The population of the dorsal root ganglion cells which have central processes in ventral root and their immunoreactivity.

Axonal transport of fluorescent dyes applied to the cut distal ends of rat L4 dorsal and ventral spinal roots was studied in order to characterize the population of dorsal root ganglion (DRG) neurons emitting axons entering the ventral root. Ca. 9% of DRG neurons, principally of small or medium size, can be labeled from the ventral root, and 55% of these display immunoreactivity for the most ubiquitous DRG neuropeptide, calcitonin gene-related peptide (CGRP). Attempts to simultaneously label cut dorsal and ventral roots revealed that double labeling was exceedingly rare and that dorsal root labeling was markedly reduced. The results are consistent with previous reports of small DRG cells emitting axons which loop into the ventral root before entering the spinal cord via the dorsal root. The few cells labeled simultaneously from cut dorsal and ventral roots indicate that axonal bifurcation distal to the DRG is very rare.