Regarding serotonin as a potential target for the treatment of rheumatic diseases, a study found that the 5-HT3 receptor antagonist tropisetron (via intra-articular injections) caused an improvement in inflammation and pain in different inflammatory rheumatic diseases, probably due to the decrease in the release of the inflammatory and pain mediator substance P, which is released after binding of serotonin to its receptor (Stratz and Müller 2000). Here, TAC1 is linked to rheumatic disorder.