Fig. 4. Cryosections from 55 h.p.f. zebrafish demonstrate the distribution of nNOS mRNA expression (blueish cells in A,C,E,F,H,I) in the brain, and its relationship to the neuronal differentiation pattern represented by AT immunoreactivity in adjacent sections (black in B,D,G). (A,B) Central telencephalon (frontal view). (C,D) Thalamic and preoptic area (frontal view). (E) The pretectum, posterior tuberculum (post. tub.), lateral hypothalamus, the brainstem and secondary matrix on the border to the cerebellum (sagittal view). (F,G) Sagittal view; (H) frontal view. (I) Weakly labelled nNOS mRNA-expressing cells in the retina (arrowhead). Scale bars: in A, 50 µm (A,B); in C, 50 µm (C–E,I); in F, 50 µm (F–H).