I am going to keep posting some related serotonin info.
This is new and may have to do with gender differences, women have more serotonin in them then men.
1: Can J Gastroenterol 2003 Mar;17(3):191-6 Related Articles, Links
Sex differences of brain serotonin synthesis in patients with irritable bowel syndrome using a-[11C]methyl-l-tryptophan, positron emission tomography and statistical parametric mapping.
Nakai A, Kumakura Y, Boivin M, Rosa P, Diksic M, D'Souza D, Kersey K.
Fukui Medical University School of Medicine, Fukui, Japan.
BACKGROUND: Irritable bowel syndrome (IBS) is the most common functional bowel disorder and has a strong predominance in women. Recent data suggest that the brain may play an important role in the pathophysiology of IBS in the brain-gut axis. It is strongly suspected that serotonin (5-HT), a neurotransmitter found in the brain and gut, may be related to the pathophysiology of IBS. It is reported that a 5-HT3 antagonist is effective only in female patients with diarrhea-predominant IBS. OBJECTIVE: In the present study, 5-HT synthesis was measured using positron emission tomography, with a-[11C]methyl-l-tryptophan as the tracer, in patients with IBS. The aim of the present study was to compare 5-HT synthesis in the IBS patients with that in the controls, and to compare 5-HT synthesis between male and female IBS patients. METHODS: Six male and six female nonconstipated IBS patients were scanned. Age-matched healthy volunteers were scanned as controls. Eighty minute dynamic scans were performed. Functional 5-HT synthesis images were analyzed using statistical parametric mapping. RESULTS: 5-HT synthesis was greater only in the female IBS patients in the right medial temporal gyrus (multimodal sensory association cortex) compared with the female controls (P<0.001). CONCLUSIONS: The greater brain 5-HT synthesis in the female IBS patients than in the controls may be related to the pathological visceral pain processing of the IBS patients, a larger female predominance of the disorder, and the sex difference of the efficacy of the 5-HT3 antagonist in treatment.