The effects of pontine or bulbar transection on the respiratory pattern in the rabbit

Rabbits were anesthetized with halothane, paralyzed with d-tubocurarine and mechanically ventilated at eucapnic level. The activity of both phrenic nerves was recorded before and after brainstem transection in animals with vagi intact and then cut. The effect of transection depended upon its level: midpontine transections elicited an apneustic pattern of firing in phrenic nerves prior to vagotomy and a considerable prolongation of expiratory time after vagotomy. Transections through the rostral part of the n. facialis in animals with vagi intact increased the duration of both inspiratory time and - even more - expiratory time. Vagotomy abolished the activities of phrenic nerves. Transection through the n. retrofacialis resulted in fast, irregular, low-amplitude volleys of phrenic nerves; vagotomy elicited inspiratory apneusis. Low frequency electrical stimulation of the vagus nerve enhanced this tonic firing, whereas high-frequency stimulation interrupted it. The results indicate that medullary neurons are capable of generating the basic respiratory pattern, and that the vagal input is integrated at the bulbar level in the rabbit.