Abstract
Since the time of Bell and Magendie, it has generally been accepted that the dorsal root contains sensory axons and the ventral root contains motor axons. But a few unmyelinated fibers have also been noted in the ventral root in electron microscopic studies, and they have proved to be afferent.
The present study demonstrated the number of unmyelinated fibers and the occurrence of nerve fibers possessing calcitonin gene-related peptide (CGRP) immunoreactivity in the mouse C7 ventral root. Electron microscopic analysis showed that 13% of all axons, 124, were unmyelinated, and gradually reduced near the spinal cord. In immunohistochemistry, CGRP-positive fibers with many varicosities entered the ventral pia mater, but did not enter the CNS directly through this root.
These observations suggest that the ventral pial afferents may, at least partly, reach the pia via ventral roots, and may be mediators of pain sensation. Furthermore, CGRP immunoreactive fibers are related to, not only sensory mechanisms, but also other functions in the ventral roots.
