Defense Date
2024
Document Type
Thesis
Degree Name
Master of Science
Department
Anatomy & Neurobiology
First Advisor
Dr. Dong Sun
Second Advisor
Dr. Andrew Ottens
Third Advisor
Dr. Kristy Dixon
Abstract
In the United States, more than 20.5 million adults over the age of 40 suffer from olfactory dysfunction, with TBI attributing to 5-17% of all olfactory dysfunction cases. Although often initially undetected and less conspicuous than other cognitive and behavioral impairments, olfactory dysfunction may have a significant negative impact on patients' quality of life and ability to accomplish activities of daily living, therefore the pathophysiology of these disorders should be understood. The production of neural stem cells enhances the repair and regeneration of the injured brain following a TBI. One of the primary endogenous neural stem cell generation sites in the adult mammalian brain is the subventricular zone (SVZ) of the lateral ventricles. Neuroblasts born in the SVZ migrate via the rostral migratory stream to the olfactory bulb (OB), giving rise to fully functional integrated cells. One of the major issues with new cells is their ability to survive to maturation and integrate into the neuronal network.
Following a TBI, the generation of new neurons and the regulatory mechanism driving their maturation and integration into the neuronal circuitry of the olfactory bulb is poorly understood. Notch1, a highly conserved transmembrane pathway plays a critical role in neural stem cell proliferation, differentiation, dendritic complexity, and apoptosis. In this current study, experiments were conducted to better understand neurogenesis in the OB following TBI and the regulatory role of Notch1 signaling. We hypothesized that TBI alters the developmental processes of adult generated neurons in the olfactory bulb and Notch1 signaling plays and important role in regulating this process. To test this hypothesis, we used transgenic mice with conditional knockout of Notch1 in nestin+ cells, along with matched control mice aged approximately 2-3 months. These mice underwent either a lateral fluid percussion injury (LFPI) or sham surgery. Following the injury, they received intraperitoneal injections of BrdU (50mg/kg) immediately after for 7 days to label newly generated injury-induced cells. At 4 or 8 weeks post-injury, the animals were sacrificed, and sections of the olfactory bulb were processed to detect the total number of cells positive for GFP and BrdU alone, or double and triple-labeled with the mature neuronal marker NeuN. The sections were then quantified using stereology.
We found that the absence of Notch1 in nestin+ cells significantly affected neural stem cell survival in the OB particularly at 8 weeks post-injury (WPI), where the injury group showed significantly higher numbers of BrdU+ and BrdU+/NeuN+ cells. These results suggest a time-dependent proliferation of neural stem cells, with notable differences observed at 8WPI compared to 4WPI. Additionally, consistent findings at 8WPI highlight the granule cell layer (GCL) as a crucial site for understanding injury's impact on OB neurogenesis and cell survival. For future studies, examining time points beyond 8 weeks could provide insights into the long-term survival of injury-dependent neurons and the effects of Notch1 inactivation on neural stem cell differentiation and proliferation in the OB. Additionally, incorporating a more severe injury model and functional assessments of olfaction would enhance our understanding of these processes.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
5-9-2024