Microneurographic analy sis of muscle sympathetic nerve activity under microgravity induced by parabolic flight

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Parabolic flight by a ject aircraft can produce approximately 20 seconds of microgravity, and hypergravity of 1.5 to 2.0 G before and after this microgravity period. Muscle sympathetic nerve activity (MSNA) recorded from the bitial nerve using microneurographic technique from healthy humans sitting in a passenger seat. We used MU-300 (Mitsubishi Heavy Industries) ject aircraft affiliated to Diamond Air Service next to Nagoya International Airport. MSNA innervating to the triceps surae was recorded using tungsten microelectrode, simultaneously with electrocardiography, respiration curve, blood pressure wave with Finapres, intrathoracic blood volume with impedance cardiography with natural and controlled (0.25Hz) respiration. MSNA was revealed to be activated (177%) under hypergravity and suppressed (52%) under microgravity, and these activation and suppression were quite transient and phasic under natural respiration. During later half of microgravity period, MSNA was then activated, which was induced through arterial baroreflex. This activation-suppression series was attenuated under controlled respiration, probably because controlling mechanism of MSNA might transfer from arterial baroreflexdominant to cardiopulmonary volume receptor dominant.