INHIBITION AND SEX-SPECIFIC INDUCTION OF SPAWNING BY SEROTONERGIC LIGANDS IN THE ZEBRA-MUSSEL DREISSENA-POLYMORPHA (PALLAS)

Serotonin (5-hydroxytryptamine, 5-HT) stimulates spawning in the zebra mussel (Dreissena polymorpha), a macrofouling European bivalve that has recently invaded North America. To develop methods of controlling zebra mussel spawning, two vertebrate serotonin antagonists, methiothepin and metergoline, known to bind with high affinity to snail 5-HT receptors, were tested for their ability to block 5-HT-induced spawning in zebra mussels. Methiothepin inhibited 5-HT-induced spawning at concentrations as low as 10(-6)M. Metergoline (10(-4)M) inhibited 5-HT-induced spawning; however, at lower concentrations (10(-8) to 10(-5)M), metergoline by itself significantly induced spawning in male, but not female zebra mussels. Metergoline (10(-5)M)-induced male spawning was inhibited by 10(-5)M methiothepin. Thus, methiothepin is the most effective inhibitor and metergoline the most powerful inducer of spawning yet tested in zebra mussels.