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Abstract

Sensory neurons in the skin provide critical input for animal movement and a wide range of behaviors. In this thesis, I analyze the pectoral fin sensory neurons of larval zebrafish with a focus on the detailed anatomy of individual neurons that innervate the fins. In chapter 2, this work shows, for the first time, that the cell bodies of pectoral fin sensory neurons are located in both the hindbrain and the spinal cord. Single cell reconstructions of the entire primary afferent arborization revealed that many fin neurons branch widely across the fin and, in many cases, innervate both medial and lateral surfaces as well as the surface of the axial trunk adjacent to the fin. Fin sensory neurons exhibit four distinct soma morphologies, but they do not have any somatotopy with respect to fin regions. Agglomerative hierarchical clustering analysis reveals that the entire population of fin sensory neurons fall into three distinct clusters based on morphological parameters, suggesting possible subtypes. In chapter 3, I next examined the full sensory innervation of the fin's surface to better understand the fin as a sensory structure. In order to do this, I quantified the terminal distributions for the whole population of fin sensory neurons and dorsal root ganglia neurons innervating the fin structure. Comparison between full population-labeled and stochastically labeled individual neurons suggests that the stochastic labeling approach under sampled innervation of the lateral fin surface. By examining distances between nearest neighbor neuron endings, I found that single cells tended to innervate the fin in an organized fashion that prioritized filling space while self-avoiding whereas the whole population did not. Finally, terminal distributions at two locations of functional importance to sensation and movement, the fin membrane margin and the blood vessel, are not notably different from a control transect in the membrane, indicating a lack of functional specificity of terminal distributions. However, the density of terminals at the fin membrane margin is significantly higher than at the blood vessel. Taken together, the results presented in this thesis establish the neuroanatomy, including terminal distributions, of a tractable in vivo model that can be utilized for both anatomical and functional studies of a whole limb sensory system.

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