Spinal and medullary dorsal cell axons in the trigeminal nerve in lampreys

The ophthalmic branch of the trigeminal nerve was labeled with horseradish peroxidase (HRP) in 3 species of adult lampreys. In each species, some medullary and spinal dorsal cells were retrogradely labeled by HRP. Approximately 30% of spinal dorsal cells were labeled ipsilateral to the injection; an occasional contralateral spinal dorsal cell was also labeled. Intracellular recordings confirmed the anatomical findings.