Substance P (SP) is an 11 amino acid. member of the tachykinin family, which also includes neurokinin A and B (Pennefather et al., 2004). Three receptor subtypes exist for these neuropeptides, with SP preferentially binding to the NK1R, while the NK2R is preferentially activated by neurokinin A, and NK3R by neurokinin B. NK1Rs are located in a range of brain regions involved in both appetitive and aversive behaviors (Figure 2).
