The effect of tetrodotoxin on the 5-hydroxytryptamine induced responses of the guinea-pig isolated gastrointestinal preparations.

Tetrodotoxin was used to investigate the site of action of 5-hydroxytryptamine on various longitudinal muscle preparations from the guinea-pig gastrointestinal tract. It was found that the contractile effect of 5-hydroxytryptamine on the oesophagus, the terminal ileum, the taenia caeci and the proximal colon was partly indirect through the activation of cholinergic fibres and partly direct on the smooth muscle. However on the stomach strip, the duodenum, the mid-intestine, the mid and terminal colons, the action is completely indirect through the stimulation of cholinergic nerves.