Document Type

Dissertation

Date of Degree

2015

Degree Name

PhD (Doctor of Philosophy)

Degree In

Genetics

First Advisor

Toshihiro Kitamoto

Abstract

Substance abuse and mental health disorders are a leading source of years lost to disability from medical causes worldwide. Unfortunately, for most neurological disorders it is unclear how underlying genetic predispositions govern behavioral response to environmental stressors. Owing to their convenience, genetic tractability, and small brains, the fruit fly, Drosophila melanogaster, has become an invaluable model in which to dissect the neurological basis of conserved complex behaviors. Here, I characterized the respective roles of two genes in alcohol response and sleep behavior.

Steroid hormones profoundly influence behavioral response to alcohol, yet the role of unconventional non-genomic steroid signaling in this process is unknown. I discovered that Drosophila DopEcR, a G-protein coupled receptor (GPCR) activated by dopamine or the major insect steroid hormone ecdysone, plays a critical role in ethanol-induced behaviors. DopEcR mutants took longer to sedate when exposed to ethanol vapor, and post-eclosion expression of DopEcR-RNAi phenocopied mutant resistance. DopEcR was necessary in particular neuronal subsets, including cholinergic and peptidergic neurons, and promoted ethanol sedation by suppressing epidermal growth factor/extracellular signal-regulated kinase signaling. In adult flies, ecdysone negatively regulated DopEcR-mediated ethanol-induced sedation. We also found that DopEcR inhibits ethanol-induced locomotion, a conserved dopaminergic behavior. Together, these findings provide novel insight into how an unconventional steroid GPCR interacts with multiple downstream signaling cascades to fine tune behavioral response to alcohol.

Despite an established link between epilepsy and sleep behavior, it remains unclear how epileptogenic mutations affect sleep and seizure susceptibility. To address this, I examined the rest/wake behavior of two fly models of epilepsy with paralytic voltage-gated sodium channel mutations known to cause human generalized epilepsy with febrile seizures plus (GEFS+) and Dravet syndrome (DS). GEFS+ and DS flies display heat-induced seizure susceptibility, but at normal temperatures I found that both mutants had exaggerated nighttime sleep behavior. GEFS+ sleep was more resistant to pharmacologic and genetic reduction of GABA transmission as compared to control’s response. This finding is consistent with augmented GABAergic suppression of wake-promoting pigment-dispersing factor (PDF) neurons in GEFS+ mutants. Contrastingly, DS sleep was almost completely resistant to pharmacologic GABA reduction, suggesting that PDF neurons are incapable of functioning despite disinhibition. The sleep of both GEFS+ and DS flies was largely suppressed, but not eliminated, by scotophase light, highlighting the importance of light stimulus and circadian signals in the manifestation of their phenotypes. Following sleep deprivation, GEFS+ and DS mutants failed show to homeostatic rebound. Sleep loss also unexpectedly reduced the seizure susceptibility of GEFS+ flies. This study revealed the sleep architecture of Drosophila voltage-gated sodium channel mutants and provides a unique platform in which to further study the sleep/epilepsy relationship.

Public Abstract

Genetic mutations are linked to nearly every human disease, including major health problems like alcoholism and epilepsy. But how can changes in our genes and environment affect these brain disorders? Fruit flies are an ideal genetic model in which to answer this question. They have simpler brains than humans, but still show complex behaviors. In this thesis, I used flies to study how specific genes influenced either drunk- or seizure-like behavior. It is still unclear which genes make people more likely to become alcoholics. I discovered that mutations in the DopEcR gene cause flies to become resistant to alcohol. Because this gene makes a unique type of protein in the brain, I looked at where, when, and how DopEcR works. My results suggest that similar human proteins are likely important in alcohol use disorders (AUDs). Next, I examined flies with human SCN1A gene mutations that cause epilepsy. Millions of people suffer from epilepsy, but why their seizures get worse without proper sleep is unknown. I found that epileptic flies not only had seizures, but also had many sleep problems. Also, after sleep loss, mutant flies were unable to recover their sleep and showed changes in seizure responses. These findings help us better understand how mutations that cause epilepsy affect the activity of brain cells in seizures and sleep. Altogether, my work highlights the value of fruit flies in scientific research and adds to our knowledge of how genes affect AUDs and epilepsy.

Keywords

publicabstract, alcohol, Drosophila, epilepsy, GPCR, sleep, steroid

Pages

xi, 73 pages

Bibliography

Includes bibliographical references (pages 66-73).

Comments

This thesis has been optimized for improved web viewing. If you require the original version, contact the University Archives at the University of Iowa: http://www.lib.uiowa.edu/sc/contact/

Copyright

Copyright 2015 Emily Kay Petruccelli

Included in

Genetics Commons

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