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. 2008 Jul;241(1-2):26-33.
doi: 10.1016/j.heares.2008.04.006. Epub 2008 Apr 22.

Age-related hearing loss in the Fischer 344/NHsd rat substrain

Eric C Bielefeld  1 , Donald Coling, Guang-Di Chen, Manna Li, Chiemi Tanaka, Bo-Hua Hu, Donald Henderson
Affiliations

Age-related hearing loss in the Fischer 344/NHsd rat substrain

Eric C Bielefeld et al. Hear Res. 2008 Jul.

Abstract

Studies of the F344 rat have shown a variety of age-related auditory anatomy and physiology changes. The current study was undertaken to clarify the ARHL in the F344 rat, by examining the auditory pathway of the F344/NHsd substrain that is distributed by Harlan Laboratories for research in the United States. The F344/NHsd rat begins to lose its hearing at about 12 months, and by 24 months, there are 50-60 dB auditory brainstem response threshold shifts at 20 and 40 kHz and 20 dB losses at 5-10 kHz. Distortion product otoacoustic emissions (DPOAE) amplitudes at 1.8-12 kHz stimuli were depressed in the older (18-24 months) rats. Amplitude input-output functions of the compound action potential (CAP) were also depressed across frequency. The endocochlear potential (EP) was 90-100 mV in the 3 month old rats. All but one of the 24 month old rats' EPs were in the +75-85 mV range. Tympanometry revealed no differences in middle ear function between the young and older rats. Collectively, these findings suggest damage to the outer hair cells, but anatomical examination of the outer hair cells revealed a relative lack of cell loss compared to the magnitude of the hearing and DPOAE loss.

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Figures

Figure 1
Figure 1
Mean ABR thresholds in response to 5, 10, 20, and 40 kHz tone burst stimuli, as well as a click stimulus for 3, 9, 12, 18, and 24 mo F344/NHsd rats. Error bars are +/− 1 standard deviation.
Figure 2
Figure 2
CAP amplitude input-output functions for 2 kHz (A), 8 kHz (B), 12 kHz (C), 24 kHz (D), 30 kHz (E), and 40 kHz (F) for 3 and 24 mo F344/NHsd rats. Error bars are +/− 1 standard deviation.
Figure 3
Figure 3
DPOAE amplitudes at 1.8 to 12 kHz in response to 65/55 dB SPL stimuli for F344NHsd rats aged 3, 11, 18, and 24 months. Error bars are +/− 1 standard deviation.
Figure 4
Figure 4
Tympanometry for F344/NHsd rats aged 3, 16, and 24 months (A) Peak pressures with error bars +/−1 standard deviation. (B) Compliance with error bars +1 standard deviation.
Figure 5
Figure 5
Mean endocochlear potentials in mV for 3 and 24 mo F344/NHsd rats. Error bars are + 1 standard deviation.
Figure 6
Figure 6
Individual rats’ EP values over time following KCN (2.5 mg/kg) injection. (A) 3 mo F344/NHsd rats (n=6). (B) 24 mo F344NHsd rats (n=8).
Figure 7
Figure 7
Individual F344/NHsd rats’ CAP thresholds. Dark symbols are 24 mo rats. Open symbols are 3 mo rats. Along the right side of each animal’s 40 kHz threshold is the animal’s EP value. No correlation between EP and CAP threshold was detected for young or old rats at any frequency. The table alongside shows the Pearson product moment correlations of EP and CAP thresholds at 9 CAP frequencies with significance values in parenthesis.
Figure 8
Figure 8
Mean OHC cochleograms for F344/NHsd rats aged 3 and 20–27 months. Dying and missing OHC were grouped together under the label “deteriorated OHC” as presented on the y-axis.
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