Cells of origin of ascending pathways in the spinal cord of the pigeon.

Horseradish peroxidase was applied to ascending spinal pathways at high cervical levels to determine the cells of origin of these pathways in the pigeon. In addition to primary afferent fibers many ipsilaterally located lamina IV neurons of cervical segments project to the dorsal columns, indicating a substantial postsynaptic dorsal column pathway in birds. Cells projecting in the dorsolateral part of the white matter were predominantly located in lamina I and V throughout the spinal cord (bilaterally) and in the avian Clarke's column (ipsilateral at cervical and contralateral at lumbar levels). Neurons in the ventral horn (laminae VI-VIII) project to lateral and ventral parts of the lateral funiculus.