Thesis (M. Sc.) -- University College London, 1998. / A project submitted (to the Institute of Laryngology and Otology) as a requirement for the degree of Master of Science in Audiological Medicine, University College London. Bibliography: leaves 83-101.

Hair cell trauma from aminoglycosides, which may lead to permanent loss of hair cells in mammals, was studied physiologically in frogs by measuring an auditory evoked potential (AEP) in Rana pipiens. The AEP was evaluated in order to measure threshold shift (TS) and recovery from TS after the administration of the aminoglycoside antibiotic, gentamicin. To obtain an AEP, chronic electrodes were implanted into the cranium near the cochlear nucleus. The frogs were then exposed to frequency-specific narrow band ~clicks" which included a single period 1 kHz sinewave, and a computer synthesized high frequency and low frequency click. Amphibians have two hearing organs, the amphibian and basilar papillae, sensitive to low (150-1500) and high (1500-2000) frequencies, respectively. The low (AP) and high (BP) frequency clicks were created to stimulate specifically the corresponding papillae. After normal thresholds were recorded for each frog, gentamicin sulfate, 200 μM, 300 μM, or 400 μM, was injected bilaterally into the otic capsules. Thresholds were recorded until the TS had disappeared, allowing the threshold recovery period to be measured. The injections of 200 μM yielded a 10 dB change in one animal and no change in two others. The injection of 300 μM into 10 frogs and 400 μM into 20 frogs yielded at least a 10 dB change in 60% and 93% of the frogs, respectively, with the concentration of 400 μM producing threshold shifts of 20 dB. Thus, the threshold shifts were dose-dependent. Recovery times varied between six and fourteen days. No apparent differences between thresholds for the high frequency click, low frequency click and sinewave clicks were observed.

Previous studies show that pure tone thresholds are strongly correlated with distortion product otoacoustic emission amplitudes when evaluating the frequency range from 1 to 8 kHz (Avan & Bonfils, 1993). Little is known about correlations between these two measures at higher frequencies from 9-16 kHz. This study compared pure tone thresholds and distortion product otoacoustic emissions (DPOAEs) in this high frequency range for 29 normal hearing subjects ages 18-30. Pure tone thresholds were obtained at 250-16 kHz and distortion product otoacoustic emissions (DPOAE) 2,211-17,675 were measured in the same ears. DPOAE amplitudes were measured using a constant F1/F2 ratio of 1.2, with F2 values ranging from 2,211-17,675 Hz. Data obtained from 50 ears showed a decline in DPOAE amplitude with increasing frequency of the F1 and F2 primary stimulus tones. Behavioral thresholds demonstrated an increase with increasing frequency of the pure tone stimulus. Pearson r-correlation analysis demonstrated a weak relationship between measures. Further investigation revealed that equipment variables prevented accurate readings.