NEUROCELLULAR PROFILE IN THE BRAIN OF THE AFRICAN GIANT RAT (Cricetomys gambianus, Waterhouse, 1840) MATTHEW AYOKUNLE, OLUDE DVM, M.Sc. (Ibadan) MATRIC NUMBER: 90513 A THESIS IN THE DEPARTMENT OF VETERINARY ANATOMY SUBMITTED TO THE FACULTY OF VETERINARY MEDICINE IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY (Ph.D.) OF THE UNIVERSITY OF IBADAN UNIVERSITY OF IBADAN LIBRARY 2014 i ABSTRACT The African Giant Rat (AGR) recently gained international prominence due to its ability to detect landmines and tuberculosis using olfactory and cognitive cues. However, a striking gap exists in the literature on the neurocellular components that govern these unique abilities. This study investigated and described the morphology of cellular components, useful morphometric parameters and neurogenesis profile of the brain of the AGR across age groups. Forty male AGR comprising 10 neonates, 15 juveniles and 15 adults obtained from the wild were used for this study. Brains were harvested, weighed and studied grossly. Cyto-architectural study on different brain regions was performed using Nissl and Haematoxylin-Eosin stains. Differential staining of sections was achieved using Golgi silver impregnation and Kluver Barrera methods for cortical neurons and myelin morphology respectively. Immunohistochemical identification of individual neurocellular populations was done using the following biomarkers: glia fibrillary acidic protein for astrocytes, 2’, 3’ cyclic nucleotide phosphodiesterase for oligodendrocytes, ionizing calcium binding adhesion molecule-1 for microglia, doublecortin for immature and migrating neurons and Ki-67 for proliferative neuronal cells. Histomorphometric analysis was carried out using the Axioskop and TSview photomicrographs. Findings were compared across age groups and quantitative data were analysed using One-way ANOVA at p = 0.01. Gross morphology showed part insertion of the falx cerebri between the olfactory bulbs (OB). Cyto-architecture revealed a persistent external granular layer in the post-neonatal cerebellum and multilayered ependymocytes in the ventricular lining. The presence of 4 to 8 glomerular cell layers and myelination across all layers were observed in the OB. Dense spiny multipolar populations of cortical neurons were found in layers II, III and V of the cerebral cortex. Astrocytes demonstrated age related changes and morphological heterogeneity with eight sub- types. Five oligodendrocyte and two microglia classes were identified. Doublecortin and Ki-67 positive cells were demonstrated in the active neurogenic sites (sub-ventricular zone (SVZ) and dentate gyrus (DG) of hippocampus). Other sites were the cortex, cerebellum, anterior commissure and olfactory bulb. Histomorphometric values in different brain regions in adults, juveniles and neonates include maximum cortex width (19.27±0.2mm, 20.67±0.2mm, and 11.75±0.6mm) and cortex volume (2.84±0.0cm3, 3.16±0.1cm3 and 0.23±0.0cm3) respectively. Ki-67 cell count in the SVZ and DG respectively were also highest in juveniles (45530±13950 and 12480±7860) as against adults (6880±340 and 1130±150) and neonates (21145±8395 and 11800±1230). Findings in the olfactory bulb, multipolar neurons and the rare occurrence of myelination across all olfactory bulb layers indicated enhanced olfactory acumen. Increased receptive fields and synaptic glomerular surface area is also indicative of greater integrative computational capabilitiesUNIVERSITY. The juvenile African giant OF rat is clearlyIBADAN shown to have LIBRARY a greater capacity for neuroplasticity and thus, proposed as a model for rodent studies on olfaction and cognition. Keywords: Neurocellular profile, Neurogenesis, Cricetomys gambianus, Neuroplasticity Word Count: 441 ii ACKNOWLEDGEMENT Special thanks go to my Supervisor Professor J.O. Olopade who has challenged and encouraged me to become a better man in this chosen career path and also to his wife Dr Mrs. F.O. Olopade for endless encouragements. To my overseas supervisor and research host, Professor Ihunwo, Amadi Ogonda, I am eternally indebted to you, your biological family and the University of Witwatersrand, Johannesburg, South Africa family. I have unwavering admiration and appreciations for my academic grandfathers; Professors B.O. Oke and S.K. Onwuka for their belief in me. Appreciation goes to the immediate past head of department (Dr P.C. Ozegbe), lecturers and staff of the department of Veterinary Anatomy University of Ibadan: Dr M.A.S. Nsien, Dr M.A. Akpan, Messrs Shina Ramoni, Chinedu Ihekanwa, Ayo Ajayi and Mrs Bukola Adeyemo. To all my colleagues during the Ph.D. course Drs Samuel, O., Olukole, S.G., Igado, O.O, Aina,O.O., Adebayo, A.O. for their encouragement and love. I wish you all great success. I thank Professor Paul Manger, Mrs Hasiena Ali, Monica Gomez, Sharon Rogers, Mr Pilani Nkomozepi. Ola Olaleye. Dr Moyo Ajao, etc. who made my three research visits to South Africa more meaningful with their useful advice and support. I acknowledge the support of my head of department in FUNAAB, Dr A.K. Akinloye, a great leader who quietly moves you forward. Also, I appreciate lecturers and Staff of the Department of Veterinary Anatomy, University of Agriculture, Abeokuta for their encouragements and prayers. Mr. Anise gave technical support, Dr Seun Mustapha for positive criticismsUNIVERSITY and constant support, Dr and OF Mrs. Adebayo,IBADAN Dr Olurode, LIBRARY Oloye, Takeet amongst many, for constant encouragement. iii I say a big thank you to Dr Tope Ogunbunmi, Dr Tope Falade, Dr Sola Idowu for ready assistance whenever needed. Thanks to the pioneering and incumbent Dean of the College of Veterinary Medicine, UNAAB, Professor E.B. Otesile who always showed no small interest in my development; a father indeed. The second Dean of COLVET, Professor Mrs. Dipeolu for support while on the seat. I thank the immediate past Dean, COLVET, FUNAAB, Professor R.O.A. Arowolo for prayers and support. To my wife (Barrister Mrs. Ibidun Ayo-Olude) and our sons Master Ogo-Oluwakiitan and IseOluwani Olude and OroOluwaMayokun; where would I be without you all? Thanks for always urging me on and understanding with me at those times I stared at the computer endlessly or went away on laboratory work for months. Ibidun, you are the most important person in my life after God. Thanks to my parents and parents in law: Mr. and Mrs. Kolawole Olude, Professor and Mrs. T.L. Olawoye. My siblings Mr. Dehinde and Mrs Olubunmi Ogundipe and their son Oluwamurewa Ogundipe, Siji Olude, Olajumoke Olude, Mr and Mrs Oyegoke, Dr and Mrs Adeyemo, Dr and Dr (Mrs.) Udoh, Bolaji Olawoye to name a few. To my church family at Restoration Bible Church, especially Pastor Richard and Ireti Asakhome, The Awotades, The Laanibas, Mr Matthew Anosike, Dr. Dare Morakinyo, .just to mention a few, you are a people of excellence, living purposefully. I love you all. I thank myself for a job considerably well done and for not giving up. It was worth my while. Finally, to the only wise God, Immortal, Invisible to whom be all the glory forever (Amen).UNIVERSITY OF IBADAN LIBRARY iv DEDICATION This project is dedicated to the glory of God, my wife and three sons who are the best mirrors of God’s love to me daily, here on earth. I’m eternally grateful. I dedicate this work again in loving remembrance of Olatubosun AnjolaOluwa (1977- 2010) and Titilope Irebowale Agbato (1980-2013). You were beautiful in your lives; sleep on in the bossom of your creator till we meet to part no more. “In such difficult fields, however, the full truth rarely emerges at one strike. It is pierced together, little by little, through many trials and corrections” Santiago Ramon y Cajal 1852-1934 Recollections of my life UNIVERSITY OF IBADAN LIBRARY v CERTIFICATION I hereby certify that this research was carried out by Olude, Matthew Ayokunle, Matric. number 90513 under my supervision. …………………………………… Professor Olopade, J. O. D.V.M, Ph.D. Department of Veterinary Anatomy, Faculty of Veterinary Medicine, University of Ibadan UNIVERSITY OF IBADAN LIBRARY vi TABLE OF CONTENTS Title Page … …… …… …… …… …… …… …… …… …… i Abstract … …… …… …… …… …… …… …… …… …… … ii Acknowledgements… …… …… …… …… …… …… …… … … iii Dedication… …… …… …… …… …… …… …… …… …… … v Certification… …… …… …… …… …… …… …… …… …… … vi Table of contents… …… …… …… …… …… …… …… …… … vii List of tables… …… …… …… …… …… …… …… …… …… … xiii List of figures… …… …… …… …… …… …… …… …… ….. xiv List of abbreviations and definitions… …… …… …… …… … … xviii CHAPTER ONE: INTRODUCTION… … … … … … … 1 1.1 Justification… … … … … … … … … … 2 1.2 Study hypothesis and Research questions… … … … … 2 1.3 General Objectives … … … … … … … … 2 1.4 Specific Objectives… … … … … … … … 3 CHAPTER TWO: LITERATURE REVIEW… … … … … … 4 2.1 Taxonomy… … … … … … … … … 4 2.1.1 Current Taxonomic Trends in AGR Classification … … … … 4 2.1.2 The Zygomasseteric System … … … … … … … 7 2.1.3 Family- Nesomyidae … … … … … … … … 9 2.1.4 Subfamily: Cricetomyinae … … … … … … … 9 2.1.5 Genus:UNIVERSITY Cricetomys … … … OF… IBADAN… … … LIBRARY… …. 10 2.2 Phylogeny … … … … … … … … … 10 2.3 Natural History … … … … … … … … … 10 2.4 Habitat … … … … … … … … … 11 vii 2.5 Physical description … … … … … … … … 11 2.6 Lifespan and longevity … … … … … … … 12 2.7 Behaviour … … … … … … … … … 12 2.8 Food habits … … … … … … … … … 12 2.9 Ecosystem roles … … … … … … … … 13 2.10 Distribution … … … … … … … … … 13 2.11 Uses and economic advantage … … … … … … 13 2.11.1 Economic Importance for Humans: Negative … … … … … 13