Date of Award

January 2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Sciences

First Advisor

Van A. Doze

Abstract

The research herein aimed to increase our understanding about potential roles of adrenergic receptor subtypes in epileptic seizures and seizure-like (epileptiform) phenomena. Previous observations in our laboratory led us to hypothesize that the alpha1A-adrenergic receptor is a critical component of the modulatory role of the alpha1-adrenergic receptor, and more broadly, norepinephrine, on epileptiform and seizure activity. We utilized a combination of genetic and pharmacological manipulation to elucidate specific effects of the alpha1A-adrenergic receptor subtype on altering hyperactivity in models of epilepsy, both in slice and in vivo. This research sought to address three main research questions: (1) What are the specific contributions of alpha1-adrenergic receptor subtypes to alterations of epileptiform activity?; (2) Do any alpha1A-adrenergic receptor alterations to epileptiform activity translate from tissue slices to in vivo models?; (3) Can we utilize genetically modified mice to identify possible candidate cell types of alpha1A-adrenergic receptor expression? All of these questions are an attempt to circumvent historical difficulties with a lack of specificity of subtype-specific ligands and antibodies.

We found that alpha1A-adrenergic receptor activation confers an antiepileptic effect, which was consistent with expectations formulated from previous observations of indirect neural circuit modulation. Specifically, previous observations from our laboratory strongly suggest that alpha1A-adrenergic receptors confer hyperexcitation of hippocampal inhibitory interneurons. Interestingly, our approach also revealed that the alpha1A-adrenergic receptor is important for maintaining optimal brain excitability, both in vitro and in vivo. This is exemplified by our characterization of unprovoked, recurrent seizures and exacerbated epileptiform burst frequency in alpha1A-adrenergic receptor knockout mice. Meanwhile, in vitro studies suggested little role for the other centrally expressed alpha1-adrenergic receptor, the alpha1B-adrenergic receptor, within our model systems. Our investigation of alpha1A-adrenergic receptor expression used fluorescence microscopy and genetically-induced receptor reporter expression to better understand the observed phenomena. We show evidence for occasional alpha1A-adrenergic receptor reporter co-localization on parvalbumin-expressing puncta and, more broadly, reporter localization consistent with inhibitory interneuron expression, within the mouse hippocampus.

Collectively, these findings suggest that the alpha1A-adrenergic receptor contributes to demonstrated antiepileptic effects of the adrenergic system and that loss of this receptor subtype is demonstrably unfavorable to the maintenance of normal brain excitability and to the resistance of epileptiform activity. Additionally, our findings demonstrate the value of genetically modified animal models when chemical characterization is infeasible. These findings suggest that the alpha1A-adrenergic receptor may represent a promising and unexplored therapeutic target and/or biomarker for epilepsy. Importantly, the proposed therapeutic pathway for alpha1A-adrenergic receptor modulation is novel and may be used more broadly to evaluate the potential of interneuron-modulation in epilepsy. Even today, one-third of all people with epilepsy have no effective therapeutic option.

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