TRPV1-dependent and -independent alterations in the limbic cortex of neuropathic mice: impact on glial caspases and pain perception

Cereb Cortex. 2012 Nov;22(11):2495-518. doi: 10.1093/cercor/bhr328. Epub 2011 Dec 1.

Abstract

During neuropathic pain, caspases are activated in the limbic cortex. We investigated the role of TRPV1 channels and glial caspases in the mouse prelimbic and infralimbic (PL-IL) cortex after spared nerve injury (SNI). Reverse transcriptase-polymerase chain reaction, western blots, and immunfluorescence showed overexpression of several caspases in the PL-IL cortex 7 days postinjury. Caspase-3 release and upregulation of AMPA receptors in microglia, caspase-1 and IL-1β release in astrocytes, and upregulation of Il-1 receptor-1, TRPV1, and VGluT1 in glutamatergic neurons, were also observed. Of these alterations, only those in astrocytes persisted in SNI Trpv1(-/-) mice. A pan-caspase inhibitor, injected into the PL-IL cortex, reduced mechanical allodynia, this effect being reduced but not abolished in Trpv1(-/-) mice. Single-unit extracellular recordings in vivo following electrical stimulation of basolateral amygdala or application of pressure on the hind paw, showed increased excitatory pyramidal neuron activity in the SNI PL-IL cortex, which also contained higher levels of the endocannabinoid 2-arachidonoylglycerol. Intra-PL-IL cortex injection of mGluR5 and NMDA receptor antagonists and AMPA exacerbated, whereas TRPV1 and AMPA receptor antagonists and a CB(1) agonist inhibited, allodynia. We suggest that SNI triggers both TRPV1-dependent and independent glutamate- and caspase-mediated cross-talk among IL-PL cortex neurons and glia, which either participates or counteracts pain.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Arachidonic Acids / metabolism
  • Behavior, Animal / physiology
  • Blotting, Western
  • Caspases / metabolism*
  • Cerebral Cortex / metabolism
  • Cerebral Cortex / physiology*
  • Endocannabinoids / metabolism
  • Ethanolamines
  • Evoked Potentials / physiology
  • Extracellular Space / physiology
  • Glycerides / metabolism
  • Immunohistochemistry
  • Limbic System / metabolism
  • Limbic System / physiology*
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Neuralgia / genetics*
  • Neuralgia / physiopathology*
  • Neuralgia / psychology
  • Neuroglia / enzymology*
  • Pain Perception / physiology*
  • Postural Balance / physiology
  • RNA / biosynthesis
  • RNA / genetics
  • Real-Time Polymerase Chain Reaction
  • Receptors, Glutamate / physiology
  • Sciatic Neuropathy / genetics
  • Sciatic Neuropathy / physiopathology
  • TRPV Cation Channels / genetics*
  • TRPV Cation Channels / physiology*

Substances

  • Arachidonic Acids
  • Endocannabinoids
  • Ethanolamines
  • Glycerides
  • N-acylethanolamines
  • Receptors, Glutamate
  • TRPV Cation Channels
  • TRPV1 protein, mouse
  • RNA
  • glyceryl 2-arachidonate
  • Caspases