Publication Date

8-2014

Advisor(s) - Committee Chair

Michael Smith (Director), Steve Huskey, Nancy Rice

Degree Program

Department of Biology

Degree Type

Master of Science

Abstract

Melanin is the dark pigment found in most organisms that gives color to the skin, hair, feathers, and eyes of vertebrates. While melanin is known to also be present in the stria vascularis of the mammalian cochlea, its function in the inner ear is still unknown. Some previous studies have indicated that melanin may serve to protect the mammalian ear from hearing loss. Minimal previous research on melanin within the inner ears of fishes has been conducted. In this study, the melanin levels in the inner ears of different color morphs of two fish species (Poecilia latipinna and Cyprinus carpio) were examined, as well as the potential protective role of melanin from acoustical stress. To identify the relationship between fish color morph and inner ear melanin, a spectrophotometric melanin assay was used for dissected inner ears, and transmission electron microscopy (TEM) was used to examine melanosome structure in the crus commune of the inner ears. For each color morph and species, hearing thresholds were quantified before and after sound exposure (150 Hz tone at 165 dB re 1 μPa for 48 h) by measuring auditory evoked potentials (AEPs). Melanin levels were associated with scale color, with black morphs having more inner ear melanin than white or golden morphs. TEM imaging showed that melanosome size varied among color morphs, with black P. latipinna morphs having larger melanosomes than white morphs. Hearing thresholds did not differ significantly among color morphs before sound exposure in either species. However, hearing thresholds post-sound exposure and the associated threshold shifts significantly differed between black morphs and other color morphs in the two species, with black morphs having lower thresholds and exhibiting less hearing loss than the other morphs. This suggests that melanin plays a protective role in the teleost inner ear, similar to what other researchers have found in mammalian models. Teleost fishes may be a new, more efficient model for testing melanin's function in the inner ear and how it interacts with stress from acoustical trauma and ototoxic drugs.

Disciplines

Biology | Marine Biology | Physiology

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