Date of Award

Spring 2015

Document Type

Dissertation

Degree Name

Doctor of Audiology (AuD)

Department

Department of Communication Sciences and Disorders

Advisor(s)

Lincoln C. Gray

Abstract

Sound localization is an important aspect of normal hearing. The Eph/ephin family of signaling proteins, studied here, is known to guide the formation of central auditory connections in early development, particularly topographic inputs from the lateral superior olive (LSO) to the inferior colliculus (IC). Processing in the LSO and its influences on the IC are known to be heavily involved in sound localization tasks. One way to study sound localization in mice is through pre-pulse inhibition (PPI). PPI is the phenomenon by which a weak prestimulus inhibits the response to a subsequent startle stimulus. In studying sound localization, the prestimulus here is a soft, ongoing sound that switches between two speakers 180o apart. If the mouse hears a change in location, the acoustic startle response will decrease. Here we report three important considerations with this PPI speaker swap procedure. First, we show that the cage in which the mouse is tested is critically important. Depending on the testing chamber, we observed 17%, 33% and 100% of responsiveness noted in previously published studies. Second, homozygous but not heterozygous EphA4 mutations appear to affect sound localization. Finally, there appears to be subtle differences in startle responses for different mouse strains, with altered responses in both heterozygous and homozygous EphA4 mutants as compared with C57BL/6J controls. The connection between genetic effects on both afferent and efferent responsiveness may provide an experimental link between audiology and speech pathology, and thereby may serve as an animal model of altered central pattern generators.

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