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

Nick J. Spencer, Michelle Walsh and Terence K. Smith

1. We present evidence that adenosine triphosphate (ATP) plays a major role in excitatory neuro-neuronal transmission in ascending and descending reflex pathways to the longitudinal (LM) and circular muscle (CM).

2. A partitioned bath was used for the pharmacological isolation of a segment of guinea-pig ileum (~6 cm in length), allowing drugs to be selectively applied to an intermediate region between the region where mucosal 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 excitation) the site of stimulation. All reflexes were abolished when tetrodotoxin (1 µM) was applied to the intermediate chamber.

4. Hexamethonium (300 µM) added to the intermediate chamber abolished the ascending contraction in 15 % of oral preparations (from 26 preparations, 18 animals) and the descending contraction in 13 % of anal preparations studied (from 53 preparations, 48 animals). In the remaining 85 % of oral preparations, hexamethonium usually attenuated the oral contraction of the LM and CM. However, in the remaining 87 % of anal preparations, hexamethonium had no effect on the anal contraction of the LM and CM.

5. Oral and anal reflexes that were hexamethonium resistant were either abolished or attenuated by the further addition of the P2 purinergic receptor antagonist pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 10 µM) or ,-methylene ATP (50-100 µM) to the intermediate chamber.

6. 1,1-Dimethyl-4-phenyl-piperazinium iodide (DMPP, 20 µM) or ,-methylene ATP (50-100 µM) stimulated both ascending and descending excitatory pathways, when applied to the intermediate chamber.

7. In conclusion, ascending and descending neuro-neuronal transmission in excitatory nervous pathways to the LM and CM is complex and clearly involves neurotransmitter(s) other than acetylcholine (ACh). We suggest mucosal stimulation releases ACh and ATP in both ascending and descending excitatory reflex pathways that synapse with excitatory motoneurons to the LM and CM.

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