PYY and Anxiety: In addition, the GI tract is known to release various gut hormones, such as peptide YY (two members of the pancreatic polypeptide (PP-fold) family, which induces satiety and improves glucose homeostasis and behavioral functions), neuropeptide Y (which regulates the activity of the immune system, anxiety, and mood), leptin, ghrelin, cholecystokinin, and glucagon-like peptide-1 (GLP-1).