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An Organizing Principle of Thalamic Plasticity An Organizing Principle of Thalamic Plasticity Jayson L. Parker, M. Sc. O Copyright 1999. A diesis submitted in conformisr with the requirements for the degree of Doctor of Philosophy, Dept. of Physiology in the University of Toronto. National Libraiy Bibliothèque nationale 1*m ofCanada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395. rue Wellington OttawaON K1AON4 Ottawa ON KIA ON4 Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or seil reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electmnic formats. la forme de microfiche/fïI.m, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor subsbntial extracts fkom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation, Why should we subsirlize intellectual curiosity ? RONALD REAGEN carnpaign speech, 1980 There is nothing which can better deserve our patronage than the promotion of science and literature. Knowledge is in every country the surest busis of public happiness. GEORGE WASHINGTON address to Congress, January 8, 1790 The effort to understand the universe is one of the very few things that lifts life, a Cittle above the level of farce, and gives it some of the grace of tragedy. STEVEN WEINBERG The First Three Minutes, 1977 Humanity is exalted not because we are so far ahove other living creatures, but because knowing them well elevates the very concept of Z$e. EDWARD O. WILSON An Organizing Principle of Thdamic Plasticity, Doctoral Program 1999, Jayson L. Parker, Dept. Physiology, University of Toronto Abstract Three dimensional reconstructions of thalamic (ventroposterolateral nucleus; VPL) sensory rnaps were used to detect somatotopic reorganization in the thalamus. Hindlimb input was removed (>60%) by nucleus graulis lesions in adult rats (control (n=8); acute (n=6); 1-week post-lesion (n=8); 1- month post-lesion (n=û)). The removal of hindlimb input by nucleus grauüs lesions revealed a focal zone of reorganization within the VPL (300 pm thick) at times 1-week and 1-month post-lesion. Shoulder sensory maps in the thalamus were found to increase in total volume by 25% as early as 1-week post-lesion (p<0.001). From this finding the "hot spot model" was postulated, which predicted that such zones were manifested at other levels of the nervous system and independent of the form of neural trauma. In the second study, nerve transection of the hindlimb was performed to see if a similar outcome was obtained (sharn (n=6);nerve-transection (n=8)). Despite numerous differences between nerve transection and nucleus gracilis lesions, the same focal zone of reorganization in the VPL was obsemed. This latter finding further underscored the importance of this focal zone and the vaiidity of the hot spot model. Finally, it was asked if higher levels of brain organization contribute to plasticity at lower levels of the nervous system. Cortical aspiration of the forelimb somatosensory cortex was performed the same day as nucleus gracilis lesions (n=8). Remarkably, the removal of the forelimb somatosensory cortex blocked al1 thalamic somatotopic reorganization (n=7) when compared to nucleus gracilis lesioned animals (n=7; p<0.05). Cortical lesions alone had no effect on the volume of thalamic sensory maps (n=6, pO.05). Importantly, if cortical lesions were performed after thalamic reorganization had occurred, thalamic plasticity was unaffected (n=6; pc0-05). In conclusion, thereisa focalzoneofsomatotopicplasticityin the thalamus that appears to be independent of the form of deafferentation, which requires the presence of an intact cortex for the induction of somafotopic reorganizafion, but not ifs maintenance. Dedication 1 dedicate this work to my parents, Gary and Till Parker. They have always been strong supporters of my academic pursuits, without which, this research would not have been possible. Sometimes issues become so esoteric in basic research, I've known 1 could always count on the unassailable interest of at least one person; my mother. My father did not have the benefit of an education beyond high school - but has showed me frorn a very early age that solutions corne from asking the right questions. In light of this 1believe that a university is a place to learn for those who choose to do so, but ultirnately, the engine of curiosity draws its strength from a much more modest source: the home. There are a number of people who have been greatly influential or helpful duxing my Doctoral researdi: Dr. Constantine Poulos, senior scientist at the Addiction Research Foundation. Dr. Poulos, with some success, has hammered home the goal of being obsessive in data analysis and attentiveness to detail. These lessons are by no means complete-an excuse for future interactions. Dr. Sandra E. Black, Dept. head of Neuroiogy at Sunnybrook Hospital. 1 owe Dr. Black a great debt. Çhe introduced me to the clinical world, while 1 kicked and screamed at its limitations, only to emerge greatly strengthened from its inter disuplinary environment. Dr. Gwen O. Ivy, professor, at the University of Toronto. Dr. Ivy to this day has taught me every major pririciple of good laboratory benchwork. My benchwork repertoire s till remains diminutive, but I've applied the lessons well. Dr. Blair Feltmate, President, Sustainable Systems. Dr. Feltmate's advice on publications, funding and statistical analysis has been great source of guidance for me in this program. 1 fear that my writing expression remains well below his expectations. Dr. Micheal L. Wood, associate professor, St. Micheal's Hospital. Dr. Wood's expertise in imaging allowed me to visualize my data sets in three dimensions and measure the images accordingly. The veterinary staff in the Dept. of Comparative Medicine in the Medical Sciences building: Dr. Renlund, Dr. Douglas, Dr. Moloo and Ms. Parisien. Their careful monitoring of the well being of animals in their faulity has been of great benefit. My committee members, Dr. Harrisson and Dr. Sessle. Their feedback on my research has been both prompt and helpful. Their critiusms were respomible for my work with nerve transection, an important study corroborating the validity of my research. Finally, my supervisor Dr. Dostrovsky. Dr. Dostrovskyfs support and experience was essential for these projects. I might add that Jonathan has one ski11 I've still been delinquent to develop - the ability to agree to disagree. Jayson L. Parker, M. Sc. Organization of Thesis Chapters outlining the author's original studies: Introduction, three papers and a Summary and Conclusion. The Introduction provides an overall framework to view the field, progressing from receptive fields to sensory maps. What follows are three chapters (2 - 4) which are self- contained papers. Because of the extensive discussions in each of the three data chapters, a brief Sumrnary and Conclusions is offered at the end of the thesis. Table of Contents Abstract Dedication Acknowledgments Organization of Thesis Chapter 1: Introduction Prologue The Rosetta stone as a metaphor in CNS organization Anatomical 0verview Receptive fields: A neural lexicon? Columnar organization: A neural lexicon? Evidence from the cerebral cortex Other levels of the Somatosensory pathway Summary Reentrant connectivity: Isomorphic content across levels? Cerebrai cortex Thalamus Dorsal column nuclei Spinal cord Summary Paradigm Chapter 2: A Focal Zone of Thalamic Plasticity Abstract Introduction Methods Results Discussion Chapter 3: A Focal Zone of Thalamic Plasticity: Independence of the Form of Deaff erentation? 108 Ab stract Introduction Methods Resdts Discussion Chapter 4: Cortical Control of nialamic Plasticity Abstract htroduction Methods Results Discussion Chapter 5: Summary and Conclusions Coda Future studies Criticisms Conclusion Re£erences Chapter I Introduction Introduction Tuthrnosis III, the reigning Pharaoh in Egypt during the approximate tune period 1600 BC, experienced a turbulent rule over his dominion (Grimal 1988). Hïs rule was made difficult by the fact that, at least initially, he was CO- regent with his stepmother queen Hatshepsut (Grimal 1988). Due to problems with the Pharaoh line prior to Tuthmosis III rise to power, Hatshepsut ruled Egypt as both king and queen, going so far as to Wear a false beard to fulfill these roles (Pellegrin0 1994). Secular archeological analysis suggest that if the Judean-Christian figure Moses (Exodus 1000 BC) actually edsted, Tuthmosis III would have had dealt with this figure (Pellegrino 1994). The Hebrew prophet Moses, through his God, commanded seven plagues on Egypt in an effort to force the release of his people (Exodus 1000 BC). Secular interpretations (Pellegrino 1994) of this period in history have suggested that the seven plagues were actually an account of events catalyzed by the most powerful volcanic eruption in the history of mankind. The volcan0 Thera erupted in the Aegean sending soot and tsunamis towards Egypt during the reign of Tuthmosis III (Stanley and Cheng 1987; Hughes 1988). While Biblical texts are often evoked to describe this period in history, until recently little attention had been paid to the Egyptian version of the event. Egyptian texts, while they do not appear to mention Moses (sic), do refer to the Hebrew emigration (Grimal 1988). The prevailing conditions described by the Egyptians are: "For nine days there was no exit from the palace and no one could see the face of his fellow. ... The Sun is covered and Introduction does not shine to the sight of men. Ra [Sun God] has turned his face from mankïnd.
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