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The Effects of Spaceflight on Cervical Lymphatic Vessel Function in Mice
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In recent years, NASA has reported that a significant number of astronauts are experiencing vision acuity loss after both short-term and long-term spaceflight missions. These visual impairments have been hypothesized to be related to the microgravity-induced cephalic fluid accumulation and the rise of the intracranial pressure during spaceflight. The cephalic and cervical lymphatics are known to play an essential role in regulating the hydrodynamic status of the cephalic region and the intracranial pressure by regulating and generating lymph flow via tonic and phasic lymphatic contractions. In this project, we measured the contractile function of pre-nodal cervical lymphatic vessels (CLVs) in male C57BL/6 mice after a 30-day spaceflight on the International Space Station. All measurements were compared with those obtained from the cohort, habitat and vivarium control mice groups. The CLV segments were isolated, cannulated and pressurized using two independently adjustable pressure reservoirs. A microscope, CCD video camera, computer and DVD/HDD recorder were used to record the live diameter changes. To determine stretch-dependent contractile responses, we evaluated the diameter changes of CLVs at 1, 2 and 4 cm H2O transmural pressures. To determine flow/shear-dependent contractile responses, we studied the diameter changes of CLVs with a 3-cm H2O-imposed trans-axial flow gradient. The passive diameters were also measured. We calculated the lymphatic contractile amplitude, contractile frequency, fractional pump flow and tone index as indicators of CLV pump and conduit function. Statistical analysis indicated there were no significantly different responses within the control groups. However, the spaceflight CLVs showed increased lymphatic tone and enhanced stretch-dependent changes in contraction frequency; while the flow/shear-induced inhibition on lymphatic phasic contraction was significantly impaired. In conclusion, our study reveals an overall more constricted vessel status and a loss in flow-sensitivity in CLVs after spaceflight, suggesting a functional adaptation of CLVs in response to the loss of gravitational force and cephalic fluid accumulation. The space-induced adaptations of CLV functions may further increase cephalic fluid accumulation and intracranial pressure, and thus potentially facilitate the development of visual impairments in space. Our findings help in understanding the possible underlying mechanisms of spaceflight-induced visual impairments to allow future prevention and therapeutic strategies.
Zhang, Xueyang (2019). The Effects of Spaceflight on Cervical Lymphatic Vessel Function in Mice. Master's thesis, Texas A&M University. Available electronically from