Comparing cognitive and screening tests for neurotoxicity - Effects of acute chlorpyrifos on visual signal detection and a neurobehavioral test battery in rats

It is often assumed that cognitive function is more sensitive to neurotoxic chemicals than are the unconditioned behaviors employed in neurobehavioral screens; however, direct comparisons of the sensitivity of these test meth ods are lacking. The present studies were conducted to compare the effects of the widely used cholinesterase-inhibiting insecticide, chlorpyrifos (O,O '-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothionate, CPF), on a visual signal detection task (SDT) with its effects on a neurobehavioral test batt ery. Adult male Long-Evans rats were trained to perform the SDT, dosed with CPF, and then assessed with both test instruments. Oral CPF (50 mg/kg) imp aired signal detection for 8 days, and subcutaneous CPF (250 mg/kg) did so for 4 weeks. CPF (30 and 50 mg/kg po and 250 mg/kg sc) also lowered activit y in the test battery for up to 18 days. Thus, CPF impaired attention and a ltered behavior in the test battery in the same dose ranges under two very different dosing scenarios. (C) 2001 Elsevier Science Inc. All rights reser ved.