A role for neuroimmune signaling in a rat model of Gulf War Illness-related pain

Michael J. Lacagnina, Jiahe Li, Sabina Lorca, Kenner C. Rice, Kimberly Sullivan, James P. O'Callaghan, Peter M. Grace

Research output: Contribution to journalArticlepeer-review

Abstract

More than a quarter of veterans of the 1990–1991 Persian Gulf War suffer from Gulf War Illness (GWI), a chronic, multi-symptom illness that commonly includes musculoskeletal pain. Exposure to a range of toxic chemicals, including sarin nerve agent, are a suspected root cause of GWI. Moreover, such chemical exposures induce a neuroinflammatory response in rodents, which has been linked to several GWI symptoms in rodents and veterans with GWI. To date, a neuroinflammatory basis for pain associated with GWI has not been investigated. Here, we evaluated development of nociceptive hypersensitivity in a model of GWI. Male Sprague Dawley rats were treated with corticosterone in the drinking water for 7 days, to mimic high physiological stress, followed by a single injection of the sarin nerve agent surrogate, diisopropyl fluorophosphate. These exposures alone were insufficient to induce allodynia. However, an additional sub-threshold challenge (a single intramuscular injection of pH 4 saline) induced long-lasting, bilateral allodynia. Such allodynia was associated with elevation of markers for activated microglia/macrophages (CD11b) and astrocytes/satellite glia (GFAP) in the lumbar dorsal spinal cord and dorsal root ganglia (DRG). Additionally, Toll-like receptor 4 (TLR4) mRNA was elevated in the lumbar dorsal spinal cord, while IL-1β and IL-6 were elevated in the lumbar dorsal spinal cord, DRG, and gastrocnemius muscle. Demonstrating a casual role for such neuroinflammatory signaling, allodynia was reversed by treatment with either minocycline, the TLR4 inhibitor (+)-naltrexone, or IL-10 plasmid DNA. Together, these results point to a role for neuroinflammation in male rats in the model of musculoskeletal pain related to GWI. Therapies that alleviate persistent immune dysregulation may be a strategy to treat pain and other symptoms of GWI.

Original languageEnglish (US)
Pages (from-to)418-428
Number of pages11
JournalBrain, behavior, and immunity
Volume91
DOIs
StatePublished - Jan 2021

Keywords

  • Cytokines
  • Glia
  • Gulf War Illness
  • Immune cell
  • Neuroimmune
  • Pain
  • Sphingolipids

ASJC Scopus subject areas

  • Immunology
  • Endocrine and Autonomic Systems
  • Behavioral Neuroscience

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