• Abstract and Figures
• Public Full-text

USING CHEMOGENETICS AND NOVEL TOOLS TO UNCOVER NEURAL CIRCUIT AND BEHAVIORAL CHANGES AFTER SPINAL CORD INJURY A Dissertation Submitted to the Temple University Graduate Board In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY OF BIOENGINEERING by Jaclyn T. Eisdorfer May 2021 Examining Committee Members: Dr. Andrew Spence, Advisory Chair, Temple University, Dept. of Bioengineering Dr. Michel A. Lemay, Temple University, Dept. of Bioengineering Dr. George M. Smith, Temple University, Dept. of Neuroscience Dr. Tonia Hsieh, Temple University, Dept. of Biology © Copyright 2021 By Jaclyn T. Eisdorfer All Rights Reserved ii ABSTRACT Spinal cord injury (SCI) results in persistent neurological deficits and significant long-term disability. Stimulation of peripheral afferents by epidural electrical stimulation (EES) has been reported to reduce spasticity by reorganizing spared and disrupted descending pathways and local circuits. However, a current barrier to the field is that the plasticity mechanisms that underly improved recovery is unknown. Using the power of hM3Dq Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), we aim to accelerate the dissection of the mechanisms underlying enhanced recovery. In these studies, we identified the effect of clozapine-N-oxide (CNO) on the H-reflex of naïve animals; investigated the baseline influence of hM3Dq DREADDs in peripheral afferents in the intact animal using a novel behavioral tool, an addition of angled rungs to the horizontal ladder walking task; and began to uncover the neural and behavioral changes that accompany hM3Dq DREADDs activation in peripheral afferents after SCI. We observed no significant differences in the H-reflex with 4 mg/kg dosage of CNO administration (pre-CNO vs. CNO-active: p=0.82; CNO-active vs. CNO wash-out: p=0.98; n=6). On our novel ladder, we found significant differences in correct hind paw placement (p=0.0002, n=7) and incorrect placement (p=0.01) when DREADDs were activated with CNO (4 mg/kg). In our SCI study, we report that acute and chronic DREADDs activation may activate extensor muscles about the hip (32 cm/s: p=0.047; controls: n=6; DREADDs: n=8 and hereafter unless otherwise stated) as well as induce sprouting and synaptogenesis within motor pools and Clarke’s column in the lumbar spinal cord (motor pool: p=0.00053; iii Clarke’s column: p=0.021; controls: n=4; DREADDs: n=6). This muscle recruitment may have long-term effects such as increased hindquarter heights (e.g., 16 cm/s: p=0.017) and more frequent hindlimb coordination (p=0.002). Results from this study suggest hM3Dq DREADDs may have the potential to recapitulate EES-activation of afferents as well as provide a platform with which to functionally map changes that occur both within targeted afferents and second order neurons they effect. Future work, such as using C-Fos to examine and map changes in interneuronal networks, could seek to more directly tie changes in kinematics to observed changes in plasticity. iv DEDICATION I dedicate everything that I have and will accomplish to my parents. They are the lights of my life and the reason I am. v ACKNOWLEDGEMENTS First, I would like to express my incomprehensible gratitude to my advisor, Dr. Andrew J. Spence, for his unwavering support and tireless efforts to bolster my success. I thank him for showing me that I am more than just a “biology kid” – that I can learn and integrate many different disciplines to answer scientific questions. On that note, I thank him for urging me to explore my own scientific questions, allowing me to flourish as a scientist before I even realized it. Dr. Spence has repeatedly steered me in the right direction, giving me endless encouragement (we are all “special rainbow unicorns!”), while allowing me room to make and fix my own mistakes. I look to him as a model for who I want to be. I am forever in debt to what he has taught me as a student, as a scientist, as a mentor, and, most importantly, as a person. I will take his advice and wisdom with me throughout my career and will be forever better because of it. I would also like to thank Drs. Michel Lemay and George Smith. I am so lucky to have had both of these professors as additional mentors, teaching and advising me throughout my entire graduate studies. I would like to thank Dr. Lemay for taking the time to teach me electrophysiology when, at the time, it was not a part of my studies. It does not go unrecognized that he took time out of his busy schedule to teach a simply curious student. And because of this, I developed a passion and a deeper understanding for motor control, which positively impacted the course of my studies. Dr. Lemay always made me feel welcome even though I was not one of his students, allowing me to take expensive cooner wire and use his precious cryostat, warmly calling me Jac-Jac all the while. Moreover, I greatly appreciate all that I’ve learned from Dr. Smith. Dr. Smith is a fountain of knowledge and the amount of time he spent letting me ask questions was invaluable. He is also the greatest contributor to the “skills” I have listed on my resume! It was ostensible that Dr. Smith cared so deeply about his students and the studies we were researching. His vi mentoring made myself as well as every other student, post-doctoral fellow, and lab technician work harder and ask tougher questions. I am, undoubtably, the scientist I am today because of all that I learned from Drs. Lemay and Smith. I greatly appreciate all of the undergraduate students, graduate students, post- doctoral fellows, and lab technicians who have helped me on my projects, especially those of whom I have had the pleasure to work with for all four years of my graduate studies. I specifically want to thank Dr. Jie Chen for always being available to assist me with experiments and teach me new skills. Dr. Chen is as kind and helpful as she is knowledgeable and skillful. I also want to thank Hannah Sobotka-Briner who, at times, would spend weekends and over 50 hours a week helping me finish my dissertation studies. What an honor it has been to have worked alongside such a bright mind, loving spirit, and profoundly funny individual. Hannah’s ability to make us laugh when we were tired, hungry, and in need of sunlight was just as much a positive influence on our success as her skills in biology and engineering. I recognize and am grateful for those in the Bioengineering and Neuroscience departments, such as Helen, Twee and Rosa, who helped me with administrative duties on numerous occasions. Just as important, these individuals became a support system when I was feeling overwhelmed. I also want to thank Jenn Patten and Sarah Moore, my forever friends, whom I could talk to about topics that ranged from high level science to gut- wrenching heartbreak and somehow, we would still end up laughing until we cried. I send an extra special thank you to my Uncle Jerry, who would pass on wisdom and advice as well as sit with me for hours, helping me to interpret my data whenever I asked. To my Me Sharon, my rock, who would always know the right thing to say to get me through even the toughest of times. And to my cousin, Adam, my (not so) Little Man, vii who is wise beyond his years and would ask me profound and probing questions, which would in turn improved my understanding of the science I was studying. I am indebted to my parents, Doreen and Allen Eisdorfer. Words cannot describe the love and support I received from them. My parents have always encouraged, but never pushed, me. They made a point to tell me they are proud of me “simply for breathing” and for that, I always felt that my potential was boundless. Lastly, I would like to recognize that my cats, Emmi and Riley Rae, deleted this dissertation several times because I was not giving them enough attention. Having them lie next to me the entire time I analyzed, interpreted, and wrote the studies presented here gave me the extra little push I needed to finish. viii TABLE OF CONTENTS ABSTRACT .......................................................................................................................III DEDICATION .................................................................................................................... V ACKNOWLEDGEMENTS .............................................................................................. VI LIST OF TABLES .......................................................................................................... XIII LIST OF FIGURES ....................................................................................................... XIV CHAPTER 1: INTRODUCTION ........................................................................................1 Spinal Cord Injury.......................................................................................................1 Epidural Electrical Stimulation ...................................................................................3 Using DREADD technology to uncover EES-induced mechanisms of recovery...........................................................................................................5 Thesis objectives and hypotheses ...............................................................................9 CHAPTER 2: PLASTICITY MECHANISMS THAT ARE HYPOTHESIZED TO ENABLE EES TO PROMOTE ENHANCED LOCOMOTOR RECOVERY AFTER SCI ........................................................................................................................12 Introduction ...............................................................................................................12

Load more

  163

Copy Link