Age-related changes in cochleas of mongolian gerbils

doi:10.1016/0378-5955(91)90142-V

Hearing Research

Volume 54, Issue 1, July 1991, Pages 123-134

https://doi.org/10.1016/0378-5955(91)90142-V Get rights and content

Abstract

The effects of aging on the gerbil cochlea were studied in 16 animals raised in a quiet environment. Animals were tested at ages ranging from 33 to 36 months, the approximate average lifespan of gerbils in our colony. Hearing sensitivity was assessed by measures of whole-nerve compound action potential (CAP) thresholds and surface preparations of the organ of Corti were subsequently examined by light microscopy for losses of sensory hair cells. These quiet-aged animals showed a wide range of hair-cell losses and threshold shifts. Outer hair cells often showed significant losses while inner hair cells were rarely absent. All animals had some threshold shift, especially at frequencies above 4 kHz. These shifts ranged from 1 to 68 dB. At high frequencies, threshold shifts often occurred without hair-cell losses at corresponding cochlear locations. At low frequencies, threshold shifts seldom reflected the losses of hair cells commonly found in the cochlear apex. Thus, the correlation of specific hair-cell losses and CAP threshold shifts at corresponding frequencies was poor. On the other hand, the total number of missing hair cells, irrespective of location, was a good, general indicator of the hearing capacity in a given ear. It appears that the factor or factors that makes cochleas susceptible to hair-cell loss with increasing age also affects other cochlear mechanisms that are necessary for normal functioning of the ear.

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Age-related hearing loss affects a large and growing segment of the population, with profound impacts on quality of life. Age-related pathology of the cochlea—the mammalian hearing organ—underlies age-related hearing loss. Because investigating age-related changes in the cochlea in humans is challenging and often impossible, animal models are indispensable to investigate these mechanisms as well as the complex consequences of age-related hearing loss on the brain and behavior. In this review, we advocate for a comparative and interdisciplinary approach while also addressing the challenges of comparing age-related hearing loss across species with varying lifespans. We describe the experimental advantages and limitations as well as areas for future research in well-established models of age-related hearing loss, including mice, rats, gerbils, chinchillas, and birds. We also indicate the need to expand characterization of age-related hearing loss in other established animal models, especially guinea pigs, cats, and non-human primates, in which auditory function is well characterized but age-related cochlear pathology is understudied. Finally, we highlight the potential of emerging animal models for advancing our understanding of age-related hearing loss, including deer mice, with their notably extended lifespans and preserved hearing, naked mole rats, with their exceptional longevity and extensive vocal communications, as well as zebrafish, which offer genetic tractability and suitability for drug screening. Ultimately, a comparative and interdisciplinary approach in auditory research, combining insights from various animal models with human studies, is key to robust and reliable research outcomes that better advance our understanding and treatment of age-related hearing loss.
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In the past decade, a large body of work has been devoted to better understand hidden hearing loss, including the causes of hidden hearing loss, their corresponding impact on the auditory pathway, and the use of auditory physiological measures for clinical diagnosis of auditory deafferentation. This review synthesizes the findings from studies in humans and animals to answer some of the key questions in the field, and it points to gaps in knowledge that warrant more investigation. Specifically, recent studies suggest that some electrophysiological measures have the potential to function as indicators of hidden hearing loss in humans, but more research is needed for these measures to be included as part of a clinical test battery.
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Besides their suitability as a model in hearing research, gerbils are also suitable subjects for studying the effects of aging on physiological functions, because they only live three to four years (Cheal, 1986). Moreover, old gerbils show increased auditory thresholds, age-related deficits in the representation of temporal structures of sounds and characteristics of strial and neural presbycusis (Gleich et al., 2016; Hamann et al., 2002; Heeringa et al., 2020; Hellstrom and Schmiedt, 1990; Kessler et al., 2020; Laumen et al., 2016; Tarnowski et al., 1991). Consequently, they have been used to study age-related hearing loss and its different structural and functional aspects (Gleich and Strutz, 2012).
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It has a short lifespan, good low-frequency hearing sensitivity, and the peripheral pathology is similar in many aspects to the human condition in the absence of noise damage (Cheal, 1986; Heeringa and Köppl, 2019; Gates and Mills, 2005; Ryan, 1976). Specifically, old gerbils show synapse loss (Gleich et al., 2016), spiral-ganglion cell loss (Keithley et al., 1989), and a lower EP due to strial dysfunction (Schmiedt et al., 2002a); the loss of hair cells is, however, minimal (Tarnowski et al., 1991). The reduction in synapse number in old, compared to young-adult, gerbils was reported to be nearly 40% in the apical, low-frequency, cochlear region, while it was relatively small in the middle and basal regions (11%–17%).
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Age-related changes in cochleas of mongolian gerbils

Abstract

Hear. Res.

Hear. Res.

Am. J. Otolaryngol.

Hear. Res.

Hear. Res.

Hear. Res.

Hear. Res.

Hear. Res.

Acoustic trauma in the guinea pig: II

Feinstrukturelle and histochemische veraenderagnen an den strukturen der cochlea beim meerschweinchen nach dosierter reintonbeschallung

Arch. Ohr. Nas., Kehlk. Heilk.

Age-related cochlear hair cell loss in the chinchilla

Ann. Otol. Rhinol. Laryngol.

Age related hair cell loss in the organ of Corti of the rabbit

Cellular pattern and nerve supply of the human organ of Corti

Acta Otolaryngol. (Suppl.)

Renal handling of sodium, chloride, water, amino acids, and glucose

The gerbil: a unique model for research on aging

Exp. Aging Res.

Disparity in the cytocochleogram and the electrocochleogram in aging LP/J and A/J inbred mice

Audiology

Cochlear damage: Audiometric correlates?

Hair cell loss as function of age in the normal cochlea of the guinea pig

Acta Otolaryngol. (Stockh)

Pathological changes in the inner ears of senile guinea pigs

Laryngoscope

An animal model for presbycusis

Laryngoscope

Analysis of age-related changes in electric responses from the inner ear of rats

Ann. Otol.

Behavioral, compound action potential and single unit thresholds: relationship in normal and abnormal ears

J. Acoust. Soc. Am.

Cochlear changes from noise, kanamycin and aging

Laryngoscope 85 (Suppl 1)

Developmental alterations in the frequency map of the mammalian cochlea

Nature

Das cochleogramm des normalen Meer-schweinchens

Arch Klin Exp Ohren Nasen Kehlkopfheild.

Critical bandwidths and the frequency coordinates of the basilar membrane

J. Acoust. Soc. Am.