TRACE AMINES AS NOVEL MODULATORS OF SPINAL MOTOR FUNCTION A Dissertation Presented to The Academic Faculty by Elizabeth A. Gozal In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the School of Biomedical Engineering Georgia Institute of Technology December 2010 COPYRIGHT 2010 BY ELIZABETH A. GOZAL TRACE AMINES AS NOVEL MODULATORS OF SPINAL MOTOR FUNCTION Approved by: Dr. Shawn Hochman, Advisor Dr. Pete Wenner Department of Physiology Department of Physiology Emory University School of Medicine Emory University School of Medicine Dr. T. Richard Nichols Dr. Patrick J. Whelan School of Applied Physiology Affiliation to Faculty Veterinary Georgia Institute of Technology Medicine and Facuty of Medicine University of Calgary Dr. Robert H. Lee Department of Biomedical Engineering Emory University School of Medicine Date Approved: November 9, 2010 ACKNOWLEDGEMENTS I would like to thank the many people who have supported and encouraged me through the long journey towards completion of the work presented in this dissertation. First and foremost, I wish to thank my advisor, Shawn Hochman, for his guidance, creativity, enthusiasm, and patience over the years. I appreciate your support through the tough times and the opportunity you gave me to learn and develop as a scientist. Thank you to my committee members, Pete Wenner, Richard Nichols, Patrick Whelan, and Bob Lee for their advice and feedback during this process. To the past and present members of the Hochman lab, thank you for your suggestions, support, and friendship. It has been a pleasure working with you. A special thank you to Heather, JoAnna, Amanda, Kate, Jacob, and Katie for their confidence and help. Thank you to all my amazing friends who have supported me through the years. I would especially like to thank Jack and Mackenzie for being such incredible and selfless friends. I cannot thank you enough for being willing to sacrifice your weekends and drive an hour and half both directions to take care of Emma so I could work. Finally, I would like to thank my wonderful family. To my parents, Don and Debby, thank you for always believing in me and giving me the foundation to succeed. I would not be who I am or where I am today without your love, patience, and support. To my sister, Pam, thank you for always being there for me and being the best sister possible. To my daughter, Emma, thank you for constantly reminding me what is really important in life. Finally, I would like to thank my husband, Yair, for his unconditional love and support. Thank you for putting life in perspective and making me laugh. I could never have done this without you. iii TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ............................................................................................... iii LIST OF TABLES ........................................................................................................... xiii LIST OF FIGURES ......................................................................................................... xiv LIST OF ABBREVIATIONS ......................................................................................... xvii SUMMARY .......................................................................................................................xx CHAPTER 1: Introduction ..................................................................................................1 1.1 The classical monoamine neurotransmitters ................................................1 1.1.1 General background of the monoamines .........................................1 1.1.2 General monoamine transmission ....................................................1 1.1.3 Structure and synthesis of the monoamines .....................................1 1.1.4 Descending monoaminergic systems ...............................................3 1.1.5 Monoamine oxidases .......................................................................4 1.2 Trace amines ................................................................................................6 1.2.1 General background of the trace amines ..........................................6 1.2.1.1 Discovery of the trace amines ..............................................7 1.2.1.2 Origin of the name “Trace Amines” ....................................8 1.2.1.3 Origin and understanding of the conventional view that the trace amines are “False Transmitters” .............................................8 1.2.2 Endogenous levels of the trace amines ..........................................10 1.2.2.1 Synthesis of the trace amines .............................................10 1.2.2.1.1 Dietary affects on the levels trace amines and aromatic amino acids .........................................................11 1.2.2.1.2 Aromatic-L-amino acid decarboxylase ...............12 iv 1.2.2.1.3 AADC positive neurons in the central nervous system and D cells .............................................................13 1.2.2.2 Degradation of the trace amines ........................................15 1.2.2.3 Concentrations and distribution of trace amines ................15 1.2.3 Transporters ...................................................................................17 1.2.3.1 Plasma membrane transporters ..........................................17 1.2.3.1.1 Monoamine transporters .....................................17 1.2.3.1.2 Organic cation transporters .................................20 1.2.3.1.3 L-type amino acid transporters ...........................20 1.2.3.1.4 Plasma membrane monoamine transporter .........21 1.2.4 Storage and release of the trace amines .........................................22 1.2.5 Trace Amine actions in the spinal cord ..........................................22 1.2.6 Disorders in which the trace amines may be involved ..................23 1.2.6.1 Phenylketonuria .................................................................23 1.3 The trace amine-associated receptors ........................................................24 1.3.1 Discovery of the trace amine receptors ..........................................24 1.3.2 Nomenclature of the trace amine-associated receptors ..................25 1.3.3 Properties of the trace amine-associated receptors ........................26 1.3.3.1 Trace amine-associated receptor 1 .....................................26 1.3.3.1.1 Pharmacological characterization of trace amine- associated receptor 1 ..........................................................26 1.3.3.1.2 Distribution and cellular location of trace amine- associated receptor 1 ..........................................................27 1.3.3.1.3 Facilitation of trace amine-associated receptor 1 by monoamine transporters ................................................27 1.3.3.1.4 Trace amine-associated receptor 1 knockout mice28 1.3.3.2 Trace amine-associated receptor 4 .....................................29 v 1.4 Spinal cord anatomy ..................................................................................29 1.5 Locomotion studies ....................................................................................31 1.5.1 Central pattern generator................................................................31 1.5.1.1 Models of the central pattern generator .............................32 1.5.1.1.1 Half-Center Model ..............................................32 1.5.1.1.2 Unit Burst Generator ...........................................33 1.5.1.1.3 Other CPG Models ..............................................33 1.5.2 The neonatal rodent preparation ....................................................35 1.5.3 Locomotor studies in the neonatal rodent ......................................36 1.5.3.1 Pharmacological activation ................................................36 1.5.3.2 Electrical activation ...........................................................36 1.5.3.3 Lesioning studies ...............................................................37 1.5.3.4 The use of molecular genetics to understand CPGs ...........37 1.6 Neuromodulation .......................................................................................39 1.7 The significance of an exquisitely regulated trace aminergic system ........40 CHAPTER 2: General methods .........................................................................................42 2.1 Electrophysiology ......................................................................................42 2.1.1 The neonatal rat isolated spinal cord preparation ..........................42 2.1.2 The neonatal isolated spinal cord with attached hindlimbs ...........45 2.2 Terminology for bursting patterns .............................................................46 2.3 SpinalMOD: A MATLAB Graphic User Interface for Burst Detection ....47 2.3.1 GUI menu structure........................................................................47 2.3.2 Running the burst detection ...........................................................50 2.3.3 Running the burst analysis .............................................................51 2.4 Contributions to this dissertation ...............................................................53 vi CHAPTER 3: The localizations of AADC, the trace amines, and TAARs provide an anatomical substrate for the trace amines in the mammalian spinal cord ..........................54 3.1 Abstract ......................................................................................................54