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Pain Med. 2017 May 1;18(5):932-946. doi: 10.1093/pm/pnw144.

Characterization of Macrophage/Microglial Activation and Effect of Photobiomodulation in the Spared Nerve Injury Model of Neuropathic Pain.

Author information

1
Center for Nursing Science and Clinical Inquiry, Landstuhl Regional Medical Center, Landstuhl, Germany.
2
Anatomy, Physiology & Genetics, The Uniformed Services University of the Health Sciences, Bethesda, MD, USA.
3
Departments of Neuroscience, Uniformed Services University, Bethesda, MD, USA.
4
Department of Medical and Clinical Psychology, Uniformed Services University of the Health Sciences , Bethesda, MD , USA.
5
Daniel K. Inouye Graduate School of Nursing, Uniformed Services University of the Health Sciences, Bethesda, MD, USA.
6
Lite Cure, LLC, Newark, Delaware, USA.
7
St. Mary's College of Maryland, St. Mary's City, MD, USA.

Abstract

Objective:

Neuropathic pain is common and debilitating with limited effective treatments. Macrophage/microglial activation along ascending somatosensory pathways following peripheral nerve injury facilitates neuropathic pain. However, polarization of macrophages/microglia in neuropathic pain is not well understood. Photobiomodulation treatment has been used to decrease neuropathic pain, has anti-inflammatory effects in spinal injury and wound healing models, and modulates microglial polarization in vitro. Our aim was to characterize macrophage/microglia response after peripheral nerve injury and modulate the response with photobiomodulation.

Methods:

Adult male Sprague-Dawley rats were randomly assigned to sham (N = 13), spared nerve injury (N = 13), or injury + photobiomodulation treatment groups (N = 7). Mechanical hypersensitivity was assessed with electronic von Frey. Photobiomodulation (980 nm) was applied to affected hind paw (output power 1 W, 20 s, 41cm above skin, power density 43.25 mW/cm 2 , dose 20 J), dorsal root ganglia (output power 4.5W, 19s, in skin contact, power density 43.25 mW/cm 2 , dose 85.5 J), and spinal cord regions (output power 1.5 W, 19s, in skin contact, power density 43.25 mW/cm 2 , dose 28.5 J) every other day from day 7-30 post-operatively. Immunohistochemistry characterized macrophage/microglial activation.

Results:

Injured groups demonstrated mechanical hypersensitivity 1-30 days post-operatively. Photobiomodulation-treated animals began to recover after two treatments; at day 26, mechanical sensitivity reached baseline. Peripheral nerve injury caused region-specific macrophages/microglia activation along spinothalamic and dorsal-column medial lemniscus pathways. A pro-inflammatory microglial marker was expressed in the spinal cord of injured rats compared to photobiomodulation-treated and sham group. Photobiomodulation-treated dorsal root ganglion macrophages expressed anti-inflammatory markers.

Conclusion:

Photobiomodulation effectively reduced mechanical hypersensitivity, potentially through modulating macrophage/microglial activation to an anti-inflammatory phenotype.

KEYWORDS:

Inflammation; Macrophage; Microglia; Neuropathic Pain; Photobiomodulation; Spared Nerve Injury

PMID:
27497321
DOI:
10.1093/pm/pnw144
[Indexed for MEDLINE]

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