Vestibular Ototoxicity in Primates

Abstract

Vestibulotoxicity of streptomycin, viomycin, gentamicin, and SCH 13706 was investigated in squirrel monkeys (Saimiri sciureus) given these compounds accordings to different regimens of dosage. Vestibular function tests performed were: squirrel monkey rail test (to test the ability of body equilibrium maintenance), postrotatory nystagmus test (and threshould caloric test), and motion sickness test in a slow rotation chamber. The internal ear specimens from all experimental subjects were subsequently investigated morpholigically. Streptomycin sulfate injured the spiral (Corti's) organ as readily as the ampullar cristae; however, it seemed to have less predilection to the maculae. Body balance maintanence, emesis in slow rotation room, and caloric threshold declined almost simultaneously after series of streptomycin sulfate injections, but all of these changes disappeared after the injections ceased. Similar to the situation after streptomycin sulfate, the monkeys which received viomycin sulfate systemically demonstrated more type I vestibular hair cell loss when compared to type II hair cell. Ampullar cristae were generally more vulnerable than the maculae. Dysequilibrium occurred repidly when high daily doses (30 or 60 mg/kg) of gentamicin were injected. However, the results obtained by the body equilibrium function tests and morphological findings were not in agreement with each other. One reason for this is that body equilibrium fuction reflects not only the internal ear function, but also systemic reaction simultaneously. Kidney involvement after high daily doses of gentamicin was severe, while SCH 13706 showed less systemic and renal toxicity when compared to that after identical daily doses. After the large total doses of SCH 13706. bodily dysequilibrium, postrotatory nystagmus decline and internal ear end organ damage were observed.