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ABSTRACT

This study was designed to compare some fear response structures in three (3) domesticated animals: Sheep (Ovis sp), Goat (Capra sp), and Dog (Canis sp.) and relate it to the different responses of these animals to threats and dangers. Seven (7) dogs, seven (7) goats, and seven (7) sheep were used in this study. The animals were decapitated, their skulls were exposed and brain tissues fixed immediately in 10% formal saline solution. After fixation, each brain was carefully removed from the skull and studied. The number of gyri and sulci on the surfaces of the cerebrum were counted. Morphometric analysis involved measurement of brain weight, volume, dimensions (cerebral and cerebellar length and width). Histomorphology and histomorphometry of layer V cells of the prefrontal cortex, CA3 region of the hippocampus, and basolateral complex and central amygdala were carried out. This also included counting the number of neurons in these brain regions to determine which region of the fear circuitry had the most number of neurons in each animal. Morphological studies revealed similar brain structure of these mammalian brains with dog having an enlongated frontal lobe, fewer gyrifications, and more caudolateral expansion of the cerebrum when compared with goat and sheep (p<0.05). Morphometry revealed significant differences in brain weight, brain volume, cerebral length and width, and cerebellar length and width between dog, goat, and sheep (p<0.05). Results showed that goat had the largest soma size (57.60±9.65μm) and dendritic aborization (153.79±35.27μm) of layer V cells of the prefrontal cortex while dog had the most number of neurons in this region. The number of CA3 cells of the hippocampus was the most in dog. However, sheep had the largest soma diameter (41.61±11.46μm) in its CA3 cells of the hippocampus. Dog basolateral cells of the amygdala were the largest in both soma size and dendritic aborization (27.93±11.10μm, 88.06±38.15μm, respectively). Sheep had the least number of neurons in its
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central amygdala, while dog had more densely packed central nucleus neurons. Although sheep had the largest brain weight and volume, it had the least densely packed cells in its Prefrontal cortex which is responsible for higher cognitive function. This could explain why dog is more intelligent than sheep and goat in their response to threatening situations. Dog Hippocampus had the most densely packed neurons. This accounts for dog’s better memory of a threatening situation and its quicker response than sheep and goat. The Central nucleus of Dog amygdala had the most densely packed neurons. This could explain why dog expresses fear emotions quickly either by fleeing or fighting back in comparison with sheep. Therefore, the local breeds of sheep, goat, and dog demonstrated significant differences in their brain morphology and morphometry, grossly and histologically, and this could be related to their different behaviours when it comes to responding to threats and danger in which sheep reacts very slow while dog responds faster in comparison.

 

 

TABLE OF CONTENTS

Cover Page i Title Page ii Declaration iii Certification iv Dedication v Acknowledgement vi Abstract vii-viii Table of Contents ix-xx List of Tables List of Figures xiv List of Plates xv CHAPTER ONE
1.0 Introduction…………………………………………………………………………………………………1
1.1 Statement of Research Problem……………………………………………………………….2 1.2 Significance of the study………………………………………………………………………2 1.3 Research Hypothesis…………………………………………………………………………..2 1.4 Aim……………………………………………………………………………………………2 1.5 Objectives……………………………………………………………………………………..2 CHAPTER TWO
2.0 Literature Review…………………………………………………………………………….3
2.1 Sheep, goat, dog and their behavior…………………………………………………………3
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2.2 Circuitry of fear……………………………………………………………………………..5 2.3 Sensory input converging at the amygdala………………………………………………….7 2.4 The Amygdaloid complex……………………………………………………………………8 2.4.1 The deep or basolateral group/ complex…………………………………………11 2.4.2 The centromedial nuclei………………………………………………………….15 2.4.3 corticomedial nuclei………………………………………………………………19 2.4.4 Other amygdaloid nuclei………………………………………………………….19 2.5 The Hippocampus: Anatomy……………………………………………………………….20 2.5.1 The hippocampus proper…………………………………………………………24 2.5.2 Dentate gyrus……………………………………………………………………..26 2.6 The Prefrontal cortex: Anatomy…………………………………………………………….27 2.6.1 Cytoarchitecture of area 10 of the prefrontal cortex…….……………………….29 2.7 A morphometric study of the amygdala in the common shrew and guinea pig……………31 2.8. The amygdala and fear conditioning………………………………………………………32 2.8.1 Memory Vs. modulation…………………………………………………………35 2.8.2 The Amygdala, prefrontal cortex, Hippocampus and fear………………………36
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CHAPTER THREE
3.0 Materials and Methods………………………………………………………………………38
3.1Materials……………………………………………………….……………………………38 3.1.1 Animal heads…………………………………………………………………….38 3.1.2 Reagents………………………………………………………………………….38 3.1.3 Equipments and instruments……………………………………………………..38 3.2 Methods……………………………………………………………………………………..38 3.2.1 Removal of brain specimen from the skull…………………………..………….38 3.2.2 Gross morphological studies…………………………………………………….40 3.2.3 Gross morphometric studies…………………………………………………….40 3.2.4. Dissection of brain specimens………………………………………………….45 3.2.5 Tissue processing……………………………………………………………….46 3.2.6 Cell count and cell measurement (Histomorphometry)…………………………49 3.2.7 Statistical analysis……………………………………………………………….50
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CHAPTER FOUR
4.0 Results…………………………………………………………………………..…………..51
4.1Gross morphological studies………………………………………………………………..51 4.2 Gross morphometric studies………………………………………………………………..60 4.3 Histomorphological and histomorphometric studies……………………………………….62 4.3.1 Histomorphology of layer V cells of the prefrontal cortex of sheep, goat, and dog…62 4.3.2 Histomorphometry of layer V cells of the prefrontal cortex of sheep, goat, and dog..63 4.3.3. Histomorphology of CA3 cells of the hippocampus of sheep, goat, and dog………..74 4.3.4 Histomorphometry of CA3 cells of the hippocampus of sheep, goat, and dog………75 4.3.5 Dentate gyrus………………………………………………………………………….75 4.3.6 Histomorphology of neurons in the basolateral complex of the amygdala of sheep, …………goat, dog …………………………………………………………………………….86 4.3.7 Purkinje-like neurons in goat basolateral complex ………….……….……………….101 4.3.8 Histomorphology and histomorphometry of protoplasmic astrocytes surrounding the ………..cortical region of the amygdala………………………………………………………..103 4.3.9 Histomorphology of neurons in the central nucleus of the amygdala of sheep, goat,.and dog……………………………………………………………………………………….…….108
4.3.10 Histomorphology of the central nucleus of dog, goat, and sheep………………….….109
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CHAPTER FIVE
5.0 Discussion………………………………………………………………………………..120
5.1 Gross morphological and morphometric studies…………………………………………120 5.2 Histomorphological and histomorphometric studies of the prefrontal cortex, hippocampus, and the amygdala……………………………………………………………………………….122 5.2.1 Prefrontal cortex………………………………………………………………………….122 5.2.2 Hippocampus……………………………………………………………………………..123 5.2.3 Dentate gyrus……………………………………………………………………….……124 5.2.4 Amygdala…………………………………………………………………………………125 5.2.4.1 Basolateral complex cells………………………………………………………126 5.2.4.2 Protoplasmic astrocytes in the cortical region of the amygdala………………..128 5.2.4.3 Central nucleus………………………………………………………………..128 CHAPTER SIX 6.0 Summary, Conclusion, and Recommendation…………………………………………… 130 6.1 Summary…………………………………………………………………………………..130 6.2 Conclusion………………………………………………………………………………….132 6.3 Recommendation………………………………………………………………………….132 References…………………………………………………………………………………….134

 

 

CHAPTER ONE

1.0 INTRODUCTION Sheep, goats, dogs, and humans have been closely associated for a long time. Man’s “bestfriend”, the dog was the first specie to be domesticated, while sheep and goat occupy second and third places interchangeably in the domestication race (Schoenian, 2007). The local names of these species in three Nigerian languages are shown in table 1 below: Table 1.0: Local names of the sheep, goat, and dog in three Nigerian languages
LANGUAGE ANIMAL
HAUSA
IGBO
YORUBA
SHEEP
Rago
Aturu
Aguntan
GOAT
Akuya
Ewu
Ewure
DOG
Kare
Nkita
Aja
Sheep, goats, and dogs have evolved a unique and fascinatqying array of behavioral characteristics which have contributed to their survival and proliferation in a unique environmental niche. Studies in the ontogeny of fear behaviors in animals have revealed that fear responses differ across and within species. The limbic system structures as well as the prefrontal cortex are components of brain circuits that are involved in the regulation of the perception of memory, processing of fears, and emotional behaviours. Knowledge of the anatomy of fear response structures in the animals is essential in understanding their behavioral responses.
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1.1 STATEMENT OF RESEARCH PROBLEM Scanty literature exist on the comparative neuroanatomy of fear response structures in sheep, goat, and dog with respect to their different response to threats and dangers. 1.2 SIGNIFICANCE OF THE STUDY Domestic animals are very useful to man. Therefore, additional insight into the anatomy of the structures of fear response will help us understand the behaviour of these animals and improve their handling. This study will also add to the body of scientific knowledge. 1.3 RESEARCH HYPOTHESIS Variation in the structures of fear response in domestic animals is related to their behavioral differences. 1.4 AIM OF THE STUDY To elucidate the differences in the neuroanatomy of structures of fear response in sheep, goat, and dog and relate this to their different responses when they face fearful situations.
1.5 OBJECTIVES OF THE STUDY To identify morphological and morphometric differences and similarities on the brains of sheep, goat, and dog. To compare the histomorphology and histomorphometry of the prefrontal cortex, hippocampus, and amygdala of sheep, goat, and dog using H and E (Heamotoxylin and Eosin), Toludine blue, and Golgi silver stain. To determine the density of neurons in the prefrontal cortex, hippocampus, and amygdala of sheep, goat, and dog.
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