摘要：In this study, the delayed effect and related mechanism after chlorpyrifos (CPF) withdrawal was studied in primary rat hippocampal neurons. The results showed that 10 μ M CPF induced no detectable cytotoxicity during 96 h continuous exposure while its withdrawal after 48 h exposure induced evident cytotoxicity, as indexed by decreased methyl thiazolyl tetrazolium (MTT) metabolism, increased loss of neurons immunostained by neuron-specific enolase (NSE) antibody, and the increased terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) positive cell rate in the following 24 h and 48 h incubation in the absence of CPF. Extracellular signal-related kinase (ERK)1/2 activation by phosphorylation was observed and persisted during CPF exposure. However, CPF withdrawal after 48 h exposure led to inhibition of ERK1/2 phosphorylation. Carbacol and nerve growth factor (NGF), which are ERK1/2 activators, protected the neurons after CPF withdrawal, while atropine and PD98059, which are ERK1/2 inhibitors, exacerbated the cytotoxicity, indicating the involvement of inhibition of ERK1/2 phosphorylation in CPF-induced delayed cytotoxicity. In conclusion, CPF withdrawal after exposure induced delayed cytotoxicity in cultured neurons. Inhibition of ERK1/2 phosphorylation was found to be related to the delayed cytotoxicity. This finding may provide a new insight into the toxicological mechanism of organophosphorus pesticides, especially chronic organophosphate-induced neuropsychiatric disorder characterized by delayed occurrence.
