Endogenous morphine in SH-SY5Y cells and the mouse cerebellum.
BACKGROUND
Morphine, the principal active agent in opium, is not restricted to plants, but is also present in different animal tissues and cell types, including the mammalian brain. In fact, its biosynthetic pathway has been elucidated in a human neural cell line. These data suggest a role for morphine in brain physiology (e.g., neurotransmission), but this hypothesis remains a matter of debate. Recently, using the adrenal neuroendocrine chromaffin cell model, we have shown the presence of morphine-6-glucuronide (M6G) in secretory granules and their secretion products, leading us to propose that these endogenous alkaloids might represent new neuroendocrine factors. Here, we investigate the potential function of endogenous alkaloids in the central nervous system.


RESULTS
Microscopy, molecular biology, electrophysiology, and proteomic tools were applied to human neuroblastoma SH-SY5Y cells (i) to characterize morphine and M6G, and (ii) to demonstrate the presence of the UDP-glucuronyltransferase 2B7 enzyme, which is responsible for the formation of M6G from morphine. We show that morphine is secreted in response to nicotine stimulation via a Ca(2+)-dependent mechanism involving specific storage and release mechanisms. We also show that morphine and M6G at concentrations as low as 10(-10) M are able to evoke specific naloxone-reversible membrane currents, indicating possible autocrine/paracrine regulation in SH-SY5Y cells. Microscopy and proteomic approaches were employed to detect and quantify endogenous morphine in the mouse brain. Morphine is present in the hippocampus, cortex, olfactory bulb, and cerebellum at concentration ranging from 1.45 to 7.5 pmol/g. In the cerebellum, morphine immunoreactivity is localized to GABA basket cells and their termini, which form close contacts on Purkinje cell bodies.


CONCLUSIONS
The presence of morphine in the brain and its localization in particular areas lead us to conclude that it has a specific function in neuromodulation and/or neurotransmission. Furthermore, its presence in cerebellar basket cell termini suggests that morphine has signaling functions in Purkinje cells that remain to be discovered.
Muller
Arnaud
A
Inserm, U575, Physiopathologie du Système Nerveux, Strasbourg, France.
Glattard
Elise
E
Taleb
Omar
O
Kemmel
Véronique
V
Laux
Alexis
A
Miehe
Monique
M
Delalande
François
F
Roussel
Guy
G
Van Dorsselaer
Alain
A
Metz-Boutigue
Marie-Hélène
MH
Aunis
Dominique
D
Goumon
Yannick
Y
D000470:Alkaloids; D000818:Animals; D001923:Brain Chemistry; D045744:Cell Line, Tumor; D002531:Cerebellum / Q000737:chemistry*; D004594:Electrophysiology; D014453:Glucuronosyltransferase / Q000032:analysis* / Q000378:metabolism; D006801:Humans; D051379:Mice; D009020:Morphine / Q000378:metabolism*; D009022:Morphine Derivatives / Q000032:analysis*; D009447:Neuroblastoma; D011689:Purkinje Cells; D009435:Synaptic Transmission
D000470:Alkaloids; D009022:Morphine Derivatives; C035349:morphine-6-glucuronide; D009020:Morphine; D014453:Glucuronosyltransferase