Study On The Effect Of Oxytetracycline On Thyroid And Inestinal Flora Of Zebrafish

Oxytetracycline(OTC)is widely used in aquaculture and medical industry.It can cause drug resistance between human and animals,and at the same time it will lead to some physiological disorders,threatening environmental health and public safety.However,the impact of Oxytetracycline(OTC)on aquatic fish is still poorly understood.Therefore,zebrafish were used as experimental animals to assess the effects of OTC at low concentrations on their thyroid and intestinal flora and the associated mechanisms.In this study,initial trials evaluated the toxicity of OTC to zebrafish embryos;Then,2 months old zebrafish were exposed to 0,1,and 100 μg/L concentration of OTC for one month,and then carried out histological,genetic,hormonal and intestinal flora analysis studies,The results showed that:(1)OTC has no effect on the survival rate and malformation rate of zebrafish embryos;(2)2 months old zebrafish were exposed to three concentrations of OTC,the 2 months old zebrafish were exposed to three concentrations of OTC,and there was no significant difference in zebrafish weight gain(p>0.05),but as the OTC concentration increased,the zebrafish showed slow movements and shorter swimming distances.,And the swimming distance of zebrafish is significantly reduced(p<0.05),but there is no obvious pathological histological changes in thyroid tissue;and the body weight growth of zebrafish did not Significant difference(p>0.05),but with the increase of OTC concentration,zebrafish showed slow movement and shorter swimming distance,and the swimming distance of zebrafish decreased significantly(p<0.05),but there was no obvious thyroid tissue Histopathological changes;(3)Through the analysis of the expression of thyroid-related genes in the fish brain,the results showed that the expression of DIO2,DIO3 and THRβ genes were significantly reduced(p<0.05),and the gene expression levels of TRH and TPO did not change significantly.Further quantification of active thyroid hormones,the content of T3 in the OTC exposure group decreased,which was consistent with the decrease in DIO2 activity.For 5-HT synthesis,OTC resulted in significant down-regulation of TPH2 and 5ht-lab gene expression(p<0.05),but there was no difference in the expression of 5ht-1bd;(4)After the combination of OTC and T3,the swimming distance of zebrafish tends to recover;(5)Further analysis of zebrafish intestinal flora found that the proportions of Fusobacteria,Proteobacteria,Actinobacteria and in the OTC exposed group changed significantly(p<0.05).The results show that long-term exposure to OTC will cause thyroid and 5-HT regulatory dysfunction,which is closely related to the change of intestinal flora.