Endomorphins: novel endogenous mu-opiate receptor agonists in regions of high mu-opiate receptor density
by
Zadina JE, Martin-Schild S, Gerall AA, Kastin AJ, Hackler L, Ge LJ, Zhang X
Department of Veterans Affairs Medical Center,
New Orleans, Louisiana 70112-1262, USA.
jzadina@mailhost.tcs.tulane.edu
Ann N Y Acad Sci 1999; 897:136-44

ABSTRACT

Endomorphin-1 (Tyr-Pro-Trp-Phe-NH2, EM-1) and endomorphin-2 (Tyr-Pro-Phe-Phe-NH2, EM-2) are peptides recently isolated from brain that show the highest affinity and selectivity for the mu (morphine) opiate receptor of all the known endogenous opioids. The endomorphins have potent analgesic and gastrointestinal effects. At the cellular level, they activate G-proteins (35S-GTP gamma-S binding) and inhibit calcium currents. Support for their role as endogenous ligands for the mu-opiate receptor includes their localization by radioimmunoassay and immunocytochemistry in central nervous system regions of high mu receptor density. Intense EM-2 immunoreactivity is present in the terminal regions of primary afferent neurons in the dorsal horn of the spinal cord and in the medulla near high densities of mu receptors. Chemical (capsaicin) and surgical (rhizotomy) disruption of nociceptive primary afferent neurons depletes the immunoreactivity, implicating the primary afferents as the source of EM-2. Thus, EM-2 is well-positioned to serve as an endogenous modulator of pain in its earliest stages of perception. In contrast to EM-2, which is more prevalent in the spinal cord and lower brainstem, EM-1 is more widely and densely distributed throughout the brain than EM-2. The distribution is consistent with a role for the peptides in the modulation of diverse functions, including autonomic, neuroendocrine, and reward functions as well as modulation of responses to pain and stress.

Pain
LAAM
Tolerance
Knockout mice
Opium timeline
Opioid receptors
Endomorphins 1 and 2
The Pleasures of Opium
Endomorphins and the mouse
Endomorphins and rodent brains
Adenylyl cyclase superactivation
The degradation of endomorphins
Endomorphins and the mu-opioid receptor
Morphine: a mood-brightening smart-drug?
Opioids, depression and learned helplessness

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