Document Type

Dissertation/Thesis

Date Created

5-6-2021

Embargo Date

5-6-2022

Abstract

In the United States, loss of hearing impacts approximately 48.1 million people. The cumulative effects of noise are experienced in every area of society whether occupational, environmental, or through aging. A number of studies have linked noise induced hearing disorders to changes in spontaneous neuronal activity in certain auditory brain regions, especially, the inferior colliculus, a region that integrates auditory inputs from both ascending and descending pathways. However, the exact neurochemical basis of these disorders remains elusive. Currently, there are several compelling pieces of evidence that implicate the monoamine neurotransmitter, dopamine, in auditory processing. Based on this data, we have hypothesized that changes in the dopamine system within the inferior colliculus would contribute to the neural dysfunction underlining noise induced hearing loss. To examine this hypothesis, 32 Adult Sprague Dawley rats were used. The present work optimized a fast scan cyclic voltammetry (FSCV) assay and used it to characterize the dopamine system in rat brain, then examined the impact of loud noise on the system and finally, explore possible mechanisms underlying noise induced changes in the system. The FSCV assay provided the speed, selectivity, sensitivity, and the spatial resolution needed for the neurochemical measurement. The assay also allowed simultaneous detection and monitoring of both dopamine and another monoamine, norepinephrine in the inferior colliculus for the first time. These signals were pharmacologically confirmed and were found to be significantly and simultaneously attenuated by exposure to loud noise that has been characterized to cause permanent deafness. This data suggest that monoamines may play a crucial role in auditory processing and that changes in both dopamine and norepinephrine neurotransmissions are associated with noise induced hearing loss. D2 receptor functionality was examined as a possible mediator of the noise-induced changes in the dopamine neurotransmission, but revealed no significantly alteration following noise exposure. Nonetheless, immunocytochemistry data demonstrated noise-induced attenuation in the receptor distribution in the inferior colliculus, an effect that implicate the D2 receptors in deafness related changes in the inferior colliculus. Overall, the combination of FSCV and immunocytochemistry provided new insights and sets the stage to further understand the role of monoamines in the central auditory processes.

Keywords

FSCV; hearing loss; fast scan cyclic voltammetry; inferior colliculus; immunocytochemistry

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