Harumitsu Ichimura

P0 mRNA expression increases during gradual nerve elongation in adult rats

Leg lengthening with nerve elongation is a common clinical treatment. We investigated morphological and molecular changes in peripheral nerves associated with femoral lengthening using animal models. Sciatic nerves of 13 week old male Wistar rats (n = 35) were elongated indirectly by leg lengthening for 14 days at 1 mm/day. At 3, 7, 14, 21, and 35 days following initiation of elongation, sciatic nerves on the elongated side and contralateral (control) side were excised at the midpoint of the femur. Internodal length was increased by 17%. Light and electron microscopic observation of transverse sections at 14 days showed elongated nerves appearing similar to control nerves with no degenerating axons and normal myelin thickness. We next examined changes of mRNA expression of a major myelin glycoprotein, P0, in elongated nerves using a quantitative reverse transcription-polymerase chain reaction and in situ hybridization. P0 mRNA expression in elongated nerves was increased during the first 3 weeks, with expression reaching 160% of control nerve expression at 14 days. Results of in situ hybridization were confirmatory. We concluded that myelin synthesis occurred during gradual nerve elongation. In adulthood, Schwann cells retain ability to synthesize myelin in response to nerve stretching.

Repair of peripheral nerve defect by direct gradual lengthening of the distal nerve stump in rats: Effect on nerve regeneration

We investigated the use of direct lengthening of the distal stump of a peripheral nerve to compare the results of nerve regeneration using the direct lengthening method with simple end-to-end suture and autografting in rats. A segment 10 mm long was resected from the rat sciatic nerve (n=18 in each group). The distal nerve stump was fixed to a ring and pulled at a rate of 1 mm/day for 20 days using an original external nerve distraction device. The results showed that the degree of nerve regeneration in the lengthened group was superior to that of the grafted group electrophysiologically and histologically, but there were no significant differences between the lengthened and end-to-end suture groups. We conclude that direct lengthening of the distal stump of a peripheral nerve can promote nerve regeneration similar to that observed in a Wallerian degenerated nerve. We think that this technique may be used for the treatment of peripheral nerve injuries.

Repair of peripheral nerve defect by direct gradual lengthening of the distal nerve stump in rats: cellular reaction.

We investigated the effects of direct gradual lengthening of the distal stump of a peripheral nerve and subsequent nerve regeneration in rats. A segment 10 mm long was resected from rat sciatic nerve. The distal nerve stump was fixed to a ring and pulled directly at a rate of 1 mm/day using an original external nerve distraction device. After distraction for 10, 15, and 20 days, the lengthened nerves were evaluated macroscopically and immunocytochemically. At day 20, the mean (SD) distances from the ring to the 3 mm and 6 mm distal part, which were marked with sutures on the epineurium, were 7 (0.5) mm and 12.1 (0.5) mm, respectively, and the number of Schwann cells in the lengthening group had increased to twice that of control group. The distal stump of a peripheral nerve including the epineurium, endoneurium, and proliferation of Schwann cells can be lengthened directly. This method also made it possible to lengthen the nerve stump longitudinally and to control both the rate and distance. We think that this method may be used in the treatment of peripheral nerve injury.

Pre-degenerated nerve shows enhanced regeneration after incremental elongation in rats.

Following nerve degeneration, we investigated effects of linear elongation on subsequent nerve regeneration in a total of 92 Wistar rats (weight 380–340 g). The nerve was ligated at the midthigh and then elongated incrementally by a total of 15 mm by leg lengthening at a rate of 3 or 5 mm/day. Seven days after initiation of nerve elongation, the external fixator was removed and normal leg length was restored with internal fixation. Then a 10 mm nerve segment at the ligature site was excised, and the nerve was repaired with sutures (group D). At 2, 4, 6, and 8 weeks after nerve suturing, we examined transverse semi‐thin nerve sections compared with group I (severed and repaired after leg lengthening without a nerve ligature) and control group (severed and repaired without leg lengthening). After lengthening at 3 mm/day, nerve regeneration in group D was enhanced at 4 weeks. After lengthening at 5 mm/day, nerve regeneration in group D also was enhanced at 6 and 8 weeks. Pre‐degenerated nerve showed better regeneration after suturing than intact nerve. Elongation holds promise as an alternative to nerve grafting in treatment of nerve injury.