All ETDs from UAB

Advisory Committee Chair

David G Standaert

Advisory Committee Members

Lori L McMahon

Robin Lester

Qin Wang

Talene Yacoubian

Document Type

Dissertation

Date of Award

2017

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

DYT1 dystonia is a neurological movement disorder characterized by sustained muscle contractions causing twisting and repetitive movements or abnormal posture. While many movement disorders are due to loss of neurons, DYT1 dystonia does not present with any gross abnormalities. As of now, the most common form of treatment is anticholinergics. Since anticholinergic are the most effective pharmacotherapy and “paradoxical excitation” has been shown in when quinpirole, D2R agonist, is bath applied on cholinergic interneurons, we began by examining acetylcholine efflux in a DYT1 knock-in mouse model. Our studies provide evidence that at basal levels, there is a hypercholinergic state present in the DYT1 knock-in mouse, but we fail to reproduce the “paradoxical excitation” in vivo. Through electrophysiology, we first identified that the “paradoxical excitation” present in the DYT1 knock-in mouse can be recapitulated in wild-type mice by increasing cholinergic tone through muscarinic receptors. The hypercholinergic state is responsible for a switch in D2R signaling from the preferred canonical pathway to the non-canonical, β-arrestin pathway. While nicotine has been studied in many neurological diseases, it has yet to be explored in dystonia. To study this, we infused nicotine directly into the striatum on DYT1 knock-in and wild-type mice. We found that striatal dopamine efflux is significantly greater in DYT1 knock-in mice compared to wild-type mice. While the DYT1 knock-in mice sustained their increased dopamine efflux the entire 60 minutes, wild-type littermates did not. The mechanism of this enhanced sensitivity may be related to the hypercholinergic state and upregulation of the α4β2-containing nicotinic receptor that is highly sensitive to cholinergic stimulation. While the previous studies were targeting receptors through pharmacology, our final experiment asked the question if direct inhibition of cholinergic interneurons could normalize striatal function. To get at this answer, designer receptors exclusively activated by designer drug (DREADDs) were injected into the striatum of ChAT-Cre or ChAT-Cre/DYT1 knock-in mice where they recombined and were expressed in cholinergic interneurons. When the mice were injected with clozapine-N-oxide to induce inactivation of DREADDs, mice with active DREADDs showed a 50% reduction in acetylcholine output from baseline levels. These findings provide important neurochemical insights into DYT1 dystonia and provide potential novel treatment strategies.

Share

COinS