Fig. 4. NOS-like IR (arrows) in neurones in the gut of zebrafish embryos, larvae and adults. At 3 d.p.f., NOS-IR was observed in the distal (A) and middle parts of the gut. One stage later (4 d.p.f.), NOS-IR was found throughout the gut (B, distal gut; C, proximal gut). (D) NOS-IR nerve cells at 5 d.p.f. (E) In adult zebrafish, NOS-IR was observed throughout the gut, with a denser innervation of the myenteric plexus and circular muscle layer. The photo shows the distal gut. Bars, 50 µm. d.p.f., days post fertilization; IR, immunoreactivity; NOS, nitric oxide synthase.