Are there efferent fibers in the dorsal roots?

Calcitonin gene-related peptide immunoreactivity in neuronal perikarya in dorsal root

Calcitonin gene-related peptide (CGRP) has been localized in neuronal cell bodies in dorsal root ganglia (DRG) and in fibers of the dorsal horn (DH), where it may be involved in transmission of a sensory signal. The capacity of neurons from DRG and dorsal roots (DR) to produce CGRP in culture was examined in this investigation. CGRP-like immunoreactivity was observed in cultured neuronal cell bodies in the DRG and DR. CGRP-positive cell bodies in the DR explains why extirpation of the DRG fails to eliminate CGRP-positive fibers from the DH.

Branching of sensory axons in the dorsal root and evidence for the absence of dorsal root efferent fibers

The present study demonstrates that there are more dorsal root axons than dorsal root ganglion cells in the L6-S1 dorsal roots of the rat. The excess fibers do not come from aberrant dorsal root ganglion cells and our control procedures indicate that there are no extraneous fibers in these dorsal roots. Accordingly many dorsal root axons must branch in the dorsal root.

Neural intersegmental connection in the spinal root and ganglion region of the rat

A study has been made of the macroscopic, microscopic and electron-microscopical appearance of intersegmental neural connections in the rat. Macroscopically, spinal roots and ganglia of adjacent segments were frequently observed to be linked by discrete, slender strands, mainly in the lumbosacral region where the roots are long. When examined under the light microscope, even the smallest was found to contain as many as 72 myelinated fibres with a range of diameters between 1.5-14 mu-m. The were commonly accompanied by blood vessels. Connections, when present, contributed to as much as 6-28% of the total number of myelinated axons in dorsal roots. Under the electron microscope, links between dorsal roots, or between dorsal roots and adjacent ganglia, contained unmyelinated fibres comparable in numbers to those found in the dorsal roots themselves. In links between ventral roots and ganglia the numbers of unmyelinated fibres proportionally exceeded those found in ventral roots. The presence of these connections may account for the reported finding of undamaged nerve fibres in the dorsal roots after dorsal root sectioning or ganglionectomy and in the ventral roots after ventral root sectioning.