Further observations of vestibular ototoxicity in the chick: effects of streptomycin on the ampullary sensory epithelium.

Starting eight days after hatching, chicks received daily subcutaneous injections of streptomycin sulfate, either 400 mg/kg for 30 days or 1,200 mg/kg for 15 days. Randomly selected chicks from each group were killed at intervals during the injection period, and the ampullae were examined for signs of vestibulotoxicity. Ampullary cell types differed in sensitivity to streptomycin. First, dark cell processes withered. Second, vacuoles formed in the apices of the light cells of the planum semilunatum. Third, nerve terminals swelled, and their organelles and ground substance clumped together, creating cleared areas. Last, hair cells and supporting cells became slightly vacuolated. However, these cells showed less overt damage than the other cell types. The onset of damage was earlier and the damage more severe with the 1,200-mg than with the 400-mg dosage. There was no evidence of hair cell loss during the experiment.