The "cuff" model was initially developed in rats to obtain a standardized and reproducible chronic constriction injury with the implantation of multiple cuffs around the sciatic nerve6. It was then modified to implant a single cuff7,8, even though some research groups still use multiple cuff insertion19-22. It was then adapted to mice9,23, which opened the possibility to use transgenic animals. The cuff is usually 2 mm long, but other lengths have also been used in rats22. The polyethylene tubing depends on the species: PE-20 in mice9, and PE-6024,25 or PE-907,8,26,27 in rats.
The mechanical allodynia is measured with von Frey hairs. In this test, the absolute values for paw withdrawal thresholds may depend upon the surface on which the animal stands28 or upon the duration of filament bending3, but these factors do not affect the detection of the neuropathic allodynia.
The "cuff" model is of interest for the study of neuropathic pain mechanisms. It was used to study morphological changes in myelinated and unmyelinated fibers6,29, and functional changes in sensory neurons, primary afferents and spinal neurons19,21,22,30-35. It allowed demonstration that glial activation and a central shift in neuronal anion gradient participate in changes in the activity and in the responses of spinal nociceptive neurons and in neuropathic allodynia24,36-38. The influence of glutamate receptors7,39-41, of opioid receptors16,42-45 and of nicotinic receptors46 was also studied in this model.
Another interest of the model is its response to current treatments of neuropathic pain, i.e., gabapentinoids and antidepressants. Similar to clinical observations: gabapentinoids display both an acute short-lasting analgesic action at high dose and a delayed sustained relieving action that is observed after a few days of treatment, tricyclic antidepressants and selective serotonin and noradrenaline reuptake inhibitors have no acute analgesic effect at relevant dose but they display a delayed sustained relieving action that requires 1 to 2 weeks of treatment, and the selective serotonin reuptake inhibitor fluoxetine is ineffective16. The model is thus appropriate to study the molecular mechanism underlying these treatments16-18,44,45,47, which may reveal new therapeutic targets to test in patients48-51.
Lastly, the model also allows the study of the anxiodepressive consequences of neuropathic pain. Clinically, these consequences affect around a third of neuropathic pain patients but are preclinically less studied than the sensory aspects of pain. In this model, a time-dependent development of anxiety-like and depressive-like phenotypes is present52 and the related mechanism can thus be addressed.
The standardized cuffs and procedures in this mouse model of neuropathic pain result in low interindividual variability for the mechanical allodynia. The possibility to use genetically modified animals17,18,44-47,52, the long-lasting allodynia, the response to clinically used treatments and the time-dependent development of anxiodepressive symptoms make this model appropriate for the study of the various aspects and consequences of neuropathic pain and its treatments, which have already brought valuable information to this field of research.