黒谷 明美

Fertilization and subsequent embryogenesis of newts occurred normally under microgravity in two Astronewt flight experiments. By accumulation of the results from the amphibian flight experiments including 'Astronewt', it is considered that gravity has rather small effects on the early development of amphibian eggs. However, some temporary abnormalities, which recover in the course of the further developmental process, have been observed. Some regulations may occur in whole embryos. For a thorough knowledge about the role of gravity in morphogenesis, we need to investigate the gravitational effects on a single cell in a whole embryo. We propose a new experimental system with sea urchin embryos and micromeres for further studies at a cellular level of the effects of gravity on morphogenesis. © 2003 Elsevier Science B.V. All rights reserved.

AstroNewt experiment explores the effects of earth gravity on the early development of Japanese red-bellied newt, Cynops pyrrhogaster. Since female newts keep spermatophore in cloaca, fertilized eggs could be obtained without mating. Fertilization of newt's egg occurs just prior to spawning, so that gonadotrophic cues applied to females in orbit leads to laying eggs fertilized just in space. A property of newt being kept in hibernation at low temperature may be of great help for the space experiment carried out with much limited resources. A general outline of the AstroNewt project is shown here in addition to some technical advances for the development of the project. Experimental schemes of two space experiments (IML-2 in summer 1994 and unmanned SFU at the beginning of 1995) are also shown. © 1995, All rights reserved.

Four adult female Japanese newts, Cynops pyrrhogaster, were carried for 15 days aboard the orbiting space shuttle, Columbia, in July of 1994, as part of the Second International Microgravity Laboratory, IML-2 aquatic animal experiments. These previously fertilized newts, after stimulation with chorionic gonadotropin by a spaceflight adapted injection procedure, deposited numerous eggs for study of early development during weightlessness. The primitive saccular lungs of the two newts which survived the spaceflight revealed by TEM marked pulmonary cytopathologic changes including basal laminar separation, microvillar degeneration, and cytoplasmic granular changes in the primary granulated pneumocytes. Also, intracellular edema in the pulmonary collagenous matrix and vacuolar changes in the ciliated pulmonary lining cell type and in vascular endothelial cells were observed. These changes, triggered by the spaceflight, and not seen in controls also relying on respiration via the skin, may reflect a chronic mild hypoxia as it is known that newts undergoing oviposition are subject to increased oxygen demand.

We report here on the amplectic behavior of the Japanese treefrog (Hyla japonica) in microgravity. Treefrogs were exposed to 35 cycles of altered gravity, including approximate to 1.5 sec of G<0.1 every 3 min and 15 sec, on the FreeFall ''G.0'' ride at Space World amusement park in Kitakyushu, Japan. During this period a pair of frogs spontaneously entered and maintained amplexus for 1 hr 20 min, before being removed from the ride. In freefall, the pair extended their hindlimbs in the characteristic posture of treefrogs in microgravity. This is the first report of a vertebrate entering and sustaining a copulatory or amplectic posture under gravitational extremes, including true freefall. These observations bode well for the potential of anurans to breed in microgravity and to be used for biological research in space.

Japanese tree frogs (Hyla japonica) were flown to the space station MIR and spent eight days in orbit during December, 1990 /1/. Under microgravity, their postures and behaviors were observed and recorded. On the MIR, floating frogs stretched four legs out, bent their bodies backward and expanded their abdomens. Frogs on a surface often bent their neck backward and walked backwards. This behavior was observed on parabolic flights and resembles the retching behavior of sick frogs on land- a possible indicator of motion sickness. Observations on MIR were carried out twice to investigate the frog's adaptation to space. The frequency of failure in landing after a jump decreased in the second observation period. After the frogs returned to earth, readaptation processes were observed. The frogs behaved normally as early as 2.5 hours after landing.

We report here on the behavioral reaction of two reptiles to abrupt decreases in gravity. One striped rat snake, Elaphe quadrivirgata, and three striped-neck pond turtles, Mauremys japonica, were exposed to microgravity (mu-G) on parabolic flight, during the filming of a documentary for the NHK television station in Japan. The video films revealed that the snake reflexively responded to the shift from hyper- to hypogravity by taking up a defensive posture-on the first parabola, the snake struck at itself. The turtles actively extended their limbs and hyper-extended their neck in mu-G, a posture which is identical to that displayed during their contact ''righting reflex'', when placed upside-down in normal gravity. The aggressive display of the snake was unexpected, although the righting response of the turtles was consistent with that shown by other vertebrates, including fish and mammals, exposed to mu-G. An implication of these observations is that the afferent signal for the righting reflex of vertebrates in normal gravity must be the unloading of ventral receptors in the sensory system, rather than the loading of dorsal receptors. These are the first behavioral records for any reptiles exposed to hypogravity.

自然界で捕獲され, 約4週間, 同一条件で飼育されたアマガエル8匹の腸内フローラを菌種レベルで検索するとともに, カエルの腸内常在微生物の至適発育温度を考慮して, 室温(23〜25℃)および37℃の培養温度で培養を行ない, それによって得られた細菌数の差も比較した. すべてのカエルから微生物が分離され, 腸内容物1グラムあたり3.1×10^9の菌数が検出されたが, 培養温度の違いによる菌数の差は認められなかった. 分離菌株を菌種レベルで検索したところ, 11菌属16菌種に分類された. 最優勢に分離された菌種はBacteroides (B.) caccaeおよびB. vulgatusであり, ついで, Escherichia coliが高い菌数で分離された. 他の嫌気性菌ではFusobacteriumおよびClostridium菌属が検出された. また, Enterococcus faecalisも高頻度に分離された. しかし, Lactobacillus, Bifidobacterium, eEubacteriumおよびPeptostreptococcusの4菌属は分離されなかった.