Estrogen Reduces Caspase-3 Expression in the Inner Ear of Guinea Pigs Exposed to Simulated Microgravity and Inboard Noises of Spaceship

th Hospital of People’s Liberation Army, Beijing, China OBJECTIVE: In different tissues, oestrogen plays different roles in cell apoptosis. In this study, we investigated the effect of oestrogen on cell apop tosis in inner ear cells of guinea pigs exposed to simulated microgravity and inboard noises of a spaceship. MATERIALS and METHODS: Three groups of guinea pigs received no oestrogen, a preventive dose of oestrogen, and treatment dose of oestrogen, respectively. Caspase-3 expression in the inner ears of different groups was evaluated using immunohistochemical staining. The hearing levels were tested by auditory brainstem response. RESULTS: On the first day of exposure to the stimulus, the auditory brainstem response thresholds were lower in the treatment group than in the control and prevention groups. After 3-day recovery, the prevention group showed a greater auditory brainstem response threshold shift than the other two groups. The expression of caspase-3 in hair cells and stria vascularis cells was weaker in the treatment group on the first day of the expo sure. However, after 3-day recovery, caspase-3 expression was weaker in the prevention group. CONCLUSION: Estrogen had a protective effect on the hearing impairment caused by the combined factors of simulated inboard noises and micro gravity of a spaceship, reflected by both the auditory brainstem response score and morphological characteristics. Different doses and periods of the administration of oestrogen showed different protective effects. Use of oestrogen for treatment resulted in a better protective effect right after the stimulus, whereas preventive use of oestrogen led to a better effect in the recovery period.