Fig. 7. Effect of serotonin agonists and antagonists upon LR Ca_i²⁺ levels. Fura-2-loaded HH6 embryos were treated with serotoneric agents and imaged ventrally. The upper panel shows a representative Fura-2 image; the lower panel is the line-scan quantitation of fluorescent intensity versus left-right axis for that embryo, at the position indicated by the yellow line in the upper panel. (A) Untreated embryo. (B) The serotonin reuptake inhibitor fluoxetine reduced LR Ca_i²⁺. (C) The 5-HT₃ receptor agonist 2-methyl-5-HT reduced LR Ca_i²⁺. (D) The 5-HT₃ receptor antagonist ondansetron elevated right-side Ca_i²⁺. (E) The 5-HT₄ receptor agonist ML10302 reduced LR Ca_i²⁺. (F) The 5-HT₄ receptor antagonist GR125487 elevated right-sided Ca_i²⁺. Asterisk indicates Hensen's node; right (R) and left (L) are as indicated in A.