The Neuroinflammatory Phenotype in a Mouse Model of Gulf War Illness is Unrelated to Brain Regional Levels of Acetylcholine as Measured by Quantitative HILIC-UPLC-MS/MS

Abstract

Many veterans of the 1991 Persian Gulf War (GW) returned with a chronic multisymptom illness that has been termed Gulf War Illness (GWI). Previous GWI studies have suggested that exposure to acetylcholinesterase inhibitors (AChEIs) in theater, such as sarin and/or pesticides, may have contributed to the symptomatology of GWI. Additionally, concomitant high physiological stress experienced during the war may have contributed to the initiation of the GWI phenotype. Although inhibition of AChE leading to accumulation of acetylcholine (ACh) will activate the cholinergic anti-inflammatory pathway, the signature symptomatology of GWI has been shown to be associated with neuroinflammation. To investigate the relationship between ACh and neuroinflammation in discrete brain regions, we used our previously established mouse model of GWI, which combines an exposure to a high physiological stress mimic, corticosterone (CORT), with GW-relevant AChEIs. The AChEIs used in this study were diisopropyl fluorophosphate (DFP), chlorpyrifos oxon (CPO), and physostigmine (PHY). After AChEI exposure, ACh concentrations for cortex (CTX), hippocampus (HIP), and striatum (STR) were determined using hydrophilic interaction liquid chromatography with ultraperformance liquid chromatography-tandem-mass spectrometry (MS/MS). CORT pretreatment ameliorated the DFP-induced ACh increase in HIP and STR, but not CTX. CORT pretreatment did not significantly alter ACh levels for CPO and PHY. Further analysis of STR neuroinflammatory biomarkers revealed an exacerbated CORT + AChEI response, which does not correspond to measured brain ACh. By utilizing this new analytical method for discrete brain region analysis of ACh, this work suggests the exacerbated neuroinflammatory effects in our mouse model of GWI are not driven by the accumulation of brain region-specific ACh.

The peroxisome proliferator-activated receptor gamma (PPARγ) agonist, rosiglitazone, ameliorates neurofunctional and neuroinflammatory abnormalities in a rat model of Gulf War Illness

“…Our focus was on amygdala and hippocampus, because of their importance for memory and complex emotive function. Several previous studies on GW models reported neuroinflammatory changes in the hippocampus [24,40,41,46,47,62], whereas fewer studies examined the amygdala [17,40]. In both regions, we found that GWE led to significant astrogliosis with GFAP upregulation, as well as microgliosis, with bushy, ameboid-appearing Iba1 positive microglia.…”

“…Animal studies of GWI have repeatedly shown evidence of neuroinflammation, which is known to lead to neurodegeneration [52]. Animal models with exposures to GW-related chemicals alone, as well as models with combined exposures to GW-related chemicals and stressors, report neuroinflammation in various brain regions, as assessed by a variety of cytokines and chemokines, including many downstream of nuclear factor κB (NF-κB) [22,24,[38][39][40][41]50]. A characteristic feature of neuroinflammation is glial activation.…”

“…Chronic unpredictable stress is a major factor of war that can have lasting consequences [37]. Several animal studies examining effects on neuroinflammation or neurofunction have modeled GWI based on exposures to both GW-related chemicals and various stressors, including the administration of corticosterone [24,[38][39][40][41] or restraint or other physical stressor [42][43][44][45][46][47][48][49][50][51].…”

The Innate Immune System and Inflammatory Priming: Potential Mechanistic Factors in Mood Disorders and Gulf War Illness

“…A follow-up study looking at exposure to DFP, CPO or PHY alone or in combination with CORT found elevations (or lack thereof) of cytokines in various brain regions did not readily correlate with region specific changes in Ach from the various treatments. These results were interpreted to suggest that off target (non-AchE) actions of OPs may be chiefly responsible for the observed changes in neuroinflammation (51). An additional study from the same group demonstrated that the observed neuroinflammatory effects of DFP+CORT in mice extend to rats as well and are accompanied by changes in microdiffusivity as detected by MRI (52).…”

Dorsoventral-Specific Effects of Nerve Agent Surrogate Diisopropylfluorophosphate on Synaptic Transmission in the Mouse Hippocampus

“…Exposure to OPs also induces persisting toxicity via multiple noncholinergic mechanisms, i.e. by affecting oxidant formation, mitochondrial energetics, axoplasmic transport, immune system functionality, and brain endocannabinoid homeostasis (Casida and Quistad, 2004;Pope et al, 2005;Mense et al, 2006;Nallapaneni et al, 2006;Kaur et al, 2007;Grigoryan et al, 2008;Nallapaneni et al, 2008;Grigoryan et al, 2009;Jiang et al, 2010;Middlemore-Risher et al, 2010;Wright et al, 2010;Rohlman et al, 2011;Banks and Lein, 2012;O'Callaghan et al, 2015;Locker et al, 2017;Miller et al, 2018;Michalovicz et al, 2019). Nevertheless, it is unknown if such noncholinergic effects differentially impact synaptic transmission along the hippocampal dorsoventral axis.…”