Blockade of glutamate mGlu5 receptors in a rat model of neuropathic pain prevents early over-expression of pro-apoptotic genes and morphological changes in dorsal horn lamina II

Neuropharmacology. 2004 Mar;46(4):468-79. doi: 10.1016/j.neuropharm.2003.10.014.

Abstract

We used rats with a sciatic nerve chronic constrictive injury (CCI) and combined behavioural, molecular and morphological approaches to assess the involvement of mGlu5 receptors in neuropathic pain-associated hyperalgesia and spinal cord neuron apoptosis. Mechanical and thermal hyperalgesia developed 2-3 days after surgery. Morphological changes in the ipsilateral L4-L5 lamina II consisted of: (i) cell loss (38 +/- 5%), (ii) increased TUNEL-positive profiles, (iii) decreased SP-immunoreactive primary afferents, and (iv) reactive gliosis. Molecular expression data suggested a bi-phasic response of bcl-2 family genes in CCI. An early (2-3 days post-CCI) E2F1- and p53-independent apoptosis appeared in the spinal cord as the pro-apoptotic bax gene increased (320 +/- 19%), followed by an increased expression of the anti-apoptotic bcl-2 and bcl-xL genes (60 +/- 11% and 110 +/- 15%, respectively) 7 days from CCI. The selective mGlu5 receptor antagonist, MPEP (2 mg/kg i.p. twice daily), prevented the development of thermal hyperalgesia and transiently reduced mechanical hyperalgesia. Despite the MPEP treatment, which normalised bax/bcl-2 and bcl-xL/bcl-xS ratios at all times post-CCI, mechanical hyperalgesia reappeared by 7 days after CCI. Similarly, MPEP was cytoprotective at 3, but not 7 days post-CCI. This study shows that: (a) spinal cord neuron loss may be triggered by a p53- and E2F1-independent apoptosis in lamina II with the participation of glutamate mGlu5 receptors, (b) these receptors seem to be involved transiently, as their blockade was no longer protective by 7 days CCI, and (c) this delayed cell death occurred in the absence of Bax activation, suggesting the involvement of an alternative death pathway.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / drug effects
  • Apoptosis / physiology*
  • Gene Expression Regulation / drug effects
  • Gene Expression Regulation / physiology
  • Male
  • Posterior Horn Cells / drug effects
  • Posterior Horn Cells / metabolism*
  • Posterior Horn Cells / pathology
  • Pyridines / pharmacology
  • Rats
  • Rats, Wistar
  • Receptor, Metabotropic Glutamate 5
  • Receptors, Metabotropic Glutamate / antagonists & inhibitors*
  • Receptors, Metabotropic Glutamate / metabolism*
  • Sciatic Neuropathy / metabolism*
  • Sciatic Neuropathy / pathology
  • Sciatic Neuropathy / prevention & control

Substances

  • Pyridines
  • Receptor, Metabotropic Glutamate 5
  • Receptors, Metabotropic Glutamate
  • 6-methyl-2-(phenylethynyl)pyridine