POSTNATAL-DEVELOPMENT AND AGING OF THE RAT VENTRAL ROOT L5 - ELECTRON-MICROSCOPIC AND IMMUNOHISTOCHEMICAL STUDIES

The ventral root L5 of neonatal and adult rats has been used in many e xperimental studies on ganglionic C-fibers. Since the normal presence of such axons in L5 roots from animals of different ages is unknown, t he results of these studies cannot be appropriately interpreted. In th e present study we examine L5 ventral roots from developing and aging rats in this respect. Electron microscopic examination revealed that C -fibers occur in neonatal roots. The adult proportion has been establi shed at day 30. Immunohistochemical analysis showed that thin ganglion ic fibers with substance P/calcitonin gene-related peptide- or tyrosin e hydroxylase-like immunoreactivity in the L5 root and the spinal pia mater seem to increase postnatally from low levels at birth. In roots from aged rats, myelinated fibers with a variety of aberrant features occur in normal numbers. The occurrence of unmyelinated axons is eleva ted. The increased presence of fibers with calcitonin gene-related pep tide- or tyrosine hydroxylase-like immunoreactivity in aged roots indi cates that the extra unmyelinated fibers may represent motor sprouts a nd sympathetic fibers, respectively. We conclude that the rat ventral root L5 contains a variable number of putative sensory and sympathetic axons at all ages. (C) 1996 Wiley-Liss, Inc.