The tachykinin family consists of amidated neuropeptides that share a carboxy-terminal sequence (Phe-X-Gly-Leu-Met-NH2). Preprotachykinin I, also designated protachykinin 1 precursor (PPT), is a common precursor of tachykinins. Preprotachykinin I alternately splices to form various isoforms. These isoforms include Substance P, Neurokinin A (NKA, Substance K, Neuromedin L), Neurokinin B, Neuropeptide K (NPK), Neuropeptide and C-terminal flanking peptide. Substance P is expressesed primarily in the small diameter primary sensory fibers of the peripheral nervous system, and in the superficial dorsal horn of the spinal cord, the substantia nigra and the medial amygdaloid nucleus of the central nervous system.