Partial Nerve Injury Induces Electrophysiological Changes in Conducting (Uninjured) Nociceptive and Nonnociceptive DRG Neurons: Possible Relationships to Aspects of Peripheral Neuropathic Pain and Paresthesias

Pain. 2012 Sep;153(9):1824-36. doi: 10.1016/j.pain.2012.04.019. Epub 2012 Jun 20.

Abstract

Partial nerve injury leads to peripheral neuropathic pain. This injury results in conducting/uninterrupted (also called uninjured)sensory fibres, conducting through the damaged nerve alongside axotomised/degenerating fibres. In rats seven days after L5 spinal nerve axotomy (SNA) or modified-SNA (added loose-ligation of L4 spinal nerve with neuroinflammation-inducing chromic-gut),we investigated (a) neuropathic pain behaviours and (b) electrophysiological changes in conducting/uninterrupted L4 dorsal root ganglion (DRG) neurons with receptive fields (called: L4-receptive-field-neurons). Compared to pretreatment, modified-SNA rats showed highly significant increases in spontaneous-foot lifting duration, mechanical-hypersensitivity/allodynia, and heathypersensitivity/hyperalgesia, that were significantly greater than after SNA, especially spontaneous-foot-lifting. We recorded intracellularly in vivo from normal L4/L5 DRG neurons and ipsilateral L4-receptive-field-neurons. After SNA or modified-SNA, L4-receptive-field-neurons showed the following: (a) increased percentages of C-, Aδ-, and Aβ-nociceptors and cutaneous Aα/β-low-thresholdmechanoreceptors with ongoing/spontaneous firing; (b) spontaneous firing in C-nociceptors that originated peripherally; this was ata faster rate in modified-SNA than SNA; (c) decreased electricalthresholds in A-nociceptors after SNA; (d) hyperpolarised membrane potentials in A-nociceptors and Aα/-low-thresholdmechanoreceptors after SNA, but not C-nociceptors; (e) decreased somatic action potential rise times in C- and A-nociceptors, not Aα/β-low-threshold-mechanoreceptors. We suggest that these changes in subtypes of conducting/uninterrupted neurons after partial nerve injury contribute to the different aspects of neuropathic pain as follows: spontaneous firing in nociceptors to ongoing/spontaneous pain; spontaneous firing in Aα/β-low-threshold-mechanoreceptors to dysesthesias/paresthesias; and lowered A-nociceptor electrical thresholds to A-nociceptor sensitization,and greater evoked pain [corrected].

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / physiology*
  • Animals
  • Axotomy
  • Behavior, Animal
  • Female
  • Ganglia, Spinal / physiopathology*
  • Hot Temperature
  • Hyperalgesia / physiopathology
  • Mechanoreceptors / physiology
  • Membrane Potentials / physiology
  • Neuralgia / physiopathology*
  • Nociceptors / physiology*
  • Paresthesia / physiopathology
  • Peripheral Nerve Injuries / physiopathology*
  • Rats
  • Rats, Wistar
  • Spinal Nerves / injuries
  • Spinal Nerves / physiology*
  • Spinal Nerves / physiopathology
  • Touch