Evidence that enteric motility reflexes can be initiated through entirely intrinsic mechanisms in the guinea-pig small intestine.

Although motility reflexes can be elicited in the intestine in vivo after all neural connections with the central nervous system are cut, or in vitro in isolated intestinal segments, it is not proven that the cell bodies of the primary sensory neurons for these reflexes are in the intestinal wall. It is feasible that the nerve cells are in dorsal root ganglia and that axon reflexes are involved in the initiation of the reflexes. We have examined reflexes in segments of guinea-pig intestine in which extrinsic denervation, 9-11 days before the intestine was removed, and isolation of the intestine in vitro were combined. The experimental segments were isolated from extrinsic inputs by severing nerves in the mesentery and those running in the gut wall that entered the segment. The effectiveness of denervation was confirmed histochemically. Ascending and descending reflexes were evoked by mucosal distortion or distension and responses were recorded by intracellular microelectrodes in the circular muscle. Reflex responses recorded after denervation were no different to those recorded from control tissue. It is concluded that, in the small intestine of the guinea-pig, cell bodies of primary sensory neurons for mucosal and probably for distension reflexes are intrinsic to the organ.