Behavioral Response And Mechanism Analysis Of Zebrafish (Danio Rerio) Under Deltamethrin And Cadmium Chloride Stress

At present,surface water pollution has become a threat to the ecological balance of water,the survival of aquatic organisms and the development of human beings,in which pyrethroids and heavy metals are two representative contaminants.Based on the behavioral monitoring of zebrafish,this study analyzed the expression of M1 receptor,acetylcholinesterase and Prokineticin 2 in zebrafish brain and heart under deltamethrin?DM?stress and the activity of acetylcholinesterase in zebrafish gill under cadmium chloride?CdCl2?stress to explore the mechanism of behavior response,and to explore suitable molecular indicators for water quality assessment.To study the effects of deltamethrin?0.52?g/L?0.1TU?,2?g/L?10%surface water??on the behavior of zebrafish?Danio rerio?,the behavior strength?BS?was continuously monitored within 168h.Comparing the average BS values of the light period and the dark period,it was found that the behavior strength of zebrafish showed obvious diurnal variation,that is,the circadian rhythm,and the results of the SOM analysis further confirmed this.Autocorrelation analysis of BS revealed that deltamethrin disturbed the circadian rhythm of zebrafish,which was manifested in the advance of the cycle?0.1TU treatment group?or postponed?10%surface water treatment group?.Moreover,the length of the cycle was also subject to varying degrees of disruption.The expression of M1,AChE and PK2 in zebrafish brain and heart was further monitored within 168 hours.The results showed that deltamethrin could affect the circadian rhythm of the cholinergic system of zebrafish.Deltamethrin made the expression level of M1 receptor at a higher level in the dark cycle?inactive state?,while acetylcholinesterase had a higher level in the photoperiod?active state?,and deltamethrin under 2?g/L concentration could produce more disturbances.In the two deltamethrin-treated groups,the expression of AChE in the brain and heart of zebrafish was higher than that of the control group at most of the time,which may cause a decrease in the acetylcholine and indirectly caused a decrease in the overall BS average of the zebrafish.In addition,after deltamethrin treatment,the high peak of PK2 was no longer normally fixed in the dark phase?inactive state?but more in the light phase.The disturbance of the normal expression rhythm of PK2 may cause the signal output of the behavioral rhythm to be affected,which in turn caused the circadian rhythm of the behavior of the zebrafish.Moreover,there was a time delay in the toxic effects of deltamethrin on the brain and heart of zebrafish,and in the expression of the three genes in the same organ.To study the effects of cadmium chloride on zebrafish behavior,the continuous behavior strength?BS?and the acetylcholinesterase?AChE?activity in the gill of zebrafish?Danio rerio?in 48 h exposure of cadmium chloride?CdCl₂??4.26 mg/L?0.1 TU,toxic unit?,42.6mg/L?1.0 TU?,and 85.2 mg/L?2.0 TU??were investigated.The experimental results showed that cadmium chloride inhibits the behavior of zebrafish,and there was a significant dose-effect relationship between cadmium chloride concentration and zebrafish behavior strength.Lower BS values could be observed in the dark period at 13–21 h and 37–45 h in all treatments,which indicated circadian rhythm.At the end of the exposure,the circadian rhythm of the 1TU treatment group was disrupted,while the 0.1 TU and 2TU treatment groups showed significant circadian rhythms.These results suggested that the online BS values could illustrate the toxicity of cadmium chloride directly.The AChE activity in the gill was strongly inhibited by cadmium chloride during 48h exposure.Cross-correlation analysis of behavioral intensity BS and acetylcholinesterase activity using the DCCA method?p<0.01,r>0.5?showed that cadmium chloride affected acetylcholinesterase activity.Given that cadmium chloride is neurotoxic and can disrupt nerve signaling,this may result in decreased swimming behavior,loss of coordination,or other types of behavioral changes.In summary,changes in circadian rhythms can be used to reflect changes in the behavior of zebrafish in certain concentrations of deltamethrin and cadmium chloride,which can be used as an indicator of environmental stress assessment to assess environmental changes more quickly and accurately.High levels of acetylcholinesterase expression,inhibition of acetylcholinesterase activity,and disturbance of M1 receptor expression may indirectly lead to a decrease in the average behavior strength of zebrafish.At the same time,the rhythm of the expression of PK2 is disturbed,which may hinder the transmission of the behavioral output signal of SCN,thus causing the zebrafish to behave abnormally in circadian rhythm.