Epilepsy is a major health care problem afflicting 4% of Americans. Partial epilepsy is refractory to currently available medical therapy in 30% of the patients. Kindling is a useful animal model of partial epilepsy. Epileptogenesis in kindling may result from loss of GABA- mediated inhibition in the hippocampus. GABA-mediated inhibition is diminished in the CA1 region of hippocampus but transiently enhanced in dentate gyrus of the hipppocampus due to kindling. Recent advances in understanding the structure and function of GABA (A) receptor (GABAR) may explain these findings. GABAR is a pentameric protein formed from 14 different subunits of 5 classes: alpha, beta, gamma and rho. There are 6 alpha, 3 beta and 3 gamma subunits described. GABAR protein delta subunit mRNA is expressed in dentate gyrus but not in the CA1 region and GABAR protein alpha5 subunit mRNA is expressed in CA1 region but not in dentate gyrus. The hypotheses to be tested are: 1) the native GABARs in dentate gyrus have distinct physiologic and pharmacologic properties, and structural composition from those in the CA1 region; 2) the BABARs in CA1 pyramidal neurons and dentate granule cells respond differently to kindling stimulus. Whole-cell BABA (A) currents and single-channel GABAR activity from native GABARs from CA1 pyramidal neurons and dentate granule cells and from recombinant GABARs expressed in mammalian L929 cells will be recorded to fulfill the specific aims of this proposal: 1) Is there differential sensitivity of native BABAR in CA1 pyramidal neurons and dentate granule cells to various benzodiazepines? 2) Do deactivation and desensitization properties of whole cell GABA (A) current in CA1 pyramidal neurons and dentate granule cells suggest differential localization of delta subunit? 3) Are the single-channel properties different for GABARs in CA1 pyramidal neurons and dentate granule cells? 4) Can GABARs of known subunit composition be expressed in a heterologous system to replicate the pharmacologic properties and single channel kinetic properties of GABARs in CA1 pyramidal neurons and dentate gyrus? 5) Does kindling differentially alter the properties of whole cell and single channel GABA (A) currents in CA1 pyramidal neurons and dentate granule cells? The proposed experiments will provide a description of heterogeneity of GABA (A) receptors in the central nervous system and may suggest a potential for development of more specific drugs acting on the receptors.
