Abnormal augmentation of the receptor potential and morphology changes of guinea pigs cochlea induced by Cisplatin

To investigate the characteristics of cochlear microphonic (CM), summating potential (SP) and compound action potential (CAP) and morphology changes of outer hair cells (OHCs) and inner hair cells (IHCs) after OHCs were selectively damaged by acute cochlear perfusion of cisplatin. Dynamic changes of CM, SP and CAP were recorded from the scala media of the third turn of the guinea pigʹs cochlea during Cisplatin perfusion into the whole cochlea for 2 hours. The results indicated that after one hour of the perfusion, the amplitude of CM, SP and CAP decreased at stimulus intensity < 60 dB SPL, while the amplitude increased at stimulus intensity > 70 dB SPL, as compared to those examined before perfusion of Cisplatin (the average of CM increased by 3.6 mV at 90 dB SPL, average of SP increased by 1.6 mV at 120 dB SPL, average of CAP increased by 0.23 mV at 90dB SPL). After two hours of perfusion, the amplitude of CM, SP and CAP decreased in all stimulus intensities. The staining of Succinic Dehydrogenase (SDH) was weak in OHCs, while the stain ing of IHCs remained normal. Transmission electron microscopic examination of organ of Corti showed varieties of morphological changes in OHCs, such as nucleus chromosome disappear, mitochondria denaturalization and number reduction, while the structure of IHC appeared normal. SDH staining showed normal staining pattern in both IHCs and OHCs when the cochlea was perfused with artificial perilymph for 2 hours. The abnormal augmentation phenomenon of CM and SP may be induced by the abnormal control of Ca+ + in IHCs and OHCs . The abnormal augmentation of CAP suggests that the suppression effects of OHCs and efferent neurotransmitter on IHCs and afferent neurotransmitter may be reduced after OHCs damaged.