Endogenous Morphine and Codeine As Possible Physiological Ligands of µ-Opiate Receptors
Published 1 January 1995
A. Tagliamonte, Massimo Guarna, Enrica Bianchi
Citations3
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TL;DR
Endogenous morphine seems to be stored in neurons as the 3-ethereal sulfate conjugate, and striatal slices exposed to high K+ concentrations showed a rapid disappearance of the morphine-like immunoreactive material from neurons, indicating that endogenous alkaloids are released from neurons by depolarization.
Abstract
Experiments carried out by indirect immunofluorescence and unlabelled antibody enzyme procedures revealed the presence of morphine-like immunoreactive material in the perikarya, fibers, and terminals of neurons in different, discrete areas of rat and human brain. The monoclonal and polyclonal anti-morphine antibodies used do not distinguish between morphine and codeine. Endogenous morphine seems to be stored in neurons as the 3-ethereal sulfate conjugate. This possibility is supported by the finding that, although active uptake of [3H]morphine has not been detected in brain synaptosomes, long-term i.c.v. injection of the tritiated opiate results in the accumulation of radioactivity inside the same neurons in which the endogenous alkaloids have been detected. Moreover, the sulfated compound showed a selective displacing effect toward [3H]DAMGO, although the affinity was lower than that of morphine HC1 and DAMGO. Finally, morphine-3-ethereal sulfate presented the same poor inhibitory action of morphine HC1 and DAMGO on rat striatal adenylate cyclase activity. Finally, striatal slices exposed to high K+ concentrations showed a rapid disappearance of the morphine-like immunoreactive material from neurons, indicating that endogenous alkaloids are released from neurons by depolarization.
Keywords
NeuroscienceBiochemistry, Genetics and Molecular Biology
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