Tachykinins

The very first peptide transmitter to be discovered was a substance P (SP). It is an excitatory transmitter in numerous brain areas involving the striatum, cerebral cortex, and substantia nigra. It is free by both central and peripheral terminals of the C fiber primary afferents. The central terminals synapse with the dorsal horn cells to convey the information about pain and temperature. The Release from the peripheral terminals outcomes in neurogenic inflammation. The SP-containing terminals are found nearby to cerebral blood vessels and abnormal release of SP might play a role in migraine and other headaches.

The gene that codes for SP also encodes the other transmitters of the tachykinin family, like the substance K and neurokinins A and B. The three tachykinin receptors (viz., NK1, NK2, and NK3) are G-protein-coupled receptors attached to phospholipase C and (for NK₁and NK₂₎ increase in the cAMP. The tachykinins have dissimilar affinities for the receptors, with SP the favored ligand of NK₁.