Date of Award

Spring 2017

Degree Name

Doctor of Philosophy

Department

Biological Sciences

First Advisor

Dr. Christine Byrd-Jacobs

Second Advisor

Dr. Cindy Linn

Third Advisor

Dr. Christopher Pearl

Fourth Advisor

Dr. Blair Szymczyna

Keywords

Retrograde tract tracing, olfactory bulb, mitral cell dendritic arbors, deafferentation, adult zebrafish

Abstract

Sensory input is known to be critical to the maintenance of adult brain structures, and the removal of afferent input to the olfactory bulb of adult zebrafish, a popular model system, causes numerous degenerative effects. To study this damage on a cellular level, the primary output neurons of the olfactory bulb, mitral cells, were examined. The dendritic arbors of neurons are complex structures, with their shape and synaptic connections necessary for the maintenance of neuronal structure and function, yet within the adult brain the cellular interactions that moderate dendritic morphology are not yet well understood. The purpose of these studies was to examine alterations in structure and complexity of mitral cell dendritic arbors of adult zebrafish that occur with afferent removal, and investigate the potential for recovery of these structures. The major focus of this dissertation was to examine the effects of removal of sensory input, known as deafferentation, on mitral cell dendritic arbor structure and complexity. In the first study I examined permanent deafferentation and found that 8 weeks of deafferentation caused significant reductions in dendritic arbor structures but no significant changes in overall dendritic complexity. In the second study I investigated the effects of 8 weeks of repeated chemical ablation of the olfactory epithelium, resulting in reversible, incomplete deafferentation. Eight weeks of chronic partial deafferentation caused significant reductions in dendritic arbor structure and overall complexity. These results were similar to permanent deafferentation and provided us with a new model to examine dendritic plasticity and the ability of dendritic arbors to recover following reinnervation. In the third study I tested the potential of dendrites to recover from chronic, partial deafferentation. With 3 weeks of recovery, no significant differences between previously deafferented and internal control mitral cell dendritic arbor structures or complexity were found, suggesting recovery due to restoration of sensory input. With 8 weeks of recovery, there were differences in dendritic arbor structures compared to unlesioned control cells, leading us to examine potential growth-related changes to mitral cell dendritic arbors. Over 16 weeks, control fish showed evidence of growth in animal length, weight, and brain weight, which correlated with the increases in dendritic arbor structures and overall complexity. The final focus of this dissertation was to develop a novel method of deafferentation through the insertion of a wax ball into the olfactory organ. While it is not known if this method is reversible, qualitative and quantitative comparisons to permanent and partial chronic deafferentation showed similar effects on olfactory organ and olfactory bulb structures, providing us with an additional technique to study the importance of afferent input in the adult zebrafish.

This dissertation details the critical influence of sensory innervation on the maintenance of mitral cell dendritic morphology in the adult zebrafish and the ability of adult brain structures to recover following injury. Understanding structural plasticity of dendritic arbors with deafferentation and reinnervation is key to the potential for restoration of function after brain injury.

Access Setting

Dissertation-Campus Only

Restricted to Campus until

4-15-2027

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