Endogenous morphine levels increase in molluscan neural and immune tissues after physical trauma

The aim of this study was to demonstrate by biochemical and immunocytochemical methods the presence of endogenous morphine in nervous and immune tissues of the freshwater snail, Planorbarius corneus. High performance liquid chromatography (HPLC) coupled to electrochemical detection performed on tissues from control snails, revealed that the CNS contains 6.20+/-2.0 pmol/g of the alkaloid, the foot tissue contains a much lower level, 0.30+/-0.03 pmol/g, whilst morphine is not detected in the hemolymph and hepatopancreas. In specimens that were traumatized, we detected a significant rise of the CNS morphine level 24 h later (43.7+/-5.2 pmol/g) and an initial decrease after 48 h (19.3+/-4.6 pmol/g). At the same times, we found the appearance of the opiate in the hemolymph (0.38+/-0.04 pmol/ml and 0.12+/-0.03 pmol/ml) but not in the hepatopancreas. Using indirect immunocytochemistry, a morphine-like molecule was localized to a number of neurons and a type of glial cell in the CNS, to some immunocytes in the hemolymph and to amoebocytes in the foot, as well as to fibers in the aorta wall. Simultaneously to the rise of morphine biochemical level following trauma, morphine-like immunoreactivity (MIR) increased in both intensity and the number of structures responding positively, i.e., neurons and fiber terminals. In another mollusc, the mussel Mytilus galloprovincialis, the same pattern of enhanced MIR was found after trauma. Taken together, the data suggest the presence of a morphinergic signaling in invertebrate neural and immune processes resembling those of classical messenger systems and an involvement in trauma response.