Fig. 8. Heart laterality after treatment with serotonin agonists or antagonists. The indicated agents were implanted to the left or right of Hensen's node at HH4-HH6; heart laterality was scored 20 hours later. The percentage of embryos with right-looped (R, situs solitus) or left-looped (L, situs inversus) hearts is shown; the number of embryos per group is indicated in parentheses. Treatments were: DMSO, serotonin reuptake inhibitor fluoxetine (100 µM), 5-HT₃ receptor agonist 2-CH3-5HT (5 mM), 5-HT₃ receptor antagonist ondansetron (5 mM), 5-HT₄ receptor agonist ML10302 (5 mM) and the 5-HT₄ receptor antagonist GR125487 (5 mM). Asterisk indicates situs inversus frequencies that significantly differ from DMSO by ² analysis (P<0.05).