EFFECT OF ANESTHETIC AGENTS AND MIDDLE-EAR PRESSURE APPLICATION ON DISTORTION-PRODUCT OTOACOUSTIC EMISSIONS IN THE GERBIL

The functional status of the middle ear system has a crucial importanc e in the measurements of distortion product otoacoustic emissions (DPO AEs), because each emission signal has to be detected indirectly in th e external canal. It was observed that DPOAEs were scarcely detectable in the gerbil anesthetized with pentobarbital. On the other hand, whe n ketamine was used as an anesthetic, the DPOAE levels were generally high. The differences in the effects of these anesthetic agents on the DPOAEs became less clear when the tympanic bulla was opened. This str ongly suggests that the effects might be due to a modification of the middle ear pressure. This study was designed to elucidate the mechanis ms of the effects of these anesthetics on the DPOAEs. Comparing the ef fects of pentobarbital and those of pressure application to the middle ear on the frequency characteristics of DPOAEs, the following conclus ions emerged: (1) pentobarbital administration causes negative middle ear pressure in the gerbil; (2) the generated pressure strongly reduce s DPOAE conduction through the middle ear; and thus (3) proper selecti on of anesthetic agents is very important in gerbil experiments that i nvolve OAE measurements.