Employment of the mouse median nerve model for the experimental assessment of peripheral nerve regeneration

The experimental investigation of nerve regeneration after microsurgical repair is usually carried out in rats, rather than mice, because of the larger sized peripheral nerves. Today however, the availability of genetically modified mice makes the use of this laboratory animal very intriguing for investigating nerve regeneration at a molecular level. In this study we aimed to provide a standardization of the experimental model based on microsurgical direct repair, by 12/0 suture, of the left median nerve in adult male mice. Postoperative recovery was regularly assessed by the grasping test. At day-75 postoperative, regenerated median nerve fibers were analyzed by design-based quantitative morphology and electron microscopy. Yet, sections were immuno-labelled using two axonal antibodies commonly employed for rat nerve fibers. Results indicated that functional recovery begun at day-15 and progressively increased reaching values not significantly different from normal by day-50. Quantitative morphology showed that, at day-75, the number of regenerated nerve fibers was not significantly different in comparison to controls. In contrast, differences were detected in fiber density, mean axon and fiber diameter and myelin thickness which were all significantly lower than controls. Immunohistochemistry showed that axonal markers commonly used for rat nerves studies are effective also for mouse nerves. Similar to the rat, the mouse median nerve model is superior to sciatic nerve model for the minimal impact on animal well-being and the effectiveness of the grasping test for motor function evaluation. The main limitation is the small nerve size which requires advanced microsurgical skills for performing 12/0 epineurial suturing.