A 5-HT1A-like receptor is involved in the regulation of the embryonic rotation of Lymnaea stagnalis L.

Abstract Cilia driven rotation of the pond snail Lymnaea stagnalis embryos is regulated by serotonin (5-HT). In the present study, physiological and biochemical assays were used to identify the 5-HT receptor type involved in rotation. The 5-HTergic agonists applied stimulated the rotation by 180–400% and their rank order potency was as follows: LSD > 5-HT > 8-OH-DPAT > WB4101 ≫ 5-CT. The applied antagonists, spiperone, propranalol and mianserin inhibited the 5-HT or 8-OH-DPAT stimulated rotation of the embryos by 50–70%. 3 H-5-HT was bound specifically to the washed pellet of the embryo homogenates. The specific binding of 3 H-5-HT was saturable and showed a single, high affinity binding site with K d 7.36 nM and B max 221 fmol/mg pellet values. This is the first report demonstrating the high affinity binding of 3 H-5-HT to the native receptor in molluscs. All of the pharmacons that stimulated the rotation or inhibited the 5-HT or 8-OH-DPAT evoked stimulation displaced effectively the binding of 3 H-5-HT. 5-HT resulted in the inhibition of forskolin stimulated cAMP accumulation, showing that 5-HT is negatively coupled to adenylate cyclase. Our results suggest that in the 5-HTergic regulation of the embryonic rotation in L. stagnalis a 5-HT 1A -like receptor of the vertebrate type is involved.