Abstract: Objective To study the effect of new-typed pesticide imidacloprid on the content of NO(nitric oxide)in nutrient solution and the activity of NOS(NO synthase)in primary-cultured rat,hippocampus neurons.Methods To poison mature primary-cultured rat's hippocampus neurons with imidacloprid of different concentration;then to observe the morphological change under phase difference microscope to determine cell mortality,the content of NO in nutrient solution and the activity of NOS respectively at time of 12h,24h and 48h after poisoning.Results Compared with DM SO control group,there are following changes for each group apart from groups of zero and 10^-6 mol/L imidacloprid with increase of poisoning concentration(10^-5-10^-3 mol/L)and prolonging of poisoning time.Hippocampus neurons become swell,the intracellular granules increase,the axon and dendrite break or even loss,the intercellular network also becomes sparser.The cell mortality and the content of NO increase after poisoning for 24h(P<0.05),and they increase much more at time of 48h(P<0.01).The activity of intracellular NOS of 10^-3 mol/L imidacloprid group increases at time of 12h(P<0.01),and it becomes higher at 24h(P<0.01),that of 10^-5-10^-4 mol/L imidacloprid groups also increases at time of 24h(P<0.01).And there is no obvious change for the activity of NOS of every group between time of 24h and 48h.Conclusion Imidacloprid with concentration range from 10^-5 mol/L to 10^-3 mol/L can result in increase of the content of NO in nutrient solution and the activity of NOS in primary-cultured rat's hippocampus neurons,which may be related to its neurotoxic effect.