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“Challenges in space exploration: space-flight associated neuro-ocular syndrome (SANS) and lymphatic

Madeeha Mia, Xueyang Zhang, Dr. Olga Gasheva, Dr. Anatoliy Gashev, Dr. Michael Delp, Dr. Pooneh Bagher, Dr. David C Zawieja

Texas A&M College of Medicine

Introduction: A significant percentage of astronauts on short and long-duration space missions have reported impairments in visual acuity, known as spaceflight associated neuro-ocular syndrome (SANS). It is difficult to imagine a medical condition more threatening to space exploration than the loss of visual acuity. Due to the loss of the head-to-foot gravity vector normally seen on Earth, these alterations are thought to be caused by a cephalad fluid shift that occurs in microgravity, which may increase intracranial pressure. Therefore, impaired function of cerebral arteries, veins and lymphatics could be responsible for impaired cranial fluid homeostasis. No studies have examined the effects of long-term spaceflight on lymphatic function. Thus, we aimed to investigate the effects of spaceflight on the contractile function and tone of pre-nodal cervical lymphatic vessels (CLVs) of male mice after 30 days in orbit. Methods: CLVs from mice after ~30 days of spaceflight on the International Space Station were studied immediately after landing and compared to cohort, cage, and vivarium control mice. Mice were euthanized and CLVs were dissected and placed in an isolated vessel chamber filled with 0.5% albumin-supplemented Krebs solution (a-KS). CLVs were cannulated onto resistance-matched glass micropipettes, transferred to the stage of a microscope, and connected to adjustable pressure reservoirs filled with a-KS. CLV segments were superfused with a-KS and their diameters at different pressures and/or flow gradients were recorded with a video camera and computer. Passive vessel diameters were then measured in calcium-free Krebs solution with EDTA. Results: CLVs of the spaceflight group had increased lymphatic tone and phasic contraction frequency. The flow/shear-dependent modulation of CLV function was impaired in space-flown mice compared to controls. Specifically, the normal flow-induced inhibition of phasic lymphatic contractions was significantly impaired in the spaceflight mice. Conclusion: CLV function is altered in response to spaceflight. Its alteration may be a physiological response to the loss of gravity passively driving lymph flow from the head into the neck and the resulting cephalad fluid shift that occurs in astronauts. This could compress the optic nerve resulting in SANS. Thus, a better understanding of the mechanisms behind the changes in lymphatic function and its potential impact on SANS may help develop countermeasures.

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