Light microscopy study of cisplatin-induced ototoxicity in rats

Although most studies on animal ototoxicity employ scanning electron microscopy, all cochlear structures may be identified with light microscopy. This paper describes a simple method of histological assessment of cisplatin-induced ototoxicity in rats, and relates morphological changes to functional changes in hearing detected by distortion product evoked otoacoustic emissions. Male Wistar rats were injected with 8 mg/kg/day cisplatin, or with an equivalent volume of saline solution, for three consecutive days. They underwent distortion product evoked otoacoustic emission testing at baseline and at 24 or 48 hours after the last administration. At the end of the experiment, the animals were sacrificed and their cochleae were retrieved and prepared for haematoxylin and eosin staining. A four-point scoring system was used to grade injury to the external ciliated cells, as indicated by the number of cells absent from the basal turn of the cochlear duct. A four-point scoring system was also used to grade stria vascularis injury, as indicated by the degree of shrinkage of the intermediate cells. Scores were significantly higher in groups treated with cisplatin compared with controls. Morphological changes were confirmed by decreased distortion product evoked otoacoustic emission amplitudes in animals treated with cisplatin. This method is simple to perform with routine histology equipment and is appropriate for the study of acute, cisplatin-induced ototoxicity in rats.