Welbutrin is one mentioned on here a few times as the driving drug inducing remission in a few people on the board here. You could search that on here.
@teddy this sort of applies to your question:
Here is an interesting "in Human" or really "from Human!" :) study on wonky seratonin uptake in patients with Crohn's disease displaying IBS symptoms while in remission.
Serotonin Synthesis and Uptake in Symptomatic Patients With Crohn’s Disease in Remission
www.cghjournal.org/article/S1542-3565(07)00184-X/fulltext#bib1_internalLinkHere's a decent paper on Seratonin in General:
Serotonin is a sword and a shield of the bowel: serotonin plays offense and defense.
www.ncbi.nlm.nih.gov/pubmed/23303993 - this one being mouse.
In general it's well established now that Seratonin effects inflammation and plays a regulatory role in the humoral immune response as well as the innate immune response. Most immune cells express 5HT and Dopamine receptors for this purpose. It's been proposed that both Seratonin and Dopamine function as the "Master Regulators" but has yet to be proven though the evidence of just such is pretty substantial.
Search Seratonin and IBS and that'll keep you busy for days! There less on the IBD side, but those that exist have some pretty intriguing results.