Postnatal development of 2f1-f2 otoacoustic emissions in pigmented rat.
Distortion-product emissions at 2f1-f2 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 at 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.
Henley
C M
CM
Department of Otorhinolaryngology and Communicative Sciences, Baylor College of Medicine, Houston, TX 77030.
Owings
M H
MH
Stagner
B B
BB
Martin
G K
GK
Lonsbury-Martin
B L
BL
D000161:Acoustic Stimulation; D000162:Acoustics; D000818:Animals; D000831:Animals, Newborn / Q000254:growth & development*; D004423:Ear / Q000502:physiology*; D010469:Perceptual Distortion; D051381:Rats; D012684:Sensory Thresholds