Date of Defense

4-21-2026

Date of Graduation

5-2026

Department

Biological Sciences

First Advisor

Christine Byrd-Jacobs

Second Advisor

Luke Kinsey

Third Advisor

Bonnie Ebendick

Keywords

Immunosuppression, microglia, regeneration, immune response, zebrafish, dexamethasone.

Abstract

Zebrafish possess a remarkable capacity for central nervous system regeneration, restoring neuronal structure and function following injury without forming the inhibitory glial scars commonly observed in mammals. This regenerative ability involves coordination across multiple biological systems and remains incompletely understood. Immune signaling, particularly the activity of microglial cells, is thought to play a critical role in this process. Experimental investigation of immune involvement in zebrafish neuroregeneration requires a reliable method for pharmacological immunosuppression. The present study evaluated the efficacy of the glucocorticoid dexamethasone (dex) as an immunosuppressive treatment in adult zebrafish by examining microglial labeling within the brain, using the olfactory system as a histologically accessible model region. Adult zebrafish (Danio rerio) were exposed to water-soluble dex (10 mg/L) for two, three, or four weeks, with partial water replacement every 48 hours to maintain drug concentration. Control animals were maintained without treatment. Following exposure, animals were euthanized and perfused with buffer. Brains containing the olfactory bulbs were dissected, paraffinembedded, and sectioned at 10 μm. Immunohistochemistry using the 4C4 microglial marker and HRPlabeled secondary antibodies was performed, and grayscale images were collected using brightfield microscopy. Microglial cells were manually quantified and classified by activation stage using a standardized counting procedure to reduce inter-rater variability. Immunohistochemical labeling successfully identified microglial cells across multiple brain regions, including the olfactory bulb, telencephalon, and diencephalon, with clear visualization of distinct activation states. Dex treatment did not produce a statistically significant reduction in microglial number within the olfactory bulbs compared to controls. These findings suggest that our sample size was too small and 10 mg/L water-soluble dexamethasone may be insufficient to induce measurable immunosuppression in adult zebrafish.

Access Setting

Honors Thesis-Restricted

Restricted to Campus until

6-25-2028

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Available for download on Saturday, June 24, 2028

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