Repeated bifenthrin exposure alters hippocampal Nurr-1/AChE and induces depression-like behavior in adult rats.

Exposure to insecticides has been associated with depression-like symptoms, especially among occupationally exposed populations, such as farmers. Although the neurotoxicity of pyrethroids such as bifenthrin (BF) is well established, it is still unclear whether exposure to BF may have deleterious effects on the hippocampus and thus behavior. We verified the hypothesis that repeated exposure to BF in a rat model elicits neurochemical and behavioral alterations, the latter of which reflects depression-related symptoms. Adult male Wistar rats (n = 12 per group) were orally administered with different doses of BF (0.6 or 2.1 mg/kg body weight (b.w.)) on a daily basis for 60 days; control rats received the vehicle (corn oil). Different biochemical changes were assessed in the hippocampus, a region of the brain regulating spatial memory; behavioral tests were also conducted. Our results revealed depressive-like behaviors that were expressed by increased despair behavior in the Forced-swimming test. Repeated exposure to BF also decreased acetylcholinesterase (AChE) activity in the hippocampus and butyrylcholinesterase (BuChE) activity in plasma. A significant reduction in the activities of hippocampal membrane-bound ATPases (Na+/K+-ATPase and Mg2+-ATPase) was also observed in BF-treated rats compared to controls. Furthermore, a significant decrease in mRNA expression and protein synthesis of both AChE and orphan nuclear receptor (Nurr-1), as well as in the expression of muscarinic-cholinergic receptor (M1 mAchR) and nicotinic-cholinergic receptor (nAchR2α) was observed in the hippocampus of treated rats compared to controls. Also, BF exposure induced apoptosis as assessed by hippocampal Casp-3 protein levels. Our findings suggest that repeated exposure to BF affects hippocampal signaling and Nurr-1/AChE, and this was accompanied by depression-like state in adult rats.