| Objective This study was designed to explore the effects of subchronic critical occupational exposure limit(OEL)level noise exposure on cognitive function and microbe-gut-brain axis in rats.The objective is to provide a scientific basis for the study of the non-auditory effects of occupational noise and its mechanism,and provide basic data for the revision of occupational noise limit standards and the health risk assessment and prevention and control strategies of people exposed to occupational noise.Methods Forty-eight healthy 6-week-old Wistar male rats were selected and randomly divided into control group,probiotic group,noise exposure group and noise exposure+probiotic group.The noise exposure group and the noise exposure+probiotic group were exposed to white noise at 88 d B sound pressure level(SPL)for 4 hours a day for 56 days using the noise exposure system.The control group and the probiotic group were placed in a clean breeding room with a background noise of <40 d B SPL.The probiotic group and the noise exposure+probiotic group were gavage with Lactobacillus rhamnosus GG(LGG)every day.The control group and the noise exposure group were gavage with normal saline every day.After the noise exposure,the learning and memory of rats were measured using the Morris water maze experiment.The pathological changes in colon tissues were observed.The contents of β-amyloid(Aβ)Aβ1-40 and Aβ1-42 in the serum and the contents of hypothalamic-pituitary-adrenal axis(HPA)related hormones corticotropin-releasing hormone(CRH)and adrenocorticotropic hormone(ACTH)in the hippocampus were determined by ELISA.The expression level of tight junction protein(Occludin and CLDN1)in the hippocampus and colon tissues were determined by Western-blot.The 16 s r RNA high-throughput sequencing technology was used to detect the differences in the composition,diversity and dominant flora of the intestinal flora of rats.The relationship between intestinal flora in phylum level and Aβ in the serum and HPA axis-related hormones in the hippocampal and were analyzed.Results 1 Compared with the control group,the weight of the noise exposure group decreased(P<0.05).Compared with the probiotic group,the weight of the noise exposure+probiotic group decreased(P<0.05).2 In the positioning navigation experiment,compared with the control group,the escape latency of the noise exposure group increased on the second training day(P<0.05).In the space exploration experiment,compared with the control group,the target quadrant time of the noise exposure group decreased(P<0.05).Compared with the probiotic group,the target quadrant time of the noise exposure+probiotic group decreased(P<0.05).3 Compared with the control group and the probiotic group,the levels of Aβ1-40 in the serum of the noise exposure group and the noise exposure+probiotic group increased(P<0.05).Compared with the control group,the levels of Aβ1-42 in the serum of the noise exposure group increased(P<0.05).Compared with the noise exposure group,the levels of Aβ1-40 and Aβ1-42 in the serum of the noise exposure+probiotic group decreased(P<0.05).4 The intestinal flora of the four groups was dominated by Firmicutes,Bacteroidetes and Proteobacteria in phylum level.Compared with the control group,the relative abundance of Tenericutes and Melainabacteria in the noise exposure group and the noise exposure+probiotic group increased.(P<0.05).Compared with the probiotic group,the relative abundance of Tenericutes in the probiotic group increased(P<0.05).5 The histopathological results of the colon tissues showed that the structure of the colonic mucosa was incomplete,the epithelium fell off,the number of goblet cells decreased,the lamina propria glands became shorter,and the arrangement was loose and irregular in the noise exposure group.Compared with the noise exposure group,the colonic mucosal structure,the length and arrangement of the lamina propria glands were slightly improved.6 The results of ultrastructure of epithelial cells in the colon tissues showed that the chromatin of the colonic epithelial cells in the noise exposure group and the noise exposure+probiotic group was marginalized,the gap between the epithelial cells was significantly widened,and the number of desmosomes under the field of view decreased.The number of mitochondria was small,the ridges dissolve and break,some of them were vacuolated,and the intracytoplasmic Golgi complex and the rough endoplasmic reticulum were slightly expanded.7 Compared with the control group,the expression levels of tight junction proteins Occludin and CLDN1 in the hippocampus and colon tissues of the noise exposure group decreased,and the expression levels of the probiotic group increased(P<0.05).Compared with the noise exposure group,the expression levels of Occludin and CLDN1 in the hippocampus and colon tissues of the noise exposure+probiotic group increased(P<0.05).8 Compared with the control group and the probiotic group,the levels of CRH and ACTH in the hippocampus of the noise exposure group and the noise exposure+probiotic group increased(P<0.05).Compared with the noise exposure group,the levels of CRH and ACTH in the noise exposure+probiotic group decreased(P<0.05).9 Correlation analysis showed that the contents of Aβ1-42 in the serum was positively correlated with the 3 OTUs in phylum level(P<0.05).The correlation coefficients are r=0.3845,r=0.3291 and r=0.3552.The contents of ACTH in the hippocampus was positively correlated with 1 OTU in phylum level in rats(P<0.05).The correlation coefficient is r=0.4210.Conclusions 1 Exposure to the critical OEL level noise can decrease memory ability in rats.2 Exposure to the critical OEL level noise can increase the levels of Aβ in the serum,causing mild AD-like pathological changes.3 Exposure to the critical OEL level noise can cause the intestinal flora to be imbalanced,and the type and quantity of the intestinal flora are changed.4 Exposure to the critical OEL level noise causes cognitive dysfunction by increasing the intestinal permeability and blood-brain barrier permeability,decreasing the expression levels of tight junction protein and activating the HPA axis.5Exposure to the critical OEL level noise can increase the relative abundance of Tenericutes and Melainabacteria,and AD-like changes in rats are related to the relative abundance of Euryarchaeota,Tenericutes and Melainabacteria,and the activation of the HPA axis is related to the relative abundance of Euryarchaeota.Figure 18;Table 10;Reference 75... |
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