The tachykinin peptide family in mammals comprises three peptides, substance P, neurokinin A and neurokinin B, which bind to the tachykinin receptor family of GPCRs, NK1, NK2 and NK3. Tachykinins have prominent activity in the GI system, in which they stimulate intestinal contraction and salivation. These effects are mediated by NK1 and NK2, and an antagonist of NK1, aprepitant, is used for treatment of chemotherapy-induced emesis. The NK1 tachykinin receptor is expressed in brain, and is thought to be involved in depression and nociception. Although NK1 appears to promote nociception in animal models, the significance of this activity is controversial, as antagonists of NK1 have not proven efficacious in pain relief in humans.