Abstract
Fischer 344 (F344) rats represent a strain that is frequently used as a model for fast aging. In this study, we systematically compare the hearing function during aging in male and female F344 rats, by recording auditory brainstem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs). In addition to this, the functional parameters are correlated with the cochlear histology. The parameters of the hearing function were not different in the young (3-month-old) male and female F344 rats; the gender differences occurred only in adult and aged animals. In 8–24-month-old males, the ABR thresholds were higher and the ABR amplitudes were smaller than those measured in females of the same age. There were no gender differences in the neural adaptation tested by recording ABRs, elicited by a series of clicks with varying inter-click interval (ICI). Amplitudes of DPOAEs in both the males and females decreased with age, but in the males, the decrease of DPOAE amplitudes was faster. In males older than 20 months, the DPOAEs were practically absent, whereas in 20–24-month-old females, the DPOAEs were still measurable. There were no gender differences in the number of surviving outer hair cells (OHC) and the number of inner hair cell ribbon synapses in aged animals. The main difference was found in the stria vascularis (SV). Whereas the SV was well preserved in females up to the age of 24 months, in most of the age-matched males the SV was evidently deteriorated. The results demonstrate more pronounced age-related changes in the cochlear morphology, hearing thresholds, ABR amplitudes and DPOAE amplitudes in F344 males compared with females.
Highlights
Age-related hearing loss is the most prevalent sensory disorder in the elderly population (Gates and Mills, 2005; Fetoni et al, 2011)
The auditory brainstem responses (ABRs) thresholds in females aged 8 months (Figure 1B, n = 4m + 4f) were the same as in 3-month-old females, while the ABR thresholds in 8-month-old males increased in comparison with 3-month-old males, and they were significantly higher at 32–40 kHz in comparison with 8-month-old females (p < 0.05, Bonferroni post hoc test)
Even though the ABR thresholds in Fischer 344 (F344) males and females were significantly different (p < 0.0001, two-way ANOVA), the differences in individual frequencies was significant only at frequency 40 kHz (p < 0.05, Bonferroni post hoc test)
Summary
Age-related hearing loss (presbycusis) is the most prevalent sensory disorder in the elderly population (Gates and Mills, 2005; Fetoni et al, 2011). Pathological processes leading to the occurrence of presbycusis, may be present in different parts of the auditory system. The central component of presbycusis, i.e., the pathological processes occuring in neurons of the central auditory system, affect the temporal processing of acoustical stimuli and cause a cognitive decline. This results in deteriorated speech-understanding and in speech-perception difficulties in a noisy environment. Presbycusis is the factor that markedly affects patients’ quality of life and represents a serious social and economic problem (World Health Organization, 2017)
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