The pungent substance of Capsicum peppers. It may be anticarcinogenic due to its antioxidative function. The capsaicin (vanilloid) receptor is a cation channel required for heat and pain perception. Bradykinin and nerve growth factors activate a G-protein-coupled and tyrosine kinase receptors and phospholipase C signals to the primary afferent neurons. The potentiation also requires the VR1 heat-sensitized ion channel on sensory neurons. PIP2 controls its receptor’s sensitivity (Prescott ED, Julius D 2003 Science 300:1284). The alkaloid galanthamine present in some Amaryllidaceae plants is also supposed to have beneficial effects on some nervous diseases, particularly on Alzheimer disease (see Fig. C20).
Capsaicin-containing fruits are generally avoided by wild mammals but not by birds (Jordt S-E, Julius D 2002 Cell 108:421). It is apparently a self-defense substance in the plants because birds are efficient dispensers of the seed but mammals are not because the seed passing through their alimentary channel loses germination in contrast to a bird’s. Some spider toxins also invoke inflammatory pain by activating capsaicin receptors (Siemens J et al 2006 Nature [Lond] 444:208). phenolics, nociceptor, kininogen, nerve growth factor, signal transduction, phospholipase, alkaloids, horseradish, PIP2; Chuang H-h et al 2001 Nature [Lond] 411:957; capsaicin synthase and biosynthetic pathway: Prasad BCN et al 2006 Proc Natl Acad Sci USA 103: 13315.
