Long-term sex selective hormonal and behavior alterations in mice exposed to low doses of chlorpyrifos in utero

Chlorpyrifos, O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl) phosphorothioate, is an organophosphate insecticide known to be present in human urine. In utero exposure to chlorpyrifos may cause long-term hormonal and behavior alterations. In this study mice were exposed to 0, 1 or 5 mg/kg chlorpyrifos on gestational days 17–20. In utero exposed mice were then tested in a novel foraging behavior maze and assayed for thyroid hormones. Free Thyroxine Index increased significantly in females, but not males. Learning latency and reduced learning ability was evident during training sessions 5–9 in female mice exposed to 1 or 5 mg/kg chlorpyrifos. No learning deficiencies were observed in male mice. No differences were seen in behavior when using a standard radial arm maze during the nine training sessions. These data suggest that mice are susceptible to neuro-endocrine reprogramming by chlorpyrifos, and demonstrate the efficacy of the novel foraging maze as an efficient behavior assay tool.