Impulsivity as long-term sequelae after chlorpyrifos intoxication: time course and individual differences.

Chlorpyrifos (CPF) is a common organophosphate (OP) insecticide that has been widely used in agriculture as a pesticide. The primary mechanism of acute toxic action of OPs is initiated by acetylcholinesterase (AChE) inhibition. However, non-AChE targets have also been proposed as alternative that contributes to the acute lethal action and side effects of short or long-term exposure. Recently, we have found that a single dose of 250 mg/kg CPF produces acceleration in acquisition on schedule-induced polydipsia (SIP) procedure 6 months after its administration. Moreover, CPF animals show a higher level of impulsivity in a delay-discounting task 1 year after acute administration, and these effects are potentiated when animals are divided into high (HD) and low (LD) drinkers in SIP. In the present study, rats were injected with a subcutaneous (sc) dose of 250 mg/kg of CPF, and 10 weeks later its effect on delay-discounting task was evaluated. Consequently, these animals were evaluated based on SIP, and divided into two populations (HD and LD) according to their rates of drinking in this task. One year after OP administration, these animals were re-evaluated in a delay-discounting task. Results revealed that the CPF-administered rats prefer immediate reward and show a more impulsive choice, 10 weeks after CPF administration. Furthermore, 1 year after it administration, only animals treated with CPF that are high drinkers on SIP are more impulsive than the rest of the groups Therefore, these data suggest that some individuals are more sensitive to OP intoxication than the others, at least in terms of durability of sequelae.