Induction and potentiation of parturition in fingernail clams (Sphaerium striatinum) by selective serotonin re-uptake inhibitors (SSRIs)

Parturition in fingernail clams (Sphaerium spp.) can be induced by external application of serotonin and serotonergic ligands. Selective serotonin re‐uptake inhibitors (SSRIs) increase neurotransmission at serotonergic synapses by blocking re‐uptake transporters. We tested the efficacy of SSRIs (fluvoxamine, fluoxetine, paroxetine) at inducing parturition in the fingernail clam Sphaerium striatinum. Parturition was induced by fluvoxamine and paroxetine, but only potentiated by fluoxetine. Fluvoxamine was potent, significantly inducing parturition at concentrations from 10 nM to 100 μM compared with negative controls. Fluvoxamine also significantly potentiated a subthreshold (10 μM) concentration of serotonin. Paroxetine also induced parturition but was less potent. Only 10 μM paroxetine significantly induced parturition compared with controls. Fluoxetine (1–100 μM) did not induce any parturitions, but at 5 μM it potentiated parturition in subthreshold serotonin concentrations as low as 50 nM. These results suggest the presence of serotonin re‐uptake transporters in bivalve molluscs and may provide a way of stimulating serotonergic mechanisms without using serotonin or its ligands. J. Exp. Zool. 280:260–264, 1998. © 1998 Wiley‐Liss, Inc.