Thyroid hormones and fear learning but not anxiety are affected in adult apoE transgenic mice exposed postnatally to decabromodiphenyl ether (BDE-209)

- The apoE4 genotype was associated with low levels of activity and increased anxiety.
- Postnatal BDE-209 exposure impaired cued fear learning in adult apoE2 and apoE3 mice.
- Postnatal BDE-209 exposure increased total T3 and T4 hormone levels in adult apoE3 female mice.

Polybrominated diphenyl ethers (PBDEs) are a family of industrial chemicals used as flame retardants. The fully brominated deca-BDE (BDE-209) is the most used and its potential risk for humans is controversial. The ability of PBDEs to target nervous and endocrine systems suggests multiple enduring effects after perinatal exposure. Cognitive and motor behavior alterations have been reported after developmental exposure to PBDEs, including BDE-209, whereas very little work has been carried out on anxiety and emotional learning. We have previously reported long-term effects of postnatal BDE-209 exposure on spatial memory dependent upon apolipoprotein E (apoE) polymorphism and age. ApoE is involved in lipid transport and its different polymorphisms (ε2, ε3, ε4) confer different vulnerabilities to neurodegeneration, cognitive impairment and anxiety. In the present study we assessed the long term effects of early exposure to BDE-209 on anxiety, fear learning and thyroid hormone levels in mice carrying different apoE polymorphisms (ε2, ε3, ε4). BDE-209 (0, 10 and 30 mg/kg) was orally administered on postnatal day 10 (PND 10). At 4 and 12 months of age mice were tested in an open field (OF) and an elevated zero maze (EZM). Fear conditioning and thyroid hormone levels were evaluated in mice at 5-6 months of age. Postnatal exposure to BDE-209 impaired cued fear learning in apoE2 and apoE3 mice. Levels of thyroid hormones were increased in apoE3 female mice exposed to BDE-209. Our findings indicate long lasting effects of BDE-209 on emotional learning and thyroid hormone levels after a single postnatal exposure.