RESPONSES OF VENTRAL RESPIRATORY GROUP NEURONS OF THE CAT TO NATURAL VESTIBULAR STIMULATION

Stimulation of vestibular otolith afferents by fore-aft tilt (pitch) e licits changes in activity of nerves innervating respiratory muscles, including the diaphragm, abdominal muscles, and tongue musculature. To determine the role of ventral respiratory group (VRG) neurons in prod ucing these vestibular-respiratory responses, the activity of VRG neur ons was recorded during natural vestibular stimulation in multiple tra nsverse planes. Only a small fraction of VRG neurons with inspiratory (I, 20 of 80 cells), expiratory (E, 11 of 59 cells), or phase spanning (4 of 16 cells) activity responded to tilts up to 15 degrees in ampli tude delivered at frequencies fi om 0.02 to 2 Hz. In particular, respo nses were infrequent in VRG neurons with projections to the spinal cor d (0 of 23 E cells and 2 of 15 degrees I cells), despite the fact that the tilts employed produced robust modulation of the activity of abdo minal (expiratory) nerves. Furthermore, the characteristics of respons es to tilt of the small fraction of VRG neurons with vestibular inputs did not match those of respiratory muscles. These data suggest that n eurons in addition to those in the VRG must participate in generating vestibular-respiratory responses.