1Department of Anatomy and Neurobiology, University of Vermont College of Medicine, Burlington, Vermont, USA
2Division of Gastroenterology and Hepatology, Department of Medicine, University of Vermont College of Medicine, Burlington, Vermont, USA
3Department of Anatomy and Cell Biology, Columbia University, New York, New York, USA
4Department of Pathology, University of Vermont College of Medicine, Burlington, Vermont, USA
5Division of Gastroenterology and Hepatology, Mayo Clinic, Scottsdale, Arizona, USA
6Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada