Skin denervation, neuropathology, and neuropathic pain in a laser-induced focal neuropathy

Hou-Yu Chiang, Chin-Tin Chen, Hsiung-Fei Chien, Sung-Tsang Hsieh

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30 Citations (Scopus)

Abstract

Small-diameter sensory nerves innervating the skin are responsive to noxious stimuli, and an injury to these nerves is presumably related to neuropathic pain. Injury-induced neuropathic pain in animals can be produced by laser irradiation, which usually requires concomitant use of photosensitive dyes, known as the photochemical approach. It is not clear whether laser irradiation alone can induce neuropathic pain. In addition, two issues are important to apply these approaches: the relationship between the extent of laser irradiation and the occurrence of neuropathic pain, and the susceptibility of small-diameter sensory nerves in the skin to laser-induced neuropathic pain. To address these issues, we designed a new model of focal neuropathy by applying a diode laser of 532 nm (100 mW) to the sciatic nerve and evaluated small-diameter nerves by quantifying skin innervation and large-diameter nerves by measuring amplitudes of the compound muscle action potential (CMAP). Immediately after laser irradiation, epineurial vessels were occluded due to the formation of thrombi, and the blood flow through these vessels was markedly reduced. On postoperative day (POD) 2, animals developed characteristic manifestations of neuropathic pain, including spontaneous pain behaviors, thermal hyperalgesia, and mechanical allodynia. These phenomena peaked during PODs 7-21, and lasted for 3-6 weeks. The neuropathology at the irradiated site of the sciatic nerve included a focal area of axonal degeneration surrounded by demyelination and endoneurial edema. The extent of damage to large-diameter motor and sensory nerves after laser irradiation was evaluated by nerve conduction studies. On the irradiated sides, amplitudes of the compound muscle action potentials and sensory nerve action potentials (SNAPs) were reduced to 65.0% (P <0.0001) and 42.5% (P <0.01) of those on the control sides, respectively. Motor innervation of the neuromuscular junctions (NMJs) on plantar muscles was examined by combined cholinesterase histochemistry and immunohistochemistry. The ratio of innervated NMJs on the operated sides decreased to 76.3% of that on the control side. Skin innervation in the territory of the irradiated sciatic nerves was evaluated by immunohistochemistry with neuronal markers. Among these markers, epidermal nerve densities for protein gene product (PGP) 9.5, calcitonin gene-related peptide (CGRP), and substance P (SP) were significantly lower on the irradiated sides than the control sides with a different degree of loss for each marker (42.1-53.1%, P <0.05). Results suggest that laser-induced focal neuropathy provides a new system for studying neuropathic pain. With this approach, the extent of nerve injury can be quantified. Both small-diameter epidermal nerves and large-diameter sensory and motor nerves are susceptible to laser-induced injury of different degrees. © 2004 Elsevier Inc. All rights reserved.
Original languageEnglish
Pages (from-to)40-53
Number of pages14
JournalNeurobiology of Disease
Volume18
Issue number1
DOIs
Publication statusPublished - 2005
Externally publishedYes

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Keywords

  • Epidermal nerves
  • Ischemic neuropathy
  • Laser irradiation
  • Neuropathic pain
  • Protein gene product 9.5
  • Skin innervation
  • Ubiquitin
  • biochemical marker
  • calcitonin gene related peptide
  • cholinesterase
  • gene product
  • substance P
  • allodynia
  • amplitude modulation
  • animal experiment
  • animal model
  • animal tissue
  • article
  • blood vessel
  • controlled study
  • demyelination
  • denervation
  • diode laser
  • edema
  • enzyme histochemistry
  • experimental model
  • hyperalgesia
  • immunohistochemistry
  • ischemia
  • male
  • motor nerve
  • muscle action potential
  • muscle innervation
  • nerve conduction
  • nerve fiber degeneration
  • nerve injury
  • neuromuscular synapse
  • neuropathic pain
  • neuropathology
  • nonhuman
  • peripheral neuropathy
  • plantaris muscle
  • priority journal
  • rat
  • sciatic nerve
  • sciatic neuropathy
  • sensory nerve
  • skin nerve
  • statistical significance
  • thrombogenesis
  • Animals
  • Biological Markers
  • Blood Vessels
  • Denervation
  • Disease Models, Animal
  • Disease Susceptibility
  • Lasers
  • Male
  • Nerve Fibers, Myelinated
  • Nerve Fibers, Unmyelinated
  • Neural Conduction
  • Neuralgia
  • Neuropeptides
  • Nociceptors
  • Peripheral Nervous System Diseases
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Sensory
  • Sciatic Nerve
  • Sciatic Neuropathy
  • Skin
  • Wallerian Degeneration

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