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Redundant Neuromodulatory Mechanisms That Control Fear Memory Consolidation University of Pennsylvania ScholarlyCommons Publicly Accessible Penn Dissertations 2013 Redundant Neuromodulatory Mechanisms That Control Fear Memory Consolidation Matthew Young University of Pennsylvania, [email protected] Follow this and additional works at: https://repository.upenn.edu/edissertations Part of the Neuroscience and Neurobiology Commons Recommended Citation Young, Matthew, "Redundant Neuromodulatory Mechanisms That Control Fear Memory Consolidation" (2013). Publicly Accessible Penn Dissertations. 822. https://repository.upenn.edu/edissertations/822 This paper is posted at ScholarlyCommons. https://repository.upenn.edu/edissertations/822 For more information, please contact [email protected]. Redundant Neuromodulatory Mechanisms That Control Fear Memory Consolidation Abstract The ability to reliably and powerfully store memories for frightening experiences is crucial to survival in an ever-changing and potentially dangerous environment. Consolidation is the process by which long-term memories are stored in the brain, and much is understood about the processes that occur within a neuron in the hours after a learning event that stabilize learning-induced changes. However, the specific mechanisms through which fear exacerbates those processes remains unclear. Neuromodulators are a prime object of research to understand the consolidation of fear memory given that their release is a hallmark of the fear response. While several neuromodulatory systems are known to facilitate consolidation, no individual system yet appears to be essential. This dissertation explores the hypothesis that several neuromodulators work together to ensure proper consolidation of fear memory. The research contained in this dissertation employs pharmacologic and genetic manipulation of individual neuromodulatory receptor systems and associated intracellular signaling pathways to determine the essential neurobiology for consolidating of Pavlovian fear conditioning in mice. The results of this investigation reveal that β2-adrenergic, D5-dopaminergic and M1-muscarinic receptors in the basolateral amygdala (BLA) are essential to fear conditioning in a redundant manner, wherein two or more receptor types must be blocked in order to prevent consolidation. Furthermore, these three receptors are observed to redundantly activate phospholipase C (PLC), which this dissertation shows is necessary for consolidation in the BLA. Finally, evidence is provided to suggest that PLC promotes fear memory consolidation by inhibiting a voltage-dependent potassium channel (KCNQ/M) that regulates neuronal excitability and also appears to control consolidation. Together, this dissertation proposes that fear- induced neuromodulatory release promotes consolidation through redundant neuromodulatory activation of PLC, which puts the BLA in an excitable state that does not persist into the consolidation window after emotionally neutral experiences. Degree Type Dissertation Degree Name Doctor of Philosophy (PhD) Graduate Group Neuroscience First Advisor Steven A. Thomas Keywords Acetylcholine, Consolidation, Dopamine, Fear Memory, KCNQ, Norepinephrine Subject Categories Neuroscience and Neurobiology This dissertation is available at ScholarlyCommons: https://repository.upenn.edu/edissertations/822 REDUNDANT NEUROMODULATORY MECHANISMS THAT CONTROL FEAR MEMORY CONSOLIDATION Matthew Brandon Young A DISSERTATION in Neuroscience Presented to the Faculties of the University of Pennsylvania in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy 2013 Supervisor of Dissertation Graduate Group Chairperson Signature___________________________ Signature___________________________ Steven A. Thomas, MD, PhD Joshua I. Gold, PhD Associate Professor, Department of Associate Professor, Department of Pharmacology, School of Medicine Neuroscience, School of Medicine Dissertation Committee R. Christopher Pierce (Chair), PhD, Associate Professor of Psychiatry, School of Medicine Marcos G. Frank, PhD, Associate Professor of Neuroscience, School of Medicine Isabel I. Muzzio, PhD, Assistant Professor of Psychology, School of Arts and Sciences Leonard L. Howell, PhD, Professor of Psychiatry and Behavioral Sciences, Emory University, Yerkes National Primate Research Center ACKNOWLEDGMENT Thanks Mom, Dad, Craig, Ryan, Hannah, and Grandma. I had grand intentions of writing a heartfelt acknowledgement to all of the people without whom I never would have completed, or even began, this journey. I thought that waiting to write those acknowledgements as the final coda of the writing process – a final reflection on the connections in my life – was a great idea. More than a hundred pages later, I’m not so sure. You see, I didn’t always want to be a scientist. In fact, I hated science in high school and through most of college, largely due to uninspired and mostly incompetent teachers. Were it not for mentors at Arizona State University like Cheryl Conrad, David Capco, Eddie Casteneda, Jennifer Fewell, and Ryan Wright, I can’t, for better or worse, imagine what I would be doing. I certainly would not be getting my doctorate in neuroscience. Sure, there have been many times in the past five years that I have found myself a fish out of water, wondering what the hell I was doing in a Ph.D. program at an Ivy League institution, surrounded by nerds—found myself dreaming begrudgingly of what I could be doing if it weren’t for all those wonderful people who inspired me to pursue a degree in neuroscience. Thankfully, I had people around me who enriched my life and made these last five years a true pleasure – Jason Rodriguez, Michael Castle Greg Dunn, Matt Nassar, Collin Challis, Misty Vaught, Natalie Rizzo, Gina Lavery, and Michelle Bland. And I had Caitlyn Dunning in my life, a dear and loving and patient woman, to serve as a beacon, even from so far away, to guide me toward an as yet undisclosed but exciting future. And it certainly goes without saying that my completion of this process would have been impossible without my advisor Steve Thomas, who handled my bouts of discontent with Buddah-like patience. Now, much like the process of this most recent phase of my life, I find myself somehow at the end of what I thought was a herculean task without really even noticing how I got there. Thanks all you people. ii ABSTRACT REDUNDANT NEUROMODULATORY MECHANISMS THAT CONTROL FEAR MEMORY CONSOLIDATION Matthew Brandon Young Steven A. Thomas The ability to reliably and powerfully store memories for frightening experiences is crucial to survival in an ever-changing and potentially dangerous environment. Consolidation is the process by which long-term memories are stored in the brain, and much is understood about the processes that occur within a neuron in the hours after a learning event that stabilize learning-induced changes. However, the specific mechanisms through which fear exacerbates those processes remains unclear. Neuromodulators are a prime object of research to understand the consolidation of fear memory given that their release is a hallmark of the fear response. While several neuromodulatory systems are known to facilitate consolidation, no individual system yet appears to be essential. This dissertation explores the hypothesis that several neuromodulators work together to ensure proper consolidation of fear memory. The research contained in this dissertation employs pharmacologic and genetic manipulation of individual neuromodulatory receptor systems and associated intracellular signaling pathways to determine the essential neurobiology for consolidating of Pavlovian fear conditioning in mice. The results of this investigation reveal that β2-adrenergic, D5-dopaminergic and M1-muscarinic receptors in the basolateral amygdala (BLA) are essential to fear conditioning in a redundant manner, wherein two or more receptor types must be blocked in order to prevent consolidation. Furthermore, these three receptors are observed to redundantly activate iii phospholipase C (PLC), which this dissertation shows is necessary for consolidation in the BLA. Finally, evidence is provided to suggest that PLC promotes fear memory consolidation by inhibiting a voltage-dependent potassium channel (KCNQ/M) that regulates neuronal excitability and also appears to control consolidation. Together, this dissertation proposes that fear-induced neuromodulatory release promotes consolidation through redundant neuromodulatory activation of PLC, which puts the BLA in an excitable state that does not persist into the consolidation window after emotionally neutral experiences. iv TABLE OF CONTENTS Abstract………………………………………………………………………………………….iii Table of Contents……………………………………………………………………………....v List of Figures……………………………………………………………………………….....vi CHAPTER 1: A General Introduction to Fear Memory Consolidation………………...1 CHAPTER 2: Redundant catecholamine signaling consolidates fear memory via phospholipase C…………………………………………………………..18 CHAPTER 3: M1-muscarinic receptors promote fear memory consolidation via phospholipase C and the M-current……………………………………48 CHAPTER 4: General Conclusions and Future Directions……………………………77 References……………………………………………………………………………………..85 v LIST OF FIGURES Chapter 2 Figure 1.1 D1/5-dopaminergic signaling is redundant with β2-adrenergic signaling for fear memory consolidation………………………………………………………………...44 Figure 1.2 Redundancy for fear memory consolidation also occurs in rats……………..44 Figure 1.3 BLA is the locus of redundant signaling in fear memory consolidation…………………………………………………………………………………….45
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