Sciatic nerve regeneration in mice and rats: recovery of sensory innervation is followed by a slowly retreating neuropathic pain-like syndrome.

Peripheral nerve regeneration has been studied extensively in the sciatic nerve crush model, at the level of both function and gene expression. The crush injury allows full recovery of sensory and motor function in about 3 weeks as assessed by the foot reflex withdrawal test and De Medinacelli walking patterns. We used the recently developed CatWalk paradigm to study walking patterns in more detail in mice and rats. We found that, following the recovery of sensory function, the animals developed a state of mechanical allodynia, which retreated slowly over time. The motor function, although fully recovered with the conventional methods, was revealed to be still impaired because the animals did not put weight on their previously injured paw. The development of neuropathic pain following successful sensory recovery has not been described before in crush-lesioned animals and may provide an important new parameter to assess full sensory recovery.