Substance P (SP), Neurokinin A (NKA) and Neurokinin B (NKB) are all peptides belonging to the Tachykinin protein family. These three peptides which demonstrate a quite heterogeneity in their distribution exert their effect via three receptors: Neurokinin 1-3 receptors, members of the G-protein coupled receptor superfamily. However, Neurokinin 1 Receptor (NK1) preferentially binds Substance P, Neurokinin 2 Receptor (NK2) to NKA and Neurokinin 3 Receptor (NK3) to NKB1.nNeurokinin receptors are distinguished by their seven transmembrane domains, an extracellular N-terminus and a cytosolic C-terminal. An unusual property of these receptors is the presence of introns as part of their structural organization. Tachykinin receptors undergo alternative splicing. For example, NK1 is detected with different C-terminal lengths. The longer receptor isoform is found in the brain whereas the truncated form is mostly detected in the periphery
