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Role of the Human Globus Pallidus in Tremorgenesis

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Role of the Human Globus Pallidus in Tremorgenesis Role of the human globus pallidus in tremorgenesis by Shane Ellis A thesis submitted in conformity with the requirements for the degree of Master’s of Science Department of Physiology University of Toronto© Copyright by Shane Ellis 2015 Role of the human globus pallidus in tremorgenesis Shane Ellis Master of Science Department of Physiology University of Toronto 2015 Abstract The GPi is a nucleus that serves as an output of the basal ganglia; a collection of nuclei which function in selecting movements to be executed. Tremor is defined as an unintentional, rhythmic, sinusoidal contraction of body parts. Currently, no scientific consensus has been reached as to where in the brain tremor arises. Using microelectrode recordings in human patients with and without tremor, we discovered a sub-population of cells that are capable of being induced into a brief theta oscillation following microstimulation. However, we found that theta burst stimulation was incapable of inducing visible tremor when microstimulating in the GPi, Vim, or STN. We also found preliminary evidence that this theta oscillation is capable of producing an LTP-like response within the GPi. We believe that this work adds strength to the “pallidocentric” view of tremor initiation which holds that the GPi is responsible for the onset of tremor. ii Acknowledgments First and foremost, I would like to thank my supervisor, Dr. Hutchison for his mentorship and guidance through these last two years; I couldn’t have completed this thesis without your help. Next, I would like to thank my parents and family for their continual support throughout the highs and lows of this journey called life. Even if you don’t understand what I’m doing, you still support me whole-heartedly and I couldn’t ask for anything more. To Diellor Basa (I hope I’ve spelt your name correctly this week) and Luka Srejic, thank you for “showing me the ropes” inside the lab. Lastly, I would like to thank Dr. Sherri Thiele and Dr. Aman Mann for keeping me sane and for taking time out of their busy days to help me when I was struggling. iii Table of Contents Acknowledgments ............................................................................................................................... iii Table of Contents .................................................................................................................................. iv List of Tables .......................................................................................................................................... vi List of Figures ........................................................................................................................................vii List of Appendices................................................................................................................................. ix List of Abbreviations ............................................................................................................................ x Chapter 1 Introduction ........................................................................................................................ 1 Introduction ............................................................................................................................................ 1 1.1 Basal Ganglia Function ............................................................................................................................ 1 1.1.1 The Human Globus Pallidus Internus ........................................................................................................ 1 1.2 Parkinson’s Disease .................................................................................................................................. 4 1.2.1.1 Genetics of Parkinson’s Disease ............................................................................................................... 5 1.2.1.2 Treatments of Parkinson’s Disease ......................................................................................................... 6 1.2.1.2.1 Pharmacological Treatments of PD ..................................................................................................... 6 1.2.1.2.2 Surgical Treatments ................................................................................................................................... 7 1.2.2 Explanatory Models of PD .............................................................................................................................. 8 1.2.2.1 The Rate Model ................................................................................................................................................ 8 1.2.2.2 The Center-Surround Model .................................................................................................................... 11 1.2.2.3 The Oscillatory Network Model .............................................................................................................. 15 1.2.3 Animal Models of Parkinson’s Disease .................................................................................................... 17 1.3 Dystonia ...................................................................................................................................................... 19 1.3.1 Etiology of Dystonia ........................................................................................................................................ 19 1.3.2 Genetics of Dystonia ........................................................................................................................................ 20 1.3.3 Treatment of Dystonia ................................................................................................................................... 20 1.4 Essential Tremor ..................................................................................................................................... 21 1.4.1 Etiology of Essential Tremor ....................................................................................................................... 21 1.4.2 Genetics, Diagnosis and Treatment of Essential Tremor ................................................................. 22 1.5.1 Tremor ..................................................................................................................................................... 23 iv 1.6 Synaptic Plasticity ................................................................................................................................... 25 1.7 Project Rationale ..................................................................................................................................... 28 1.8 Hypothesis and Aims .............................................................................................................................. 30 Chapter 2- Methods ............................................................................................................................ 31 2.1 General Methods ...................................................................................................................................... 31 2.2 Intraoperative Microelectrode Recordings ................................................................................... 36 2.3 Tremor Entrainment with Theta Burst Stimulation ................................................................... 38 2.3 Effects of Theta Burst Stimulation on Plasticity in GPi .............................................................. 38 3.0 Chapter 3- Results ....................................................................................................................... 42 3.1 Stimulation-Induced Oscillation Characterization...................................................................... 42 3.2 Tremor Entrainment with Theta Burst Stimulation ................................................................... 52 3.2.1 Theta Burst Stimulation in the Globus Pallidus Internus ................................................................ 52 3.2.2 Tremor Entrainment with Theta Burst Stimulation Outside of The GPi ................................... 55 3.3 Effect of Theta Burst Stimulation on Plasticity within the GPi ................................................ 60 4.0 Chapter 4- Discussion ................................................................................................................ 63 4.1 Stimulation-Induced Oscillations ...................................................................................................... 64 4.2 Tremor Modification due to Theta Burst Stimulation in the Basal Ganglia ....................... 67 4.2.1 Theta Burst Stimulation in GPi ................................................................................................................... 67 4.2.2 Theta Burst Stimulation in Motor Thalamus ........................................................................................ 69 4.2.3 Theta Burst Stimulation in Sub Thalamic Nucleus ............................................................................. 70 4.3 Effect of Theta Burst Stimulation on Plasticity within the GPi ................................................ 70 4.4 Future Directions..................................................................................................................................... 73 4.5 Conclusions ...............................................................................................................................................
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