Development of endocochlear potential and its negative component in mouse cochlea

The chronological developmental processes of endocochlear potential (EP) and negative endocochlear potential (-EP) were investigated as a function of age from birth in the basal and second cochlear turns in normal ICR-strain mice. The EP of the basal turn developed between 5 and 17 days after birth (DAB). The -EP of the basal turn attained to its mature level on 11 DAB and it increased its absolute value further between 12 and 16 DAB and then, recovered to its mature level again on 20 DAB. The developmental processes of EP and -EP of the second turn followed similar courses to those of the basal turn although they were several millivolts different on each day in detail. The results suggest that the developmental processes of the +EP and the -EP are different. The time of reaching minimum -EP during anoxia were measured and the rate of EP decline were calculated on each animal. The rate of EP decline increased rapidly on 10 DAB, almost coinciding the day which EP began to increase abruptly. Although the rate of EP decline is influenced by several processes, this result showed one of the possibility that the sensitivity of the stria vascularis to hypoxia may develop parallel to the development of the EP.