Two descending nerve pathways activated by distension of guinea-pig small intestine.

1. Intracellular recordings were made from myenteric neurones of the guinea-pig small intestine in preparations which had a synaptic input from an orally situated segment of intestine. 2. Excitatory synaptic potentials could be evoked in most neurones by distension of the attached intestinal segment. 3. It was possible to distinguish two distinct firing patterns of synaptic potentials in response to distension. A transient short latency discharge was recorded from some neurones. From the others, a persistent synaptic discharge was recorded only after a long latency (2-11 sec). 4. Distension of intestinal segments evoked short latency transient inhibitory junction potentials in the circular muscle layer followed by excitatory junction potentials in both the circular and longitudinal muscle layers. 5. It is suggested that distension may cause both descending inhibition and, after a delay, descending excitation of the guinea-pig small intestine.