Frog experiment onboard space station Mir.

Japanese tree frogs (Hyla japonica) showed unique postures and behavior during an 8-day flight to the Russian space station Mir. When floating in the air, the animals arched their back and extended their four limbs. This posture resembles that observed during jumping or parachuting of the animals on the ground. Frog sitting on a surface bent their neck backward sharply, did not fold their hind limbs completely, and pressed their abdomen against the substrate. They walked backwards in this posture. The typical posture resembles that adopted during the emetic behavior process on the ground, although the posture in space lasts much longer. The possible mechanism of induction of this unique posture in orbit is discussed. Frogs in this posture might be in an emetic state, possibly due to motion sickness. Response behavior to some stimuli was observed in orbit. Body color change in response to the background color appeared to be delayed or slowed down. Response behavior to other stimuli showed little change as long as the animal maintained contact with a substrate. Once it left the surface, the floating frog could not control its movements so as to provide coordinated motility for locomotion and orientation. Adaptation to microgravity was observed in the landing behavior after jumping. Readaptation of the frogs to the Earth environment took place within a few hours after return. Postflight histological and biochemical analysis of organs and tissues showed some changes after the 8-day spaceflight. Weakening and density loss in vertebrae was noted. The beta-adrenoreceptor activity of the gastrocnemius was natriuretic decreased. Skin collagen and liver protein synthesis were lowered. The distribution of the atrial factor-like peptides in the brain was changed.