• Ryutaro Iwasaki, Yusuke Matsuura, Seiji Ohtori, Takane Suzuki, Kazuki Kuniyoshi, and Kazuhisa Takahashi.
• Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
• J Hand Surg Am. 2013 May 1;38(5):841-6.

PurposeBrachial plexus pain is thought to be generated not by avulsed roots but rather by nonavulsed roots, because avulsed roots could not transmit action potentials to central nerves. The aim of this study was to evaluate pain-related behavior and the extent of glial activation in a model of brachial plexus avulsion (BPA).MethodsWe used 24 male Wistar rats. For rats in the BPA group, the C8-T1 roots were avulsed from the spinal cord at the level of the lower trunk (n = 10). Rats in a sham-surgery group had a similar surgery without the root avulsion (n = 7). Rats in an untreated group had no surgery (n = 7). Mechanical hyperalgesia of the forelimb plantar surfaces corresponding to C6 and C7 dermatomes was evaluated using a Semmes-Weinstein monofilament test every third day for 3 weeks (n = 15). Activation of astrocytes and microglia was examined immunohistochemically using anti-glia fibrillary acidic protein and anti-Iba1 antibodies 3 days after surgery (n = 9).ResultsWhen compared with rats in the sham-surgery and naive control groups, rats in the BPA group displayed significant mechanical hyperalgesia in the dermatome innervated by uninjured nerves both ipsilaterally and contralaterally and continuing through day 21. Iba1-immunoreactive microglia and glia fibrillary acidic protein-immunoreactive astrocytes were significantly activated on the ipsilateral side in the BPA group from levels C3 to T3 compared with the sham-surgery and untreated groups of rats.ConclusionsActivation of glia at uninjured levels of the dorsal horn may facilitate pain transmission following BPA injury. Consequently, spared spinal glial cells may represent therapeutic targets for treatment of pain related to BPA injury.Clinical RelevanceOur findings may indicate why neuropathic pain is so frequent and intense following BPA injury.Copyright © 2013 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

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