Nucleus retroambigualis respiratory neurons: responses to intercostal and abdominal muscle afferents.

Studies were performed on anesthetized (Dial), paralyzed, vagotomized, artificially ventilated cats. Phrenic efferent activity, ventral respiratory group neuron activity in the region of the nucleus retroambigualis and, in some instances, thoracic dorsal root compound action potentials were recorded during electrical stimulation of intercostal nerve afferents (INS). Phrenic activity and inspiratory (I) neurons were inhibited by stimulating external, internal and lateral intercostal nerve afferents. Some expiratory (E)-neurons were also inhibited by these afferents. No I or E-neurons were facilitated with INS. Changes in I and E activity were correlated with muscle proprioceptor and cutaneous receptor afferent fibers. It is concluded that the dominant effect of intercostal and abdominal muscle proprioceptive afferent information on medullary respiratory activity in inhibition of inspiratory activity.