Date of Award


Document Type


First Advisor

Stephen Gardner

Second Advisor

Edward Bartlett

Third Advisor

Kevin Moore


Aging is an increasingly important research topic due to the aging populations in the United States and other developed countries. One aspect of aging, age-related hearing loss, is caused by changes in the peripheral and the central auditory systems. The age-related changes in the central auditory system, including the integrating midbrain area inferior colliculus (IC), are not well understood. Studies have revealed that GABA levels in the IC decrease with age. However, no studies have quantified the age-related changes in IC glutamate levels or the relationship between GABA and glutamate levels in the aging IC. This study aimed to elucidate the agerelated changes in glutamate levels and to understand the role of the inhibition—excitation balance in the aging IC. Auditory brainstem responses (ABR) were collected from four young and four aged Fischer-344 rats prior to neural tissue processing. Secondary immunofluorescent staining for GAD67 and VGluT2 was performed on 35 μm sections of IC. Confocal images were captured at 63x and the GAD67 and VGluT2 images were analyzed separately. We found that the staining intensity of both GAD67-immunoreactive (-ir) and VGluT2-ir presynaptic terminals decreased significantly with age; however, terminal size was not related to age. Additionally, we found a significant relationship between click ABR wave IV amplitude and the GAD67:VGluT2 ratio for both terminal area and terminal staining intensity, indicating the importance of the inhibition—excitation relationship to IC function. This contributes to the understanding of agerelated hearing loss and may be translated into more effective hearing loss treatments.


Honor Scholar thesis