Abstract
Fluoride which is widespread in our environment and food due to its geological origin and industrial pollution has been identified as a developmental neurotoxicant. Gut-brain axis provides new insight into brain-derived injury. We previously found the psychoactive effects of a probiotic strain, Lactobacillus johnsonii BS15 against fluoride-induced memory dysfunction in mice by modulating the gut-brain axis. In this study, we aimed to detect the link between the reconstruction of gut microbiota and gut-brain axis through which probiotic alleviate fluoride-induced memory impairment. We also added an hour of water avoidance stress (WAS) before behavioral tests and sampling, aiming to demonstrate the preventive effects of the probiotic on fluoride-induced memory impairment after psychological stress. Mice were given fluoridated drinking water (sodium fluoride 100 ppm, corresponding to 37.8 ± 2.4 ppm F¯) for 70 days and administered with PBS or a probiotic strain, Lactobacillus johnsonii BS15 for 28 days prior to and throughout a 70 day exposure to sodium fluoride. Results showed that fluoride increases the hyperactivity of hypothalamic-pituitary-adrenal (HPA) axis and reduces the exploration ratio in novel object recognition (NOR) test and the spontaneous exploration during the T-maze test in mice following WAS, which were significantly improved by the probiotic. 16S rRNA sequencing showed a significant separation in ileal microbiota between the fluoride-treated mice and control mice. Lactobacillus was the main targeting bacteria and significantly reduced in fluoride-treated mice. BS15 reconstructed the fluoride-post microbiota and increased the relative abundance of Lactobacillus. D-lactate content and diamine oxidase (DAO) activity, two biomarkers of gut permeability were reduced in the serum of probiotic-inoculated mice. ZO-1, an intestinal tight junction protein was reduced by fluoride in mRNA, and its protein levels were increased by the probiotic treatment. Moreover, the hippocampus which is essential to learning and memory, down-regulated mRNA level of both the myelin-associated glycoprotein (MAG), and protein levels of brain-derived neurotrophic factor (BDNF), including the improvement of cAMP response element-binding protein (CREB) by BS15 in fluoride-exposed mice after WAS. Via spearman correlation analysis, Lactobacillus displayed significantly positive associations with the behavioral tests, levels of nerve development related factors, and intestinal tight junction proteins ZO-1, and negative association with TNF-α of the hippocampus, highlighting regulatory effects of gut bacteria on memory potential and gut barrier. These results suggested the psychoactive effects of BS15 on fluoride-induced memory dysfunction after psychological stress. In addition, there may be some correlations between fluoride-induced memory dysfunction and reconstruction of gut microbiota. Availability of data and materials16S rRNA sequencing reads have uploaded to NCBI. The accession code of 16S rRNA sequencing reads in the National Center for Biotechnology Information (NCBI) BioProject database: PRJNA660154.
Highlights
Fluoride which is widespread in our environment and food due to geological origin and industrial pollution has been identified as developmental neurotoxicants
Results showed that fluoride reduces the exploration ratio in Novel object recognition (NOR) test and the spontaneous exploration during the T-maze test in mice following an hour water avoidance stress (WAS), which were significantly improved by the probiotic. 16S rRNA sequencing showed a significant seperation in ileal microbiota between the fluoride-treated mice and control mice
zonula occludens protein 1 (ZO-1), an intestinal tight junction protein, which was reduced by fluoride in mRNA and protein levels were increased by the probiotic treatment
Summary
Mice were given fluoridated drinking water (sodium fluoride, 100 mg/L) for 70 days and administered with PBS or a probiotic strain, Lactobacillus johnsonii BS15 for 28 days prior to and throughout a 70 day exposure to sodium fluoride. L. johnsonii BS15 cells were centrifuged (10,000×g, 10 min at 4 °C), washed three times by phosphate-buffered saline (PBS), and re-suspended in PBS (pH 7.0) at a density of 1×109 cfu cells/mL (daily consumption dose: 0.2 mL/mice). WAS, a well-established model of psychological stress in mice, was used in our study as a psychological stressor. Mice were exposed to WAS, as Gareau et al (2011) described with minor modifications. Mice were placed on a small platform surrounded by room-temperature water (1 cm below the platform) in the middle of the home cage for 1 h. All the WAS and behavioral tests were carried out at 7:00 am– 11:30 am
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
