Organization of facial nerve parasympathetic cell columns in the chicken (Gallus gallus var domesticus)

In avians little is known of the organization of facial nerve, preganglionic visceromotor components. This report, using the horseradish peroxidase-tetramethylbenzidine technique, describes the location, extent, number and distribution of parasympathetic somata whose axons project via greater superficial petrosal (GSP) and chorda tympani (CT) nerves in the adult chicken. Animals were utilized 24-96 hours postsurgery. In transverse, counterstained sections (40 μm) through pontomedullary brainstem, peroxidase-labelled perikarya displaying a complete somal envelope and distinct nucleus were selected and their location marked on camera lucida drawings. GSP and CT visceromotor cell columns extend approximately 1.5 mm in ventrolateral brainstem, between the levels of superior olivary and magnocellular nuclei. The ratio of GSP:CT somata is 3-4:1. The density of GSP somata is greater in the rostal, and that of CT in the caudal halves of their cell columns. The relative locations of avian facial parasympathetic cell columns differ from those described in the rat.