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 h as recently invaded North America. To develop methods of controlling z ebra mussel spawning, two vertebrate serotonin antagonists, methiothep in and metergoline, known to bind with high affinity to snail 5-HT rec eptors, were tested for their ability to block 5-HT-induced spawning i n zebra mussels. Methiothepin inhibited 5-HT-induced spawning at conce ntrations as low as 10(-6)M. Metergoline (10(-4)M) inhibited 5-HT-indu ced spawning; however, at lower concentrations (10(-8) to 10(-5)M), me tergoline by itself significantly induced spawning in male, but not fe male zebra mussels. Metergoline (10(-5)M)-induced male spawning was in hibited by 10(-5)M methiothepin. Thus, methiothepin is the most effect ive inhibitor and metergoline the most powerful inducer of spawning ye t tested in zebra mussels.