Level: Advanced

Number of Slides: 32

Abstract:

INTRODUCTION: Carboplatin is a antitumour drug which selectively alters the micromechanical function of the inner hair cells (IHCs) of the organ of Corti. Data from an earlier study (Wake et al, 1996) from a chinchilla model support the hypothesis that carboplatin administration not only disrupts the IHC function but affects the efferent feedback loop to the cochlea, causing an amplification of the otoacoustic emission responses. The present study was designed to verify the OAE amplification-issue, using distortion product emissions (DPOAEs) in a wider bandwidth range.
MATERIALS AND METHODS: Carboplatin (Paraplatin,10 mg/ml, Brystol Myers) was administered by a 30 min low infusion. Pre and 72-hour post DPOAE and ABR recordings were acquired from a group of 12 Sprague -Dawley rats (mean weight 360 ± 35 gr). The animals were anesthetized with a ketamine-atropin anesthesia administered in two consecutive phases.The DPOAE responses (cubic distortion products) were recorded with 4 asymmetrical protocols P1= 60-50 ; P2 = 50-40 ; P3= 40-30 and P4= 30-20 dB SPL, in the frequency range from 5.0 to 16 kHz. ABR responses were obtained for bipolar clicks and tone-pips at the frequencies 8.0, 10.0, 20.0 and 30 kHz using stimuli in the range from 100 to 30 dB SPL . Wave-III was used to identify shifts in hearing threshold. Four animals randomly selected, underwent a SEM evaluation assessment. A repeated measures model was used for the analysis of the DPOAE responses .
RESULTS: ABR threshold shifts of 20 dB were observed in the frequencies from 20 to 30 kHz and shifts of 10 dB in the frequencies 8.0 and 10.0 kHz. The comparison of pre and post treatment DPOAE responses did not revealed any significant changes for protocols P1, P2 and P4. Border line differences were observed for the P3 protocol.
CONCLUSIONS: The findings from the rat model contrast the data available in the literature from a gerbil animal model and suggest that different efferent mechanisms might suppress or enhance the activity of the OHCs of the organ of Corti across various species.