Norlaudanosoline and nicotine increase endogenous ganglionic morphine levels: nicotine addiction

Abstract

1. Given the presence of morphine, its metabolites and precursors, e.g., norlaudanosoline, in mammalian and invertebrate tissues, it became important to determine if exposing normal excised ganglia to norlaudanosoline would result in increasing endogenous morphine levels. 2. Mytilus edulis pedal ganglia contain 2.2 +/- 0.41 ng/g wet weight morphine as determined by high pressure liquid chromatography coupled to electrochemical detection and radioimmunoassay. 3. Incubation of M. edulis pedal ganglia with norlaudanosoline, a morphine precursor, resulted in a concentration- and time-dependent statistical increase in endogenous morphine levels (6.9 +/- 1.24 ng/g). 4. Injection of animals with nicotine also increased endogenous morphine levels in a manner that was antagonized by atropine, suggesting that nicotine addiction may be related to altering endogenous morphine levels in mammals. 5. We surmise that norlaudanosoline is being converted to morphine, demonstrating that invertebrate neural tissue can synthesize morphine.

Fig. 1.

Norlaudanosoline enhances endogenous ganglionic morphine levels in Mytilus edulis pedal ganglia. (A) Ganglia (20 per treatment) were incubated with 1.0, 10, 50, and 100 ng of norlaudanosoline for 60 min. Morphine quantification was by RIA. One Way ANOVA analysis shows the morphine level in ganglion incubated with norlaudanosoline were significantly higher (^*** denotes P < 0.001) than control at 50 and 100 ng of norlaudanosoline (THP). (B) Norlaudanosoline (100 ng/ganglia) incubation of Mytilus edulis pedal ganglia exhibit an increase in endogenous morphine levels, which is time-dependent. Saline incubation served as a control. Morphine levels were determined RIA. One Way ANOVA analysis shows the morphine level in ganglia incubated with norlaudanosoline was significantly higher than control at 30 and 60 min (^*** denotes P < 0.001). All determinations were replicated four times and the mean graphed ± SEM.

Fig. 2.

Cholinergic influences on ganglionic morphine levels. Animals were injected in the foot with nicotine (10 μg/100 μl), atropine (10 μg/100 μl) or a mixture of both chemicals for 1 h. Each group contained 15 animals. Ganglia were dissected and extracted (see Section ‘‘MATERIALSAND METHODS’’). One way ANOVA analysis shows the morphine level in the ganglia injected with nicotine were significantly higher (^*** denotes P < 0.001) than control (saline injection). Atropine alone did not affect morphine level in the ganglia; also, injection of atropine with nicotine did not increase morphine level. Morphine levels were determined by RIA. All treatments were replicated three times and mean graphed ± SEM.

Fig. 3.

Morphine formation in M. edulis pedal ganglia (see Zhu et al., 2005b). Our previous and present report demonstrates that morphine is synthesized by the precursors listed in the fig. CYP2D6, a member of CYP450 enzyme family, mediates the conversion of tyramine to dopamine, reticuline (or norlaudanosoline) to morphine, and codeine to morphine. Other enzymes also are involved and will be the subject of future work.