Group III metabotropic glutamate receptors and transient receptor potential vanilloid 1 co-localize and interact on nociceptors

R. M. Govea, S. Zhou, S. M. Carlton

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

Several lines of evidence indicate group III metabotropic glutamate receptors (mGluRs) have systemic anti-hyperalgesic effects. We hypothesized this could occur through modulation of transient receptor potential vanilloid 1 (TRPV1) receptors on nociceptors. To address this question we performed anatomical studies to determine if group III mGluRs were expressed on cutaneous axons and if they co-localized with TRPV1. Immunostaining at the electron microscopic level demonstrated that 22% of unmyelinated axons labeled for mGluR8. Immunostaining at the light microscopic level in lumbar dorsal root ganglia (DRG) demonstrated that 80% and 28% of neurons labeled for mGluR8 or TRPV1, respectively. Of those neurons labeled for mGluR8, 25% labeled for TRPV1; of those labeled for TRPV1, 71% labeled for mGluR8. In behavior studies intraplantar injection of the group III mGluR agonist, L-(+)-2-amino-4-phosphonobutyric acid (L-AP-4: 0.1, 1.0, and 10.0 μM) had no effect on paw withdrawal latency (PWL) to heat in naïve rats but administration of 10 μM L-AP-4 prior to 0.05% capsaicin (CAP), significantly attenuated CAP-induced lifting/licking and reduced flinching behavior. The L-AP-4 effect was specific since administration of a group III antagonist α-methyl-3-methyl-4-phosphonophenylglycine (UBP1112) (100 μM) blocked the L-AP-4 effect on CAP, resulting in behaviors similar to CAP alone. Intraplantar injection of UBP1112 alone did not result in nociceptive behaviors, indicating group III mGluRs are not tonically active. Finally, the anti-hyperalgesic effect of group III in this paradigm was local and not systemic since intraplantar administration of L-AP-4 in one hind paw did not attenuate nociceptive behaviors following CAP injection in the contralateral hind paw. Adenyl cyclase/cyclic AMP/PKA may be the second messenger pathway linking these two receptor families because intraplantar injection of forskolin (FSK, 10 μM) reduced PWL to heat and L-AP-4 reversed this FSK effect. Taken together, these results suggest group III mGluRs can negatively modulate TRPV1 through inhibition of adenyl cyclase and downstream intracellular activity, blocking TRPV1-induced activation of nociceptors.

Original languageEnglish (US)
Pages (from-to)130-139
Number of pages10
JournalNeuroscience
Volume217
DOIs
StatePublished - Aug 16 2012

Fingerprint

Nociceptors
Metabotropic Glutamate Receptors
Capsaicin
Injections
Adenylyl Cyclases
Axons
Hot Temperature
Neurons
Spinal Ganglia
Second Messenger Systems
Colforsin
vanilloid receptor subtype 1
Cyclic AMP
Electrons
Light
Skin
metabotropic glutamate receptor 8

Keywords

  • Anti-hyperalgesia
  • Capsaicin
  • L-AP-4
  • MGluR8
  • Primary afferents
  • Sensory neurons

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Group III metabotropic glutamate receptors and transient receptor potential vanilloid 1 co-localize and interact on nociceptors. / Govea, R. M.; Zhou, S.; Carlton, S. M.

In: Neuroscience, Vol. 217, 16.08.2012, p. 130-139.

Research output: Contribution to journalArticle

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