Effects of Chronic Dietary and Repeated Acute Exposure to Chlorpyrifos on Learning and Sustained Attention in Rats

Cognitive and motor impairment often follow acute poisoning with an organophosphorous (OP) pesticide. However, the persistence of these effects and the conditions necessary for their appear-ance are not clear: two specific concerns are whether symptom-atic poisoning is necessary for persistent effects, and whether inhibition of cholinesterase (ChE) activity is a protective metric of OP exposure. This study examined the effects of chronic dietary and repeated high-level acute exposure to the pesticide chlorpyrifos (diethyl 3,5,6-trichloro-2-pyridyl phosphorothionate, CPF) on learning and attention. Beginning at 3 months of age, male Long-Evans rats received dietaryCPFat a daily dose of 0, 1, or 5mg/kg for 1 year. Half of each dietary group also received an acute oral dose of CPF (initial dose at 60 mg/kg, 5 doses at 45 mg/kg) every 2 months. Beginning 2 weeks before the fourth acute dose, behavioral assess-ments were conducted on the eight rats in each of the six exposur