Postnatal development of [formula omitted] otoacoustic emissions in pigmented rat

• Published in: Hearing research Vol. 43; no. 2-3; pp. 141 - 148
• Main Authors: Henley, C.M., Owings, M.H., Stagner, B.B., Martin, G.K., Lonsbury-Martin, B.L.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.1990
• Subjects: Cochlear development; Distortion-product emissions; Pigmented rat; Distortion-product emissions; Cochlear development; Pigmented rat
• ISSN: 0378-5955; 1878-5891
• DOI: 10.1016/0378-5955(90)90223-C

Distortion-product emissions at 2ƒ1−ƒ2 were measured in developing, pigmented rats to determine the characteristics of the functional onset and maturation of these emitted responses. Distortion-product testing was conducted on postnatal days 12, 14, 18, 21, 24, 28, and 51. The geometric-mean frequencies of the primaries were tested at one-half octave intervals, between 4 and 11.3 kHz. No emissions were detected on postnatal day 12: however, by day 14, emissions were measured at geometric-mean frequencies between 5.7 and 11.3 kHz, but not 4 kHz. By the 18th postnatal day, all animals had measurable emissions at 4, 5, 7, 8, and 11.3 kHz. Both the functional onset and maturation of high- to midfrequency emissions developed before those elicited by lower-frequency primaries. Response/growth or input/output functions for the higher frequencies exhibited ‘adult-like’ properties that included an increase in maximum amplitude and ‘saturation’ at high levels of stimulation by the third to fourth postnatal week. Maturation of the lower-frequency responses progressed at a slower rate. These results differ somewhat from those reported previously for the neonatal albino rat. However, the present findings were based upon a wider frequency range of primary tones, lower levels of acoustic stimulation, and a measuring system with a significantly lower noise floor. These results are consistent with documented periods of the anatomical maturation of the rat outer hair-cell system and establish a functional ‘baseline’ for future studies utilizing agents that damage the developing cochlea.