Gut-Brain Communication In Hyperfunction Of 5-Hydroxytryptamine Induced By Oral Zinc Oxide Nanoparticles Exposure In Young Mice

Objectives: To investigate whether oral exposure to ZnONPs causes the adverse effects on young animals and the potential molecular mechanisms underlying this process.Methods: 30 male C57BL/6J mice,aged 4 weeks,randomly divided into the following 2 groups: vehicle group and ZnONPS group,15 mice in each group.The treatment group was given 26 mg/kg ZnONPs by intragastric administration,while the vehicle group was given the same amount of normal saline for 30 days.The histopathological changes of hippocampus,cortex and gut were observed by H&E staining;the expression of serotonin(5-HT)transporter SERT was detected by Western blot;the 5-HT receptor(5-HT3 A,5-HT3 B,5-HT4R)expression in gut and hippocampus was determined by q PCR;expression of intestinal neuron markers Tu J1 and Hu C/D was detected by Immunofluorescence;expression of 5-HT synthesis rate-limiting enzyme TPH1 was examined by immunohistochemistry;16s sequencing to detect intestinal flora changes;Morris water maze and the field test to assess changes in neurological function.Results: The number of neurons in the hippocampus and cortex of the treated group was decreased,meanwhile,the intestinal mucosa was injuried.The expression of SERT,TPH1,Tuj1 and Hu C/D in the gut tissue was significantly increased.The expression of 5-HT3 A and 5-HT3 B in hippocampus and gut tissue was significantly increased,while 5-HT4 R was not significantly changed.Besides,the results of 16 s sequencing showed that there were 30 differential metabolites between the two groups,18 of which were lipid and lipid molecules.The composition of intestinal microflora and the levels of 15 bacterial branches were significant differences in the two groups and the relative abundance of Actinobacteria was significantly reduced in treatment group.Additionally,behavioral results showed that ZnONPs intragastric administration could cause damage of spatial learning and memory function and spontaneous activity behavior in mice.Conclusion: Oral ZnONPs exposure causes hyperfunction of 5-HT in gut in young mice which may further spread to brain via gut-brain communication.