KRAJNIAK, KG.*; LU, J.; EDER, S.: Immunohistochemical Localization of Serotonin in the Zebra Mussel,Dreissena polymorpha

The zebra mussel, Dreissena polymorpha, is a non-indigenous bivalve mollusc that is present in the waterways of North America. Previous research has shown that the neurotransmitter serotonin or 5-hydroxytryptamine (5-HT) can induce spawning in these animals. In other bivalves serotonin is also involved in the control of heart rate, smooth muscle tone, and neuronal activity. Therefore, we decided to search for serotonin in a variety of zebra mussel organs and tissues, including heart, transcardiac rectum, and anterior byssal retractor muscle (ABRM). Specimens were collected from the Mississippi River near Grafton, IL and kept at 10^o C until used. Tissues were removed, fixed in Bouin’s fixative, embedded in paraffin, and sectioned in preparation for the staining process. The tissues were stained with rabbit polyclonal antibodies to serotonin. The secondary antibodies used to visualize the primary antibodies were goat anti-rabbit antibodies conjugated to fluorescein isothiocyanate. All tissues were examined with a fluorescent microscope and photographed. Control slides were stained with serotonin antibodies, preincubated with 1 mM serotonin. The heart and transcardiac rectum contained a large number of immunoreactive fibers and varicosities. Control sections of both rectum and heart showed no positive staining. In contrast the ABRM displayed no specific stainining. The data suggest that serotonin is likely involved in the control of the heart and digestive tract as in other molluscs. Since this neurotransmitter can either be excitatory or inhibitory in other molluscs, we will need to perform bioassays with these tissues to establish its role. We are currently examining other zebra mussel tissues for the presence of serotonin.