Microgravity in the STS-29 space shuttle discovery affected the vestibular system of chick embryos

Abstract

Out of 32 embryos flown (16 @ E2 + 16 @ E9) for 5 days, 16 survived. Al1 sixteen E2 were dead at landing. Eight were opened and eight were incubated at 1 .OG. Autopsy showed that 4 E2 survived over 24 hours in space. Eight E14 hatched without anatomical malformations, and 8 E14 were fixed. The height of the macular epithelia was 31 ym (mean) in control and 26 pm in flight chicks. The cross-sectional area of macular nuclei of control was 17 ym2 for hair cells and 14 ym2 in supporting cells. In flight, cross-sectional area was 17 pm2 in hair cells and 15 Iim2 in supporting cells (n=250). The shape factor of cartilage cells (1.0 = perfect circle) between control (mean = 0.70) and flight (mean = 0.72), and the area of cartilaginous cells between controls (mean = 9 pm2) and flight (mean = 9 Iirn2) did not differ (n=300). The nuclei of support cells were closer to the basement membrane in flight than in control chicks. The immunoreactivity of otoconia with anti keratan, fibronectin or chrondroitin sulfate was not different between flight and control ears. There were more afferent fibers inside the macular epithelia of flight (p<0.05) than control. Three of 8 flight animals had elevated vestibular thresholds (VT), with normal mean response amplitudes and latencies. Modified afferent innervation pattems requiring weeks to compensate are sufficient to elevate VT, and should be investigated further. Other reversible (sublethal) microgravity effects on sensory epithelia (vacuoles, swelling, etc) require quantification.