The present study aimed to understand the crosstalk between anxiety and gut microbiota. Exposure of mice to immobilization stress (IS) led to anxiety-like behaviors, increased corticosterone and tumor necrosis factor-α levels in the blood, increased nuclear factor (NF)-κB activation and microglia/monocyte populations in the hippocampus, and suppressed brain-derived neurotrophic factor (BDNF) expression in the hippocampus. Furthermore, IS exposure increased NF-κB activation and monocyte population in the colon and increased Proteobacteria and Escherichia coli populations in the gut microbiota and fecal and blood lipopolysaccharide (LPS) levels while decreasing the lactobacilli population. Oral administration of the fecal microbiota of mice treated with IS (FIS) or E. coli led to the increased NF-κB activation and monocyte population in the colon. These treatments increased blood corticosterone and LPS levels and anxiety-like behaviors, decreased BDNF expression, and induced NF-κB activation and microglia/monocyte populations in the hippocampus. Intraperitoneal injection of LPS purified from E. coli also led to anxiety and colitis in mice. Oral administration of commensal lactobacilli, particularly Lactobacillus johnsonii, attenuated IS- or E. coli-induced colitis and anxiety-like behaviors and biomarkers. These findings suggest that exposure to stressors can increase Proteobacteria populations and fecal LPS levels and cause gastrointestinal inflammation, resulting in the deterioration of anxiety through NF-κB activation. However, the amelioration of gastrointestinal inflammation by treatment with probiotics including L. johnsonii can alleviate anxiety.

The aim of the present study was to determine whether there is the mechanistic connection between antibacterial-dependent gut microbiota disturbance and anxiety. First, exposure of mice to ampicillin caused anxiety and colitis and increased the population of Proteobacteria, particularly Klebsiella oxytoca, in gut microbiota and fecal and blood lipopolysaccharide levels, while decreasing lactobacilli population including Lactobacillus reuteri. Next, treatments with fecal microbiota of ampicillin-treated mouse (FAP), K. oxytoca, or lipopolysaccharide isolated from K. oxytoca (KL) induced anxiety and colitis in mice and increased blood corticosterone, IL-6, and lipopolysaccharide levels. Moreover, these treatments also increased the recruitment of microglia (Iba1), monocytes (CD11b/CD45), and dendritic cells (CD11b/CD11c) to the hippocampus, as well as the population of apoptotic neuron cells (caspase-3/NeuN) in the brain. Furthermore, ampicillin, K. oxytoca, and KL induced NF-κB activation and IL-1β and TNF-α expression in the colon and brain as well as increased gut membrane permeability. Finally, oral administration of L. reuteri alleviated ampicillin-induced anxiety and colitis. These results suggest that ampicillin exposure can cause anxiety through neuro-inflammation which can be induced by monocyte/macrophage-activated gastrointestinal inflammation and elevated Proteobacteria population including K. oxytoca, while treatment with lactobacilli suppresses it.

To understand the role of commensal gut bacteria on the progression of cognitive decline in Alzheimer’s disease via the microbiota-gut-brain axis, we isolated anti-inflammatory Bifidobacterium longum (NK46) from human gut microbiota, which potently inhibited gut microbiota endotoxin production and suppressed NF-κB activation in lipopolysaccharide (LPS)-stimulated BV-2 cells, and examined whether NK46 could simultaneously alleviate gut dysbiosis and cognitive decline in male 5xFAD-transgenic (5XFAD-Tg, 6 months-old) and aged (18 months-old) mice. Oral administration of NK46 (1 × 10 9 CFU/mouse/day for 1 and 2 months in aged and Tg mice, respectively) shifted gut microbiota composition, particularly Proteobacteria, reduced fecal and blood LPS levels, suppressed NF-κB activation and TNF-α expression, and increased tight junction protein expression in the colon of 5XFAD-Tg and aged mice. NK46 treatment also alleviated cognitive decline in 5XFAD-Tg and aged mice. Furthermore, NK46 treatment suppressed amyloid-β, β/γ-secretases, and caspase-3 expression and amyloid-β accumulation in the hippocampus of 5XFAD-Tg mice. NK46 treatment also reduced Iba1 + , LPS + /CD11b + , and caspase-3 + /NeuN + cell populations and suppressed NF-κB activation in the hippocampus of 5XFAD-Tg and aged mice, while BDNF expression was increased. These findings suggest that the suppression of gut dysbiosis and LPS production by NK46 can mitigate cognitive decline through the regulation of microbiota LPS-mediated NF-κB activation.

FDS and C29 alleviates the decrease in cognitive function and inhibited amyloid-β expression in Tg mice by regulating microglia activation and gut microbiota composition.

Lactobacillus plantarum C29-fermented defatted soybean (FDS), which contains soyasaponins such as soyasaponin I (SI) and soyasapogenol B (SB) and isoflavones such as genistin (GE) and genistein (GT), attenuated memory impairment in mice. Moreover, in the preliminary study, FDS and its soyasaponins and isoflavones significantly inhibited NF-κB activation in LPS-stimulated microglial BV2 cells. Therefore, we examined the effects of FDS and its constituents SI, SB, GT, and GE on LPS-induced memory impairment in mice. Oral administration of FDS (80 mg/kg), which has higher concentrations of SB and GE than DS, recovered LPS-impaired cognitive function in Y-maze (55.1 ± 3.5%) and passive avoidance tasks (50.9 ± 19.2 s) to 129.2% (74.1 ± 3.5%) and 114.2% (290.0 ± 22.4 s) of normal mice, respectively (P < 0.05). SB and GE (10 μM) also more potently attenuated LPS-impaired cognitive behavior than SI and GT, respectively. SB (10 mg/kg) was the most effective: treatment recovered LPS-impaired spontaneous alternation and latency time to 105.7% and 126.8% of normal control mice, respectively (P < 0.05). SB and GE significantly increased BDNF expression and CREB phosphorylation in LPS-treated mice and corticosterone-stimulated SH-SY5Y cells. Furthermore, SB and GE (10 μM) also significantly inhibited NF-κB activation in LPS-treated mice. These findings suggested that FDS and its constituent soyasaponins and isoflavones may attenuate memory impairment by the regulation of NF-κB-mediated BDNF expression.