Distortion product otoacoustic emissions in the C57BL/6J mouse model of age-related hearing loss.
One of the earliest histopathological changes associated with age-related hearing loss appears to be the disruption of outer hair cells (OHCs). To evaluate age-related changes in OHC function, distortion product otoacoustic emissions (DPOAEs) were recorded in the young and aging C57BL/6J mouse. Starting in young adulthood, the C57 mouse displays age-related elevation of auditory brainstem response thresholds, beginning in the high frequencies and progressing toward lower frequencies. The 2f1-f2 DPOAEs of mice between 2 and 20 months of age were examined for f2s between 8 and 16 kHz. In this octave region, the features of 2f1-f2 DPOAEs in the 2-month-old C57 mouse were comparable to those described for non-murine rodents in the literature in terms of optimum f2/f1 ratio, optimum primary level difference, input/output (I/O) function features and microstructure. It was determined that f2/f1 = 1.2 and L1-L2 = 20 dB were optimal stimulus parameters for investigation of the effects of age on C57 DPOAEs. Age-related changes in DPOAE I/O functions consisted of a right shift (i.e. increased DPOAE detection thresholds), disappearance of 'notches' and shallowing of the slopes after 8 months of age. As DPOAE I/O functions continued to shift to the right and DPOAE levels decreased with age, the appearance of I/O functions became complex to include regions of steep or shallow slopes and plateaus. The present results suggest that the age-related elevation of auditory thresholds in the C57 mice is associated with substantial progressive changes in OHC function.
Parham
K
K
Department of Surgery, The School of Medicine, University of Connecticut Health Center, Farmington 06030-1110, USA. parham@neuron.uchc.edu
D000161:Acoustic Stimulation; D000375:Aging / Q000473:pathology / Q000502:physiology*; D000818:Animals; D001309:Auditory Threshold / Q000502:physiology; D003051:Cochlea / Q000473:pathology / Q000503:physiopathology; D004195:Disease Models, Animal; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D011304:Presbycusis / Q000209:etiology / Q000473:pathology / Q000503:physiopathology*