Mammals
Deformities in mammalian embryos in microgravity have been noted: “Fritzsch and Bruce (1995) reported that utricular and saccular axons of microgravity-exposed [rat] fetuses were largely unbranched generally ending in growth cones, whereas corresponding axons in controls showed elaborated branching. In contrast, facial sensory neurons of microgravity-exposed fetuses had exuberant branches to the utricle that were virtually absent in the controls.” (Ronca and Alberts, 2000) Experiments have been done on rats in microgravity but, due to a lack of standardization, it is difficult to compare results (Ronca, 2003). Rats were allowed to mate in a Cosmos 1129 biosatellite experiment and the females failed to become pregnant, although fertilization had occurred (Serova et al., 1982). Development of mice in microgravity has not been successful to date when they were exposed to microgravity throughout the whole developmental period: Kojima et al. (2000) noted that the pre-implantation embryos were resorbed. A flight of the space shuttle Columbia (STS-80) had 49 mice embryos onboard. None of the two cell stage embryos showed any sign of development and they all died (Shenker and Forkheim, 1998 ). Human pregnancy is counter indicated by NASA with microgravity listed as one of the factors. The reasons for this are that microgravity “May have impact on in utero embryonic development and reproductive physiology in both males and females as evidenced by animal studies” (Jennings and Santy, 1989)