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.