A strong species of lichens was sorted out to expose the extreme conditions which will be encountered by interplanetary space, followed our previous work of fungal and moss spores. Caloplaca flavovirescens was the most resistant lichen among 10 kinds (9 species) of the lichens examined against temperature fluctuations in vacuum, UV irradiation and cosmic ion irradiation (examined 3 species). The survival rate decreased about 24% by the thermal cycle treatment under vacuum (<1Pa) for 6 weeks under the condition of temperature fluctuations between −80°C and 80°C once every 90 min. The rate after one year is extrapolated to be 4.7% (cultivation method) and 7.1% (fluorescent method) under the supposition of the exponential decrease of survival rate continue for a long period of time. The growth rates did not decrease after the temperature fluctuations between −60°C and 60°C with the same periodicity. The survival rate of the lichen was decreased by 5% at 1,413mJ/cm² of UV-C (254nm) irradiation. The survival rate of the lichen was decreased by about 20% after 335Gy irradiation of helium beam, and the 10% survival rate (D10) was calculated for 1,640 Gy from the extrapolation of regression equation. This amount will be equivalent to 130 - 1,300 year irradiation at the outer environment of ISS. The reduction rate of carbon beam seems somewhat larger than that of helium beam. As far as these factors concerned, C. flavovirescens inside the container which prevent UV, will survive for several years at the ISS outer environment.

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In order to determine the effect of gravity perception on brain activity, we immunohistochemically studied the density of c-Fos protein-positive cells in various brain regions of adult wild-type and ha mutant medaka fish. Some ha fish form utricular otoliths (lapilli) in later growing stages and are designated ha(3-3), whereas others continue to lack lapilli and are designated ha(2-2). In most regions, wild-type fish expressed a higher density of c-Fos-positive cells than ha(3-3) and ha(2-2) mutant fish following exposure to hypergravity (3 G) for 3 h. Prominent differences between wild-type and ha mutants were quantitatively demonstrated in the telencephalon, fasciculus longitudinalis medialis, and posterior octavus nucleus with the caudal nucleus. An exception was the stratum periventriculare region, which showed the highest density in ha(2-2) fish and the lowest in wild-types. The results showed that the lapillus is the otolith mainly responsible for the gravity perception of medaka and that the ha mutant can serve as a model for fish born and raised in microgravity. The use of ha fish can help us to understand what changes occur in the gravity-sensing system of medaka fish born and raised for life cycle experiments aboard the International Space Station (ISS).

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