Peripheral calcium-permeable AMPA receptors regulate chronic inflammatory pain in mice
Vijayan Gangadharan, … , Gary R. Lewin, Rohini Kuner
Vijayan Gangadharan, … , Gary R. Lewin, Rohini Kuner
Published March 7, 2011
Citation Information: J Clin Invest. 2011;121(4):1608-1623. https://doi.org/10.1172/JCI44911.
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Research Article Neuroscience

Peripheral calcium-permeable AMPA receptors regulate chronic inflammatory pain in mice

Abstract

α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid–type (AMPA-type) glutamate receptors (AMPARs) play an important role in plasticity at central synapses. Although there is anatomical evidence for AMPAR expression in the peripheral nervous system, the functional role of such receptors in vivo is not clear. To address this issue, we generated mice specifically lacking either of the key AMPAR subunits, GluA1 or GluA2, in peripheral, pain-sensing neurons (nociceptors), while preserving expression of these subunits in the central nervous system. Nociceptor-specific deletion of GluA1 led to disruption of calcium permeability and reduced capsaicin-evoked activation of nociceptors. Deletion of GluA1, but not GluA2, led to reduced mechanical hypersensitivity and sensitization in models of chronic inflammatory pain and arthritis. Further analysis revealed that GluA1-containing AMPARs regulated the responses of nociceptors to painful stimuli in inflamed tissues and controlled the excitatory drive from the periphery into the spinal cord. Consequently, peripherally applied AMPAR antagonists alleviated inflammatory pain by specifically blocking calcium-permeable AMPARs, without affecting physiological pain or eliciting central side effects. These findings indicate an important pathophysiological role for calcium-permeable AMPARs in nociceptors and may have therapeutic implications for the treatment chronic inflammatory pain states.

Authors

Vijayan Gangadharan, Rui Wang, Bettina Ulzhöfer, Ceng Luo, Rita Bardoni, Kiran Kumar Bali, Nitin Agarwal, Irmgard Tegeder, Ullrich Hildebrandt, Gergely G. Nagy, Andrew J. Todd, Alessia Ghirri, Annette Häussler, Rolf Sprengel, Peter H. Seeburg, Amy B. MacDermott, Gary R. Lewin, Rohini Kuner

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Figure 1

Generation and characterization of mice lacking GluA1 or GluA2 in Nav1.8-expressing neurons (nociceptors) of the DRG.

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Generation and characterization of mice lacking GluA1 or GluA2 in Nav1.8...
(A) Immunohistochemistry with anti-GluA1, anti-Cre, and anti-GluA2/3 antibodies on sections of the DRG, spinal dorsal horn, and forebrain (anterior cingulate cortex is shown) of control mice (GluA1fl/fl mice), nociceptor-specific GluA1 knockout mice (SNS-GluA1–/– mice), and mice globally lacking GluA1 (GluA1–/– mice). (B) Immunohistochemistry with an antibody recognizing GluA2 and GluA3 (anti-GluA2/3) and anti-GluA1 and anti-Cre antibodies on sections of the DRG, spinal dorsal horn, and forebrain of control mice (GluA2fl/fl mice), nociceptor-specific GluA2 knockout mice (SNS-GluA2–/– mice), and mice globally lacking GluA2 (GluA2–/– mice). (A and B) Scale bars: 50 μm (DRG images); 100 μm (spinal cord and brain images). (C and D) Quantitative size frequency analysis of DRG neurons immunoreactive against anti-GluA1 or anti-GluA2/GluA3 confirms that small-diameter neurons lose and large-diameter neurons maintain expression of the respective genetically targeted subunits in (C) SNS-GluA1–/– mice and (D) SNS-GluA2–/– mice. (C) In contrast, anti-GluA2/GluA3 immunoreactivity is maintained in SNS-GluA1–/– mice, and (D) anti-GluA1 is maintained in SNS-GluA2–/– mice. (E) Dual immunofluorescence quantitative analysis of anti-GluA1 and anti-GluA2 with markers of peptidergic nociceptors (CGRP) and nonpeptidergic nociceptors (IB4) confirms a near complete loss of GluA1 in nociceptors of SNS-GluA1–/– mice and loss of anti-GluA2 in SNS-GluA2–/– mice. In C–E, y axes represent immunopositive cells represented as a percentage of all cells counted in corresponding DRG sections. *P < 0.05 as compared to corresponding flox control mice. (F) Western blot analyses confirm DRG-specific deletion of GluA1 or GluA2 in SNS-GluA1–/– and SNS-GluA2–/– mice, respectively. Units for numbers in F are kDa. α-Tubulin represents a loading control.