Somatic origin of mouse and zebra finch vocal motoneurons. (A–D) Confocal mosaic images of ChAT (A,C) and Phox2b (B,D) immunohistochemistry (IHC) in neonate mouse mid to rostral medulla. Phox2b is co-expressed with ChAT in DMV and cNA branchial motoneurons. Phox2b is expressed in non-cholinergic NTS and ventrolateral medulla neurons (B,D). E–G. Confocal mosaic images of ChAT IHC (green) and pseudocolor ISH for Phox2b (magenta) in zebra finch caudal medulla. F–G Expansion from E showing combined (left) and single color images (middle – brightfield Phox2b, right – ChAT). F Images showing the absence of Phox2b co-expression in tracheosyringeal hypoglossal (XIIts) ChAT expressing motoneurons. Phox2b is expressed in the NTS. G Images showing Phox2b is co-expressed within a subset of NA motoneurons and in a small number of non-cholinergic interneurons. White arrows indicate Phox2b and ChAT co-expression. Green arrow indicates ChAT single expression. Magenta arrow indicates Phox2b single expression. Scale bars = 200 μm, D – dorsal, M - medial. ChAT – choline acetyltransferase, cNA – compact formation of the nucleus ambiguus, DMV – dorsal motonucleus of the vagus, NTS - nucleus tractus solitarius, scNA – semi-compact formation of the nucleus ambiguus, XII – hypoglossal motonucleus, XIIts – tracheosyringeal hypoglossal motonucleus.