Effects of acute and repeated oral exposure to the organophosphate insecticide chlorpyrifos on open-field activity in chicks

The effects of the organophosphate insecticide chlorpyrifos on 5 min open-field activity were examined in a 7–15 days old chick model. Chlorpyrifos was acutely administered taking into account cholinesterase inhibition and determination of the acute (24 h) median lethal dose (LD50). The oral LD50 value of chlorpyrifos in chicks was 18.14 mg/kg, with cholinergic toxicosis observed on intoxicated chicks. Chlorpyrifos at the dose rates of 5,10 and 20 mg/kg orally produced within 2 h signs of cholinergic toxicosis in the chicks and significantly inhibited plasma (40–70%), whole brain (43–69%) and liver (31–46%) cholinesterase activities in a dose-dependent manner. Chlorpyrifos at 2 and 4 mg/kg, orally did not produce overt signs of cholinergic toxicosis, but decreased (30, 60 and 90 min after dosing) the general locomotor activity of the chicks as seen by a significant increase in the latency to move from the central square of the open-field arena, decreases in the numbers of lines crossed and vocalization score. Repeated daily chlorpyrifos treatments (2 and 4 mg/kg, orally) for seven consecutive days also caused hypoactivity in chicks in the open-field behavioral paradigm. Only the high dose of chlorpyrifos (4 mg/kg, orally) given repeatedly for 7 days caused significant cholinesterase inhibition in the whole brain (37%) and the liver (22%). In conclusion, chlorpyrifos at single or short-term repeated doses-induced behavioral changes in 7–15 days old chicks, in a model that could be used for further neurobehavioral studies involving subtle effects of organophosphates on chicks.