NEURAL CONTROL OF SMALL-INTESTINAL GIANT MIGRATING CONTRACTIONS

We investigated the neural mechanisms of control of giant migrating co ntractions (GMCs) in five conscious dogs. After control recordings, a Thiry-Vella loop was prepared from the middle segment, and the remaini ng two segments were reanastomosed. GMCs were stimulated by intravenou s administration of fentanyl and erythromycin lactobionate, oral admin istration of loperamide and erythromycin stearate, and gastric or intr aluminal administration of cider vinegar in the loop. In the intact st ate, the agents stimulated GMCs in all three segments, and they propag ated uninterruptedly from the point of their origin to the terminal il eum. The propagation velocity of GMCs increased, whereas that of migra ting motor complexes (MMCs) decreased distally. After Thiry-Vella loop formation, the agents stimulated GMCs independently in the three segm ents, and they propagated only to the end of the segment in which they started. In the intact small intestine, the GMCs produced ascending a nd descending inhibition of spontaneous phase II contractions but did not interrupt the caudad propagation of the ongoing MMC. After Thiry-V ella loop formation, the ascending inhibition was unaltered, but the d escending inhibition occurred only in the segment containing the GMC. We conclude that the propagation of GMCs in the small intestine is con trolled by the enteric nerves. The extrinsic nerves control the ascend ing inhibition produced by GMCs, whereas the enteric nerves control th e descending inhibition.