Probiotic Treatment Ameliorates Exercise Intolerance, Deficits in Fear Learning and Systemic and Neuro-inflammation in a Mouse Model of Gulf War Illness

Abstract

Veterans of the Persian Gulf War (GW) continue to suffer from Gulf War Illness (GWI) characterized by cognitive deficit and fatigue. Our group and others have suggested possible involvement of the microbiota-gut-brain axis in GWI pathology (Kozlova et a., 2021a; 2021b). The current study tested the hypothesis that probiotic treatment (P) prevents GWI symptoms, and systemic and neuro-inflammation. Adult male C57Bl/6N mice were separated into 4 groups (n=16/group): GW group was exposed to 8.7 mg/kg/d pyridostigmine bromide (PB) in saline (150uL/30g bw, oral gavage), 1.3 mg/kg PER in 100% DMSO (dermal), and 33% DEET in 70% EtOH (dermal) for 28 days (5 days/week). CON/S group was sham-treated. CON/S+P and GW+P groups were treated with a probiotic (P) cocktail of L. reuteri, L. rhamnosus, L. casei, B. longum (10 8 CFU/mL, oral gavage) 3 times/week for 2 weeks prior to and during sham/GW agent treatment and until sacrifice (post-treatment (PT) 150). All groups were subjected to restraint stress (5 min/d for 28 d). RT-qPCR on fecal pellets showed bacteria colonization of all strains except L. rhamnosus and B. longum after administration of 6-7 doses. At PT1, all strains showed increased colonization relative to baseline, which persisted to PT150, except B. longum. Body weight, fat, lean mass at PT150 showed no changes among groups. An exercise endurance (EE) test was performed to measure differences in fatigue. GW mice tired faster relative to CON/S at PT56 which persisted at PT150. Probiotic normalized exercise endurance to CON/S levels at PT56. On the passive avoidance test all groups behaved normally at PT50 but GW showed deficits on day 1 acquisition trial of fear learning when tested again 14 weeks later at PT150. GW+P behaved similarly to CON/S. Strength and depression-like behavior was examined before and after exercise stress to simulate post-exertional malaise. Mean percent time spent mobile on tail suspension test (TST) were significantly lower for GW but not GW+P at PT50. All groups were normal at PT150. There was no effect of GW agents or probiotics on the hanging wire test. Systemic and neuroinflammatory markers: C-reactive protein (CRP), high mobility group box 1 (HMGB1), and interleukin-6 (IL-6) were examined using ELISA. Liver and plasma CRP was increased in GW group but not GW+P in liver (p=0.06 in plasma). Plasma HMGB1 was reduced and brain IL-6 was elevated in GW mice but not GW+P. Immunofluorescence analysis in fixed hippocampal sections showed more Iba-1 positive cells in CA1 and DG in GW vs CON/S, while GW+P showed no significant changes vs CON/S. These results show that GW mice can be used to model long-lasting fatigue and other GWI symptoms as well as systemic and neuro-inflammation concurrently. After exercise stress GW agents produced depression. Importantly, probiotic treatment improved exercise endurance, depression, systemic and neuro-inflammation in GW mice, indicating its potential therapeutic use in GWI. Clara Berdasco and Elena Kozlova are co-first authors. Supported by DoD #W81XWH-19-1-0802 (MCC). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.