[Streptomycin toxicity on dark cells of utricles in guinea pigs]

Thirty guinea pigs were divided into three groups. The first group received intramuscular injection of streptomycin sulfate 400 mg/kg/day for one week; the second group received the same dosage for two weeks; the third group served as the control. The cochlea was dissected after treatment and the utricle observed under electron microscope. The nystagmus lasted 11.3 sec. clockwise and 12.75 sec. counter-clockwise before treatment, 10.75 sec. and 9.25 sec. after one week and 6.0 sec. and 5.5 sec. after two weeks. Histopathologic study showed the normal dark cells in the control group. In the one week group, the dark cell remained in cuboidal shape. On the luminal surface of the cell were a few microvilli and invaginations which were in the process of forming pinocytotic vesicles. In the apical cytoplasm, the coated pinocytotic vesicles, vacuoles and rough endoplasmic reticula markedly decreased. The crest of mitochondria was blur, coalescent and vacuous. The plasmalemma in the lower part of the cell reduced. In the two-weeks group, the cells became squamous with less cytoplasm and organelle. There was no pinocytotic vesicles and vacuoles in the apical cytoplasm. The luminal membrane of the cells were bulging out into the cavity. In case the membrane ruptured, the cytoplasmic organelle run into the endolymphatic space and the cell dissolved and damaged. The morphological changes indicated that streptomycin damaged the cytoplasmic granules and the plasma membrane of dark cells. These cytologic characteristics of dark cells which engaged in the fluid transport were similar to those of the secretory cells in other organs.(ABSTRACT TRUNCATED AT 250 WORDS)