Neurokinin receptors include neurokinin 1 receptor (NK1R), neurokinin 2 receptor (NK2R) and neurokinin 3 receptor (NK3R). These tachykinin receptors belong to the Class I (rhodopsinoid) G protein-coupled receptors (GPCR) family. Various tachykinins have different binding affinities for neurokinin receptors: NK1R, NK2R, and NK3R. These kinin receptors are located in the superfamily of transmembrane G-protein-coupled receptors (GPCR) and contain seven transmembrane rings. The neurokinin 1 receptor interacts with Gαq-protein and induces the activation of phospholipase C, which then produces inositol triphosphate (IP3), leading to the elevation of intracellular calcium as a second messenger. In addition, cyclic AMP (cAMP) is stimulated by NK1R coupled to Gα S-protein. Neurokinin receptors are expressed in many cell types and tissues.