Respiratory activity generated by a split brainstem preparation of the rabbit

Mid-sagittal incisions of the brainstem were performed in anaesthetized, vagotomised, paralysed and artificially ventilated rabbits. The activity of both phrenic nerves, blood pressure and end-tidal CO2 percent were continuously monitored. The results fell into two groups: in one of them a relatively small separation of both halves of the medulla extending from the obex to at least 4 mm rostrally elicited asynchronous firing in both phrenic nerves ("split respiratory centre"). In the other group, in which the incisions were placed either more caudally or more rostrally, or when small strands of the nervous tissue were left to provide connections between both sides of the brainstem, this. phenomenon did not appear. It is concluded that there are two symmetrical respiratory networks in both halves of. the brainstem and that their synchronous firing depends upon intact connections extending from the obex to the caudal end of nucleus of VII nerve.