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Brain Advance Access published online on October 17, 2006

Brain, doi:10.1093/brain/awl287
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© The Author (2006). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received May 30, 2006
Revised September 10, 2006
Accepted September 11, 2006

Article

Altered expression of {alpha}3-containing GABAA receptors in the neocortex of patients with focal epilepsy

Fabienne Loup 1 *, Fabienne Picard 2, Véronique M. André 3, Pierre Kehrli 4, Yasuhiro Yonekawa 5, Heinz-Gregor Wieser 6, and Jean-Marc Fritschy 7

1 Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland; Present address: Swiss Epilepsy Center, Zurich, Switzerland
2 Department of Neurology, University Hospital and Medical School of Geneva, Geneva, Switzerland
3 INSERM Faculty of Medicine, Hôpitaux Universitaires de Strasbourg, Strasbourg, France; Present address: The Mental Retardation Research Center, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
4 Service de Neurochirurgie, Hôpitaux Universitaires de Strasbourg, Strasbourg, France
5 Department of Neurosurgery, University Hospital Zurich, Zurich, Switzerland
6 Department of Neurology, University Hospital Zurich, Zurich, Switzerland
7 Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland

* To whom correspondence should be addressed.
Fabienne Loup, E-mail: loupf{at}pharma.unizh.ch


   Abstract

Impaired transmission in GABAergic circuits is thought to contribute to the pathogenesis of epilepsy. Although it is well established that major reorganization of GABAA receptor subtypes occurs in the hippocampus of patients with medically refractory temporal lobe epilepsy (TLE), it is unclear whether this disorder is also associated with alterations in GABAA receptor subtypes in the neocortex. Here we have investigated immunohistochemically the subunit composition and neocortical distribution of three major GABAA receptor subtypes using antibodies specifically recognizing the subunits {alpha}1, {alpha}2, {alpha}3, {beta}2/3 and {gamma}2. Cortical tissue was obtained at surgery from patients with TLE and hippocampal sclerosis (HS; n = 9), TLE associated with neocortical lesions (non-HS; n = 12) and frontal lobe epilepsy (FLE; n = 5), with post-mortem samples serving as controls (n = 4). A distinct laminar and neuronal expression pattern of the {alpha}-subunit variants was found across the neocortical regions examined in the temporal and frontal lobes in both control and patient tissue samples. In the five patients with FLE, GABAA receptor subunit staining was unchanged as compared to controls. In patients with TLE we observed a marked decrease in {alpha}3-subunit staining in the superficial neocortical layers (I-III), but no change in the deep layers (V and VI) or in the expression pattern of the {alpha}1 and {alpha}2-subunits. Reduced expression in {alpha}3-containing GABAA receptors was detected in six out of nine patients of the HS group and four out of twelve patients of the non-HS group. Histopathological changes were present in eight out of the ten patients with decreased {alpha}3-subunit staining. The selective reduction in {alpha}3-containing GABAA receptors was confirmed using semiquantitative measurements of optical density (OD). The specific changes unique to {alpha}3-subunit expression in the superficial neocortical layers of patients with TLE suggest that this subtype is of particular significance in the reorganization of cortical GABAergic systems in focal epilepsy.

Keywords: cerebral cortex; GABA; human; seizures; temporal lobe epilepsy.
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