These are peptides found in the nervous system that act as NEUROTRANSMITTERS or neuromodulators (see NEUROMODULATION). Until the mid-1970s or so, it was generally believed that there were six or seven neurotransmitters in the nervous system, with relative small, simple structures, such as acetylcholine, noradrenaline, GABA and glutamate. Ground-breaking work during this decade on hypothalamic peptide control of pituitary function, largely through development of RADIOIMMUNOASSAY and techniques in IMMUNOHISTOCHEMISTRY, led to the eventual discovery and characterization of scores of neuropeptides.
In 1977, the Nobel Prize was awarded to Roger Guillemin, Andrew Schally and Rosalyn Yalow for their work on neuropeptides. It is now known that neuropeptides play an important functional role in many areas of the central and peripheral nervous system. Neuropeptides differ from classical transmitters in many aspects of their synthesis, action, and degradation. For example, neuropeptides are synthesized from large precursor molecules in the cell body and transported to the terminal; classical transmitters can be synthesized in the terminal. Examples of well-known neuropeptides include SUBSTANCE P, ENKEPHALIN, ENDORPHIN, NEUROPEPTIDE Y, NEUROTENSIN, CHOLECYSTOKININ and CORTICOTROPIN-RELEASING FACTOR.
