Influence of exogenous glutamic acid on cochlea inner ear hair cells and hearing threshold

    QU Juan, LIU Shunª²Li, QIU Jianª²Hua, WANG Jinª²Ling, QIU Shuª²Ping

    PLA Center of Otorhinolaryngology, Xijing Hospital, Fourth Military Medical University, Xi¬ðan 710033, China

    ¡¾Abstract¡¿ AIM: To observe the influence of exogenous glutamic acid on inner ear hair cells and the hearing threshold. METHODS: 24 adult guinea pigs were divided randomly into three groups and given Glu (5 mmol/L, 10 mmol/L, 20 mmol/L), respectively through the holes drilled into the scala tympani of cochlea. The left ears were taken as the treatment ones and the right as the control ones. The changes in the audiology and morphology at different periods before and after giving the drug were observed by applying the technologies of auditory brainstem response (ABR), distortionª²product otoacoustic emission (DPOAE), cochlear preparation, silver nitrate dying and transmission electron microscope. RESULTS: After giving the drug to the operated ears, the average threshold level of ABR at 1KHz was (25.0¡À3.4 dB), (33. 9¡À2.7 dB) and (32.2¡À4.2 dB), respectively, and that at 8 KHz was (28.9¡À3.7 dB), (38.3¡À2.8 dB) and (37.8¡À3.8 dB), respectively (P<0.05). The sharp differences were observed in comparison with the control ears. The DPOAE showed that after giving Glu of low concentration, the signals were above the background noise. The concentration above 5 mmol/L could not evoke DPOAE signals. When Glu of low concentration was injected into the cochlear scala tympani, there was a slight disorder of the outer hair cells (OHCs), but the inner hair cells (IHCs) were comparatively consistent in morphology. With the increase of Glu concentration, there were obvious changes in morphology and absence in three rows of the OHCs. The similar morphological changes occurred in IHCs, which corresponded with the changes of audiology. CONCLUSION: Glu probably has some toxic effects on inner ear hair cells. ......