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Ransom BR, Goldberg MP, Arai K, Baltan S. White Matter Pathophysiology. Stroke 2022. [DOI: 10.1016/b978-0-323-69424-7.00009-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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2
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Kukharsky MS, Skvortsova VI, Bachurin SO, Buchman VL. In a search for efficient treatment for amyotrophic lateral sclerosis: Old drugs for new approaches. Med Res Rev 2020; 41:2804-2822. [DOI: 10.1002/med.21725] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2020] [Revised: 07/23/2020] [Accepted: 08/08/2020] [Indexed: 12/11/2022]
Affiliation(s)
- Michail S. Kukharsky
- Faculty of Medical Biology Pirogov Russian National Research Medical University Moscow Russian Federation
- Institute of Physiologically Active Compounds Russian Academy of Sciences Moscow Region Russian Federation
| | - Veronika I. Skvortsova
- Faculty of Medical Biology Pirogov Russian National Research Medical University Moscow Russian Federation
| | - Sergey O. Bachurin
- Institute of Physiologically Active Compounds Russian Academy of Sciences Moscow Region Russian Federation
| | - Vladimir L. Buchman
- Institute of Physiologically Active Compounds Russian Academy of Sciences Moscow Region Russian Federation
- School of Biosciences Cardiff University Cardiff United Kingdom
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Nakagawa H, Munakata T, Sunami A. Mexiletine Block of Voltage-Gated Sodium Channels: Isoform- and State-Dependent Drug-Pore Interactions. Mol Pharmacol 2018; 95:236-244. [PMID: 30593458 DOI: 10.1124/mol.118.114025] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2018] [Accepted: 12/19/2018] [Indexed: 12/24/2022] Open
Abstract
Mexiletine is a class Ib antiarrhythmic drug and is also used clinically to reduce or prevent myotonia. In addition, mexiletine has neuroprotective effects in models of brain ischemia. We compared state-dependent affinities of mexiletine for Nav1.2, Nav1.4, and Nav1.5 and examined the effects of mutations of transmembrane segment S6 residues on mexiletine block of Nav1.5. Three channel isoforms had similar affinities of mexiletine for the rested state, and Nav1.4 and Nav1.5 had similar affinities for the open and inactivated states, while Nav1.2 had lower affinity for these states than Nav1.4 and Nav1.5. Mutational studies revealed that the largest affinity change was observed for an Ala substitution of Phe in domain IV S6. In our homology modeling based on the bacterial Na+ channel, mexiletine changed its location and orientation in the pore depending on the state of the channel, irrespective of the channel isoform. Mexiletine occurred in the upper part in the pore in the open state and lower in the closed state. High-affinity binding of mexiletine in the open states of Nav1.4 and Nav1.5 was caused by a π-π interaction with Phe, whereas mexiletine was located away from Phe in the open state of Nav1.2. These results provide crucial information on the mechanism of isoform differences in state-dependent block by local anesthetics and related drugs. Mexiletine at upper locations in the open state may effectively cause an electrostatic mechanism of block.
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Affiliation(s)
- Hiroki Nakagawa
- Department of Pharmaceutical Sciences, International University of Health and Welfare, Tochigi, Japan
| | - Tatsuo Munakata
- Department of Pharmaceutical Sciences, International University of Health and Welfare, Tochigi, Japan
| | - Akihiko Sunami
- Department of Pharmaceutical Sciences, International University of Health and Welfare, Tochigi, Japan
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Portaro S, Naro A, Bramanti A, Leo A, Manuli A, Balletta T, Trinchera A, Bramanti P, Calabrò RS. Beyond the muscular involvement in non-dystrophic myotonias: The emerging role of neuromodulation. Restor Neurol Neurosci 2018; 36:459-467. [PMID: 29889082 DOI: 10.3233/rnn-170796] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
BACKGROUND The central nervous system involvement, in terms of a maladaptive sensory-motor plasticity, is well known in patients with dystrophic myotonias (DMs). To date, there are no data suggesting a central nervous system involvement in non-dystrophic myotonias (NDMs). OBJECTIVE To investigate sensory-motor plasticity in patients with Myotonia Congenita (MC) and Paramyotonia Congenita (PMC) with or without mexiletine. METHODS Twelve patients with a clinical, genetic, and electromyographic evidence of MC, fifteen with PMC, and 25 healthy controls (HC) were included in the study. TMS on both primary motor cortices (M1) and a rapid paired associative stimulation (rPAS) paradigm were carried out to assess M1 excitability and sensory-motor plasticity. RESULTS patients showed a higher cortical excitability and a deterioration of the topographic specificity of rPAS aftereffects, as compared to HCs. There was no correlation among neurophysiological and clinical-demographic characteristics. Noteworthy, the patients who were under mexiletine showed a minor impairment of the topographic specificity of rPAS aftereffects as compared to those who did not take the drug. CONCLUSION our findings could suggest the deterioration of cortical sensory-motor plasticity in patients with NDMs as a trait of the disease.
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Affiliation(s)
| | - Antonino Naro
- IRCSS Centro Neurolesi Bonino Pulejo, Messina, Italy
| | - Alessia Bramanti
- Institute of Applied Sciences and Intelligent Systems "Edoardo Caianello" (ISASI), National Research Council of Italy, Messina, Italy
| | - Antonino Leo
- IRCSS Centro Neurolesi Bonino Pulejo, Messina, Italy
| | | | - Tina Balletta
- IRCSS Centro Neurolesi Bonino Pulejo, Messina, Italy
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Inglese M, Fleysher L, Oesingmann N, Petracca M. Clinical applications of ultra-high field magnetic resonance imaging in multiple sclerosis. Expert Rev Neurother 2018; 18:221-230. [PMID: 29369733 PMCID: PMC6300152 DOI: 10.1080/14737175.2018.1433033] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2017] [Accepted: 01/23/2018] [Indexed: 10/18/2022]
Abstract
INTRODUCTION Magnetic resonance imaging (MRI) is of paramount importance for the early diagnosis of multiple sclerosis (MS) and MRI findings are part of the MS diagnostic criteria. There is a growing interest in the use of ultra-high-field strength -7 Tesla- (7T) MRI to investigate, in vivo, the pathological substrate of the disease. Areas covered: An overview of 7T MRI applications in MS focusing on increased sensitivity for lesion detection, specificity of the central vein sign and better understanding of MS pathophysiology. Implications for disease diagnosis, monitoring and treatment planning are discussed. Expert commentary: 7T MRI provides increased signal-to-noise and contrast-to-noise-ratio that allow higher spatial resolution and better detection of anatomical and pathological features. The high spatial resolution reachable at 7T has been a game changer for neuroimaging applications not only in MS but also in epilepsy, brain tumors, dementia, and neuro-psychiatric disorders. Furthermore, the first 7T device has recently been cleared for clinical use by the food and drug administration.
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Affiliation(s)
- Matilde Inglese
- Department of Neurology, Icahn School of Medicine, Mount
Sinai, New York
- Radiology, Icahn School of Medicine, Mount Sinai, New
York
- Neuroscience, Icahn School of Medicine, Mount Sinai, New
York
| | - Lazar Fleysher
- Radiology, Icahn School of Medicine, Mount Sinai, New
York
| | | | - Maria Petracca
- Department of Neurology, Icahn School of Medicine, Mount
Sinai, New York
- Department of Neuroscience, Federico II University, Naples,
Italy
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Rehni AK, Liu A, Perez-Pinzon MA, Dave KR. Diabetic aggravation of stroke and animal models. Exp Neurol 2017; 292:63-79. [PMID: 28274862 PMCID: PMC5400679 DOI: 10.1016/j.expneurol.2017.03.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Revised: 02/03/2017] [Accepted: 03/03/2017] [Indexed: 12/16/2022]
Abstract
Cerebral ischemia in diabetics results in severe brain damage. Different animal models of cerebral ischemia have been used to study the aggravation of ischemic brain damage in the diabetic condition. Since different disease conditions such as diabetes differently affect outcome following cerebral ischemia, the Stroke Therapy Academic Industry Roundtable (STAIR) guidelines recommends use of diseased animals for evaluating neuroprotective therapies targeted to reduce cerebral ischemic damage. The goal of this review is to discuss the technicalities and pros/cons of various animal models of cerebral ischemia currently being employed to study diabetes-related ischemic brain damage. The rational use of such animal systems in studying the disease condition may better help evaluate novel therapeutic approaches for diabetes related exacerbation of ischemic brain damage.
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Affiliation(s)
- Ashish K Rehni
- Cerebral Vascular Disease Research Laboratories, University of Miami Miller School of Medicine, Miami, FL 33136, USA; Department of Neurology, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Allen Liu
- Cerebral Vascular Disease Research Laboratories, University of Miami Miller School of Medicine, Miami, FL 33136, USA; Department of Neurology, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Miguel A Perez-Pinzon
- Cerebral Vascular Disease Research Laboratories, University of Miami Miller School of Medicine, Miami, FL 33136, USA; Department of Neurology, University of Miami Miller School of Medicine, Miami, FL 33136, USA; Neuroscience Program, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Kunjan R Dave
- Cerebral Vascular Disease Research Laboratories, University of Miami Miller School of Medicine, Miami, FL 33136, USA; Department of Neurology, University of Miami Miller School of Medicine, Miami, FL 33136, USA; Neuroscience Program, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
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Petracca M, Fleysher L, Oesingmann N, Inglese M. Sodium MRI of multiple sclerosis. NMR IN BIOMEDICINE 2016; 29:153-61. [PMID: 25851455 PMCID: PMC5771413 DOI: 10.1002/nbm.3289] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2014] [Revised: 02/25/2015] [Accepted: 02/26/2015] [Indexed: 05/11/2023]
Abstract
Multiple sclerosis (MS) is the most common cause of non-traumatic disability in young adults. The mechanisms underlying neurodegeneration and disease progression are poorly understood, in part as a result of the lack of non-invasive methods to measure and monitor neurodegeneration in vivo. Sodium MRI is a topic of increasing interest in MS research as it allows the metabolic characterization of brain tissue in vivo, and integration with the structural information provided by (1)H MRI, helping in the exploration of pathogenetic mechanisms and possibly offering insights into disease progression and monitoring of treatment outcomes. We present an up-to-date review of the sodium MRI application in MS organized into four main sections: (i) biological and pathogenetic role of sodium; (ii) brief overview of sodium imaging techniques; (iii) results of sodium MRI application in clinical studies; and (iv) future perspectives.
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Affiliation(s)
- Maria Petracca
- Department of Neurology, Icahn School of Medicine, Mount Sinai, New York, USA
- Department of Neuroscience, Federico II University, Naples, Italy
| | - Lazar Fleysher
- Department of Radiology, Icahn School of Medicine, Mount Sinai, New York, USA
| | | | - Matilde Inglese
- Department of Neurology, Icahn School of Medicine, Mount Sinai, New York, USA
- Department of Radiology, Icahn School of Medicine, Mount Sinai, New York, USA
- Department of Neuroscience, Icahn School of Medicine, Mount Sinai, New York, USA
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8
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Ransom BR, Goldberg MP, Arai K, Baltan S. White Matter Pathophysiology. Stroke 2016. [DOI: 10.1016/b978-0-323-29544-4.00009-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Richardson S, Siow B, Batchelor AM, Lythgoe MF, Alexander DC. A viable isolated tissue system: a tool for detailed MR measurements and controlled perturbation in physiologically stable tissue. Magn Reson Med 2012; 69:1603-10. [PMID: 22821404 DOI: 10.1002/mrm.24410] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2012] [Revised: 06/19/2012] [Accepted: 06/20/2012] [Indexed: 11/09/2022]
Abstract
In vivo magnetic resonance imaging (MRI) assessment of neuronal tissue is prone to artifacts such as movement, pulsatile flow, and tissue susceptibility. Furthermore, stable in vivo scans of over 3 h are difficult to achieve, experimental design is therefore limited. Using isolated tissue maintained in a viable physiological state can mitigate many of these in vivo issues. This work describes the fabrication and validation of an MRI compatible viable isolated tissue maintenance chamber. Parameters measured from maintained rat optic nerves did not change significantly over 10 h: (i) mean axon radius [electron microscopy--0 h: 0.75±0.46; 5 h: 0.74±0.35; 10 h: 0.76±0.35 μm (P>>0.05, t-test], (ii) action potentials [grease-gap electrophysiology--4.89±0.16 mv, (P>>0.05, Pearson test], and (iii) diffusion tensor imaging parameters [fractional anisotropy: 0.86±0.02 (P>>0.05, Pearson test), mean diffusivity: 1.48E-06±9.74E-08 cm2/s, (P>>0.05, Pearson test)]. In addition, a thorough diffusion-weighted MR protocol demonstrated the comparable stability of viable isolated and chemically fixed rat optic nerve. This MRI compatible viable isolated tissue system allows researchers to probe neuronal physiology in a controlled environment by limiting in vivo artifacts and allowing extended MRI acquisitions.
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Affiliation(s)
- S Richardson
- Division of Medicine and Institute of Child Health, UCL Centre for Advanced Biomedical Imaging, Department of Computer Science, University College London, London, United Kingdom.
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10
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Abstract
Stroke is a devastating neurological disease with limited functional recovery. Stroke affects all cellular elements of the brain and impacts areas traditionally classified as both gray matter and white matter. In fact, stroke in subcortical white matter regions of the brain accounts for approximately 30% of all stroke subtypes, and white matter injury is a component of most classes of stroke damage. However, most basic scientific information in stroke cell death and neural repair relates principally to neuronal cell death and repair. Despite an emerging biological understanding of white matter development, adult function, and reorganization in inflammatory diseases, such as multiple sclerosis, little is known of the specific molecular and cellular events in white matter ischemia. This limitation stems in part from the difficulty in generating animal models of white matter stroke. This review will discuss recent progress in studies of animal models of white matter stroke, and the emerging principles of cell death and repair in oligodendrocytes, axons, and astrocytes in white matter ischemic injury.
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Affiliation(s)
- Elif G. Sozmen
- Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095 USA
| | - Jason D. Hinman
- Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095 USA
| | - S. Thomas Carmichael
- Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095 USA
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Molecular Pathophysiology of White Matter Anoxic-Ischemic Injury. Stroke 2011. [DOI: 10.1016/b978-1-4160-5478-8.10008-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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12
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Waxman SG. Mechanisms of Disease: sodium channels and neuroprotection in multiple sclerosis—current status. ACTA ACUST UNITED AC 2008; 4:159-69. [DOI: 10.1038/ncpneuro0735] [Citation(s) in RCA: 156] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2007] [Accepted: 11/23/2007] [Indexed: 11/09/2022]
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Cheng KI, Shieh JP, Lin CN, Chu KS, Kwan AL, Hou CH, Wang JJ. Mexiletine has a local anesthetic effect on sciatic nerve blockade in rats. Drug Dev Res 2007. [DOI: 10.1002/ddr.20162] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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14
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Schaffer A, Levitt AJ. Double-blind, placebo-controlled pilot study of mexiletine for acute mania or hypomania. J Clin Psychopharmacol 2005; 25:507-8. [PMID: 16160638 DOI: 10.1097/01.jcp.0000177852.08287.08] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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McAdoo DJ, Hughes MG, Nie L, Shah B, Clifton C, Fullwood S, Hulsebosch CE. The effect of glutamate receptor blockers on glutamate release following spinal cord injury. Lack of evidence for an ongoing feedback cascade of damage --> glutamate release --> damage --> glutamate release --> etc. Brain Res 2005; 1038:92-9. [PMID: 15748877 DOI: 10.1016/j.brainres.2005.01.024] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2004] [Revised: 01/03/2005] [Accepted: 01/09/2005] [Indexed: 11/25/2022]
Abstract
It is widely hypothesized that excitotoxicity of released glutamate following a CNS insult is propagated by the cyclic cascade: glutamate release --> damage --> glutamate release --> further damage --> etc. We tested this hypothesis by determining the effects of attempting to interrupt the loop by administering glutamate receptor antagonists and Na(+)-channel blockers on glutamate release following spinal cord injury (SCI). The effects of administering the NMDA receptor blockers MK-801 and memantine, the AMPA/kainate receptor blockers NBQX and GYKI 52466, the AMPA receptor desensitization blocker cyclothiazide and the sodium channel blockers riluzole, mexiletine and QX-314 on post-SCI were determined. Agents were administered into the site of injury by direct injection, by microdialysis or systemically. None of these agents had an appreciable effect on glutamate release following SCI. Thus, it is unlikely that the above cascade produces significant secondary glutamate release and ongoing damage following SCI, although such cascades may worsen other CNS insults. We attribute our results to overwhelming effects of much greater release by direct mechanical damage and reversal of transport following SCI.
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Affiliation(s)
- David J McAdoo
- Department of Neuroscience and Cell Biology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-1043, USA.
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Hendriks JJA, Teunissen CE, de Vries HE, Dijkstra CD. Macrophages and neurodegeneration. ACTA ACUST UNITED AC 2005; 48:185-95. [PMID: 15850657 DOI: 10.1016/j.brainresrev.2004.12.008] [Citation(s) in RCA: 187] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2004] [Accepted: 12/09/2004] [Indexed: 12/23/2022]
Abstract
Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS). Demyelination is a classical feature of MS lesions, and neurological deficits are often ascribed to the reduced signal conduction by demyelinated axons. However, recent studies emphasize that axonal loss is an important factor in MS pathogenesis and disease progression. Axonal loss is found in association with cellular infiltrates in MS lesions. In this review, we discuss the possible contribution of the innate immune system in this process. In particular, we describe how infiltrated macrophages may contribute to axonal loss in MS and in experimental autoimmune encephalomyelitis (EAE), the animal model for MS. An overview is given of the possible effects of mediators, which are produced by activated macrophages, such as such as pro-inflammatory cytokines, free radicals, glutamate and metalloproteases, on axonal integrity. We conclude that infiltrated macrophages, which are activated to produce pro-inflammatory mediators, may be interesting targets for therapeutic approaches aimed to prevent or reduce axonal loss during exacerbation of inflammation. Interference with the process of infiltration and migration of monocytes across the blood-brain barrier is one of the possibilities to reduce the damage by activated macrophages.
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Affiliation(s)
- Jerome J A Hendriks
- Department of Molecular Cell Biology and Immunology, VU University Medical Center, Amsterdam, The Netherlands
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Lavinsky D, Arterni NS, Achaval M, Netto CA. Chronic bilateral common carotid artery occlusion: a model for ocular ischemic syndrome in the rat. Graefes Arch Clin Exp Ophthalmol 2005; 244:199-204. [PMID: 15983810 DOI: 10.1007/s00417-005-0006-7] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2005] [Revised: 02/27/2005] [Accepted: 04/10/2005] [Indexed: 10/25/2022] Open
Abstract
BACKGROUND Ocular ischemic syndrome is a devastating eye disease caused by severe carotid artery stenosis. The reduction of blood flow produced by bilateral common carotid artery occlusion (BCCAO) of rats for 7 days induces events related to gliosis with no evident histological damage. However, retinal degeneration and cellular death occur after 90 days of BCCAO. Our purpose has been to investigate the effects of BCCAO for 30 days in the retina of adult rats. METHODS Adult Wistar rats were submitted to BCCAO or sham surgery. Both direct and consensual pupillary light reflexes were investigated before and after surgery, everyday for the first week and weekly for 30 days. After 1 month, eyes were enucleated and embedded in paraffin. The retinal ganglion cell (RGC) density and thickness of the internal plexiform (IPL), internal nuclear, outer plexiform, and outer nuclear layers were estimated. RESULTS Four rats of the BCCAO group (50%) lost the direct pupillary reflex in both eyes, three rats (37%) lost this reflex in one eye, and only one (13%) maintained it in both eyes. RGC density (cells/mm) was diminished in the BCCAO group, and a significant decrease was found in the total retina and IPL thickness; however, no changes were evident in the other layers. BCCAO pupillary-reflex-negative rats presented with a significant decrease in total retinal thickness and retinal ganglion cell density compared with the sham group. Both BCCAO pupillary-reflex-positive) and -negative rats showed a decrease in IPL compared with the sham group. CONCLUSION This study demonstrates that BCCAO for 30 days induces functional and morphological damage to the retina with loss of the pupillary reflex and a decrease in IPL thickness and RGC number. We suggest that this protocol might be used as a model for ocular ischemic syndrome in the rat.
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Affiliation(s)
- Daniel Lavinsky
- Biochemistry Department, ICBS, Federal University of Rio Grande do Sul, Pôrto Alegre, RS, Brazil.
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Abstract
Axonal degeneration is a major cause of permanent neurological deficit in multiple sclerosis (MS). The mechanisms responsible for the degeneration remain unclear, but evidence suggests that a failure to maintain axonal sodium ion homeostasis may be a key step that underlies at least some of the degeneration. Sodium ions can accumulate within axons due to a series of events, including impulse activity and exposure to inflammatory factors such as nitric oxide. Recent findings have demonstrated that partial blockade of sodium channels can protect axons from nitric oxide-mediated degeneration in vitro, and from the effects of neuroinflammatory disease in vivo. This review describes some of the reasons why sodium ions might be expected to accumulate within axons in MS, and recent observations suggesting that it is possible to protect axons from degeneration in neuroinflammatory disease by partial sodium channel blockade.
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Affiliation(s)
- David A Bechtold
- Department of Neuroimmunology, Guy's Campus, King's College, London SE1 1UL, UK
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Bolton S, Butt AM. The optic nerve: A model for axon–glial interactions. J Pharmacol Toxicol Methods 2005; 51:221-33. [PMID: 15862467 DOI: 10.1016/j.vascn.2004.08.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/25/2004] [Indexed: 11/24/2022]
Abstract
The rodent optic nerve is a model tissue for the physiological investigation of axonal-glial interactions in a typical CNS white matter tract. There is strong evidence that nerve transmission is maintained by a considerable degree of dynamic signalling between axons and glia through a variety of mechanisms, such as regulation of the ionic environment, energy metabolism and calcium signalling. This review focuses on the methods used to examine axonal and glial functions and interactions, primarily in the rodent optic nerve. Techniques encompass intracellular microelectrodes, sucrose- and grease-gap recordings of membrane potentials, suction electrode to measure compound action potentials, the use of ion-sensitive electrodes, patch clamping and imaging. An overview of the advantages and drawbacks of each technique is given and the application of each to the understanding glial and axonal physiology is briefly discussed.
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Affiliation(s)
- Sally Bolton
- Centre for Neuroscience Research, Hodgkin Building, GKT Guy's Campus, King's College, London Bridge, London, SE1 1UL, UK
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Osborne NN, Chidlow G, Layton CJ, Wood JPM, Casson RJ, Melena J. Optic nerve and neuroprotection strategies. Eye (Lond) 2005; 18:1075-84. [PMID: 15534592 DOI: 10.1038/sj.eye.6701588] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND Experimental studies have yielded a wealth of information related to the mechanism of ganglion cell death following injury either to the myelinated ganglion cell axon or to the ganglion cell body. However, no suitable animal models exist where injury can be directed to the optic nerve head region, particularly the unmyelinated ganglion cell axons. The process of relating the data from the various animal models to many different types of optic neuropathies in man must, therefore, be cautious. RESULTS Extensive studies on the isolated optic nerve have yielded valuable information on the way white matter is affected by ischaemia and how certain types of compounds can attenuate the process. Moreover, there are now persuasive data on how ganglion cell survival is affected when the ocular blood flow is reduced in various animal models. As a consequence, the molecular mechanisms involved in ganglion cell death are fairly well understood and various pharmacological agents have been shown to blunt the process when delivered before or shortly after the insult. CONCLUSIONS A battery of agents now exist that can blunt animal ganglion cell death irrespective of whether the insult was to the ganglion cell body or the myelinated axon. Whether this information can be applied for use in patients remains a matter of debate, and major obstacles need to be overcome before the laboratory studies may be applied clinically. These include the delivery of the pharmacological agents to the site of ganglion cell injury and side effects to the patients. Moreover, it is necessary to establish whether effective neuroprotection is only possible when the drug is administered at a defined time after injury to the ganglion cells. This information is essential in order to pursue the idea that a neuroprotective strategy can be applied to a disease like glaucoma, where ganglion cell death appears to occur at different times during the lifetime of the patient.
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Affiliation(s)
- N N Osborne
- Nuffield Laboratory of Ophthalmology, Oxford University, Oxford, UK.
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Kurnellas MP, Nicot A, Shull GE, Elkabes S. Plasma membrane calcium ATPase deficiency causes neuronal pathology in the spinal cord: a potential mechanism for neurodegeneration in multiple sclerosis and spinal cord injury. FASEB J 2004; 19:298-300. [PMID: 15576480 PMCID: PMC2896328 DOI: 10.1096/fj.04-2549fje] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Dysfunction and death of spinal cord neurons are critical determinants of neurological deficits in various pathological conditions, including multiple sclerosis (MS) and spinal cord injury. Yet, the molecular mechanisms underlying neuronal/axonal damage remain undefined. Our previous studies raised the possibility that a decrease in the levels of plasma membrane calcium ATPase isoform 2 (PMCA2), a major pump extruding calcium from neurons, promotes neuronal pathology in the spinal cord during experimental autoimmune encephalomyelitis (EAE), an animal model of MS, and after spinal cord trauma. However, the causal relationship between alterations in PMCA2 levels and neuronal injury was not well established. We now report that inhibition of PMCA activity in purified spinal cord neuronal cultures delays calcium clearance, increases the number of nonphosphorylated neurofilament H (SMI-32) immunoreactive cells, and induces swelling and beading of SMI-32-positive neurites. These changes are followed by activation of caspase-3 and neuronal loss. Importantly, the number of spinal cord motor neurons is significantly decreased in PMCA2-deficient mice and the deafwaddler(2J), a mouse with a functionally null mutation in the PMCA2 gene. Our findings suggest that a reduction in PMCA2 level or activity leading to delays in calcium clearance may cause neuronal damage and loss in the spinal cord.
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Affiliation(s)
- Michael P. Kurnellas
- Neurology and Neuroscience, UMDNJ-New Jersey Medical School, Newark, NJ 07103
- Neurology Service, Veterans Affairs, East Orange, NJ, 07018
| | - Arnaud Nicot
- INSERM EMI 0350, Hôpital St. Antoine, Paris, France
| | - Gary E. Shull
- Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati, Cincinnati, OH 45267
| | - Stella Elkabes
- Neurology and Neuroscience, UMDNJ-New Jersey Medical School, Newark, NJ 07103
- Neurology Service, Veterans Affairs, East Orange, NJ, 07018
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22
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Veach J. Functional dichotomy: glutathione and vitamin E in homeostasis relevant to primary open-angle glaucoma. Br J Nutr 2004; 91:809-29. [PMID: 15182385 DOI: 10.1079/bjn20041113] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Primary open-angle glaucoma (POAG) is a complex chronic neurological disease that can result in blindness. The goal of understanding the aetiology of POAG is to be able to target effective treatment to individuals who will eventually go blind without it. Epidemiological studies of POAG have not specifically addressed the possibility that nutrition may play a role in the development of POAG. A handful of papers have considered that nutrition may have an impact on POAG patients. POAG is not believed to be a 'vitamin-deficiency disease'. The concept of 'vitamin-deficiency diseases' and the recommended daily allowances have not kept pace with the growing understanding of the cellular and molecular functions of vitamins and other micronutrients. The aetiology of POAG remains a mystery. Discoveries in cell physiology can be assimilated from the literature and applied to known homeostatic mechanisms of the eye. In this way the possible roles of nutritional components involved in the aetiology of POAG can be described. The mechanisms may be subject to many influences in ways that have yet to be defined. Two distinct changes in the trabecular meshwork can be identified: trabecular meshwork changes that cause intra-ocular pressure to increase and trabecular meshwork changes that are directly correlated to optic nerve atrophy. Compelling evidence suggests that collagen trabecular meshwork extracellular matrix (ECM) remodelling is correlated to increased intraocular pressure in POAG. Elastin trabecular meshwork ECM remodelling is correlated to POAG optic nerve atrophy. There appear to be two different pathways of ECM remodelling and apoptosis induction in POAG. The pathway for collagen remodelling and apoptosis induction seems to be exogenously influenced by water-soluble antioxidants, for example, glutathione. The pathway for elastin remodelling and apoptosis induction seems to be influenced by endogenous lipid-soluble antioxidants, for example, vitamin E. Roles can be defined for antioxidants in the two different pathways of ECM remodelling and apoptosis induction. This suggests that antioxidants are important in maintaining cellular homeostasis relevant to the aetiology of POAG.
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Dave JR, Lin Y, Ved HS, Koenig ML, Clapp L, Hunter J, Tortella FC. RS-100642-198, a novel sodium channel blocker, provides differential neuroprotection against hypoxia/hypoglycemia, veratridine or glutamate-mediated neurotoxicity in primary cultures of rat cerebellar neurons. Neurotox Res 2004; 3:381-95. [PMID: 14715468 DOI: 10.1007/bf03033199] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The present study investigated the effects of RS-100642-198 (a novel sodium channel blocker), and two related compounds (mexiletine and QX-314), in in vitro models of neurotoxicity. Neurotoxicity was produced in primary cerebellar cultures using hypoxia/hypoglycemia (H/H), veratridine or glutamate where, in vehicle-treated neurons, 65%, 60% and 75% neuronal injury was measured, respectively. Dose-response neuroprotection experiments were carried out using concentrations ranging from 0.1-500 micro M. All the sodium channel blockers were neuroprotective against H/H-induced injury, with each exhibiting similar potency and efficacy. However, against veratridine-induced neuronal injury only RS-100642-198 and mexiletine were 100% protective, whereas QX-314 neuroprotection was limited (i.e. only 54%). In contrast, RS-100642-198 and mexiletine had no effect against glutamate-induced injury, whereas QX-314 produced a consistent, but very limited (i.e. 25%), neuroprotection. Measurements of intraneuronal calcium [Ca(2+)]i) mobilization revealed that glutamate caused immediate and sustained increases in [Ca(2+)]i which were not affected by RS-100642-198 or mexiletine. However, both drugs decreased the initial amplitude and attenuated the sustained rise in [Ca(2+)]i mobilization produced by veratridine or KCl depolarization. QX-314 produced similar effects on glutamate-, veratridine- or KCl-induced [Ca(2+)]i dynamics, effectively decreasing the amplitude and delaying the initial spike in [Ca(2+)]i, and attenuating the sustained increase in [Ca(2+)]i mobilization. By using different in vitro models of excitotoxicity, a heterogeneous profile of neuroprotective effects resulting from sodium channel blockade has been described for RS-100642-198 and related drugs, suggesting that selective blockade of neuronal sodium channels in pathological conditions may provide therapeutic neuroprotection against depolarization/excitotoxicity via inhibition of voltage-dependent Na(+) channels.
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Affiliation(s)
- J R Dave
- Division of Neurosciences, Walter Reed Army Inst of Research, Silver Spring, MD 20910, USA.
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Menkü A, Koç RK, Tayfur V, Saraymen R, Narin F, Akdemir H. Effects of mexiletine, ginkgo biloba extract (EGb 761), and their combination on experimental head injury. Neurosurg Rev 2003; 26:288-91. [PMID: 12884054 DOI: 10.1007/s10143-003-0277-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2002] [Revised: 03/25/2003] [Accepted: 04/03/2003] [Indexed: 10/26/2022]
Abstract
Lipid peroxidation (LP) and brain edema are important factors that produce tissue damage in head injury. The purpose of this study was to investigate the effect of mexiletine, gingko biloba extract (EGb 761), and their combination on LP and edema after moderate head trauma. Forty rats were randomly and blindly divided into four groups of ten animals each: control group (bolus injection of physiological saline), mexiletine group (50 mg/kg per injection), EGb 761 group (30 mg/kg per injection), and mexiletine plus EGb 761 group (50 mg/kg and 30 mg/kg per injection, respectively). The injections were given intraperitoneally at 1 h, 9 h, and 17 h after trauma. Twenty-four hours after injury, the rats were killed, and malondialdehyde (MDA) levels and brain water content were determined. Rats treated with mexiletine, EGb 761, and mexiletine plus EGb 761 had significantly lower MDA levels than the control group (P<0.01). The lowest MDA levels were measured in the mexiletine plus EGb 761 group. However, there was no significant difference in brain water content between treated groups and the control group (P>0.05). These findings show the usefulness of mexiletine and its combination with EGb 761 as a cerebroprotective agent in this model of experimental head injury.
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Affiliation(s)
- Ahmet Menkü
- Department of Neurosurgery, Erciyes University Medical School, 38039 Kayseri, Turkey.
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26
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Canavero S, Bonicalzi V, Narcisi P. Safety of magnesium-lidocaine combination for severe head injury: the Turin lidomag pilot study. SURGICAL NEUROLOGY 2003; 60:165-9; discussion 169. [PMID: 12900133 DOI: 10.1016/s0090-3019(03)00159-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
BACKGROUND Neuroprotection in the setting of severe head injury (SHI) remains an unsettled problem. We tested a combination of high-dose magnesium and low-dose lidocaine, infused over 3 days, in a pilot study to assess safety. This combination appears indicated to protect both gray and white matter from secondary injury following SHI. METHODS We studied 32 consecutive patients admitted to the emergency department of our hospital, a large tertiary referral center. RESULTS No toxicity was observed. Mortality was lower than published statistics. CONCLUSIONS These results open the stage to a controlled randomized study.
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Affiliation(s)
- Sergio Canavero
- Department of Neurosciences and Anesthesiology, Molinette Hospital, Turin, Italy
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Halmosi R, Deres P, Toth A, Berente Z, Kalai T, Sumegi B, Hideg K, Toth K. 2,2,5,5-Tetramethylpyrroline-based compounds in prevention of oxyradical-induced myocardial damage. J Cardiovasc Pharmacol 2002; 40:854-67. [PMID: 12451318 DOI: 10.1097/00005344-200212000-00006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Reactive oxygen species have been known to play a major role in a wide variety of pathophysiologic processes. A new compound, H-2545, based on a 2,2,5,5-tetramethyl-3-pyrroline-3-carboxamide structure, has been reported to exhibit antiarrhythmic function as well as favorable antioxidant properties. Studies were performed in an isolated rat heart model to measure the efficacy of H-2545 and its metabolite, H-2954, in preventing ischemia-reperfusion and hydrogen peroxide-induced oxidative myocardial damage: lipid peroxidation, protein oxidation, activity of respiratory complexes, NAD, and high-energy phosphate metabolism. The cardioprotective effects of examined compounds were compared with that of a well-known water-soluble vitamin E analog, Trolox. To determine whether the antioxidant property of H-2545 is due to the pyrroline ring, the scavenger effects of mexiletine and HO-2434 (mexiletine substituted with a pyrroline group) were compared. The results showed that H-2545 decreased significantly the ischemia-reperfusion-induced thiobarbituric acid reactive substance (TBARS) formation, the protein oxidation and ssDNA break formation in perfused rat hearts. H-2545 decreased the NAD loss in postischemic hearts. The activity of respiratory complexes, myocardial energy metabolism, and functional myocardial recovery were also improved during reperfusion by adding H-2545 to the perfusion medium. H-2954 exerted significantly lower protection against ischemia-reperfusion-induced myocardial injury than H-2545, and it was comparable to that of Trolox. Both H-2545 and H-2954 are highly effective against H O -induced oxidative myocardial cell damage. The findings show that substitution of mexiletine with a 2,2,5,5-tetramethyl-pyrroline group (HO-2434) increased its antioxidant and cardioprotective effects. In conclusion, these results suggest that sterically hindered pyrroline derivatives accumulating in membranes can be highly effective at preventing oxidative myocardial cell damage.
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Affiliation(s)
- Robert Halmosi
- University of Pecs, Medical School 1st Department of Medicine, Pecs, Hungary
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29
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Del Bigio MR, Wang X, Wilson MJ. Sodium Channel-blocking Agents Are Not of Benefit to Rats with Kaolin-induced Hydrocephalus. Neurosurgery 2002. [DOI: 10.1227/00006123-200208000-00029] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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30
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Del Bigio MR, Wang X, Wilson MJ. Sodium channel-blocking agents are not of benefit to rats with kaolin-induced hydrocephalus. Neurosurgery 2002; 51:460-6; discussion 466-7. [PMID: 12182785 DOI: 10.1097/00006123-200208000-00029] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2001] [Accepted: 03/13/2002] [Indexed: 11/26/2022] Open
Abstract
OBJECTIVE Hydrocephalus causes damage to periventricular white matter at least in part through chronic ischemia. The sodium channel-blocking agents mexiletine and riluzole have been shown to be of some protective value in various models of neurological injury. We hypothesized that these agents would ameliorate the effects of experimental childhood-onset hydrocephalus. METHODS Hydrocephalus was induced in 4-week-old rats by injection of kaolin into the cisterna magna. Tests of cognitive and motor function were performed on a weekly basis. In a blinded and randomized manner, mexiletine (0.7, 7, or 42 mg/kg/d) or riluzole (1.4 or 13.6 mg/kg/d) was administered by osmotic minipump for 2 weeks, beginning 2 weeks after induction of hydrocephalus. The brains were then subjected to histopathological and biochemical analyses. RESULTS Compared with untreated hydrocephalic rats, neither mexiletine nor riluzole was associated with a protective effect on behavioral, structural, or biochemical abnormalities. CONCLUSION Protection of hydrocephalic brains through pharmacological sodium channel blockade is probably an approach not worth pursuing.
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Affiliation(s)
- Marc R Del Bigio
- Department of Pathology, University of Manitoba, and Manitoba Institute for Child Health, Winnipeg, Canada.
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31
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Stevens WD, Fortin T, Pappas BA. Retinal and optic nerve degeneration after chronic carotid ligation: time course and role of light exposure. Stroke 2002; 33:1107-12. [PMID: 11935068 DOI: 10.1161/01.str.0000014204.05597.0c] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND AND PURPOSE Carotid artery disease can cause chronic retinal ischemia, resulting in transient or permanent blindness, pupillary reflex dysfunction, and retinal degeneration. This experiment investigated the effects of chronic retinal ischemia in an animal model involving permanent carotid occlusion. The time course of retinal pathology and the role of light in this pathology were examined. METHODS Sprague-Dawley rats underwent permanent bilateral occlusion of the common carotid arteries or sham surgery. Half of the animals were postsurgically housed in darkness, and half were housed in a 12-hour light/dark cycle. Animals were killed at 3, 15, and 90 days after surgery. Stereological techniques were used to count the cells of the retinal ganglion cell layer. Thy-1 immunoreactivity was assessed to specifically quantify loss of retinal ganglion cells. The thicknesses of the remaining retinal sublayers were measured. Optic nerve degeneration was quantified with the Gallyas silver staining technique. RESULTS Permanent bilateral occlusion of the common carotid arteries resulted in loss of the pupillary reflex to light in 58% of rats. Eyes that lost the reflex showed (1) optic nerve degeneration at 3, 15, and 90 days after surgery; (2) a reduction of retinal ganglion cell layer neurons and Thy-1 immunoreactivity by 15 and 90 days; and (3) a severe loss of photoreceptors by 90 days when postsurgically housed in the light condition only. CONCLUSIONS Ischemic damage to the optic nerve caused loss of pupillary reflex and death of retinal ganglion cells in a subset of rats. Subsequently, light toxicity induced death of the photoreceptors.
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Affiliation(s)
- W Dale Stevens
- Institute of Neuroscience, Carleton University, Ottawa, Ontario, Canada
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32
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Laird JM, Carter AJ, Grauert M, Cervero F. Analgesic activity of a novel use-dependent sodium channel blocker, crobenetine, in mono-arthritic rats. Br J Pharmacol 2001; 134:1742-8. [PMID: 11739251 PMCID: PMC1572907 DOI: 10.1038/sj.bjp.0704428] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. Although sodium channel blockers are effective analgesics in neuropathic pain, their effectiveness in inflammatory pain has been little studied. Sodium channels are substantially up-regulated in inflamed tissue, which suggests they play a role in maintenance of chronic inflammatory pain. We have examined the effects of sodium channel blockers on mobility, joint hyperalgesia and inflammation induced by complete Freund's adjuvant injected in one ankle joint of adult rats. The clinically effective sodium channel blocker, mexiletine, was compared with crobenetine (BIII 890 CL), a new, highly use-dependent sodium channel blocker. 2. Rats were treated for 5 days, starting on the day of induction of arthritis and were tested daily for joint hyperalgesia, hind limb posture and mobility. At post-mortem, joint stiffness and oedema were assessed. Dose response curves were constructed for each test compound (3 - 30 mg kg day(-1)). Control groups were treated with vehicle or with the non-steroidal anti-inflammatory drug, meloxicam (4 mg kg day(-1) i.p.). 3. Both sodium channel blockers produced dose dependent and significant reversal of mechanical joint hyperalgesia and impaired mobility with an ID50 of 15.5+/-1.1 mg kg day(-1) for crobenetine and 18.1+/-1.2 mg kg day(-1) for mexiletine. Neither compound affected the responses of the contralateral non-inflamed joint, nor had any effect on swelling and stiffness of the inflamed joint. 4. We conclude that sodium channel blockers are analgesic and anti-hyperalgesic in this model of arthritis. These data suggest that up regulation of sodium channel expression in primary afferent neurones may play an important role in the pain and hyperalgesia induced by joint inflammation.
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Affiliation(s)
- J M Laird
- Department of Physiology, University of Alcalá, Alcalá de Henares, E-28871 Madrid, Spain.
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Rosenberg LJ, Wrathall JR. Time course studies on the effectiveness of tetrodotoxin in reducing consequences of spinal cord contusion. J Neurosci Res 2001; 66:191-202. [PMID: 11592114 DOI: 10.1002/jnr.1211] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Focal injection of the sodium channel blocker tetrodotoxin (TTX) into the injury site at either 5 or 15 min after a standardized thoracic contusion spinal cord injury (SCI) reduces white matter pathology and loss of axons in the first 24 hr after injury. Focal injection of TTX at 15 min after SCI also reduces chronic white matter loss and hindlimb functional deficits. We have now tested the hypothesis that the reduction in chronic deficits with TTX treatment is associated with long-term preservation of axons after SCI and compared both acute (24 hr) and chronic (6 weeks) effects of TTX administered at 15 min prior to and 5 min or 4 hr after SCI. Our results indicate a significant reduction of acute white matter pathology in rats treated with TTX at 15 min before and 5 min after injury but no effect when treatment was delayed until 4 hr after contusion. Compared with injury controls, groups treated with TTX at 5 min and 4 hr after injury did not show a significant deficit reduction, nor was there a significant sparing of white matter at 6 weeks compared with injury controls. In contrast, the group treated with TTX at 15 min before SCI demonstrated significantly reduced hindlimb functional deficits beginning at 1 week after injury and throughout the 6 weeks of the study. This was associated with a significantly higher axon density in the ventromedial white matter at 6 weeks. The results demonstrate that blockade of sodium channels preserves axons from loss after SCI and points to the importance of time of administration of such drugs for therapeutic effectiveness.
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Affiliation(s)
- L J Rosenberg
- Department of Neuroscience, Georgetown University, 3970 Reservoir Road NW, Washington, DC 20007, USA
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Weiser T, Wienrich M, Brenner M, Kubiak R, Weckesser G, Palluk R. The AMPA receptor/Na(+) channel blocker BIIR 561 CL is protective in a model of global cerebral ischaemia. Eur J Pharmacol 2001; 421:165-70. [PMID: 11516432 DOI: 10.1016/s0014-2999(01)01031-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
In this study, we investigated whether the novel neuroprotective compound dimethyl-[2-[2-(3-phenyl-[1,2,4]oxadiazol-5-yl)-phenoxy]-ethyl]-amine hydrochloride, BIIR 561 CL, a combined non-competitive antagonist of AMPA receptors and blocker of voltage-gated Na+ channels, is protective in a rat model of severe global ischaemia. BIIR 561 CL administered immediately after 10 min of ischaemia (occlusion of both carotid arteries plus reduction of arterial blood pressure to 38-40 mm Hg) significantly reduced hippocampal damage at 4 x 26.8 mg/kg (subcutaneous injections). The competitive AMPA receptor antagonist 2,3-dihydro-6-nitro-7-sulfamoyl-benz(F)quinoxaline, NBQX, was used as a reference compound and was protective at 3x30 mg/kg (intraperitoneal and/or subcutaneous administration). BIIR 561 CL significantly reduced the ischaemia-induced premature mortality from 33.6% in the controls to 14.3%, whereas NBQX treatment had no statistically significant effect.Thus, BIIR 561 CL could be shown to reduce hippocampal damage and premature mortality in a model of severe global ischaemia. A compound with these properties might be an interesting candidate for the treatment of disorders related to global cerebral ischaemia in man.
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Affiliation(s)
- T Weiser
- Department of CNS Research, Boehringer Ingelheim Pharma KG, D-52218 Ingelheim, Germany
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Hewitt KE, Stys PK, Lesiuk HJ. The use-dependent sodium channel blocker mexiletine is neuroprotective against global ischemic injury. Brain Res 2001; 898:281-7. [PMID: 11306014 DOI: 10.1016/s0006-8993(01)02195-3] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Mechanisms responsible for anoxic/ischemic cell death in mammalian CNS grey and white matter involve an increase in intracellular Ca2+, however the routes of Ca2+ entry appear to differ. In white matter, pathological Ca2+ influx largely occurs as a result of reversal of Na+-Ca2+ exchange, due to increased intracellular Na+ and membrane depolarization. Na+ channel blockade has therefore been logically and successfully employed to protect white matter from ischemic injury. In grey matter ischemia, it has been traditionally presumed that activation of agonist (glutamate) operated and voltage dependent Ca2+ channels are the primary routes of Ca2+ entry. Less attention has been directed towards Na+-Ca2+ exchange and Na+ channel blockade as a protective strategy in grey matter. This study investigates mexiletine, a use-dependent sodium channel blocker known to provide significant ischemic neuroprotection to white matter, as a grey matter protectant. Pentobarbital (65 mg/kg) anesthetized, mechanically ventilated Sprague-Dawley rats were treated with mexiletine (80 mg/kg, i.p.). Then 25 min later the animals were subjected to 10 min of bilateral carotid occlusion plus controlled hypotension to 50 Torr by temporary partial exsanguination. Animals were sacrificed with perfusion fixation after 7 days. Ischemic and normal neurons were counted in standard H&E sections of hippocampal CA1 and the ratio of ischemic to total neurons calculated. Mexiletine pre-treatment reduced hippocampal damage by approximately half when compared to control animals receiving saline alone (45 vs. 88% damage, respectively; P<0.001). These results suggest that mexiletine (and perhaps other drugs of this class) can provide protection from ischemia to grey matter as well as white matter.
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Affiliation(s)
- K E Hewitt
- Loeb Health Research Institute, Division of Neuroscience, Ottawa Hospita -Civic Campus, University of Ottawa, 725 Parkdale Avenue, Ont., K1Y 4K9, Ottawa, Canada
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Kiguchi S, Ichikawa K, Kojima M. Suppressive effects of oxcarbazepine on tooth pulp-evoked potentials recorded at the trigeminal spinal tract nucleus in cats. Clin Exp Pharmacol Physiol 2001; 28:169-75. [PMID: 11207671 DOI: 10.1046/j.1440-1681.2001.03431.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
1. The purpose of the present study was to evaluate the antinociceptive effect of oxcarbazepine, a keto derivitive of carbamazepine (an anticonvulsant), in an animal model. To evoke a nociceptive response, we electrically stimulated the maxillary canine tooth pulp (MCTP) in anaesthetized (allobarbital-urethane), spontaneously breathing cats. 2. The evoked potentials were recorded from the superficial layers of the caudal part of the trigeminal spinal tract nucleus (5ST). We examined a slow component with a large amplitude (the P3 component) in evoked compound potentials; its mean conduction velocity was 1.7 m/s, suggesting a response mediated by C-fibres. 3. To confirm that the P3 component was related to pain sensation, we used morphine, a most efficacious antinociceptive agent, in the present study. The P3 component was significantly suppressed by intravenous administration of morphine (3 mg/kg) and was also suppressed by microinjection of morphine (2 microg) into the recording site of the 5ST. These results suggest that the P3 component is involved in the transmission of nociceptive information. 4. We compared the effect of oxcarbazepine with mexiletine; both are known to block neuronal Na+ channels. Intravenous administration of mexiletine suppressed the P3 component at a dose of 5 mg/kg. Microinjection of mexiletine (10 microg) into the recording site of the 5ST tended to suppress the P3 component, but this effect was not significant. 5. Intravenous administration of oxcarbazepine (1-10 mg/kg) caused a dose-dependent inhibition of the P3 component, which was significantly suppressed at 10 mg/kg oxcarbazepine. Intravenous administration of 10,11-dihydro-10-hydroxy-5H-dibenz[b,f]azepine-5-carboxamide (MHD), a metabolite of oxcarbazepine, at doses of 3-30 mg/kg caused a dose-dependent inhibition of the P3 component. Oxcarbazepine was not available for the microinjection study because it is not water soluble. We used MHD for the microinjection study instead of oxcarbazepine, because MHD can be dissolved in water up to 3 mg/mL. Microinjections of MHD (6 microg) into the recording site of the 5ST suppressed the P3 component. These results indicate that oxcarbazepine has an antinociceptive action.
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Affiliation(s)
- S Kiguchi
- Pharmacology Laboratory, Kissei Pharmaceutical Co. Ltd, Minamiazumi, Nagano, Japan.
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Puka-Sundvall M, Gajkowska B, Cholewinski M, Blomgren K, Lazarewicz JW, Hagberg H. Subcellular distribution of calcium and ultrastructural changes after cerebral hypoxia-ischemia in immature rats. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2000; 125:31-41. [PMID: 11154758 DOI: 10.1016/s0165-3806(00)00110-3] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Recent data imply that mitochondrial regulation of calcium is critical in the process leading to hypoxic-ischemic brain injury. The aim was to study the subcellular distribution of calcium in correlation with ultrastructural changes after hypoxia-ischemia in neonatal rats. Seven-day-old rats were subjected to permanent unilateral carotid artery ligation and exposure to hypoxia (7.7% oxygen in nitrogen) for 90 min. Animals were perfusion-fixed after 30 min, 3 h or 24 h of reperfusion. Sections were sampled for light microscopy and electron microscopy combined with the oxalate-pyroantimonate technique. At 30 min and 3 h of reflow, a progressive accumulation of calcium was detected in the endoplasmic reticulum, cytoplasm, nucleus and, most markedly, in the mitochondrial matrix of neurons in the gray matter in the core area of injury. Some mitochondria developed a considerable degree of swelling reaching a diameter of several microm at 3 h of reflow whereas the majority of mitochondria appeared moderately affected. Chromatin condensation was observed in nuclei of many cells with severely swollen mitochondria with calcium deposits. A whole spectrum of morphological features ranging from necrosis to apoptosis was seen in degenerating cells. After 24 h, there was extensive injury in the cerebral cortex as judged by breaks of mitochondrial and plasma membranes, and a general decrease of cellular electron density. In the white matter of the core area of injury, the axonal elements exhibited varicosity-like swellings filled with calcium-pyroantimonate deposits. Furthermore, the thin myelin sheaths were loaded with calcium. Numerous oligodendroglia-like cells displayed apoptotic morphology with shrunken cytoplasm and chromatin condensation, whereas astroglial necrosis was not seen. In conclusion, markedly swollen 'giant' mitochondria with large amounts of calcium were found at 3 h of reperfusion often in neuronal cells with condensation of the nuclear chromatin. The results are discussed in relation to mitochondrial permeability transition and activation of apoptotic processes.
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Affiliation(s)
- M Puka-Sundvall
- Perinatal Center, Department of Anatomy and Cell Biology, Göteborg University, Göteborg, Sweden.
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Del Bigio MR. Calcium-mediated proteolytic damage in white matter of hydrocephalic rats? J Neuropathol Exp Neurol 2000; 59:946-54. [PMID: 11089572 DOI: 10.1093/jnen/59.11.946] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Hydrocephalus is a pathological dilatation of the cerebrospinal fluid (CSF)-containing ventricles of the brain. Damage to periventricular white matter is multifactorial with contributions by chronic ischemia and gradual physical distortion. Acute ischemic and traumatic brain injuries are associated with calcium-dependent activation of proteolytic enzymes. We hypothesized that hydrocephalus is associated with calcium ion accumulation and proteolytic enzyme activation in cerebral white matter. Hydrocephalus was induced in immature and adult rats by injection of kaolin into the cisterna magna and several different experimental approaches were used. Using the glyoxal bis (2-hydroxyanil) method, free calcium ion was detected in periventricular white matter at sites of histological injury. Western blot determinations showed accumulation of calpain I (mu-calpain) and immunoreactivity for calpain I was increased in periventricular axons of young hydrocephalic rats. Proteolytic cleavage of a fluorogenic calpain substrate was demonstrated in white matter. Immunoreactivity for spectrin breakdown products was detected in scattered callosal axons of young hydrocephalic rats. The findings support the hypothesis that periventricular white matter damage associated with experimental hydrocephalus is due, at least in part, to calcium-activated proteolytic processes. This may have implications for supplemental drug treatments of this disorder.
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Affiliation(s)
- M R Del Bigio
- Department of Pathology, University of Manitoba, Winnipeg, Canada
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Maynard KI, Quiñones-Hinojosa A, Malek JY. Neuroprotection against ischemia by metabolic inhibition revisited. A comparison of hypothermia, a pharmacologic cocktail and magnesium plus mexiletine. Ann N Y Acad Sci 2000; 890:240-54. [PMID: 10668430 DOI: 10.1111/j.1749-6632.1999.tb07999.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Previous studies have suggested that metabolic inhibition is neuroprotective, but little evidence has been provided to support this proposal. Using the in vitro rabbit retina preparation as an established model of the central nervous system (CNS), we measured the rate of glucose utilization and lactate production, and the light-evoked compound action potentials (CAPs) as indices of neuronal energy metabolism and electrophysiologic function, respectively. We examined the effect of three (3) treatments options: hypothermia (i.e., 33 degrees C and 30 degrees C), a six-member pharmacologic "cocktail" (tetrodotoxin (0.1 microM), 2-amino-4-phosphonobutyric acid (20 microM), 2-amino-5-phosphonovaleric acid (1 mM), amiloride (1 mM), magnesium (10 mM) and lithium (10 mM) and the combination of magnesium (Mg2+ 1 mM) and mexiletine (Mex, 300 microM) on in vitro rabbit retinas, to see if there is a correlation between neuronal energy metabolism during ischemia (simulated by the reduction of oxygen from 95% to 15% and glucose from 6 mM to 1 mM), and the subsequent recovery of function. Hypothermia and the "cocktail" significantly inhibited both the rate of glucose utilization and lactate production, whereas Mg2+ and/or Mex showed only a nonsignificant tendency toward a reduction, compared to control retinas. Recovery of light-evoked CAPs was significantly improved in hypothermia- and cocktail-treated retinas, as well as with retinas exposed to the combination of Mg2+ plus Mex, but not with Mg2+ or Mex alone, relative to control retinas. A linear regression analysis of the % recovery of function versus the % reduction in the rate of glucose utilization during ischemia showed a significant correlation (r2 = 0.80, correlation coefficient = 0.9, p < 0.05) between these two parameters. This and other data discussed provide convincing evidence that there is a correlation between metabolic inhibition, achieved during ischemia, and neuroprotection.
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Affiliation(s)
- K I Maynard
- Neurophysiology Laboratory, Massachusetts General Hospital, Boston, USA.
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Abstract
BACKGROUND The purpose of this study was to evaluate the efficacy and safety of mexiletine, a medication with antiarrhythmic, anticonvulsant and analgesic properties, in treatment-resistant bipolar disorder patients. METHODS Twenty subjects with rapid-cycling bipolar disorder who had failed to respond or were intolerant to lithium, valproic acid and carbamazepine were entered into the 6-week, open label study. Subjects were followed on a weekly basis for dosing of mexiletine, blood levels, and completion of the Hamilton Depression Rating Scale (HAM-D) and the Manic State Rating Scale (MSRS). "Burden of Mood Symptoms" (BMS) was calculated by combining scores for the HAM-D and MSRS. RESULTS Thirteen subjects (10 female, 3 male), mean age 41 years (S.D.=7.6), and mean duration of illness 20 years (S.D.=7.7) completed the study. The dose range of mexiletine was 200-1200 mg/day. Full response (>/=50% reduction in BMS) was seen in 46% of the subjects, and a partial response (25-49% reduction in BMS) in 15%. Of note, 5/5 subjects with a mixed or manic state demonstrated a full or partial response. LIMITATIONS This study has an open label design, and a small number of subjects. CONCLUSIONS Mexiletine may be effective and safe in patients with highly treatment-resistant, chronic bipolar disorder. Randomized, controlled trials are required to confirm the current results.
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Affiliation(s)
- A Schaffer
- Department of Psychiatry, Sunnybrook Health Science Center, 2075 Bayview Avenue, Room FG46, University of Toronto, Toronto, Canada
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Lee EJ, Ayoub IA, Harris FB, Hassan M, Ogilvy CS, Maynard KI. Mexiletine and magnesium independently, but not combined, protect against permanent focal cerebral ischemia in Wistar rats. J Neurosci Res 1999. [DOI: 10.1002/(sici)1097-4547(19991101)58:3<442::aid-jnr10>3.0.co;2-4] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Jeffery ND, Blakemore WF. Spinal cord injury in small animals 2. Current and future options for therapy. Vet Rec 1999; 145:183-90. [PMID: 10501582 DOI: 10.1136/vr.145.7.183] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Although there can be substantial spontaneous improvements in functional status after a spinal cord injury, therapeutic intervention is desirable in many patients to improve the degree of recovery. At present only decompressive surgery and the neuroprotective drug methylprednisolone sodium succinate are effective and in widespread clinical use. There are limitations to the efficacy of these therapies in some clinical cases and they cannot restore satisfactory functional status to all patients. Many drugs have been investigated experimentally to assess their potential to preserve injured tissue and promote functional recovery in clinically relevant settings, and several of them would be suitable for assessment in future veterinary clinical trials. In addition, experimental techniques designed to mould the response of the CNS to injury, by the promotion of axonal regeneration across the lesion and the encouragement of local sprouting of undamaged axons, have recently been successful, suggesting that effective therapy for even very severe spinal cord injury may soon be available.
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Affiliation(s)
- N D Jeffery
- Department of Clinical Veterinary Medicine, MRC Cambridge Centre for Brain Repair, University of Cambridge
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Dewar D, Yam P, McCulloch J. Drug development for stroke: importance of protecting cerebral white matter. Eur J Pharmacol 1999; 375:41-50. [PMID: 10443563 DOI: 10.1016/s0014-2999(99)00280-0] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Multiple pharmacological mechanisms have been identified over the last decade which can protect grey matter from ischaemic damage in experimental models. A large number of drugs targeted at neurotransmitter receptors and related mechanisms involved in ischaemic damage have advanced to clinical trials in stroke and head injury based on their proven ability to reduce grey matter damage in animal models. The outcome to date of the clinical trials of neuroprotective drugs has been disappointing. Although the failure to translate preclinical pharmacological insight into therapy is multifactorial, we propose that the failure to ameliorate ischaemic damage to white matter has been a major factor. The recent development of quantitative techniques to assess ischaemic damage to cellular elements in white matter, both axons and oligodendrocytes, allows rigorous evaluation of pharmacologic mechanisms which may protect white matter in ischaemia. Such pharmacological approaches provide therapeutic opportunities which are both additional or alternatives to those currently being evaluated in man.
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Affiliation(s)
- D Dewar
- Wellcome Surgical Institute and Hugh Fraser Neuroscience Laboratories, University of Glasgow, Garscube Estate, UK
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Demirpençe E, Caner H, Bavbek M, Kilinç K. Antioxidant Action of the Antiarrhythmic Drug Mexiletine in Brain Membranes. ACTA ACUST UNITED AC 1999. [DOI: 10.1016/s0021-5198(19)30802-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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Maynard KI, Quiñones-Hinojosa A, Ogilvy CS. Magnesium plus mexiletine inhibit energy usage and protect retinas against ischemia. Neuroreport 1998; 9:4141-4. [PMID: 9926863 DOI: 10.1097/00001756-199812210-00026] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
We determined whether exogenous Mg2+ and/or mexiletine (Mex), which are reported to be neuroprotective agents, reduced neuronal energy requirements and protected against ischemia, using isolated rabbit retinas. Under non-ischemic conditions, Mex (300 microM) and the combination of Mg2+ (1 mM) plus Mex (300 microM) significantly reduced glucose utilization, by 19% and 31%, respectively. The combination of Mg2+ plus Mex, but not either agent alone, significantly reduced lactate production (by 18%; p < 0.05). When added during 2 h of ischemia (simulated by the reduction of oxygen from 95% to 15% and of glucose from 6 mM to 1 mM), Mg2+ plus Mex improved the recovery of glucose utilization (p < 0.01), lactate production (p < 0.05) and neuronal function (p < 0.05) for 3 h following return to control (post-ischemia/recovery) conditions. Thus reducing energy demands by blocking functions during temporary ischemia, protects neurons from irreversible functional damage.
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Affiliation(s)
- K I Maynard
- Neurosurgical Service, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
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Abstract
Preventing the loss of ion homeostasis or promoting its recovery are two primary targets of neuroprotective strategies. The contribution of excitatory neurotransmitter receptor linked ion channels is now well established. Sodium and calcium may also enter neurons and glia through voltage sensitive channels and exchangers, contributing directly and indirectly to injury.
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Affiliation(s)
- J J Vornov
- Department of Neurology, Johns Hopkins Hospital, Baltimore, MD 21287-6953, USA
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Stys PK, Lopachin RM. Mechanisms of calcium and sodium fluxes in anoxic myelinated central nervous system axons. Neuroscience 1998; 82:21-32. [PMID: 9483500 DOI: 10.1016/s0306-4522(97)00230-3] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Electron probe X-ray microanalysis was used to measure water content and concentrations of elements (i.e. Na, K, Cl and Ca) in selected morphological compartments of rat optic nerve myelinated axons. Transaxolemmal movements of Na+ and Ca2+ were modified experimentally and corresponding effects on axon element and water compositions were determined under control conditions and following in vitro anoxic challenge. Also characterized were effects of modified ion transport on axon responses to postanoxia reoxygenation. Blockade of Na+ entry by tetrodotoxin (1 microM) or zero Na+/Li(+)-substituted perfusion reduced anoxic increases in axonal Na and Ca concentrations. Incubation with zero-Ca2+/EGTA perfusate prevented axoplasmic and mitochondrial Ca accumulation during anoxia but did not affect Na increases or K losses in these compartments. Inhibition of Na(+)-Ca2+ exchange with bepridil (30 microM) selectively prevented increases in intra-axonal Ca, whereas neither nifedipine (5 microM) nor nimodipine (5 microM) influenced the effects of anoxia on axonal Na, K or Ca. X-ray microanalysis also showed that prevention of Na and Ca influx during anoxia obtunded severe elemental deregulation normally associated with reoxygenation. Results of the present study suggest that during anoxia, Na+ enters axons mainly through voltage-gated Na+ channels and that subsequent increases in axoplasmic Na+ are functionally coupled to extra-axonal Ca2+ import. Na+i-dependent, Ca2+o entry is consistent with reverse operation of the axolemmal Na(+)-Ca2+ exchanger and we suggest this route represents a primary mechanism of Ca2+ influx. Our findings also implicate a minor route of Ca2+ entry directly through Na+ channels.
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Affiliation(s)
- P K Stys
- Loeb Research Institute, Ottawa Civic Hospital, University of Ottawa, Canada
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Stys PK. Anoxic and ischemic injury of myelinated axons in CNS white matter: from mechanistic concepts to therapeutics. J Cereb Blood Flow Metab 1998; 18:2-25. [PMID: 9428302 DOI: 10.1097/00004647-199801000-00002] [Citation(s) in RCA: 236] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
White matter of the brain and spinal cord is susceptible to anoxia and ischemia. Irreversible injury to this tissue can have serious consequences for the overall function of the CNS through disruption of signal transmission. Myelinated axons of the CNS are critically dependent on a continuous supply of energy largely generated through oxidative phosphorylation. Anoxia and ischemia cause rapid energy depletion, failure of the Na(+)-K(+)-ATPase, and accumulation of axoplasmic Na+ through noninactivating Na+ channels, with concentrations approaching 100 mmol/L after 60 minutes of anoxia. Coupled with severe K+ depletion that results in large membrane depolarization, high [Na+]i stimulates reverse Na(+)-Ca2+ exchange and axonal Ca2+ overload. A component of Ca2+ entry occurs directly through Na+ channels. The excessive accumulation of Ca2+ in turn activates various Ca(2+)-dependent enzymes, such as calpain, phospholipases, and protein kinase C, resulting in irreversible injury. The latter enzyme may be involved in "autoprotection," triggered by release of endogenous gamma-aminobutyric acid and adenosine, by modulation of certain elements responsible for deregulation of ion homeostasis. Glycolytic block, in contrast to anoxia alone, appears to preferentially mobilize internal Ca2+ stores; as control of internal Ca2+ pools is lost, excessive release from this compartment may itself contribute to axonal damage. Reoxygenation paradoxically accelerates injury in many axons, possibly as a result of severe mitochondrial Ca2+ overload leading to a secondary failure of respiration. Although glia are relatively resistant to anoxia, oligodendrocytes and the myelin sheath may be damaged by glutamate released by reverse Na(+)-glutamate transport. Use-dependent Na+ channel blockers, particularly charged compounds such as QX-314, are highly neuroprotective in vitro, but only agents that exist partially in a neutral form, such as mexiletine and tocainide, are effective after systemic administration, because charged species cannot penetrate the blood-brain barrier easily. These concepts may also apply to other white matter disorders, such as spinal cord injury or diffuse axonal injury in brain trauma. Moreover, whereas many events are unique to white matter injury, a number of steps are common to both gray and white matter anoxia and ischemia. Optimal protection of the CNS as a whole will therefore require combination therapy aimed at unique steps in gray and white matter regions, or intervention at common points in the injury cascades.
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Affiliation(s)
- P K Stys
- Ottawa Civic Hospital Loeb Medical Research Institute, University of Ottawa, Ontario, Canada
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Local blockade of sodium channels by tetrodotoxin ameliorates tissue loss and long-term functional deficits resulting from experimental spinal cord injury. J Neurosci 1997. [PMID: 9151752 DOI: 10.1523/jneurosci.17-11-04359.1997] [Citation(s) in RCA: 100] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Although relatively little is known of the mechanisms involved in secondary axonal loss after spinal cord injury (SCI), recent data from in vitro models of white matter (WM) injury have implicated abnormal sodium influx as a key event. We hypothesized that blockade of sodium channels after SCI would reduce WM loss and long-term functional deficits. To test this hypothesis, a sufficient and safe dose (0.15 nmol) of the potent Na+ channel blocker tetrodotoxin (TTX) was determined through a dose-response study. We microinjected TTX or vehicle (VEH) into the injury site at 15 min after a standardized contusive SCI in the rat. Behavioral tests were performed 1 d after injury and weekly thereafter. Quantitative histopathology at 8 weeks postinjury showed that TTX treatment significantly reduced tissue loss at the injury site, with greater effect on sparing of WM than gray matter. TTX did not change the pattern of chronic histopathology typical of this SCI model, but restricted its extent, tripled the area of residual WM at the epicenter, and reduced the average length of the lesions. Serotonin immunoreactivity caudal to the epicenter, a marker for descending motor control axons, was nearly threefold that of VEH controls. The increase in WM at the epicenter was significantly correlated with the decrease in functional deficits. The TTX group exhibited a significantly enhanced recovery of coordinated hindlimb functions, more normal hindlimb reflexes, and earlier establishment of a reflex bladder. The results demonstrate that Na+ channels play a critical role in WM loss in vivo after SCI.
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50
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LoPachin RM, Lehning EJ. Mechanism of calcium entry during axon injury and degeneration. Toxicol Appl Pharmacol 1997; 143:233-44. [PMID: 9144441 DOI: 10.1006/taap.1997.8106] [Citation(s) in RCA: 123] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Axon degeneration is a hallmark consequence of chemical neurotoxicant exposure (e.g., acrylamide), mechanical trauma (e.g., nerve transection, spinal cord contusion), deficient perfusion (e.g., ischemia, hypoxia), and inherited neuropathies (e.g., infantile neuroaxonal dystrophy). Regardless of the initiating event, degeneration in the PNS and CNS progresses according to a characteristic sequence of morphological changes. These shared neuropathologic features suggest that subsequent degeneration, although induced by different injury modalities, might evolve via a common mechanism. Studies conducted over the past two decades indicate that Ca2+ accumulation in injured axons has significant neuropathic implications and is a potentially unifying mechanistic event. However, the route of Ca2+ entry and the involvement of other relevant ions (Na+, K+) have not been adequately defined. In this overview, we discuss evidence for reverse operation of the Na+-Ca2+ exchanger as a primary route of Ca2+ entry during axon injury. We propose that diverse injury processes (e.g., axotomy, ischemia, trauma) which culminate in axon degeneration cause an increase in intraaxonal Na+ in conjunction with a loss of K+ and axolemmal depolarization. These conditions favor reverse Na+-Ca2+ exchange operation which promotes damaging extraaxonal Ca2+ entry and subsequent Ca2+-mediated axon degeneration. Deciphering the route of axonal Ca2+ entry is a fundamental step in understanding the pathophysiologic processes induced by chemical neurotoxicants and other types of nerve damage. Moreover, the molecular mechanism of Ca2+ entry can be used as a target for the development of efficacious pharmacotherapies that might be useful in preventing or limiting irreversible axon injury.
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Affiliation(s)
- R M LoPachin
- Department of Anesthesiology, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, New York 10467, USA
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