Effect of Anoxia on Cochlear Potentials

Abstract

The anterior inferior cerebellar artery of guinea pigs was occluded, thereby interrupting the blood supply to the cochlea. Durations of occlusion ranged from ! through 60 min. Cochlear microphonics, summating potential, action potential, and endocochlear potential were recorded before, during, and subsequent to occlusion. The differential effect of anoxia on the various potentials was observed, as well as the appearance of the large negative dc potential in scala media as anoxia progressed. For the brief occlusion durations, the amplitudes of all potentials except cochlear microphonics became greater than normal soon after the blood supply returned. Even for the longer anoxic intervals, the summating potential and the endocochlear potential exhibited supernormality during the recovery process.

Reversibility of the Endolymphatic Potential after Transient Anoxia

“…It is really surprising that the stria vascularis can recover even in part after this long period of anoxia. Konishi et al (1961) also reported the partial recovery of the EP after 60 min anoxia. Light microscopical studies along this line indicate that the stria vascularis exhibits marked damage and separation from the underlying spiral ligament within 1 hr of anoxia (Kimura and Perlman 1958).…”

“…Recently, vascular disorder is thought to be one of the possible causes of sudden deafness, and the special attention is paid to the relation between the cochlear damage and the duration of anoxia. Investigation along this line was reported by Konishi et al (1961), but they mainly observed the effect of anoxia upon the cochlear microphonics and the action potential, and there was only a short description on the endolymphatic potential (abbr. EP).…”

Cation Transport and Cochlear Function

“…There is a remarkable similarity between the effects of ouabain, anoxemia (Konishi et al, 1961) and of cyanide (Konishi and Kelsey, 1968 c) on the cochlear potentials. This warrants the conclusion that the energy supply for the activity of the cation pump is supplied by the oxidative metabolism.…”

“…This agrees with the mechanical movement of the basilar membrane (von Bekesy, 1960). The CMP, like the positive ERP, has been shown to be highly dependent on oxidative metabolism (Misrahy et al, 1958 a;Konishi et al, 1961;Rice and Shinaberger, 1961;Chambers and Lucchina, 1966;Konishi and Kelsey, 1968 c), although an anoxemic fraction of about ]0 r /( persists for hours after death (Davis, 1957).…”

“…A particularly intngueing phenomenon is that prolonged anoxemia lowers the ERP beyond zero to negative values of 40-50 mV within a few minutes, whereupon the potential gradually returns to zero in one or two hours (Konishi et al, 1961). Measurements of the endolymphatic K + /Na + ratio during anoxemia revealed no great changes in this ratio in the first minutes when the potential becomes negative, while the ratio dropped concurrently with the return of the negative potential to zero, suggesting that the negative potential represents an ionic diffusion potential (Johnstone, 1965).…”