CENTRAL PROJECTIONS OF PRIMARY AFFERENTS FROM THE INTEROSSEOUS NERVE IN THE PIGEON

The interosseous nerve in the pigeon's leg innervates a string of Herb st corpuscles. Because Herbst corpuscles are vibration-sensitive, this study, using neuronal tracing methods, was expected to show the centr al representation of vibration sense. After application of a mixture o f free and lectin-conjugated horseradish peroxidase to the interosseou s nerve, labeled cell bodies of sensory and postganglionic neurons wer e mainly located in the dorsal root ganglia and paravertebral sympathe tic ganglia L3/L4. In spinal segments L3/L4 fibers and terminals were mainly distributed at the lateral border of the head of the dorsal hor n. In more cranial or caudal segments terminal fields were at intermed iate parts of laminae I/II and laminae IV/V. Some labeled fibers enter ed the dorsal horn from medial to terminate in lamina IV. Primary affe rents of the interosseous nerve projected directly to the gracile nucl eus 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 t o reach the brainstem via the dorsal column primary afferents.