Presence of morphine in rat amygdala: evidence for the mu3 opiate receptor subtype via nitric oxide release in limbic structures
Zhu W, Ma Y, Bell A, Esch T, Guarna M,
Bilfinger TV, Bianchi E, Stefano GB.
Neuroscience Research Institute,
State University of New York, College at Old Westbury,
Old Westbury, NY 11568-0210, USA.
Med Sci Monit. 2004 Dec;10(12):BR433-9.


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. MATERIAL/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. CONCLUSION: 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.
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Is morphine an antidepressant?
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Morphinergic signalling system utilising NO
Opioids, depression and learned helplessness
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Morphine directly inhibits nociceptors in inflamed skin
The detection of morphine and codeine in human teeth
Opioids, pain and the immune system in evolutionary perspective

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