The Role of Stress, Glucocorticoids & Β-Adrenergic
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University of Pennsylvania ScholarlyCommons Publicly Accessible Penn Dissertations Spring 2011 The Role of Stress, Glucocorticoids & β-Adrenergic Signaling in Aversive, Hippocampus-Dependent Memory Retrieval Keith B. Schutsky University of Pennsylvania, [email protected] Follow this and additional works at: https://repository.upenn.edu/edissertations Part of the Pharmacy and Pharmaceutical Sciences Commons Recommended Citation Schutsky, Keith B., "The Role of Stress, Glucocorticoids & β-Adrenergic Signaling in Aversive, Hippocampus-Dependent Memory Retrieval" (2011). Publicly Accessible Penn Dissertations. 990. https://repository.upenn.edu/edissertations/990 This paper is posted at ScholarlyCommons. https://repository.upenn.edu/edissertations/990 For more information, please contact [email protected]. The Role of Stress, Glucocorticoids & β-Adrenergic Signaling in Aversive, Hippocampus-Dependent Memory Retrieval Abstract Studies in wild-type rats and mice, and mutant mice lacking norepinephrine (NE) demonstrate that NE, β1-adrenergic, cAMP/PKA and Epac signaling are required for intermediate-term hippocampus-dependent memory retrieval. Although it has been proposed that glucocorticoids (GCs) facilitate β-adrenergic signaling to impair retrieval, neither a specific equirr ement for NE nor a definitive mechanism as to how this interaction occurs has been established. This thesis provides compelling evidence that 1) GCs do not require (but can synergize with) the adrenergic system to impair hippocampus-dependent memory retrieval; 2) GCs and xamoterol interact with the β2 receptor to impair retrieval; 3) β2 receptors signal through Gi/o in the hippocampus to impair retrieval, acting to negate the facilitation of hippocampus- dependent memory retrieval mediated by β1-Gs signaling; 4) GCs impair retrieval through possibly direct interaction with the β2 receptor; 5) β2 signaling is required for retrieval and may be required for short-term maintenance of fear memory; 6) β3 signaling influences etrier val; 7) interactions between β receptors are important and net effects of β receptor stimulation (or antagonism) on hippocampal cAMP signaling likely determine the degree of retrieval impairment expressed, as individual β receptors can have similar or opposing effects on cAMP levels; and 8) adrenergic and glucocorticoid influences on etrier val are limited by the age of the memory. Degree Type Dissertation Degree Name Doctor of Philosophy (PhD) Graduate Group Pharmacology First Advisor Steven A. Thomas Keywords stress, glucocorticoids, norepinephrine, beta-adrenergic receptor, fear memory retrieval, hippocampus Subject Categories Medicine and Health Sciences | Pharmacy and Pharmaceutical Sciences This dissertation is available at ScholarlyCommons: https://repository.upenn.edu/edissertations/990 THE ROLE OF STRESS, GLUCOCORTICOIDS & -ADRENERGIC SIGNALING IN AVERSIVE, HIPPOCAMPUS-DEPENDENT MEMORY RETRIEVAL Keith Schutsky A Dissertation in Pharmacology Presented to the Faculties of the University of Pennsylvania in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy 2011 Supervisor of Dissertation Supervisor Signature _______________________________________________________________ Dr. Steven A. Thomas, M.D., Ph.D., Associate Professor of Pharmacology Graduate Group Chairperson Signature_______________________________________________________________ Dr. Vladimir Muzykantov, M.D., Ph.D., Associate Professor of Pharmacology and Medicine Dissertation Committee Dr. Judith Meinkoth, Ph.D., Associate Professor of Pharmacology Dr. Edwin Abel, III, Ph.D., Brush Family Professor of Biology Dr. Julie Blendy, Ph.D., Associate Professor of Pharmacology Dr. Benoit Giasson, Ph.D., Assistant Professor of Pharmacology DEDICATION To my wife, Tina, for her love, strength and support. ii ACKNOWLEDGEMENTS I am extremely grateful to Dr. Steven Thomas for giving me the opportunity join his research group, and I am privileged to have studied under his guidance. He has supported me in every aspect of the scientific process - in forming hypotheses, designing experiments, analyzing results, writing and submitting papers for publication. His mentorship and tireless efforts have enabled me to prosper as an independent-thinking scientist and prepared me to face obstacles that may lie ahead in my career. I want to give special thanks to Ming Ouyang, Sung-Ha Jin and Hong-Mei Luo for their technical expertise and for taking the time to train me. I must acknowledge current lab members, Christina Castelino and Lei Zhang for assistance with experiments and past lab members for their friendship and support. I want to thank my thesis committee members, Dr. Judith Meinkoth, Dr. Ted Abel, Dr. Julie Blendy and Dr. Benoit Giasson for their helpful suggestions to maintain progress in my research and for strengthening my ability to answer questions concerning my research, its implications and its limitations. I must acknowledge my family and friends for their encouragement and wisdom. Most importantly, I want to thank my wife, Tina and my two children, Jake and Logan for their unconditional love and for helping me realize the things in life that are truly important. iii ABSTRACT THE ROLE OF STRESS, GLUCOCORTICOIDS & -ADRENERGIC SIGNALING IN AVERSIVE, HIPPOCAMPUS-DEPENDENT MEMORY RETRIEVAL Keith Schutsky Steven A. Thomas Studies in wild-type rats and mice, and mutant mice lacking norepinephrine (NE) demonstrate that NE, 1-adrenergic, cAMP/PKA and Epac signaling are required for intermediate-term hippocampus-dependent memory retrieval. Although it has been proposed that glucocorticoids (GCs) facilitate-adrenergic signaling to impair retrieval, neither a specific requirement for NE nor a definitive mechanism as to how this interaction occurs has been established. This thesis provides compelling evidence that 1) GCs do not require (but can synergize with) the adrenergic system to impair hippocampus-dependent memory retrieval; 2) GCs and xamoterol interact with the 2 receptor to impair retrieval; 3) 2 receptors signal through Gi/o in the hippocampus to impair retrieval, acting to negate the facilitation of hippocampus-dependent memory retrieval mediated by 1-Gs signaling; 4) GCs impair retrieval through possibly direct interaction with the 2 receptor; 5) signaling is required for retrieval and may be required for short-term maintenance of fear memory; 6) signaling influences retrieval; 7) interactions between receptors are important and net effects of receptor stimulation (or antagonism) on hippocampal cAMP signaling likely determine the degree of retrieval impairment expressed, as individual receptors can have similar or opposing effects on iv cAMP levels; and 8) adrenergic and glucocorticoid influences on retrieval are limited by the age of the memory. v TABLE OF CONTENTS Dedication ............................................................................................. ii Acknowledgements.............................................................................. iii Abstract ................................................................................................ iv Table of Contents ................................................................................. vi List of Tables ...................................................................................... xii List of Figures .................................................................................... xiii Abbreviations ...................................................................................... xv Chapter 1: Introduction 1.1 Memory Types & Importance of Hippocampus in Episodic Memory ..............2 1.2 Strength of Memory is Influenced by Environment and Emotional State .........3 1.3 Animal Models of Fear Memory & Brain Structures Involved 1.3.1 Auditory (Cued) Fear Conditioning ....................................................4 1.3.2 Contextual Fear Conditioning .............................................................5 1.3.3 Inhibitory (Passive Avoidance) ...........................................................7 1.3.4 Spatial Navigation ...............................................................................9 1.4 Role of NE/E & -adrenergic Signaling in Fear Memory 1.4.1 Epinephrine & Enhanced Consolidation ...........................................10 1.4.2 Norepinephrine & Enhanced Consolidation .....................................11 1.4.3 NE/E is not Required for Fear Memory Consolidation ....................12 1.4.4 Signaling is not Required for Fear Memory Consolidation ...........13 1.4.5 NE/E is Required for Intermediate-term Memory Retrieval vi 1.4.5.1 NE/E and Spatial Retrieval ...................................................14 1.4.5.2 NE/E and Contextual Memory Retrieval ..............................14 1.4.6 Signaling is Required for Intermediate-term Memory Retrieval 1.4.6.1 Signaling and Spatial Retrieval .........................................15 1.4.6.2 1 Signaling and Contextual Memory Retrieval ...................16 1.4.6.3 2 & 3 Receptors Influence Retrieval Independently & in Concert with 1 .........................................................................17 1.5 Role of Stress & Glucocorticoids in Fear Memory 1.5.1 Stress, Glucocorticoids (GCs) & Consolidation ...............................18 1.5.2 Stress, GCs & Retrieval ....................................................................18 1.6 Interactions between Adrenergic & GC Signaling in Fear Memory 1.6.1 NE/E, Receptor & GC