Fig. 1. Expression of Phox2a (A,D,G, J, arrow), DBH (B,E,H,K, arrow) and TH (C,F,I,L, arrow) in r1 at various stages of chick development. At stage 14, transcripts of Phox2a (arrow) are observed in the dorsal aspect of r1 (A), while no expression of DBH (B) and TH (C) is detected. (D-F) At stage 20, Phox2a, DBH and TH transcripts are found in a more ventral position (arrow) and become finally localised to a region (arrow) ventrolateral to the fourth ventricle at stage 29 (G-I) and stage 34 (J-K). Arrowheads in A,D indicate the ventrally localised trochlear nuclei.