Environmentally relevant imidacloprid exposure elicits hippocampal microglial apoptosis via JNK-FOXO3 pathway: Implication for latent central neurotoxicity.

Imidacloprid (IMI), a widely used neonicotinoid insecticide, has been frequently detected in drinking water and food; however, whether long-term low-dose exposure to environmentally relevant levels of IMI induces neurotoxic effects in the central nervous system remains unclear. In this study, C57BL/6 N mice were exposed to IMI in drinking water for three, six months at doses derived from human exposure estimates (0, 3 μg/kg, 103 μg/kg, and 6.55 mg/kg). Behavioral tests, including the Morris water maze and novel object recognition, revealed no overt cognitive impairment following IMI exposure. Nevertheless, IMI significantly increased microglial apoptosis in the hippocampus. Mechanistic analyses showed that IMI exposure enhanced JNK phosphorylation and promoted nuclear translocation of FOXO3, accompanied by increased expression of pro-apoptotic proteins BIM and BAX and decreased BCL-2 levels. Consistently, IMI induced apoptosis in BV2 microglial cells through activation of the JNK-FOXO3 signaling pathway, whereas FOXO3 knockdown or JNK inhibition with SP600125 markedly attenuated this effect. These findings indicate that environmentally relevant IMI exposure can trigger hippocampal microglial apoptosis via JNK-FOXO3 signaling even in the absence of overt behavioral deficits, suggesting a potential early neurotoxic effect of neonicotinoid exposure.