serotonin http://www.nlm.nih.gov/medlineplus/ency/article/003562.htm serotonin serotonin http://www.nlm.nih.gov/medlineplus/ency/article/003562.htm www.nlm.nih.gov www.nlm.nih.gov http://www.nlm.nih.gov/medlineplus/ency/article/003562.htm MedlinePlus: Serum Serotonin Level http://www.nlm.nih.gov/medlineplus/ency/article/003562.htm http://www.nlm.nih.gov/medlineplus/ency/article/003562.htm http://www.nlm.nih.gov/medlineplus/ency/article/003562.htm serotonin