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Cervetto C, Amaroli A, Amato S, Gatta E, Diaspro A, Maura G, Signore A, Benedicenti S, Marcoli M. Photons Induce Vesicular Exocytotic Release of Glutamate in a Power-Dependent Way. Int J Mol Sci 2023; 24:10977. [PMID: 37446155 DOI: 10.3390/ijms241310977] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2023] [Revised: 06/20/2023] [Accepted: 06/27/2023] [Indexed: 07/15/2023] Open
Abstract
Increasing evidence indicates that photobiomodulation, based on tissue irradiation with photons in the red to near-infrared spectrum, may be an effective therapeutic approach to central nervous system disorders. Although nervous system functionality has been shown to be affected by photons in animal models, as well as in preliminary evidence in healthy subjects or in patients with neuropsychiatric disorders, the mechanisms involved in the photobiomodulation effects have not yet been clarified. We previously observed that photobiomodulation could stimulate glutamate release. Here, we investigate mechanisms potentially involved in the glutamate-releasing effect of photons from adult mouse cerebrocortical nerve terminals. We report evidence of photon ability to induce an exocytotic vesicular release of glutamate from the terminals of glutamatergic neurons in a power-dependent way. It can be hypothesized that photobiomodulation, depending on the potency, can release glutamate in a potentially neurotoxic or physiological range.
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Affiliation(s)
- Chiara Cervetto
- Department of Pharmacy, Section of Pharmacology and Toxicology, University of Genova, Viale Cembrano 4, 16148 Genova, Italy
- Interuniversity Center for the Promotion of the 3Rs Principles in Teaching and Research (Centro 3R), 56122 Pisa, Italy
| | - Andrea Amaroli
- Department of Earth, Environment and Life Sciences, University of Genova, Viale Benedetto XV 5, 16132 Genova, Italy
| | - Sarah Amato
- Department of Pharmacy, Section of Pharmacology and Toxicology, University of Genova, Viale Cembrano 4, 16148 Genova, Italy
| | - Elena Gatta
- DIFILAB, Department of Physics, University of Genova, Via Dodecaneso 33, 16146 Genova, Italy
| | - Alberto Diaspro
- DIFILAB, Department of Physics, University of Genova, Via Dodecaneso 33, 16146 Genova, Italy
- Nanoscopy, Nanophysics, Istituto Italiano di Tecnologia-IIT, Via Morego 30, 16133 Genova, Italy
- Biophysics Institute, National Research Council-CNR, Via de Marini, 6, 16149 Genova, Italy
| | - Guido Maura
- Department of Pharmacy, Section of Pharmacology and Toxicology, University of Genova, Viale Cembrano 4, 16148 Genova, Italy
| | - Antonio Signore
- Therapeutic Dentistry Department, Institute of Dentistry, Sechenov First Moscow State Medical University, Trubetskaya Str. 8, b. 2, 119992 Moskow, Russia
| | - Stefano Benedicenti
- Department of Surgical Sciences and Integrated Diagnostics, University of Genova, Viale Benedetto XV 6, 16132 Genova, Italy
| | - Manuela Marcoli
- Department of Pharmacy, Section of Pharmacology and Toxicology, University of Genova, Viale Cembrano 4, 16148 Genova, Italy
- Interuniversity Center for the Promotion of the 3Rs Principles in Teaching and Research (Centro 3R), 56122 Pisa, Italy
- Center of Excellence for Biomedical Research, University of Genova, 16132 Genova, Italy
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2
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Zeng ML, Cheng JJ, Kong S, Yang XL, Jia XL, Cheng XL, Chen L, He FG, Liu YM, Fan YT, Gongga L, Chen TX, Liu WH, He XH, Peng BW. Inhibition of Transient Receptor Potential Vanilloid 4 (TRPV4) Mitigates Seizures. Neurotherapeutics 2022; 19:660-681. [PMID: 35182379 PMCID: PMC9226259 DOI: 10.1007/s13311-022-01198-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/02/2022] [Indexed: 02/08/2023] Open
Abstract
Astrocytes are critical regulators of the immune/inflammatory response in several human central nervous system (CNS) diseases. Emerging evidence suggests that dysfunctional astrocytes are crucial players in seizures. The objective of this study was to investigate the role of transient receptor potential vanilloid 4 (TRPV4) in 4-aminopyridine (4-AP)-induced seizures and the underlying mechanism. We also provide evidence for the role of Yes-associated protein (YAP) in seizures. 4-AP was administered to mice or primary cultured astrocytes. YAP-specific small interfering RNA (siRNA) was administered to primary cultured astrocytes. Mouse brain tissue and surgical specimens from epileptic patient brains were examined, and the results showed that TRPV4 was upregulated, while astrocytes were activated and polarized to the A1 phenotype. The levels of glial fibrillary acidic protein (GFAP), cytokine production, YAP, signal transducer activator of transcription 3 (STAT3), intracellular Ca2+([Ca2+]i) and the third component of complement (C3) were increased in 4-AP-induced mice and astrocytes. Perturbations in the immune microenvironment in the brain were balanced by TRPV4 inhibition or the manipulation of [Ca2+]i in astrocytes. Knocking down YAP with siRNA significantly inhibited 4-AP-induced pathological changes in astrocytes. Our study demonstrated that astrocytic TRPV4 activation promoted neuroinflammation through the TRPV4/Ca2+/YAP/STAT3 signaling pathway in mice with seizures. Astrocyte TRPV4 inhibition attenuated neuroinflammation, reduced neuronal injury, and improved neurobehavioral function. Targeting astrocytic TRPV4 activation may provide a promising therapeutic approach for managing epilepsy.
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Affiliation(s)
- Meng-liu Zeng
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Donghu Rd185#, 430071 Wuhan, Hubei China
| | - Jing-jing Cheng
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Donghu Rd185#, 430071 Wuhan, Hubei China
| | - Shuo Kong
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Donghu Rd185#, 430071 Wuhan, Hubei China
| | - Xing-liang Yang
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Donghu Rd185#, 430071 Wuhan, Hubei China
| | - Xiang-lei Jia
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Donghu Rd185#, 430071 Wuhan, Hubei China
| | - Xue-lei Cheng
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Donghu Rd185#, 430071 Wuhan, Hubei China
| | - Ling Chen
- Institute of Forensic Medicine, School of Basic Medical Sciences, Wuhan University, 430071 Wuhan, Hubei China
| | - Fang-gang He
- Institute of Forensic Medicine, School of Basic Medical Sciences, Wuhan University, 430071 Wuhan, Hubei China
| | - Yu-min Liu
- Department of Neurology, Zhongnan Hospital, Wuhan University, Donghu Road 169#, 430071 Wuhan, Hubei China
| | - Yuan-teng Fan
- Department of Neurology, Zhongnan Hospital, Wuhan University, Donghu Road 169#, 430071 Wuhan, Hubei China
| | - Lanzi Gongga
- Tibet University Medical College, 850000 Lhasa, Tibet China
| | - Tao-xiang Chen
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Donghu Rd185#, 430071 Wuhan, Hubei China
| | - Wan-hong Liu
- Department of Immunology, School of Basic Medical Sciences, Wuhan University, 430071 Wuhan, Hubei China
| | - Xiao-hua He
- Department of Pathophysiology, School of Basic Medical Sciences, Wuhan University, 430071 Wuhan, Hubei China
| | - Bi-wen Peng
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Donghu Rd185#, 430071 Wuhan, Hubei China
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3
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Fedor FZ, Paraczky C, Ravasz L, Tóth K, Borhegyi Z, Somogyvári Z, Juhász G, Fekete Z. Electrophysiological and behavioral properties of 4-aminopyridine-induced epileptic activity in mice. Biol Futur 2021; 71:427-434. [PMID: 34554464 DOI: 10.1007/s42977-020-00047-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Accepted: 09/14/2020] [Indexed: 10/23/2022]
Abstract
4-aminopyridine (4-AP) is a widely used drug that induces seizure activity in rodents, especially in rats, although there is no consensus in the literature on the dose to be used in mice. The aim of the present study was to investigate the effect of the intraperitoneal administration of 4-AP in two doses (4 and 10 mg/kg) in vivo. EEG, movement, and video recordings were made simultaneously in male B6 mice to specify the details of the seizures and to determine whether there is a suitable non-lethal dose for seizure induction and for further molecular studies. Seizure behavior in mice differs from that seen in rats, with no characteristic stages of epileptic seizures, but with spiking and seizure activity. Seizure activity, although produced at both doses without being lethal, induced different changes of the EEG pattern. Smaller dose induced a lower amplitude seizure activity, decreased spiking activity and later onset of seizures, while higher dose induced a much more intense brain seizure activity and severe trembling. It is concluded that the intraperitoneal administration of 4-AP at a dose of 10 mg/kg induces explicit seizure activity in mice which is repeatable and can be suitable for further molecular research.
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Affiliation(s)
- F Z Fedor
- Doctoral School of Chemical Engineering and Material Sciences, University of Pannonia, Veszprém, 8200, Hungary. .,ELTE NAP Neuroimmunology Research Group, Department of Biochemistry, Institute of Biology, Eötvös Loránd University, Budapest, 1117, Hungary.
| | - C Paraczky
- Institute of Experimental Medicine, Budapest, 1083, Hungary
| | - L Ravasz
- ELTE NAP Neuroimmunology Research Group, Department of Biochemistry, Institute of Biology, Eötvös Loránd University, Budapest, 1117, Hungary
| | - K Tóth
- Laboratory of Molecular Neuroendocrinology, Institute of Experimental Medicine, 1083, Budapest, Hungary
| | - Z Borhegyi
- Department of Biochemistry, Eötvös Loránd University, Budapest, 1117, Hungary
| | - Z Somogyvári
- Theoretical Neuroscience and Complex Systems Research Group, Department of Computational Sciences, Wigner Research Centre for Physics, Budapest, 1121, Hungary
| | - G Juhász
- Department of Biochemistry, Eötvös Loránd University, Budapest, 1117, Hungary
| | - Z Fekete
- Research Group for Implantable Microsystems, Faculty of Information Technology and Bionics, Pázmány Péter Catholic University, Budapest, 1083, Hungary.,Centre for Energy Research, Budapest, 1121, Hungary
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4
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Shao L, Jiang GT, Yang XL, Zeng ML, Cheng JJ, Kong S, Dong X, Chen TX, Han S, Yin J, Liu WH, He XH, He C, Peng BW. Silencing of circIgf1r plays a protective role in neuronal injury via regulating astrocyte polarization during epilepsy. FASEB J 2021; 35:e21330. [PMID: 33417289 DOI: 10.1096/fj.202001737rr] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Revised: 12/02/2020] [Accepted: 12/14/2020] [Indexed: 01/09/2023]
Abstract
Epilepsy is a common brain disorder, repeated seizures of epilepsy may lead to a series of brain pathological changes such as neuronal or glial damage. However, whether circular RNAs are involved in neuronal injury during epilepsy is not fully understood. Here, we screened circIgf1r in the status epilepticus model through circRNA sequencing, and found that it was upregulated after the status epilepticus model through QPCR analysis. Astrocytes polarizing toward neurotoxic A1 phenotype and neurons loss were observed after status epilepticus. Through injecting circIgf1r siRNA into the lateral ventricle, it was found that knocking down circIgf1r in vivo would induce the polarization of astrocytes to phenotype A2 and reduce neuronal loss. The results in vitro further confirmed that inhibiting the expression of circIgf1r in astrocytes could protect neurons by converting reactive astrocytes from A1 to the protective A2. In addition, knocking down circIgf1r in astrocytes could functionally promote astrocyte autophagy and relieve the destruction of 4-AP-induced autophagy flux. In terms of mechanism, circIgf1r promoted the polarization of astrocytes to phenotype A1 by inhibiting autophagy. Taken together, our results reveal circIgf1r may serve as a potential target for the prevention and treatment of neuron damage after epilepsy.
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Affiliation(s)
- Lin Shao
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Wuhan, China
| | - Guang-Tong Jiang
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Wuhan, China
| | - Xing-Liang Yang
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Wuhan, China
| | - Meng-Liu Zeng
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Wuhan, China
| | - Jing-Jing Cheng
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Wuhan, China
| | - Shuo Kong
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Wuhan, China
| | - Xin Dong
- Department of Pathophysiology, School of Basic Medical Sciences, Wuhan University, Wuhan, China
| | - Tao-Xiang Chen
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Wuhan, China
| | - Song Han
- Department of Pathophysiology, School of Basic Medical Sciences, Wuhan University, Wuhan, China
| | - Jun Yin
- Department of Pathophysiology, School of Basic Medical Sciences, Wuhan University, Wuhan, China
| | - Wan-Hong Liu
- Department of Immunology, School of Basic Medical Sciences, Wuhan University, Wuhan, China
| | - Xiao-Hua He
- Department of Pathophysiology, School of Basic Medical Sciences, Wuhan University, Wuhan, China
| | - Chunjiang He
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Wuhan, China.,College of Biomedicine and Health, Huazhong Agricultural University, Wuhan, China
| | - Bi-Wen Peng
- Department of Physiology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Wuhan, China
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5
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Positive Allosteric Modulation of CB1 and CB2 Cannabinoid Receptors Enhances the Neuroprotective Activity of a Dual CB1R/CB2R Orthosteric Agonist. Life (Basel) 2020; 10:life10120333. [PMID: 33302569 PMCID: PMC7763181 DOI: 10.3390/life10120333] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2020] [Revised: 12/04/2020] [Accepted: 12/06/2020] [Indexed: 12/13/2022] Open
Abstract
Preclinical studies highlighted that compounds targeting cannabinoid receptors could be useful for developing novel therapies against neurodegenerative disorders. However, the chronic use of orthosteric agonists alone has several disadvantages, limiting their usefulness as clinically relevant drugs. Positive allosteric modulators might represent a promising approach to achieve the potential therapeutic benefits of orthosteric agonists of cannabinoid receptors through increasing their activity and limiting their adverse effects. The aim of the present study was to show the effects of positive allosteric ligands of cannabinoid receptors on the activity of a potent dual orthosteric agonist for neuroinflammation and excitotoxic damage by excessive glutamate release. The results indicate that the combination of an orthosteric agonist with positive allosteric modulators could represent a promising therapeutic approach to the treatment of neurodegenerative disorders.
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6
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Bazzigaluppi P, Weisspapir I, Stefanovic B, Leybaert L, Carlen PL. Astrocytic gap junction blockade markedly increases extracellular potassium without causing seizures in the mouse neocortex. Neurobiol Dis 2016; 101:1-7. [PMID: 28007587 DOI: 10.1016/j.nbd.2016.12.017] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Revised: 11/24/2016] [Accepted: 12/18/2016] [Indexed: 10/20/2022] Open
Abstract
Extracellular potassium concentration, [K+]o, is a major determinant of neuronal excitability. In the healthy brain, [K+]o levels are tightly controlled. During seizures, [K+]o increases up to 15mM and is thought to cause seizures due to its depolarizing effect. Although astrocytes have been suggested to play a key role in the redistribution (or spatial buffering) of excess K+ through Connexin-43 (Cx43)-based Gap Junctions (GJs), the relation between this dynamic regulatory process and seizure generation remains unknown. Here we contrasted the role of astrocytic GJs and hemichannels by studying the effect of GJ and hemichannel blockers on [K+]o regulation in vivo. [K+]o was measured by K+-sensitive microelectrodes. Neuronal excitability was estimated by local field potential (LFP) responses to forepaw stimulation and changes in the power of resting state activity. Starting at the baseline [K+]o level of 1.61±0.3mM, cortical microinjection of CBX, a broad spectrum connexin channel blocker, increased [K+]o to 11±3mM, Cx43 GJ/hemichannel blocker Gap27 increased it from 1.9±0.7 to 9±1mM. At these [K+]o levels, no seizures were observed. Cx43 hemichannel blockade with TAT-Gap19 increased [K+]o by only ~1mM. Microinjection of 4-aminopyridine, a known convulsant, increased [K+]o to ~10mM and induced spontaneously recurring seizures, whereas direct application of K+ did not trigger seizure activity. These findings are the first in vivo demonstration that astrocytic GJs are major determinants for the spatial buffering of [K+]o and that an increase in [K+]o alone does not trigger seizures in the neocortex.
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Affiliation(s)
- Paolo Bazzigaluppi
- Fundamental Neurobiology, Krembil Research Institute, University Health Network, M5T 2S8 Toronto, Ontario, Canada; Physical Sciences, Sunnybrook Research Institute, M4N 3M5 Toronto, Ontario, Canada.
| | - Iliya Weisspapir
- Fundamental Neurobiology, Krembil Research Institute, University Health Network, M5T 2S8 Toronto, Ontario, Canada
| | - Bojana Stefanovic
- Physical Sciences, Sunnybrook Research Institute, M4N 3M5 Toronto, Ontario, Canada; Department of Medical Biophysics, University of Toronto, Ontario, Canada
| | - Luc Leybaert
- Department of Basic Medical Sciences, University of Ghent, 9000 Ghent, Belgium
| | - Peter L Carlen
- Fundamental Neurobiology, Krembil Research Institute, University Health Network, M5T 2S8 Toronto, Ontario, Canada
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7
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Kasatkina LA. 4-Аminopyridine sequesters intracellular Ca 2+ which triggers exocytosis in excitable and non-excitable cells. Sci Rep 2016; 6:34749. [PMID: 27703262 PMCID: PMC5050491 DOI: 10.1038/srep34749] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Accepted: 09/16/2016] [Indexed: 12/19/2022] Open
Abstract
4-aminopyridine is commonly used to stimulate neurotransmitter release resulting from sustained plasma membrane depolarization and Ca2+-influx from the extracellular space. This paper elucidated unconventional mechanism of 4-aminopyridine-stimulated glutamate release from neurons and non-neuronal cells which proceeds in the absence of external Ca2+. In brain nerve terminals, primary neurons and platelets 4-aminopyridine induced the exocytotic release of glutamate that was independent of external Ca2+ and was triggered by the sequestration of Ca2+ from intracellular stores. The initial level of 4-aminopyridine-stimulated glutamate release from neurons in the absence or presence of external Ca2+ was subequal and the difference was predominantly associated with subsequent tonic release of glutamate in Ca2+-supplemented medium. The increase in [Ca2+]i and the secretion of glutamate stimulated by 4-aminopyridine in Ca2+-free conditions have resulted from Ca2+ efflux from endoplasmic reticulum and were abolished by intracellular free Ca2+ chelator BAPTA. This suggests that Ca2+ sequestration plays a profound role in the 4-aminopyridine-mediated stimulation of excitable and non-excitable cells. 4-Aminopyridine combines the properties of depolarizing agent with the ability to sequester intracellular Ca2+. The study unmasks additional mechanism of action of 4-aminopyridine, an active substance of drugs for treatment of multiple sclerosis and conditions related to reduced Ca2+ efflux from intracellular stores.
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Affiliation(s)
- Ludmila A Kasatkina
- The Department of Neurochemistry, Palladin Institute of Biochemistry, NAS of Ukraine 9, Leontovicha Street, Kyiv, 01030, Ukraine
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8
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Correlation between the increased release of catecholamines evoked by local anesthetics and their analgesic and adverse effects: Role of K + channel inhibition. Brain Res Bull 2016; 124:21-6. [DOI: 10.1016/j.brainresbull.2016.03.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Revised: 03/11/2016] [Accepted: 03/16/2016] [Indexed: 01/05/2023]
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9
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Cao Z, Cui Y, Busse E, Mehrotra S, Rainier JD, Murray TF. Gambierol inhibition of voltage-gated potassium channels augments spontaneous Ca2+ oscillations in cerebrocortical neurons. J Pharmacol Exp Ther 2014; 350:615-23. [PMID: 24957609 DOI: 10.1124/jpet.114.215319] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Gambierol is a marine polycyclic ether toxin produced by the marine dinoflagellate Gambierdiscus toxicus and is a member of the ciguatoxin toxin family. Gambierol has been demonstrated to be either a low-efficacy partial agonist/antagonist of voltage-gated sodium channels or a potent blocker of voltage-gated potassium channels (Kvs). Here we examined the influence of gambierol on intact cerebrocortical neurons. We found that gambierol produced both a concentration-dependent augmentation of spontaneous Ca(2+) oscillations, and an inhibition of Kv channel function with similar potencies. In addition, an array of selective as well as universal Kv channel inhibitors mimicked gambierol in augmenting spontaneous Ca(2+) oscillations in cerebrocortical neurons. These data are consistent with a gambierol blockade of Kv channels underlying the observed increase in spontaneous Ca(2+) oscillation frequency. We also found that gambierol produced a robust stimulation of phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2). Gambierol-stimulated ERK1/2 activation was dependent on both inotropic [N-methyl-d-aspartate (NMDA)] and type I metabotropic glutamate receptors (mGluRs) inasmuch as MK-801 [NMDA receptor inhibitor; (5S,10R)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate], S-(4)-CGP [S-(4)-carboxyphenylglycine], and MTEP [type I mGluR inhibitors; 3-((2-methyl-4-thiazolyl)ethynyl) pyridine] attenuated the response. In addition, 2-aminoethoxydiphenylborane, an inositol 1,4,5-trisphosphate receptor inhibitor, and U73122 (1-[6-[[(17b)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione), a phospholipase C inhibitor, both suppressed gambierol-induced ERK1/2 activation, further confirming the role of type I mGluR-mediated signaling in the observed ERK1/2 activation. Finally, we found that gambierol produced a concentration-dependent stimulation of neurite outgrowth that was mimicked by 4-aminopyridine, a universal potassium channel inhibitor. Considered together, these data demonstrate that gambierol alters both Ca(2+) signaling and neurite outgrowth in cerebrocortical neurons as a consequence of blockade of Kv channels.
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Affiliation(s)
- Zhengyu Cao
- State Key Laboratory of Natural Medicines, Department of Complex Prescription of Traditional Chinese Medicine, China Pharmaceutical University, Nanjing, People's Republic of China (Z.C.); Department of Pharmacology, School of Medicine, Creighton University, Omaha, Nebraska (Z.C., Y.C., E.B., S.M., T.F.M.); and Department of Chemistry, University of Utah, Salt Lake City, Utah (J.D.R.)
| | - Yanjun Cui
- State Key Laboratory of Natural Medicines, Department of Complex Prescription of Traditional Chinese Medicine, China Pharmaceutical University, Nanjing, People's Republic of China (Z.C.); Department of Pharmacology, School of Medicine, Creighton University, Omaha, Nebraska (Z.C., Y.C., E.B., S.M., T.F.M.); and Department of Chemistry, University of Utah, Salt Lake City, Utah (J.D.R.)
| | - Eric Busse
- State Key Laboratory of Natural Medicines, Department of Complex Prescription of Traditional Chinese Medicine, China Pharmaceutical University, Nanjing, People's Republic of China (Z.C.); Department of Pharmacology, School of Medicine, Creighton University, Omaha, Nebraska (Z.C., Y.C., E.B., S.M., T.F.M.); and Department of Chemistry, University of Utah, Salt Lake City, Utah (J.D.R.)
| | - Suneet Mehrotra
- State Key Laboratory of Natural Medicines, Department of Complex Prescription of Traditional Chinese Medicine, China Pharmaceutical University, Nanjing, People's Republic of China (Z.C.); Department of Pharmacology, School of Medicine, Creighton University, Omaha, Nebraska (Z.C., Y.C., E.B., S.M., T.F.M.); and Department of Chemistry, University of Utah, Salt Lake City, Utah (J.D.R.)
| | - Jon D Rainier
- State Key Laboratory of Natural Medicines, Department of Complex Prescription of Traditional Chinese Medicine, China Pharmaceutical University, Nanjing, People's Republic of China (Z.C.); Department of Pharmacology, School of Medicine, Creighton University, Omaha, Nebraska (Z.C., Y.C., E.B., S.M., T.F.M.); and Department of Chemistry, University of Utah, Salt Lake City, Utah (J.D.R.)
| | - Thomas F Murray
- State Key Laboratory of Natural Medicines, Department of Complex Prescription of Traditional Chinese Medicine, China Pharmaceutical University, Nanjing, People's Republic of China (Z.C.); Department of Pharmacology, School of Medicine, Creighton University, Omaha, Nebraska (Z.C., Y.C., E.B., S.M., T.F.M.); and Department of Chemistry, University of Utah, Salt Lake City, Utah (J.D.R.)
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10
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Toprani S, Durand DM. Long-lasting hyperpolarization underlies seizure reduction by low frequency deep brain electrical stimulation. J Physiol 2013; 591:5765-90. [PMID: 23981713 DOI: 10.1113/jphysiol.2013.253757] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Mesial temporal lobe epilepsy (MTLE) is a common medically refractory neurological disease. Deep brain electrical stimulation (DBS) of grey matter has been used for MTLE with limited success. However, stimulation of a white matter tract connecting the hippocampi, the ventral hippocampal commissure (VHC), with low frequencies that simulate interictal discharges has shown promising results, with seizure reduction greater than 98% in bilateral hippocampi during stimulation and greater than 50% seizure reduction in bilateral hippocampi after treatment. A major hurdle to the implementation and optimization of this treatment is that the mechanisms of seizure reduction by low frequency electrical stimulation (LFS) are not known. The goal of this study is to understand how commissural fibre tract stimulation reduces bilateral hippocampal epileptic activity in an in vitro slice preparation containing bilateral hippocampi connected by the VHC. It is our hypothesis that electrical stimuli induce hyperpolarization lasting hundreds of milliseconds following each pulse which reduces spontaneous epileptic activity during each inter-stimulus interval (ISI). Stimulus-induced long-lasting-hyperpolarization (LLH) can be mediated by GABA(B) inhibitory post-synaptic potentials (IPSPs) or slow after-hyperpolarization (sAHP). To test the role of LLH in effective bilateral seizure reduction by fibre tract stimulation, we measured stimulus-induced hyperpolarization during LFS of the VHC using electrophysiology techniques. Antagonism of the GABA(B) IPSP and/or sAHP diminished stimulus-induced hyperpolarization concurrently with LFS efficacy (greater than 50% reduction). Blocking both the GABA(B) IPSP and sAHP simultaneously eliminated the effect of electrical stimulation on seizure reduction entirely. These data show that LFS of the VHC is an effective protocol for bilateral hippocampal seizure reduction and that its efficacy relies on the induction of long-lasting hyperpolarization mediated through GABA(B) IPSPs and sAHP. Based on this study, optimization of the timing of LFS and LFS-induced-LLH may lead to improved outcomes from DBS treatments for human epilepsy.
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Affiliation(s)
- Sheela Toprani
- D. M. Durand: Neural Engineering Center, Departments of Biomedical Engineering and Neurosciences, Case Western Reserve University, Cleveland, OH 44106, USA.
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Fiber tract stimulation can reduce epileptiform activity in an in-vitro bilateral hippocampal slice preparation. Exp Neurol 2012; 240:28-43. [PMID: 23123405 DOI: 10.1016/j.expneurol.2012.10.022] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2012] [Accepted: 10/24/2012] [Indexed: 11/21/2022]
Abstract
Mesial temporal lobe epilepsy (MTLE) is a common medically refractory neurological disease that has been treated with electrical stimulation of gray matter with limited success. However, stimulation of a white matter tract connecting the hippocampi could maximize treatment efficacy and extent. We tested low-frequency stimulation (LFS) of a novel target that enables simultaneous targeting of bilateral hippocampi: the ventral hippocampal commissure (VHC) with a novel in-vitro slice preparation containing bilateral hippocampi connected by the VHC. The goal of this study is to understand the role of hippocampal interplay in seizure propagation and reduction by commissural fiber tract stimulation. LFS is applied to the VHC as extracellular and intracellular recording techniques are combined with signal processing to estimate several metrics of epilepsy including: (1) total time occupied by seizure activity (%); (2) seizure duration (s); (3) seizures per minute (#); and (4) power in the ictal (V(2)Hz(-1)); as well as (5) interictal spectra (V(2)Hz(-1)). Bilateral epileptiform activity in this preparation is highly correlated between hippocampi. Application of LFS to the VHC reduces all metrics of epilepsy during treatment in an amplitude and frequency dependent manner. This study lends several insights into the mechanisms of bilateral seizure reduction by LFS of the VHC, including that depolarization blocking, LTD/LTP and GABA(A) are not involved. Importantly, enhanced post-stimulation 1-Hz spiking correlates with long-lasting seizure reduction and both are heightened by targeting bilateral hippocampi via the VHC. Therefore, stimulating bilateral hippocampi via a single electrode in the VHC may provide an effective MTLE treatment.
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Sitges M, Sanchez-Tafolla B, Chiu L, Aldana B, Guarneros A. Vinpocetine inhibits glutamate release induced by the convulsive agent 4-aminopyridine more potently than several antiepileptic drugs. Epilepsy Res 2011; 96:257-66. [DOI: 10.1016/j.eplepsyres.2011.06.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2010] [Revised: 06/08/2011] [Accepted: 06/11/2011] [Indexed: 10/18/2022]
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13
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Effects of 4-Aminopyridine on Organelle Movement in Cultured Mouse Dorsal Root Ganglion Neurites. J Mol Neurosci 2009; 40:295-302. [DOI: 10.1007/s12031-009-9219-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2009] [Accepted: 07/13/2009] [Indexed: 10/20/2022]
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14
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Simultaneous glutamate and EEG activity measurements during seizures in rat hippocampal region with the use of an electrochemical biosensor. J Neurosci Methods 2008; 168:48-53. [DOI: 10.1016/j.jneumeth.2007.09.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2007] [Revised: 09/05/2007] [Accepted: 09/07/2007] [Indexed: 11/17/2022]
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Mora G, Tapia R. Effects of retigabine on the neurodegeneration and extracellular glutamate changes induced by 4-aminopyridine in rat hippocampus in vivo. Neurochem Res 2006; 30:1557-65. [PMID: 16362775 DOI: 10.1007/s11064-005-8834-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/23/2005] [Indexed: 01/21/2023]
Abstract
We have previously shown that microdialysis perfusion of the K+ channel blocker 4-aminopyridine (4-AP) in rat hippocampus induces convulsions and neurodegeneration, due to the stimulation of glutamate release from synaptic terminals. Retigabine is an opener of the KCNQ2/Q3-type K+ channel that possesses antiepileptic action and may be neuroprotective, and we have therefore studied its effect on the hyperexcitation, the neuronal damage and the changes in extracellular glutamate induced by 4-AP. Retigabine and 4-AP were co-administered by microdialysis in the hippocampus of anesthetized rats, with simultaneous recording of the EEG, and the extracellular concentration of glutamate was measured in the microdialysis fractions. In 70-80% of the rats tested retigabine reduced the 4-AP-induced stimulation of glutamate release and prevented the neuronal damage observed at 24 h in the CA1 hippocampal region. However, retigabine did not block the EEG epileptic discharges and their duration was reduced in only 20-25% of the tested animals. We conclude that the neuroprotective action of retigabine is probably due to the blockade of the 4-AP-induced stimulation of glutamate release. This inhibition, however, was not sufficient to block the epileptic activity.
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Affiliation(s)
- Gabriela Mora
- Departamento de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, AP 70-253, 04510, México, D. F., México
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Lees G, Stöhr T, Errington AC. Stereoselective effects of the novel anticonvulsant lacosamide against 4-AP induced epileptiform activity in rat visual cortex in vitro. Neuropharmacology 2006; 50:98-110. [PMID: 16225894 DOI: 10.1016/j.neuropharm.2005.08.016] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2005] [Revised: 08/10/2005] [Accepted: 08/25/2005] [Indexed: 10/25/2022]
Abstract
We examined effects of the novel anticonvulsant lacosamide and its inactive isomer (SPM 6953) in an in vitro model of epileptiform activity. Focal field potential recordings (34+/-0.2 degrees C) were obtained from 17 to 22 day old rat brain slices. Physiological synaptic transmission (fEPSP amplitude and duration) in CA1 of rat hippocampus was not significantly altered (P > 0.05, n = 4) by lacosamide (1 microM-1 mM). Recording from visual cortex during application of 4-aminopyridine (4-AP; 100 microM) revealed both spontaneous and evoked 'ictal like' discharges. Spontaneous ictal like discharges in the visual cortex were blocked by 100 microM carbamazepine (CBZ), 100 microM pentobarbital and 200 microM phenobarbital (PHB) but were insensitive to the anti-absence drug ethosuximide (750 microM; n = 4, P > 0.05). Lacosamide reduced tonic duration and maximal firing frequency with EC(50)s of 41 and 71 microM, respectively. In contrast, the S stereoisomer (100-320 microM) produced no significant effect on spontaneous ictal activity (n = 3-4, P > 0.05). Seizures induced by high frequency (100 Hz, 1s) stimulation were selectively reduced in amplitude by PHB (200 microM) and frequency by CBZ (100 microM; n = 6) and lacosamide (100 microM; n = 4). GABAergic negative going potentials were attenuated by CBZ (irreversible with washing) and lacosamide (reversible) but not by PHB. We conclude that lacosamide blocks 4-AP induced epileptiform activity in the visual cortex. This novel anticonvulsant drug appears to inhibit epileptogenesis (seizure spread) by interacting with a stereoselective, but as yet unidentified, target site in rodent neocortex in the mid-micromolar range.
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Affiliation(s)
- George Lees
- Department of Pharmacology and Toxicology, Otago School of Medical Sciences, University of Otago, Dunedin, New Zealand.
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17
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Yang XF, Ouyang Y, Kennedy BR, Rothman SM. Cooling blocks rat hippocampal neurotransmission by a presynaptic mechanism: observations using 2-photon microscopy. J Physiol 2005; 567:215-24. [PMID: 15961429 PMCID: PMC1474157 DOI: 10.1113/jphysiol.2005.088948] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Over the past decade there has been great interest in the therapeutic potential of brain cooling for epilepsy, stroke, asphyxia and other neurological diseases. However, there is still no consensus regarding the neurophysiological effect(s) of brain cooling. We employed standard physiological techniques and 2-photon microscopy to directly examine the effect of temperature on evoked neurotransmitter release in rat hippocampal slices. We observed a monotonic decline in extracellular synaptic potentials and their initial slope over the temperature range 33-20 degrees C, when the slices were cooled to a new set point in less than 5 s. Imaging the fluorescent synaptic marker FM1-43 with 2-photon microscopy showed that the same cooling protocol dramatically reduced transmitter release between 33 and 20 degrees C. Cooling also reduced the terminal FM1-43 destaining that was induced by direct depolarization with elevated K+, indicating that axonal conduction block cannot account for our observations. The temperature dependence of FM1-43 destaining correlated well with the effect of temperature on field potential slope, compatible with a presynaptic explanation for our electrophysiological observations. Optical measurement of FM1-43 dissociation from cell membranes was not affected by temperature, and rapid cooling of slices loaded with FM1-43 did not increase their fluorescence. Our experiments provide visible evidence that a major neurophysiological effect of cooling in the mammalian brain is a reduction in the efficacy of neurotransmitter release. This presynaptic effect may account for some of the therapeutic benefits of cooling in epilepsy and possibly stroke.
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Affiliation(s)
- Xiao-Feng Yang
- Department of Neurology, Box 8111, Washington University School of Medicine, 660 South Euclid Avenue, St Louis, MO 63110, USA.
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Gu Y, Ge SY, Ruan DY. Effect of 4-aminopyridine on synaptic transmission in rat hippocampal slices. Brain Res 2004; 1006:225-32. [PMID: 15051526 DOI: 10.1016/j.brainres.2004.02.008] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/02/2004] [Indexed: 10/26/2022]
Abstract
Extracellular field excitatory postsynaptic potentials (fEPSPs) were recorded in area CA1 of rat hippocampal slices in vitro. The responses evoked by spontaneously released glutamate and GABA were recorded from area CA1 pyramidal neurons in rat hippocampal slices in whole-cell mode. The glutamate and GABA receptor-associated ligand-gated currents were obtained from dissociated single hippocampal pyramidal cells. The results showed that 4-aminopyridine (4-AP) had obvious effects on both presynaptic and postsynaptic events. Applications of 4-AP in micromolar concentration resulted in persistent enhancement of the initial slope of fEPSPs with the half-maximal enhancement concentration (EC(50)) of 46.7+/-2.68 microM. At the concentration of 200 microM, 4-AP increased the initial slopes of the total fEPSPs, NMDA- and AMPA-mediated fEPSPs components to 225.6+/-23.8%, 177.4+/-20.1% and 142.3+/-18.9%, respectively, but had no effect on the fiber volley. The half-maximal stimulus intensity to induce responses was reduced from 5.14+/-0.27 to 3.58+/-0.23 V. The frequencies of mEPSCs and mIPSCs were increased to 324.2+/-25.4% and 287.3+/-36.3% by 200 microM 4-AP. The amplitude histograms of mEPSCs and mIPSCs were fitted with Gaussian distributions. After 200 microM 4-AP application, the first and second peaks in Gaussian distributions of mEPSCs were shifted from 8.73+/-0.94 and 17.78+/-2.13pA to 10.48+/-0.82 and 21.14+/-2.45 pA, while those of mIPSCs were shifted from 13.65+/-0.96 and 25.51+/-2.95 pA to 11.21+/-1.04 and 23.08+/-2.37 pA. At 200 microM, 4-AP reduced paired-pulse facilitation and accelerated synaptic fatigue induced by stimulation at 10 Hz (for 1 s) and the ratio of fEPSPs(10)/fEPSPs(1) was decreased from 1.62+/-0.16 to 0.61+/-0.15. At 200 microM, 4-AP inhibited postsynaptic GABA currents induced by 5 microM GABA to 68.2+/-15.5%: by countering the effect of enhanced release of GABA from presynaptic terminals, this could depress the inhibitory pathway. Also at 200 microM, 4-AP increased NMDA currents to 155.3+/-17.8%, but had no significant effect on AMPA currents (94.2+/-15.6%). Our experimental results thus show that 4-AP-induced changes of synaptic transmission in area CA1 of rat hippocampus may be attributed to 4-AP's effects on both presynaptic terminals and postsynaptic receptors.
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Affiliation(s)
- Yan Gu
- School of Life Science, University of Science and Technology of China, Hefei, Anhui 230027, PR China
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19
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Galván E, Sitges M. Characterization of the participation of sodium channels on the rise in Na+ induced by 4-aminopyridine (4-AP) in synaptosomes. Neurochem Res 2004; 29:347-55. [PMID: 15002730 DOI: 10.1023/b:nere.0000013737.17288.ce] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The participation of voltage-sensitive Na+ channels (VSSC) on the changes on internal (i) Na+, K+, Ca2+, and on DA, Glu, and GABA release caused by different concentrations of 4-AP was investigated in striatum synaptosomes. TTX, which abolished the increase in Na(i) (as determined with SBFI), induced by 0.1 mM 4-AP only inhibited by 30% the rise in Na(i) induced by 1 mM 4-AP. One millimolar 4-AP markedly decreased the fluorescence of the K+ indicator dye PBFI but 0.1 mM 4-AP did not. Like 1 mM 4-AP, ouabain decreased PBFI fluorescence and increased a considerable fraction of Na(i) in a TTX-insensitive manner. In contrast with the different TTX sensitivity of the rise in Na(i) induced by 0.1 and 1 mM 4-AP, the rise in Ca(i) (as determined with fura-2) induced by the two concentrations of 4-AP was markedly inhibited by TTX, as well as by omega-agatoxin in combination with omega-conotoxin GVIA, indicating that only the TTX-sensitive fraction of the rise in Na(i) induced by 4-AP is linked with the activation of presynaptic Ca2+ channels. It is concluded that the TTX-sensitive fraction of neurotransmitter release evoked by 4-AP is released by exocytosis, and the TTX insensitive fraction involves reversal of the neurotransmitters transporters. This contrasts with the exocytosis evoked by high K+ that is unchanged by TTX and with the neurotransmitter-transporter-mediated release evoked by veratridine, which is highly TTX sensitive and does not require activation of Ca2+ channels.
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Affiliation(s)
- Emilio Galván
- Departmento de Biología Celular y Fisiología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Mexico City, Mexico
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Fehr C, Shirley RL, Metten P, Kosobud AEK, Belknap JK, Crabbe JC, Buck KJ. Potential pleiotropic effects of Mpdz on vulnerability to seizures. GENES BRAIN AND BEHAVIOR 2004; 3:8-19. [PMID: 14960011 DOI: 10.1111/j.1601-183x.2004.00035.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
We previously mapped quantitative trait loci (QTL) responsible for approximately 26% of the genetic variance in acute alcohol and barbiturate (i.e., pentobarbital) withdrawal convulsion liability to a < 1 cM (1.8 Mb) interval of mouse chromosome 4. To date, Mpdz, which encodes the multiple PSD95/DLG/ZO-1 (PDZ) domain protein (MPDZ), is the only gene within the interval shown to have allelic variants that differ in coding sequence and/or expression, making it a strong candidate gene for the QTL. Previous work indicates that Mpdz haplotypes in standard mouse strains encode distinct protein variants (MPDZ1-3), and that MPDZ status is genetically correlated with severity of withdrawal from alcohol and pentobarbital. Here, we report that MPDZ status cosegregates with withdrawal convulsion severity in lines of mice selectively bred for phenotypic differences in severity of acute withdrawal from alcohol [i.e., High Alcohol Withdrawal (HAW) and Low Alcohol Withdrawal (LAW) lines] or pentobarbital [High Pentobarbital Withdrawal (HPW) and Low Pentobarbital Withdrawal (LPW) lines]. These analyses confirm that MPDZ status is associated with severity of alcohol and pentobarbital withdrawal convulsions. Using a panel of standard inbred strains of mice, we assessed the association between MPDZ status with seizures induced by nine chemiconvulsants. Our results show that MPDZ status is genetically correlated with seizure sensitivity to pentylenetetrazol, kainate and other chemiconvulsants. Our results provide evidence that Mpdz may have pleiotropic effects on multiple seizure phenotypes, including seizures associated with withdrawal from two classes of central nervous system (CNS) depressants and sensitivity to specific chemiconvulsants that affect glutaminergic and GABAergic neurotransmission.
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Affiliation(s)
- C Fehr
- Department of Behavioral Neuroscience and Portland Alcohol Research Center, Oregon Health & Science University, Portland, OR 97239-3098, USA
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Abraham H, Losonczy A, Czéh G, Lázár GY. Potassium channel blockers tetraethylammonium and 4-aminopyridine fail to prevent microglial activation induced by elevated potassium concentration. ACTA BIOLOGICA HUNGARICA 2003; 54:63-78. [PMID: 12712959 DOI: 10.1556/abiol.54.2003.1.7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The effect of potassium channel blocker tetraethylammonium and 4-aminopyridine was examined on the elevated K+ concentration-induced microglial activation on rat hippocampal slice preparations. Microglial cells were detected by immunohistochemisty with a monoclonal antibody (OX 42) raised against a type 3 complement receptor. During activation the morphology of the microglial cells changes and the staining intensity increases. The degree of microglial activation was determined by measuring the integrated optical density of the cells. Tetraethylammonium and 4-aminopyridine failed to reduce the elevated K+ concentration-induced microglial activation. Both potassium channel blockers, when applied on the hippocampal slices without K+, caused significantly increased microglial activation as compared to the control slices. In order to check whether the functional alteration of the neuronal population induced by 4-aminopyridine caused the activation of the microglial cells, Schaffer collaterals were cut to block spreading of epileptiform hyperactivity of the CA3 pyramidal cells to the CA1 region. No significant differences were found in microglial activation between the CA3 and CA1 regions, indicating that the effect of 4-aminopyridine on microglial cells is independent of the epileptiform activity caused by the drug.
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Affiliation(s)
- Hajnalka Abraham
- Central Electron Microscopic Laboratory, Pécs University, Medical Faculty, Szigeti út 12, H-7643 Pécs, Hungary
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22
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Salazar P, Tapia R, Rogawski MA. Effects of neurosteroids on epileptiform activity induced by picrotoxin and 4-aminopyridine in the rat hippocampal slice. Epilepsy Res 2003; 55:71-82. [PMID: 12948618 DOI: 10.1016/s0920-1211(03)00112-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The neurosteroids allopregnanolone (5alpha-pregnan-3alpha-ol-20-one; 5alpha,3alpha-P) and its 5beta-epimer pregnanolone (5beta,3alpha-P), and pregnenolone sulfate (PS) were examined for effects on spontaneous epileptiform discharges induced by 100 microM picrotoxin (PTX) and 55 microM 4-aminopyridine (4-AP) in the CA3 region of the rat hippocampal slice. At a concentration of 10 microM, 5alpha,3alpha-P partially reduced PTX-induced bursting and at 30 and 90 microM completely suppressed bursting. In contrast, 100 microM 5beta,3alpha-P failed to alter the discharge frequency. 5alpha,3alpha-P depressed 4-AP-induced bursting with similar potency as in the PTX model; 100 microM 5beta,3alpha-P was also partially effective. In the 4-AP model, 5alpha,3alpha-P inhibited both the more frequent predominantly positive-going potentials as well as the less frequent negative-going potentials that may be generated by synchronous GABAergic interneuron firing. PS enhanced the PTX bursting frequency and, in the 4-AP model, increased the frequency of negative potentials but did not alter the frequency of positive potentials. By itself, PS did not induce bursting. The effects of the steroids in the in vitro seizure models largely correspond with their activities on GABA(A) receptors; suppression of discharges may occur as a result of direct activation of these receptors rather than modulation of GABA-mediated synaptic responses. PTX and 4-AP-induced bursting in the hippocampal slice are useful models for directly assessing neurosteroid effects on seizure susceptibility under conditions that eliminate the factor of brain bioavailability.
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Affiliation(s)
- Patricia Salazar
- Epilepsy Research Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 49 Convent Drive Room 5A75 MSC 4457, Bethesda, MD 20892-4457, USA
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Westphalen RI, Hemmings HC. Selective depression by general anesthetics of glutamate versus GABA release from isolated cortical nerve terminals. J Pharmacol Exp Ther 2003; 304:1188-96. [PMID: 12604696 DOI: 10.1124/jpet.102.044685] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The role of presynaptic mechanisms in general anesthetic depression of excitatory glutamatergic neurotransmission and facilitation of GABA-mediated inhibitory neurotransmission is unclear. A dual isotope method allowed simultaneous comparisons of the effects of a representative volatile (isoflurane) and intravenous (propofol) anesthetic on the release of glutamate and GABA from isolated rat cerebrocortical nerve terminals (synaptosomes). Synaptosomes were prelabeled with L-[(3)H]glutamate and [(14)C]GABA, and release was determined by superfusion with pulses of 30 mM K(+) or 1 mM 4-aminopyridine (4AP) in the absence or presence of 1.9 mM free Ca(2+). Isoflurane maximally inhibited Ca(2+)-dependent 4AP-evoked L-[(3)H]glutamate release (99 +/- 8% inhibition) to a greater extent than [(14)C]GABA release (74 +/- 6% inhibition; P = 0.023). Greater inhibition of L-[(3)H]glutamate versus [(14)C]GABA release was also observed for the Na(+) channel antagonists tetrodotoxin (99 +/- 4 versus 63 +/- 5% inhibition; P < 0.001) and riluzole (84 +/- 5 versus 52 +/- 12% inhibition; P = 0.041). Propofol did not differ in its maximum inhibition of Ca(2+)-dependent 4AP-evoked L-[(3)H]glutamate release (76 +/- 12% inhibition) compared with [(14)C]GABA (84 +/- 31% inhibition; P = 0.99) release. Neither isoflurane (1 mM) nor propofol (15 microM) affected K(+)-evoked release, consistent with a molecular target upstream of the synaptic vesicle exocytotic machinery or voltage-gated Ca(2+) channels coupled to transmitter release. These findings support selective presynaptic depression of excitatory versus inhibitory neurotransmission by clinical concentrations of isoflurane, probably as a result of Na(+) channel blockade.
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Affiliation(s)
- Robert I Westphalen
- Department of Anesthesiology, Weill Medical College of Cornell University, New York, New York, USA
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Szakács R, Weiczner R, Mihály A, Krisztin-Péva B, Zádor Z, Zádor E. Non-competitive NMDA receptor antagonists moderate seizure-induced c-fos expression in the rat cerebral cortex. Brain Res Bull 2003; 59:485-93. [PMID: 12576146 DOI: 10.1016/s0361-9230(02)00965-6] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We examined the effects of non-competitive NMDA glutamate receptor antagonists on seizures elicited by 4-aminopyridine (4-AP), and in particular, on the expression of the transcription factor c-fos induced by these seizures. Induction of c-fos mRNA due to 4-AP-elicited seizures was ascertained by reverse transcription polymerase chain reaction in samples of the neocortex. Adult rats were pretreated with the NMDA receptor antagonists amantadine (40 mg/kg), ketamine (3mg/kg), dizocilpine (MK-801; 1mg/kg) or dextrometorphan (40 mg/kg); 4-AP (5mg/kg) was then injected i.p. Controls were treated with either antagonist only or with 4-AP only. Pretreatment with the antagonists (with the exception of amantadine) increased the latency of behavioural seizures, but not all of the antagonists caused symptomatic seizure protection. In the brains which were processed for Fos immunohistochemistry, quantitative evaluation of immunostained cells was performed in the neocortex and hippocampus. Treatment with either antagonist did not induce by itself c-fos expression, with the exception of amantadine, which caused slight Fos induction in the neocortex. Pretreatment with all the antagonists resulted in decrease of seizure-induced Fos immunoreactivity with respect to non-pretreated animals. Decrease of immunostained cells was significant in the neocortex, in the granule cell layer and hilus of the dentate gyrus, in hippocampal areas CA1 and CA2. MK-801, ketamine and dextrometorphan decreased significantly Fos immunoreactivity also in area CA3. The decrease of Fos immunostaining was not directly correlated with a suppression of behavioural seizures. The results support an important role of NMDA receptors in c-fos gene induction in acute 4-AP seizures.
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Affiliation(s)
- Réka Szakács
- Department of Psychiatry, Faculty of Medicine, University of Szeged, Szeged, Hungary
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25
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Gulyás-Kovács A, Dóczi J, Tarnawa I, Détári L, Banczerowski-Pelyhe I, Világi I. Comparison of spontaneous and evoked epileptiform activity in three in vitro epilepsy models. Brain Res 2002; 945:174-80. [PMID: 12126879 DOI: 10.1016/s0006-8993(02)02751-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Rat neocortical slices express spontaneous epileptiform activity after incubation with GABA(A) receptor blocker bicuculline (BIC, 20 microM), with potassium channel blocker 4-aminopyridine (4-AP, 50 microM) or in Mg(2+)-free medium (LMG). Various parameters of spontaneous and evoked epileptiform discharges and their pharmacological sensitivity were analysed using extracellular field potential recordings in this comparative in vitro study. All types of convulsant solution induced spontaneous epileptiform activity, however, the analysed parameters showed that characteristics of epileptiform discharges are rather different in the three models. The longest duration of discharges was recorded in LMG, while the highest frequency of spontaneous events was detected in 4-AP. The epileptiform field responses elicited by electrical stimulation appeared in an all-or-none manner in BIC. On the contrary, in 4-AP and in LMG the amplitude of the responses increased gradually with increasing stimulation intensities. The NMDA receptor antagonist D,L-2-amino-5-phosphonovaleric acid (APV, 25 microM) abolished the LMG induced spontaneous epileptiform activity and significantly reduced the frequency of the epileptiform discharges in BIC and 4-AP. Blocking the AMPA type of glutamate transmission with 1-(aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466, 40 microM) rapidly abolished BIC-induced spontaneous epileptiform activity and caused a significant decrease in the frequency of 4-AP induced spontaneous epileptiform discharges. However, it had only a weak effect on the LMG-induced epileptiform activity. We conclude that the contribution of NMDA and AMPA types of glutamate receptors to the development and maintenance of epileptiform activity in cortical cell assemblies is different in the three models. There are significant alterations in contribution of NMDA and AMPA types of glutamate receptors to the above-mentioned processes in the different convulsants. In BIC the synchronisation is mainly due to the altered network properties, namely inhibition is reduced in the local circuits. Although inhibition is reduced in the local circuits, the AMPA receptor antagonist relatively easily blocked the synchronised excitation. In 4-AP, and especially in LMG, changes in the membrane characteristics of neurones play a crucial role in the increased excitability. In this case the AMPA antagonist was less effective.
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Affiliation(s)
- A Gulyás-Kovács
- Department of Physiology and Neurobiology, Eötvös Loránd University, Pázmány Péter sétány 1/C, 1117 Budapest, Hungary
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Peña F, Bargas J, Tapia R. Paired pulse facilitation is turned into paired pulse depression in hippocampal slices after epilepsy induced by 4-aminopyridine in vivo. Neuropharmacology 2002; 42:807-12. [PMID: 12015207 DOI: 10.1016/s0028-3908(02)00024-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Modifications in synaptic plasticity seem to play a key role in the origin and persistence of epilepsy. 4-Aminopyridine (4-AP) induces intense and long lasting epileptic seizures and neurodegeneration when applied into the hippocampus in vivo, effects that seem to be mediated by overactivation of glutamate receptors due to the enhancement of glutamate release from nerve endings. We have studied presynaptic modifications of CA1 responses, using the paired pulse paradigm, in hippocampal slices obtained from 4-AP-treated rats killed during epileptic activity (ex vivo). The paired pulse facilitation (PPF) observed in control slices with interstimulus intervals of 10-30 ms was changed into paired pulse depression (PPD) after 100 microM 4-AP added in vitro. A strikingly similar change was observed in the ex vivo slices even though 4-AP was no longer present in the tissue. We conclude that the facilitation of glutamate release induced by 4-AP becomes chronic after a transient exposure to the drug. This suggests that the facilitated neurotransmitter release induced by 4-AP triggers a more permanent plastic change that may be responsible for the persistence of epilepsy.
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Affiliation(s)
- F Peña
- Departamento de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, AP 70-253, 04510 Mexico, DF, Mexico
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Peña F, Tapia R. Seizures and neurodegeneration induced by 4-aminopyridine in rat hippocampus in vivo: role of glutamate- and GABA-mediated neurotransmission and of ion channels. Neuroscience 2001; 101:547-61. [PMID: 11113304 DOI: 10.1016/s0306-4522(00)00400-0] [Citation(s) in RCA: 147] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Infusion of the K(+) channel blocker 4-aminopyridine in the hippocampus induces the release of glutamate, as well as seizures and neurodegeneration. Since an imbalance between excitation and inhibition, as well as alterations of ion channels, may be involved in these effects of 4-aminopyridine, we have studied whether they are modified by drugs that block glutamatergic transmission or ion channels, or drugs that potentiate GABA-mediated transmission. The drugs were administered to anesthetized rats subjected to intrahippocampal infusion of 4-aminopyridine through microdialysis probes, with simultaneous collection of dialysis perfusates and recording of the electroencephalogram, and subsequent histological analysis. Ionotropic glutamate receptor antagonists clearly diminished the intensity of seizures and prevented the neuronal damage, but did not alter substantially the enhancement of extracellular glutamate induced by 4-aminopyridine. None of the drugs facilitating GABA-mediated transmission, including uptake blockers, GABA-transaminase inhibitors and agonists of the A-type receptor, was able to reduce the glutamate release, seizures or neuronal damage produced by 4-aminopyridine. In contrast, nipecotate, which notably increased extracellular levels of the amino acid, potentiated the intensity of seizures and the neurodegeneration. GABA(A) receptor antagonists partially reduced the extracellular accumulation of glutamate induced by 4-aminopyridine, but did not exert any protective action. Tetrodotoxin largely prevented the increase of extracellular glutamate, the electroencephalographic epileptic discharges and the neuronal death in the CA1 and CA3 hippocampal regions. Valproate and carbamazepine, also Na(+) channel blockers that possess general anticonvulsant action, failed to modify the three effects of 4-aminopyridine studied. The N-type Ca(2+) channel blocker omega-conotoxin, the K(+) channel opener diazoxide, and the non-specific ion channel blocker riluzole diminished the enhancement of extracellular glutamate and slightly protected against the neurodegeneration. However, the two former compounds did not antagonize the 4-aminopyridine-induced epileptiform discharges, and riluzole instead markedly increased the intensity and duration of the disharges. Moreover, at the highest dose tested (8mg/kg, i.p.), riluzole caused a 75% mortality of the rats. We conclude that 4-aminopyridine stimulates the release of glutamate from nerve endings and that the resultant augmented extracellular glutamate is directly related to the neurodegeneration and is involved in the generation of epileptiform discharges through the concomitant overactivation of glutamate receptors. Under these conditions, a facilitated GABA-mediated transmission may paradoxically boost neuronal hyperexcitation. Riluzole, a drug used to treat amyotrophic lateral sclerosis, seems to be toxic when combined with neuronal hyperexcitation.
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Affiliation(s)
- F Peña
- Departamento de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, AP 70-253, 04510, D.F., Mexico City, Mexico
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Medina-Ceja L, Morales-Villagrán A, Tapia R. Action of 4-aminopyridine on extracellular amino acids in hippocampus and entorhinal cortex: a dual microdialysis and electroencehalographic study in awake rats. Brain Res Bull 2000; 53:255-62. [PMID: 11113578 DOI: 10.1016/s0361-9230(00)00336-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In order to study the role of amino acids in the hippocampus and the entorhinal cortex during the convulsive process induced by 4-aminopyridine (4-AP), we have used a device allowing the simultaneous microdialysis and the recording of their electrical activity of both regions in freely moving rats. We found that infusion of 4-AP into the entorhinal cortex resulted in a large increase in extracellular glutamate and glutamine and small increases in glycine and taurine levels. Likewise, infusion of 4-AP into the hippocampus resulted in a major increase in glutamate, as well as slight increases in taurine and glycine. In both infused regions the peak concentration of extracellular glutamate was observed 15 min after 4-AP administration. No significant changes were found in the non-infused hippocampus or entorhinal cortex of the same rats. Simultaneous electroencephalographic recordings showed intense epileptiform activity starting during 4-AP infusion and lasting for the rest of the experiment (1 h) in both the entorhinal cortex and the hippocampus. The discharges were characterized by poly-spikes and spike-wave complexes that propagated almost immediately to the other region studied. These findings suggest that increased glutamatergic synaptic function in the circuit that connects both regions is involved in the epileptic seizures induced by 4-AP.
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Affiliation(s)
- L Medina-Ceja
- Departamento de Biología Celular y Molecular, CUCBA, Universidad de Guadalajara, Guadalajara, Jal, Mexico
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29
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Brückner C, Heinemann U. Effects of standard anticonvulsant drugs on different patterns of epileptiform discharges induced by 4-aminopyridine in combined entorhinal cortex-hippocampal slices. Brain Res 2000; 859:15-20. [PMID: 10720610 DOI: 10.1016/s0006-8993(99)02348-3] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Application of 4-aminopyridine (4-AP) has previously been reported to produce different patterns of epileptiform discharges in entorhinal cortex (EC)-hippocampal slices: recurrent short discharges (RSDs) in hippocampal area CA1, seizure-like events (SLEs) and negative-going potentials (NGPs) in the medial entorhinal cortex (mEC). Using recordings of field potentials, we investigated the pharmacological effects of the clinically employed standard anticonvulsant drugs phenytoin (PHT), carbamazepine (CBZ), valproic acid (VPA) and phenobarbital (PHB) and those of pentobarbital (PB) on 4-AP-induced epileptiform activity. The anticonvulsant drugs showed different effects: SLEs were completely blocked by all tested drugs. Valproic acid, which suppressed all epileptiform activities, seemed to have the most fundamental effect of all drugs on 4-AP induced activity, because under phenytoin and carbamazepine, some epileptiform activity was still observable. The RSDs in hippocampal area CA1 of the hippocampus did not respond to the different anticonvulsants. In contrast, PB decreased the frequency of the RSDs in CA1 and enhanced the frequency of the NGPs in the EC. We propose that the activities induced by 4-AP in the combined entorhinal cortex-hippocampal slices may provide an in vitro model for the development of new drugs against difficult-to-treat focal epilepsy.
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Affiliation(s)
- C Brückner
- Johannes-Müller-Institut für Physiologie, Universitätsklinikum Charité, Tucholskystr. 2, 10117, Berlin, Germany.
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Zhang LP, Chen Y, Clark BP, Sher E, Westlund KN. The Role of Type 1 Metabotropic Glutamate Receptors in the Generation of Dorsal Root Reflexes Induced by Acute Arthritis or the Spinal Infusion of 4-Aminopyridine in the Anesthetized Rat. THE JOURNAL OF PAIN 2000; 1:151-161. [PMID: 20882110 DOI: 10.1016/s1526-5900(00)90100-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Antidromically propagated action potentials can be recorded in the proximal end of the severed medial articular nerve (MAN) on mechanical stimulation of an inflamed knee in rats and are referred to as dorsal root reflex (DRR) activity. The absence of DRR activity in normal rats suggests that the activity could be the result of hyperexcitability of spinal neurons induced by inflammation. In this study, the role of spinal type 1 metabotropic glutamate (mGlu(1)) receptors in the generation of DRR activity in the MAN during acute knee inflammation was investigated. Four hours after an injection of a mixture of kaolin and carrageenan (k/c) into a knee joint, DRR activity could be evoked in the ipsilateral MAN by mechanical stimulation of the inflamed limb. Spinal application of a selective mGlu(1) receptor antagonist, [RS]-1-Aminoindan-1,5-dicarboxylic acid/UPF 523 (AIDA), or a potent, but less specific mGlu(1) receptor antagonist, LY393053, both depressed the DRR activity significantly. AIDA and LY39053 had no effect on recordings in the MAN from noninflamed control animals. However, spinal administration of AIDA did suppress DRR activity generated by infusion of 4-aminopyridine (4-AP), a K(+) channel blocker, into the dorsal horn of noninflamed animals. These observations suggest that mGlu(1) receptors support the generation of DRR activity in the MAN following sensitization of spinal cord neurons.
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Affiliation(s)
- Li Ping Zhang
- Department of Anatomy and Neuroscience, Marine Biomedical Institute, The University of Texas Medical Branch at Galveston, Galveston, TX; and Eli Lilly and Co, Windlesham, Surrey, United Kingdom
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31
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Morales-Villagrán A, López-Pérez S, Medina-Ceja L, Tapia R. Cortical catecholamine changes and seizures induced by 4-aminopyridine in awake rats, studied with a dual microdialysis-electrical recording technique. Neurosci Lett 1999; 275:133-6. [PMID: 10568517 DOI: 10.1016/s0304-3940(99)00759-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
We describe a rotatory electrical device that permits the simultaneous microdialysis and electroencephalographic (EEG) recording, by means of bipolar electrodes attached to the microdialysis probe, in two brain regions of awake rats. Using this device, we have found that the microdialysis infusion of 4-aminopyridine (4-AP) in the motor cerebral cortex produces intense behavioral convulsions and EEG seizures in both the infused and the contralateral cortex. This convulsant action is accompanied by a remarkable increase of extracellular dopamine (about 15-fold), norepinephrine (2.4-fold) and vanillylmandelic acid (1.8-fold) concentration in the infused cortex. Delayed increases of these amines were observed also in the contralateral cortex. The results suggest that 4-AP induces the release of catecholamines either through a direct effect on nerve endings or as a consequence of seizures.
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Affiliation(s)
- A Morales-Villagrán
- Departamento de Biología Celular y Molecular, CUCBA., Universidad de Guadalajara, Jal., Mexico
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32
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Dóczi J, Banczerowski-Pelyhe I, Barna B, Világi I. Effect of a glutamate receptor antagonist (GYKI 52466) on 4-aminopyridine-induced seizure activity developed in rat cortical slices. Brain Res Bull 1999; 49:435-40. [PMID: 10483921 DOI: 10.1016/s0361-9230(99)00079-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In the present experiments we have tested the effect of the noncompetitive AMPA antagonist GYKI 52466 (20-80 microM) on spontaneous epileptic discharges developed as the consequence of 4-aminopyridine application in neocortex slices of adult rats. Parallel to the changes of spontaneous activity, the field potentials, evoked by electrical stimulation of the corpus callosum, were also analyzed. Glass microcapillary extracellular recording electrode was positioned in the third layer of the somatosensory cortex slice, while the stimulating electrode was placed at the border of the white and gray matter. 4-aminopyridine and GYKI 52466 were bath-applied. The application of 40 microM GYKI 52466 caused about 40% decrease in the frequency and the amplitude of spontaneous seizures as well as the duration of each discharges developed in 4-amino-pyridine. Pre-incubation with the AMPA antagonist effectively inhibited both the development of seizure activity and the maintenance of the discharges. GYKI 52466 also decreased the duration and amplitude of field responses evoked by stimulation of the corpus callosum. This inhibitory effect was dose-dependent. Our data in the in vitro cortex slice epilepsy model suggest that the non-competitive AMPA antagonist GYKI 52466 is a potent anticonvulsant and neuroprotective compound because it reduced the fully developed epileptic discharges or prevented their development.
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Affiliation(s)
- J Dóczi
- Department of Physiology and Neurobiology, Eötvös Loránd University, Budapest, Hungary
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33
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Brückner C, Stenkamp K, Meierkord H, Heinemann U. Epileptiform discharges induced by combined application of bicuculline and 4-aminopyridine are resistant to standard anticonvulsants in slices of rats. Neurosci Lett 1999; 268:163-5. [PMID: 10406030 DOI: 10.1016/s0304-3940(99)00341-9] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Application of 4-aminopyridine (4AP) has previously been reported to produce different patterns of epileptiform discharges in entorhinal cortex-hippocampal-slices. Here we describe that 4-AP induced epileptiform activity in the EC becomes insensitive to anticonvulsant drugs (phenytoin, carbamazepine, valproic acid, phenobarbital) when GABAergic transmission is blocked by bicuculline. We propose that the activities induced by 4-aminopyridine and bicuculline may provide an in vitro model for the development of new drugs against difficult-to-treat focal epilepsy.
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Affiliation(s)
- C Brückner
- Institute für Physiologie, Abt. Neurophysiologie, Universitätsklinikum Charité, Medizinische Fakultät der Humboldt-Universität zu Berlin, Germany.
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34
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Peña F, Tapia R. Relationships among seizures, extracellular amino acid changes, and neurodegeneration induced by 4-aminopyridine in rat hippocampus: a microdialysis and electroencephalographic study. J Neurochem 1999; 72:2006-14. [PMID: 10217278 DOI: 10.1046/j.1471-4159.1999.0722006.x] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
4-Aminopyridine is a powerful convulsant that induces the release of neurotransmitters, including glutamate. We report the effect of intrahippocampal administration of 4-aminopyridine at six different concentrations through microdialysis probes on EEG activity and on concentrations of extracellular amino acids and correlate this effect with histological changes in the hippocampus. 4-Aminopyridine induced in a concentration-dependent manner intense and frequent epileptic discharges in both the hippocampus and the cerebral cortex. The three highest concentrations used induced also a dose-dependent enhancement of extracellular glutamate, aspartate, and GABA levels and profound hippocampal damage. Neurodegenerative changes occurred in CA1, CA3, and CA4 subfields, whereas CA2 was spared. In contrast, microdialysis administration of a depolarizing K+ concentration and of tetraethylammonium resulted in increased amino acid levels but no epileptic activity and no or moderate neuronal damage. These results suggest that seizure activity induced by 4-aminopyridine is due to a combined action of excitatory amino acid release and direct stimulation of neuronal firing, whereas neuronal death is related to the increased glutamate release but is independent of seizure activity. In addition, it is concluded that the glutamate release-inducing effect of 4-aminopyridine results in excitotoxicity because it occurs at the level of nerve endings, thus permitting the interaction of glutamate with its postsynaptic receptors, which is probably not the case after K+ depolarization.
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Affiliation(s)
- F Peña
- Departamento de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México, DF
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35
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Affiliation(s)
- D G Nicholls
- Department of Pharmacology, University of Dundee, Scotland, UK
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36
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Butcher JW, Paton JF. K+ channel blockade in the NTS alters efficacy of two cardiorespiratory reflexes in vivo. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:R677-85. [PMID: 9530233 DOI: 10.1152/ajpregu.1998.274.3.r677] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We investigated the role of potassium conductances in the nucleus of the solitary tract (NTS) in determining the efficacy of the baroreceptor and cardiopulmonary reflexes in anesthetized rats. The baroreceptor reflex was elicited with an intravenous injection of phenylephrine to evoke a reflex bradycardia, and the cardiopulmonary reflex was evoked with a right atrial injection of phenylbiguanide. Microinjection of two Ca-dependent potassium channel antagonists (apamin and charybdotoxin) into the NTS potentiated the baroreceptor reflex bradycardia. This may reflect the increased neuronal excitability observed previously in vitro with these blockers. In contrast, the Ca-dependent potassium channel antagonists attenuated the cardiopulmonary reflex, whereas voltage-dependent potassium channel antagonists (4-aminopyridine and dendrotoxin) attenuated both the baro- and cardiopulmonary reflexes when microinjected into the NTS. The possibility that the reflex attenuation observed indicates a predominant distribution of certain potassium channels on gamma-aminobutyric acid interneurons is discussed.
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Affiliation(s)
- J W Butcher
- Department of Physiology, School of Medical Sciences, University of Bristol, United Kingdom
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37
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González L, Nekrassov V, Castell A, Sitges M. Characterization of melittin effects in synaptosomes. Neurochem Res 1997; 22:189-99. [PMID: 9016845 DOI: 10.1023/a:1027319708321] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The effects of melittin at increasing concentrations on: [3H]GABA release from mouse brain synaptosomes; on the radioactivity released from [3H]arachidonic acid labeled synaptosomal membranes; on synaptosomes ultrastructure and on the leakage of the cytoplasmic marker, lactate-dehydrogenase (LDH) was investigated. Melittin 0.3, 1, 3, 7, and 10 microM progressively increases [3H]GABA release, but the efficacy of melittin is decreased when the amount of tissue exposed to a constant concentration of the toxin increases. The release of [3H]GABA induced by melittin below 3 microM is Ca2+ dependent, but not that induced by the higher concentrations. The Ca2+ dependent fraction of the [3H]GABA released by 0.3 microM melittin is selectively inhibited by 10 microM quinacrine and 1 microM nordihydroguaiaretic acid (NDGA) and facilitated by 3 microM indomethacin, whereas the Ca2+ independent fraction of the [3H]GABA released by melittin is not. In the presence of Ca2+, melittin 0.3, 1 and 10 microM progressively increases [3H]arachidonic acid release over control release, but the effectiveness of melittin is also decreased as the amount of tissue increases. No apparent changes in synaptosomes ultrastructure are observed in 0.3 microM treated synaptosomes, but a noticeable disorganization is produced in 10 microM melittin-treated synaptosomes, independently on the presence of external Ca2+. LDH activity only increases over control activity in the supernatant solutions of 10 microM melittin treated synaptosomes, also in a Ca2+ independent manner. Our interpretation of these results is that the Ca2+-dependent, pharmacologic sensitive component of melittin-induced release of [3H]GABA, unmasked when 0.3 microM melittin was used, involves the activation of a Ca2+-dependent type of membrane PLA2. The Ca2+-independent release of [3H]GABA is in contrast, highly probable to be due to the membrane perturbation produced by complex melittin/lipid interactions.
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Affiliation(s)
- L González
- Instituto de Investigaciones Biomédicas, Dpto. de Biología Celular, UNAM and Instituto Mexicano de Psiquiatría, SSA (PUIS)
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38
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Singh VK. Immunotherapy for brain diseases and mental illnesses. PROGRESS IN DRUG RESEARCH. FORTSCHRITTE DER ARZNEIMITTELFORSCHUNG. PROGRES DES RECHERCHES PHARMACEUTIQUES 1997; 48:129-46. [PMID: 9204685 DOI: 10.1007/978-3-0348-8861-5_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- V K Singh
- Department of Pharmaceutics, College of Pharmacy, University of Michigan, Ann Arbor 48109-1065, USA
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39
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Gleitz J, Friese J, Beile A, Ameri A, Peters T. Anticonvulsive action of (+/-)-kavain estimated from its properties on stimulated synaptosomes and Na+ channel receptor sites. Eur J Pharmacol 1996; 315:89-97. [PMID: 8960869 DOI: 10.1016/s0014-2999(96)00550-x] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Kava pyrones are constituents of the intoxicating pepper (Piper methysticum Forst), which has been shown to be anticonvulsive. The question of how the excitability of neurons is affected was investigated by determining the interaction of (+/-)-kavain with epitopes (site 1, site 2) of voltage-dependent Na+ channels and the action of (+/-)-kavain on 4-aminopyridine-stimulated synaptosomes as model of repetitive firing neurons. [3H]Saxitoxin and [3H]batrachotoxin were used for radioligand-binding assays performed with synaptosomal membranes. Gultamate released from 4-aminopyridine-stimulated cerebrocortical synaptosomes and the cytosolic concentrations of Na+ and Ca2+ ([Na+]i, [Ca+]i) were detected fluorometrically by using an enzyme-linked assay, sodium-binding benzofuranisophthalate (SBFI) and Fura-2, respectively. (+/-)-Kavain failed to compete with [3H]saxitoxin up to 400 mumol/l but dose-dependently suppressed binding of [3H]batrachotoxin with an IC50 value of 88 mumol/l (Ki = 72 mumol/l) although displacement of [3H]batrachotoxin was restricted to 33% of control at 400 mumol/l (+/-)-kavain. In stimulated synaptosomes, 5 mmol/l 4-aminopyridine provoked an increase in [Na+]i and [Ca2+]i by 9 mmol/l Na+ and 235 nmol/l Ca2+. Comparable to the reduction in [3H]batrachotoxin binding, 400 mumol/l (+/-)-kavain suppressed the increase in [Na+]i and [Ca2+]i to 38 and 29% of control, respectively. Consistent with the increase in [Na+]i and [Ca2+]i, 5 mmol/l 4-aminopyridine provoked glutamate release (rate: 38 pmol/s*mg protein) which was dose-dependently diminished to 60% of control by 400 mumol/l (+/-)-kavain. KCl depolarization (40 mmol/l) provoked an increase in [Ca2+]i and glutamate release almost identical to the responses elicited by 4-aminopyridine but 400 mumol/l (+/-)-kavain suppressed only the rate of glutamate release by 9% of control. The data suggest an interaction of (+/-)-kavain with voltage-dependent Na+ and Ca2+ channels, thereby suppressing the 4-aminopyridine-induced increase in [Na+]i, [Ca2+]i and the release of endogenous glutamate.
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Affiliation(s)
- J Gleitz
- University Clinics Ulm, Institute of Naturheilkunde, Germany.
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40
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Morales-Villagrán A, Ureña-Guerrero ME, Tapia R. Protection by NMDA receptor antagonists against seizures induced by intracerebral administration of 4-aminopyridine. Eur J Pharmacol 1996; 305:87-93. [PMID: 8813536 DOI: 10.1016/0014-2999(96)00157-4] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The effects of NMDA receptor antagonists on the convulsant action of the administration of 4-aminopyridine in the rat lateral cerebral ventricle (i.c.v. injection) and motor cerebral cortex (i.cx. injection) were studied. 4-Aminopyridine administration in both regions induced various preconvulsive symptoms, such as salivation, tremors, chewing and rearing, followed by continuous clonic convulsions and, only after i.c.v. injection, running fits and generalized tonic convulsions. This behavioral pattern appeared 5-9 min after administration of 4-aminopyridine and persisted for 100-150 min. 4-Aminopyridine also generated epileptiform electroencephalographic (EEG) discharges characterized by isolated spikes, poly-spikes and spike-wave complexes, which began some seconds after administration of the drug and were present for more than 2 h. The NMDA receptor antagonists (+/-)-3-(2-carboxy-piperazin-4-yl)-propyl-1-phosphonic acid (CPP), (+/-)-2-amino-7-phosphono-heptanoic acid (AP7) and (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801) clearly protected against some of the behavioral alterations induced by i.c.v. 4-aminopyridine, particularly the tonic convulsions, but were less effective against those produced by i.cx. 4-aminopyridine. These antagonists also delayed the appearance of EEG epileptiform discharges, reduced its amplitude, frequency and duration, and blocked their propagation to other cortical regions after i.cx. 4-aminopyridine. These results, together with previous data showing that 4-aminopyridine stimulates the release of glutamate in vivo, suggest that an excessive glutamatergic neurotransmission involving NMDA receptors is implicated in 4-amino-pyridine-induced seizures.
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Affiliation(s)
- A Morales-Villagrán
- División de Ciencias Biológicas, C.U.C.B.A., Universidad de Guadalajara, Jal., Mexico
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41
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Sánchez-Prieto J, Budd DC, Herrero I, Vázquez E, Nicholls DG. Presynaptic receptors and the control of glutamate exocytosis. Trends Neurosci 1996; 19:235-9. [PMID: 8761959 DOI: 10.1016/0166-2236(96)10031-x] [Citation(s) in RCA: 116] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
When a typical glutamate-containing neurone fires, an action potential is propagated down the branching axon through more than a thousand varicosities. At each of these release sites the probability that a synaptic vesicle will be exocytosed into the synaptic cleft is individually controlled by means of presynaptic receptors: autoreceptors responding by positive or negative feedback to previously released transmitter, or heteroreceptors under the influence of other neurotransmitters or modulators. The simplest system in which to investigate presynaptic modulation is the isolated nerve terminal or synaptosome; studies with this preparation have revealed a complex interplay of signal-transduction pathways.
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Affiliation(s)
- J Sánchez-Prieto
- Dept of Biochemistry, Veterinary Faculty, Complutense University, Madrid, Spain
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42
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Morales-Villagrán A, Tapia R. Preferential stimulation of glutamate release by 4-aminopyridine in rat striatum in vivo. Neurochem Int 1996; 28:35-40. [PMID: 8746762 DOI: 10.1016/0197-0186(95)00064-f] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The potassium channel blocker 4-aminopyridine (4-AP) is a potent convulsant drug which, in vitro, stimulates the release of neurotransmitter amino acids. We have studied the effect of 4-AP in vivo on the extracellular concentration of amino acids in rat striatum, by means of microdialysis and HPLC. Perfusion with 4-AP in the awake animal produced intense motor alterations, including barrel turning and running fits. Therefore, most microdialysis experiments were carried out in anesthetized rats. Perfusion with 20-75 mM 4-AP for 12.5 min resulted in a massive increase in extracellular glutamate (up to 20-fold), smaller increases in aspartate and taurine (up to 10-fold) and slight increments in glutamine, alanine, glycine and GABA. In contrast, perfusion with 100 mM K+ produced, mainly, an increment in taurine (7-fold) and modest increases in glutamate and aspartate (100-300%), as well as a notable decrease in glutamine. Tetraethylammonium (TEA, 120 mM) perfusion induced taurine and glutamate elevations similar to those after high K+, but glutamine was not affected. In unanesthetized rats, perfusion with 40 mM 4-AP induced changes in extracellular amino acids similar to those observed under anesthesia. In these animals neither high K+ nor TEA affected significantly the motor behavior. The results suggest that an enhancement of glutamatergic synaptic transmission, rather than a general depolarizing action, is an important factor in the neuronal hyperexcitability induced by 4-AP, which is consistent with the previously demonstrated inhibition of its convulsant effect by glutamate receptor antagonists.
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Affiliation(s)
- A Morales-Villagrán
- División de Ciencias Biológicas, C.U.C.B.A., Universidad de Guadalajara, México
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Sitges M, Chiu LM. Characterization of the type of calcium channel primarily regulating GABA exocytosis from brain nerve endings. Neurochem Res 1995; 20:1073-80. [PMID: 8570012 DOI: 10.1007/bf00995562] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
In an attempt to further characterize the type of Ca2+ channels primarily regulating GABA exocytosis, the effects of increasing concentrations of omega CTx MVIIC,-omega-Aga IVA and other Ca2+ channel blockers (nitrendipine, Cd2+ and Ni2+), commonly used for pharmacologically discerning among the various types of Ca2+ channels, were tested on the dissected Ca2+ dependent fraction of the depolarization evoked release of GABA from mouse brain synaptosomes. Our results show that omega-CTx MVIIC inhibits GABA exocytosis with a calculated IC50 of 3 microM and omega-Aga IVA with a calculated IC50 of 50 nM. The divalent cation Cd2+ only diminishes GABA exocytosis at 70 microM, but does not modify this response at lower concentrations (i.e. 1 and 10 microM). Neither nitrendipine (10 microM) nor Ni2+ (100 microM and 500 microM) modified GABA exocytosis. The failure of nitrendipine at a high concentration to inhibit GABA exocytosis discards L-type Ca2+ channels as the main regulators of this response; likewise that of Ni2+ discards Ca2+ channels of the N-type, and the failure of nM concentrations of omega-CTx MVIIC or 500 microM Ni2+, also discards alpha 1A/Q-type Ca2+ channels as the main regulators of the GABA response. On the basis of these results and in particular of the higher potency of omega-Aga IVA than omega-CTx MVIIC, it is concluded that the type of Ca2+ channels that primarily determine the exocytosis of GABA belong to a P-like type of Ca2+ channels.
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Affiliation(s)
- M Sitges
- Instituto de Investigaciones Biomédicas, Depto. de Biología Molecular, UNAM, México, D.F
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Sitges M, Chiu LM. omega-Aga IVA selectively inhibits the calcium-dependent fraction of the evoked release of [3H]GABA from synaptosomes. Neurochem Res 1995; 20:1065-71. [PMID: 8570011 DOI: 10.1007/bf00995561] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The effect of omega-Aga IVA, a P-type Ca2+ channel blocker, on the release of the inhibitory neurotransmitter GABA and on the elevation of Cai induced by depolarization was investigated in [3H]GABA and fura-2 preloaded mouse brain synaptosomes, respectively. Two strategies (i.e. 20 mM external K+ and veratridine) that depolarize by different mechanisms the preparation were used. High K+ elevates Cai and induces [3H]GABA release in the absence of external Na+ and in the presence of TTX, conditions that abolish veratridine induced responses. The effect of omega-Aga IVA on the Ca2+ and Na+ dependent fractions of the depolarization evoked release of [3H]GABA were separately investigated in synaptosomes depolarized with high K+ in the absence of external Na+ and with veratridine in the absence of external Ca2+, respectively. The Ca2+ dependent fraction of the evoked release of [3H]GABA and the elevation of Ca2+ induced by high K+ are markedly inhibited (about 50%) in synaptosomes exposed to omega-Aga IVA (300 nM) for 3 min before depolarization, whereas the Na+ dependent, Ca2+ independent carrier mediated release of [3H]GABA induced by veratridine, which is sensitive to verapamil and amiloride, is not modified by omega-Aga IVA. Our results indicate that an omega-Aga IVA sensitive type of Ca2+ channel is highly involved in GABA exocytosis.
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Affiliation(s)
- M Sitges
- Instituto de Investigaciones Biomédicas, México, D.F
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Buyukuysal RL, Ulus IH, Aydin S, Kiran BK. 3,4-Diaminopyridine and choline increase in vivo acetylcholine release in rat striatum. Eur J Pharmacol 1995; 281:179-85. [PMID: 7589205 DOI: 10.1016/0014-2999(95)00241-c] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We investigated the effects of choline, 3,4-diaminopyridine and their combination on acetylcholine release from the corpus striatum of freely moving rats which were treated or not with atropine. Intraperitoneal administration of choline or intrastriatal administration of 3,4-diaminopyridine increased acetylcholine levels in striatal dialysates in a dose-dependent manner. When 3,4-diaminopyridine treatment was combined with choline, the observed effect was considerably greater than the sum of the increases produced by choline or 3,4-diaminopyridine alone. Administration of atropine (1 microM) in the dialysing medium was also found to be effective to stimulate striatal acetylcholine levels. 3,4-Diaminopyridine did not affect acetylcholine levels under these conditions. Whereas the choline-induced increase in acetylcholine release was significantly potentiated by atropine, co-administration of 3,4-diaminopyridine with choline failed to produce a further significant increase in the presence of atropine. These results suggest that a highly effective means for increasing acetylcholine release involves two concurrent treatments that increase neuronal choline levels and inhibition of the negative feedback modulation of acetylcholine release.
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Affiliation(s)
- R L Buyukuysal
- Uludag University, Medical School, Department of Pharmacology, Bursa, Turkey
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Versteeg DH, Heemskerk FM, Spierenburg HA, de Graan PN, Schrama LH. 4-Aminopyridine differentially affects the spontaneous release of radiolabelled transmitters from rat brain slices in vitro. Brain Res 1995; 686:233-8. [PMID: 7583288 DOI: 10.1016/0006-8993(95)00515-r] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
4-Aminopyridine increased the release of [3H]noradrenaline from dorsal hippocampus slices in vitro in a concentration-dependent manner. When the slices were exposed to 4-aminopyridine for 5 min, the overflow of radioactivity returned to pre-exposure values within 20-25 min. When the exposure of the slices was continued, a sustained enhancement of the release of [3H]noradrenaline was observed for the duration of the exposure. 4-Aminopyridine, 10(-4) M, had an effect of similar magnitude, or an even more pronounced effect, on the release of [3H]catecholamine from cortex, septum, periaqueductal gray and striatum slices. The effects of the compound on the release of [3H]5-hydroxytryptamine and [14C]acetylcholine were less pronounced. At this concentration 4-aminopyridine had no effect on the release of [3H]D-aspartate from hippocampus or septum slices, whereas the effect on the release of this transmitter in striatal slices was marginal. The effect of 4-aminopyridine on the release of [3H]noradrenaline in hippocampus slices was largely dependent on the presence of Ca2+ in the superfusion medium. This was also the case for the effect on the release of [3H]noradrenaline from preloaded dorsal hippocampus synaptosomes. In the presence of nitrendipine the effect of 4-aminopyridine was dose-dependently reduced, but the maximal reduction, at a nitrendipine concentration of 10(-4) M, was only 40%. Cd2+ completely abolished the effect of 4-aminopyridine on the release of [3H]noradrenaline. These results confirm that the enhancing effect of 4-aminopyridine on the release of [3H]noradrenaline depends on the entry of extracellular Ca2+ into the nerve terminals.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- D H Versteeg
- Department of Pharmacology, Rudolf Magnus Institute for Neurosciences, Utrecht University, The Netherlands
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Sitges M, Dunkley PR, Chiu LM. A role for calcium/calmodulin kinase(s) in the regulation of GABA exocytosis. Neurochem Res 1995; 20:245-52. [PMID: 7609823 DOI: 10.1007/bf00969539] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
A possible role for protein kinases in the regulation of GABA exocytosis in nerve endings was investigated. The effect on the release of the radioactive neurotransmitter ([3H]GABA) from mouse brain synaptosomes of several protein kinase inhibitors was estimated after treatment with 37 mM K+ in the absence of external Na+, a condition under which [3H]GABA release is completely Ca2+ dependent. Among the inhibitors one group inhibit the kinases by the catalytic site (i.e. staurosporine and H7) and others (TFP, sphingosine and W7) act on the regulatory site of protein kinases. The compounds of the second group, which are reported to inhibit calmodulin dependent events and the increase in cytosolic Ca2+ (Cai) induced by high K+ depolarization, were the most efficient inhibitors of [3H]GABA release. The selective inhibitor of CaMPK II, KN-62, also markedly diminished [3]GABA release as well as the increase in Cai induced by high K+. The kinase inhibitors from the first group that are unable to diminish the increase in Cai induced by high K+ were also less efficient inhibitors of [3H]GABA release even at high concentrations. The present results indicate that at the doses tested all the drugs inhibit to some extent the release of the Ca2+ dependent fraction of [3H]GABA perhaps by inhibiting a CaMPK II mediated phosphorylation step triggered by depolarization and facilitated by the elevation of Cai. In addition, the second group of antagonists and KN-62 inhibit the elevation of Cai to high K+ thus exhibiting a higher efficiency on [3H]GABA release than the first group of antagonists.
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Affiliation(s)
- M Sitges
- Unidad de Psicofarmacología Molecular, PUIS, UNAM of Depto. de Biología Molecular, Instituto de Investigaciones Biomédicas, Mexico City, Mexico
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Patterson TA, Kim EK, Meldrum MJ, Dawson R. Glutamate efflux from rat brain slices and cultures: a comparison of the depolarizing agents potassium, 4-aminopyridine, and veratrine. Neurochem Res 1995; 20:225-32. [PMID: 7783845 DOI: 10.1007/bf00970548] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The major excitatory amino acid neurotransmitter in the mammalian brain is glutamate (GLU). GLU release from nerve terminals is both calcium-dependent and -independent, yet these mechanisms of release are not fully understood. Potassium, 4-aminopyridine (4-AP) and veratrine are commonly used depolarizing agents that were studied for their ability to stimulate GLU efflux from brain slices. These agents produced significant regional variations in GLU efflux from rat brain slices. Potassium was the most potent of the three secretogogues tested. 4-AP produced a significant GLU efflux only in the cerebellum. Veratrine produced consistent stimulation of GLU efflux from all brain regions tested. Potassium was the only depolarizing agent tested that stimulated GLU release from primary astroglial cultures of rat cerebral cortex. All three agents also demonstrated an ability to inhibit GLU reuptake in brain slice preparations. This data suggest that both GLU release and uptake are modulated in a regionally selective manner, and that commonly used depolarizing agents affect not only calcium-dependent neuronal release, but also uptake and glial responses.
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Affiliation(s)
- T A Patterson
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville 32610, USA
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Sitges M, Reyes A, Chiu LM. Dopamine transporter mediated release of dopamine: role of chloride. J Neurosci Res 1994; 39:11-22. [PMID: 7807588 DOI: 10.1002/jnr.490390103] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Using a rapid (0.5 ml/min) flow rate superfusion system, the dopamine (DA) transporter mediated release of DA is further explored, and compared to the depolarization evoked release of DA in rat striatal synaptosomes preloaded with radioactive DA (3H-DA). In this system external DA in the low microM range efficaciously releases the preloaded transmitter, the maximal response being reached at 3 microM DA. The external DA stimulated release is Ca(2+)-independent, Cl(-)-dependent, and blocked by both bupropion and nomifensine. The atypical antidepressant bupropion inhibits 3H-DA accumulation to rat striatal synaptosomes with a calculated IC50 of 1.3 x 10(-6) M. Among DA uptake blockers some are known to act as DA releasing agents. Here we found that the DA uptake blocker nomifensine (30 microM) is unable to modify the baseline release of 3H-DA, whereas bupropion (10 microM) clearly elevates the baseline release of 3H-DA in a Ca(2+)-independent and Cl(-)-dependent manner. The non releasing agent nomifensine blocks the release of 3H-DA induced by bupropion. The Ca(2+)-dependent, high K+ depolarization evoked release of 3H-DA is not modified by nomifensine and does not depend on the external Cl- concentration. When the depolarizing medium contains DA the carrier mediated release of 3H-DA induced by the external DA is additive to the high K+ induced response. A drastic drop in the external Cl- concentration induces 3H-DA release. This release of 3H-DA induced by low external Cl- levels is completely blocked by nomifensine, which only slightly diminished the release of 3H-DA induced by the absence of external Na+. On the basis of these results, it is concluded that: 1) Rapid perfusion flow rates eliminate DA reuptake. 2) DA uptake inhibitors either with or without DA releasing capabilities block the release of DA induced by microM levels of external DA. 3) By preventing translocation of the DA transporter mobile moiety, nomifensine may inhibit the release of DA induced by external DA or bupropion and by drastic drops in the external Cl- concentration. 4) In the absence of nomifensine, the DA transporter works under both resting and depolarized conditions, but in contrast to the GABA transporter (Sitges et al.: Neurochem Res 18:1081-1087, 1993), the DA transporter does not contribute to the amount of the DA released by depolarization. 5) Reversal of the DA uptake carrier is favored by conditions increasing the internal DA levels. 6) Cl- rather than Na+ is a major determinant in 3H-DA movements through the DA transporter.
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Affiliation(s)
- M Sitges
- División de Investigaciones Clínicas, Instituto Mexicano de Psiquiatría, SSA, Mexico
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Saito T. 4-Aminopyridine causes reduction of cytochromes partly originated in glia with enhanced evoked potentials in the olfactory cortex slice. Brain Res 1993; 612:9-15. [PMID: 8330217 DOI: 10.1016/0006-8993(93)91638-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Enhanced electrical and metabolic activities with addition of 4-aminopyridine (4-AP) were investigated in the olfactory cortex slice by recording evoked potentials, the redox state of cytochromes and the rate of oxygen uptake. During perfusion with 4-AP (0.01-0.1 mM), the late N-wave was dose-relatedly elicited in the evoked potential, concomitant with reduction of cytochromes and acceleration of oxygen uptake. These enhanced responses by 4-AP (0.1 mM) depended on the extracellular Ca2+. When the slice was subject to 2-deoxy-D-glucose (2-DG) (10 mM), initiation of the late N-wave by 4-AP (0.1 mM) was delayed, and both the reduction of cytochromes and the raised oxygen uptake prompted by the same dose of 4-AP were also significantly attenuated. Nevertheless, the presynaptic potential and N-wave, which markedly diminished by 2-DG, became tolerant to glycopenia after addition of 4-AP. By prior exposure to fluoroacetate (1 mM), the N-wave was gradually increased, but the late N-wave was rapidly decreased in amplitude by adding 4-AP (0.1 mM). The cytochrome reduction and the accelerated oxygen uptake by 4-AP (0.1 mM) were suppressed in the presence of fluoroacetate (1 mM). These results indicate that cytochromes become reduced by 4-AP, concomitant with the enhanced evoked potentials and oxygen uptake in a Ca(2+)-dependent manner, and that glial cells probably contribute to the enhanced electrical and metabolic activities in the olfactory cortex slice.
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Affiliation(s)
- T Saito
- Department of Physiology, Faculty of Veterinary Medicine, Hokkaido University, Sapporo, Japan
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