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      The Spared Nerve Injury (SNI) Model of Induced Mechanical Allodynia in Mice


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          Peripheral neuropathic pain is a severe chronic pain condition which may result from trauma to sensory nerves in the peripheral nervous system. The spared nerve injury (SNI) model induces symptoms of neuropathic pain such as mechanical allodynia i.e. pain due to tactile stimuli that do not normally provoke a painful response [1].

          The SNI mouse model involves ligation of two of the three branches of the sciatic nerve (the tibial nerve and the common peroneal nerve), while the sural nerve is left intact [2]. The lesion results in marked hypersensitivity in the lateral area of the paw, which is innervated by the spared sural nerve. The non-operated side of the mouse can be used as a control. The advantages of the SNI model are the robustness of the response and that it doesn’t require expert microsurgical skills.

          The threshold for mechanical pain response is determined by testing with von Frey filaments of increasing bending force, which are repetitively pressed against the lateral area of the paw [3], [4]. A positive pain reaction is defined as sudden paw withdrawal, flinching and/or paw licking induced by the filament. A positive response in three out of five repetitive stimuli is defined as the pain threshold.

          As demonstrated in the video protocol, C57BL/6 mice experience profound allodynia as early as the day following surgery and maintain this for several weeks.

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          A new and sensitive method for measuring thermal nociception in cutaneous hyperalgesia.

          A method to measure cutaneous hyperalgesia to thermal stimulation in unrestrained animals is described. The testing paradigm uses an automated detection of the behavioral end-point; repeated testing does not contribute to the development of the observed hyperalgesia. Carrageenan-induced inflammation resulted in significantly shorter paw withdrawal latencies as compared to saline-treated paws and these latency changes corresponded to a decreased thermal nociceptive threshold. Both the thermal method and the Randall-Selitto mechanical method detected dose-related hyperalgesia and its blockade by either morphine or indomethacin. However, the thermal method showed greater bioassay sensitivity and allowed for the measurement of other behavioral parameters in addition to the nociceptive threshold.
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            Spared nerve injury: an animal model of persistent peripheral neuropathic pain.

            Peripheral neuropathic pain is produced by multiple etiological factors that initiate a number of diverse mechanisms operating at different sites and at different times and expressed both within, and across different disease states. Unraveling the mechanisms involved requires laboratory animal models that replicate as far as possible, the different pathophysiological changes present in patients. It is unlikely that a single animal model will include the full range of neuropathic pain mechanisms. A feature of several animal models of peripheral neuropathic pain is partial denervation. In the most frequently used models a mixture of intact and injured fibers is created by loose ligation of either the whole (Bennett GJ, Xie YK. A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen in man. Pain 1988;33:87-107) or a tight ligation of a part (Seltzer Z, Dubner R, Shir Y. A novel behavioral model of neuropathic pain disorders produced in rats by partial sciatic nerve injury. Pain 1990;43:205-218) of a large peripheral nerve, or a tight ligation of an entire spinal segmental nerve (Kim SH, Chung JM. An experimental model for peripheral neuropathy produced by segmental spinal nerve ligation in the rat. Pain 1992;50:355-363). We have developed a variant of partial denervation, the spared nerve injury model. This involves a lesion of two of the three terminal branches of the sciatic nerve (tibial and common peroneal nerves) leaving the remaining sural nerve intact. The spared nerve injury model differs from the Chung spinal segmental nerve, the Bennett chronic constriction injury and the Seltzer partial sciatic nerve injury models in that the co-mingling of distal intact axons with degenerating axons is restricted, and it permits behavioral testing of the non-injured skin territories adjacent to the denervated areas. The spared nerve injury model results in early ( 6 months), robust (all animals are responders) behavioral modifications. The mechanical (von Frey and pinprick) sensitivity and thermal (hot and cold) responsiveness is increased in the ipsilateral sural and to a lesser extent saphenous territories, without any change in heat thermal thresholds. Crush injury of the tibial and common peroneal nerves produce similar early changes, which return, however to baseline at 7-9 weeks. The spared nerve injury model may provide, therefore, an additional resource for unraveling the mechanisms responsible for the production of neuropathic pain.
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              A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen in man.

              A peripheral mononeuropathy was produced in adult rats by placing loosely constrictive ligatures around the common sciatic nerve. The postoperative behavior of these rats indicated that hyperalgesia, allodynia and, possibly, spontaneous pain (or dysesthesia) were produced. Hyperalgesic responses to noxious radiant heat were evident on the second postoperative day and lasted for over 2 months. Hyperalgesic responses to chemogenic pain were also present. The presence of allodynia was inferred from the nocifensive responses evoked by standing on an innocuous, chilled metal floor or by innocuous mechanical stimulation, and by the rats' persistence in holding the hind paw in a guarded position. The presence of spontaneous pain was suggested by a suppression of appetite and by the frequent occurrence of apparently spontaneous nocifensive responses. The affected hind paw was abnormally warm or cool in about one-third of the rats. About one-half of the rats developed grossly overgrown claws on the affected side. Experiments with this animal model may advance our understanding of the neural mechanisms of neuropathic pain disorders in humans.

                Author and article information

                J Vis Exp
                Journal of Visualized Experiments : JoVE
                MyJove Corporation
                18 August 2011
                18 August 2011
                : 54
                : 3092
                The Lundbeck Foundation Research Center MIND, Department of Biomedicine, Aarhus University
                Department of Pharmacology and Pharmacotherapy, Faculty of Pharmaceutical Sciences, University of Copenhagen
                Author notes

                Correspondence to: Christian B. Vaegter at cv@ 123456biokemi.au.dk

                Copyright © 2011, Journal of Visualized Experiments

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.




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