[45]

Ongoing Comparative Study of the Effects of Microgravity During Foton M2 and M3 on Cancellous Bone Mass in the Aquatic Newt Pleurodeles waltl and the Terrestrial Gecko Pachydactylus bibronii.    E. Almeida ^1,3, N. Dvorchkin ¹, R. Turner ², R. Globus ¹ N. Searby ^{1       1}NASA Ames Res. Ctr., ²Oregon State U, Corvallis, ³U C San Francisco

   Rapid cancellous bone degeneration occurs in mammalian species exposed to microgravity during spaceflight, and is a serious health concern for long-term human presence in space.  In this study we are examining the effects of microgravity on cancellous bone mass in two comparable lower vertebrates, the terrestrial gecko Pachydactylus bibronii and the aquatic newt Pleurodeles waltl).  Newts and geckos were flown simultaneously in the Russian/US collaborative experiments “Regeneration” and “Gecko” in Foton M2, and will fly again in Foton M3.  Both species can withstand moderate periods without food and in the case of the Gecko, also without water, have relatively small size and similar body plans. During the 16-day Foton M2 spaceflight newts were provided with a wet PVA sponge and no food, but geckos had no water or food.  Since the newt is adapted to reduced mechanical loading in limbs, due to its neutral buoyancy in the aquatic environment, we hypothesized that it might not lose long-bone mass in space.  Conversely, we hypothesized that the weight-bearing gecko may require gravitational loading to maintain cancellous long-bone mass.  Thus far in these ongoing studies, the effects on long-bone mass, analyzed using micro-computed tomography (µCT), is consistent with no significant bone loss in the newt during spaceflight (radius and fibula; n=14 spaceflight animals, n=15 ground controls, and n=8 basal controls, total 148 bones analyzed). In the Gecko experiment we previously reported indiscriminate cancellous bone loss in the tibia both in spaceflight, and ground controls likely due to water deprivation. These results, although incomplete, support the hypothesis of amphibian bone pre-adaptation to the space environment, but are not informative about the gecko.  Ongoing and upcoming efforts include improvement of spaceflight habitat hardware conditions in Foton M3 for the Gecko, including water delivery, to minimize non-microgravity induced body and bone mass loss.  Supported by NASA Project Foton M2/M3.