DEPRESSION IN ORDER OF FREQUENCY OF THE ELECTRICAL COCHLEAR RESPONSE OF CATS

Abstract

Cochlear action currents from the round window of cats under barbiturate anesthesia were measured from a total of 31 animals. In 24 the opposite ear served as a control. 5 stimulus tones covered the range from 256 to 10,000 vibrations. Agents were applied to the round window membrane. NaCl and CaCl2, quinine dihydrochloride powder and pure glycerine produced a loss which appeared first in the higher frequencies and progressed regularly to the lower. Solutions of 10 and 25% showed a similar but slower effect. Dextrose crystals, 1% NaCl and distilled water produced little or no loss. Sections showed a progressive degeneration of hair cells. The first observable degeneration occurred in the outer hair cells and in the external sulcus only. The histological plcture is identical with that in the deafness of old age, drug poisoning and stimulation deafness. The results constitute evidence for localization along the cochlear splral of end organs which record tones of medium intensity, in order of frequency. They indicate that the hair cells are indispensable for maximum sensitivity of potential response and are primary in the normal activation of the nerve. It is suggested that the loss results from an alteration of the permeability of sensory cell membranes such as to interfere with a chemical mediator or with membrane polarization potentials.