Histamine in THE Bivalve Crassostrea virginica  

Histamine is a neurotransmitter in a number of invertebrates, but rarely has been reported in bivalves.  Work in our lab is showing that histamine is an endogenous biogenic amine in various tissues of the bivalve Crassostrea virginica, and is involved in physiological activities.  We used an HPLC method with pre-column NDA (2,3-naphthalene-dicarboxaldehyde) derivatization and fluorescence detection to quantify histamine in the animal and found that histamine is present in ng amounts in cerebral ganglia, visceral ganglia, gill, palps, heart, hemolymph, posterior adductor muscle, mantle and mantle rim.  By means of immunohistofluorescence using primary antibodies to histamine and histamine receptors, and fluorescently labeled secondary antibodies, we identified histamine and histamine H2-like receptors in cryostat cut sections and whole mounts of visceral ganglia, gill interfilamental fibers, mantle body and sensory tentacles of the mantle rim. We also performed immunoblotting to demonstrate the presence of a strong band at 70 kDa correlating with histamine H2 receptors in Western Blots.  In physiological studies of the sensory-motor integration between mantle rim sensory receptors and gill lateral ciliated cells, we found histamine to be a sensory signaling molecule involved in photoreception and in regulating cilia beating rates in gill lateral cells.  These histamine mediated responses were blocked by famotidine, an H2 receptor antagonist.  The immunohistofluorescence results of gill interfilamental fibers prompted us to look for a physiological role for histamine there.  We found that histamine caused a dose dose-dependent (10^-3-10^-5M) contraction of the interfilamental fibers, which also could be blocked when famotidine (10^-3-10^-5M) was applied prior to histamine.  The study has been demonstrating that in C. virginica, as in various other invertebrates, histamine is an endogenous biogenic amine, histamine H2-like receptors are present, and that histamine is involved in physiological functions in sensory and motor activities.  This work was supported in part by 2R25GM06003 of the Bridge Program of NIGMS and 0516041071 of NYSDOE.