Stimulation of the 5-HT4R with the agonists cisapride, mosapride, or tegaserod improved PD-related gastrointestinal dysfunction, including constipation and reduced gastric motility in patients with PD.640, 641, 642, 643, 644, 645, 646 However, whether 5-HT4R activation might improve motor function remains elusive. Here, HTR4 is linked to Parkinson disease.