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KMID : 0811720050090000057
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Korean Journal of Physiology & Pharmacology
2005 Volume.9 No. 0 p.57 ~ p.0
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Uninjured C-Afferents are Responsible for Mechanical Hyperalgesia following Peripheral Nerve Injury of the Rat
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Jang Jun-Ho
Lee H.J.
Leem Joong-Woo
Nam Taick-Sang
Paik Kwang-Se
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Abstract
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A partial peripheral nerve injury causes neuropathic pain including hyperalgesia to mechanical stimuli. There is evidence for contribution of uninjured afferent fibers to mechanical hyperalgesia (MH) in the neuropathic state. In this study, we examined whether A- or C- afferents in uninjured nerves are responsible for nerve injury-induced MH. Nerve injury was performed with L5 spinal nerve lesion (SNL) of the rat. Mechanical sensitivity of hind paw was assessed as paw withdrawal threshold (PWT) to von Frey filament applications. Capsaicin or vehicle was applied for 30 minutes onto a portion of left sciatic nerve. The capsaicin-, vehicle-treated, and naive rats were subjected to behavioral testing, measuring compound action potentials (CAPs) in L4 dorsal root, and analyzing cell proportions in L4 dorsal root ganglion (DRG). Nociceptive responses to intraplantar (i.pl.) injection of CGRP and, me-ATP, which are ligands for CGRP and P2X3 receptors, respectively, present predominantly in C-afferent neurons, were examined. After L5 SNL, MH developed as evidenced by decreased PWTs. When MH developed, capsaicin treatment on the sciatic nerve relieved MH. In situation of MH being relieved, the followings were observed: 1) CAPs in L4 dorsal root was reduced in size for C-component without change for A-component when compared with those from vehicle-treated or naive rats, 2) cell proportions of L4 DRG showed a reduction of small-sized neurons without changes of medium- and large-sized ones when compared with those from vehicle-treated or naive rats, 3) i.pl. injection of CGRP or, me-ATP to affected hind paw failed to produce MH, which otherwise produced MH in naive rats. These results suggest that following peripheral nerve injury, C-afferents among uninjured intact afferents are responsible for maintaining neuropathic pain.
Support Contributed By: a grant from Stem Cell Research Center of 21 C Frontier Research Program, Ministry of Science and Technology, Republic of Korea (SC11060)
Source: Korean Journal of Physiology & Pharmacology.2005 Oct;9(Suppl I):S83-S83
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KEYWORD
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Capsaicin, Uninjured intact afferents, Mechanical hyperalgesia
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