Phrenic motoneurone activity in split-brainstem cats and monkeys

A mid-line incision of the lower brainstem (from 2 mm caudal to 14 mm rostral to the obex) was performed in 14 cats and (from 2 mm caudal to 7 mm rostral to the obex) in three green monkeys and its effects on the respiratory activity of both phrenic nerves were studied under similar experimental conditions (halothane anaesthesia, artificial ventilation). Splitting the medulla in cats abolished the phrenic nerve activity under eupnoeic conditions, but hypercapnia or (with more rostral cuts) hypercapnia with hypoxia restored synchronous, rhythmic firing in both phrenic nerves. The response to splitting in eupnoeic monkeys was qualitatively different and consisted in a 'desynchronisation', i.e. independent firing of both phrenic nerves at different rhythms and patterns. It is concluded that cats and monkeys have basically different functional organisation of the respiratory controller.