Projection of wing nerves to spinal cord and brain stem of the pigeon as studied by transganglionic transport of Fast Blue.

To see whether there is a topographic organization of forelimb nerves in the CNS of birds, the termination pattern of afferents from wing nerves of the pigeon in the cervical spinal cord and the brain stem was determined by the transganglionic transport of Fast Blue and HRP. Fast Blue turned out to be a very sensitive and nonselective tracer with a wider distribution of terminal labeling than with HRP. Thus, Fast Blue is a useful marker for complete mapping of the terminal fields of peripheral nerves. Despite considerable overlap of the terminal fields of individual nerves the areas of densest labeling were somatotopically organized in the spinal dorsal horn. This organization is very similar to that described for the mammalian forelimb. In the rostral cervical segments all nerves have a projection field in ventromedial parts of the dorsal horn but there is no topographic organization. In the medulla terminal fields appear in the dorsal column nuclei including the external cuneate nucleus and group x near the descending vestibular nucleus. In sharp contrast to mammalian species there is no topographic representation of individual wing nerves in these brain stem areas.