Date of Award

Summer 8-16-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Engineering

First Advisor

Teresa Murray

Abstract

Following traumatic brain injury (TBI) and stroke, secondary injury cascades can lead to axonal damage and persistent microglia activation, respectively, in subcortical regions of mice. Current techniques, such as diffusion tensor imaging (DTI) and histology are used to observe features related to damage, but DTI lacks cellular resolution and histology is conducted on fixed tissue, preventing longitudinal studies in the same mouse. The combination of cranial windows and multiphoton microscopy (MPM) is used to image cells in the upper layers of the mouse cortex, but resolution rapidly degrades with imaging depth, making it difficult to observe white matter and subcortical regions following TBI and stroke. To circumvent this challenge, a novel imaging system was developed capable of obtaining longitudinal data related to this secondary damage in subcortical regions of mice.

An existing technology, gradient refractive index (GRIN) lenses, was used in conjunction with MPM to image mice before and after injury models. GRIN lenses were attached to low profile head plates and surgically implanted into the brain of mice to acquire time-lapse images of white matter for 60 days following midline fluid percussion injury and microglia 24 hours after a MCAo stroke model. Thy1-YFP and Cx3cr1- tdTomato mice were used to compare changes in white matter fiber tracks and microglia dynamics, respectively. In a model of stroke, injured mice exhibited larger soma areas as compared to control treated animals, demonstrating their activated morphology. When the potential therapeutic, Annexin A1, was administered, treated animals had smaller soma areas as compared to the saline treated animals, signifying Annexin A1’s potential to mitigate inflammation. The system was also used in a model of TBI and the results indicated injured animals developed significantly more varicosities and terminal bulbs than uninjured animals. When minocycline, an FDA approved antibiotic, was administered, treated animals had fewer varicosities and terminal bulb development, demonstrating the potential of the therapeutic to protect against axonal degeneration following TBI. Overall, the imaging system was successfully used in preclinical trials to demonstrate the effectiveness of two potential therapeutics in two brain injury models.

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