Chronic postnatal DE-71 exposure: Effects on learning, attention and thyroxine levels

Polybrominated diphenyl ethers (PBDEs) are ubiquitous, bioaccumulative flame retardants. Much remains to be learned about their developmental toxicological properties, particularly with regards to chronic exposure. In two experiments, male Long–Evans rats ingested the commercial pentaBDE mixture DE-71 from birth onward, first through the milk of lactating dams (who ingested 5 or 7.5 mg DE-71/day in a custom-mixed chow), then directly via chow consumption (at a dose of 3 or 4.5 mg/day). Control rats consumed the same brand of chow without DE-71. As adults, the rats were assessed for learning and attention using a series of five-choice serial reaction time tasks. A challenge with the muscarinic cholinergic antagonist scopolamine (0, 0.01, 0.03, or 0.05 mg/kg injected s.c.) was conducted on the final attention task. Serum total thyroxine (T4) levels were obtained at the end of testing. Total T4 was significantly lower in both DE-71 groups than in controls. Visual discrimination learning was unaffected by DE-71, but rats ingesting 4.5 mg/day DE-71 demonstrated significant impairments in sustained attention and inhibitory control, as evidenced by increased premature responding and decreased accuracy of responding in Attention Task 1. However, the DE-71-exposed rats did not respond differentially to the effects of scopolamine on attention compared to controls. These effects of chronic developmental DE-71 exposure differ from effects seen with brief postnatal exposure, suggesting that more research needs to be done on the more environmentally relevant chronic exposure model.