Presence of morphine in rat amygdala: evidence for the mu3 opiate receptor subtype via nitric oxide release in limbic structures.
BACKGROUND
We have identified a novel mu opiate receptor, p3, which is expressed in several human tissues, is selective for opiate alkaloids, insensitive to opioid peptides, and also is coupled to constitutive nitric oxide release. We, and others, have also demonstrated the presence of opiate alkaloids as endogenous substances in various nerve tissues taken from mammals, man and invertebrates.


METHODS
Morphine isolation and identification was achieved by high pressure liquid chromatography coupled to electrochemical detection. This material was finally identified by nano-electrospray ionization quadruple time-of-flight tandem mass spectrometry (Q-TOF MS/MS). Morphine's ability to release nitric oxide from limbic tissues was determined in real-time via an amperometric probe.


RESULTS
We demonstrate the presence of morphine in rat brain amygdala at 12.7 +/- 5.4 ng/g wet tissue. Morphine was able to stimulate the release of nitric oxide from hippocampus and amygdalar tissues in a naloxone and L-NAME sensitive manner. Furthermore, rat chow, incubation medium etc, did not contain morphine, eliminating the possibility of contamination.


CONCLUSIONS
This finding provides evidence that morphine biosynthesis occurs in mammalian neural tissues. It also demonstrates that morphine releases nitric oxide in limbic tissues. Given the limbic system involvement in modulating emotion, including experiences related to pain perception, it appears that morphine is involved with this activity.
Zhu
Wei
W
Neuroscience Research Institute, State University of New York, College at Old Westbury, Old Westbury, NY 11568-0210, USA.
Ma
Yuliang
Y
Bell
Achim
A
Esch
Tobias
T
Guarna
Massimo
M
Bilfinger
Thomas V
TV
Bianchi
Enrica
E
Stefano
George B
GB
D000679:Amygdala / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D006624:Hippocampus / Q000378:metabolism; D009020:Morphine / Q000032:analysis* / Q000378:metabolism / Q000494:pharmacology; D009569:Nitric Oxide / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000502:physiology*
D017450:Receptors, Opioid, mu; D009569:Nitric Oxide; D009020:Morphine