Morphological effects caused by exposing zebrafish embryos, at the 6- to 7-somite stage, to 250 μM citral for 2 hr. (A and B) Dorsal views, obtained by Nomarski differential interference contrast optics, of anterior neuraxis at the level of the prospective midbrain and hindbrain of treated (A) and control (B) embryos immediately at the end of the 2-hr treatment. (C and D) Low-power lateral view of a 1.5-day embryo which had been treated for 2 hr with 250 μM citral at the 6- to 7-somite stage (C) and of a control embryo (D). Anterior is to the left. (Bars = 50 μm in A and B and 500 μm in C and D.)

Effect of citral on retinal morphogenesis. Lateral view, obtained by Nomarski differential interference contrast optics, of eyes from 1-day embryos: (A) control embryo; (B) embryo which had been treated with 250 μM citral for 2 hr starting at the 2- to 4-somite stage; (C) embryo treated only with 3 μM retinoic acid for 2 hr starting at the 9- to 12-somite stage; (D) embryo treated with 250 μM citral and 1 μM retinoic acid for 2 hr starting at the 9- to 12-somite stage; and (E) embryo treated with 250 μM citral and 3 μM retinoic acid for 2 hr starting at the 9- to 12-somite stage (see Table 2). Arrow in C shows a thickened optic stalk; arrow in E shows the pigmented bifurcation that is indicative of a retinal duplication (15). Anterior is to the left. (Bars = 50 μm.)

Absence of a ventral retina as shown by transverse sections through the eyes of 5-day control embryo (A) and embryos which had been treated with 250 μM citral for 2 hr starting at the 2- to 4-somite stage (B and C). Large arrow points to secondary inner plexiform layer. Small arrow points to degenerating photoreceptor cells. (Bars = 50 μm.)