5-Hydroxytryptamine (5-HT)-induced depolarization in isolated abdominal vagus nerves in the rat: involvement of 5-HT3 and 5-HT4 receptors.

In this study, we developed an electrophysiological technique for the in vitro measurement of isolated abdominal vagus nerve depolarization in the rat. This technique was used to compare abdominal and cervical vagus nerve depolarization values. Both 5-HT and a selective 5-HT3 agonist, 2-CH3-5HT, caused a concentration-dependent depolarization in rat isolated abdominal vagus nerves in vitro. Isolated cervical vagus nerves also showed concentration-dependent depolarization, although the isolated cervical vagus nerve depolarization was approximately 60% of that of the isolated abdominal vagus nerves at similar concentration ranges of 5-HT and 2-CH3-5HT in vitro. In isolated abdominal vagus nerves, a selective 5-HT3 antagonist, granisetron, produced a concentration-dependent decrease, but reduced the maximal response of 5-HT-induced depolarization in vitro. In isolated abdominal vagus nerves, selective 5-HT4 antagonist, SB204070, produced parallel and concentration-dependent shifts to the right on the concentration-response curves to 5-HT in vitro. These findings suggest that this electrophysiological method for evaluating isolated abdominal vagus nerve depolarization is a useful technique for the estimation of 5-HT-induced depolarization.