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Pizzo F, Roehri N, Catenoix H, Medina S, McGonigal A, Giusiano B, Carron R, Scavarda D, Ostrowsky K, Lepine A, Boulogne S, Scholly J, Hirsch E, Rheims S, Bénar CG, Bartolomei F. Epileptogenic networks in nodular heterotopia: A stereoelectroencephalography study. Epilepsia 2017; 58:2112-2123. [DOI: 10.1111/epi.13919] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/12/2017] [Indexed: 01/06/2023]
Affiliation(s)
- Francesca Pizzo
- Inserm; Institut de Neurosciences des Systèmes (INS); Aix Marseille Univ; Marseille France
| | - Nicolas Roehri
- Inserm; Institut de Neurosciences des Systèmes (INS); Aix Marseille Univ; Marseille France
| | - Hélène Catenoix
- Department of Functional Neurology and Epileptology; Hospices Civils de Lyon (Lyon University Hospital); Hospital for Neurology and Neurosurgery Pierre Wertheimer; Lyon France
| | - Samuel Medina
- Inserm; Institut de Neurosciences des Systèmes (INS); Aix Marseille Univ; Marseille France
| | - Aileen McGonigal
- Inserm; Institut de Neurosciences des Systèmes (INS); Aix Marseille Univ; Marseille France
- Clinical Neurophysiology; APHM; Timone Hospital; Marseille France
| | - Bernard Giusiano
- Inserm; Institut de Neurosciences des Systèmes (INS); Aix Marseille Univ; Marseille France
| | - Romain Carron
- Inserm; Institut de Neurosciences des Systèmes (INS); Aix Marseille Univ; Marseille France
- Functional and Stereotactic Neurosurgery; APHM; Timone Hospital; Marseille France
| | - Didier Scavarda
- Inserm; Institut de Neurosciences des Systèmes (INS); Aix Marseille Univ; Marseille France
- Functional and Stereotactic Neurosurgery; APHM; Timone Hospital; Marseille France
| | - Karine Ostrowsky
- Department of Functional Neurology and Epileptology; Hospices Civils de Lyon (Lyon University Hospital); Hospital for Neurology and Neurosurgery Pierre Wertheimer; Lyon France
| | - Anne Lepine
- Pediatric Neurology Department; Timone Hospital; APHM; Marseille France
| | - Sébastien Boulogne
- Department of Functional Neurology and Epileptology; Hospices Civils de Lyon (Lyon University Hospital); Hospital for Neurology and Neurosurgery Pierre Wertheimer; Lyon France
| | - Julia Scholly
- Medical and Surgical Epilepsy Unit; Hautepierre Hospital; University of Strasbourg; Strasbourg France
| | - Edouard Hirsch
- Medical and Surgical Epilepsy Unit; Hautepierre Hospital; University of Strasbourg; Strasbourg France
| | - Sylvain Rheims
- Department of Functional Neurology and Epileptology; Hospices Civils de Lyon (Lyon University Hospital); Hospital for Neurology and Neurosurgery Pierre Wertheimer; Lyon France
| | - Christian-George Bénar
- Inserm; Institut de Neurosciences des Systèmes (INS); Aix Marseille Univ; Marseille France
| | - Fabrice Bartolomei
- Inserm; Institut de Neurosciences des Systèmes (INS); Aix Marseille Univ; Marseille France
- Clinical Neurophysiology; APHM; Timone Hospital; Marseille France
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Watrin F, Manent JB, Cardoso C, Represa A. Causes and consequences of gray matter heterotopia. CNS Neurosci Ther 2014; 21:112-22. [PMID: 25180909 DOI: 10.1111/cns.12322] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Revised: 07/30/2014] [Accepted: 08/06/2014] [Indexed: 12/17/2022] Open
Abstract
The objective of this article is to review the pathophysiological bases of gray matter heterotopia and to appreciate their involvement in brain cortical development and functional consequences, namely epilepsy. The development of the cerebral cortex results from complex sequential processes including cell proliferation, cell migration, cortical organization, and formation of neuronal networks. Disruption of these steps yields different types of cortical malformations including gray matter heterotopia, characterized by the ectopic position of neurons along the ventricular walls or in the deep white matter. Cortical malformations are major causes of epilepsy, being responsible for up to 40% of drug-resistant epilepsy, and the cognitive level of affected patients varies from normal to severely impaired. This review reports data from human patients and animal models highlighting the genetic causes for these disorders affecting not only neuronal migration but also the proliferation of cortical progenitors. Therefore, gray matter heterotopias should not be considered as solely due to an abnormal neuronal migration and classifying them as such may be too restrictive. The review will also summarize literature data indicating that besides ectopic neurons, neighbor cortical areas also play a consistent role in epileptogenesis, supporting the notion that plastic changes secondary to the initial malformation are instrumental in the pathophysiology of epilepsy in affected patients.
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Affiliation(s)
- Françoise Watrin
- INSERM, INMED, Marseille, France; Aix-Marseille University, UMR 901, Marseille, France
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3
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STRACK BEATA, JACOBS KIMBERLEM, CIOS KRZYSZTOFJ. SIMULATING VERTICAL AND HORIZONTAL INHIBITION WITH SHORT-TERM DYNAMICS IN A MULTI-COLUMN MULTI-LAYER MODEL OF NEOCORTEX. Int J Neural Syst 2014; 24:1440002. [DOI: 10.1142/s0129065714400024] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The paper introduces a multi-layer multi-column model of the cortex that uses four different neuron types and short-term plasticity dynamics. It was designed with details of neuronal connectivity available in the literature and meets these conditions: (1) biologically accurate laminar and columnar flows of activity, (2) normal function of low-threshold spiking and fast spiking neurons, and (3) ability to generate different stages of epileptiform activity. With these characteristics the model allows for modeling lesioned or malformed cortex, i.e. examine properties of developmentally malformed cortex in which the balance between inhibitory neuron subtypes is disturbed.
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Affiliation(s)
- BEATA STRACK
- Department of Computer Science, Virginia Commonwealth University, Richmond, VA, USA
| | - KIMBERLE M. JACOBS
- Department of Anatomy and Neurobiology, Virginia Commonwealth University, Richmond, VA, USA
| | - KRZYSZTOF J. CIOS
- Department of Computer Science, Virginia Commonwealth University, Richmond, VA, USA
- IITiS Polish Academy of Sciences, Poland
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Cid E, Gomez-Dominguez D, Martin-Lopez D, Gal B, Laurent F, Ibarz JM, Francis F, Menendez de la Prida L. Dampened hippocampal oscillations and enhanced spindle activity in an asymptomatic model of developmental cortical malformations. Front Syst Neurosci 2014; 8:50. [PMID: 24782720 PMCID: PMC3995045 DOI: 10.3389/fnsys.2014.00050] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Accepted: 03/18/2014] [Indexed: 11/13/2022] Open
Abstract
Developmental cortical malformations comprise a large spectrum of histopathological brain abnormalities and syndromes. Their genetic, developmental and clinical complexity suggests they should be better understood in terms of the complementary action of independently timed perturbations (i.e., the multiple-hit hypothesis). However, understanding the underlying biological processes remains puzzling. Here we induced developmental cortical malformations in offspring, after intraventricular injection of methylazoxymethanol (MAM) in utero in mice. We combined extensive histological and electrophysiological studies to characterize the model. We found that MAM injections at E14 and E15 induced a range of cortical and hippocampal malformations resembling histological alterations of specific genetic mutations and transplacental mitotoxic agent injections. However, in contrast to most of these models, intraventricularly MAM-injected mice remained asymptomatic and showed no clear epilepsy-related phenotype as tested in long-term chronic recordings and with pharmacological manipulations. Instead, they exhibited a non-specific reduction of hippocampal-related brain oscillations (mostly in CA1); including theta, gamma and HFOs; and enhanced thalamocortical spindle activity during non-REM sleep. These data suggest that developmental cortical malformations do not necessarily correlate with epileptiform activity. We propose that the intraventricular in utero MAM approach exhibiting a range of rhythmopathies is a suitable model for multiple-hit studies of associated neurological disorders.
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Affiliation(s)
- Elena Cid
- Laboratorio de Circuitos Neuronales, Instituto Cajal, CSIC Madrid, Spain
| | | | - David Martin-Lopez
- Laboratorio de Circuitos Neuronales, Instituto Cajal, CSIC Madrid, Spain ; Servicio de Neurofisiologia Clínica, Hospital General Universitario Gregorio Marañón Madrid, Spain
| | - Beatriz Gal
- Laboratorio de Circuitos Neuronales, Instituto Cajal, CSIC Madrid, Spain ; Universidad Europea de Madrid, Ciencias Biomédicas Básicas Madrid, Spain
| | - François Laurent
- Laboratorio de Circuitos Neuronales, Instituto Cajal, CSIC Madrid, Spain
| | - Jose M Ibarz
- Servicio de Neurobiología, Instituto Ramón y Cajal de Investigación Sanitaria Madrid, Spain
| | - Fiona Francis
- Institut du Fer à Moulin Paris, France ; Sorbonne Universités, Université Pierre et Marie Curie Paris, France ; Institut National de la Santé et de la Recherche Médicale UMRS 839 Paris, France
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5
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Doi K. Mechanisms of neurotoxicity induced in the developing brain of mice and rats by DNA-damaging chemicals. J Toxicol Sci 2012; 36:695-712. [PMID: 22129734 DOI: 10.2131/jts.36.695] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
It is not widely known how the developing brain responds to extrinsic damage, although the developing brain is considered to be sensitive to diverse environmental factors including DNA-damaging agents. This paper reviews the mechanisms of neurotoxicity induced in the developing brain of mice and rats by six chemicals (ethylnitrosourea, hydroxyurea, 5-azacytidine, cytosine arabinoside, 6-mercaptopurine and etoposide), which cause DNA damage in different ways, especially from the viewpoints of apoptosis and cell cycle arrest in neural progenitor cells. In addition, this paper also reviews the repair process following damage in the developing brain.
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Affiliation(s)
- Kunio Doi
- Nippon Institute for Biological Science, Ome, Tokyo, Japan.
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6
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Manent JB, Represa A. Neurotransmitters and brain maturation: early paracrine actions of GABA and glutamate modulate neuronal migration. Neuroscientist 2007; 13:268-79. [PMID: 17519369 DOI: 10.1177/1073858406298918] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Migration of neurons from their birthplace to their final destination is an extremely important step in brain maturation, and cortical migration disorders are the most common brain developmental alteration observed in human patients. Among the mechanisms that govern neuronal migration, the neurotransmitters GABA and glutamate deserve particular attention: 1) neurotransmitters and receptors are expressed early in the developing brain, 2) neurotransmitters may act as paracrine signaling molecules in the immature brain, and 3) neurotransmitters regulate intracellular calcium required for many cellular functions, including cytoskeletal dynamic changes. Thus, many reports reviewed here aimed to demonstrate that the activation of specific GABA and glutamate receptors is instrumental in cell migration by acting as motility promoting, acceleratory, or stop signal. Interestingly, the regulation of migration by neurotransmitters and receptors depends on the type of migration (radial, tangential, or chain migration), the type of cells (principal glutamatergic neurons vs. GABAergic interneurons), and the brain area (neocortex, cerebellum, rostral migratory stream). A hypothesis is proposed that these differential actions in different cell types arise from a "homeostatic-like" regulation that controls final position, timing, and number of cells at destination.
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Affiliation(s)
- Jean-Bernard Manent
- Institut de Neurobiologie de la Méditerranée (INMED)-Institut National de la Santé et de la Recherche Médicale (INSERM), Marseille, France
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Rosen GD, Bai J, Wang Y, Fiondella CG, Threlkeld SW, LoTurco JJ, Galaburda AM. Disruption of neuronal migration by RNAi of Dyx1c1 results in neocortical and hippocampal malformations. Cereb Cortex 2007; 17:2562-72. [PMID: 17218481 PMCID: PMC3742088 DOI: 10.1093/cercor/bhl162] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The brains of individuals with developmental dyslexia have neocortical neuronal migration abnormalities including molecular layer heterotopias, laminar dysplasias, and periventricular nodular heterotopias (PNH). RNA interference (RNAi) of Dyx1c1, a candidate dyslexia susceptibility gene, disrupts neuronal migration in developing embryonic neocortex. Using in utero electroporation, we cotransfected cells in the rat neocortical ventricular zone (VZ) at E14/15 with short hairpin RNA vectors targeting Dyx1c1 along with either plasmids encoding enhanced green fluorescent protein or plasmids encoding monomeric red fluorescent protein only. RNAi of Dyx1c1 resulted in pockets of unmigrated neurons resembling PNH. The pattern of migration of transfected neurons was bimodal, with approximately 20% of the neurons migrating a short distance from the VZ and another 40% that migrated past their expected lamina. Approximately 25% of the transfected brains had hippocampal pyramidal cell migration anomalies. Molecular layer ectopias, which were not related to injection site artifacts, were also seen in 25% of the animals. These results support the hypothesis that targeted disruption of the candidate dyslexia susceptibility gene, Dyx1c1, results in neuronal migration disorders similar to those seen in the brains of dyslexics.
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Affiliation(s)
- Glenn D Rosen
- Dyslexia Research Laboratory and Charles A Dana Research Institute, Department of Neurology, Division of Behavioral Neurology, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
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Feng Y, Chen MH, Moskowitz IP, Mendonza AM, Vidali L, Nakamura F, Kwiatkowski DJ, Walsh CA. Filamin A (FLNA) is required for cell-cell contact in vascular development and cardiac morphogenesis. Proc Natl Acad Sci U S A 2006; 103:19836-41. [PMID: 17172441 PMCID: PMC1702530 DOI: 10.1073/pnas.0609628104] [Citation(s) in RCA: 236] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Mutations in the human Filamin A (FLNA) gene disrupt neuronal migration to the cerebral cortex and cause cardiovascular defects. Complete loss of Flna in mice results in embryonic lethality with severe cardiac structural defects involving ventricles, atria, and outflow tracts, as well as widespread aberrant vascular patterning. Despite these widespread developmental defects, migration and motility of many cell types does not appear to be affected. Instead, Flna-null embryos display abnormal epithelial and endothelial organization and aberrant adherens junctions in developing blood vessels, heart, brain, and other tissues. Essential roles for FLNA in intercellular junctions provide a mechanism for the diverse developmental defects seen in patients with FLNA mutations.
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Affiliation(s)
- Yuanyi Feng
- *Division of Genetics and
- Beth Israel Deaconess Medical Center, Howard Hughes Medical Institute, and
| | - Ming Hui Chen
- Department of Cardiology, Children's Hospital Boston, Boston, MA 02215
- Cardiology and Women's Health, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115
| | - Ivan P. Moskowitz
- Department of Genetics, Harvard Medical School, Boston, MA 02115; and
| | - Ashley M. Mendonza
- *Division of Genetics and
- Beth Israel Deaconess Medical Center, Howard Hughes Medical Institute, and
| | | | | | - David J. Kwiatkowski
- Divisions of **Hematology and
- To whom correspondence may be addressed. E-mail:
or
| | - Christopher A. Walsh
- *Division of Genetics and
- Beth Israel Deaconess Medical Center, Howard Hughes Medical Institute, and
- To whom correspondence may be addressed. E-mail:
or
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Paredes M, Pleasure SJ, Baraban SC. Embryonic and early postnatal abnormalities contributing to the development of hippocampal malformations in a rodent model of dysplasia. J Comp Neurol 2006; 495:133-48. [PMID: 16432901 PMCID: PMC2827607 DOI: 10.1002/cne.20871] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
While there are many recent examples of single gene deletions that lead to defects in cortical development, most human cases of cortical disorganization can be attributed to a combination of environmental and genetic factors. Elucidating the cellular or developmental basis of teratogenic exposures in experimental animals is an important approach to understanding how environmental insults at particular developmental junctures can lead to complex brain malformations. Rats with prenatal exposure to methylazoxymethanol (MAM) reproduce many anatomical features seen in epilepsy patients. Previous studies have shown that heterotopic clusters of neocortically derived neurons exhibit hyperexcitable firing activity and may be a source of heightened seizure susceptibility; however, the events that lead to the formation of these abnormal cell clusters is unclear. Here we used a panel of molecular markers and birthdating studies to show that in MAM-exposed rats the abnormal cell clusters (heterotopia) first appear postnatally in the hippocampus (P1-2) and that their appearance is preceded by a distinct sequence of perturbations in neocortical development: 1) disruption of the radial glial scaffolding with premature astroglial differentiation, and 2) thickening of the marginal zone with redistribution of Cajal-Retzius neurons to deeper layers. These initial events are followed by disruption of the cortical plate and appearance of subventricular zone nodules. Finally, we observed the erosion of neocortical subventricular zone nodules into the hippocampus around parturition followed by migration of nodules to hippocampus. We conclude that prenatal MAM exposure disrupts critical developmental processes and prenatal neocortical structures, ultimately resulting in neocortical disorganization and hippocampal malformations.
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Affiliation(s)
- Mercedes Paredes
- Epilepsy Research Laboratory, Department of Neurological Surgery, University of California, San Francisco
| | - Samuel J. Pleasure
- Department of Neurology, University of California, San Francisco
- Correspondence to either: SC Baraban, Box 0520, Department of Neurological Surgery, 513 Parnassus Avenue, UCSF, San Francisco, CA 94143. Phone: (415) 476-9473; Fax: (415) or SJ Pleasure, Box 0435, Department of Neurology, 513 Parnassus Avenue, UCSF, San Francisco, CA 94143. Phone: (415) 502-5683; Fax: (415) 476-5229;
| | - Scott C. Baraban
- Epilepsy Research Laboratory, Department of Neurological Surgery, University of California, San Francisco
- Correspondence to either: SC Baraban, Box 0520, Department of Neurological Surgery, 513 Parnassus Avenue, UCSF, San Francisco, CA 94143. Phone: (415) 476-9473; Fax: (415) or SJ Pleasure, Box 0435, Department of Neurology, 513 Parnassus Avenue, UCSF, San Francisco, CA 94143. Phone: (415) 502-5683; Fax: (415) 476-5229;
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10
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Mothersill C, Seymour CB. Actions of radiation on living cells in the "post-bystander" era. EXS 2006:159-77. [PMID: 16383018 DOI: 10.1007/3-7643-7378-4_7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Over the past 20 years there has been increasing evidence that cells and the progeny of cells surviving a dose of ionizing radiation can exhibit a wide range of effects inconsistent with the level of dose received. Recently, the cause of these delayed effects has been ascribed to so-called bystander effects, occurring in cells not directly hit by an ionizing track, but which are influenced by signals from irradiated cells. These effects are not necessarily deleterious, although most of the literature deals with adverse delayed effects. What is important to consider is what, if anything, these effects mean for what is still the central dogma of radiobiology and radiation protection, i.e., that DNA double-strand breaks are the primary radiation-induced lesion that can be quantifiably related to received dose, and which determine the probability that a cancer will result from a radiation exposure. In this chapter we review the history of radiation biology which led to the DNA paradigm. We explore the issues and the evidence which are now challenging the view that dose deposition in DNA is all important. We conclude that in the low-dose region, the primary determinant of radiation exposure outcome is the genetic and epigenetic background of the individual and not the dose. This effectively dissociates dose from effect as a quantitative relationship, but it does not necessarily mean that the effect is unrelated to DNA damage somewhere in the system.
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Affiliation(s)
- Carmel Mothersill
- Medical Physics and Applied Radiation Sciences Unit, McMaster University, Hamilton, Ontario L8S 4K1, Canada.
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11
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Castro PA, Pleasure SJ, Baraban SC. Hippocampal heterotopia with molecular and electrophysiological properties of neocortical neurons. Neuroscience 2003; 114:961-72. [PMID: 12379251 DOI: 10.1016/s0306-4522(02)00296-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cortical malformations resulting from aberrant brain development can be associated with mental retardation, dyslexia, and intractable forms of epilepsy. Despite emerging interest in the pathology and etiology of cortical malformations, little is known about the phenotype of cells within these lesions. In utero exposure to the DNA methylating agent methylazoxymethanol acetate (MAM) during a critical stage in neurodevelopment results in animals with distinct clusters of displaced neurons in hippocampus, i.e. nodular heterotopia. Here we examined the molecular and electrophysiological properties of cells within hippocampal heterotopia using rats exposed to MAM during gestation. Molecular analysis revealed that heterotopic cells do not express mRNA markers normally found in hippocampal pyramidal cells or dentate granule cells (SCIP, Math-2, Prox-1, neuropilin-2). In contrast, Id-2 mRNA, normally abundant in Layer II-III supragranular neocortical neurons but not in CA1 pyramidal neurons, was prominently expressed in hippocampal heterotopia. Current-clamp analysis of the firing properties of heterotopic neurons revealed a striking similarity with supragranular cortical neurons. In particular, both cells were characterized by small hyperpolarizing 'sag' potentials, high input resistance values, slow spike-train afterhyperpolarizations, and the absence of a depolarizing afterpotential. Normotopic CA1 pyramidal neurons (e.g. pyramidal cells with normal lamination adjacent to a heterotopia) in the MAM brain exhibited molecular and electrophysiological properties that were nearly identical to those of age-matched CA1 pyramidal neurons from control rats. We conclude that neuronal heterotopiae in the hippocampus of MAM-exposed rats are comprised of neurons with a Layer II-III supragranular cortex phenotype. The MAM model, therefore, may serve as a useful tool in examination of the factors influencing aberrant brain development and epilepsy.
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Affiliation(s)
- P A Castro
- Epilepsy Research Laboratory, Department of Neurological Surgery, University of California, San Francisco, Box 0520, 513 Parnassus Avenue, 94143, USA
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12
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Pentney AR, Baraban SC, Colmers WF. NPY sensitivity and postsynaptic properties of heterotopic neurons in the MAM model of malformation-associated epilepsy. J Neurophysiol 2002; 88:2745-54. [PMID: 12424309 DOI: 10.1152/jn.00500.2002] [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: 11/22/2022] Open
Abstract
Neuronal migration disorders (NMDs) can be associated with neurological dysfunction such as mental retardation, and clusters of disorganized cells (heterotopias) often act as seizure foci in medically intractable partial epilepsies. Methylazoxymethanol (MAM) treatment of pregnant rats results in neuronal heterotopias in offspring, especially in hippocampal area CA1. Although the neurons in dysplastic areas in this model are frequently hyperexcitable, the precise mechanisms controlling excitability remain unclear. Here, we used IR-DIC videomicroscopy and whole cell voltage-clamp techniques to test whether the potent anti-excitatory actions of neuropeptide Y (NPY) affected synaptic excitation of heterotopic neurons. We also compared several synaptic and intrinsic properties of heterotopic, layer 2-3 cortical, and CA1 pyramidal neurons, to further characterize heterotopic cells. NPY powerfully inhibited synaptic excitation onto normal and normotopic CA1 cells but was nearly ineffective on responses evoked in heterotopic cells from stimulation sites within the heterotopia. Glutamatergic synaptic responses on heterotopic cells exhibited a comparatively small, D-2-amino-5-phosphopentanoic acid-sensitive, N-methyl-D-aspartate component. Heterotopic neurons also differed from normal CA1 cells in postsynaptic membrane currents, possessing a prominent inwardly rectifying K(+) current sensitive to Cs(+) and Ba(2+), similar to neocortical layer 2-3 pyramidal cells. CA1 cells instead had a prominent Cs(+)- and 4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino) pyrimidinium chloride-sensitive I(h) and negligible inward rectification, unlike heterotopic cells. Thus heterotopic CA1 cells appear to share numerous physiological similarities with neocortical neurons. The lack of NPY's effects on intra-heterotopic inputs, the small contribution of I(h), and abnormal glutamate receptor function, may all contribute to the lowered threshold for epileptiform activity observed in hippocampal heterotopias and could be important factors in epilepsies associated with NMDs.
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Affiliation(s)
- A R Pentney
- Department of Pharmacology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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Sun XZ, Takahashi S, Kubota Y, Sato H, Cui C, Fukui Y, Inouye M. Types and three-dimensional distribution of neuronal ectopias in the brain of mice prenatally subjected to X-irradiation. JOURNAL OF RADIATION RESEARCH 2002; 43:89-98. [PMID: 12056333 DOI: 10.1269/jrr.43.89] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The types and three-dimensional distribution of neocortical ectopias following prenatal exposure to X-irradiation were studied by a histological examination and computer reconstruction techniques. Pregnant ICR mice were subjected to X-irradiation at a dose of 1.5 Gy on embryonic day 13. The brains from 30-day-old mice were serially sectioned on the frontal plane at 15 microns, stained with HE and observed with a microscope. The image data for the sections were input to a computer, and then reconstructed to three-dimensional brain structures using the Magellan 3.6 program. Sectional images were then drawn on a computer display at 240 microns intervals, and the positions of the different types of neocortical ectopias were marked using color coding. Three types of neocortical ectopias were recognized in the irradiated brains. Neocortical Lay I ectopias were identified as small patches in the caudal occipital cortex, and were located more laterally in the neocortex in caudal sections than in the rostral sections. Periventricular ectopias were located more rostrally than Lay I ectopias, and were found from the most caudal extent of the presumed motor cortex to the most caudal extent of the lateral ventricle. Hippocampal ectopias appeared as continuous linear bands, and were frequently associated with the anterior parts of the periventricular ectopias.
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Affiliation(s)
- Xue-Zhi Sun
- Environmental and Toxicological Sciences Research Group, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage-ku, Chiba 263-8555, Japan.
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14
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Santi MR, Golden JA. Periventricular heterotopia may result from radial glial fiber disruption. J Neuropathol Exp Neurol 2001; 60:856-62. [PMID: 11556542 DOI: 10.1093/jnen/60.9.856] [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: 11/13/2022] Open
Abstract
Periventricular heterotopia (PVH) are collections of neurons and glia heterotopically located adjacent to the ventricles. The pathogenesis of periventricular heterotopia is believed to be a failure of cells to migrate from the ventricular zone. Mutations in filamin-1 (FLN1) have recently been identified as a genetic defect that results in an X-linked dominant form of PVH. In addition to this X-linked form, PVH may be found sporadically or occasionally as part of other syndromes. The pathogenesis(es) of PVH has not been entirely elucidated for patients with or without FLN1 mutation. In an attempt to better understand the pathogenesis of PVH, we examined 5 fetuses (gestational ages 21 to 34 wk), 3 females and 2 males, with PVH. Neuropathologic examination of these 5 fetuses revealed several to multiple periventricular nodules. No case showed the extensive periventricular heterotopia most commonly found in females with FLN1 mutations. By immunohistochemistry, neurofilament-positive cells were identified within the PVH in 3 of 5 cases and glial fibrillary acidic protein-positive cells surrounded the nodules in all 5 cases, but positive cells were only found within the nodules of 3 cases. Surprisingly, small collections of CD68-positive macrophages were found at the base of the nodules in 4 of the 5 cases. Moreover, in all cases, the radial glia highlighted with vimentin, showed disorganization specifically around the nodules. These data suggest that at least one pathogenesis for PVH is a disruption of the radial glial organization, resulting in a failure of cells to migrate from the ventricular zone.
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Affiliation(s)
- M R Santi
- Armed Forces Institute of Pathology, Washington, DC, USA
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15
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Schwartzkroin PA, Walsh CA. Cortical malformations and epilepsy. MENTAL RETARDATION AND DEVELOPMENTAL DISABILITIES RESEARCH REVIEWS 2001; 6:268-80. [PMID: 11107192 DOI: 10.1002/1098-2779(2000)6:4<268::aid-mrdd6>3.0.co;2-b] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Brain malformations, resulting from aberrant patterns of brain development, are highly correlated with childhood seizure syndromes, as well as with cognitive disabilities and other neurological disorders. The structural malformations, often referred to as cortical dysplasia, are extremely varied, reflecting diverse underlying processes and critical timing of the developmental aberration. Recent studies have revealed a genetic basis for many forms of dysplasia. Gene mutations responsible for such common forms of dysplasia as lissencephaly and tuberous sclerosis have been identified, and investigators are beginning to understand how these gene mutations interrupt and/or misdirect the normal developmental pattern. Laboratory investigations, using animal models of cortical dysplasia, are beginning to elucidate how these structural malformations give rise to epilepsy and other functional pathologies.
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Affiliation(s)
- P A Schwartzkroin
- Department of Neurological Surgery, University of Washington, Health Sciences Center, Seattle, Washington, USA
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16
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Kubota Y, Takahashi S, Sun XZ, Sato H, Aizawa S, Yoshida K. Radiation-induced tissue abnormalities in fetal brain are related to apoptosis immediately after irradiation. Int J Radiat Biol 2000; 76:649-59. [PMID: 10866287 DOI: 10.1080/095530000138312] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
PURPOSE To investigate the relation between the incidence of radiation-induced tissue abnormalities in fetal brain and the extent of p53-dependent apoptosis. MATERIALS AND METHODS Pregnant mice with wild-type p53(+/+), heterozygous p53(+/-) and homozygous mutant p53(-/-) fetuses received whole-body X-irradiation on day 13 of gestation. The extent of apoptosis 6 hr after irradiation and the incidence of tissue abnormalities 3 days after irradiation in the brain were evaluated by histological examination of brain mantle. RESULTS The percentage of apoptotic cells increased linearly with dose in p53(+/+) and p53(+/-) fetuses, but no increase was found in p53(-/-). Approximately twice the dose was necessary in p53(+/-) fetuses to induce an apoptotic response to the extent observed in p53(+/+). Fetuses with brain-tissue abnormalities, such as a destroyed ventricular lining and rosettes with a central hollow appeared at a dose of 1.5 and 3.0 Gy, and the incidence was markedly increased following a dose of 2.25 and 3.75Gy in p53(+/+) and p53(+/-) mice, respectively, but no fetus with tissue abnormalities appeared in p53(-/-) at up to 3.75 Gy. Approximately twice the dose was necessary in p53(+/-) fetuses to induce brain-tissue abnormalities to the extent seen in p53(+/+) mice. CONCLUSION The extent of apoptosis 6 hr after irradiation and the incidence and severity of brain-tissue abnormalities 3 days after irradiation corresponded well, suggesting that radiation-induced tissue abnormalities, such as destroyed ventricular lining, deranged glial fibre and appearance of rosettes in fetal brain were closely related to apoptosis seen 6 hr after irradiation.
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Affiliation(s)
- Y Kubota
- Environmental and Toxicological Sciences Research Group, National Institute of Radiological Sciences, Chiba, Japan.
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Baraban SC, Wenzel HJ, Hochman DW, Schwartzkroin PA. Characterization of heterotopic cell clusters in the hippocampus of rats exposed to methylazoxymethanol in utero. Epilepsy Res 2000; 39:87-102. [PMID: 10759297 DOI: 10.1016/s0920-1211(99)00104-7] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Cortical disorganization represents one of the major clinical findings in many children with medically intractable epilepsy. To study the relationship between seizure propensity and abnormal cortical structure, we have begun to characterize an animal model exhibiting aberrant neuronal clusters (heterotopia) and disruption of cortical lamination. In this model, exposing rats in utero to the DNA methylating agent methylazoxymethanol acetate (MAM; embryonic day 15) disrupts the sequence of normal brain development. In MAM-exposed rats, cells in hippocampal heterotopia exhibit neuronal morphology and do not stain with immunohistochemical markers for glia. In hippocampal slices from MAM-exposed animals, extracellular field recordings within heterotopia suggest that these dysplastic cell clusters make synaptic connections locally (i.e. within the CA1 hippocampal subregion) and also make aberrant synaptic contact with neocortical cells. Slice perfusion with bicuculline or 4-aminopyridine leads to epileptiform activity in dysplastic cell clusters that can occur independent of input from CA3. Taken together, our findings suggest that neurons within regions of abnormal hippocampal organization are capable of independent epileptiform activity generation, and can project abnormal discharge to a broad area of neocortex, as well as hippocampus.
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Affiliation(s)
- S C Baraban
- Department of Pediatrics, Case Western Reserve University, Cleveland, OH 44106, USA.
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18
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Kábová R, Velísková J, Velísek L. Prenatal methotrexate exposure decreases seizure susceptibility in young rats of two strains. Exp Neurol 2000; 161:167-73. [PMID: 10683282 DOI: 10.1006/exnr.1999.7318] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Effects of prenatal exposure to methotrexate (MTX) administered in Sprague-Dawley (one 5 mg/kg dose of MTX on gestational day 15; E15) or Wistar (one 5 mg/kg dose of MTX on E14 or E15 or two such doses on E15) pregnant rat dams were studied in developing offspring. Young Sprague-Dawley rats were subjected to rapid kindling on postnatal days (PN) 15 and 16, and to flurothyl seizures on PN 15 and PN 30. Offspring of the Wistar strain were tested in flurothyl on PN 30. In Sprague-Dawley rats, prenatal exposure to MTX decreased susceptibility to kindling-induced seizures on PN 15 and to flurothyl-induced clonic seizures on PN 30. In Wistar rats, a single dose of MTX on E15 was ineffective, but two doses significantly decreased susceptibility to flurothyl-induced seizures. Additionally, due to a shorter duration of pregnancy in Wistar rats, exposure to a single dose of MTX on E14 also decreased susceptibility to flurothyl seizures. MTX, as folic acid antagonist, interferes with DNA synthesis. However, unlike other treatments that suppress DNA synthesis (such as methylazoxymethanol exposure or X-ray radiation), MTX exposure results in anticonvulsant effects in surviving offspring. The data suggest that not all prenatal impairments of DNA have proconvulsant features postnatally.
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Affiliation(s)
- R Kábová
- Department of Normal, Pathological, and Clinical Physiology, Charles University, Prague, Czech Republic
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19
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Abstract
The presence of developmental cortical malformations is associated with epileptogenesis and other neurological disorders. In recent years, animal models specific to certain malformations have been developed to study the underlying epileptogenic mechanisms. Teratogens (chemical, thermal or radiation) applied during cortical neuroblast division and migration result in lissencephaly and focal cortical dysplasia. Animals with these malformations have a lowered seizure threshold as well as histopathologies typical of those found in human dysgenic brains. Alterations that may promote epileptogenesis have been identified in lissencephalic brains, such as increased numbers of bursting types of neurons, and abnormal connections between hippocampus, subcortical heterotopia, and neocortex. A distinct set of pathological properties is present in animal models of 4-layered microgyria, induced with cortical lesions made during late stages of cortical neuroblast migration. Hyperexcitability has been demonstrated in cortex adjacent to the microgyrus (paramicrogyral zone) in in vitro slice preparations. A number of observations suggest that cellular differentiation is delayed in microgyric brains. Other studies show increases in postsynaptic glutamate receptors and decreases in GABA(A) receptors in microgyric cortex. These alterations could promote epileptogenesis, depending on which cell types have the altered receptors. The microgyrus lacks thalamic afferents from sensory relay nuclei, that instead appear to project to the paramicrogyral region, thereby increasing excitatory connectivity within this epileptogenic zone. These studies have provided a necessary first step in understanding molecular and cellular mechanisms of epileptogenesis associated with cortical malformations.
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Affiliation(s)
- K M Jacobs
- Department of Neurology and Neurological Sciences, Stanford University Medical Center, CA 94305, USA
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20
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Chevassus-au-Louis N, Baraban SC, Gaïarsa JL, Ben-Ari Y. Cortical malformations and epilepsy: new insights from animal models. Epilepsia 1999; 40:811-21. [PMID: 10403203 DOI: 10.1111/j.1528-1157.1999.tb00786.x] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In the last decade, the recognition of the high frequency of cortical malformations among patients with epilepsy especially children, has led to a renewed interest in the study of the pathophysiology of cortical development. This field has also been spurred by the recent development of several experimental genetic and non-genetic, primarily rodent, models of cortical malformations. Epileptiform activity in these animals can appear as spontaneous seizure activity in vivo, in vitro hyperexcitability, or reduced seizure susceptibility in vitro and in vivo. In the neonatal freeze lesion model, that mimics human microgyria, hyperexcitability is caused by a reorganization of the network in the borders of the malformation. In the prenatal methylazoxymethanol model, that causes a diffuse cortical malformation, hyperexcitability is associated with alteration of firing properties of discrete neuronal subpopulations together with the formation of bridges between normally unconnected structures. In agreement with clinical evidence, these experimental data suggest that cortical malformations can both form epileptogenic foci and alter brain development in a manner that causes a diffuse hyperexcitability of the cortical network.
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Sun XZ, Takahashi S, Fukui Y, Hisano S, Kuboda Y, Sato H, Inouye M. Different patterns of abnormal neuronal migration in the cerebral cortex of mice prenatally exposed to irradiation. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1999; 114:99-108. [PMID: 10209247 DOI: 10.1016/s0165-3806(99)00029-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A characteristic abnormal cortical architecture in the adult brain was produced in mice subjected to 1.5 Gy of X-irradiation on embryonic day 14. Neurons in the lateral regions were organized into an essentially six-layered structure, while neurons in the dorsal regions formed a unique four-layered cortex. The patterns of neuronal migration in these different cortical regions were examined with immunohistochemistry for anti-bromodeoxyuridine (BrdU), anti-midkine (MK), and anti-glial fibrillary acidic protein (GFAP) antibodies. In the cortical lateral region, BrdU-labeled cells in the upper layers were fewer, and those in lower layers more numerous in prenatally irradiated mice than in control, while in the dorsal region (four-layered region), BrdU-labeled cells were very few in layer 2, and a large number of labeled-cells remained in layer 4. These results indicated that some neuroblasts in the lateral cortical region could not migrate to the upper layers, and that most neuroblasts in the dorsal cortical region failed to pass through the earlier migration zone. MK- and GFAP-stained radial glial fibers showed that the radial fibers were consistently oriented in the direction of neuronal migration in the control brains. However, in the irradiated brain, such radial fibers were crumpled in the lateral region, or were reduced markedly in number in some parts of the dorsal region. These results revealed that neuronal migratory pathways (radial glial fibers) were destroyed differently in different regions, and that X-rays killed some cells including radial glial cells or their precursors during the embryonic stage. These effects of radiation on the developing brain may result from the possibility that neurogenetic time is different or there are cellular mechanisms involved in the radiosensitivity among different regions.
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Affiliation(s)
- X Z Sun
- The 4th Research Group, National Institute of Radiological Sciences, Chiba 263-8555, Japan.
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Colacitti C, Sancini G, Franceschetti S, Cattabeni F, Avanzini G, Spreafico R, Di Luca M, Battaglia G. Altered connections between neocortical and heterotopic areas in methylazoxymethanol-treated rat. Epilepsy Res 1998; 32:49-62. [PMID: 9761308 DOI: 10.1016/s0920-1211(98)00039-4] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
We are currently investigating various treatments which could determine, in the rat brain, structural abnormalities mimicking those reported in human brain dysgeneses. We can induce the formation of neuronal heterotopia in the progeny of rats by means of a double injection of the cytotoxic agent methylazoxymethanol acetate (MAM) on embryonic day 15. We have now investigated the anatomical connections of these heterotopia by means of anterograde and retrograde tract tracing techniques. The induced heterotopia along the border of the lateral ventricles shared common anatomical features with the periventricular nodules in human periventricular or subcortical nodular heterotopia (PNH). The tract tracing data demonstrated the existence of reciprocal connections between the neuronal heterotopia and the ipsilateral and contralateral cortical areas, and the presence of abnormal cortico-hippocampal and cortico-cortical connections. On the basis of the connectivity patterns, it may be speculated that some cells in the heterotopia could be neurons originally committed to the cortex, that were interrupted in their migration by the MAM treatment. Given the common morphological features seen in human PNH and MAM-induced brain heterotopia, the anatomical and developmental analysis of MAM-treated rats may shed light on the mechanisms by which human brain dysgeneses develop in human patients.
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Affiliation(s)
- C Colacitti
- Department of Neurophysiology, Neurological Institute C. Besta, Milano, Italy
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Chevassus-Au-Louis N, Congar P, Represa A, Ben-Ari Y, Gaïarsa JL. Neuronal migration disorders: heterotopic neocortical neurons in CA1 provide a bridge between the hippocampus and the neocortex. Proc Natl Acad Sci U S A 1998; 95:10263-8. [PMID: 9707635 PMCID: PMC21496 DOI: 10.1073/pnas.95.17.10263] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Neuronal migration disorders have been involved in various pathologies, including epilepsy, but the properties of the neural networks underlying disorders have not been determined. In the present study, patch clamp recordings were made from intrahippocampal heterotopic as well as from neocortical and hippocampal neurons from brain slices of rats with prenatally methylazoxymethanol-induced cortical malformation. We report that heterotopic neurons have morphometrical parameters and cellular properties of neocortical supragranular neurons and are integrated in both neocortical and hippocampal networks. Thus, stimulation of the white matter induces both antidromic and orthodromic response in heterotopic and neocortical neurons. Stimulation of hippocampal afferents evokes a monosynaptic response in the majority of heterotopic neurons and a polysynaptic all-or-none epileptiform burst in the presence of bicuculline to block gamma-aminobutyric acid type A inhibition. Furthermore, hippocampal paroxysmal activity generated by bath application of bicuculline can spread directly to the neocortex via the heterotopia in methylazoxymethanol-treated but not in naive rats. We conclude that heterotopias form a functional bridge between the limbic system and the neocortex, providing a substrate for pathological conditions.
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Affiliation(s)
- N Chevassus-Au-Louis
- Institut National de la Santé et de la Recherche Médicale U29, Université Paris 5 René Descartes, 123 Boulevard de Port Royal, 75 674 Paris cedex 14, France.
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Chevassus-Au-Louis N, Rafiki A, Jorquera I, Ben-Ari Y, Represa A. Neocortex in the hippocampus: an anatomical and functional study of CA1 heterotopias after prenatal treatment with methylazoxymethanol in rats. J Comp Neurol 1998; 394:520-36. [PMID: 9590559 DOI: 10.1002/(sici)1096-9861(19980518)394:4<520::aid-cne9>3.0.co;2-3] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Migration disorders cause neurons to differentiate in an abnormal heterotopic position. Although significant insights have been gained into the etiology of these disorders, very little is known about the anatomy of heterotopias. We have studied heterotopic masses arising in the hippocampal CA1 region after prenatal treatment with methylazoxymethanol (MAM) in rats. Heterotopic cells were phenotypically similar to neocortical supragranular neurons and exhibited the same temporal profile of migration and neurogenesis. However, they did not express molecules characteristic of CA1 neurons such as the limbic-associated membrane protein. Horseradish peroxidase injections in heterotopia demonstrated labeled fibers not only in the neocortex and white matter but also in the CA1 stratum radiatum and stratum lacunosum. To study the pathophysiological consequences of this connectivity, we compared the effects of neocortical and limbic seizures on the expression of Fos protein and on cell death in MAM animals. After metrazol-induced seizures, Fos-positive cells were present in CA1 heterotopias, the only hippocampal region to be activated with the neocortex. By contrast, kainic acid-induced seizures caused a prominent delayed cell death in limbic regions and in CA1 heterotopias. Together, these results suggest that neocortical heterotopias in the CA1 region are integrated in both the hippocampal and neocortical circuitry.
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Sancini G, Franceschetti S, Battaglia G, Colacitti C, Di Luca M, Spreafico R, Avanzini G. Dysplastic neocortex and subcortical heterotopias in methylazoxymethanol-treated rats: an intracellular study of identified pyramidal neurones. Neurosci Lett 1998; 246:181-5. [PMID: 9792622 DOI: 10.1016/s0304-3940(98)00258-4] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Intracellular recordings were obtained using biocytin-filled electrodes from 78 neurones located in both dysplastic neocortex and subcortical heterotopic aggregates in a model of neuronal migration disorder induced in rats by means of a double methylazoxymethanol injection given on embryonic day 15. Both regular spiking and intrinsically bursting pyramidal neurones were found in all of the examined structures and were synaptically activated by subcortical stimulation. In a neuronal subpopulation (22%) located in the neocortex as well as in the subcortical heterotopic aggregates, the injection of depolarising current pulses elicited aberrant firing patterns, consisting of repetitive bursts of APs that gradually increased in duration and eventually merged in a long-lasting discharge. The gradual development of this 'excessive' bursting behaviour suggests a progressive run-down of the slow components of the hyperpolarising afterpotential.
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Affiliation(s)
- G Sancini
- Istituto Nazionale Neurologico C. Besta Laboratorio di Neurofisiologico, Sperimentale, Milan, Italy
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