Although the individual toxicity of lead (Pb) and cadmium (Cd) was intensively studied, little is known about their joint toxicity on the development of circadian behavioral rhythm. Therefore, we co-exposed zebrafish to Pb and Cd to investigate the alterations of behavioral rhythm and the potential mechanism. Inductively coupled plasma mass spectrometry analysis was used to detect the internal exposure level of heavy metals. The behavioral rhythm was monitored by a video-track tracking system. The changes of gene expression regarding melatonin-related molecules and clock genes were analyzed by quantitative polymerase chain reaction and JTK-Cycle analysis. The results showed that the level of Pb²⁺ and Cd²⁺ accumulated in the co-exposure group were significantly lower than that in the Pb or Cd group. Exposed to Pb reduced the locomotor activity; the behavioral rhythms were disrupted by Cd, while the pattern in the co-exposure group showed an antagonistic effect on locomotor activity and behavioral rhythm. The expression rhythm of aanat1 was disturbed and the expression levels of mtnr1aa and mtnr1bb were decreased by co-exposure treatment, but mtnr1c was increased in Pb and Cd group, respectively. Exposure to Cd caused the disruption of expression rhythm in clock genes, like clock1b, clock2, and cry1b, while only the rhythm of clock2 was disrupted in the co-exposure group. The results suggest that the behavioral rhythm disruption caused by Cd exposure is associated with the disturbance of certain circadian genes, whereas Pb exposure only abates the locomotor activity; an antagonistic effect on the behavioral pattern when co-exposed zebrafish larvae to Pb and Cd.

尽管铅（Pb）和镉（Cd）的个体毒性已得到深入研究，但人们对它们对昼夜行为节律发展的联合毒性知之甚少。因此，我们将斑马鱼同时暴露于 Pb 和 Cd，以研究行为节律的改变及其潜在机制。采用电感耦合等离子体质谱分析法检测重金属内暴露水平。行为节奏由视频跟踪系统监控。通过定量聚合酶链反应和JTK-Cycle分析分析褪黑素相关分子和时钟基因的基因表达变化。结果表明，共暴露组Pb ^~(2+)和Cd ^~(2+)积累水平显着低于Pb或Cd组。暴露于 Pb 会降低运动能力；行为节律被 Cd 打乱，而同时暴露组的模式对运动活动和行为节律表现出拮抗作用。 Pb组和Cd组中aanat1的表达节律受到干扰， mtnr1aa和mtnr1bb的表达水平降低，而mtnr1c的表达水平分别升高。暴露于Cd会导致时钟基因（如clock1b、clock2和cry1b ）的表达节律被破坏，而在共同暴露组中只有clock2的节律被破坏。 结果表明，Cd 暴露引起的行为节律紊乱与某些昼夜节律基因的紊乱有关，而 Pb 暴露仅减弱运动活动。当斑马鱼幼虫同时暴露于 Pb 和 Cd 时，对行为模式产生拮抗作用。