Abstract: Objective To observe the effect of lanthanum chloride (LaCl₃) exoposure on tight junction proteins expression and genes transcription in hippocampus of offspring rats.Methods Forty pregnant Wistar rats were randomly divided into a control group and three LaCl₃ treated groups with 0.25%,0.5%,1.0% (w/v) of LaCl₃ in drinking water.The offspring rats were exposed to LaCl₃ through maternal milk during lactation,and through drinking water for one month after delectation.Claudin-5 (Cldn5),occludin (Ocln),and zonula occludens-1 (ZO-1) protein expression in hippocampus were measured with Western blot;while Cldn5,Ocln,and tight junction protein 1 (Tjp1) mRNA level in hippocampus were detected with real-time PCR.Results There were significant reductions in protein expression of claudin-5 (0.059±0.007 vs.0.085±0.004) and Ocln (0.041±0.003 vs.0.067±0.004) in hippocampus tissues of the offspring rats exposed to 0.5% and 1.0% LaCl₃ compared to those of the controls (both P<0.05).In addition,Cldn5,Ocln and Tjp1 mRNA level in in hippocampus tissues of the offspring rats exposed to 1.0% LaCl₃ were 0.743±0.026,0.900±0.119,and 0.931±0.100,respectively,and there was only a significant difference in Cldn5 mRNA level compared to the control group.Conclusion LaCl₃ exposure during development period down-regulates the expression of claudin-5 and occludin,thus causes damage of blood-brain barrier tight junctions in hippocampus of offspring rats.