Biology Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2749

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    Peripheral neural coding strategies for spectral analysis and sound source location in the non-teleost bony fish, Acipenser fulvescens
    (2008-04-26) Meyer, Michaela; Popper, Arthur N.; Fay, Richard R.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This work is an investigation of coding strategies for spectral analysis and sound source location in Acipenser fulvescens, the lake sturgeon. A. fulvescens belongs to one of the few extant non-teleost ray-finned fishes. The sturgeon taxonomic family, the (Acipenseridae), has a phylogenetic history that dates back about 200 million years. Studies on sensory coding in any species of this family or any other non-teleost species have not been conducted before. Thus, this is the first study on peripheral coding strategies by the auditory system in a non-teleost bony fish. For this study, a shaker system, similar to that used in previous experiments on teleosts, was used to simulate particle motion of sound at the ears and auditory periphery of A. fulvescens. Simultaneously, electrophysiological recordings of isolated single units from the eighth nerve were obtained. Peripheral coding strategies for spectral analysis and sound source location in A. fulvescens resembled those found in teleosts. Frequency data resembled the characteristics found for auditory afferents (with preferences for lower frequencies) in land vertebrates. In addition, the auditory periphery in A. fulvescens appears to be well suited to encode the intensity of sound. In terms of mechanisms for sound source location, eighth nerve afferents responded to directional stimuli in a cosine-like manner (as in teleosts), which can generally serve as the basis for coding the location of a sound source. Certain differences to teleosts were also found in A. fulvescens and these may have implications for the mechanisms for sound source location in azimuth. The common physiological characteristics between A. fulvescens, teleosts, and land vertebrates may reflect important functions (that are part of the process of auditory scene analysis) of the auditory system that have been conserved throughout the evolution of vertebrates.
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    Unconventional Myosins in Fish Ears
    (2005-04-21) Coffin, Allison; Popper, Arthur N; Kelley, Matthew W; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Unconventional myosins are critical motor proteins in the vertebrate inner ear. Mutations in both myosins VI and VIIa cause multiple forms of human hereditary deafness but the precise function of these proteins is unknown. This dissertation uses a comparative approach to better understand the role of myosins VI and VIIa in vertebrate ears. Gene expression and protein distribution for these two myosins is examined in the ears of evolutionarily diverse fishes. RT-PCR data shows that myo7a is expressed in the ears of all taxonomically diverse fish species examined here, and immunofluorescence reveals that myo7a protein is distributed throughout the sensory hair bundles of all inner ear regions. Myosin VI expression and distribution is more complex. Studies in other laboratories show that zebrafish (Danio rerio) have two myo6 paralogs with differing gene expression patterns. This dissertation extends previous findings by showing that all teleost fishes have two myo6 genes while non-teleost fishes and tetrapods have one, suggesting that myo6 duplication occurred in an ancestral teleost, probably during a genome-wide duplication. RT-PCR experiments suggest that both myo6 paralogs are expressed in teleost ears. mRNA localization with in situ hybridization shows, however, that myo6a is not expressed in sensory epithelia. Immunocytochemical data shows that myo6 protein is distributed throughout hair bundles in all inner ear end organs of the sea lamprey (Petromyzon marinus) and the zebrafish but is not found in utricular hair bundles in other fishes. While protein expression studies find that the myo6 antibody used in this dissertation binds to both myo6 proteins in the zebrafish, the gene expression studies suggest that only myo6b is expressed in hair cells, and therefore that this is differential distribution of a single protein. This dissertation adds depth to current studies of myo6-associated hereditary deafness and suggests that comparative studies between zebrafish and other fishes such as shad (Alosa sapidissima) that differ in myo6 protein distribution will help elucidate the function of this critical hair cell protein. Comparisons between the two myo6 paralogs will further aid in functional studies and shed light on evolutionary processes during the teleost radiation.