Endorphins

Endorphins ("endogenous morphine") are endogenous opioid neuropeptides. They are produced by the central nervous system and the pituitary gland. The term implies a pharmacological activity (analogous to the activity of the corticosteroid category of biochemicals) as opposed to a specific chemical formulation. It consists of two parts: endo- and -orphin; these are short forms of the words endogenous and morphine, intended to mean "a morphine-like substance originating from within the body".^[1] The class of endorphin compounds includes α-endorphin, β-endorphin, γ-endorphin, α-neo-endorphin, and β-neo-endorphin. The principal function of endorphins is to inhibit the transmission of pain signals; they may also produce a feeling of euphoria very similar to that produced by other opioids.^[2]

History

Opioid neuropeptides were first discovered in 1974 by two independent groups of investigators:

• John Hughes and Hans Kosterlitz of Scotland isolated — from the brain of a pig — what some called enkephalins (from the Greek εγκέφαλος, cerebrum).^[3][4]
• Around the same time, in a calf brain, Rabi Simantov and Solomon H. Snyder of the United States found^[5] what Eric Simon (who independently discovered opioid receptors in vertebral brains) later termed "endorphin" by an abbreviation of "endogenous morphine", meaning "morphine produced naturally in the body".^[1] Importantly, recent studies have demonstrated that human and diverse animal tissues are in fact capable of producing morphine itself, which is not a peptide.^[6][7]

Activity

Scientists sometimes debate whether specific activities release measurable levels of endorphins. Much of the current data comes from animals which may not be relevant to humans. The studies that do involve humans often measure endorphin plasma levels, which do not necessarily correlate with levels in the central nervous system. Other studies use a blanket opioid antagonist (usually naloxone) to indirectly measure the release of endorphins by observing the changes that occur when any endorphin activity that might be present is blocked.

Depersonalization disorder

Endorphins are known to play a role in depersonalization disorder. The opioid antagonists naloxone and naltrexone have both been proven to be successful in treating depersonalization.^[8][9] To quote a 2001 naloxone study, "In [3] of 14 patients, depersonalization symptoms disappeared entirely, and [7] patients showed a marked improvement. The therapeutic effect of naloxone provides evidence for the role of the endogenous opioid system in the pathogenesis of depersonalization."

Etymology

From the words ἔνδον / Greek: éndon meaning "within" (endogenous, ἐνδογενής / Greek: endogenes, "proceeding from within") and morphine, from Morpheus (Μορφεύς / Ancient Greek: Morpheús, the god of sleep in the Greek mythology, thus 'endo(genous) (mo)rphine’.

References

1. Goldstein A, Lowery PJ (September 1975). "Effect of the opiate antagonist naloxone on body temperature in rats". Life Sciences 17 (6): 927–31. doi:10.1016/0024-3205(75)90445-2. PMID 1195988.
2. "Is there a link between exercise and happiness?". Retrieved 18 September 2014.
3. "Role of endorphins discovered". PBS Online: A Science Odyssey: People and Discoveries. Public Broadcasting System. 1 January 1998. Retrieved 15 October 2008.
4. Hughes J, Smith T, Kosterlitz H, Fothergill L, Morgan B, Morris H (1975). "Identification of two related pentapeptides from the brain with potent opiate agonist activity". Nature 258 (5536): 577–80. doi:10.1038/258577a0. PMID 1207728.
5. Simantov R, Snyder S (1976). "Morphine-like peptides in a mammalian brain: isolation, structure elucidation, and interactions with an opiate receptor". Proc Natl Acad Sci USA 73 (7): 2515–9. doi:10.1073/pnas.73.7.2515. PMC 430630. PMID 1065904.
6. Poeaknapo C, Schmidt J, Brandsch M, Dräger B, Zenk MH (September 2004). "Endogenous formation of morphine in human cells". Proceedings of the National Academy of Sciences of the United States of America 101 (39): 14091–6. doi:10.1073/pnas.0405430101. PMC 521124. PMID 15383669.
7. Kream RM, Stefano GB (October 2006). "De novo biosynthesis of morphine in animal cells: an evidence-based model". Medical science monitor : international medical journal of experimental and clinical research 12 (10): RA207–19. PMID 17006413.
8. Nuller YL, Morozova MG, Kushnir ON, Hamper N (June 2001). "Effect of naloxone therapy on depersonalization: a pilot study". J. Psychopharmacol. (Oxford) 15 (2): 93–5. doi:10.1177/026988110101500205. PMID 11448093.
9. Simeon, Daphne. "An Open Trial of Naltrexone in the Treatment of Depersonalization Disorder". Journal of Clinical Psychopharmacology. Retrieved 13 October 2011.

External links

• Endorphins at the US National Library of Medicine Medical Subject Headings (MeSH)