Ultrasound Accelerates The Regeneration Of The Sciatic Nerve After Neurotmesis In Rats

Background and Objectives: Peripheral nerve injury is commonly occurred in daily life, and often associated with severe long-term personal and societal costs. So it is very important to accelerate the functional recovery of damaged nerves. Although many methods could accelerate the regeneration of damage nerves, their effects were not good. Ultrasound (US) is one of the mechanical waves. It can induce mechanical effect and stimulate tissues to regeneration or repair. Some scholars have found US can accelerate nerve regeneration from an axonotmetic injury. Doubts are existed whether US can accelerate nerve regeneration from a neurotmetic injury. In this study, we investigated the effect of US on the neurotmetic injury of peripheral nerves and its primary mechanism.Methods: The right sciatic nerves of 64 adult Wistar rats were crushed with forceps to form the experimental animal models. Then they were equally divided into treatment group and control group: The treatment received the US exposure, control group with sham exposure. US was applied every other day to the crush site of rats, which had a spatial peak, time-averaged intensity of 0.25W/cm 2 operated at 1.0MHz for 1 minute per application. At various stages after operation, the sciatic nerve function index (SFI), the sensory nerve conduction velocity (SNCV) and its histology were detected. The synthesis and secretion of nerve growth factor (NGF) were also observed by immunohistochemistry.Results: The course of Wallerian degeneration was accelerated by ultrasound treatment at 2 weeks after operation, Schwann's cell proliferation and axon regeneration did at 2 and 4 weeks after operation. The thickness of myelin sheath was gradually increased with time and the thickness of treatment group was superior to that of control group. The density of nerve fibers with myelin sheath of treatment group was significantly higher than that of control group (p < 0.05). The recovery of SFI and SNCV was also significantly improved at 4, 6 and 8 weeks postoperatively compared with control group (both p < 0.05). NGF was found in axon area of the fibers of distal stumps. The synthesis and secretion of NGF of treatment group and control group were higher than that of normal group, treatment group higher than control group (p < 0.05). After operation, the synthesis and secretion of NGF were gradually up-graded with time after sciatic nerve injury. Conclusions: US can accelerate the course of Wallerian degeneration and promote the regeneration and functional recovery of peripheral nerves from a neurotmetic injury at forepart stages after operation. As a new way of promoting peripheral nerves to regeneration, Ultrasound is a noninvasive, safe, convenient and time-saved treat modality. The up-graded expression of NGF induced by ultrasound treatment is one of the mechanisms of promoting peripheral nerves to regeneration.