Serotonin stimulates migrating myoelectric complex via 5-HT3-receptors dependent on cholinergic pathways in rat small intestine

We have investigated the effect of 5-hydroxytryptamine (5-HT) and different 5-HT-receptor antagonists and atropine on the migrating myoelectric complex in the rat small intestine.
Infusion of 5-HT dose-dependently shortened the interval between phase III of the migrating myoelectric complex (MMC). In untreated animals the interval in upper jejunum was 19.1 (16.0–22.1) min. At doses of 10 and 20 nmol kg^–1 min^–1, the interval decreased to 15.2 (12.0–18.4) and 10.2 (9.4–11.0) min, respectively. The 5-HT₃-receptor antagonist ondansetron (0.5 mg kg^–1) alone increased the MMC interval from 20.8 (15.1–26.5) to 33.9 (19.4–48.4) min. Neither methiothepin (0.5 mg kg^–1) nor ketanserin (0.5 mg kg^–1), selective for 5-HT₁5-HT₂-and 5-HT₂-receptors, respectively, changed the MMC interval. The 5-HT₄-receptor antagonist GR 113808 (0.5 mg kg^–1) disrupted the MMC and induced irregular spiking activity.
Ondansetron and atropine antagonized the 5-HT-induced shortening of the MMC interval. Neither methiothepin nor ketanserin affected the response to 5-HT. GR 113808 did not block the response to 5-HT in half of the animals; however, in the remaining ones MMC was disrupted and irregular spiking induced.
In conclusion, these results show that 5-HT dose-dependently stimulates the cycling of the MMC in the small intestine via 5-HT₃-receptors and a cholinergic final pathway. Our findings encourage further studies on the role of the 5-HT₃-receptor in the control of gastrointestinal motility.