Short-latency phrenic response to vagal stimulation after midsagittal lesion of the medulla in rabbit.

The effect of midsagittal lesions of the medulla on the phrenic nerve output and the central transmission of the vagal input were studied. The rabbits were anaesthetized with a mixture of chloralose with urethane, paralysed and artificially ventilated. Both vagi were sectioned in the neck and one of them was prepared for electrical stimulation of its proximal end. Lesions of the medulla were performed in steps and at each stage the short-latency phrenic response to a single electrical shock applied to the vagus was studied. The results indicate that, at the levels 1 to 5 mm rostra1 to the obex and 3 mm in depth from the dorsal medullary surface, there is a maximal density of crossing connections important for transmission of the descending respiratory activity, synchronization of the respiratory activity generated by left and right part of the medulla and transmission of the vagal signal.