Purinergic and cholinergic neuro-neuronal transmission underlying reflexesactivated by mucosal stimulation in the isolated guinea-pig ileum

1. We present evidence that adenosine triphosphate (ATP) plays a major role in excitatory neuro-neuronal transmission in ascending and descending refl ex pathways to the longitudinal (LM) and circular muscle (CM). 2. A partitioned bath was used for the pharmacological isolation of a segme nt of guinea-pig ileum (similar to 6 cm in length), allowing drugs to be se lectively applied to an intermediate region between the region where mucosa l stimulation was applied and that where mechanical recordings were made. 3. Brush stroking the mucosa (3 strokes) elicited a synchronous contraction of the LM and CM both above (ascending excitation) and below (descending e xcitation) the site of stimulation. All reflexes were abolished when tetrod otoxin (1 mu M) was applied to the intermediate chamber. 4. Hexamethonium (300 mu M) added to the intermediate chamber abolished the ascending contraction in 15% of oral preparations (from 26 preparations, 1 8 animals) and the descending contraction in 13% of anal preparations studi ed (from 53 preparations, 48 animals). In the remaining 85% of oral prepara tions, hexamethonium usually attenuated the oral contraction of the LM and CM. However, in the remaining 87% of anal preparations, hexamethonium had n o effect on the anal contraction of the LM and CM. 5. Oral and anal reflexes that were hexamethonium resistant were either abo lished or attenuated by the further addition of the P2 purinergic receptor antagonist pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 1 0 mu M) or alpha,beta-methylene ATP (50-100 mu M) to the intermediate chamb er. 6. 1,1-Dimethyl-4-phenyl-piperazinium iodide (DMPP, 20 mu M) or alpha,beta- methylene ATP (50-100 mu M) stimulated both ascending and descending excita tory pathways, when applied to the intermediate chamber. 7. In conclusion, ascending and descending neuro-neuronal transmission in e xcitatory nervous pathways to the LM and CM is complex and clearly involves neurotransmitter(s) other than acetylcholine (ACh). We suggest mucosal sti mulation releases ACh and ATP in both ascending and descending excitatory r eflex pathways that synapse with excitatory motoneurons to the LM and CM.