Lack of effect of vagal afferent input on central neural respiratory afterdischarge.

The effect of respiratory inhibition caused by vagal stimulation or lung inflation on the central neural mechanism that maintains respiration after cessation of a facilitatory stimulus was studied in anesthetized cats. Phrenic activity was increased by carotid sinus nerve stimulation or by squeezing or stretching calf muscle. On cessation of stimulation there was an immediate decrease in respiratory output followed by a slow decrease (afterdischarge) over a period of 5 min. Vagal stimulation or lung inflation, which caused marked inhibition of inspiration, had no effect on the development of the afterdischarge or on the course of the subsequent recovery process. The mechanism causing afterdischarge is probably a buildup of activity in a neural network in the medulla and pons. Since its activity is unaffected by vagal inhibition of respiration, it can be concluded that the network is separate from inspiratory output neurons and those involved in phase switching and that it is not dependent on increased central inspiratory neuron activity.