Analysis of dorsal light tilt reaction and cerebellar activities in carp during aircraft parabolic-flight weightlessness

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The dorsal light tilt reaction (DLTR) of carp and electrical activity of the cerebellum were examined under parabolic-flight low gravity. This project belongs to a series of preliminary experiments for our proposal of "space motion sickness" research for the Space Shuttle mission of Japan (Spacelab-J) which was originally scheduled in 1988 but changed later to 1991 after the accident of Challenger. Since such parabolic-flight application to scientific research had never been performed in Japan until the present project was realized, an evaluation of capability for the aircraft chosen (Mitsubishi MU-300) also involved in this research. The conclusion and results obtained are as follows:1. About 20 seconds of duration with a microgravity below 0.05 Gz could be attained for each parabolic flight. The duration and gravity level may be satisfactorily long and low enough to advance some kinds of preliminary studies for scientific research in space.2. A completely light-dependent reaction with a rather high speed of the tilting (DLTR) was a characteristic feature of the intact carp exposed to the parabolic-flight low gravity. It indicates unbalanced visual-vestibular interaction for the posture control due to loss of the vestibular input. Possible modification of DLTR pattern will be examined during the prolonged weightlessness in space.3. A power spectral analysis of the cerebellar activity under microgravity showed enhancement of the power at the frequency ranges below 8 Hz and between 12-25 Hz. Possible recovery in the activity will be followed in the space mission.