Abstract
The ability to maintain the body relative to the external environment is important for adaptation to altered gravity. However, the physiological limits for adaptation or the disruption of body orientation are not known. In this study, we analyzed postural changes in mice upon exposure to various low gravities. Male C57BL6/J mice (n = 6) were exposed to various gravity-deceleration conditions by customized parabolic flight-maneuvers targeting the partial-gravity levels of 0.60, 0.30, 0.15 and μ g (<0.001 g). Video recordings of postural responses were analyzed frame-by-frame by high-definition cineradiography and with exact instantaneous values of gravity and jerk. As a result, the coordinated extension of the neck, spine and hindlimbs was observed during the initial phase of gravity deceleration. Joint angles widened to 120%–200% of the reference g level, and the magnitude of the thoracic-curvature stretching was correlated with gravity and jerk, i.e., the gravity deceleration rate. A certain range of jerk facilitated mouse skeletal stretching efficiently, and a jerk of −0.3~−0.4 j (g/s) induced the maximum extension of the thoracic-curvature. The postural response of animals to low gravity may undergo differential regulation by gravity and jerk.
Highlights
Within their particular physiological limits, terrestrial life forms have the ability to adapt to changes in the physical properties of the environment, such as temperature, atmospheric pressure, humidity and other conditions
Upon entering into the “dive” phase of parabolic flight, all of the mice showed a typical pattern of postural change, initial extension and later flexion, regardless of the target-gravity level (Figure 4)
cervical curvature (CC) stretching increased until 2.0 s in the “dive” phase of the 0.3 g-targeting flight, but not so much as in the flights targeting 0.15 or μ g
Summary
Within their particular physiological limits, terrestrial life forms have the ability to adapt to changes in the physical properties of the environment, such as temperature, atmospheric pressure, humidity and other conditions. A certain degree of adaptability to changes in gravity is expected, but the physiological limits to these changes remain unclear [1,2,3,4]. The distressing symptoms of exposure to microgravity (μ g) have been reported extensively. Recent studies have attempted to examine the physiological changes that occur in partial-gravity conditions, such as those encountered on the moon (≈0.16 g) or on Mars (≈0.38 g) [14,15,16,17,18,19,20]
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