Distribution of glutamate receptor subunits in experimentally induced cortical malformations

doi:10.1016/S0306-4522(02)00959-4

Neuroscience

Volume 117, Issue 4, 10 April 2003, Pages 991-1002

https://doi.org/10.1016/S0306-4522(02)00959-4 Get rights and content

Abstract

Electrophysiological studies in humans and animal models have revealed an intrinsic epileptogenicity of cortical dysplasias which are a frequent cause of drug-resistant epilepsy. An imbalance of inhibition and excitation has been causative related. Receptor-binding studies in rodents demonstrated reduced binding to GABA and increased binding to glutamate receptors within cortical dysplasias and increments of AMPA- and kainate-receptor binding in its surround. Immunohistochemically a differential downregulation of GABA_A receptor subunits could be demonstrated in widespread areas within and around dysplasias. As receptor binding critically depends on receptor subunit composition the observed changes in binding properties might be related to this. Here, we immunohistochemically analyzed the regional expression of four NMDA receptor subunits and two major AMPA- and kainate-receptor complexes in adult rats after neonatal freeze lesions. These lesions are characterized by a three- to four-layered cortex and a microsulcus which mimic human polymicrogyria. Using antibodies against NR1, NR2A, NR2B, NR2D, GluR2,3, and GluR5,6,7 receptor subunits we demonstrated a pronounced disturbance of cortical immunostaining pattern in the cortical malformation. These changes reflected the structural disorganization of the microgyrus with some distortion of the apical dendrites of paramicrogyral pyramidal cells, a decrease and disorganization of cells at the bottom of the microsulcus, and an inflection of apical dendrites toward the microsulcus. The neuronal staining pattern of large pyramidal cells in the neighborhood of the dysplasia did not differ for any subunit investigated. No remote or widespread changes of glutamate-receptor subunit distribution could be detected. The lack of gross and/or widespread alterations of glutamate-receptor subunit distribution in the surround of focal cortical dysplasia suggests the presence of other or additional mechanisms underlying the increased excitatory neurotransmitter binding and excitability in cortical malformations.

Section snippets

Lesion induction

Several litters of newborn Wistar rats (Experimental Animal Laboratory of the Heinrich Heine University Duesseldorf) were used for the experiments. All experiments were in strict adherence with local government requirements and according to approved guidelines. Any effort was made to minimize the number of animals and to avoid suffering. Focal freeze lesions were induced on the day of birth (P0, <24 h) using a modification of the method of Dvorak and Feit (Dvorak et al., 1977) as previously

Dysplastic cortex

All freeze-lesioned animals displayed typical cortical malformations consisting of a longitudinal microgyrus located in parallel to the midline with a length of 3–5 mm (Fig. 1). The microgyrus had a distance to midline of 2–4 mm and mainly involved the sensory cortex Par1 (Zilles, 1985).The laminar architecture of the cortical malformation showed some variability. Most animals revealed the formation of a sulcus with an underlying three- to four-layered cortex as reported previously Dvorak et al

Discussion

The main findings of the present study on the distribution of glutamate-receptor subunits in an animal model of neocortical migration disorder are as follows. (i) The immunostaining pattern for the NMDA receptor subunits NR1, NR2A, NR2B, NR2D, the AMPA receptor subunits GluR2,3 and the kainate receptor subunits GluR5,6,7 was locally disturbed at the site of the cortical malformation reflected the structural organization of the three- or four-layered microgyrus. (ii) Remote changes in the

Acknowledgements

This work was in part supported by a grant of the Heinrich-Heine-University to G.H. and by grants from the Deutsche Forschungsgemeinschaft SFB 194/B4 (H.J.L.). The authors are most grateful to D. Steinhoff for excellent technical assistance.

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In the present study, we focused on the focal freeze-lesion model of MCD to compare antiepileptic drugs with distinct mechanisms of action, including NKCC1 inhibition by bumetanide. For this purpose, we combined electrophysiological and optical methods in slice preparations and assessed the properties of seizure like events (SLE) induced by 4-aminopyridine. In freeze-lesioned but not control slices, SLE onset was confined to the perilesional area, confirming that this region is hyperexcitable and likely triggers pathological activity. Bumetanide selectively reduced epileptic activity in lesion-containing slices but not in slices from sham-treated control rats. Moreover, bumetanide caused a shift in the SLE onset site away from the perilesional area. In contrast, effects of other antiepileptic drugs including carbamazepine, lacosamide, acezatolamide and zonisamide occurred mostly independently of the lesion and did not result in a shift of the onset region.
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Research paperDistribution of glutamate receptor subunits in experimentally induced cortical malformations

Abstract

Section snippets

Lesion induction

Dysplastic cortex

Discussion

Acknowledgements

J Biol Chem

Trends Pharmacol Sci

Curr Opin Neurobiol

Neuroscience

Epilepsy Res

I. Expression of epileptiform activity in an animal model. Epilepsy Res

Neurosci

Prog Neurobiol

Brain Res

Prog Neurobiol

Brain Res

Epilepsy Res

Trends Neurosci

Exp Neurol

Epileptiform discharges in the human dysplastic neocortexin vitro physiology and pharmacology

Ann Neurol

International Union of Pharmacology. XV. Subtypes of gamma-aminobutyric acidA receptorsclassification on the basis of subunit structure and receptor function

Pharmacol Rev

Cortical malformations and epilepsynew insights from animal models

Epilepsia

The right neuron at the wrong placebiology of heterotopic neurons in cortical neuronal migration disorders, with special reference to associated pathologies

Cell Mol Life Sci

Differential expression of glutamate and GABA-A receptor subunit mRNA in cortical dysplasia

Neurology

Animal models of cerebral strokepharmacological protection of function

Eur Neurol

The regulation of AMPA receptor-binding sites

Mol Neurobiol

Regional and ontogenic expression of the NMDA receptor subunit NR2D protein in rat brain using a subunit-specific antibody

J Neurochem

Migration of neuroblasts through partial necrosis of the cerebral cortex in newborn ratscontribution to the problems of morphological development and developmental period of cerebral microgyria: histological and autoradiographical study

Acta Neuropathol Berl

Experimentally induced focal microgyria and status verrucosus deformis in ratspathogenesis and interrelation: histological and autoradiographical study

Acta Neuropathol Berl

Mechanisms underlying neuronal migration disorders and epilepsy

Curr Opin Neurol

Cortical dysplasias, genetics, and epileptogenesis

Adv Neurol

Freezing lesions of the developing rat braina model for cerebrocortical microgyria

J Neuropathol Exp Neurol

Hyperexcitability in a model of cortical maldevelopment

Cereb Cortex

Focal epileptogenesis in a rat model of polymicrogyria

J Neurophysiol

Research paper
Distribution of glutamate receptor subunits in experimentally induced cortical malformations