Fig. 6. nNOS mRNA expression in peripheral organs of developing zebrafish (at 72 h.p.f.). (A–D) (A) Sagittal section, low magnification, demonstrating nNOS-expressing cell clusters in the posterior portion of the swim bladder (sb; see transversal section in B), and in the rostral portion of the alimentary system (putative enteric ganglia shown in C,D). (E–G) Sagittal sections demonstrating how the rostral nNOS-expressing cell clusters become a population with evenly distributed cells in the mesenchyme along the alimentary tract and nephritic duct. Brownish structures are pigments. Scale bars: in A, 100 µm (A,G); in B, 10 µm (B–E). sb, swim bladder.