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Mechanisms of Seizure During Pregnancy and Preeclampsia Abbie Chapman Johnson University of Vermont

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Mechanisms of Seizure During Pregnancy and Preeclampsia Abbie Chapman Johnson University of Vermont University of Vermont ScholarWorks @ UVM Graduate College Dissertations and Theses Dissertations and Theses 2015 Mechanisms of Seizure during Pregnancy and Preeclampsia Abbie Chapman Johnson University of Vermont Follow this and additional works at: https://scholarworks.uvm.edu/graddis Part of the Neurosciences Commons Recommended Citation Johnson, Abbie Chapman, "Mechanisms of Seizure during Pregnancy and Preeclampsia" (2015). Graduate College Dissertations and Theses. 336. https://scholarworks.uvm.edu/graddis/336 This Dissertation is brought to you for free and open access by the Dissertations and Theses at ScholarWorks @ UVM. It has been accepted for inclusion in Graduate College Dissertations and Theses by an authorized administrator of ScholarWorks @ UVM. For more information, please contact [email protected]. MECHANISMS OF SEIZURE DURING PREGNANCY AND PREECLAMPSIA A Dissertation Presented by Abbie Chapman Johnson to The Faculty of the Graduate College of The University of Vermont In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Specializing in Neuroscience May, 2015 Defense Date: February 23, 2015 Dissertation Examination Committee: Marilyn J. Cipolla, Ph.D., Advisor George C. Wellman, Ph.D., Chairperson Margaret A. Vizzard, Ph.D. Marjorie C. Meyer, M.D. Cynthia J. Forehand, Ph.D., Dean of the Graduate College ABSTRACT Eclampsia is defined as de novo seizure in a woman with the hypertensive complication of pregnancy known as preeclampsia (PE), and is a leading cause of maternal and fetal morbidity and mortality worldwide. The pathogenesis of eclamptic seizure remains unknown, but is considered a form of hypertensive encephalopathy where an acute rise in blood pressure causes loss of cerebral blood flow (CBF) autoregulation and hyperperfusion of the brain that results in vasogenic edema formation and subsequent seizure. However, eclamptic seizure can occur during seemingly uncomplicated pregnancies, in the absence of hypertension and PE, suggesting that normal pregnancy may predispose the brain to hypertensive encephalopathy or seizure, independently of PE. The overall goal of this dissertation was to investigate the effect of pregnancy and PE on the cerebrovasculature and neurophysiological properties that may promote brain injury and eclamptic seizure. For this dissertation project, a rat model of PE was established that combined placental ischemia, induced by restricting blood flow to the uteroplacental unit, and maternal endothelial dysfunction that was induced by a prolonged high cholesterol diet. Rats with PE developed several PE-like symptoms, including elevated blood pressure, fetal growth restriction, placental dysfunction, and were in a state of oxidative stress and endothelial dysfunction. We found that pregnancy had an overall protective effect on the maintenance of CBF that was potentially due to a nitric-oxide dependent enhancement of the vasodilation of cerebral arteries to decreased intravascular pressure. Further, maintenance of CBF during acute hypertension was similar in pregnancy and PE. Thus, it does not appear that pregnancy and PE are states during which CBF autoregulation is compromised in a manner that would promote the development of hypertensive encephalopathy. However, the brain was found to be in a hyperexcitable state during normal pregnancy that was augmented in PE, and could contribute to onset of eclamptic seizure. Under chloral hydrate anesthesia, generalized seizure was induced by timed infusion of the convulsant pentylenetetrazole (PTZ), with simultaneous electroencephalography that was stopped at the first onset of spikewave discharge indicative of electrical seizure. Seizure threshold was determined as the amount of PTZ required to elicit seizure. Compared to the nonpregnant state, seizure threshold was ~44% lower in pregnant rats and ~80% lower in rats with PE. Further, pregnant rats were more susceptible to seizure-induced vasogenic edema formation than the nonpregnant state. Mechanisms by which pregnancy and PE lowered seizure threshold appeared to be through pregnancy-associated decreases in cortical γ-aminobutyric acid type A receptor (GABAAR) subunits and PE-induced disruption of the blood-brain barrier (BBB) and microglial activation, indicative of neuroinflammation. Magnesium sulfate (MgSO4), the leading treatment for seizure prophylaxis in women with PE, restored seizure threshold to control levels by reversing neuroinflammation in PE rats, without affecting BBB permeability. Overall, this dissertation provides evidence that pregnancy increases susceptibility of the brain to seizure and vasogenic edema formation that likely contribute to the onset of eclampsia during seemingly uncomplicated pregnancies. Further, the pathogenesis of eclampsia during PE likely involves breakdown of the BBB and subsequent neuroinflammation, resulting in a state of greater seizure susceptibility that is ameliorated by MgSO4 treatment. CITATIONS Material from this dissertation has been published in the following form: Chapman, A.C., Cipolla, M.J., and Chan, S.L.. (2013) Effect of pregnancy and nitric oxide on the myogenic vasodilation of posterior cerebral arteries and the lower limit of cerebral blood flow autoregulation. Repro Sci, 20(9): 1046-54. Johnson, A.C., Tremble, S.M., Chan, S.L., Moseley, J., LaMarca, B., Nagle, K.J., and Cipolla, M.J.. (2014) Magnesium sulfate treatment reverses seizure susceptibility and decreases neuroinflammation in a rat model of severe preeclampsia. PLoS One, Nov 19;9(11):e113670. doi: 10.1371/journal.pone.0113670. eCollection 2014. Material from this dissertation has been submitted for publication to PLoS One on January 26, 2015 in the following form: Johnson, A.C., Nagle, K.J., Tremble, S.M., and Cipolla, M.J.. (2015) The contribution of normal pregnancy to eclampsia. ii ACKNOWLEDGEMENTS First and foremost, I need to thank my mentor, Dr. Marilyn J. Cipolla for being, in a word, tremendous. You have provided me for the better part of a decade (really? that long?) with continuous guidance, advisement, and patience. You have taught me many things, too many to list, but most importantly to be fearless, to face things head on, and never go backwards, professionally or personally. Your high expectations of me at times felt impossible to meet, and even more impossible to maintain, yet your confidence in me that often far surpassed my own helped me get there. I will keep my eye on the forest through the trees. Thank you. I also thank my wonderful lab family for being constant and understanding, and for all of your technical and emotional support over the years. In particular, Julie Sweet and Kelvin Chan: “We shall not separate!” To my goofy, full-hearted husband, Travis Johnson: You, I do not know how to thank. It’s too much. Embarking on this seemingly endless long distance lifestyle has often felt like a cruel joke, yet both of our careers have benefited from it. Without your unyielding love and support I do not know where we would be, but I doubt it would be here. You have been there to celebrate the best times, albeit sometimes from 3000+ miles away, and more importantly, you have applied coat after coat of glue, sticking me back together during the worst. You haven’t let me lose those silly, carefree parts of myself that you fell in love with, even though at times over the past 5 years there has been no room for them. You are my night sky. For that I will always be thankful, and I cherish you very much. I would like to thank my parents who, in each of their own way, have contributed an enormous amount to my motivation, determination and stubbornness. From a young age you gave me perspective, and taught me the crucial value of perseverance. I sometimes forget that I don’t just get my hard-headed qualities from you, but I get many of my best qualities from you as well (like my laugh-so-hard-my-body-doesn’t-know-if- it’s-still-laughing-or-now-crying cackle that is indistinguishable from yours, Mom). Dad, I thank you for being relentless, in all meanings of the word. Mom, I thank you for being a bottomless well of love and kindness. To my co-inhabitants of Ph.D. Land: What a strange and unique existence. These friendships have been odd, and some have shifted like the tide. Cheers to the shared successes, years of misery, hours of early morning coffee rants and pity parties, and to learning to celebrate the most minute of successes and to capitalize on those times to let loose or lose your mind. Thank you Matt LeComte, Liana Merrill, Eric Gonzalez, Stephanie Spohn, Dave Harris, and Anthony Pappas, for we are, or have been, fortunate to have one another as leaning posts. To all of my other friends and family, particularly from Down East, thank you for giving quieter strength and encouragement from the sidelines. iii TABLE OF CONTENTS CITATIONS ....................................................................................................................... ii ACKNOWLEDGEMENTS ............................................................................................... iii LIST OF TABLES ............................................................................................................ vii LIST OF FIGURES ......................................................................................................... viii CHAPTER 1: COMPREHENSIVE LITERATURE REVIEW ......................................... 1 1.1 Preeclampsia and Eclampsia ....................................................................................
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