Construction Of Magnetic Resonance Imaging Brain Atlas Of Model Animal Tree Shrew

Tree shrews are squirrel-like small mammals now commonly classified in the order of Scandentia.They process a variety of characteristics ideal in an model animal,such as small adult body size,short reproductive cycle and life span,low cost of maintenance,and high brain-to-body mass ratio.Comparative studies have revealed that the genome and neuroanatomical character of tree shrew share more similarities with that of primates than that of rodents.For several decades,tree shrews have long been proposed to be better model animals than rodents,and alternatives to non-human primates in biomedical researches.For studying on neurological/psychiatric diseases,tree shrew models have been used for psychosocial stress/depression,senile diseases,Parkinson's disease and drug addiction.Magnetic Resonance Imaging(MRI)has becoming a routinely used tool to study human and animal brain structure and function.Applying MRI neuroimaging approach to study the brain often requires digital atlas or/and template to delineate region-of-interest for morphological analysis and studying the structural and functional connection.Currently,few researches have applied MRI to study tree shrew brain.In addition,it remains lack of sufficient knowledge about tree shrew brain anatomy,e.g.,no detailed information on white matter fiber tract.The main goal of this dissertation was studying the anatomy and constructing atlas of tree shrew brain with MRI.This dissertation contains:1)construction of T2-weighted MRI atlas of tree shrew brain with major structure labeled;2)applying diffusion tensor imaging(DTI)and super-resolution track-density imaging(TDI)to characterize the micro-organization of gray matter structures in tree shrew brain;3)investigating white matter(WM)fiber tract in tree shrew brain thoroughly with DTI,constructing DTI-based WM atlas of tree shrew brain,and discussing the characteristics of tree shrew WM from the view of evolution.The chapter one introduced the basic information of tree shrew,MRI technology,and the goal and research scheme of this dissertation.The basic information contained the evolutionary status of tree shrew,tree shrew models of neurological/psychiatric diseases,and the research situation of tree shrew brain anatomy and atlas.The principle of MRI and diffusion weighted MRI methods used in this dissertation were introduced.The chapter two applied conventional T2-weighted structural MRI to construct tree shrew brain atlas with the major gray matter and some white matter structures labeled.The chapter three applied DTI and super-resolution TDI to characterize the micro-organization of tree shrew brain gray matter structures.The results demonstrated that DTI can properly reveal the laminar organization of superior colliculus and hippocampus,and distinguish some nuclei of amygdala and thalamus;compared with DTI,the super-resolution TDI could provide enhanced visualization of brain structures as well as novel meaningful anatomical information,such as the laterodorsal and anteroventral thalamic nucleus,and the laminar organization of primary visual cortex etc.The chapter four applied DTI to investigate tree shrew brain WM fiber tracts thoroughly.Immunohistochemical staining method was also carried out to reveal the microscopic properties of some elusive WM structures.Finally,a DTI-based WM atlas of tree shrew brain was constructed.In this chapter,the results also demonstrated that the WM of tree shrew brain shared more similarities with that of primates than that of rodents.For example,tree shrew possessed inchoate form of extreme capsule and arcuate fasciculus in primate which were not existed in rodents.The chapter five summarized the entire study of this dissertation,stated the limitation of this study,and offered some suggestions for constructing more complete MRI atlas of tree shrew brain.