CNS myeloid cells critically regulate heat hyperalgesia
Stefanie Kälin, … , Christian Witzel, Frank L. Heppner
Stefanie Kälin, … , Christian Witzel, Frank L. Heppner
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 1

PSNL evokes reactive microgliosis and infiltration of bone marrow–derived myeloid cells into the DHi of WT mice.

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PSNL evokes reactive microgliosis and infiltration of bone marrow–derive...
(A) An increase in Iba1-IR in the lumbar spinal cord of WT animals was observed in the DHi and VHi. Scale bars: 500 μm and 25 μm (insets). (B) The temporal profile of Iba1+ microglia activation was determined in the DHi and DHc of the lumbar spinal cord (8–10 sections/mouse, 4 mice/time point) and revealed a significant increase in the Iba1-covered area from 2 to 10 dpi, peaking at 7 dpi. (C) Increased numbers of BrdU+ cells were detected in the lumbar DHi and VHi. Scale bars: 500 μm and 25 μm (insets). (D) Within the DHi, the highest number of BrdU+ cells was found at 2 and 4 dpi (8–10 sections/mouse, 4 mice/time point). (E) Pie chart shows that 94% of total BrdU+ cells were also Iba1+. (F) PSNL-induced proliferation of Iba1 (green) and BrdU (blue) double-positive cells (merge) was restricted to the DHi. Scale bar: 25 μm. (G) Confocal microscopy revealed bone marrow–derived GFP+ cells (green) colocalizing with the myeloid cell marker Iba1 (red) in the DHi of GFP–bone marrow chimeric mice on day 7 after PSNL. Scale bar: 50 μm. Error bars indicate the SEM. *P < 0.05, **P < 0.01, and ***P < 0.001, by paired, 2-tailed Student’s t test for comparison of DHc and DHi at each time point. S, sham.