Shinichiro Asakuma

Experimental Study of the Mechanism of the Decrease in Endocochlear d.c. Potential after Administration of Nitrogen Mustard-N-Oxide

20 mg/kg of body weight of nitrogen mustard-N-oxide hydrochloride ( NMNO ) causes a transient decrease in the magnitude of the endocochlear d.c. potential (EP) in the same manner as does nitrogen mustard (NM). NMNO does not, however, change the electrical resistance of the cochlear partition. When the administered dose of NMNO is increased to 40, 60 and 80 mg/kg body weight, a corresponding diminution in the EP is not observed. No ultrastructural changes in the stria vascularis are observed, even in animals administered 80 mg/kg body weight. The reduction of the EP with NMNO could not be attributed to a loss of the electrical insulator effect of the cochlear partition, or to a functional derangement of the stria vascularis. In the experimental animals whose organ of Corti was already destroyed with kanamycin sulfate (KM), NMNO did not reduce the magnitude of the EP. The organ of Corti may be central in understanding the mechanism of NMNO -induced reduction of the EP.

Effect of Glycerol on Cochlear Potentials in the Guinea Pig

To study the rationale of the glycerol test, cochlear potentials were measured in albino guinea pigs after intravenous administration of 50% glycerol solution. The endocochlear dc potential was reduced slightly within a few minutes after glycerol injection and the negative summating potential also decreased simultaneously. However, these changes were merely transient and almost disappeared within ten minutes. Several investigators have pointed out that the reduction of inner ear pressure caused by glycerol injection takes place after about ten minutes. Therefore, it may be that the changes observed in this study are not due to dehydration by glycerol in the cochlea and, in turn, that the osmotic force of glycerol does not affect directly cochlear potentials, at least in normal guinea pigs.

Effect on Cochlear Microphonics of Nacl Crystals Placed on the Round Window Membrane

The effects of NaCl crystals placed on the round window membrane in the cochlea were studied by observing changes in cochlear microphonic potential (CM) at the first and the third turn of the cochlea of guinea pigs by means of a differential electrodes technique. The CM at the first turn showed polyphasic changes in output with lapse of time, that is the overshoot phase, the primary decrease phase, the recovery phase and the secondary decrease phase. In contrast, the CM at the third turn showed only an overshoot followed by a gradual decrease to the original level. It was confirmed that the effect of NaCl crystals placed on the round window membrane in a small dose was localized only in the basal part of the cochlea. The possible mechanism of the polyphasic changes of CM at the first turn is discussed and the metabolism of the inner ear fluids is emphasized as the main factor of the changes.