Sympathetic response to horizontally linear acceleration in humans.

There is considerable evidence that stimulation of the vestibular system has effects on the activities of sympathetic preganglionic neurons in animals and of postganglionic nerves in animals and humans. In previous studies, we showed that the muscle sympathetic nerve activity (MSNA) from the human tibial nerve is enhanced after caloric vestibular stimulation (Cui et al. 1997), whereas the skin sympathetic nerve activity is suppressed during the nystagmus evoked by the caloric vestibular stimulation (Cui et al. 1999). These results suggest that the stimulation of the horizontal semicircular canal has effects on sympathetic outflows to muscle and skin in humans. However, much less is known about the MSNA response to dynamic stimulation of otolith organs in humans. To clarify this issue, we used a linear accelerator to stimulate the vestibular organs, especially otolith organs, and observed the MSNA and hemodynamic responses during movement.