GANGLIONIC AXONS IN MOTOR ROOTS AND PIA MATER

In addition to motor axons and preganglionic axons, Ventral roots cont ain unmyelinated or thin myelinated sensory axons and postganglionic s ympathetic axons. It has been said that ventral roots channel sensory axons to the CNS. However, it now seems that these axons end blindly, shift to the pia or loop and return towards the periphery and that the se units reach the CNS via dorsal roots. Sensory ventral root axons pr oject from a variety of somatic or Visceral receptors; some of them ar e third branches of dorsal root afferents and some seem to lack a CNS projection. Many ventral root afferents contain substance P (SP) and/o r calcitonin gene-related peptide (CGRP). These fibres are not affecte d by neonatal capsaicin treatment and they cannot induce radicular or pial extravasation. Some thin Ventral root axons are sympathetic and r elate to blood vessels. Afferents containing SP and/or CGRP and sympat hetic axons also occur in the spinal pia mater. The sensory axons medi ate pain. They might also have vasomotor, tissue-regulatory and/or mec hanoreceptive functions. The motor roots of cranial nerves IV, VI and XI contain unmyelinated axons arranged like in ventral roots outside t he autonomic outflow. However, the motor root of cranial nerve V chann els some unmyelinated axons into the CNS. The occurrence of thin axons in ventral roots and pia mater changes during development and ageing. After peripheral nerve injury, ipsilateral ventral roots and pia are invaded by new sensory and postganglionic sympathetic axons. (C) 1997 Elsevier Science Ltd.