Vestibular influences on hypoglossal nerve activity in the cat.

The purpose of the present study was to determine if selective activation of vestibular receptors during movement produces changes in hypoglossal nerve activity. Responses were recorded from the hypoglossal nerves during trapezoidal and sinusoidal head rotations in cats with extensive denervations to eliminate non-labyrinthine inputs that could be produced by the movements. Large (50 degrees) nose-up trapezoidal tilts produced an increase in nerve discharge; ear-down tilt was also effective in one-fourth of the animals. The responses to nose-up tilt were abolished following intracranial transections of the VIIIth cranial nerves. Smaller (20 degrees) sinusoidal head rotations in the roll, pitch and yaw planes were ineffective in producing responses. These data suggest that vestibular inputs elicited by nose-up pitch contribute to tongue protrusion and participate in maintaining airway patency by preventing the tongue from falling to the back of the mouth.