Loss of GABAergic interneurons in laminae I-III of the spinal cord dorsal horn contributes to reduced GABAergic tone and neuropathic pain after spinal cord injury

J Neurotrauma. 2010 Apr;27(4):729-37. doi: 10.1089/neu.2009.1166.

Abstract

Abstract In this study we explore if loss of GABAergic inhibitory interneurons in the superficial dorsal horn of the spinal cord contributes to reduced GABAergic tone and neuropathic pain following spinal cord injury (SCI). A moderate contusion injury to T11 resulted in the development of mechanical hyperalgesia and thermal hyperalgesia below the level of the lesion in gad1:GFP mice that were alleviated by IP administration of the GABA transporter antagonist tiagabine. Six weeks following SCI a decreased number of GFP(+) neurons were observed in the dorsal horn of SCI animals relative to sham mice. Tissue from a mouse 2 weeks post-SCI was subsequently observed to express activated caspase-3, indicative of apoptosis, co-localized to some GFP(+) GABAergic neurons. Glutamate decarboxylase (GAD)65 and GAD67 immunohistochemical staining was reduced in the dorsal horn of SCI animals. This observation was confirmed in Western blots showing reduced immunoreactivity for GAD67, as well as GABA transporter (GAT)1. Reversal of post-SCI neuropathic pain by tiagabine suggests that reduced GABAergic tone may contribute to hyperalgesia symptoms. This is supported by the subsequent observation that SCI reduced the number of GFP(+) inhibitory neurons, and the finding that some GABAergic GFP(+) neurons undergo cell death at a time point consistent with the development of neuropathic pain following SCI. Concordantly, reductions in both GAD65 and GAD67 and GAT1 immunoreactivity also support the observation of a loss of GABAergic inhibition and the associated spinal interneurons.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / genetics
  • Caspase 3 / metabolism
  • Cell Count
  • Disease Models, Animal
  • Down-Regulation / genetics
  • GABA Agonists / pharmacology
  • GABA Plasma Membrane Transport Proteins / metabolism
  • GABA Uptake Inhibitors
  • Glutamate Decarboxylase / genetics
  • Glutamate Decarboxylase / metabolism
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • Interneurons / metabolism*
  • Interneurons / pathology
  • Male
  • Mice
  • Mice, Transgenic
  • Nerve Degeneration / etiology
  • Nerve Degeneration / metabolism*
  • Nerve Degeneration / physiopathology
  • Neural Inhibition / drug effects
  • Neural Inhibition / genetics
  • Neuralgia / etiology
  • Neuralgia / metabolism*
  • Neuralgia / physiopathology
  • Nipecotic Acids / pharmacology
  • Pain Measurement
  • Pain Threshold / physiology
  • Posterior Horn Cells / metabolism*
  • Posterior Horn Cells / pathology
  • Promoter Regions, Genetic / genetics
  • Spinal Cord Injuries / complications
  • Spinal Cord Injuries / metabolism*
  • Spinal Cord Injuries / physiopathology
  • Tiagabine
  • gamma-Aminobutyric Acid / deficiency*

Substances

  • GABA Agonists
  • GABA Plasma Membrane Transport Proteins
  • GABA Uptake Inhibitors
  • Nipecotic Acids
  • Slc6a1 protein, mouse
  • Green Fluorescent Proteins
  • gamma-Aminobutyric Acid
  • Caspase 3
  • Glutamate Decarboxylase
  • glutamate decarboxylase 1
  • glutamate decarboxylase 2
  • Tiagabine