Rl. Carr et al., Effects of repeated oral postnatal exposure to chlorpyrifos on open-field behavior in juvenile rats, TOXICOL SCI, 59(2), 2001, pp. 260-267
Organophosphorus (OP) insecticides have the potential to cause behavioral e
ffects in children. This study was designed to determine if repeated oral e
xposure of preweanling rats to chlorpyrifos would produce behavioral change
s at both pre- and postweanling ages. Treatment occurred every second day b
eginning on postnatal day (PND) 1, and continued through PND 21. The rats r
eceived one of the following regimens: a low-dosage (3 mg/kg) from PND 1-21
; a medium dosage (mg/kg from PND 1-5, and then 6 mg/kg from PND 7-21; or a
high-dosage schedule of 3 mg/kg on PND 1-5, then 6 mg/kg from PND 7-13, an
d 12 mg/kg from PND 15-21. 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 13-21. An open field was used to me
asure locomotor activity on PND 10, 12, 14, 16, 18, 20, 25, and 30. There w
ere no differences in locomotor activity levels or treatment effects betwee
n 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 activit
y was significantly decreased with the medium- and high-dosage groups. Brai
n cholinesterase (ChE) inhibition mas about 25-38% on PND 25 and 14-34% on
PND 30. On PND 25 but not 30, lung and diaphragm ChE and serum butyrylcholi
nesterase (BChE), with the high-dosage animals, and heart ChE with the medi
um- and high-dosage groups were significantly inhibited. There was no signi
ficant inhibition of skeletal muscle ChE or serum acetylcholinesterase (ACh
E) on PND 25 and 30. These data suggest that early postnatal chlorpyrifos e
xposures will depress locomotor activity in juvenile rats, with the effects
most pronounced after brain ChE activity has substantially recovered.