Toxicological Sciences 59, 260-267 (2001)
Copyright © 2001 by the Society of Toxicology
NEUROTOXICOLOGY |
Effects of Repeated Oral Postnatal Exposure to Chlorpyrifos on Open-Field Behavior in Juvenile Rats

* Center for Environmental Health Sciences, Box 9825, College of Veterinary Medicine; and
Department of Entomology and Plant Pathology, Mississippi State University, Mississippi State, Mississippi 39762
Organophosphorus (OP) insecticides have the potential to cause behavioral effects in children. This study was designed to determine if repeated oral exposure of preweanling rats to chlorpyrifos would produce behavioral changes at both pre- and postweanling ages. Treatment occurred every second day beginning on post-natal day (PND) 1, and continued through PND 21. The rats received one of the following regimens: a low-dosage (3 mg/kg) from PND 121; a medium dosage (mg/kg from PND 15, and then 6 mg/kg from PND 721; or a high-dosage schedule of 3 mg/kg on PND 15, then 6 mg/kg from PND 713, and 12 mg/kg from PND 1521. There were no differences in body weights among the control-, low-, and medium-dosage groups but the high-dosage group had significantly lower body weights on PND 1321. An open field was used to measure locomotor activity on PND 10, 12, 14, 16, 18, 20, 25, and 30. There were no differences in locomotor activity levels or treatment effects between males and females. On PND 10, 12, 14, 16, 18, and 20 there was no effect on locomotor activity with any dosage. On days 25 and 30, locomotor activity was significantly decreased with the medium- and high-dosage groups. Brain cholinesterase (ChE) inhibition was about 2538% on PND 25 and 1434% on PND 30. On PND 25 but not 30, lung and diaphragm ChE and serum butyrylcholinesterase (BChE), with the high-dosage animals, and heart ChE with the medium- and high-dosage groups were significantly inhibited. There was no significant inhibition of skeletal muscle ChE or serum acetylcholinesterase (AChE) on PND 25 and 30. These data suggest that early postnatal chlorpyrifos exposures will depress locomotor activity in juvenile rats, with the effects most pronounced after brain ChE activity has substantially recovered.
Key Words: acetylcholinesterase (AChE); neural developmental aberrations; chlorpyrifos; development; behavior; motor activity..
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