INFORMATION TO USERS This manuscript has been reproduced fiom the microfilm master. UMI films the text directly firom the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be fi’om any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy subm itted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely afifect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing fi~om left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6” x 9” black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. UMI A Bell & £towell Infonnation Company 300 North Zed) Road, Ann Arbor NO 48106-1346 USA 313/761-4700 800/521-0600 EFFECTS OF ACUTE AND CHRONIC CHORDA TYMPAN! DENERVATION ON TASTE RESPONSES IN THE NUCLEUS OF THE SOLITARY TRACT DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Mark E. Dinkins, B.S., D.D.S ***** The Ohio State University 1999 Dissertation Committee: Approved by Susan Travers, Ph.D., Adviser Keith Alley. D.D.S., Ph.D. Michael Beattie, Ph.D. Susan Travers, Ph.D. Adviser Scott Herness, Ph.D. Oral Biology Graduate Program ÜMX Number: 9919858 UMI Microform 9919858 Copyright 1999, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 ABSTRACT The central effects of peripheral deafferentatlcn have been well described in visual, somatosensory and auditory systems. However little is known of central plasticity in the gustatory system. A limited number of anatomical, neurophysiological, behavioral and psychophysical studies suggest that changes do occur in the central taste system after peripheral deafferentation. The purpose of this project was to determine whether physiological changes occur in the first order central taste relay, the nucleus of the solitary tract (NST) after acute or chronic chorda tympani (CT) denervation. Ten percent of multi- and single-unit sites in NST increased their response to taste stimulation by an average of 33% during acute CT denervation (anesthesia). In addition, we noted a decrease in the mean spontaneous rate of NST cells during anesthesia. This effect was robust for cells that responded to taste mixture stimulation of the anterior tongue and hard palate. The CT innervates taste buds located on the anterior tongue and the greater superficial petrosal nerve innervates taste buds on the hard palate. Since the taste response elicited by palatal stimulation was affected little by anesthesia, but the spontaneous rate greatly decreased, in essence, there was an increase in the signal-to-noise ratio for these cells. It appears that taste compensation after CT anesthesia may be partly due to disinhibition and an increase in the signal-to-noise ratio of a subset of NST cells. Chronic CT denervation (transection) resulted in increased posterior tongue- elicited taste responses of NST cells. Also, there was a trend for increased palatal-elicited taste responses of NST cells. However, the orotopic organization of taste and tactile responses in the NST was unaltered after denervation. These results suggest that intact nerves increase their functional input in their normal terminal fields in the NST. Based on these studies, the gustatory system at the level of the NST has the potential for neural plasticity to compensate for lost input, but appears more resistant to the large-scale changes that have been found in other sensory systems. More importantly, these results provide us with more information concerning the normal processing of taste input in the central nervous system. Ill First of all, I would like to dedicate this to my parents, Susan and William, my stepfather, Paul, and my sister, Lori, who through hard work impressed upon me the values and principles that I believe in. Secondly, to my grandmother, Macil, who allowed me the opportunity to pursue higher education at The Ohio State University. Finally, to my wife, Susan, and my son, Jake, who have made my life so fulfilling. I thank all of you for your love and encouragement. IV ACKNOWLEDGMENTS I would like to thank my adviser, Dr. Susan Travers, for her tireless mentorship and dedication to this project. I have learned a great deal from this experience due to her expertise and knowledge. I thank Dr. Joe Travers for his many insightful comments on several manuscripts that I have written. I am also grateful for his guidance in this project. Many individuals associated with the lab have helped me immensely in this endeavor and I am sincerely grateful. I have had many interesting conversations with Drs. Chris Halsell, Hamid Karimnimazi, and Lisa DiNardo who have aided me in the direction of this project. I am fortunate to have had help from the following research assistants/associates who have done an excellent job: Mrs. Elizabeth Hauswirth, Dr. Hecheng Hu, and Mr. Kevin Urbaneck. I would like to thank the members of the Dissertation Committee for their commitment and helpful comments that have improved the quality of this dissertation as well as enriching my educational experience. I thank Dr. Ilene Bernstein and Mr. Mitch Roitman for their role in the second study. This research was supported by a Dentist-Scientist Award from the National Institutes of Health (NIDCR). VITA February 25, 1967 ........................Bom-Canton, Ohio 1992............................................... B.S. in absentia. Microbiology, The Ohio State University D.D.S., Dentistry, The Ohio State University 1992-present................................ Graduate Teaching and Research Associate, Endodontics and Oral Biology, The Ohio State University PUBLICATIONS Manuscripts 1. Zwilling, B.S., M. Dinkins, R. Christner, M. Paris, A. Griffin, M. Hilburger, M. McPeek, D. Pearl. Restraint stress-induced suppression of major histocompatibility class II expression by murine peritoneal macrophages. J. Neuroimmunology. 29:125-130. 1990. Abstracts 2. Dinkins, M.E. and C.F. Shuler. Keratin analysis of full thickness oral mucosal equivalents. J. Dental Research. 69(special issue):225. March 1990. Abstract 1174. 3. Dinkins, M. and E.L. Dabreo. Color change of two maxillofacial elastomers during polymerization. J. Dental Research. 70(special issue):290. April 1991. Abstract 200. VI 4. Harrer, M. I., M. Dinkins, J. B. Travers, and S. P. Travers. Gustatory elicited c-fos expression in brainstem nuclei. Society for Neuroscience Abstracts, 1993 5. Dinkins, M.E. and S.P. Travers. Neurophysiologic study of taste compensation following nerve anesthetization in rats. J D ental Research, 75(special issue). 1996. Abstract 743. 6. Dinkins, M.E. and S.P. Travers. Alternative Mechanism for Taste Compensation Following Chorda Tympani Anesthetization. Chemical Senses, abstract, 1996. 7. Dinkins, M.E., I. Bernstein, M. Roitman and S.P. Travers. Lack of Orotopic Reorganization in the Adult NST Following Neonatal Chorda Tympani Transection. J D ental Research, abstract, 1998. 8. Dinkins, M.E. and S.P. Travers. Chorda Tympani Nerve Transection in Neonatal Rats Results in Altered Taste Responses of Adult NST Neurons. Society for Neuroscience Abstracts, 1998. FIELDS OF STUDY Major Field: Oral Biology VII TABLE OF CONTENTS ABSTRACT..................................................................................................................ii DEDICATION..............................................................................................................iv ACKNOWLEDGMENTS............................................................................................ v VITA............................................................................................................................ Vi LIST OF FIGURES................................................................................................. xi CHAPTERS: 1. INTRODUCTION...............................................................................................1 1.1 Plasticity in sensory system s .................................................................1 1.1.1 Overview.....................................................................................1 1.1.2 Visual sy stem ............................................................................2 1.1.3 Somatosensory system ...........................................................2 1.1.4 Trigeminal system ................................................................... 6 1.1.5 Mechanisms of plasticity .........................................................7 1.2 Plasticity in the gustatory system ........................................................7 1.2.1 Developmental plasticity