Serotonin Deficiency Is Associated With Delayed Gastric Emptying

BACKGROUND & AIMS: Gastrointestinal (GI) motility is regulated by serotonin (5-hydroxytryptamine [5-HT]), which is primarily produced by enterochromaffin (EC) cells in the GI tract. However, the precise roles of EC cellderived 5-HT in regulating gastric motility remain a major point of conjecture. Using a novel transgenic mouse line, we investigated the distribution of EC cells and the pathophysiologic roles of 5- HT deficiency in gastric motility in mice and humans. METHODS: We developed an inducible, EC cell-specific Tph1(CreERT2/+) mouse, which was used to generate a reporter mouse line, Tph1-tdTom, and an EC cell-depleted line, Tph1-DTA. We examined EC cell distribution, morphology, and subpopulations in reporter mice. GI motility was measured in vivo and ex vivo in EC cell-depleted mice. Additionally, we evaluated 5-HT content in biopsy and plasma specimens from patients with idiopathic gastroparesis (IG). RESULTS: Tph1-tdTom mice showed EC cells that were heterogeneously distributed throughout the GI tract with the greatest abundance in the antrumand proximal colon. Two subpopulations of EC cells were identified in the gut: self-renewal cells located at the base of the crypt and mature cells observed in the villi. Tph1-DTA mice displayed delayed gastric emptying, total GI transit, and colonic transit. These gutmotility alterationswere reversed by exogenous provision of 5-HT. Patients with IG had a significant reduction of antral EC cell numbers and 5-HT content, which negatively correlated with gastric emptying rate. CONCLUSIONS: The Tph1(CreERT2/+) mouse provides a powerful tool to study the functional roles of EC cells in the GI tract. Our findings suggest a new pathophysiologic mechanism of 5-HT deficiency in IG.