Non-vagal reflex effects on medullary inspiratory neurons during inspiratory loading

Studies were conducted to compare the first-breath responses of medullary Dorsal and Ventral Respiratory Group inspiratory (I) neurons to the mechanical loading (tracheal occlusion, TO) of inspiration in unanesthetized (decerebrate) and anesthetized (Dial) vagotomized cats, and to determine the sources of the sensory activity causing the changes in I-neuron activity. In decerebrate cats, TO resulted in a prolongation of the firing duration in 49% of the I-neurons. There was a delayed onset of firing in 7% of the I-neurons. The responses of I-neurons to TO in anesthetized cats were similar to the responses in decerebrate cats. Changes in I-neuron activity with TO were still present in cats with their cervical (C3-7) or thoracic (T1-9) dorsal roots cut, and absent when both cervical and thoracic dorsal roots were cut. The most probable sources of the cervical and thoracic afferent information altering medullary I-neuron activity during loading are the diaphragm and inspiratory intercostal muscles.