Abstracts

Rationale: Expression of the protein subunits that make up the GABA-A receptor pentamer is known to change during brain development. In animal models of epilepsy, both ongoing seizures and antiepileptic medications have been found to alter GABA-A subunit expression and receptor pharmacology. In the present study, analysis of cortical GABA-A subunit expression and function was performed in control human tissue obtained from infancy through adolescence, and was compared to that from similarly aged children with intractable epilepsy. Methods: Frozen control neocortical specimens were obtained from the NICHD Brain and Tissue Bank for Developmental Disorders at the University of Maryland. Fresh cortical tissue from children undergoing surgery for intractable epilepsy was frozen in liquid nitrogen and stored at -80° C. The membrane fraction of the frozen tissue was isolated and subjected to Western blot analysis using standard techniques and commercially available antibodies. An additional membrane fraction was injected into Xenopus oocytes, resulting in incorporation of the brain membrane vesicles with their associated receptors into the oocyte cellular membrane. Two-electrode voltage clamp analysis of GABA-A receptor currents was performed 18-72 hours after injection. Results: In control cortical samples, α1 and γ2 GABA-A receptor subunits exhibited low expression in infancy which increased into adolescence. In contrast, α4 subunit expression was higher in infants than in older children. Expression of the α5 and δ subunits was relatively stable throughout development. Levels of the K+/Cl- cotransporter KCC2 increased markedly with age. These patterns were all absent in the age-matched epileptic children, both in those with pathologies of focal cortical dysplasia and in those with gliosis. Subunit expression in the epileptic samples was not related to the extent of astrocytosis as assessed by GFAP expression. Functional studies of GABA-A receptor pharmacology from the control and epileptic specimens were correlated with receptor subunit expression. Conclusions: Intractable epilepsy in children is associated with disruption of the normal developmental pattern of cortical GABA-A receptor maturation.