SENSORY C-FIBERS IN RAT VENTRAL ROOTS ARE CAPSAICIN-INSENSITIVE AND THEY DO NOT MEDIATE EXTRAVASATION FROM PIAL VESSELS

Mammalian ventral roots and pia mater contain sensory C-fibers, some o f which exhibit a substance P- and/or calcitonin gene-related peptide (CGRP)-like immunoreactivity. At some locations, sensory axons contain ing these neuropeptides evoke peripheral plasma protein extravasation after antidromic electrical stimulation. Such axons usually disappear following treatment of neonatal rats with capsaicin. The purpose of th e present study is to find out if afferent C-fibers in the rat ventral roots L4 and L5 are capsaicin-sensitive, and if antidromic stimulatio n of these fibers elicits extravasation in the root and/or the ventral pia mater. The results show (1) that the number of C-fibers in these ventral roots is unaffected by neonatal capsaicin treatment, as seen i n the electron microscope; (2) that the occurrence and general configu ration of axons with substance P- and CGRP-like immunoreactivity do no t appear abnormal in neonatally capsaicin-treated rats, as revealed by fluorescence microscopy on longitudinal frozen sections; (3) that Eva ns blue albumin is not extravasated in the ventral root or pia mater a fter electrical ventral root stimulation or following systemic injecti on of capsaicin. We conclude, that ventral root afferents are function ally different from otherwise similar afferents at other locations.