parietal cortex of EL mice when compared with DDY controls. The glial glutamate transporter down-regulation reported here may play a role in seizure initiation, spread and maintenance in the EL mouse.
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Affiliation(s)
- E M Ingram
- Laboratory of Molecular Neuroscience, Department of Neurobiology, The Babraham Institute, Cambridge, UK.
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27
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Doi T, Ueda Y, Tokumaru J, Mitsuyama Y, Willmore LJ. Sequential changes in AMPA and NMDA protein levels during Fe(3+)-induced epileptogenesis. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 2001; 92:107-14. [PMID: 11483247 DOI: 10.1016/s0169-328x(01)00159-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Seizure susceptibility is related to enhanced glutamatergic excitatory synaptic transmission with alterations in the expressions of ionotropic glutamate receptors. We wondered if levels of AMPA and NMDA receptor subunits changed following epileptogenesis induced by amygdalar FeCl(3) injection. We used Western blots to measure levels of subunits in the ipsilateral and contralateral hippocampus at various times after FeCl(3) injection into the amygdaloid body. With acute seizures, at +5 days after the injection, levels of GluR1, NMDAR1, and NMDAR2 were markedly increased in both hippocampi, with quantities at least 2-4 times baseline. By +15 and +30 days after injection, when chronic spontaneous seizures were occurring, the levels of GluR2 were increased, while GluR1 and NMDAR1&2A/B were decreased. Increased NMDAR1&2A/B levels at +5 days are consistent with the occurrence of upregulation of NMDA receptor production in the early stages of epileptogenesis. Since GluR2 suppresses glutamate receptor-mediated Ca(2+)-influx, increased expression of GluR2 with development of chronic, recurrent seizures may be a compensatory effect during epileptogenesis from neural responses to propagated seizures.
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Affiliation(s)
- T Doi
- Miyazaki Medical College, Department of Psychiatry, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan
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28
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Abstract
Brain tissue has a remarkable ability to accumulate glutamate. This ability is due to glutamate transporter proteins present in the plasma membranes of both glial cells and neurons. The transporter proteins represent the only (significant) mechanism for removal of glutamate from the extracellular fluid and their importance for the long-term maintenance of low and non-toxic concentrations of glutamate is now well documented. In addition to this simple, but essential glutamate removal role, the glutamate transporters appear to have more sophisticated functions in the modulation of neurotransmission. They may modify the time course of synaptic events, the extent and pattern of activation and desensitization of receptors outside the synaptic cleft and at neighboring synapses (intersynaptic cross-talk). Further, the glutamate transporters provide glutamate for synthesis of e.g. GABA, glutathione and protein, and for energy production. They also play roles in peripheral organs and tissues (e.g. bone, heart, intestine, kidneys, pancreas and placenta). Glutamate uptake appears to be modulated on virtually all possible levels, i.e. DNA transcription, mRNA splicing and degradation, protein synthesis and targeting, and actual amino acid transport activity and associated ion channel activities. A variety of soluble compounds (e.g. glutamate, cytokines and growth factors) influence glutamate transporter expression and activities. Neither the normal functioning of glutamatergic synapses nor the pathogenesis of major neurological diseases (e.g. cerebral ischemia, hypoglycemia, amyotrophic lateral sclerosis, Alzheimer's disease, traumatic brain injury, epilepsy and schizophrenia) as well as non-neurological diseases (e.g. osteoporosis) can be properly understood unless more is learned about these transporter proteins. Like glutamate itself, glutamate transporters are somehow involved in almost all aspects of normal and abnormal brain activity.
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Affiliation(s)
- N C Danbolt
- Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, P.O. Box 1105, Blindern, N-0317, Oslo, Norway
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Abstract
A diversity of animal models are available for the study of epilepsy and these models have a proven history in advancing our understanding of basic mechanisms underlying epileptogenesis and have been instrumental in the screening of novel antiepileptic drugs. This review addresses the criteria that should be met in a valid animal model and provides an overview of current animal models that are relevant to human conditions. In addition, models not specific for any one human condition but rather exhibiting partial or generalized seizures are discussed. While most human disorders are without any animal model, those models that are clinically relevant have strengths and weaknesses. Finally, although few relevant, well-characterized animal models have been added to the list over recent years, major advancements in molecular genetics are contributing to the discovery of novel pathways involved in epileptogenesis.
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Massie A, Vandesande F, Arckens L. Expression of the high-affinity glutamate transporter EAAT4 in mammalian cerebral cortex. Neuroreport 2001; 12:393-7. [PMID: 11209956 DOI: 10.1097/00001756-200102120-00041] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
RT-PCR, immunocytochemistry and Western blotting were used to study the expression of the glutamate transporter EAAT4 in the cerebral cortex of cat and mouse. By means of RT-PCR we were able to detect EAAT4 mRNA in the cerebral cortex of both species. Sequencing ensured the specificity of the amplified fragment. Immunocytochemistry and Western blotting enabled us to localize EAAT4 protein in cat and mouse cerebral cortex. Intense EAAT4 immunoreactivity was found in the soma and dendrites of neurons mainly of layers II, III and V. For both species, the signal in the cerebellum was very intense and confined to the molecular and Purkinje cell layer.
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Affiliation(s)
- A Massie
- Laboratory of Neuroendocrinology and Immunological Biotechnology, Katholieke Universiteit Leuven, Belgium
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Ueda Y, Doi T, Tokumaru J, Yokoyama H, Nakajima A, Mitsuyama Y, Ohya-Nishiguchi H, Kamada H, Willmore LJ. Collapse of extracellular glutamate regulation during epileptogenesis: down-regulation and functional failure of glutamate transporter function in rats with chronic seizures induced by kainic acid. J Neurochem 2001; 76:892-900. [PMID: 11158261 DOI: 10.1046/j.1471-4159.2001.00087.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We used northern and western blotting to measure the quantity of glutamate and GABA transporters mRNA and their proteins within the hippocampal tissue of rats with epileptogenesis. Chronic seizures were induced by amygdalar injection of kainic acid 60 days before death. We found that expression of the mRNA and protein of the glial glutamate transporters GLAST and GLT-1 were down-regulated in the kainic acid-administered group. In contrast, EAAC-1 and GAT-3 mRNA and their proteins were increased, while GAT-1 mRNA and protein were not changed. We performed in vivo microdialysis in the freely moving state. During the interictal state, the extracellular glutamate concentration was increased, whereas the GABA level was decreased in the kainic acid group. Following potassium-induced depolarization, glutamate overflow was higher and the recovery time to the basal release was prolonged in the kainic acid group relative to controls. Our data suggest that epileptogenesis in rats with kainic acid-induced chronic seizures is associated with the collapse of extracellular glutamate regulation caused by both molecular down-regulation and functional failure of glutamate transport.
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Affiliation(s)
- Y Ueda
- Department of Psychiatry, Miyazaki Medical College, Miyazaki, Japan.
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