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THE NEUROPHARMACOLOGICAL EVALUATION OF Ocimum kenyense, Ocimum kilimandscharicum and Ocimum masaiense SPECIES FOUND IN KENYA. By Peter Waweru jMwangi (B.Pharm UoN, M.Sc UoN) H80/80382/10 Department of Medical Physiology, School of Medicine, College of Health Sciences, University of Nairobi. A thesis submitted in fulfillment of conditions for the award of the degree of Doctor of Philosophy (PhD) of the University of Nairobi November 2011 University ot NAIROBI Library 0451786 8 l DECLARATION. This thesis is my original work and has not been presented for examination for a degree in any other university. Peter Waweru Mwangi (B.Pharm UoN, M.Sc UoN) Signature _____ JL.----------------- Date This thesis has been submitted for examination with our approval as university supervisors. 1. Professor Titus I. Kanui PhD, Department of Veterinary Anatomy and Physiology, University of Nairobi. Signature 2. Dr. David K. Kariuki PhD, Department of Chemistry, University of Nairobi. k J !. Signature Date IX' !!■ Loll 3. Dr. P. M. Mbugua PhD, Department of Medical Physiology, University of Nairobi Signature Date IZ ' 11 -2ct\ I u DEDICATION. This thesis is dedicated to the following people; My beloved son Sean Murigi who changed my life and inspires everything I do, My late mother Jedidah Njoki whose sacrifice and dedication made all this possible, Larry Kamamia for showing me that a friend in need is a friend indeed and Dr. Simon Gicharu the Chairman Board of Trustees, Mt. Kenya University who daily by word and deed reminds me that one should strive to construct the world as it should be and not wallow and complain of what it currently is. “There is a tide in the affairs of men, Which, taken at the flood, leads on to fortune; Omitted, all the voyage of their life Is bound in shallows and in miseries. On such a full sea are we now afloat; And we must take the current when it serves, Or lose our ventures.” (Brutus in Julius Caesar by W. Shakespeare) 111 ACKNOWLEDGEMENTS; The completion of this PhD project would not have been possible without the help of the following; 1. My esteemed supervisors and mentors; Prof. Kanui, Dr. Mbugua and Dr. Kariuki for their valued guidance and advice. Without their help this project would not have taken off leave alone been completed. To them I give my deepest thanks and gratitude. I would like to pay particular tribute to Prof. Kanui for introducing me to the exciting and novel world of pain physiology. 2. The academic and technical staff of the department of Medical Physiology. I would like to particularly thank the chairman Prof. N.B. Patel for always been available to provide the needed administrative support. In particular 1 want to thank him for providing me with an office from which I could operate from. My deepest thanks to him. I would also like to thank Dr. Fred Bukachi whose arrival in the Department has been one of the most positive developments. I want to thank him for his encouragement and for his deep intellectual insights into science as well as positivity which are really rare attributes. I want to thank Opiyo, Moseti, Wafula, Nzivo and Mwaura for their valued help especially Wafula for his design of the animal restrainer used in the Tail Flick Test. 3. Past and present members of the lab for Neurophysiology and Nuropharmacology; that is Wambugu, Dulu, Musembi, Catherine, Githinji, Helen, Joachim. They provided a richly stimulating intellectual environment that 1 personally benefited from greatly. 4. Jackson Mugweru and Vivian Atieno from the Department of Vet Anatomy and Physiology. It is no exaggeration to say that without their technical help this project would not have been possible. 5. I would also like to thank all those people who contributed financially or in kind to the success of this project. In particular, I want to thank Drs, J.C. Irungu, Dr. Simon Muigai, Larry Kamamia, Githui and Nderitu as well as Edwin of Madawa Pharmaceuticals. My gratitude is beyond words. I would also like to express my deepest gratitude to Patrick Mutiso of Herbarium for his aid in collection and identification of plant samples and Tim Wango for always being there to help me sort out my computer problems. IV TABLE OF CONTENTS DECLARATION......................................................................................................................... H DEDICATION............................................................................................................................Ill ACKNOWLEDGEMENTS;....................................................................................................IV LIST OF FIGURES............................................................................................................... VIII LIST OF TABLES...................................................................................................................... X LIST OF APPENDICES............................................................................................................X LIST OF SYMBOLS AND ABBREVIATIONS.................................................................. XI ABSTRACT................................................................................................................................... 1 CHAPTER 1..................................................................................................................................3 CHAPTER TWO......................................................................................................................... 9 2.1 Pain and nociception..........................................................................................................10 2.2 The nociceptor and nociceptive transmission................................................................11 2.2.1. Mechanonociceptors....................................................................................................14 2.2.2. Chemonociceptors........................................................................................................15 2.2.3. Nociceptive transmission in the dorsal horn..............................................................16 2.2.4. Ascending nociceptive pathways................................................................................17 2.3. Pathological pain states.................................................................................................21 2.3.1. Peripheral sensitization...............................................................................................21 2.3.2. Central sensitization.................................................................................................... 24 2.4. Algogenic substances.................................................................................................... 27 2.4.1. Substance P.................................................................................................................. 27 2.4.2. Arachidonic acid metabolites.................................................................................... 28 2.5. Neurotransmitter systems in nociceptive transmission.......................................... 29 v 2.5.1. Cholinergic system...................................................................................................... 29 2.5.2. Glutaminergic system..................................................................................................30 2.5.3. Noradrenergic system................................................................................................. 33 2.5.4. Serotonergic system.....................................................................................................34 2.5.5. Gaba-ergic system...................................................................................................... 35 2.5.6. Opioidergic system..................................................................................................... 37 2.5.7. Endocannabinoid system............................................................................................39 2.6. Antinociceptive mechanisms........................................................................................41 2.6.1. Descending modulation of nociceptive transmission............................................... 41 2.6.2. Anatomical sites of origin of descending modulatory pathways.............................. 42 2.6.3. The dorsal horn of the spinal cord..............................................................................44 2.6.4. The hypothalamus........................................................................................................44 2.6.5. Nucleus tractus solitarius (NTS) and parabrachial nucleus..................................... 45 2.6.6. Rostroventral medulla (rvm)...................................................................................... 46 2.6.7. The periaqueductal grey area (PAG)......................................................................... 47 2.6.8. Medullary reticular nucleus........................................................................................ 48 2.6.9. Cortical and sub-cortical structures............................................................................48 2.7. Mechanisms of action of analgesics............................................................................ 49 2.8. Depression...................................................................................................................... 51 2.8.1. Monoamine hypothesis of depression..................................................................... 51 2.8.2.