Tonic inhibition is a major form of inhibition in the central nervous system (CNS) and could play a key role in epileptogenesis and seizure generation. Nonsynaptic GABAA receptor (GABAAR) subunits that mediate tonic inhibition, including the ? subunit, are frequently altered in animal models of lesion-induced epilepsy. However, it remains unclear whether several of these changes contribute to or limit seizure activity. It becomes particularly important to understand the functional effects of these changes as new pharmacological agents that can modify the function of ? subunit-containing receptors are developed. A set of new technologies, reagents and mice will be used to study the functional effects of altering GABAAR subunit expression in granule cells of the dentate gyrus which are considered to be major players in seizure generation or propagation within the hippocampal network. The proposed studies will use Cre recombinase-dependent viral vectors to express GABAAR ? subunit selectively in granule cells and determine the effects of this alteration on epileptiform activity within the network in a mouse model of epilepsy. A combination of light and electron microscopic immunohistochemical methods will be used to evaluate changes in GABAAR subunit expression, and the functional correlates will be studied with electrophysiological methods, behavioral memory tasks, and Fos expression as a marker of neuronal activity in vivo. The broad goal of the project is to determine if increasing nonsynaptic GABAAR subunits in a cell-type selective manner will influence tonic inhibition and epileptiform activity in a mouse model of epilepsy.
Specific Aim 1 will test the hypothesis that transfection of the ? subunit in dentate granule cells will rescue the decreased expression of this subunit that frequently occurs in mouse models of epilepsy and, in the process, normalize expression of two related subunits, ?4 and ?2, that are also altered in mouse models of epilepsy.
Specific Aim 2 will test the hypothesis that an increase in ? subunit expression will enhance GABAAR-mediated tonic inhibition in dentate granule cells and reduce heightened responses of these neurons to perforant path stimulation in seizure-prone mice.
Specific Aim 3 will test the hypothesis that increasing ? subunit expression in dentate granule cells will reduce network hyperexcitability and propagation of epileptiform activity in an animal model of epilepsy, using a novel hippocampal-entorhinal cortex slice preparation.
Specific Aim 4 will test the hypothesis that enhancing ? subunit expression in dentate granule cells will lead to improved performance on a working memory task in which pilocarpine-treated mice are normally deficient. The effects of increased ? subunit expression on granule cell activity in vivo during an elicited seizure will also be determined. Together these studies will increase our understanding of the effects of altering ? subunit-mediated tonic inhibition selectively in dentate granule cells on hippocampal network function in an animal model of epilepsy. The results could suggest GABAAR subtype and neuron-specific targets for reducing seizure activity and associated cognitive deficits.
This proposal is relevant to public health because it will provide new information about the role of GABA receptors in controlling seizure activity. Altered inhibitory control of neurons in the brain is likely to contribute to many forms of epilepsy. These studies will evaluate the effects of increasing inhibition in a major group of neurons in the hippocampus, the dentate granule cells, with the goal of finding new ways to control their activity and thus prevent seizures.
|Zhang, Nianhui; Peng, Zechun; Tong, Xiaoping et al. (2017) Decreased surface expression of the ? subunit of the GABAA receptor contributes to reduced tonic inhibition in dentate granule cells in a mouse model of fragile X syndrome. Exp Neurol 297:168-178|
|Tong, Xiaoping; Peng, Zechun; Zhang, Nianhui et al. (2015) Ectopic Expression of ?6 and ? GABAA Receptor Subunits in Hilar Somatostatin Neurons Increases Tonic Inhibition and Alters Network Activity in the Dentate Gyrus. J Neurosci 35:16142-58|
|Peng, Zechun; Zhang, Nianhui; Chandra, Dave et al. (2014) Altered localization of the ? subunit of the GABAA receptor in the thalamus of ?4 subunit knockout mice. Neurochem Res 39:1104-17|
|Houser, Carolyn R (2014) Do structural changes in GABA neurons give rise to the epileptic state? Adv Exp Med Biol 813:151-60|
|Peng, Zechun; Zhang, Nianhui; Wei, Weizheng et al. (2013) A reorganized GABAergic circuit in a model of epilepsy: evidence from optogenetic labeling and stimulation of somatostatin interneurons. J Neurosci 33:14392-405|
|Mathews, Paul J; Lee, Ka Hung; Peng, Zechun et al. (2012) Effects of climbing fiber driven inhibition on Purkinje neuron spiking. J Neurosci 32:17988-97|
|Houser, Carolyn R; Zhang, Nianhui; Peng, Zechun et al. (2012) Neuroanatomical clues to altered neuronal activity in epilepsy: from ultrastructure to signaling pathways of dentate granule cells. Epilepsia 53 Suppl 1:67-77|