The papers in the present review were generally selected under the scope of EECs and endocrine molecules including serotonin, glucagon-like peptide 1 (GLP1), glucagon-like peptide 2 (GLP2), peptide YY (PYY), as well as their involvement in particular neurological psychiatric disorders, such as PD, schizophrenia, visceral pain, neuropathic pain, and depression. This evidence concerns the gene GCG and depressive symptom measurement.