Central projections of primary afferents from the interosseous nerve in the pigeon

The interosseous nerve in the pigeon's leg innervates a string of Herbst corpuscles. Because Herbst corpuscles are vibration-sensitive, this study, using neuronal tracing methods, was expected to show the central representation of vibration sense. After application of a mixture of free and lectin-conjugated horseradish peroxidase to the interosseous nerve, labeled cell bodies of sensory and postganglionic neurons were mainly located in the dorsal root ganglia and paravertebral sympathetic ganglia L3/L4. In spinal segments L3/L4 fibers and terminals were mainly distributed at the lateral border of the head of the dorsal horn. In more cranial or caudal segments terminal fields were at intermediate parts of laminae I/II and laminae IV/V. Some labeled fibers entered the dorsal horn from medial to terminate in lamina IV. Primary afferents of the interosseous nerve projected directly to the gracile nucleus in the brainstem and distributed all along its rostrocaudal extent. Because the main terminal fields in the spinal cord are typical for the projection of small afferent fibers, vibration information seems to reach the brainstem via the dorsal column primary afferents.