OBJECTIVE We want to investigate the mechanism of organophosphate- induced delayed neuropathy (OPIDN) and find appropriate therapeutic medicine. OPIDN, often leads to pares?thesias, ataxia and paralysis, occurs in the late-stage of acute poisoning or after repeated exposures to organophosphate (OP) insecticides or nerve agents, and may contribute to the Gulf War Syndrome. METHODS FDSS Ca2 +-influx assays, single-cell calcium imaging and patch-clamp electrophysiology were the major testing techniques. Transfected HEK293 cells and dorsal root ganglion (DRG) neurons were used to evaluate the effects of compounds. Wild type and trpa1 knockout mice and adult hyline brown hens were used to evaluate the neuropathological damages caused by the OPs. Transmission electron microscopy imaging was used to observe the nerve injuries ultrastructurally. High-throughput screen for TRPA1 inhibitors was accomplished by Ion Works Barracuda (IWB) automated electrophysiology assay. RESULTS TRPA1 (Transient receptor potential cation channel, member A1) channel mediates OPIDN. A variety of OPs, exemplified by malathion, activates TRPA1 but not other neuronal TRP channels. Malathion increases the intracellular calcium levels and upregulates the excitability of mouse DRG neurons in vitro. Mice with repeated exposures to malathion also develop local tissue nerve injuries and pain-related behaviors, which resembles the early symptoms of OPIDN. Both the neuropathological changes and the nocifensive behaviors can be attenuated by treatment of TRPA1 antagonist HC030031 or abolished by knockout of Trpa1 gene. In the classic hens OPIDN model, malathion causes nerve injuries and ataxia to a similar level as the positive inducer tri-ortho-cresyl phosphate (TOCP), which also activates TRPA1 channel. Treatment with HC030031 reduces the damages caused by malathion or TOCP. Duloxetine and Ketotifen, two commercially available drugs exhibiting TRPA1 inhibitory activity, show neuroprotective effects against OPIDN and might be used in emergency situations. CONCLUSION TRPA1 is the major mediator of OPIDN and targeting TRPA1 is an effective way for the treatment of OPIDN.