Short-term observations of the regenerative potential of injured proximal sensory nerves crossed with distal motor nerves

Abstract

Motor nerves and sensory nerves conduct signals in different directions and function in different ways. In the surgical treatment of peripheral nerve injuries, the best prognosis is obtained by keeping the motor and sensory nerves separated and repairing the nerves using the suture method. However, the clinical consequences of connections between sensory and motor nerves currently remain unknown. In this study, we analyzed the anatomical structure of the rat femoral nerve, and observed the motor and sensory branches of the femoral nerve in the quadriceps femoris. After ligation of the nerves, the proximal end of the sensory nerve was connected with the distal end of the motor nerve, followed by observation of the changes in the newly-formed regenerated nerve fibers. Acetylcholinesterase staining was used to distinguish between the myelinated and unmyelinated motor and sensory nerves. Denervated muscle and newly formed nerves were compared in terms of morphology, electrophysiology and histochemistry. At 8 weeks after connection, no motor nerve fibers were observed on either side of the nerve conduit and the number of nerve fibers increased at the proximal end. The proportion of newly-formed motor and sensory fibers was different on both sides of the conduit. The area occupied by autonomic nerves in the proximal regenerative nerve was limited, but no distinct myelin sheath was visible in the distal nerve. These results confirm that sensory and motor nerves cannot be effectively connected. Moreover, the change of target organ at the distal end affects the type of nerves at the proximal end.

Keywords: acetylcholinesterase staining; muscle denervation; nerve conduit; nerve regeneration; nerve remodeling; neural anastomosis; neural regeneration; peripheral nerve.

Figure 1

Weakness in extending the right knee.

Figure 2

Electrophysiological function in rats with and without sensory-motor nerve crosses. (A) A newly-formed nerve crossing the conduit. (B, C) Typical compound muscle action potentials of rats in the control (B) and experimental (C) groups. A regular compound action potential was present in rats in the control group, but no impulses were observed among rats in the experimental groups.

Figure 3

Morphometric changes in the quadriceps of rats that underwent sensory-motor nerve crosses (hematoxylin-eosin staining, × 100). (A) Quadriceps of a rat in the control group. (B, C) Quadriceps of rats in the sensory-motor nerve cross groups at 4 weeks (B), and 8 weeks (C) after surgery. The diameter of the muscle fibers decreased while the number of muscle fibers per unit area increased, and the muscle-fiber boundary became blurred.

Figure 4

Morphological changes in the saphenous and femoral nerves following crossing of the proximal stump of the saphenous nerve to the distal stump of the quadriceps nerve (acetylcholinesterase staining, × 200). Upper panel: A strong positive reaction, indicating the presence of abundant acetylcholinesterase enzymes was observed in the unmyelinated zone (arrows) owing to the presence of sympathetic nerves. Lower panel: Sympathetic postganglionic fibers (arrow) in the femoral nerve were similar in appearance to those of the saphenous nerve, although the two nerves can be distinguished by the presence of an obvious circular limit, reflecting the presence of a medullary sheath.