A Chronic Longitudinal Characterization of Neurobehavioral and Neuropathological Cognitive Impairment in a Mouse Model of Gulf War Agent Exposure

Abstract

Gulf War Illness (GWI) is a chronic multisymptom illness with a central nervous system component that includes memory impairment as well as neurological and musculoskeletal deficits. Previous studies have shown that in the First Persian Gulf War conflict (1990–1991) exposure to Gulf War (GW) agents, such as pyridostigmine bromide (PB) and permethrin (PER), were key contributors to the etiology of GWI. For this study, we used our previously established mouse model of GW agent exposure (10 days PB+PER) and undertook an extensive lifelong neurobehavioral characterization of the mice from 11 days to 22.5 months post exposure in order to address the persistence and chronicity of effects suffered by the current GWI patient population, 24 years post-exposure. Mice were evaluated using a battery of neurobehavioral testing paradigms, including Open Field Test (OFT), Elevated Plus Maze (EPM), Three Chamber Testing, Radial Arm Water Maze (RAWM), and Barnes Maze (BM) Test. We also carried out neuropathological analyses at 22.5 months post exposure to GW agents after the final behavioral testing. Our results demonstrate that PB+PER exposed mice exhibit neurobehavioral deficits beginning at the 13 months post exposure time point and continuing trends through the 22.5 month post exposure time point. Furthermore, neuropathological changes, including an increase in GFAP staining in the cerebral cortices of exposed mice, were noted 22.5 months post exposure. Thus, the persistent neuroinflammation evident in our model presents a platform with which to identify novel biological pathways, correlating with emergent outcomes that may be amenable to therapeutic targeting. Furthermore, in this work we confirmed our previous findings that GW agent exposure causes neuropathological changes, and have presented novel data which demonstrate increased disinhibition, and lack of social preference in PB+PER exposed mice at 13 months after exposure. We also extended upon our previous work to cover the lifespan of the laboratory mouse using a battery of neurobehavioral techniques.

Trends in brain cancer mortality among U.S. Gulf War veterans: 21 year follow-up

“…Both human (Gulf War veteran populations) and animal studies have reported neurological outcomes associated with the exposures present during Gulf War deployment, including neuro-inflammation [16], changes in brain volume [17], hippocampal dysfunction [18,19], decreased white matter [7,9,20] and alterations in executive function and cognition [21,22]. …”

Innate immune signaling and sex differences contribute to neurocognitive impairment, neuroinflammation, and mitochondrial rewiring in a mouse model of Gulf War illness

“…At 5 months post-exposure, we used the elevated plus maze test (EPMT) (Supplemental Figure 2A) to determine unconditioned response to a potentially dangerous environment and anxiety-related behavior 28,29 . We observed a trend in which female, not male, GWIC-exposed mice spent…”

“…Based on evidence of MD and inflammation in GWI, and on the documented link between the two, we hypothesized that exposure to GWIC might alter mitochondria-innate immune crosstalk, contributing to inflammatory responses that exacerbate neuropathology and cognitive symptoms of GWI. To test this hypothesis, we employed an established mouse model of GWI in which mice are exposed to the GWIC by intraperitoneal injection for a period of 10 days, developing cognitive impairment and neuroinflammation beginning at 5 months post-exposure [22][23][24] . In our study, we employed a longitudinal analysis regimen, performing neurocognitive tests at both 5 months and 12 months after acute exposure to GWIC, followed by analysis of mitochondrial protein expression and neuroinflammation in the brain at the terminal timepoint.…”

Oligodendrocyte involvement in Gulf War Illness

“…Key diagnostic features of GWI include musculoskeletal pain, impaired cognitive functioning, disturbances of mood, and debilitating fatigue; symptoms that have persisted over time (Binns et al, ; Maule et al, ; White et al, ). GWI animal models replicate many of these symptoms (Zakirova et al, ), including impaired working memory (Phillips & Deshpande, ) and social memory (Zakirova et al, ). The established animal model of GWI includes treatment with corticosterone (Cort) for 7 days before exposure to diisopropyl fluorophosphate (DFP), an irreversible AChE inhibitor used as a proxy for sarin nerve gas (Koo et al, ; O'Callaghan, Kelly, Locker, Miller, & Lasley, ; Zakirova et al, ).…”

“…GWI animal models replicate many of these symptoms (Zakirova et al, ), including impaired working memory (Phillips & Deshpande, ) and social memory (Zakirova et al, ). The established animal model of GWI includes treatment with corticosterone (Cort) for 7 days before exposure to diisopropyl fluorophosphate (DFP), an irreversible AChE inhibitor used as a proxy for sarin nerve gas (Koo et al, ; O'Callaghan, Kelly, Locker, Miller, & Lasley, ; Zakirova et al, ). This necessitates studying the effects of Cort exposure independently, and together with DFP, on oligodendrocyte development and function.…”