VENTRAL RESPIRATORY GROUP BULBOSPINAL INSPIRATORY NEURONS PARTICIPATEIN VESTIBULAR-RESPIRATORY REFLEXES

1. The vestibular system responds to accelerations of the head and pro duces reflex responses that serve a variety of compensatory functions. The neuronal circuitry that mediates vestibulo-respiratory reflexes i s largely unknown. The purpose of the present study was to investigate the possible role of bulbospinal inspiratory neurons located in the p ara-ambiguual region of the ventral respiratory group (VRG) in mediati ng these reflexes. Experiments were carried out in cats that were dece rebrated, paralyzed, and artificially ventilated. 2. Activation of the vestibular nerve by electrical stimulation produced prominent bilater al reflex responses recorded from the phrenic nerve, which supplies th e diaphragm. The responses could be complex and consisted of a decreas e and/or increase in nerve discharge. 3. Extracellular recordings were made from 35 VRG inspiratory neurons that were antidromically activat ed from the upper cervical spinal cord. Almost one-half of these neuro ns (15/35, 43%) responded to vestibular stimulation. The neuronal resp onse patterns were consistent with VRG inspiratory neurons contributin g to the vestibular reflex response simultaneously recorded from the p hrenic nerve. 4. The present results indicate that approximately one-h alf of VRG bulbospinal inspiratory neurons contribute to vestibulo-res piratory reflexes. These findings are in contrast to our recent neuroa natomic and electrophysiological studies which revealed a paucity of v estibular inputs to the dorsal respiratory group (DRG) located in the ventrolateral nucleus of the solitary tract. Thus there appears to be a difference between inspiratory neurons in the DRG and VRG in regard to participating in vestibulo-respiratory reflexes.