Other members belonging to this family are hemokinin-1, neurokinin A/B, kassinin, ranakinin, eledoisin and neuropeptide K. These peptides (including SP) are involved, after binding to the metabotropic neurokinin (NK)-1, NK-2 and NK-3 receptors, in many physiological/pathophysiological processes (e.g., cancer, pruritus, emesis, inflammation, viral and bacterial infection, pain, alcohol addiction, depression, anxiety, hematopoiesis) [8,9,10]. This evidence concerns the gene TAC1 and major depressive disorder.