Distortion Product Otoacoustic Emissions in Infant, Pregnant and Non-pregnant Adult Rabbits: Comparison for Different Stimulus Levels

Objectives: In the present study, we investigated Distortion Product Otoacoustic Emissions in pregnant (Group 1); non-pregnat adult female rabbits (Group 2) and infant rabbits (Group 3). We assessed Distortion Product Otoacoustic Emission amplitudes in both stimulus levels of F2/F1=1.22 and 1.14; and analyzed the amplitude differences in different groups. Methods: Thirty-six New Zealand White rabbits were included into the study. They were divided into three groups. Group 1 consisted of 9 each 13-month-old, adult, pregnant female rabbits. Group 2 consisted of 9 each 13-month-old, adult, nonpregnant female rabbits. Group 3 consisted of 18 each one-month-old, infant rabbits (Nine of them, male; and nine of them, female). In all groups, cochlear functions were assessed by Distortion Product Otoacoustic Emissions at 1.0-8.0 kHz. Stimulus parameters were used as F2/F1=1.22 in the first recording; and 1.14, in the second recording for each of the ears. Results: In all groups (1 to 3), Distortion Product Otoacoustic Emission amplitudes were found as higher with F2/F1:1.22 measurements than F2/F1:1.14 measurements. In F2/F1:1.22; and F2/F1:1.14 measurements seperately; at each Distortion Product Otoacoustic Emission frequencies (1.0-8.0 kHz), the difference between Distortion Product Otoacoustic Emission amplitudes of Group1-3 were analyzed by "Kruskal Wallis Variance Analysis": The statistically significant difference were present at frequencies of 1.5-2.0 kHz and 8.0 kHz for F2/F1:1.22 measurements; and 1.0-2.0 kHz and 4.0-8.0 kHz for F2/F1:1.14 measurements. In F2/F1:1.22 measurements, at 1.5 kHz, the mean value of Group 1 (Pregnant rabbits) was significantly higher than that of Group 3 (Infant rabbits). In F2/F1:1,14 measurements, at 1.0, 4.0 and 8.0 khz, the mean values of Group 1 (Pregnant rabbits) was significantly higher than those of Group 3 (Infant rabbits); and at 1.0, 2.0 and 4.0 kHz, the mean values of Group 2 (Non-pregnant rabbits) were significantly higher than those of Group 3 (Infant rabbits) Conclusion: Our study demonstrated that, in pregnant rabbits, higher corticosteroid levels may cause higher DPOAE amplitudes than infant rabbits by F2/F1:1.14 measurements. In all rabbits and especially in infant rabbits, Distortion Product Otoacoustic Emissions could be taken by F2/F1:1.22 measurements with higher amplitudes. The importance of our study is, when Distortion Product Otoacoustic Emission measurement is planned, measurements should be done using F2/F1: 1.22 to get healthy and accurate results in experimental studies. In measurements made by F2/F1: 1.14, amplitudes can be observed as lower than F2/F1: 1.22 measurements. This decline is evident especially in infant rabbit groups. Water containing medium in the middle ear of infant rabbits may cause the reduce in Distortion Product Otoacoustic Emission amplitudes than adult rabbits at both F2/F1:1.22 and 1.14 measurements.