The Role of Epsilon Subunit in GABA Receptor Function

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DESCRIPTION (provided by applicant): The GABAA receptor provides the major inhibitory drive to neurons in the mammalian central nervous system. Mutations in GABAA subunit genes that reduce the function or expression of these receptors can cause epilepsy. On the other hand anticonvulsant benzodiazepines and anesthetics that increase GABAA receptor activity are anticonvulsant. Seizures alter the expression of several GABAA receptor subunits including the e subunit. Recombinant GABAA receptors containing the e subunit are relatively insensitive to anesthetics and benzodiazepines. Functionally the e subunit mimics the actions of anesthetics on GABAA receptors causing spontaneous gating, increased GABA affinity and prolonged deactivation. Our preliminary data suggest that e subunits participate in spontaneous (tonic) GABAA receptor activity in hippocampal neurons, which is seen in the absence of exogenous GABA. Quantitative PCR, immunocytochemistry with an E subunit specific antibody, and pharmacological studies suggest that hippocampal pyramidal neurons express native GABAA receptors containing e subunits. Furthermore, up regulation of e subunit expression in hippocampal pyramidal neurons following epileptiform electrical activity (EEA) may contribute to GABAA receptor remodeling. The specific aims of the proposal are to: 1) Examine the functional contribution of the e subunit to synaptic (phasic) and extrasynaptic (tonic) receptors in hippocampal pyramidal neurons, 2) Examine the functional properties of phasic and tonic GABAA receptors following EEA or introduction of the epilepsy mutant y2(R43Q) subunit, 3) Use chimeric e/y2 constructs to determine the & subunit's structure/function relationship. We will test the hypothesis that the e subunit confers anesthetic resistance to extrasynaptic GABAA receptors and alters receptor gating and kinetics by inducing an anesthetic-bound receptor conformation. These experiments will help uncover important structural determinants of GABAA receptor function. A better understanding of GABAA receptors and their potential for adaptation will help increase our understanding of changes in neuronal inhibition during epilepsy.