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Streptomycin in the chick embryo: post-hatching vestibular behavior and morphology
R V Kenyon1, R Kerschmann, R Silbergleit
1Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge 02139.
Insights
Streptomycin exposure in chick embryos after day 7 causes vestibular and head movement abnormalities. Early exposure (before day 7) increases mortality but not vestibular issues, suggesting a critical developmental window.
Area of Science:
- Developmental biology
- Neuroscience
- Pharmacology
Background:
- The vestibular system is crucial for balance and spatial orientation.
- Understanding developmental effects of ototoxic drugs is important for human health.
- Chick embryos offer a model for studying early developmental processes.
Purpose of the Study:
- To investigate the effects of streptomycin on vestibular system development in chick embryos.
- To identify critical developmental periods for streptomycin-induced ototoxicity.
- To evaluate the chick embryo as a model for vestibular research.
Main Methods:
- Developing chick embryos were exposed to streptomycin via injection on days 5-13.
- Histological analysis examined damage to the vestibular system.
- Behavioral tests assessed responses to vestibular stimuli and head movements.
- Tissue analysis measured streptomycin levels in embryos.
Main Results:
- Exposure after day 7 led to vestibular and behavioral deficits (head posture, tremor, impaired compensation).
- Head tremor ranged from 10-35 Hz with amplitudes up to 10 degrees.
- Histology revealed damage to the dark cells of the membranous labyrinth.
- Early exposure (before day 7) resulted in higher mortality, not vestibular dysfunction.
- Significant streptomycin levels were detected in embryos only after day 10.
Conclusions:
- Streptomycin exposure during specific embryonic periods can induce vestibular abnormalities.
- The chick embryo model demonstrates a critical window for streptomycin's ototoxic effects.
- Findings support the utility of this model for studying vestibular system development and drug effects.
Abstract:
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.