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KMID : 0614520020120010027
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Journal of the Korean Pain Research Society
2002 Volume.12 No. 1 p.27 ~ p.31
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Animal Models of Neuropathic Pain - Morphine Efficacy Depends on the Lapse of Time after Peripheral Nerve Injury -
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Na Heung-Sik
Back Seung-Keun
Hong Seung-Kil
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Abstract
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Peripheral nerve injury sometimes results in chronic neuropathic pain such as causalgia. This type of pain is characterized by spontaneous burning pain accompanied by hyperalgesia and allodynia lasting variable times. At present, the mechanisms underlying neuropathic pain are not completely understood. Recently several experimental animal models for neuropathic pain, produced by a partial injury of the nerves, were developed by Bennett and Xie (1988), Seltzer, Dubner and Shir (1990), Kim and Chung (1992), Na et al. (1994), Decosterd and Woolf (2002), and Lee et al. (2002), respectively. These models are attractive in that the characteristic symptoms of neuropathic pain such as allodynia and hyperalgesia are clearly observed. In the present study, using ’tail’ model (Na et al, 1994), we examined whether the effectiveness of morphine on mechanical allodynia could be changed by the lapse of time following peripheral nerve injury. To this aim, we compared the effectiveness of morphine between the two groups of rats subjected to unilateral transection of inferior and superior caudal trunks at the level between S1 and S2 spinal nerves; one group was intraperitoneally injected morphine (1 and 2 mg/kg) 2 weeks after the nerve injury (2 W group) and the other group was administered morphine 16 weeks after the same nerve injury (16 W group). Mechanical allodynia was assessed by the tail withdrawal response following the application of von Frey hair (2.0 g) stimulation to the tail. Morphine significantly reduced the mechanical allodynia 1 and 4 hr after the injection in the 2 W group. Whereas, in the 16 W group, morphine slightly attenuated mechanical allodynia at only 1 hr after the injection. These results suggest that the effectiveness of morphine on mechanical allodynia can be alleviated according to the lapse of time following peripheral nerve injury.
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KEYWORD
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Neuropathic pain, Allodynia, Hyperalgesia, Animal model, Morphine
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