Distortion product otoacoustic emissions in the CBA/J mouse model of presbycusis Kourosh Parham a; *, Xiao-Ming Sun a;b , D.O. Kim a;b a Division of Otolaryngology, Department of Surgery, University of Connecticut Health Center, Farmington, CT 06030-1110, USA b Department of Communication Science, University of Connecticut, Storrs, CT, USA Received 24 September 1998; received in revised form 20 March 1999; accepted 26 March 1999 Abstract CBA mice do not exhibit age-related loss of auditory sensitivity or cochlear pathology until relatively late in life. Therefore, this strain is believed to be an excellent animal model for the examination of the effects of age on the cochlea. To evaluate the effects of age on outer hair cell function, 2f 1 3f 2 distortion product otoacoustic emissions (DPOAEs) were measured for f 2 between 8 and 16 kHz in CBA/J mice between 1 and 25 months of age. CBA mice exhibited mild age-related changes in DPOAE level and detection threshold at 17 months of age, and changes of 20^40 dB by 25 months of age. The DPOAE level decreased and detection threshold increased with age in a frequency-dependent manner, starting at high frequencies and eventually extending to low frequencies. The range of frequencies in which notches were observed in the DPOAE input/output (I/O) functions extended toward lower frequencies by 17 months of age. Notches were absent in the I/O functions of 25-month-old mice. The present results for a frequency range of 8^16 kHz suggest that age has modest effects on outer hair cell function in CBA mice. ß 1999 Elsevier Science B.V. All rights reserved. Key words: Distortion product otoacoustic emission; Aging; Mouse; Hearing loss; Outer hair cell 1. Introduction Human presbycusis, hearing loss due to increasing chronological age, is characterized by elevation of hear- ing thresholds, usually beginning with high frequencies and gradually progressing to lower frequencies. Because of the complex interactions of genetic and environmen- tal variables that can contribute to age-related hearing loss, human presbycusis is a challenging research topic, particularly the late-onset, progressive hearing impair- ment, which is the most common type of presbycusis in humans (for review see Willott, 1991). The di¤culties faced by investigations of presbycusis in human sub- jects, including limitations on evaluating the correlation between functional and histological data of the same ear, have prompted the utilization of animal models to gain a better understanding of presbycusis. A popular animal model for the study of aging in the auditory system is the inbred CBA mouse strain. Age- related changes in the auditory system of CBA mice have been investigated behaviorally (Parham and Wil- lott, 1988; Willott et al., 1994), anatomically (e.g. Henry and Chole, 1980; Li and Hultcrantz, 1994; Shone et al., 1991; Spongr et al., 1997; Willott et al., 1987, 1988, 1991) and electrophysiologically, including single neuron (e.g. Walton et al., 1998; Willott, 1986; Willott et al., 1988, 1991) and auditory evoked potential recordings (e.g. Henry, 1982; Henry and Chole, 1980; Hunter and Willott, 1987; Li and Borg, 1991; Shone et al., 1991; Sjostrom and Anniko, 1990; Wenngren and Anniko, 1988). These studies have demonstrated that the auditory system of the CBA mouse does not display signi¢cant behavioral, anatomical or physiological changes until relatively late in life. Histopathological studies are in general agreement that age-related hearing loss is associated with a pro- gressive degeneration of cochlear hair cells and spiral ganglion cells, usually beginning with and most severely 0378-5955 / 99 / $ ^ see front matter ß 1999 Elsevier Science B.V. All rights reserved. PII:S0378-5955(99)00059-3 * Corresponding author. Tel.: +1 (860)679-2554; Fax: +1 (860)679-2451; E-mail: parham@neuron.uchc.edu Hearing Research 134 (1999) 29^38