Intramedullary pathways of the vago-vagal reflexes with special reference to those evoked by stimulation of the abdominal vagus.

An electrophysiological study has been made on the central relay pathway of the vago-vagal reflexes with special reference to those evoked by afferent stimulation of the abdominal vagus in cats under chloralose (50mg/kg i.v.) anesthesia. 1. Stimulation of the central cut end of the cervical or thoracic vagus nerve produced three mass reflex discharges in the contralateral cervical vagus nerve. On the other hand, stimulation of the abdominal vagal branch caused only the most delayed mass discharge. 2. Among the three mass discharges caused by cervical or thoracic vagal stimulation, at least the third one was regarded as the same discharge as that caused by afferent stimulation of the abdominal vagus nerve. 3. The maximum conduction velocity of the afferent fibres which caused the third response ranged between 1.0-1.4 m/sec. 4. Transection of the medulla oblongata at the level of 5-6mm rostral to the obex did not abolish the vagal mass discharges but transection at the level of 4mm abolished or markedly reduced all of them. 5. The third mass discharge and sometimes the second ones were abolished by a superficial dorsal sagittal section (1-2mm deep) of the obex with its immediate caudal region. On the other hand, the first and sometimes the second were still recorded after such a section. 6. The possibility of the existence of the specific reflex pathway at least for the mass reflex discharge caused by afferent stimulation of the abdominal vagus nerve was discussed.