Endogenous morphine: opening new doors
for the treatment of pain and addiction

Pryor SC, Zhu W, Cadet P, Bianchi E,
Guarna M, Stefano GB.
State University of New York - College at Old Westbury,
Neuroscience Research Institute,
Old Westbury, NY 11568, USA.
Expert Opin Biol Ther. 2005 Jul;5(7):893-906.


Nitric oxide (NO) signalling is at the forefront of intense research interest because its many effects remain controversial and seemingly contradictory. This paper examines its role as a potential mediator of pain and tolerance. Within this context discussion covers endogenous morphine, documenting its ability to be made in animal tissues, including nervous tissue, and in diverse animal phyla. Supporting morphine as an endogenous signalling molecule is the presence of the newly cloned mu3 opiate receptor subtype found in animal (including human) immune, vascular and neural tissues, which is coupled to NO release. Importantly, this mu opiate receptor subtype is morphine-selective and opioid peptide-insensitive, further highlighting the presence of morphinergic signalling coupled to NO release. These findings provide novel insights into pain and tolerance as morphinergic signalling exhibits many similarities with NO actions. Taken together, a select morphinergic signalling system utilising NO opens the gate for the development of novel pharmaceuticals and/or the use of old pharmaceuticals in new ways.
Morphine: structure
Endogenous morphine
Morphine biosynthesis?
Is morphine an antidepressant?
Opioids, depression and learned helplessness
Human white blood cells synthesize morphine
Morphine in amygdala and the mu3 opiate receptor
Morphine directly inhibits nociceptors in inflamed skin
Endogenous morphine and ACTH association in the brain
Opioids, pain and the immune system in evolutionary perspective

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