Psychiatric implications of endogenous morphine: up-to-date review

For over 30 years empirical studies have repeatedly demonstrated that the biosynthesis of morphine by diverse animal and human tissues occurs. Recently, the blue mussel's neural tissues and human white blood cells were used to demonstrate the de novo biosynthesis of morphine for small precursor molecules derived from the aromatic amino acid L-tyrosine. Because catecholamine precursors, i.e., L-3,4-dihydroxyphenylalanine (L-DOPA), were also found to be utilized as morphine precursors, a novel reciprocally interactive mechanism is apparent that links catecholamine and opioid pathways in the activation and inhibition of diverse tissue responses. Additionally, these observations provide new insights into morphinergic signalling that transcend analgesia and addiction. We have also linked the biological effects of nitric oxide into a common effect in endogenous morphine signalling. Given the singular importance of dopamine and morphine's interaction in the CNS, the presence and association of this signalling with nitric oxide all promises to provide novel answers for mental health phenomena, which have been lacking because of the inability in accepting the empirical endogenous morphine studies.