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 μm. They 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.