Normative data on the cochlear microphonic in rat using differential electrodes

Isopotential (1-muV) cochleograms were obrained from 19 anesthetized rats from electrodes inserted into scala vestibuli and scala tympani of the first turn. The differential electrode technique is suitable for frequencies above 1-2 kc/s in the rat. CM sensitivity in rats as measured with intracochlear electrodes (26 micrometer in diameter) was considerably poorer than in guinea pigs at frequencies below 2 kc/s, but was within 10-14 db at 2 kc/s and above. The shape of the CM input-output functions were similar to those in the guinea pig and chinchilla, except that the intensity level where the CM becomes non-linear is higher in the rat.