FIG. 5.

Ultrastructural analysis of arecoline-induced alterations in zebrafish embryos. Electron micrographs of tail muscle myofibrils from zebrafish embryos treated with different concentrations of arecoline: control [(A) 24 hpf, (B) 48 hpf and (C) 120 hpf], 0.01% arecoline [(D) 24 hpf, (E) 48 hpf and (F) 120 hpf], 0.02% arecoline [(G) 24 hpf, (H) 48 hpf and (I) 120 hpf] or 0.04% arecoline [(J) 24 hpf; (K) 48 hpf and (L) 120 hpf). (A–C) Compact sarcoplasm with mitochondria (m) surround the densely packed and highly organized myofibrils. S, sarcomere; A, A-band; Z, Z-line; H, H-band. (D–F) Well-organized myofibrils were not evident. Small patches of disorganized fibers and mitochondria are scattered throughout the cytoplasm. In (G) and (H), it should be noted that the intercellular spaces (asterisks) are greatly enlarged compared with 0.02% arecoline-incubated embryos. The 0.02% arecoline causes defects in muscle fibers, although defects are not as bad as those in embryos with 0.04% arecoline treatment (J–L). Those defects lead to the shortage of length and decrease of swimming ability of embryos. Scale bars: 1 μm.