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dc.contributor.advisorReddy, Doodipala Samba
dc.creatorChuang, Shu-Hui
dc.date.accessioned2019-10-15T15:34:06Z
dc.date.created2019-05
dc.date.issued2019-03-27
dc.date.submittedMay 2019
dc.identifier.urihttp://hdl.handle.net/1969.1/183836
dc.description.abstractEpilepsy is a chronic neurological disorder characterized by unpredicted recurrent seizures. Dysfunction of GABA-A receptors (GABA-ARs) in the brain plays a key role in the pathophysiology of epilepsy. Neurosteroids are powerful allosteric agonists of GABA-ARs and are more efficacious on extrasynaptic  subunit-containing GABA-ARs that mediate tonic inhibition. Endogenous neurosteroids such as allopregnanolone (AP) have broad-spectrum anticonvulsant activity and possess therapeutic potential for epilepsy. There are many synthetic neurosteroids in trials. Ganaxolone (GX) is the 3-methylated synthetic analog of AP. Although GX was previously tested in recombinant GABA-ARs, its precise mechanisms of action on native neurons in the brain, including its ability to modulate extrasynaptic GABA-ARs, and its interactions with other molecules, remain unknown. The main objective of this dissertation is to investigate the molecular, cell-specific, and phosphorylation-dependent mechanisms of action of synthetic neurosteroid GX and related neurosteroid agents at extrasynaptic GABA-ARs using pharmacological, electrophysiological, and behavioral approaches. In addition, structure-activity relationships of analogs are tested in native neurons. Several GABA-AR subunits contain phosphorylation sites regulated by protein kinases. Therefore, this study examines the influences of protein kinase activity on neurosteroid actions in native neurons. In addition, we explore the physiological interactions between neurosteroids and zinc and the potential combination strategy of neurosteroids with other clinical GABAergic agents. We established concentration-response profiles of GX in two cell types: (i) -abundant dentate gyrus granule cells (DGGCs) and (ii) -rich CA1 pyramidal cells (CA1PCs). Our results show that GX and analogs are preferential allosteric modulators and direct activators of extrasynaptic GABA-ARs regulating network inhibition and seizures in the dentate gyrus. The potentiation of tonic inhibition by GX is subunit-dependent and protein kinase C activity-mediated. Zinc concentration-dependently blocks GX- potentiated GABA-gated currents in DGGCs and CA1PCs. Zinc reduces antiseizure activity of GX by the selective blockade of extrasynaptic GABA-AR-mediated tonic inhibition in the hippocampus. Combination therapies of neurosteroids with clinically used antiepileptic drugs tiagabine and midazolam exhibit strong synergistic effects on antiseizure activity and hippocampal tonic inhibition. Overall, these findings signify a unique role for extrasynaptic δGABA-ARs as key modulators of excitability in the brain and provide valuable mechanistic rationales for the clinical synergistic potential of neurosteroids in epilepsy and seizure disorders.en
dc.format.mimetypeapplication/pdf
dc.language.isoen
dc.subjectNeurosteroidsen
dc.subjectGanaxoloneen
dc.subjectGABA-A receptorsen
dc.subjectTonic inhibitionen
dc.subjectHippocampusen
dc.subjectDentate gyrus granule cellsen
dc.subjectSeizuresen
dc.subjectEpilepsyen
dc.subjectZincen
dc.subjectIsobolographic analysisen
dc.subjectTiagabineen
dc.subjectMidazolamen
dc.titleCell-Specific and Phosphorylation-Dependent Actions of Neurosteroids at Extrasynaptic GABA-A Receptors in the Brainen
dc.typeThesisen
thesis.degree.departmentCollege of Medicineen
thesis.degree.disciplineMedical Sciencesen
thesis.degree.grantorTexas A & M Universityen
thesis.degree.nameDoctor of Philosophyen
thesis.degree.levelDoctoralen
dc.contributor.committeeMemberWinzer-Serhan, Ursula H.
dc.contributor.committeeMemberLi, Peng
dc.contributor.committeeMemberWang, Jun
dc.type.materialtexten
dc.date.updated2019-10-15T15:34:07Z
local.embargo.terms2021-05-01
local.embargo.lift2021-05-01
local.etdauthor.orcid0000-0002-7704-914X


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