SEROTONIN-INDUCED PARTURITION IN THE FINGERNAIL CLAM SPHAERIUM (MUSCULIUM) TRANSVERSUM (SAY)

Parturition in the freshwater fingernail clam Sphaerium (=Musculium) t ransversum (Say) was induced by external application of both 10(-4) an d 10(-3) M serotonin [5-hydroxytryptamine (5-HT)]. 5-HT induced releas e of viable juveniles within 30-60 min of application. Parturitions in 5-HT (10(-3) M) occurred sooner and more often than in 5-KT (10(-5) o r 10(-4) M) or in artificial pond water. The numbers of juveniles per parturition in 5-HT varied from one to nine. The parturition response to 5-HT was completely blocked by 10(-4) M methiothepin (a vertebrate 5-HT1/5-HT2 receptor antagonist) known to bind with high affinity to g astropod 5-KT receptors and to black 6-HT-induced spawning in other fr eshwater bivalves. However, parturition was not induced by 8-OH-DPAT ( 8-hydroxy-dipropylaminotetralin HBr, a vertebrate 5-HT1A receptor agon ist), a potent inducer of spawning in freshwater bivalves. Thus, the p harmacological profile of the 5-HT receptor(s) mediating parturition i n S. transversum may be unlike that mediating spawning in other bivalv es. This is the first report of 5-HT-induced parturition in any broodi ng bivalve. (C) 1995 Wiley-Liss, Inc.