Postnatal exposure to chlorpyrifos produces long-term effects on spatial memory and the cholinergic system in mice in a sex- and APOE genotype-dependent manner

Organophosphorus pesticides - and in particular chlorpyrifos (CPF) - are extensively used worldwide. They mainly exert their toxicity by targeting the cholinergic system. Several studies suggested that the gene coding for apolipoprotein E (apoE), which is a risk factor for several diseases, can also confer different vulnerability to toxic insults. This study was aimed at assessing the long-term effects of postnatal exposure to CPF on learning and memory as well as the expression levels of several genes involved in cholinergic neurotransmission in mice. Both male and female apoE4-TR and C57BL/6 mice were exposed to either 0 or 1 mg/kg/day of CPF by oral gavage using a micropipette on postnatal days 10-15. At 9 months, they were tested in a Morris Water Maze (MWM) and the gene expression in the frontal cortex and hippocampus was evaluated. Our results show that, in males, CPF had an effect on the spatial retention, while in females, it altered the expression levels of nicotinic receptors. Furthermore, apoE4-TR mice performed the worst during the MWM retention and presented low expression levels in a considerable number of cholinergic genes. Taken together, the current results reveal long-term effects in mice nine months after postnatal exposure to CPF, which are modulated by sex and apoE4 genotype.