Selective Removal of the Nerve Discharge component from the Cochlear Potential during Anoxia.

Abstract

Summary.The relationship between the cochlear and the action potentials of the ear during oxygen deprivation was studied by simultaneously recording the two potentials by means of electrodes in the apical part of the cochlea (third turn). The experimental animals were 12 guinea pigs under not too deep urethane anesthesia. In only 9 of 17 operated ears both potentials were strong enough to be studied and compared. It was found that: During incipient hypoxia, the hump in the composite curve representing the action potential disappears before the amplitude of the cochlear potential decreases. During the recovery phase, the action potential reappears only after complete restitution of the cochlear potential. Repeated, successive anoxia experiments are always followed by complete restitution of the cochlear potential, whereas the action potential gradually disappears, provided that the anoxia is not carried too far. This provides a simple method of eliminating the action potential without affecting the cochlear potential, a technique suitable for cochlear potential threshold measurements. When the action potential reappears in the recovery phase of hypoxia, there is a transient phase difference of about 0.2 msec., which after some minutes is no longer present. This difference is attributable to a temporary prolongation of the latent period of the action potential. The effect of hypoxia on the latent period of the action potential is equivalent to that obtained by a reduction of stimulus intensity.