Background

Peripheral nerve injuries (PNIs) are an important clinical problem and recovery outcomes are generally poor (Jensen et al., 2001; Höke and Brushart, 2010). Additionally, treatments for these injuries have not much changed in the last 100 years (Mundie, 1920; Taylor et al., 2008). As such, models of PNI have become important to understand potential barriers to regeneration and treatments for enhancing it. While in humans and larger mammals, such as cats, suturing through the epineurium is a common mechanism of repair (Lundborg, 2002; Grinsell and Keating, 2014; Raslan et al., 2014), this treatment is not reliably performed in mice. First, the diameter of the sciatic nerve is less than 2 mm making the placement of epineurial sutures technically challenging. Second, in comparison to nerves in larger animals, axons in mouse nerves are more likely to exude from cut nerves or “mushroom out” when the epineurium is penetrated during placement of sutures, making clean repair of the cut nerves difficult. Finally, placement of sutures in small rodents can interfere with the blood supply of regenerating nerves. One method that can overcome these challenges is the use of fibrin glue, a tool that was first utilized in human patients (Egloff and Narkas, 1983; MacGillivray, 2003). The implementation of fibrin glue in experimental animals (as models to assess its benefits for human nerve repair) also has a long history; decades ago it was found to be as effective as epineurial sutures for repair of the rat sciatic nerve (Nishihira, 1988). We describe a method to repair a mouse sciatic nerve injury that facilitates nerve regeneration in experimental situations. First, we use a fibrin glue formula, derived from human and bovine blood components, that was previously found to enhance repair in central nervous system axon tracts (Guest et al., 1997). Second, we secure the nerve by adhering it to a silastic mat prior to transection. This ensures a minimal gap between the proximal and distal nerve stumps and enhanced stability, without having to leave a piece of the epineurium intact, which is a technically difficult approach and can result in leaving some axons uninjured. The improved coaptation and increased stability diminishes the incidence of dehiscence reported without suture stabilization (Cruz et al., 1986). While the components of fibrin glue may interact with the immune system (Schoenecker et al., 2001; Mosesson, 2005; Kelsh et al., 2014), this strategy has been used extensively in both rats and mice with great success. Comprehensive comparisons of nerve repair efficiency using fibrin glues compared to epineurial sutures have been recently published (Adel et al., 2017; Koulaxouzidis et al., 2017, Wang et al., 2018). In our hands, the protocol described facilitates sciatic nerve reformation in mice by two months following injury as quantified by complete motor muscle reinnervation assessed by re-occupancy of neuromuscular junctions and electromyography with an almost 100% success rate (Wilhelm et al., 2012; Rotterman et al., 2019). As a further advantage, drugs or other compounds can be added to the glue to test how different factors administered peripherally (and directly on the nerve) may impact regeneration (Wilhelm et al., 2012). These nerve repair surgeries are all done in adult (3+ month) C57Blk/6 mice, but can easily be transferred to other species and ages.