Long ascending unmyelinated primary afferent axons in the rat dorsal column: immunohistochemical localizations.

The present study demonstrates a significant number of calcitonin gene-related peptide (CGRP) immunolabeled unmyelinated axons in the C3 fasciculus gracilis of the rat. Approximately 88% of these axons are lost following dorsal rhizotomies from midthoracic levels caudally. Assuming that CGRP labels primary afferent axons, these findings support the hypothesis that there are significant numbers of long ascending unmyelinated primary afferent axons in the dorsal columns of the rat. If these findings can be generalized, they may have clinical import.