Abstract In the clinical world of diagnosis and treatment options for the spectrum of gastroparesis (GP) symptoms, there are still numerous and challenging needs to understand, while at the same time further investigating the pathophysiology of this entity, which affects > 10 million of patients in the US. GP patients exhibit a range of symptoms which do not always correlate with the objective tests we rely on for diagnosis, as well as for assessing their clinical reactions to pharmacological agents. Our response to the NIDDK Gastroparesis Consortium (U01) under RFA-DK-20-504 has the following aims: 1) A) Continue and complete already approved studies initiated by the GpCRC, which specifically entails enrolling qualified patients to Gastroparesis Registry 3, with all relevant clinical and bio-samples, including also PBMC isolation (peripheral blood mononuclear cells), as well as completing the Buspirone (BESST) clinical trial; B) Continue obtaining gastric antral and pyloric smooth muscle tissue samples at the time of surgeries to further advance our knowledge of pathological basis of gastroparesis (PBG) protocol. C) Investigate Pyloric Sphincter Abnormalities in Patients with Gastroparesis Symptoms (PSAGS) per the EndoFlip assessment protocol. B) Our additional proposals for the GP Registry 4 (GpR4) are: 1) During the routine EGD for GpR4 and possible PSAGS studies, we would like to collect samples of duodenal and gastric microbiota by obtaining brushings of gastric and duodenal mucosa; 2) biopsy antral muscularis propria tissue using Endoscopic Submucosal Dissection (ESD) methodology during upper GI endoscopy . 2) As a new research strategy, we propose to investigate whether microbiota obtained at the time of endoscopy by brushing the mucosa of the stomach and duodenum, will differ in their composition in idiopathic and diabetic GP and control patients. We hypothesize that dysbiosis of the upper GI microbiota may contribute to the delayed gastric emptying and symptoms in GP patients, particularly in the idiopathic subgroup of our cohort. 3) Our clinical trial proposal is to investigate the therapeutic efficacy of a new selective 5-HT4 receptor agonist, Pruclalopride, to improve the symptoms and gastric emptying in idiopathic and diabetic GP patients while at the same time having an excellent safety profile. A multicenter, double blind, randomized, placebo- controlled, parallel study, will be conducted were all GpR4 patients from all centers will be invited to be enroll into 2 parallel 4-week treatment periods with placebo or pruclalopride 2mg QD trial.