We have recently developed and tested a new computational method for experiment prototyping at the Advanced Test Reactor (ATR). The method significantly reduces neutronic computation time while maintaining computational accuracy. In this thesis, we present the method and describe the techniques that we used to implement it. We then qualitatively and quantitatively analyze its performance for absorptive and multiplicative experiment perturbations over a single region and across multiple regions of the ATR. We conclude with a discussion of future research that might be conducted on the method. / text

published_or_final_version / Physiology / Doctoral / Doctor of Philosophy

published_or_final_version / Orthopaedics and Traumatology / Master / Master of Medical Sciences

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Anatomy / Doctoral / Doctor of Philosophy

published_or_final_version / Anatomy / Master / Master of Philosophy

published_or_final_version / Pharmacology and Pharmacy / Master / Master of Philosophy

Upon aging, the intervertebral disc (IVD) inevitably undergoes degeneration characterized by biochemical and morphologic changes. IVD degeneration can lead to multiple clinical disorders such as back and neck pain, and myelopathy. Low back pain can disable up to 85% of the adult population and results in a significant restriction of social activities and inability to work. Such disorder incurs billions of dollars in medical expenditures each year. Despite advances in the detection and treatment of the degeneration, the regeneration of the IVD remains low because current therapies are limited by exogenous curing approaches. New strategies for the reversal of IVD degeneration, including gene, cytokine, and stem cell therapies that can influence the anabolic and catabolic pathways in disc cells have been under investigation. These therapies aim to rejuvenate or replace diminished nucleus pulposus cells in the degenerative IVD. Recent reports have put forth a proposal of “endogenous disc stem cells”, suggesting that cells derived from the degenerative IVD tissue possess stem cell properties. These putative stem cells are believed to regulate the development and homeostasis of the IVD tissue. In this study, we identified and characterized a stem cell population from the IVD of healthy Rhesus monkey, termed disc stem/progenitor cells (DSCs). We show that the DSCs possess clonogenicity, multipotency and self-renewal capacity. The DSCs are phenotypically similar to bone marrow mesenchymal stem cells (BMSCs) but they are not identical. The DSCs show a faster growth rate under hypoxia than normoxia. DSCs derived from nucleus pulposus (DSCNP) show a stable expression level of hypoxia inducible factor-1 alpha (Hif-1ａ) in response to hypoxia. DSCs derived from annulus fibrosus (DSCAF) are more resistant to apoptosis under hypoxia than DSCNP. More importantly, small leucine-rich proteoglycans (SLRPs) are identified as important DSC niche components. We show that biglycan (bgn) and decorin (dcn) reduce the susceptibility of DSCs to hypoxia-induced apoptosis by promoting the expression of hypoxia inducible factors (HIFs). Our findings suggest that DSCs rely on the unique niche components for survival. In summary, our findings propose the existence of endogenous stem cells in IVD. Further study of the DSCs may provide new insights into the biology of IVD and facilitate the design of new strategies to treat disc degeneration in future. / published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Benefiting from higher SNR as well as better spatial, temporal and spectral resolution, magnetic resonance imaging (MRI) at high field has proved to be a valuable neuroimaging modality which provides comprehensive evaluation of the central nervous system non-invasively. The objectives of this doctoral work were to develop MRI methodologies and to assess the functional, metabolic and structural alterations in rodent brains under normal and manipulated conditions. Firstly, to improve the functional sensitivity and spatial precision, a novel functional MRI (fMRI) method using balanced steady state free precession with intravascular susceptibility contrast agent was proposed and its feasibility was evaluated in rat visual system. This new approach was sensitized to cerebral blood volume (CBV) changes. It provided comparable sensitivity to conventional CBVweighted fMRI using echo planar imaging but with no severe image distortion and signal dropout. Robust negative responses during visual stimulation were observed and activation patterns were in excellent agreement with known neuroanatomy. As a promising alternative to conventional CBV-weighted fMRI, it was particularly suited for fMRI investigation of animal models at high field. Secondly, the relationship between anatomical connections and resting-state fMRI connectivity was explored using a well-controlled animal model of corpus callosotomy. Both complete and partial callosotomy resulted in significant loss of interhemispheric connectivity in the cortical areas whose primary interhemispheric connections via corpus callosum (CC) were severed. Partial restoration of interhemispheric connectivity and increased intrahemispheric connectivity were also observed. The experimental findings directly supported that anatomical connections via CC play a primary and indispensable role in resting-state connectivity, and that resting-state networks could be dynamically reorganized or acquired directly or indirectly through the remaining anatomical connections. Thirdly, proton magnetic resonance spectroscopy (1H MRS) was employed to monitor the longitudinal metabolic alterations elicited by exogenous stimulation and endogenous modification, respectively. Significantly lower hippocampal N-acetylaspartate (NAA) was observed in fear conditioning animals, indicating reduced neuronal dysfunction and/or integrity, which contributed to the trauma-related symptoms. Meanwhile, pregnant animals exhibited prominently higher hippocampal NAA level, reflecting the increased density of neurons in this region, which might facilitate supporting behaviors that involving learning and memory. The 1H MRS detection of ongoing neurochemical changes induced by fear conditioning and pregnancy, especially in the hippocampus, can shed light on the mechanisms of learning and memory and the neurochemical underpinnings of behavioral improvement in pregnant animals. Lastly, manganese-enhanced MRI (MEMRI) was employed to investigate the hypoxic-ischemic (HI) injury in the late phase and the neural response to conditioned fear. Significantly higher enhancement in T1-weighted images was found in the peri-lesional region 24 hours after manganese administration and it colocalized with the increase in glial cell density in histological staining, demonstrating the existence of reactive gliosis in the late phase after HI injury. In fear conditioned animals, higher manganese uptake was observed in amygdala, hippocampus, paraventricular nucleus of hypothalamus and cingulate cortex, which were all highly-involved in the process of fear. These findings suggested MEMRI approach were useful in investigation of post-injury cellular events and functional reorganization as well as for in vivo mapping of neuronal activity. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

　　Vad1.3 is an evolutionarily-conserved, testis-specific gene identified from a retinol-treated Vitamin A-deficiency (VAD) rat model. VAD1.3 is expressed throughout spermiogenesis at the acrosome of spermatids and epididymal spermatozoa, suggesting a role in acrosome biogenesis or acrosome reaction. The present study aimed to explore the functional role of VAD1.3 in spermatogenesis and sperm functions by the cellular and gene-knockout approaches. 　　Double immunofluorescent microscopy confirmed the co-localization of VAD1.3 and syntaxin 1 in mouse spermatids and spermatozoa. Deletion analysis of the Vad1.3 gene in transfected mouse spermatocyte GC2-spd and human cervical cancer HeLa cells revealed a polarized peri-nuclear/Golgi expression pattern for the N-terminal GFP-VAD fusion proteins which contain a bipartite nucleus localization (BNL) motif, but a nuclear expression pattern for the C-terminal GFP-VAD. The N-terminal sequences of VAD1.3 mediated its interaction with syntaxin 1, as demonstrated by both co-localization and co-immunoprecipitation studies. The full-length GFP-VAD co-localized with the Golgi markers and was redistributed into the endoplasmic reticulum after brefeldin A treatment, suggesting that VAD1.3 was recruited through the ER-Golgi-acrosome pathway. 　　Vad1.3+/- mice was previously generated by the conventional knockout approach. The heterozygous mice had normal spermatogenesis during postnatal days and adulthood (6-8 weeks). At the age of 8-19 months, 6 out of 17 heterozygous mice but no wild-type exhibited a decrease in the epididymal sperm count and testicular weight (p < 0.05). Histological analyses unveiled disarrangement of the seminiferous epithelium and sloughing of germ cells, predominantly spermatids, which was mediated partially by apoptosis as a higher percentage of TUNEL-positive cells were detected in these heterozygous mice (p < 0.05). This phenotype was associated with a decrease in the mRNA (p < 0.05) and protein levels of VAD1.3 in the testis. 　　Crossing of the Vad1.3+/- mice produced wild-type and heterozygous offspring in a ratio of 1:3, but no Vad1.3-/- mice were found. There was no significant difference between the heterozygous intercrosses and the wild-type intercrosses in the number of oocytes ovulated, the developmental rate of embryos from zygotes to blastocysts, the number of implantation site, resorption site or the offspring could result from defective fertilization between Vad1.3 null gametes rather than developmental lethality. The role of VAD1.3 in fertilization was supported by the inhibitory effects of the anti-VAD1.3 antibody on in vitro fertilization and progesterone-induced acrosome reaction. Immuno-staining revealed that VAD1.3 was present in the acrosome-intact spermatozoa but not in acrosome-reacted spermatozoa, indicating a role of VAD1.3 in ZP-binding or acrosome reaction rather than sperm-egg fusion. In oocytes VAD1.3 was distributed in the cytoplasm near the cortex. litter size. Only a few Vad1.3-/- embryos were found at the zygotic (3.7%) and 2-cell (3%) stages in the heterozygous intercrosses. These findings suggested that the absence of the Vad1.3-/- 　　In sum, VAD1.3 may play important roles in fertilization and spermatogenesis in mice. The BNL motif of VAD1.3 directs its Golgi expression and the N-terminal sequence of the protein mediates its interaction with syntaxin 1. The use of tissue-specific knockout approach may help to answer the functional role of VAD1.3 in future. / published_or_final_version / Obstetrics and Gynaecology / Doctoral / Doctor of Philosophy