Abstract
Modifications of gravity levels induce generalized adaptation of mammalian physiology, including vascular, brain, muscle, bone and immunity functions. As a crucial interface between the vascular system and the brain, the blood–brain barrier (BBB) acts as a filter to protect neurons from pathogens and inflammation. Here we compare the effects of several protocols of hypergravity induced by centrifugation and whole-body vibrations (WBV) on BBB integrity. The immunohistochemistry revealed immunoglobulin G (IgG) extravasation from blood to hippocampal parenchyma of mice centrifuged at 2 × g during 1 or 50 days, whereas short exposures to higher hypergravity mimicking the profiles of spaceflight landing and take-off (short exposures to 5 × g) had no effects. These results suggest prolonged centrifugation (>1 days) at 2 × g induced a BBB leakage. Moreover, WBV were similarly tested. The short exposure to +2 × g vibrations (900 s/day at 90 Hz) repeated for 63 days induced IgG extravasation in hippocampal parenchyma, whereas the progressive increase of vibrations from +0.5 to +2 × g for 63 days was not able to affect the IgG crossing through the BBB. Overall, these results suggest that the BBB permeability is sensitive to prolonged external accelerations. In conclusion, we advise that the protocols of WBV and centrifugation, proposed as countermeasure to spaceflight, should be designed with progressively increasing exposure to reduce potential side effects on the BBB.
Highlights
During spaceflights, organisms are exposed to confinement, radiations and successive modifications of gravity levels, including hypergravity (HG) during take-off and landing phases and microgravity during the orbital flight
The comparison by two-way analysis of variance (ANOVA) of the body weight of Ctrl-HG and long-term hypergravity (Long-HG) mice indicated that both groups presented similar weights before as well as just after the end of the centrifugation and that both groups increased their body mass (p < 0.0001, Fig. 1a)
The increase of body weight was reduced after a long-lasting exposure to HG, which has been proposed as an index of the centrifugation.[20,21,22]
Summary
Organisms are exposed to confinement, radiations and successive modifications of gravity levels, including hypergravity (HG) during take-off and landing phases and microgravity during the orbital flight. Spaceflight affects the cardiovascular system via the blood shift responsible for the decreases in plasma volume and cardiac performance and probably the increase of intracranial blood pressure. In vertebrates, these gravity changes and alteration of blood pressure impact many sensory systems (vision; taste and olfaction; proprioception) but have prominent consequences on the vestibular system with major impact on balance, posture and spatial representation. Exposition to artificial gravity during and/or after spaceflight by centrifugation has been proposed as a countermeasure to limit or suppress neurovestibular consequences of prolonged weightlessness such as the orthostatic intolerance observed after spaceflight.[5,6] Likewise, whole-body vibrations (WBV) serves as a countermeasure against cardiovascular alterations due to aging and obesity, as it enhances vasodilation of small arterioles, and possibly capillaries in human leg muscles,[7,8] and reduces the bone loss classically observed after spaceflight.[9,10]
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