Experimental Study on the Mutual Relation between Endocochlear DC potential and Cochlear Microphonics

Abstract

Since the mechanoelectrical hypothesis on the production of cochlear microphonics (CM) was adovocated by Davis in 1958 and 1968, it has been agreed that the DC potential gradient of 160mV which consists of endocochlear DC potential (EP) and negative DC potential in the organ of Corti across the cuticular plate is the electrical source to produce CM. In order to investigate the minute relation between the DC potential gradient and CM, the effects of general anoxia, local anoxia and the injection of furosemide (30mg/kg) were studied on EP and CM in this paper.During anoxia CM declined expectedly parallel with the magnitude of the DC potential gradient. After the injection of furosemide both EP and CM declined rapidly and reached to the lowest level within 1 minute. Subsequently, the potentials showed the tendency of immediate recovery. At the stage of this recovery, CM recovered more rapidly than EP and the remarkable overshoot of the amplitude of CM has already been observed even when EP still stayed at the lower level. This is the important finding to neglect the general consideration about the relation between CM and the DC potential gradient. In other words the experimental fact suggests that it does not always need the high voltage of EP to produce CM.To clarify the relation between the complete recovery of CM amplitude and the lower voltage of EP, the further investigations should be necessary by changing ionic concentration in endolymph and the resistance change at the cuticular plate.