MICROGRAVITY IN THE STS-29 SPACE-SHUTTLE DISCOVERY AFFECTED THE VESTIBULAR SYSTEM OF CHICK-EMBRYOS

Out of 32 embryos flown (16 @ E2 + 16 @ E9) for 5 days, 16 survived. A ll sixteen E2 were dead at landing. Eight were opened and eight were i ncubated at 1.0G. Autopsy showed that 4 E2 survived over 24 hours in s pace. Eight E14 hatched without anatomical malformations, and 8 E14 we re fixed. The height of the macular epithelia was 31 mu m (mean) in co ntrol and 26 pm in flight chicks. The cross-sectional area of macular nuclei of control was 17 mu m(2) for hair cells and 14 mu m(2) in supp orting cells. In flight, cross-sectional area was 17 mu m(2) in hair c ells and 15 mu m(2) in supporting cells pm (n = 250). The shape factor of cartilage cells (1.0 = perfect circle) between control (mean = 0.7 0) and flight (mean = 0.72), and the area of cartilaginous cells betwe en controls (mean = 9 mu m(2)) and flight (mean = 9 mu m(2)) did not d iffer (n = 300). The nuclei of support cells pm were closer to the bas ement 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 affere nt fibers inside the macular epithelia of flight (p < 0.05) than contr ol, Three of 8 flight animals had elevated vestibular thresholds (VT), with normal mean response amplitudes and latencies. Modified afferent innervation patterns requiring weeks to compensate are sufficient to elevate VT, and should be investigated further. Other reversible (subl ethal) microgravity effects on sensory epithelia (vacuoles, swelling, etc) require quantification.