Lab resourceEffects of repeated nerve injuries at different time intervals on functional recovery and nerve innervation
Introduction
There are a few reports regarding effects of repeated crush injuries on the sciatic nerve of rodents. Our previous report [1] showed that the recovery of motor function was delayed after repeated (2 and 3 times at 1-week intervals) crush injuries in rats. Recently, Sakuma et al. [2] reported that there was a gradual failure in the recovery of motor function after 3, 4, and 5 crushes at 1-week intervals in mice. However, to our knowledge, there is no literature describing effects of repeated nerve crush injuries at different time intervals on the recovery of motor function, although the time intervals between repeated injuries are diverse in the clinical cases.
After a single nerve crush of the sciatic nerve, regenerating axons begin to reach the tibialis anterior muscle, a main muscle innervated by the common peroneal nerve, between 2 and 3 weeks after the injury and almost reach the muscle by 4 weeks after the injury [1]. Therefore, in case of repeated nerve crush injuries at 1- and 2-week intervals, a second injury is supposed to be inflicted on the sciatic nerve whose regenerating axons are extending toward the target muscle. In the same sense, a second injury is supposed to be inflicted on the nerve whose regenerating axons are consisted of various stages of axons that have reached or are extending toward the muscle at 3-week intervals, while a second injury is supposed to be inflicted on the nerve whose regenerating axons have mostly reached the muscle at 4-week intervals.
Because the time interval between repeated injuries is an essential factor for the recovery of motor function in addition to the number of injuries, we examined in detail the effects of repeated nerve crush injuries on functional recovery at different numbers of repetitions (2 and 3 times) and at different time intervals (1-, 2-, 3-, and 4-week intervals). Motor function of the lower limb was assessed by the static sciatic index (SSI) for sciatic function. In addition, we evaluated muscle fiber reinnervation by immunohistochemically visualized βIII-tubulin, an axonal marker, and histochemically visualized α-bungarotoxin, an acetylcholine receptor antagonist.
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Animals
Adult female Wistar rats (180–220 g body weight; Japan SLC Inc., Hamamatsu, Japan) were used for this study. All procedures were conducted in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals, and protocols were approved by our Institutional Animal Care and Use Committee. All efforts were made to minimize animal suffering and pain. Surgical procedures were performed under general anesthesia induced with an intraperitoneal injection of a mixture
SSI scores
Figs. 3 and 4 show the changes in SSI scores for the single (1c, n = 6) and double nerve crush (1w2c, 2w2c, 3w2c, 4w2c) groups and the single (1c, n = 7) and triple nerve crush (1w3c, 2w3c, 3w3c, 4w3c) groups until 56 days after the final crush, respectively. Over the first week, all the rats in all the groups showed very severe motor dysfunction with SSI scores below −80, and some rats could not place the sole of the foot on the floor (SSI = −100.0). In group 1c of both the experiments (n
Discussion
Previous studies [1], [2] have demonstrated that multiple nerve crush injuries at 1-week intervals resulted in delayed functional recovery. Similarly, the results of the present study demonstrated that the recovery of motor function was delayed after repeated crush injuries according to the number of repetitions in all cases. Against our expectations, the time interval between repeated injuries did not seem to be associated with functional recovery. After a single nerve crush, the motor
Conclusion
The recovery of motor function and the rate of nerve innervation were delayed according to the number of repetitions of nerve crush injuries. The time interval between repeated injuries did not seem to be associated with functional recovery.
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Present address: Department of Anatomy, Faculty of Medicine, Tohoku Medical and Pharmaceutical University, Sendai, Miyagi, Japan.