title: Adaptation of distortion product otoacoustic emissions predicts susceptibility to acoustic over-exposure in alert rabbits.
abstract: A noninvasive test was developed in rabbits based on fast adaptation measures for 2f1-f2 distortion-product otoacoustic emissions (DPOAEs). The goal was to evaluate the effective reflex activation, i.e., "functional strength," of both the descending medial olivocochlear efferent reflex (MOC-R) and the middle-ear muscle reflex (MEM-R) through sound activation. Classically, it is assumed that both reflexes contribute toward protecting the inner ear from cochlear damage caused by noise exposure. The DP-gram method described here evaluated the MOC-R effect on DPOAE levels over a two-octave (oct) frequency range. To estimate the related activation of the middle-ear muscles (MEMs), the MEM-R was measured by monitoring the level of the f1-primary tone throughout its duration. Following baseline measures, rabbits were subjected to noise over-exposure. A main finding was that the measured adaptive activity was highly variable between rabbits but less so between the ears of the same animal. Also, together, the MOC-R and MEM-R tests showed that, on average, DPOAE adaptation consisted of a combined contribution from both systems. Despite this shared involvement, the amount of DPOAE adaptation measured for a particular animal's ear predicted that ear's subsequent susceptibility to the noise over-exposure for alert but not for deeply anesthetized rabbits.
authors.affiliation: Departments of Neurobiology and Anatomy and Biomedical Engineering, University of Rochester Medical Center, Rochester, New York 14534.
authors.forename: Anne E
authors.initials: AE
authors.lastname: Luebke
authors.affiliation: Research Service, Veterans Affairs Loma Linda Healthcare System, Loma Linda, California 92357.
authors.forename: Barden B
authors.initials: BB
authors.lastname: Stagner
authors.affiliation: Research Service, Veterans Affairs Loma Linda Healthcare System, Loma Linda, California 92357.
authors.forename: Glen K
authors.initials: GK
authors.lastname: Martin
authors.affiliation: Research Service, Veterans Affairs Loma Linda Healthcare System, Loma Linda, California 92357.
authors.forename: Brenda L
authors.initials: BL
authors.lastname: Lonsbury-Martin
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D001143:Arousal; D001305:Auditory Fatigue; D001306:Auditory Pathways / Q000502:physiology*; D003051:Cochlea / Q000294:innervation*; D004432:Ear, Middle / Q000294:innervation*; D030141:Feedback, Psychological; D009622:Noise / Q000009:adverse effects*; D009847:Olivary Nucleus / Q000502:physiology*; D017084:Otoacoustic Emissions, Spontaneous; D011817:Rabbits; D012022:Reflex, Acoustic; D013997:Time Factors