Graduation Date

Fall 12-18-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Pharmacology and Experimental Neuroscience

First Advisor

Dr. Yutong Liu

Abstract

Manganese-enhanced magnetic resonance imaging (MEMRI) opens the great opportunity to study complex paradigms of central nervous system (CNS) in freely behaving animals and reveals new pathophysiological information that might be otherwise difficult to gain. Due to advantageous chemical and biological properties of manganese (Mn2+), MEMRI has been successfully applied in the studies of several neurological diseases using translational animal models to assess comprehensive information about neuronal activity, morphology, neuronal tracts, and rate of axonal transport. Although previous studies highlight the potential of MEMRI for brain imaging, the limitations concerning the use of Mn2+ in living animals and applications of MEMRI in neuroscience research are in their infancy. Therefore, development of MEMRI methods for experimental studies remains essential for diagnostic findings, development of therapeutic as well as pharmacological intervention strategies.

Our lab has been dedicating to develop novel MEMRI methods to study the pathophysiology underlying neurodegenerative diseases in murine models. In the first study, we investigated the cellular mechanism of MEMRI signal change during neuroinflammation in mice. The roles of neural cells (glia and neurons) in MEMRI signal enhancement were delineated, and ability of MEMRI to detect glial (astrocyte and microglia) and neuronal activation was demonstrated in mice treated with inflammatory inducing agents. In vitro work demonstrated that cytokine-induced glial activation facilitates neuronal uptake of Mn2+,and that glial Mn2+ content was not associated with glial activation. The in vivo work confirmed that MEMRI signal enhancement in the CNS is induced by astrocytic activation by stimulating neuronal Mn2+ uptake. In conclusion, our results supported the notion that MEMRI reflects neuronal excitotoxicity and impairment that can occur through a range of insults that include neuroinflammation.

In the second study, we evaluated the efficacy of MEMRI in diagnosing the complexities of neuropathology in an ananimal model of a neurodegenerative disease, neuroAIDS. This study demonstrated that MEMRI reflects brain region specific HIV-1-induced neuropathology in virus-infected NOD/scid-IL-2Rγcnull humanized mice. Altered MEMRI signal intensity was observed in affected brain regions. These included, but were not limited to, the hippocampus, amygdala, thalamus, globus pallidus, caudoputamen, substantia nigra and cerebellum. MEMRI signal was coordinated with levels of HIV-1 infection, neuroinflammation (astro- and micro- gliosis), and neuronal injury.

Following the application of MEMRI to assess HIV-1 induced neuropathology in immune deficient mice humanized with lymphoid progenitor cells, our successful collaboration with Dr. Sajja BR (Department of Radiology, UNMC, Omaha, NE) led to the generation of a MEMRI-based NOD/scid-IL-2Rγcnull (NSG) mouse brain atlas. Mouse brain MRI atlases allow longitudinal quantitative analyses of neuroanatomical volumes and imaging metrics. As NSG mice allow human cell transplantation to study human disease, these animals are used to assess brain morphology. MEMRI provided sufficient contrast permitting 41 brain structures to be manually labeled on average brain of 19 mice using alignment algorithm. The developed atlas is now made available to researchers through Neuroimaging Informatics Tools and Resources Clearinghouse (NITRC) website (https://www.nitrc.org/projects/memribrainatlas/).

Finally, we evaluated the efficacy of N-acetylated-para-aminosalicylic acid (AcPAS) to accelerate Mn2+ elimination from rodent brain, enabling repeated use of MEMRI to follow the CNS longitudinally in weeks or months as well as inhibiting the confounding effects of residual Mn2+ from preceding administrations on imaging results. Two-week treatment with AcPAS (200 mg/kg/dose × 3 daily) accelerated the decline of Mn2+ induced enhancement in MRI. This study demonstrated that AcPAS could enhance MEMRI utility in evaluating brain biology in small animals.

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