The common marmoset (Callithrix jacchus) as a model for research in age-related hearing loss

Date

2012

Authors

Valero, Michelle Denise

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Abstract

This thesis describes the results from projects that investigated auditory function in the common marmoset (Callithrix jacchus) with the goal of developing this species as a model for studying human age-related hearing loss. The auditory brainstem response (ABR) was used to estimate hearing thresholds, and suprathreshold ABRs were measured to assess neural function. Distortion-product otoacoustic emissions (DPOAEs) were used to assess cochlear function. As the first to measure DPOAEs in marmosets, I first examined the reliability of DPOAE measurements in marmosets (Chapter 2) in different test/retest conditions. The general findings were in agreement with previous reports of reliability in DPOAEs measured from humans: reliability was best at high stimulus levels and lower frequencies, and refitting the probe tended to reduce the reliability of high-frequency DPOAEs. Furthermore, long-term repeatability was better in males than females. The poorest reliability was observed in the same-day condition that involved a 10-minute wait-period between test and retest (the short-term interval). I proposed that this poor reliability may have been due to the use of ketamine, an injectable anesthetic, which cannot be maintained at a constant circulating concentration throughout the procedure. I tested this by assessing reliability in a subset of the same marmosets under isoflurane, an inhalation anesthetic, which can be maintained at a constant level throughout the procedure (Chapter 3), and I found that repeatability in the short-term interval was improved under the isoflurane protocol, demonstrating one strength of isoflurane over ketamine anesthesia. Finally, ABRs and DPOAEs were measured in marmosets ranging from 1-12 years of age (Chapter 4). By comparing the individual ABR thresholds of marmosets older than 6 years of age, I demonstrated that marmosets exhibit variability in the age of onset, severity, and pattern of hearing loss. Subjects older than 6 years with high-frequency hearing loss exhibited changes in DPOAE levels and in waves I and II of the ABR, which represent peripheral and cochlear nucleus function, respectively. Central deficits such as increases in the wave I-V and II-V interpeak intervals were observed in older subjects regardless of their ABR thresholds. The results of Chapter 4 suggest that the common marmoset may be a valuable model system for research in presbycusis.

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Keywords

Aging, Auditory Brainstem Response, Distortion-product otoacoustic emissions, Marmoset, Non-human primate

Citation

Department

Integrative Biology