Aging cochleas in the F344 rat: morphological and functional changes

Area of Science:

• Otolaryngology
• Gerontology
• Cell Biology

Background:

• The Fischer 344 rat is a common model for accelerated aging.
• Age-related hearing loss (presbycusis) is a significant health concern.
• Understanding the cellular mechanisms of presbycusis is crucial for developing interventions.

Purpose of the Study:

• To investigate the presence of apoptotic cells in the inner ear of aged Fischer 344 rats.
• To correlate inner ear cell apoptosis with cochlear function.
• To validate the Fischer 344 rat as a model for strial presbycusis.

Main Methods:

• Apoptotic cells were identified using cresyl violet staining and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) assay.
• Cochlear function was assessed using distortion product otoacoustic emissions (DPOAEs).
• Comparisons were made between aged (20-24 months) and young (4 months) Fischer 344 rats, and aged Long Evans rats (24-28 months).

Main Results:

• Aged Fischer 344 rats exhibited a high incidence of apoptotic cells in the stria vascularis and spiral ligament.
• Significant reduction or absence of DPOAE amplitudes was observed in aged Fischer 344 rats, indicating outer hair cell dysfunction.
• Young Fischer 344 rats and aged Long Evans rats showed fewer apoptotic cells and preserved DPOAE amplitudes.

Conclusions:

• Apoptotic cell accumulation in the stria vascularis and spiral ligament leads to strial detachment and outer hair cell dysfunction in aged Fischer 344 rats.
• These findings support the use of aged Fischer 344 rats as a relevant animal model for strial presbycusis.
• The study highlights the cellular basis of age-related hearing impairment in this specific rat model.