Relationships were examined between outflows of the lumbar colonic nerve (LCN) and rectal branch of the pelvic nerve (RB) and distal colonic motility (DCM) during proximal colonic distension in anesthetized and decerebrate dogs. Distension of the proximal colon (PC) reflexively elicited an increase in outflows of both the LCN and RB, often accompanied with an initial inhibition followed by an augmentation of DCM. Increasing responses in both the RB outflow and DCM were demonstrable after transection of the brain stem at the subcollicular level, but they disappeared after midpontine transection just caudal to the pontine defecation reflex center. The afferent pathways mainly involved the vagus nerves and partly the abdominal sympathetic nerves. While the increase in the outflow of the LCN and inhibition of DCM remained after bilateral cervical vagotomy as well as spinal transection (Th 6-7), but they disappeared after destruction of the spinal cord. These results indicate that the pontine defecation reflex center is an indispensable to the proximal-distal colonic augmentative reflex, while the inhibitory reflex originates in the spinal cord
