Repeated exposure to chlorpyrifos alters the performance of adolescent male rats in animal models of depression and anxiety

Chlorpyrifos (CPF) is a broad spectrum, highly effective organophosphorus (OP) pesticide that has been largely used worldwide. Over the past decades, numerous studies have assessed the potential neurotoxic effects of either acute or chronic exposure to CPF on developing brain. Despite being an acetylcholinersterase inhibitor, the effects of CPF are not only confined to cholinergic system, but are involved in a wide variety of neurotransmitter systems, especially the serotonin (5-HT) system, which leads to long-lasting changes in 5-HT-related emotional behaviors. In our present study, 4-week-old adolescent male Sprague–Dawley rats were repeatedly exposed to CPF at daily doses of 10, 20, 40, 80, and 160 mg/kg/day (s.c., 7 days), and then subjected to a battery of emotional behavioral tests that related to serotonergic function in order to determine CPF effects in adolescent rats. Results in behavioral tests demonstrated CPF significantly increased the entries to and time spent in the open arms in the elevated plus-maze test at the dose of 40–160 mg/kg, the number of shocks in the Vogel's conflict test at the dose of 20–160 mg/kg, and significantly decreased the latency to feed in the novelty-suppressed feeding test in both dose range. Interestingly, in the forced swimming test, at the dose of 10 mg/kg, CPF significantly increased the immobility time, whereas it significantly decreased the immobility time at the dose of 160 mg/kg. Our data suggest that repeated exposure to CPF elicits alterations of the emotional behaviors related to serotonergic nervous system in adolescent male rats. However, the underlying mechanism needs further investigations.

► Repeated exposure to chlorpyrifos elicited evident alterations of emotional behaviors on adolescent male rats.
► Chlorpyrifos induced depressive state on adolescent male rats at the lower dose, resembling animal model of depression. However, at the dose of 160 mg/kg chlorpyrifos significantly decreased the immobility time.
► Repeated exposure to chlorpyrifos produced a reduced anxiety state on adolescent male rats in the elevated plus-maze test, the novelty-suppressed feeding test, and Vogel's conflict test.