Peristalsis, which involves enteric nervous reflexes, is the co-ordinated movements of the longitudinal (LM) and circular (CM) muscle layers that propel intraluminal contents down the bowel. Although the movements of the CM during peristalsis are reasonably clear the relative movements of the LM are poorly understood. 2. We studied the oral and anal movements of the LM and CM during a peristaltic wave in isolated segments of guinea-pig distal colon. Dissection techniques were used to prevent mechanical interactions between the LM and CM; also, the colonic segment was passed through a partition to prevent mechanical disturbances created by a peistaltic wave in the bulk of the colon from influencing the end from which recordings were made. 3. Peristalsis was generated by slowly filling the lumen of the colon with fluid. At threshold, the LM and CM synchronously contracted oral (ascending excitation) to, and relaxed anal (descending inhibition) to, a peristaltic wave. The anal relaxation was followed by a contraction (descending excitation) of both muscle layers. 4. Atropine (1 microM) in the recording chamber reduced both the oral (LM by 40% and CM by 27%) and anal (LM by 36% and CM by 36%) contractile responses as well as the anal relaxation response in both muscle layers. Hexamethonium (300 microM) almost blocked the oral contractile responses of the LM and CM but had no affect on the anal responses of either muscle layer. 5. N omega-nitro-L-arginine (L-NA; 100 microM) reduced the oral contractile response of the LM and CM by 50%, the anal contractile response of the LM by 30%, and the anal relaxation response of the LM and CM by about 30%. The anal contractile response of the CM was unaffected by L-NA. 6. Apamin (0.5 microM) also reduced the evoked anal relaxation of both the LM and CM by about 50%. Further addition of L-NA nearly abolished the relaxation response in the LM, but did not cause any further reduction in the relaxation response of the CM observed in apamin alone. 7. It is concluded, that the LM and CM exhibit synchronous movements during peristalsis in the colon. Also, peristalsis consists of activation of ascending excitatory, and descending inhibitory and excitatory nervous pathways to the LM and CM, which are cholinergic and non-cholinergic, respectively. Nitric oxide is an important neuromodulator within the intrinsic nervous pathways.
