Glutamate immunoreactivity in rat dorsal root axons.

Approximately 8.5% of the unmyelinated and 2.5% of the myelinated primary afferent axons in lumbar dorsal roots of normal rats are immunostained for glutamate. Thus unmyelinated fibers are the predominantly immunostained population under the conditions of our experiments. The mean size of the unmyelinated fibers is greater at L6 than at L4 and L2. The meaning of this is not clear, but it may imply that pelvic visceral afferents are slightly larger than afferents from other areas. We emphasize that the immunostained axons can be demonstrated in otherwise normal animals, so changes in the percentages of labeled axons in response to various stimuli will be of interest.