No abstract

Gulf War Illness (GWI) is a multi-symptom disorder with features characteristic of persistent sickness behavior. Among conditions encountered in the Gulf War (GW) theater were physiological stressors (e.g., heat/cold/physical activity/sleep deprivation), prophylactic treatment with the reversible AChE inhibitor, pyridostigmine bromide (PB), the insect repellent, N, N-diethyl-meta-toluamide (DEET), and potentially the nerve agent, sarin. Prior exposure to the anti-inflammatory glucocorticoid, corticosterone (CORT), at levels associated with high physiological stress, can paradoxically prime the CNS to produce a robust proinflammatory response to neurotoxicants and systemic inflammation; such neuroinflammatory effects can be associated with sickness behavior. Here, we examined whether CORT primed the CNS to mount neuroinflammatory responses to GW exposures as a potential model of GWI. Male C57BL/6 mice were treated with chronic (14 days) PB/ DEET, subchronic (7-14 days) CORT, and acute exposure (day 15) to diisopropyl fluorophosphate (DFP), a sarin surrogate and irreversible AChE inhibitor. DFP alone caused marked brain-wide neuroinflammation assessed by qPCR of tumor necrosis factor-a, IL6, chemokine (C-C motif) ligand 2, IL-1b, leukemia inhibitory factor, and oncostatin M. Pretreatment with high physiological levels of CORT greatly augmented (up to 300-fold) the neuroinflammatory responses to DFP. Anti-inflammatory pre-treatment with minocycline suppressed many proinflammatory responses to CORT+DFP. Our findings are suggestive of a possible critical, yet unrecognized interaction between the stressor/environment of the GW theater and agent exposure(s) unique to this war. Such exposures may in fact prime the CNS to amplify future neuroinflammatory responses to pathogens, injury, or toxicity. Such occurrences could potentially result in the prolonged episodes of sickness behavior observed in GWI. Abbreviations used: AChE, acetylcholinesterase; CB, cerebellum; CCL2, chemokine (C-C motif) ligand 2; CNS, central nervous system; CORT, corticosterone; DEET, N,N-diethyl-meta-toluamide; DFP, diisopropyl fluorophosphate; EtOH, ethanol; FC, frontal cortex; FDA, Food and Drug Administration; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; GFAP, glial fibrillary acidic protein; GW, Gulf War; GWI, Gulf War Illness; HIP, hippocampus; HYPO, hypothalamus; Iba1, ionized calcium-binding adapter molecule 1; IkBa, nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha; IL6, interleukin 6; LIF, leukemia inhibitory factor; LPS, lipopolysaccharide; MINO, minocycline; NA, numerical aperture; NF-jB, nuclear factor kappa light chain enhancer of activated B-cells; OB, olfactory bulb; OSM, oncostatin M; PB, pyridostigmine bromide; PBS, phosphatebuffered saline; RAC, research advisory council; SDS, sodium dodecyl sulfate; STR, striatum; TNF-a, tumor necrosis factor-alpha. 708© Several conditions and exposures have been hypothesized to serve as instigating events that precipitated the recurring/ chronic sy...

Many of the symptoms of Gulf War Illness (GWI) that include neurological abnormalities, neuroinflammation, chronic fatigue and gastrointestinal disturbances have been traced to Gulf War chemical exposure. Though the association and subsequent evidences are strong, the mechanisms that connect exposure to intestinal and neurological abnormalities remain unclear. Using an established rodent model of Gulf War Illness, we show that chemical exposure caused significant dysbiosis in the gut that included increased abundance of phylum Firmicutes and Tenericutes, and decreased abundance of Bacteroidetes. Several gram negative bacterial genera were enriched in the GWI-model that included Allobaculum sp. Altered microbiome caused significant decrease in tight junction protein Occludin with a concomitant increase in Claudin-2, a signature of a leaky gut. Resultant leaching of gut caused portal endotoxemia that led to upregulation of toll like receptor 4 (TLR4) activation in the small intestine and the brain. TLR4 knock out mice and mice that had gut decontamination showed significant decrease in tyrosine nitration and inflammatory mediators IL1β and MCP-1 in both the small intestine and frontal cortex. These events signified that gut dysbiosis with simultaneous leaky gut and systemic endotoxemia-induced TLR4 activation contributes to GW chemical-induced neuroinflammation and gastrointestinal disturbances.