EFFECT OF TEMPERATURE ON THE TRANSIENT EVOKED AND DISTORTION-PRODUCT OTOACOUSTIC EMISSIONS IN RATS

In order to study the energy dependence of the cochlear amplifier, tra nsient evoked otoacoustic emissions (TEOAEs) and distortion product ot oacoustic emissions (DPOAEs) were recorded in rats during gradual cool ing to 27 degrees C and heating to 40 degrees C, In the range 33-39 de grees C, the TEOAEs and DPOAEs were Otoacoustic emissions maximal in a mplitude and almost insensitive to temperature, However, they were sig nificantly depressed (reversibly) at higher and lower temperatures. In tensity functions were plotted at 37, 27 and 40 degrees C for both typ es of oto-acoustic emissions. At 37 degrees C intensity functions were nonlinear, with a notch at mid-intensity regions. At 27 degrees C, th e magnitudes were depressed more at the lower intensities and threshol d elevations were observed. As a result, the intensity functions were more linear and the notch was no longer seen. This result provides fur ther evidence for a more active, energy-dependent component of the oto acoustic emissions at lower intensities for both TEOAEs and DPOAEs. Th e cooling probably affects the lower intensity otoacoustic emissions b y inducing a depression in the endocochlear potential, by reducing the motility of the outer hair cells and by introducing a small conductiv e hearing loss.