Atropine counteracts the depressive-like behaviour elicited by acute exposure to commercial chlorpyrifos in rats.

Acute organophosphate (OP) poisoning induces well-known signs of toxicosis related to acetylcholinesterase (AChE) inhibition. However, the relationship between acute OP poisoning and the onset of psychiatric disorders remains unclear. Thus, we investigated behavioural and biochemical consequences of acute exposure to the OP chlorpyrifos in male rats and also the effectiveness of the antidotes atropine and pralidoxime on reversing these changes. A sub-lethal dose of commercial chlorpyrifos (20 mg/kg, i.p.) elicited signs of acute toxicosis during the first hours after its injection in rats. Twenty-four hours after treatment, this single dose of chlorpyrifos induced a depressive-like behaviour in the rat forced swimming test without impairing locomotor activity. At this time (24 h), chlorpyrifos decreased plasma butyrylcholinesterase (BChE) activity and hippocampal, striatal and prefrontal cortical AChE activity in rats. The behavioural and biochemical consequences of acute chlorpyrifos poisoning do not seem to be long lasting, since 30 days later they were absent. We evaluated whether these behavioural and biochemical consequences of acute chlorpyrifos treatment would be reversed by the antidotes atropine (10 mg/kg i.p.) and/or pralidoxime (40 mg/kg; i.p.) given 1 h after poisoning. Pralidoxime partially reactivated the AChE activity in the prefrontal cortex, but not in the hippocampus and striatum. Atropine attenuated the depressive-like behaviour induced by chlorpyrifos in rats. Our results suggest that acute chlorpyrifos poisoning induces a transient depressive-like behaviour possible related to hippocampal AChE inhibition. They suggest that treatment with atropine and pralidoxime seems to be insufficient to counteract all the effects of OP acute poisoning, at least in rats.