Early-Life Seizures and Development of GABAergic Inhibition in the Human Brain

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DESCRIPTION (provided by applicant): Seizures in infants and neonates are common, are often resistant to currently used treatments, and can have devastating outcomes. The most frequently used anticonvulsant medications in this age group, the barbiturates and the benzodiazepines, act by enhancement of current through neuronal GABAA receptors. The focus of the current study is to characterize the development of human cortical GABAergic inhibition from late gestation through early childhood, and further to assess how this development is disrupted by conditions causing seizures in this age group. The underlying hypothesis of this proposal is that immature patterns of GABAA receptor subunit and cation-chloride cotransporter expression in human cortex result in pharmacologic properties predictive of low efficacy or even harmful consequences of the use of GABAergic agents in the treatment of premature infants, neonates, and young children. The Specific Aims of this proposal include: 1) Define the time course of the developmental maturation of human cortical GABAA receptor subunit and cation-chloride cotransporter expression, and assess abnormalities in expression related to early-life seizures due to malformations of cortical development. This aim will be achieved through the use of quantitative Western blot analysis with infrared fluorescence detection. Frozen postmortem and surgical cortical specimens will be collected from control infants at 20 weeks gestation through 3 years of age, as well as similarly-aged infants with seizures due to glioneuronal malformations of cortical development or migrational disorders. In addition, a clinical database will be constructed and correlated with our experimental data to assess whether variables that have been shown to modulate receptor or transporter expression in experimental epilepsy models might also play a significant role in our human epilepsy population. 2) Determine the functional and pharmacological consequences of developmental and seizure-associated changes in GABAA receptor subunit and cation-chloride cotransporter expression in human cortex. An innovative experimental paradigm will be utilized which allows electrophysiological analysis of GABAA receptors from frozen human brain tissue resulting in "microtransplantation" of native human receptors into the Xenopus oocyte plasma membrane. 3) Analyze alterations in the cellular distribution of GABAA receptor subunits and chloride transporters in human cortex related to early-life seizures. Funding from this Career Development Award will permit the PI to acquire expertise in the techniques of fluorescence immunohistochemistry and in situ hybridization to determine the cortical cell populations exhibiting changes in GABAergic properties during both normal human development and its disruption by seizures due to cortical malformations. Information gained as a result of this study could have direct clinical applications that produce improved medical and neurologic care of infants and neonates.