CNS myeloid cells critically regulate heat hyperalgesia
Stefanie Kälin, … , Christian Witzel, Frank L. Heppner
Stefanie Kälin, … , Christian Witzel, Frank L. Heppner
Published July 2, 2018; First published April 10, 2018
Citation Information: J Clin Invest. 2018;128(7):2774-2786. https://doi.org/10.1172/JCI95305.
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Research Article Neuroscience

CNS myeloid cells critically regulate heat hyperalgesia

Abstract

Activation of non-neuronal microglia is thought to play a causal role in spinal processing of neuropathic pain. To specifically investigate microglia-mediated effects in a model of neuropathic pain and overcome the methodological limitations of previous approaches exploring microglia function upon nerve injury, we selectively ablated resident microglia by intracerebroventricular ganciclovir infusion into male CD11b-HSVTK–transgenic mice, which was followed by a rapid, complete, and persistent (23 weeks) repopulation of the CNS by peripheral myeloid cells. In repopulated mice that underwent sciatic nerve injury, we observed a normal response to mechanical stimuli, but an absence of thermal hypersensitivity ipsilateral to the injured nerve. Furthermore, we found that neuronal expression of calcitonin gene–related peptide (CGRP), which is a marker of neurons essential for heat responses, was diminished in the dorsal horn of the spinal cord in repopulated mice. These findings identify distinct mechanisms for heat and mechanical hypersensitivity and highlight a crucial contribution of CNS myeloid cells in the facilitation of noxious heat.

Authors

Stefanie Kälin, Kelly R. Miller, Roland E. Kälin, Marina Jendrach, Christian Witzel, Frank L. Heppner

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Figure 7

Reduced CGRP expression in the dorsal spinal cord of GFP>TK animals.

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Reduced CGRP expression in the dorsal spinal cord of GFP>TK animals. ...
(A) Differentially expressed Calca in GFP>TK mice relative to GFP>WT mice in array (n = 4/genotype) and by qPCR (n = 3–4/genotype) analyses. Data were normalized to Gapdh levels. (B) Central termination of sensory neurons. Representative images of CGRP-IR in cross sections of the lumbar dorsal spinal cord 7 dpi in GFP>WT and GFP>TK mice. Scale bars: 500 μm and 50 μm (insets). (C) Quantitative morphometric analysis of lamina I of the DH revealed a significantly lower CGRP-covered area in GFP>TK (n = 5) mice than in GFP>WT (n = 6) littermates. (D) Quantification of the number of NeuN+ neurons within the lumbar spinal cord of GFP>WT (n = 6) and GFP>TK (n = 4) mice revealed no differences. (E) F11 DRG cells treated with conditioned medium derived from microglia or from peritoneal macrophages (technical triplicates) showed reduced CGRP protein release compared with those that were treated with fresh medium alone. In the absence of ATP and substance P (SP), CGRP was not detectable (ND). CM, conditioned medium. Error bars indicate the SEM. *P < 0.05 and **P < 0.01, by paired, 2-tailed Student’s t test (A, C, and D) and 1-way ANOVA with Bonferroni’s post hoc analysis (E).