Streptomycin in the chick embryo: post-hatching vestibular behavior and morphology.

Developing chick embryos were exposed to streptomycin injected on days 5 through 13 of the 21 day developmental period. Histological and behavioral abnormalities were found almost exclusively in chicks exposed after day 7. The nature of the behavioral deficits included abnormal head posture, head tremor, and inability to compensate for applied vestibular stimuli. Head movement measurements showed that the head tremor had frequencies of oscillations from 10-35 Hz. The amplitude of the tremor was a large as 10 degrees. Histology showed damage to the secretory dark cells of the membranous labyrinth in those chicks that showed behavior changes. Even with increased dosages chicks exposed prior to day 7 rarely showed abnormal vestibular behavior but instead experienced increased mortality. Further tests examining tissue levels of streptomycin showed little or no streptomycin in embryos until day 10. These results are discussed in terms of their utility as an alternative model to surgical manipulation of the vestibular system in developing embryos. Behavioral consequences are compared to other work with drugs and to the effects of weightlessness and unusual environments on vestibular orientation and behavior.